US 4,267,458 AGrant
System and Method for Starting, Synchronizing and Operating a Steam Turbine With Digital Computer Control
Issue Date:1981-05-12
•15 Claims
•97 Drawing Sheets
Abstract
Steam flow and pressure conditions needed in a turbine to satisfy the speed and load demand of an electric power generating system are controlled by a programmed digital computer system during start-up, synchronization and load operation. Manual backup control is provided for the computer control. Throttle valve tests are provided under digital control and transfers are made to manual backup control if predetermined task errors occur.
Metadata
Assignee
- Westinghouse Electric Corp.
Inventors
- Robert Uram
- Theodore C. Giras
Application Information
Application Number:US 4089626
Filing Date:1973-10-23
Priority Date:1972-04-24
Art Unit:217
Classifications
IPC:
H02P 904
Field of Search:
60290105;73;646;657;660-66740;2;522;40
Patent Drawings (97 sheets)
Description
1. Ser. No. 722,779, entitled "Improved System and Method for Operating a Steam Turbine and an Electric Power Generating Plant" filed by Theodore C. Giras and Manfred Birnbaum on Apr. 4, 1968, assigned to the present asignee, and continued as Ser. No. 124,993 on Mar. 16, 1971, and Ser. No. 319,115, on Dec. 29, 1972.
2. Ser. No. 247,597, entitled "System and Method for Operating a Turbine with Speed Channel Failure Detection System Applied to Digital Computer Control" filed by Francesco Lardi on Apr. 26, 1972, and assigned to the present assignee and continued as Ser. No. 407,011 on Oct. 1 6, 1973.
3. Ser. No. 247,577, entitled "System and Method for Initially Loading a Turbine Generator on Synchronization" filed by Francesco Lardi on Apr. 26, 1972, assigned to the present assignee and continued as Ser. No. 377,174 on July 6, 1973.
4. Ser. No. 247,883, entitled "System and Method for Tracking of Digital Controller and Manual Analog Controller for Operating a Steam Turbine with Digital Computer Control" filed by Francesco Lardi on Apr. 26, 1972, assigned to the present assignee and continued as Ser. No. 385,613 on Aug. 13, 1973.
5. Ser. No. 247,855, entitled "System and Method for Operating a Steam Turbine with Digital Computer Control Having Automatic Startup Combined with Speed and Load Control" filed by Manfred Birnbaum on Apr. 26, 1972 and assigned to the present assignee.
6. Ser. No. 247,847, entitled "System and Method for Operating a Steam Turbine with Digital Computer Control Having an Analog Backup System" filed by G. W. Berkebile on Apr. 26, 1972 and assigned to the present assignee.
7. Ser. No. 247, 878, entitled "System and Method for Operating a Steam Turbine with Digital Computer Control with Initial Load Increase on Synchronization" filed by Francesco Lardi and Robert Uram on Apr. 26, 1972 and assigned to the present assignee.
8. Ser. No. 247,600, entitled "System and Method for Operating a Steam Turbine with Digital Computer Control and with Improved Monitoring Capability" filed by Donald Jones on Apr. 26, 1972 and assigned to the prsent assignee.
9. Ser. No. 247,850, entitled "System and Method for Operating a Steam Turbine with Digital Computer Control with Accelerating Setpoint Change" filed by Andrew Braytenbah on Apr. 26, 1972, assigned to the present assignee and continued as Ser. No. 387,582 on Aug. 10, 1973.
10. Ser. No. 247,848, entitled "System and Method for Operating a Steam Turbine with Digital Computer Control Having Setpoint and Valve Position Limiting" filed by Gerald Waldron and Andrew Braytenbah on Apr. 26, 1972, assigned to the present assignee and continued as Ser. No. 385, 612 on Aug. 3, 1973.
11. Ser. No. 247, 880, entitled "System and Method for Operating a Steam Turbine with Digital Computer Control Having Absolute Value Limit Parameters" filed by Gerald Waldron on Apr. 26, 1972, assigned to the present assignee and continued as Ser. No. 377,173 on July 6, 1973.
12. Ser. No. 247,882, entitled "System and Method for Operating a Steam Turbine with Digital Computer Control Having Data Transmission to Additional Digital Computer" filed by Theodore C. Giras and Klaus Pasemann on Apr. 26, 1972, assigned to the present assignee and continued as Ser. No. 390,471 on Aug. 22, 1973.
13. Ser. No. 247,884, entitled "System and Method for Operating a Steam Turbine with Digital Computer Control Having Data Link with Another Computer" filed by Klaus Pasemann on Apr. 26, 1972, assigned to the present assignee and continued as Ser. No. 427, 281 on Dec. 21, 1973.
14. Ser. No. 247,866, entitled "System and Method for Operating a Steam Turbine with Digital Computer Control Having Monitor Parameter Conversion and Recording" filed by George Daum on Apr. 26, 1972, assigned to the present assignee and continued as Ser. No. 407,026 on Oct. 16, 1973.
15. Ser. No. 247,851, entitled "System and Method for Operating a Steam Turbine with Digital Computer Control Having Integrator Limit", filed by Andrew Braytenbah and Leaman Podolsky on Apr. 26, 1972, assigned to the present assignee and continued as Ser. No. 407,361 on Oct. 17, 1973.
16. Ser. No. 247,887, entitled "Systems and Method for Organizing Computer Programs for Operating a Steam Turbine with Digital Computer Control" filed by Robert Uram and Juan J. Tanco on Apr. 26, 1972, assigned to the present assignee and continued as Ser. No. 391,406 on Aug. 24, 1973.
17. Ser. No. 247,852, entitled "System and Method for Operating a Steam Turbine with Digital Computer Control Having a Turbine Simulator", filed by Robert Uram and Gerald Waldron on Apr. 26, 1972, assigned to the present assignee and continued as Ser. No. 396,160 on Sept. 11, 1973.
18. Ser. No. 247,854, entitled "System and Method for Operating a Steam Turbine with Digital Computer Controlled from an Operator Interface", filed by Richard Heiser and Anthony Scott on Apr. 26, 1972, assigned to the present assignee and continued as Ser. No. 407,025 on Oct. 16, 1973.
19. Ser. No. 247, 599, entitled "System and Method for Operating a Steam Turbine with Digital Computer Control Having Improved Operator Interface Layout", filed by Anthony Scott on Apr. 26, 1972, assigned to the present assignee and continued as Ser. No. 407,371 on Oct. 17, 1973.
20. Ser. No. 247,881, entitled "System and Method for Operating a Steam Turbine with Digital Computer Control Having Improved Display Functions" filed by Theodore C. Giras and Leaman Podolsky on Apr. 26, 1972, assigned to the present assignee and continued as Ser. No. 387,578 on Aug. 10, 1973.
21. Ser. No. 247,849, entitled "System and Method for Operating a Steam Turbine with Digital Computer Control Having Mode Selection", filed by Robert Uram on Apr. 26, 1972 and assigned to the present assignee.
22. Ser. No. 247,853, entitled "System and Method for Operating a Steam Turbine with Digital Computer Control Having Contingency Functions Therein", filed by Andrew Braytenbah and Leaman Podolsky on Apr. 26, 1972, assigned to the present assignee and continued as Ser. No. 404,057 on Oct. 5, 1973.
23. Ser. No. 247,551, entitled "System and Method for Operating a Steam Turbine with Improved Logic Task Functions in a Digital Computer Control", filed by Robert Uram on Apr. 26, 1972, assigned to the present assignee and continued as Ser. No. 407,024 on Oct. 16, 1973.
24. Ser. No. 247,885, entitled "System and Method for Starting, Synchronizing and Operating a Steam Turbine with Digital Computer Control Having Implementation for Rotor Bore Temperature Measuring" filed by Gerald Waldron on Apr. 26, 1972 and assigned to the present assignee.
25. Ser. No. 247,598, entitled "System and Method for Operating a Steam Turbine with Digital Computer Control Having Automatic Startup Sequential Programming" filed by Juan J. Tanco on Apr. 26, 1972 and assigned to the present assignee.
26. Ser. No. 189,322, entitled "System and Method for Operation of a Steam Turbine with Dual Hydraulic Independent Overspeed Protection" filed by James M. Fieglein and M. Csanady, Jr. on Oct. 14, 1971, and assigned to the present assignee.
27. Ser. No. 99,491, entitled "System and Method Employing a Digital Computer for Automatically Synchronizing a Gas Turbine or Other Electrical Power Plant Generator with a Power System" filed by John F. Reuther on Dec. 18, 1970, assigned to the present assignee and continued as Ser. No. 276,508 on July 31, 1972.
28. Ser. No. 99,493, entitled "System and Method Employing a Digital Computer for Automatically Synchronizing an Electric Power Plant Generator with a Power System" filed by T. J. Reed on Dec. 18, 1970, assigned to the present assignee and continued as Ser. No. 276,343 on July 31, 1972.
29. Ser. No. 247,888, entitled "Improved Turbine Speed Controlling Valve Operators" filed by John F. Reuther on Apr. 26, 1972, assigned to the present assignee and continued as Ser. No. 412,513 on Nov. 2, 1973.
30. Ser. No. 815,882, now U.S. Pat. No. 3,552,872 entitled "Computer Positioning Control System with Manual Backup Control Especially Adapted for Operating Steam Turbine Valves" filed by Theodore C. Giras and William W. Barns, Jr. on Apr. 14, 1969 and assigned to the present assignee.
31. Ser. No. 080,710, now U.S. Pat. No. 3,741,246 entitled "Steam Turbine System with Digital Computer Position Control Having Improved Automatic-Manual Interaction" filed by Andrew S. Braytenbah on Oct. 14, 1970 and assigned to the present assignee.
BACKGROUND OF THE INVENTION
The present invention relates to the elastic fluid turbines and more particularly to systems and methods for operating steam turbines and electric power plants in which generators are operated by steam turbines.
With respect to steam turbine control, prime mover turbine control usually operates to determine turbine rotor shaft speed, turbine load, and/or turbine throttle pressure as end control system variables. In the case of large electric power plants in which throttle pressure is steam-generating system controlled, turbine control is typically directed to the megawatt amount of electric load and the frequency participation of the turbine after the turbine rotor speed has been controllably brought to the synchronous value and the generator has been connected to the electric power system.
In addition to the conventional steam turbine generating system, another type of power generating system in which steam turbine control is needed is a combined cycle generating system. The combined cycle generating system involves a combination of heat sources and energy conversion apparatus organized to produce an electric power output. For example, gas turbines can drive generators and use their exhaust gases to supply heat for steam to be used in driving a steam turbine. A separate boiler can also be included in the system to provide steam generating heat. Electric power is supplied by separate generators driven by the turbines.
The end controlled plant or plant system variables and the turbine operation are normally determined by controlled variation of the steam flow to one or more of the various stages of the particular type and particular design of the turbine in use. In prime mover turbine applications such as drum type boiler electric power plants where turbine throttle pressure is externally controlled by the boiler operation, the turbine inlet steam flow is an end controlled steam characteristic or an intermediately controlled system variable which controllably determines in turn the end control system variables, i.e., turbine speed, electric load or the turbine speed and the electric load. It is noteworthy, however, that some supplemental or protective control may be placed on the end control variable by additional downstream steam flow control such as by control of reheat valving and to that extent inlet turbine steam flow control is not strictly wholly controllably determinative of the end controlled system variables under all operating conditions.
In determining turbine operation and the end controlled system variables, turbine steam flow control has generally been achieved by controlled operation of valves disposed in the steam flow path or paths. To illustrate the nature of the turbine valve control in general and to establish simultaneously some background for subsequent description, consideration will now be directed to the system structure and the operation of a typical large electric power tandem steam turbine design for use with a fossil fuel drumtype boiler steam generating system.
Steam generated at controlled pressure may be admitted to the turbine steam chest through one or more throttle or stop valves operated by the turbine control system. Governor or control valves are arranged to supply steam inlets disposed around the periphery of a high pressure turbine section casing. The governor valves are also operated by the turbine control system to determine the flow of steam from the steam chest through the stationary nozzles or vanes and the rotor blading of the high pressure turbine section.
Torque resulting from the work performed by steam expansion causes rotor shaft rotation and reduced steam pressure. The steam is usually then directed to a reheat stage where its enthalpy is raised to a more efficient operating level. In the reheat stage, the high pressure section outlet steam is ordinarily directed to one or more reheaters associated with the primary steam generating system where heat energy is applied to the steam. In large electric power nuclear turbine plants, turbine reheater stages are usually not used and instead combined moisture separator reheaters are employed between the tandem nuclear turbine sections.
Reheated steam crosses over the next or immediate pressure section of a large fossil fuel turbine where additional rotor torque is developed as intermediate pressure steam expands and drives the intermediate pressure turbine blading. One or more interceptor and/or reheater stop valves are usually installed in the reheat steam flow path or paths in order to cut off or reduce the flow of turbine contained steam as required to protect against turbine overspeed. Reheat and/or interceptor valve operation at best produces late corrective turbine response and accordingly is normally not used controllably as a primary determinant of turbine operation.
Additional reheat may be applied to the steam after it exits from the intermediate pressure section. In any event, steam would typically be at a pressure of about 1200 psi as it enters the next or low pressure turbine section usually provided in the large fossil fuel turbines. Additional rotor torque is accordingly developed and the vitiated steam then exhausts to a condenser.
In both the intermediate pressure and the low pressure sections, no direct steam flow control is normally applied as already suggested. Instead, steam conditions at these turbine locations are normally determined by mechanical system design subject to time delayed effects following control placed on the high pressure section steam admission conditions.
In a typical large fossil fuel turbine just described, 30% of the total steady state torque might be generated by the high pressure section and 70% might be generated by the intermediate pressure and low pressure sections. In practice, the mechanical design of the turbine system defines the number of turbine sections and their respective torque ratings as well as other structural characteristics such as the disposition of the sections of one or more shafts, the number of reheat stages, the blading and vane design, the number and form of turbine stages and steam flow paths in the sections, etc.
A variety of valve arrangements may be used for steam control in the various turbine types and designs, and hydraulically operated valve devices have generally been used for steam control in the various valving arrangements. The use of hydraulically operated valves has been predicated largely on their relatively low cost coupled with their ability to meet stroke operating power and positioning speed and accuracy requirements.
Turbine valve control and automatic turbine operation have undergone successive stages of development. With increasing plant sizes, mechanical-hydraulic controls have been largely subplanted by analog of electrohydraulic controllers sometimes designated as AEH controllers. The aforementioned Giras and Birnbaum Patent application, Ser. No. 319,115, provides a further description of the turbine control technology development and the earlier prior patent and publication art. The latter application discloses a programmed digital computer controller which generally provides improved turbine and electric power plant operation over the earlier prior art. U.S. Pat. No. 3,588,265 issued to W. Berry, entitled "System and Method for Providing Steam Turbine Operation With Improved Dynamics", and assigned to the present assignee, is also directed to a digital computer controller which provides improved automatic turbine startup and loading operations. U.S. Pat. No. 3,552,872 issued to T. Giras and T. C. Barns, Jr. entitled "Computer Positioning Control System With Manual Backup Control Especially Adapted For Operating Steam Turbine Valves", and assigned to the present assignee, discloses a digital computer controller interfaced with a manual backup controller. A general publication pertaining to turbine digital controllers has appeared in Electrical World Magazine.
At this point in the background writeup, it is noted that prior art citations are made herein in an attempt to characterize the context within which the presently disclosed subject matter has been developed. No representations are made that the cited art is the best art nor that the cited art is immune to alternative interpretations.
Generally, the earlier Berry and the earlier Giras and Birnbaum DEH turbine operating system comprise basic hardware and software elements and control loops which bear some similarity to a number of basic elements and loops described herein. However, the present disclosure involves improvements largely stemming from the combined application of principles associated with the turbine technology and principles associated with the computer and control technologies in the determination of a particular detailed system arrangement and operation. Thus, the earlier DEH is largely directed to central control concepts which, although implementable with conventional know-how, open up opportunities for improvement-type developments related to the more central aspects of turbine control and operation as well as the more supportive aspects of turbine control and operation including areas such as turbine protection, remote system interfacing, accuracy and reliability, computer utilization efficiency, operator interface, maintenance and operator training.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a schematic diagram on an electric power plant including a large steam turbine and a fossile fuel fired drum type boiler and control devices which are all operable in accordance with the principles of the invention;
FIG. 2 shows a schematic diagram on a programmed digital computer control system operable with a steam turbine and its associated devices shown in FIG. 1 in accordance with the principles of the invention;
FIG. 3 shows a hydraulic system for supplying hydraulic fluid to valve actuators of the steam turbine;
FIG. 4 shows a schematic diagram of a servo system connected to the valve actuators;
FIG. 5 shows a schematic diagram of a hybrid interface between a manual backup system and the digital computer connected with the servo system controlling the valve actuators;
FIG. 6 shows a simplified block diagram of the digital Electro Hydraulic Control System in accordance with the principle of the invention;
FIG. 7 shows a block diagram of a control program used in accordance with the principles of the invention;
FIG. 8 shows a block diagram of the programs and subroutines of the digital Electro Hydraulic and the automatic turbine startup and monitoring program in accordance with the principles of the invention;
FIG. 9 shows a table of program or task priority assignments in accordance with the principles of the invention;
FIG. 10 shows the location of subroutines in accordance with the principles of the invention;
FIG. 11 shows a block diagram of a proportional-plus-reset controller program which is operable in accordance with the principles of the invention;
FIG. 12 shows a flow chart of the proportional-plus-reset subroutine (PRESET) which is operable in accordance with the principles of the invention;
FIG. 13 shows a block diagram of a proportional controller function with dead band which is operable in accordance with the principles of the invention;
FIG. 14 shows a flow chart of a speed loop (SPDLOOP) subroutine which is operable in accordance with the principles of the invention;
FIG. 15 shows a block diagram of a subroutine for scanning contact close inputs of the Digital Electro Hydraulic System which is operable in accordance with the principles of the invention; and
FIG. 16 shows a block diagram of an auxiliary synchronizer computer program which is operable in accordance with the principles of the invention.
FIG. 17 shows a view of a part of an operator's control panel which is operable in accordance with the principles of the invention;
FIG. 18 shows a view of a part of the operator's control panel which is operable in accordance with the principles of the invention;
FIG. 19 shows a view of a portion of the operator's control panel which is operable in accordance with the principles of the invention;
FIG. 20 shows a flow chart of a flash task which is operable in accordance with the principles of the invention;
FIG. 21 is a flow chart of a contact closure output test program which is operable in accordance with the principles of the invention;
FIG. 22 is a block diagram of a contact input scan program with a sequence of events interrupt program therein which is operable in accordance with the principles of the invention;
FIG. 23 is a flow chart of the sequence of the events interrupt program which is operable in accordance with the principles of the invention;
FIG. 24 is a block diagram of a breaker upon interrupt program which is operable in accordance with the principles of the invention;
FIG. 25 is a flow chart of the breaker open interrupt program which is operable in accordance with the principles of the invention;
FIG. 26 is a block diagram of error action with a task error program which is operable in accordance with the principles of the invention;
FIG. 27 is a block diagram of a turbine trip interrupt program which is operable in accordance with the principles of the invention;
FIG. 28 is a block diagram of a panel interrupt program which is operable in accordance with the principles of the invention;
FIG. 29 is a block diagram of a valve interrupt program which is operable in accordance with the principles of the invention;
FIG. 30 is a flow chart of a stop/initializer program which is operable in accordance with the principles of the invention;
FIG. 31 is a table of display buttons which is operable in accordance with the principles of the invention;
FIG. 32 is a block diagram of a visual display system which is operable in accordance with the principles of the invention;
FIG. 33 is a block diagram of the execution of a two-part visual display function which is operable in accordance with the principles of the invention;
FIG. 34 is a block diagram of an analog scan system which is operable in accordance with the principles of the invention;
FIG. 35 is a timing chart of the various programs and functions within the Digital Electro Hydraulic System which is operable in accordance with the principles of the invention;
FIG. 36 is a flow chart of a logic contact closure output subroutine which is operable in accordance with the principles of the invention;
FIG. 37 is a block diagram of conditions which cause initiation of a logic program which is operable in accordance with the principles of the invention;
FIG. 38 is a simplified block diagram of a portion of the logic function which is operable in accordance with the principles of the invention;
FIG. 39 is a block diagram of the logic program which is operable in accordance with the principles of the invention;
FIG. 40 is a flow chart of a maintenance test logic program which is operable in accordance with the principles of the invention.
FIG. 41 is a flow chart of a turbine supervision of logic program which is operable in accordance with the principles of the invention;
FIG. 42 is a flow chart of a transfer to manual operation subroutine which is operable in accordance with the principles of the invention;
FIG. 43 is a block diagram of a load control system which is operable in accordance with the principles of the invention;
FIG. 44 is a flow chart of a breaker logic program which is operable in accordance with the principles of the invention;
FIG. 45 is a flow chart of a logic pressure control logic subroutine which is operable in accordance with the principles of the invention;
FIG. 46 is a block diagram of megawatt feedback loop subroutine which is operable in accordance with the principles of the invention;
FIG. 47 is a block diagram of an impulse pressure loop with megawatt loop in service which is operable in accordance with the principles of the invention;
FIG. 48 is a flow chart of an automatic synchronize logic program which is operable in accordance with the principles of the invention;
FIG. 49 is a flow chart of an automatic dispatch logic program which is operable in accordance with the principles of the invention;
FIG. 50 is a flow chart of an automatic turbine startup program which is operable in accordance with the principles of the invention;
FIG. 51 is a flow chart of remote transfer logic subroutine which is operable in accordance with the principles of the invention;
FIG. 52 is a block diagram showing a panel task interaction function which is operable in accordance with the principles of the invention;
FIG. 53 is a block diagram of a panel program which is operable in accordance with the principles of the invention;
FIG. 54 is a block diagram showing a control task interface which is operable in accordance with the principles of the invention;
FIG. 55 is a block diagram showing a control program which is operable in accordance with the principles of the invention;
FIG. 56 is a block diagram showing a valve position limit function which is operable in accordance with the principles of the invention;
FIG. 56a is a block diagram showing a valve position limit adjustment function which is operable in accordance with the principles of the invention;
FIG. 57 shows an interaction between the DEH program and a valve test function which is operable in accordance with the principles of the invention;
FIG. 58 is a flow chart showing a valve contingency program which is operable in accordance with the principles of the invention;
FIG. 59 shows a block diagram of a speed instrumentation and computation interface with special speed sensing circuitry which is operable in accordance with the principles of the invention;
FIGS. 60a and 60b show flow charts of a speed selection function which is operable in accordance with the principles of the invention;
FIG. 61 shows a block diagram of an operating mode selection function which is operable in accordance with the principles of the invention;
FIG. 61a shows a flow chart of a select operating mode function which is operable in accordance with the principles of the invention;
FIG. 61b shows a flow chart of a select operating mode function which is operable in accordance with the principles of the invention;
FIG. 62 shows a symbolic diagram of the use of a speed/load reference function which is operable in accordance with the principles of the invention;
FIG. 63 shows a speed/load reference graph which is operable in accordance with the principles of the invention;
FIG. 64 is a block diagram showing a speed control function which is operable in accordance with the principles of the invention;
FIG. 65 shows a block diagram of the load control system which is operable in accordance with the principles of the invention;
FIG. 65a includes a flow chart of the load control system which is operable in accordance with the principles of the invention;
FIG. 66 shows a block diagram of the throttle valve control function which is operable in accordance with the principles of the invention;
FIG. 67 shows a mixed block diagram of a governor control function program which is operable in accordance with the principles of the invention;
FIG. 67-1 shows a block diagram of the data link program which is operable in accordance with the principles of the invention;
FIG. 67-2 shows a block diagram of the sense parameters in the automatic turbine startup and monitoring program which is operable in accordance with the principles of the invention;
FIG. 67-3 shows a flow chart of a program for determining the rotor stresses in the turbine rotor which is operable in accordance with the principles of the invention;
FIG. 67-4 shows a flow chart of the ATS roll-off subroutine which is operable in accordance with the principles of the invention;
FIG. 67-5A and B show a flow chart of the ATS turbine latching and load references which are operable in accordance with the principles of the invention;
FIG. 67-6A, B and C show a portion of the flow chart of the ATS program which is operable in accordance with the principles of the invention;
FIG. 67-7A and B show a flow chart of the ATS program with library charts which is operable in accordance with the principles of the invention;
FIG. 67-8 shows the flow chart of the ATS acceleration program which is operable in accordance with the principles of the invention;
FIG. 67-9 shows a chart of generator conditions which is operable in accordance with the principles of the invention;
FIG. 67-10A and B show a flow chart of the ATS program governor valve control and drain control which are operable in accordance with the principles of the invention;
FIG. 67-11A and B shows a flow chart of the ATS program sensor failure detection subroutine which is operable in accordance with the principles of the invention;
FIG.67-12A and B shows a flow chart of the ATS vibration scan, reaheat temperature monitoring and heat soak time calculation which are operable in accordance with the principles of the invention;
FIG. 67-13A and B shows a flow chart of the ATS program resetting and clear functions which are operable in accordance with the principles of the invention;
FIG. 67-14A and B shows a flow chart of the ATS generator monitor which is operable in accordance with the principles of the invention;
FIG. 67-15A and B shows a flow chart of the ATS transfer logic front speed to load control which is operable in accordance with the principles of the invention;
FIG. 67-16A and B show a flow chart of the ATS program turbine latch which is operable in accordance with the principles of the invention;
FIG. 67-17 shows a graph of no load and light load guides which are operable in accordance with the principles of the invention;
FIG. 67-18 shows a schematic representation of turbine generator differential expansion which is operable in accordance with the principles of the invention;
FIG. 67-19 shows a schematic representation of turbine generator differential expansion which is operable in accordance with the principles of the invention;
FIG. 67-20A and B show a section with an indication of buildup of rotor stresses in the rotor of the turbine generator which is operable in accordance with the principles of the invention;
FIG. 68 shows a block diagram of the Digital Electro Hydraulic System which is operable in accordance with the principles of the invention.
FIG. 69 is an over view block diagram of the computer system;
FIG. 70 is a block diagram representation of the arithmetic and logic portions of the computer system;
FIG. 71A illustrates the words within the executive level which controls the operation of sixteen different task levels;
FIG. 71B is a block diagram representation of the computer system executive program in which FIG. 71A illustrates the words within this executive which control the operation of sixteen different task levels;
FIG. 72A is a block diagram representation of an analog to digital converter;
FIG. 72B illustrates graphically the operation of this converter;
FIG. 73 illustrates miscellaneous system tables which are called upon by a subtask processor program;
FIG. 74A and B show a valve test panel of the DEH system;
FIG. 75 shows operational amplifier and logical circuitry in the DEH system;
FIG. 76 shows transistor and operational amplifier circuitry;
FIG. 77 shows logic circuitry for the DEH system;
FIG. 78 shows electronic circuitry connected to a throttle valve;
FIG. 79A and B show metering and detecting circuitry and LVDT circuit connections;
FIG. 80 shows logic circuitry of the DEH system;
FIG. 81 shows logic and operational amplifier circuitry of the DEH systems;
FIG. 82 shows governor valve circuitry;
FIG. 83A and B show flip-flop circuitry and other analog circuitry;
FIG. 84 shows operator panel interface circuitry;
FIG. 85 shows throttle pressure transmission circuitry;
FIG. 86 shows a power supply control panel;
FIG. 87A and B show interconnections between overspeed protection control, interceptor valve and throttle control circuitry.
DESCRIPTION OF THE PREFERRED EMBODIMENT
A. Power Plant
More specifically, there is shown in FIG. 1 a large single reheat steam turbine constructed in a well known manner and operated and controlled in an electric power plant 12 in accordance with the principles of the invention. As will become more evident through this description, other types of steam turbines can also be controlled in accordance with the principles of the invention and particularly in accordance with the broader aspects of the invention. The generalized electric power plant shown in FIG. 1 and the more general aspects of the computer control system to be described in connection with FIG. 2 are like those disclosed in the aforementioned Giras and Birnbaum Pat. application No. 319,115. As already indicated, the present application is directed to general improvements in turbine operation and control as well as more specific improvements related to digital computer operation and control of turbines.
The turbine 10 is provided with a single output shaft 14 which drives a conventional large alternating current generator 16 to produce three-phase electric power (or any other phase electric power) as measured by a conventional power detector 18 which measures the rate of flow of electric energy. Typically, the generator 16 is connected through one or more breakers 17 per phase to a large electric power network and when so connected causes the turbo-generator arrangement to operate at synchronous speed under steady state conditions. Under transient electric load change conditions, system frequency may be affected and conforming turbon-generator speed changes would result. At synchronism, power contribution of the generator 16 to the network is normally determined by the turbine steam flow which in this instance is supplied to the turbine 10 at substantially constant throttle pressure.
In this case, the turbine 10 is of the multistage axial flow type and includes a high pressure section 20, an intermediate pressure section 22, and a low pressure section 24. Each of these turbine sections may include a plurality of expansion stages provided by stationary vanes and an interacting bladed rotor connected to the shaft 14. In other applications, turbines operating in accordance with the present invention may have other forms with more or fewer sections tandemly connected to one shaft or compoundly coupled to more than one shaft.
The constatnt throttle pressure steam for driving the turbine 10 is developed by a steam generating system 26 which is provided in the form of a conventional drum type boiler operated by fossil fuel such as pulverized coal or natural gas. From a generalized standpoint, the present invention can also be applied to steam turbines associated with other types of steam generating systems such as nuclear reactor or once through boiler systems.
The turbine 10 in this instance is of the plural inlet front end type, and steam flow is accordingly directed to the turbine steam chest (not specifically indicated) through four throttle inlet valves TV1-TV4. Generally, the plural inlet type and other front end turbine types such as the single ended type or the end bar lift type may involve different numbers and/or arrangements of valves.
Steam is directed from the admission steam chest to the first high pressure section expansion stage through light governor inlet valves GV1-GV8 which are arranged to supply steam to inlets arcuately spaced about the turbine high pressure casing to constitute a somewhat typical governor valving arrangement for large fossil fuel turbines. Nuclear turbines might on the other hand typically utilize only four governor valves.
During start-up, the governor valves GV1-GV8 are typically all fully opened and steam flow control is provided by a full arc throttle valve operation. At some point in the start-up process, transfer is made from full arc throttle valve control to full arc governor valve control because of throttling energy losses and/or throttling control capability. Upon transfer the throttle valves TV1-TV4 are fully opened, and the governor valves GV1-GV8 are normally operated in the single valve mode. Subsequently, the governor valves may be individually operated in a predetermined sequence usually directed to achieving thermal balance on the rotor and reduced rotor blade stressing while producing the desired turbine speed and/or load operating level. For example, in a typical governor valve control mode, governor valves GV5-GV8 may be initially closed as the governor valves GV1-GV4 are jointly operated from time to time to define positions producing the desired corresponding total steam flows. After the governor valves GV1-GV4 have reached the end of their control region, i.e., upon being fully opened, or at some overlap point prior to reaching their fully opened position, the remaining governor valves GV5-GV8 are sequentially placed in operation in numerical order to produce continued steam flow control at higher steam flow levels. This governor valve sequence of operation is based on the assumption that the governor valve controlled inlets are arcurately spaced about the 360.degree. periphery of the turbine high pressure casing and that they are numbered consecutively around the periphery so that the inlets corresponding to the governor valves GV1 and GV8 are arcuately adjacent to each other.
The preferred turbine start-up method is to raise the turbine speed from the turning gear speed of about 2rpm to about 8% of the synchronous speed under throttle valve control and then transfer to governor valve control and raise the turbine speed to the synchronous speed, then close the power system breakers and meet the load demand. On shutdown, similar but reverse practices or simple coastdown may be employed. Other transfer practice may be employed, but it is unlikely that transfer would be made at a loading point above 40% rated load because of throttling efficiency considerations.
After the steam has crossed past the first stage impulse blading to the first stage reaction blading of the high pressure section, it is directed to a reheater system 28 which is associated with a boiler or steam generating system 26. In practice, the reheater system 28 may typically include a pair of parallel connected reheaters coupled to the boiler 26 in heat transfer relation as indicated by the reference character 29 and associated with opposite sides of the turbine casing.
With a raised enthalpy level, the reheated steam flows from the reheater system 28 through the intermediate pressure turbine section 22 and the low pressure turbine section 24. From the latter, the vitiated steam is exhausted to a condenser 32 from which water flow is directed (not indicated) back to the boiler 26.
To control the flow of reheat steam, a stop valve SV including one or more check valves is normally open and closed only when the turbine is tripped. Interceptor valves IV (only one indicated), are also provided in the reheat steam flow path, and they are normally open and if desired they may be operated over a range of position control to provide reheat steam flow cutback modulation under turbine overspeed conditions. Further description of an appropriate overspeed protection system in presented in U.S. Pat. No. 3,643,437 issued to M. Birnbaum, A. Braytenbah and A. Richardson and assigned to the present assignee.
In the typical fossil fuel drum type boiler steam generating system, the boiler control system controls boiler operations so that steam throttle pressure is held substantially constant. In the present description, it is therefore assumed as previously indicated that throttle pressure is an externally controlled variable upon which the turbine operation can be based. A throttle pressure detector 38 of suitable conventional design measures the throttle pressure to provide assurance of substantially constant throttle pressure supply, and, if desired as a programmed computer protective system override control function, turbine control action can be directed to throttle pressure control as well as or in place of speed and/or load control if the throttle pressure falls outside predetermined constraining safety and turbine condensation protection limits.
In general, the steady state power or load developed by a steam turbine supplied with substantially constant throttle pressure steam is determined as follows: Equation (1)
where
P.sub.i =first stage impulse pressure
P.sub.0 =throttle pressure
K.sub.p =constant of proportionality
S.sub.F =steam flow
K.sub.F =constant of proportionality
Where the throttle pressure is held substantially constant by external control as in the present case, the turbine load is thus proportional to the first stage impulse pressure P.sub.i. The ratio P.sub.i /P.sub.0 may be used for control purposes, for example to obtain better anticipatory control of P.sub.i (i.e. turbine load) as th boiler control throttle pressure P.sub.0 undergoes some variation within protective constraint limit values. However, it is preferred in the present case that the impulse pressure P.sub.i be used for feedback signalling in load control operation as subsequently more fully described, and a conventional pressure detector 40 is employed to determine the pressure P.sub.i for the assigned control usage.
Within its broad field of applicability, the invention can also be applied in nuclear reactor and other applications involving steam generating systems which produce steam without placement of relatively close steam generator control on the constancy of the turbine throttle pressure. In such cases, throttle control and operating philosophies are embodied in a form preferred for and tailored to the type of plant and turbine involved. In cases of unregulated throttle pressure supply, turbine operation may be directed with top priority to throttle pressure control or constraint and with lower priority to turbine load and/or speed control.
Respective hydraulically operated throttle valve actuators indicated by the reference character 42 are provided for the four throttle valves TV1-TV4. Similarly, respective hydraulically operated governor valve actuators indicated by the reference character 44 are provided for the eight governor valves GV1-GV8. Hydraulically operated actuators indicated by the reference characters 46 and 48 are provided for the reheat stop and interceptor valves SV and IV. A computer monitored high pressure fluid supply 50 provides the controlling fluid for actuator operation of the valves TV1-TV4, GV1-GV8, SV and IV. A computer supervised lubricating oil system (not shown) is separately provided for turbine plant lubricating requirements.
The respective actuators 42, 44, 46 and 48 are of conventional construction, and the inlet valve actuators 42 and 44 are operated by respective stabilizing position controls indicated by the reference characters 50 and 52. If desired, the interceptor valve actuators 48 can also be operated by a positon control 56 although such control is not employed in the present detailed embodiment of the invention. Each position control includes a conventional analog controller (not shown in FIG. 1) which drives a suitably known actuator servo valve (not indicated) in the well known manner. The reheat stop valve actuators 46 are fully open unless the conventional trip system or other operating means causes them to close and stops the reheat steam flow.
Since the turbine power is proportional to steam flow under the assumed control condition of substantially constant throttle pressure, steam valve positions are controlled to produce control over steam flow as an intermediate variable and over turbine speed and/or load as an end control variable or variables. Actuator operation provides the steam valve positioning, and respective valve position detectors PDT1-PDG1-PDG8 and PDI are provided to generate respective valve position feedback signals for developing position error signals to be applied to the respective position controls 50, 52 and56. One or more contact sensors CSS provides status data for the stop valving SV. The position detectors are provided in suitable conventional form, for example, they may make conventional use of linear variable differential transformer operation in generating negative position feedback signals for algebraic summing with respect to position setpoint signals SP in developing the respective input error signals. Position controlled operation of the interceptor valving IV would typically be provided only under a reheat steam flow cutback requirement.
The combined position control, hydraulic actuator, valve position detector element and other miscellaneous devices (not shown) form a local hydraulic electric analog valve position control for each throttle or governor inlet steam valve. The position setpoints SP are computer determined and supplied to the respective local loops and updated on a periodic basis. Setpoints SP may also be computed for the interceptor valve controls when the latter are employed. A more complete general background description of electrohydraulic steam valve positioning and hydraulic fluid supply systems for valve actuation is presented in the aforementioned Birnbaum and Noyes paper.
In the present case, the described hybrid arrangement incuding local loop analog electrohydraulic position control is preferred primarily because of the combined effects of control computer operating speed capabilities and computer hardware economics, i.e., the cost of manual backup analog controls is less than that for backup computer capacity at present control computer operating speeds for particular applications so far developed. Further consideration of the hybrid aspects of the turbine control system is presented subsequently herein. However, economic and fast operating backup control computer capability is expected and direct digital computer control of the hydraulic valve actuators will then likely be preferred over the digital control of local analog controls described herein.
A speed detector 58 is provided for determining the turbine shaft speed for speed control and for frequency participation control purposes. The speed detectors 58 can for example be in the form of a reluctance pickup (not shown) magnetically coupled to a notched wheel (not shown) on the turbo-generator shaft 14. In the detailed embodiment subsequently described herein, a plurality of sensors are employed for speed detection. Analog and/or pulse signals produced by the speed detector 58, the electric power detector 18, the pressure detectors 38 and 40, the valve position detectors PDT1-PDT4, PDG1-PDG8 and PDI, the status contact or contacts CSS, and other sensors (not shown) and status contacts (not shown) are employed in programmed computer operation of the turbine 10 for various purposes including controlling turbine performance on an on-line real time basis and further including monitoring, sequencing, supervising, alarming, displaying and logging.
B. DEH - COMPUTER CONTROL SYSTEM
As generally illustrated in FIG. 2, a Digital Electro-Hydraulic control system (DEH) 1100 includes a programmed digital computer 210 to operate the turbine 10 and the plant 12 with improved performance and operating characteristics. The computer 210 can include conventional hardware including a central processor 212 and a memory 214. The digital computer 210 and its associated input/output interfacing equipment is a suitable digital computer system such as that sold by Westinghouse Electric Corporation under the trade name of P2000. In cases when the steam generating system 26 as well as the turbine 10 are placed under computer control, use can be made of one or more P2000 computers or alternatively a larger computer system such as that sold by Xerox Data Systems and known as the Sigma 5. Separate computers, such as P2000 computers, can be employed for the respective steam generation and turbine control functions in the controlled plant unit and interaction is achieved by interconnecting the separate computers together through data links or other means.
The digital computer used in the DEH control system 1100 is a P2000 computer which is designed for real time process control applications. The P2000 typically uses a 16 bit word length with 2's complement, a single address and fixed word length operated in a parallel mode. All the basic DEH system functions are performed with a 16,000 word (16K), 3 mircosecond magnetic core memory. The integral magnetic core memory can be expanded to 65,000 words (65K).
The equipment interfacing with the computer 210 includes a contact interrupt system 124 which scans contacts representing the status of various plant and equipment conditions in plant wiring 1126. The status contacts might typically be contacts of mercury wetted relays (not shown) which operate by energization circuits (not shown) capable of sensing the predetermined conditions associated with the various system devices. Data from status contacts is used in interlock logic functioning and control for other programs, protection analog system functioning, programmed monitoring and logging and demand logging, etc.
Operator's panel button 1130 transmit digital information to the computer 2010. The operator's panel buttons 1130 can set a load reference, a pulse pressure, megawatt output, speed, etc.
In addition, interfacing with plant instrumentation 1118 is provided by an analog input system 1116. The analog input system 1116 samples analog signals at a predetermined rate from predetermined input channels and converts the signals sampled to digital values for entry into the computer 210. The analog signals sensed, in the plant instrumentation 1118 represent parameters including the impulse chamber pressure, the megawatt power, the valve positions of the throttle valves TV1 through TV4 and the governor valves GV1 through GV8 and the interceptor valve IV, throttle pressure, steam flow, various steam temperatures, miscellaneous equipment operating temperature, generator hydrogen cooling pressure and temperature, etc. A detailed list of all parameters is provided in Appendix 1. Such parameters include process parameters which are sensed or controlled in the process (turbine or plant) and other variables which are defined for use in the programmed computer operation. Interfacing from external systems such as an automatic dispatch system is controlled through the operator's panel buttons 1130.
A conventional programmer's console and tape reader 218 is provided for various purposes including program entry into the central processor 212 and the memory 214 thereof. A logging typewriter 1146 is provided for logging printouts of various monitored parameters as well as alarms generated by an automatic turbine startup system (ATS) which includes program system blocks 1140, 1142, 1144 (FIG. 8) in the DEH control system 1100. A trend recorder 1147 continuously records predetermined parameters of the system. An interrupt system 124 is provided for controlling the input and output transfer of information between the digital computer 210 and the input/output equipment. The digital computer 210 acts on interrupt from the interrupt system 124 in accordance with an executive program. Interrupt signals from the interrupt system 124 stop the digital computer 210 by interrupting a program in operation. The interrupt signals are serviced immediately.
Output interfacing is provided by contacts 1128 for the computer 210. The contacts 1128 operate status display lamps, and they operate in conjunction with a conventional analog/output system and a valve position control output system comprising a throttle valve control system 220 and a governor valve control system 222. A manual control system is coupled to the valve position control output system 220 and is operable therewith to provide manual turbine control during computer shut-down. The throttle and governor valve control systems 220 and 222 correspond to the valve position control 50 and 52 and the actuators 42 and 44 in FIG. 1. Generally the manual control system is similar to those disclosed in prior U.S. Pat. 3,552,872 by T. Giras et al. and U.S. Pat. No. 3,741,246 by A. Braytenbah, both assigned to the present assignee.
Digital output data from the computer 210 is first converted to analog signals in the analog output system 24 and then transmitted to the valve control system 220 and 222. Analog signals are also applied to auxiliary devices and systems, not shown, and interceptor valve systems, not shown.
C. SUBSYSTEMS EXTERNAL TO THE DEH COMPUTER
At this point in the description, further consideration of certain subsystems external to the DEH computer will aid in reaching an understanding of the invention. Making reference now to FIG. 3, a high pressure HP fluid supply system 310 for use in controlled actuation of the governor valves GV1 through GV8, the throttle valves TV1 through TV4 and associated valves is shown. The high pressure fluid supply system 310 corresponds to the supply system 49 in FIG. 1 and it uses a synthetic, fire retardant phosphate ester-based fluid and operates in the range of 1500 and 1800 psi. Nitrogen charged piston type accumulators 312 maintain a flow of fluid to the actuators for the governor valves GV1-GV8, the throttle valves TV1-TV4, etc. when pumps 314 and 316 are discharging to a reservoir 318 through unloader valves 320 and 321. In addition, the accumulators 312 provide additional transient flow capacity for rapid valve movements.
Referring now to FIG. 4, a typical electrohydraulic valve actuation system 322 is shown in greater detail for positioning a modulating type valve actuator 410 against the closing force of a large coil spring. A servo-valve 412 which is driven by a servo-amplifier 414 controls the flow of fluid therethrough. The servo-valve 412 controls the flow of fluid entering or leaving the valve actuator cylinder 416 relative to the HP fluid supply system 310. A linear voltage differential transformer LVTD generates a valve position indicating transducer voltage which is summed with a valve position demand voltage at connection 418. The summation of the two previously mentioned voltages produces a valve position error input signal to the servo-amplifier 414. The linear voltage differential transformer LVTD has a linear voltage characteristic with respect to displacement thereof in the preferred embodiment. Therefore, the position of the valve actuator 410 is made proportional to the valve position demand voltage at connection 418.
Making reference now to FIG. 5, a hardwired digital/analog system forms a part of the DEH control system 1100 (FIG. 2). Structurally, it embraces elements which are included in the blocks 50, 52, 42 and 44 of FIG. 1 as well as additional elements. A hybrid interface 510 is included as a part of the hardwired system. The hybrid interface 510 is connected to actuator system servoamplifier 414 for the various steam valves which in turn are connected to a manual controller 516, an overspeed protection controller, not shown, and redundant DC power supplies, not shown.
A controller shown in FIG. 5 is employed for throttle valve TV1-TV4 control in the TV control system 50 of FIG. 1. The governor valves GV1-GV8 are controlled in an analogous fashion by the GV control system 52.
While the steam turbine is controlled by the digital computer 210, the hardwired system 511 tracks single valve analog outputs 520 from the digital computer 210. A comparator 518 compares a signal from a digital-to-analog converter 522 of the manual system with the signal 520 from the digital computer 210. A signal from the comparator 518 controls a logic system 524 such that the logic system 524 runs an up-down 526 to the point where the output of the converter 522 is equal to the output signal 520 from the digital computer 210. Should the hardwired system 511 fail to track the signal 520 from the digital comparator 210 a monitor light will flash on the operator's panel.
When the DEH control system reverts to the control of the backup manual controller 516 as a result of an operator selection or due to a contigency condition, such as loss of power on the automatic digital computer 210, or a stoppage of a function in the digital computer 210, or a loss of a speed channel in the wide range speed control all as described in greater detail infra, the input of the valve actuation system 322 (FIG. 4) is switched by switches 528 from the automatic controllers in the blocks 50, 52 (FIG. 1) or 220, 222 (FIG. 2) to the control of the manual controller 516. Bumpless transfer is thereby accomplished between the digital computer 210 and the manual controller 516.
Similarly, tracking is provided in the computer 210 for switching bumplessly from manual to automatic turbine control. As previously indicated, the presently disclosed hybrid structural arrangement of software and hardware elements is the preferred arrangement for the provision of improved turbine and plant operation and control with backup capability. However, other hybrid arrangements can be implemented within the field of application of the invention.
D. DEH PROGRAM SYSTEM
DEH Program System Organization, DEH Control Loops and Control Task Program
With reference now to FIG. 6, an overall generalized control system of this invention is shown in block diagram form. The digital electrohydraulic (DEH) control system 1100 operates valve actuators 1012 for the turbine 10. The digital electrohydraulic control system 1100 comprises a digital computer 1014, corresponding to the digital computer 210 in FIG. 2, and it is interconnected with a hardwired analog backup control system 1016. The digital computer 1014 and the backup system 1016 are connected to an electronic servo system 1018 corresponding to blocks 220 and 222, in FIG. 2. The digital computer control system 1014 and the analog backup system 1016 track each other during turbine operations in the event it becomes necessary or desirable to make a bumpless transfer of control from a digital computer controlled automatic mode of operation to a manual analog backup mode or from the manual mode to the digital automatic mode.
In order to provide plant and turbine monitor and control functions and to provide operator interface functions, the DEH computer 1014 is programmed with a system of task and task support programs. The program system is organized efficiently and economically to achieve the end operating functions. Control functions are achieved by control loops which structurally include both hardware and software elements, with the software elements being included in the computer program system. Elements of the program system are considered herein to a level of detail sufficient to reach an understanding of the invention. More functional detail on various programs is presented in Appendix 2. Further, a detailed listing of a DEH system program substantially conforming to the description presented herein is presented in Appendix 3 in symbolic and machine language. Most of the listing is compiled by a P2000 compiler from instructions written in Fortran IV. A detailed dictionary of system parameters is presented in Appendix 1, and a detailed computer input/output signal list is presented in Appendix 4. Appendix 5 mainly provides additional hardware information related to the hardwired system previously considered as part of the DEH control system.
As previously discussed, a primary function of the digital electrohydraulic (DEH) system 1100 is to automatically position the turbine throttle valves TV1 through TV4 and the governor valves GV1 through GV8 at all times to maintain turbine speed and/or load. A special periodically executed program designated the CONTROL task is utilized by the P2000 computer along with other programs to be described in greater detail subsequently herein.
With reference now to FIG. 7, a functional control loop diagram in its preferred form includes the CONTROL task or program 1020 which is executed in the computer 1010. Inputs representing demand and rate provide the desired turbine operating setpoint. The demand is typicallyeither the target speed in specified revolutions per minute of the turbine systems during startup or shutdown operations or the target load in metawatts of electrical output to be produced by the generating system 16 during load operations. The demand enters the block diagram configuration of FIG. 7 at the input 1050 of a compare block 1052.
The rate input either in specified RPM per minute or specified megawatts per minute, depending upon which input is to be used in the demand function, is applied to an integrator block 1054. The rate inputs in RPM and megawatts of loading per minute are established to limit the buildup of stresses in the rotor of the turbine-generator 10. An error output of the compare block 1052 is applied to the integrator block 1054. In generating the error output the demand value is compared with a reference corresponding to the present turbine operating setpoint in the compare block 1052. The reference value is representative of the setpoint RPM applied to the turbine system or the setpoint generator megawatts output, depending upon whether the turbine generating system is in the speed mode of operation or the load mode of operation. The error output is applied to the integrator 1054 so that a negative error drives the integrator 1054 in one sense and a positive error drives it in the opposite sense. The polarity error normally drives the integrator 1054 until the reference and the demand are equal or if desired until they bear some other predetermined relationship with each other. The rate input to the integrator 1054 varies the rate of integration, i.e. the rate at which the reference or the turbine operating setpoint moves toward the entered demand.
Demand and rate input signals can be entered by a human operator from a keyboard. Inputs for rate and demand can also be generated or selected by automatic synchronizing equipment, by automatic dispatching system equipment external to the computor, by another computer automatic turbine startup program or by a boiler control system. The inputs for demand and rate is automatic synchronizing and boiler control modes are preferably discrete pulses. However, time control pulse widths or continuous analog input signals may also be utilized. In the automatic startup mode, the turbine acceleration is controlled as a function of detected turbine operating conditions including rotor thermal stress. Similarly, loading rate can be controlled as a function of detected turbine operating conditions.
The output from the integrator 1054 is applied to a breaker decision block 1060. The breaker decision block 1060 checks the state of the main generator circuit breaker 17 and whether speed control or load control is to be used. The breaker block 1060 then makes a decision as to the use of the reference value. The decision made by the breaker block 1060 is placed at the earliest possible point in the control task 1020 thereby reducing computational time and subsequently the duty cycle required by the control task 1020. If the main generator circuit breaker 17 is open whereby the turbine system is in wide range speed control the reference is applied to the compare block 1062 and compared with the actual turbine generator speed in a feedback type control loop. A speed error value from the compare block 1062 is fed to a proportional plus reset controller block 1068, to be described in greater detail later herein. The proportional plus reset controller 1068 provides an integrating function in the control task 1060 which reduces the speed error signal to zero. In the prior art, speed control systems limited to proportional controllers are unable to reduce a speed error signal to zero. During manual operation an offset in the required setpoint is no longer required in order to maintain the turbine speed at a predetermined value. Great accuracy and precision of turbine speed whereby the turbine speed is held within one RPM over tens of minutes is also accomplished. The accuracy of speed is so high that the turbine 10 can be manually synchronized to the power line without an external synchronizer typically required. An output from the proportional plus reset controller block 1068 is then processed for external actuation and positioning of the appropriate throttle and/or governor valves.
If the main generator circuit breaker 17 is closed, the CONTROL task 1020 advances from the breaker block 1060 to a summer 1072 where the REFERENCE acts as a feedforward setpoint in a combined feedforward-feedback load control system. If the main generator circuit breaker 17 is closed, the turbine generator system 10 is being loaded by the electrical network connected thereto.
In the control task 1020 of the DEH system 1100 utilizes the summer 1072 to compare the reference value with the output of speed loop 1310 in order to keep the speed correction independent of load. A multiplier function has a sensitivity to varying load which is objectionable in the speed loop 1310.
During the load mode of operation the DEMAND represents the specified loading in MW of the generator 16, which is to be held at a predetermined value by the DEH system 1100. However, the actual load will be modified by any deviations in system frequency in accordance with a predetermined regulation value. To provide for frequency participation, a rated speed value in box 1074 is compared in box 1078 with a "two signal" speed value represented by box 1076. The two signal speed system provides high turbine operating reliability to be described infra herein. An output from the compare function 1078 is fed through a function 1080 which is similar to a proportional controller which converts the speed error value in accordance with the regulation value. The speed error from the proportional controller 1080 is combined with the feedforward megawatt reference, i.e., the speed error and the megawatt reference are summed in summation function or box 1072 to generate a combined speed compensated reference signal.
The speed compensated load reference is compared with actual megawatts in a compare box or function 1082. The resultant error is then run through a proportional plus reset controller represented by program box 1084 to generate a feedback megawatt trim.
The feed forward speed compensated reference is trimmed by the megawatt feedback error multiplicatively to correct load mismatch, i.e. they are multiplied together in the feedforward turbine reference path by multiplication function 1086. Multiplication is utilized as a safety feature such that if one signal e.g. MW should fail a large value would not result which could cause an overspeed condition but instead the DEH system 1100 would switch to a manual mode. The resulting speed compensated and megawatt trimmed reference serves as an impluse pressure setpoint in an impulse pressure controller and it is compared with a feedback inpulse chamber pressure representation from input 1088. The difference between the feedforward reference and the impulse pressure is developed by a comparator function 1090, and the error output therefrom functions in a feedback impulse pressure control loop. Thus, the impulse pressure error is applied to a proportional plus reset controller function 1092.
During load control the megawatt loop comprising in part blocks 1082 and 1084 may be switched out of service leaving the speed loop 1310 and an impulse pressure loop operative in the DEH system 1100.
Impulse pressure responds very quickly to changes of load and steam flow and therefore provides a signal with minimum lag which smooths the output response of the turbine generator 10 because the lag dynamics and subsequent transient response is minimized. The impulse pressure input may be switched in and out from the compare function 1090. An alternative embodiment embracing feedforward control with impulse pressure feedback trim is applicable.
Between block 1092 and the governor valves GV1-GV8 a valve characterization function for the purpose of linearizing the presponse of the valves is interposed. The valve characterization function described in detail in Appendix III infra herein is utilized in both automatic modes and manual modes of operation of the DEH system 1100. The output of the proportional plus reset controller function 1092 is then ultimately coupled to the governor valves GV1-GV8 through electrohydraulic position control loops implemented by equipment considered elsewhere herein. The proportional plus reset controller output 1092 causes positioning of the governor valves GV1-GV8 in load control to achieve the desired megawatt demand while compensation is made for speed, metawatt and impulse pressure deviations from desired setpoints.
Making reference to FIG. 8, the control program 1020 is shown with interconnections to other programs in the program system employed in the Digital Electro Hydraulic (DEH) system 1100. The periodically executed program 1020 receives data from a logic task 1110 where mode and other decisions which affect the control program are made, a panel task 1112 where operator inputs may be determined to affect the control program, an auxiliary synchronizer program 1114 and an analog scan program 1116 which processes input process data. The analog scan task 1116 receives data from plant instrumentation 1118 external to the computer as considered elsewhere herein, in the form of pressures, temperatures, speeds, etc. and converts such data to proper form for use by other programs. Generally, the auxiliary synchronizer program 1114 measures time for certain important events and it periodically bids or runs the control and other programs. An extremely accurate clock function 1120 operates through a monitor program 1122 to run the auxiliary synchronizer program 1114.
The monitor program or executive package 1122 also provides for controlling certain input/output operations of the computer and, more generally, it schedules the use of the computer to the various programs in accordance with assigned priorities. For more detail on the P2000 computer system and its executive package, reference is made to Appendix 4. In the appendix description, the executive package is described as including analog scan and contact closure input routines, whereas these routines are considered as programs external to the executive package in this part of the disclosure.
The logic task 1110 is fed from outputs of a contact interrupt or sequence of events program 1124 which monitors contact variables in the power plant 1126. The contact parameters include those which represent breaker state, turbine auto stop, tripped/latched state interrogation data states, etc. Bids from the interrupt program 1124 are registered with and queued for execution by the executive program 1111. The control program 1110 also receives data from the panel task 1112 and transmits data to status lamps and output contacts 1128. The panel task 1112 receives data instruction based on supervision signals from the operator panel buttons 1130 and transmits data to panel lamps 1132 and to the control program 1020. The auxiliary synchronizer program 1114 synchronizes through the executive program 1111 the bidding of the control program 1020, the analog scan program 1116, a visual display task 1134 and a flash task 1136. The visual display task transmits data to display windows 1138.
The control program 1020 receives numerical quantities representing process variables from the analog scan program 1116. As already generally considered, the control program 1020 utilizes the values of the various feedback variables including turbine speed, impulse pressure and megawatt output to calculate the position of the throttle valves TV1-TV4 and governor valves GV1-GV8 in the turbine system 10, thereby controlling the megawatt load and the speed of the turbine 10.
To inteface the control and logic programs efficiently, the sequence of events program 1124 normally provides for the logic task 1110 contact status updating on demand rather than periodically. The logic task 1110 computes all logical states according to predetermined conditions and transmits this data to the control program 1020 where this information is utilized in determining the positioning control action for the throttle valves TV1-TV4, and the governor valves GV1-GV8. The logic task 1110 also controls the state of various lamps and relay type contact outputs in a predetermined manner.
Another important part of the DEH system is the OPERATOR'S PANEL program. The operator communicates through the panel with the DEH control programs by means of various buttons which have assigned functions. When any button is pressed, a special interrupt is generated; this interrupt triggers a PANEL INTERRUPT program which decodes the button pressed, and then bids the PANEL task. The PANEL program processes the button and takes the proper action, which usually means manipulating some panel lamps, as well as passing on the button information to both the LOGIC and the CONTROL tasks.
The operator's Panel also has two sets of display windows which allow display of all turbine program parameters, variables, and constants. A visual display task presents this information in the windows at the request of the operator through various dedicated display buttons and a numerical keyboard. The visual display values are periodically updated in the windows as the quantity changes.
Certain important turbine operating conditions are communicated to the DEH operator by way of flashing lamps on the panel. Therefore a special FLASH program is part of the DEH system. Its function is to monitor and detect such contingency conditions, and flash the appropriate lamp to alert the operator to the state.
E. TASK PRIORITY ASSIGNMENTS
With reference now to FIG. 9, a table of program priority assignments is shown as employed in the executive monitor. A program with the highest priority is run first under executive control if two or more programs are ready to run. The stop/initializer program function has top priority and is run on startup of the computer or after the computer has been shut down momentarily and is being restarted. The control program 1020 is next in order of priority. The operator's panel program 1130, which generates control data, follows the control task 1020 in priority. The analog scan program 11116 also provides information to the control task 1020 and operates at a level of priority below that of the operator's panel 1130. The automatic turbine starting (ATS) periodic program 1140 is next in the priority list. ATS stands for automatic turbine startup and monitoring program, and is shown as a major task program 1140 of FIG. 8 for the operation of the DEH system 1100. The ATS-periodic program 1140 monitors the various temperatures, pressures, breaker states, rotational velocity, etc. during start-up and during load operation of the turbine system.
The logic task 1110, which generates control and operating mode data, follows in order of operating priority. The visual display task program 1134 follows the logic task program 1110 and makes use of outputs from the latter. A data link program for transmitting data from the DEH system to an external computer follows. An ATS-analog conversion task program 1142 for converting the parameters provided by the ATS-periodic program 1142 to usable computer data follows in order of priority. The flash task program 1136 is next, and it is followed by a programmer's console program which is used for maintenance testing and initial loading of data tapes. The next program is an ATS-message writer 1144 which provides for printout of information from the ATS analog conversion program 1142 on a suitable typewriter 1146. The next program in the priority list is an analog/digital trend which monitors parameters in the turbine system 10 and prints or plots them out for operator perusal. The remaining two programs are for debugging and special applications.
In the preferred embodiment, the stop/initialize program is given the highest priority in the table of FIG. 9 because certain initializing functions must be completed before the DEH system 1100 can run. The auxiliary synchronizer program 1114 provides timing for all programs other than the stop/initialize program while the DEH system 1100 is running. Therefore, the auxiliary synchronizer task program 1400 has the second order of priority of the programs listed. The control program 1020 follows at the third descending order of priority since the governor valves GV1 through GV8 and the throttle valves TV1 through TV4 must be controlled at all times while the DEH system 1100 is in operation.
The operator's panel program 1130 is given the next order of priority in order to enable an operator to exercise direct and instantaneous control of the DEH system 1100. The analog scan program 1116 provides input data for the control program 1020 and, therefore, is subordinate only to the initialize synchronizer control and operator functions.
In the preferred embodiment the ATS-periodic program 1140 is next in order of priority. During automatic turbine startup, the scanning of inputs by the ATS-periodic program 1140 is almost on the same order of priority as the inputs to the DEH system 1100. However, the ATS program 1140 in alternative embodiments, could be reduced in its priority, without any considerable adverse effect, because of the relatively limited duty cycle problems in the ATS system.
The logic task 1110 which control the operations of some of the functions of the control task program 1020 is next in order of priority. The visual display task 1134 follows in order of priority in order to provide an operator with a visual indication of the operation of the DEH program 1100. The visual display program 1134 is placed in the relatively low eighth descending order of priority since the physical response of an operator is limited in speed to 0.2 to 0.5 sec. as to a visual signal. The rest of the programs are in essentially descending order of importance in the preferred embodiment. In alternative embodiments of the inventions, alternate priority assignments can be employed for the described or similar programs, but the general priority listing described is preferred for the various reasons presented.
A series of interrupt programs interrupt the action of the computer and function outside the task priority assignments to process interrupts. One such program in FIG. 8 is the sequence events of contact interrupt program 1124 which suspends the operation of the computer for a very short period of time to process an interrupt. Between the operator panel buttons 1130 and the panel task program 1112 a panel interrupt program 1156 is utilized for signalling any changes in the operator's panel buttons 1130. A valve interrupt program 1158 is connected directly between the operator's panel buttons 1130 and the panel task program 1112 for operation during a valve test or in case of valve contingency situations.
Proportional plus reset controller subroutine 1154 (FIG. 11) is called by the control task program 1020 of FIG. 7 as previously described when the turbine control system is in the speed mode of control and also, for computer use efficiency, when the turbine 10 is in the load mode of control with the megawatt and impulse pressure feedback loops in service. Utilizing the proportional plus reset function 1068 during speed control provides very accurate control of the angular velocity of the turbine system.
In addition to previously described functions, the auxiliary synchronizer program 1114 is connected to and triggers the ATS periodic program 1140, the ATS analog conversion routine 1142 and the message writer 1144. The ATS program 1140 monitors a series of temperature, vibration, pressures, speed, etc. in the turbine system and also contains a routine for automatically starting the turbine system 10. The ATS analog conversion routine 1142 converts the digital computer signals from the ATS periodic program 1140 to analog or digital or hybrid form which can be typed out through the message writer task 1144 to the logging typewriter 1146 or a similar recorder.
The auxiliary synchronizer programs 1114 also controls an analog/digital trend program 1148. The analog digital trend program 1148 records a set of variables in addition to the variables of the ATS periodic program 1140.
Ancillary to a series of other programs is a plant CCI subroutine 1150 where CCI stands for contact closure inputs. The plant CCI subroutine 1150 responds to changes in the state of the plant contacts as transmitted over the plant wiring 1126. Generally, the plant contacts are monitored by the CCI subroutine 1150 only when a change in contact state is detected. This scheme conserves computer duty cycle as compared to periodic CCI monitoring. However, other triggers including operator demand can be employed for a CCI scan.
As shown in FIG. 8, the control task 1020 calls ancillary thereto a speed loop task 1152 and the preset or proportional plus reset controller program 1154. Ancillary to the executive monitoring program 1122 is a task error program 1160. In conjunction with the clock program 1120 a stop/initialize program 1162 is used. Various other functions in FIG. 8 are described in greater detail infra.
F. DEH PROGRAMS OF TASKS
1. Preset subroutine
making reference now to FIG. 11, a functional diagram of the proportional plus reset controller task program 1068 of FIG. 7 is shown in greater detail. The proportional plus reset controller subroutine 1068 is called by the control program 1020 of FIG. 7 when the DEH turbine control system 1100 is in the speed mode of control and also when the DEH turbine control system 1100 is in the load mode of control with the megawatt and impulse pressure feedback loops in service. As already indicated utilizing a proportional plus reset function during speed control provides very accurate control of the angular velocity of the turbine system.
the proportional plus reset controller 1068 provides an output which is composed of the sum of two parts. One part of the output is proportional to an input and the other part is an integral of the input. Therefore, instantaneous response is available as well as the capability of zero input error. A setpoint or dynamic reference from a demand source is applied to an input 1210 of a difference function 1212. The difference function 1212 compares the input and the actual controlled process value. An output from the difference function 1212 is fed to a proportional gain function 1216 and to an input of an integrator or integrating function 1218 having a reset time TR. An output from the integrator 1218 is high and low limited by the program as represented by the reset windup prevention function 1220 in order to avoid excessive integrator outputs which could occur with a reset windup.
Proportional and integral outputs from the gain function 1216 and the windup limited integrator 1218 are summed in a summing function 1222. The total output from the summing function 1222 is high and low limited by another function 1224 and fed to a process function 1226 thereby limiting the total output to a useful output range.
Making reference now to FIG. 12, a pictorial representation of a flow chart for the proportional plus reset controller program is shown. In the preferred embodiment the Preset program is designed such that a call from the control program 1030 provides a list of variables necessary to evaluate the controller 1068 output. The structure of the subroutine is indicated by the Fortran statement given below.
SUBROUTINE PRESET (ERR, ERRX, G, TR, HL, XLL, RES, PRES)
The variables in the above equation are defined as follows:
Again making reference to FIG. 12, where standard FORTRAN notation is used, the Preset subroutine 1068 first evaluates the integral part of the controller output according to equation: ##EQU1## The subroutine 1068 next saves the current input ERR in storage location ERRX 1250 for the following call to the subroutine 1068. The controller integral output RES 1252 is then checked against the high limit 1254 and the low limit 1256 to prevent reset/windup. The proportional part of the output is computed and added to the integral part of the output integrator 1218 to form the total output PRES 1258. PRES 1258 is checked against high limit 1260 and low limit 1262 after which the proportional plus reset controller subroutine 1068 returns to the control task 1020.
As previously considered, the proportional plus reset controller subroutine 1068 is used by the control task program 1020 during three different phases of operation of the turbine system. During startup of the turbine system 10, the proportional plus reset controller, subroutine program 1068 is used as a speed controller in order to regulate and hold the speed of the turbine 10 at a predetermined value or at a predetermined acceleration rate. Because of the integral function of the proportional plus reset controller subroutine program 1068 the speed of the turbine system 10 can be held to within 1 rpm. Also, in order for an operator to keep the speed of the turbine system 10 at a predetermined value, an error offset input signal typical of a purely proportional system is not required. Therefore, the reference and the controlled variable, both turbine speed in this case, will be equal. The proportional plus reset controller subroutine program 1068 is also used in the megawatt controller feedback loop and the impulse chamber pressure controller feedback loop.
During turbine startup, the quantity REFDMD is the internal speed reference while WS is the actual turbine speed. GS1 and T1 are the proportional gain and reset time, HLS and O. are the high and low limits, RESSPD is the integral part of the output, SPDSP is the total output, and RESSPDX is the last value of the input.
In the megawatt controller during megawatt loop operation, REF1 is the megawatt set point, MW is the megawatt feedback, and GR2 is a ranging gain to convert from engineering unit, to per-unit form. GL2 and T2 are the proportional gain and the reset time, while HEL and LEL are high and low limits. RESMW is the integral output, Y is the total output, and RESMWX is the last input.
With impluse pressure loop operation, PISP is the set point for the impulse pressure controller, PI is the feedback and GL3 and T3 are the proportional gain and the reset time. GR4 and O. are the high and low limits, RESPI is the integral output, VSP is the total output, and RESPIX is the last input.
Reset Integrator Algorithm
To perform the mathematical function of integration in a digital computer it is desirable to use numerical techniques to approximate the exact value of the integral. In the preferred embodiment, the algorithm uses the trapezoidal rule for integration and it is simple in format, requires little computer storage and is executed very rapidly. The algorithm uses one value of input past history to achieve a high degree of accuracy.
The following algorithm is used in the computer:
Definitions of the terms in this equation follow:
(N)--The current instant of real time
(N-1)--The last instant of real time.
DT--The sampling interval, or the time duration between evaluations of the integration algorithm. In the DEH Control System this is normally 1 sec.
TR--The controller reset time in sec.
X(N)--The current value of the input.
X(N-1)--The last value of the input.
Y(N)--The current value of the output.
Y(N-1)--The last value of the output.
To use the integrator algorithm, the DEH control system is orgainized so that the parameters DT and TR, the input variables X(N) and X(N-1), and the output variables Y(N) and Y(N-1) are in known areas of COMMON storage. The CONTROL task computes the current value of X(N) and calls the PRESET subroutine. The PRESET subroutine evaluates the current value of Y(N) according to the integrator algorithm and stores the value for use by all other parts of the DEH system.
2. Speed Loop Subroutine
Making reference now to FIG. 13, a speed loop program 1310 which functionally is part of the arrangement shown in FIG. 7 is shown in greater detail. The speed loop (SPDLOOP) program 1310 normally computes data required in the functioning of the speed feedback loop in the load control comprising as shown in FIG. 7 the rated speed reference 1074, the actual turbine speed 1076, the compare function 1078, the proportional controller 1080 and the summing function 1072. During the load control, the speed feedback loop adjusts the load reference (and thus the governor valves) to correct for any turbine speed deviation from rated speed. The speed feedback loop uses a proportional controller to accomplish this function. The speed loop subroutine 1310 is called upon to perform speed control loop functions by the control program 1020. In FIG. 13, the functioning of the proportional controller 1080 is shown in detail. The error output from the compare function 1078 is fed through a deadband function 1312. A proportionality constant (GR1) 1314 and a high limit function(HLF) 1316 are included in the computation.
The speed loop (SPDLOOP) subroutine is called by the control task during the load control mode and when switching occurs between actual speed signals. Subroutine form reduces the requirement for memory storage space thereby reducing the computer expense required for operation of the DEH system 1100.
The deadband function 1312 provides for bypassing small noise variations in the speed error generated by the compare function 1078 so as to prevent turbine speed changes which would otherwise occur. Systems without a deadband continuously respond to small variations which are random in nature resulting in undue stress in the turbine 10 and unnecessary, time and duty cycle consuming operation of the control system. A continuous hunting about the rated speed due to the gain of the system would occur without the deadband 1312. The speed regulation gain GR1 at 1314 is set to yield rated megawatt output power speed correction for a predetermined turbine speed error. The high limit function HLS at 1316 provides for a maximum speed correction factor.
The turbine speed 1076 is derived from three transducers. The turbine digital speed transducer arrangement is that disclosed in greater element and system implementation detail in the aforementioned Reuther Application Ser. No. 412,513. Briefly, in the preferred embodiment for determining the speed of the turbine, the system comprises three independent speed signals. These speed signals consist of a very accurate digital signal generated by special electronic circuitry from a magnetic pickup, an accurate analog signal generated by a second independent magnetic pickup, and a supervisory analog instrument signal from a third independent pickup. the DEH system compares these signals and through logical decisions selects the proper signal to use for speed control or speed compensated load control. This selection process switches the signal used by the DEH control system 1100 from the digital channel signal to the accurate analog channel signal or vice versa under predetermined dynamic conditions. In order to hold the governor valves at a fixed position during this speed signal switching the control program 1020 uses the speed loop subroutine 1310 and performs a computation to maintain a bumpless speed signal transfer.
Making reference to FIG. 14, the speed loop (SPDLOOP) subroutine flow chart 1310 is shown in greater detail. Two FORTRAN statements signify the operations of the speed loop subroutine program flow chart 1310. These statements are:
Variables in the flow chart 1310 are defined as follows:
3. PLANT CONTACT CLOSURE INPUT (PLANTCCI) SUBROUTINE
A plant contact closure input subroutine 1150 as shown in FIG. 8 scans all the contact inputs tied to the computer through the plant wiring 1126 and sets logic data images of these in designated areas within the memory 214 of the computer 210. Various situations call for the PLANTCCI subroutine. The most common case represents a basic design feature of the DEH system; that is, the situation in which a change of state of any contact input triggers a sequence of events interrupt. A corresponding interrupt program then calls the PLANTCCI subroutine to do a scan of all contact inputs and to update the computer contact image table. Thus (under normal conditions) a contact scan is carried out only when necessary. A block diagram illustrating the operation of the plant contact closure input subroutine 1150 is shown in FIG. 15. The plant contact closure input subroutine 1150 is also utilized when power to the computer 210 is turned on or when the computer buttons reset-run-reset are pressed on a maintenance panel 1410. Under these circumstances, a special monitor power-on routine 1412 is called upon. This executes the computer STOP/INITIALIZE task program 1414 described previously, which in turn calls the plant contact closure input subroutine 1150 for performance of the initializing procedure.
The operator can also call the plant contact closure input subroutine 1150 through the auxiliary synchronizer program 1114, if desired, whereby a periodic scan of the entire computer CCI system is implemented for checking the state of any one or group of relays in the CCI system. This call is contingent upon the entry of a nonzero value for the constant PERCCI from the DEH Operator's Panel keyboard.
4. Auxliary Synchonizer Program
With reference to FIG. 16, the block diagram shows an overall scheme which illustrates the operation of the auxiliary synchronizer program 1510. The auxiliary synchronizer program 1510 has two functions. It performs accurate counting to determine the time duration of important events to be described in more detail and it synchronizes the bidding for execution of all periodic programs in the digital electrohydraulic system 1100 on a predetermined schedule.
The AUX SYNC task is on priority level E.sub.16 (14.sub.10) and is initiated by the 60 Hz synchronizing program of the Monitor every 1/10 sec. Highly accurate and stable timing is provided by a clock to align all parts of the system in a repetitive working pattern. Such timing sources are called clocks or synchronizers. Clocks may generate their timing pulses in a number of ways; the most common clocks consist either of a very accurate electronic oscillator, or a timing circuit triggered by the 60 Hz supply frequency to the computer.
The DEH control system utilizes the line frequency as its timing source. As shown in FIG. 16, a clock pulse is generated every cycle (1/60 sec), and triggers a counting circuit in the computer Monitor system. The Monitor is initialized to generate an interrupt every six cycles (1/10 sec). When this interrupt occurs, the Monitor executes its own internal scheduling functions and then bids the AUX SYNC task to run. AUX SYNC proceeds to carry out its various timing calculations and bids all remaining periodic DEH programs.
OPERATOR'S PANEL AND FLASH PROGRAM
Referring now to FIGS. 17, 18 and 19, the control panel 1130 for the digital electrohydraulic system 1100 is shown in detail. Specified functions have control panel buttons which flash in order to attract the attention of an operator. The FLASH task has two functions: it flashes appropriate lights to alert the operator to various important conditions in the DEH system, and it sets contact outputs to pass these same conditions to the Analog Backup and Boiler Control Systems. The FLASH task is on priority level 5 and is bid by the AUX SYNC task every 1/2 sec.
FIG. 20 shows a detailed flow chart of the flash task 1136. The flash task is included in FIG. 8 as the flash task block 1136.
The concept behind the FLASH task is that flashing will attract the operator's attention much more quickly than simply maintaining a steady on condition. Most of the flashing lights indicate contingency conditions; a few indicate such things as invalid keyboard entries or that the DEH system is ready to go on automatic control. The flashing frequency is set at 1/2 sec on and 1/2 sec off as long as the condition exists. At the termination of the flashing condition, the corresponding lights and contacts are turned off.
A total of nine conditions are continually monitored for flashing by the FLASH task. These are listed below with a brief description of each.
1. Reference Low Limit--The turbine load reference is being limited by the low load limit.
2. Reference High Limit--The turbine load reference is being limited by the high load limit.
3. Valve Position Limit--The turbine governor valve output is being limited by the valve position limit.
4. Throttle Pressure Limit--The turbine load reference is being run back because throttle pressure is below set point. No light is flashed in this case but a contact output is set during the throttle pressure limiting.
5. DEH Ready for Automatic--The DEH control system has tracked the manual backup system and is ready to go on automatic control.
6. Valve Status Contingency--While on automatic control, the DEH system has detected a valve LVDT position not in agreement with its corresponding analog output.
7. Governor Valve Contingency--A governor valve LVDT position is not in agreement with its analog output.
8. Throttle Valve Contingency--A throttle valve LVDT position is not in agreement with its analog output.
9. Invalid Request--An invalid keyboard entry has been made.
In order to determine whether to flash a light or to suppress flashing, the FLASH task maintains two arrays in core memory. One of these is called LIMIT and contains the current value of the nine limiting or flashing conditions listed above, as they are set by various other DEH programs. The second array is called OLDLIMIT and is an image of the immediate past value of the LIMIT array. These two arrays are examined every 1/2 sec by the FLASH task according to the following table of combinations:
After the proper action is taken by the FLASH task, the OLDLIMIT array is then updated to agree with the current LIMIT array for the next pass through the task 1/2 sec later.
A third array called CCOFLAG is also maintained by the FLASH task in order to set contact outputs when a limiting condition exists. The contact outputs are not set and reset regularly (as are the flashing lights) but rather the contacts are set and remain on as long as the flashing condition exists. When the flashing condition ceases the contacts are reset. A table of combinations illustrating this action follows:
It should be noted that only the first five flash conditions listed above have contact outputs associated with them; the remaining four simply flash Operator's Panel lights.
The control of the operation of the DEH control system 1100 is greatly facilitated for the operator by the novel layout of the operator's panel 1130, the flashing and warning capabilities thereof, and the interface provided with the turbine control and monitor functions through the pushbutton switches. In addition, simulated turbine operation is provided by the DEH system for operator training or other purposes through the operation of the appropriate panel switches during turbine down time. Further, it is noteworthy that manual and automatic operator controls are at the same panel location for good operator interface under all operating conditions. More detail on the functioning of the panel pushbuttons is presented in Appendix 2 and elsewhere in the description of the DEH programs herein.
In addition the layout of the panel 1130 of FIGS. 17, 18 and 19 is unique and very efficient from operation and operator interface considerations. The control of the DEH system 1100 by the buttons of the panel 1130 and the software programs thereto provides improved operation of the computer 210 and turbine generator 10.
Software details of the panel 1130 interface are available in the appendices 3, 4, 5 and 6.
5. CONTACT CLOSURE OUTPUT TEST PROGRAM
In FIG. 21, a flow chart of a contact closure output test program 1610 is shown. The contact closure output test program 1610 provides a mechanism for setting any contact output or any group of consecutive contact outputs in the plant 1126. The contact closure output test task facilitates debugging of programs and testing computer hardware and plant wiring in field installations of the digital electrohydraulic system 1100.
In the field-installation phase of computer control systems, checkout of all parts of the system can be a tedious and frustrating chore. Debugging of programs, computer hardware and plant wiring is often a slow and painful process, and isolation of problems to one of these areas is sometimes difficult. It is during this time that the CCO TEST task provides a powerful tool for helping to bring the DEH system to full operating capabilities quickly.
The CCO TEST task is patterned along the lines of the DEH Input/Output (I/O) listing. The I/O list has a description of all contact outputs in numerically increasing order, from C001 to C224. The list includes a verbal description of the contact output function, its bit position, hardware word, set channel, and cabinet-half-shell terminal connection information. Since each contact output is identified by its C-number, to set or reset a contact or group of consecutive contacts, it is necessary only to type in the contact number(s) from the Programmer's Console and bid the CCO TEST task. Since analog outputs are essentially groups of contact outputs, the CCO TEST task may also be used to set any value on an analog output. This allows additional software and hardware testing prior to interfacing of the entire system.
6. SEQUENCE OF EVENTS INTERRUPT PROGRAM
The sequence of events interrupt program 1124 is shown in block form in FIG. 22. In order to carry out its functions properly, a computer control system must be provided with status input signals which represent the various states of the process or plant which is to be controlled. These status signals represent contacts which are normally open or closed (set or reset). Traditionally such contacts have been periodically scanned at some reasonable rate, such as every 1 sec. However, this method of processing contact inputs has two drawbacks. First, periodic contact scanning imposes a regular duty cycle on the computer; even through it may be small, it is unnecessary for the largest percentage of time when status contacts are not changing at a high rate. Secondly, when a contact does change state, the periodic scanning method (in the worst case) may not make this information available to the computer control system until a full scan period (say 1 sec) later. This situation clearly is undesirable for those control systems in which fast response is a necessity.
To minimize these effects, the DEH contact input scan is organized on a demand basis; a scan is initiated by a change of state on any of the contact inputs. Any contact status change generates a sequence of events interrupt which is processed by the Monitor interrupt handler. Identification of the interrupt causes the Monitor to run the SEQUENCE OF EVENTS INTERRUPT program, which calls the PLANTCCI subroutine to scan all of the contact inputs to the DEH system 1100. Once the PLANTCCI subroutine identifies the plant condition that changed state and activated the sequence of events program 1124 the execution of an appropriate function program may be initiated in accordance with the task priorities. Contact inputs scanned by the CCI subroutine are set forth in the input/output signal list in Appendix 4.
7. BREAKER OPEN INTERRUPT PROGRAM
Referring now to FIG. 1, if the breaker 17 opens thereby removing electrical load 19 from the generator 16, the turbine system 10 will begin to accelerate. The acceleration will overspeed the turbine generator system 10 and damage the turbine generator system 10 if it is not checked. It is mandatory that the turbine governor valves be closed an instant after the breaker opens, to cut off steam flow. The control system then reverts to speed control and positions the governor valves to maintain synchronous speed.
In order to restrict turbine overspeed when the breaker 17 opens, the breaker open contact is used to produce an interrupt. The Monitor interrupt handler than runs a BREAKER OPEN INTERRUPT program 1710 (FIG. 24), which immediately closes the governor valves by setting the appropriate analog output to zero.
FIG. 25 shows in detail the breaker open interrupt program flow chart. An independent hydraulic overspeed protection system shown in Ser. No. 189,322 by Fiegbein and Csanady also acts directly under predetermined conditions to close the governor valves GV1-GV8 and the throttle valves TV1-TV4 by dumping the hydraulic fluid in the valve actuators thereby giving additional protection to the turbine system 10. When the hydraulic overspeed protection system reacts to a breaker open operation (i.e. a full load rejection), the turbine steam valves are directly and immediately closed and the DEH system functions on a following basis to update its valve position outputs to call for valve closure. When a partial load rejection occurs, i.e. the breaker remains closed, a control strategy like that described in the aforementioned Birnbaum, Braytenbah and Richardson patent 3,552,872 is effected by the DEH system.
8. TASK ERROR PROGRAM
A task error program 1810 shown in FIG. 8 has supervisory control over all the other programs in the DEH system 1100. If any program is not functioning properly in correspondence to certain predefined error conditions, the task error program 1810 will switch the DEH system 1100 to manual control thereby preventing any accident, overload, underload, overspeed, or underspeed from happening. Thus, the TASK ERROR program 1810 switches control of the turbine from automatic to manual if certain important control tasks are disabled by the Monitor during input/output activity. The TASK ERROR program 1810 is initialized by the Monitor error handler.
The P2000 Monitor is composed of a variety of programs which handle all I/O activity for the DEH system. Thus, when some turbine control program wishes to use the I/O system, it calls the proper Monitor handler with a set of arguments describing the function to be performed. The handler then carries out the request and returns to the calling task at the completion of the function. However, in usual applications, if the handler finds erroneous information in the arguments passed along by the calling task, then the I/O request is ignored and the calling task is disabled. An example of such an error is a zero, negative or non-existent register number when calling the contact output handler.
An example of the usual operation of the P2000 Monitor in this particular case, i.e. in the DEH system, would be when a turbine operating program such as the panel task 1112 calls to use an input/output system such as the panel lamp program 1132. The panel task 1112 calls the monitor program 1122 with a set of arguments describing the function to be performed. The monitor program 1122 then carries out the request and returns to the panel task program 1112 at the completion of the function. However, if the monitor program 1122 finds erroneous information in the arguments or data passed along by the panel task 1112 then the input/output request for the panel lamp 1132 is ignored and the panel task 1112 is disabled. A monitor reference manual, TP043, of the Computer and Instrumentation Division of the Westinghouse Electric Corporation describes in detail all possible error conditions.
To give the DEH control system ability to take appropriate action if such an error occurs, the Monitor initialization provides an option SERO to indicate that a special TASK ERROR program will be available. This variable has been initialized with a zero value to indicate the option has been selected, and the task error table (Z:EROR) filled out with the transfer address of the TASK ERROR program. Reference to the DEH Monitor listing in Appendix 7 indicates which tasks will switch control to manual. When the Monitor handler detects an error condition it aborts the I/O request, disables the calling task, and runs the TASK ERROR program which switches the turbine to manual control.
FIG. 26 shows a block diagram of the task error program 1810. High safety and high reliability of operation of the DEH system 1100 are assured by the linking of the task error program 1810 to other DEH programs.
9. TURBINE TRIP INTERRUPT PROGRAM
TURBINE TRIP INTERRUPT program provides for throttle and governor valve closure immediately after the turbine latch mechanism is released. The TURBINE TRIP INTERRUPT program is initiated by the Monitor interrupt handler.
The mechanical latching mechanism of a turbine has a series of interlocks which are designed to trip the turbine off the line when any serious discrepancy is found in the system. Such factors as hydraulic fluid system, mechanical levers, emergency trip button, and solenoids operated by detection circuits may unlatch the turbine. When this happens, all throttle and governor valves must be closed to cut off steam flow immediately, after which the turbine begins to decelerate.
In FIG. 8, a turbine trip interrupt program 1850 is shown coupled to the plant wiring 1126 and to the throttle valves TV1-TV4 and the governor valves GV1-GV8 1021. If the turbine system 10 reaches a trip condition, a latch open contact 1852 changes state and indicates a trip to the turbine trip interrupt program 1850 by means of an interrupt signal. The Monitor interrupt handler then runs the TURBINE TRIP INTERRUPT program, which immediately calls for throttle and governor valve closure. Simultaneously the analog backup system detects the trip condition and provides a large closing bias voltage to the throttle and governor valve servo system, thus assuring via redundant circuits that all valves are closed. By closing all the valves in the turbine system 10, dangerous turbine overspeed and other conditions are avoided. A block diagram of the turbine trip interrupt system 1850 is shown in FIG. 27.
10. PANEL INTERRUPT PROGRAM
A block diagram of the panel interrupt program 1156 is shown in FIG. 28.
The PANEL INTERRUPT program responds to Operator's Panel pushbutton requests by decoding the pushbutton identification and bidding the PANEL task to carry out the appropriate response. The PANEL INTERRUPT program is initiated by the Monitor interrupt handler.
The DEH turbine control system is designed to provide maximum flexibility to plant personnel in performing their function of operating the turbine. This flexibility is evidenced by an Operator's Panel with an array of pushbuttons arranged in functional groups, and an internal software organization which responds immediately to pushbutton requests by the operator. The heart of this instant response is the interrupt capability of the DEH control system.
Pressing any panel pushbutton activates a diode-decoding network which identifies the pushbutton, sets a group of six contacts to an appropriate coded pattern, and generates an interrupt to the computer. The Monitor interrupt handler responds within microseconds and runs the PANEL INTERRUPT program, which does a demand contact input scan of the special panel pushbutton contacts and bids the PANEL task to carry out the function requested by the operator.
11. VALVE TEST, VALVE POSITION LIMIT AND VALVE INTERRUPT PROGRAM
Certain valve testing and limiting functions have been a traditional turbine control feature over the years to provide assurance of the emergency performance of valves and to give the operator a final override on the control valve position. Thus, on line testing of throttle valves periodically will detect potential malfunctions of the throttle valve mechanism which could be dangerous if not corrected. In addition, valve position limiting of the governor valves during on line operation provides a manual means of limiting steam flow from the Operator's Panel.
In the DEH control system these two important functions are initiated by appropriate pushbuttons on the panel. As long as the operator presses one of these pushbuttons, the proper action is carried out by the CONTROL program. When the operator releases any of these pushbuttons, this generates a special interrupt to terminate the action which has been performed.
Referring again to FIG. 8, a valve test program 1810 and a valve position limit program 1812 are subroutines of the control task program 1020. The valve test program 1810 tests the operation of any predetermined valve or valves such as the throttle valves TV1 through TV4 by the operator pressing a valve test button 1814 of FIG. 18 on the operator's panel 1130. The valve position limit program 1812 of the control task 1020 operates when an operator presses either of the two buttons, valve position limit lower 1816 or valve position limit raise 1818 of FIG. 18.
Referring again to FIG. 18, upon the release of the valve test button 1814, the valve position limit lower button 1816 or the valve position limit raise button 1818 by an operator, the valve interrupt program 1158 shown in FIG. 8, is run by the monitor program 1122. The monitor program 1122 runs the valve interrupt program 1158 and thereby resets various flags and counters thus signaling to the control task 1020 that the action is to cease. In FIG. 29 a block diagram of the valve interrupt program is shown.
12. STOP INITIALIZER PROGRAM
The STOP/INITIALIZE task 1162 (FIG. 8) initializes the DEH system to a known starting condition after the computer has stopped for any reason. (Note that stop here includes placing the computer out of sync.) The STOP/INITIALIZE task is assigned the highest priority level F.sub.16 (15.sub.10) and is bid by special insert instructions in the Monitor POWER-ON routine.
To control a continuously operating process successfully, a computer must be designed to run for very long periods of time without stopping. However, it must be recognized that power failures, computer hardware malfunctions of program errors will eventually cause all control computers to stop at some time in their operation. At these times, backup systems take over the process while the necessary maintenance is done on the computer or its software.
In FIG. 8, a stop/initializer program 1162 is shown ancillary to the clock program 1120. Should the DEH system 1100 have a power failure or be turned off, the stop/initializer program 1162, which has the highest priority (FIG. 9) of any program in the DEH system 1100, starts to run. Within the time that the voltages of the power supplies, not shown, decay to an unusable limit, the stop/initializer program 1162 sets the DEH system 1100 into a known state for the impending stop. Upon restarting, the stop/initializer program 1162 resets the system to the known state, i.e. it sets all contact and analog outputs to the throttle valves TV1 through TV4 and the governor valves GV1 through GV8 shown in box 1021 at reset position; all internal counters and logic states are reset; certain systems counters are set to starting values; a scan of all contact inputs from the plant wiring 1126 is carried out and the logic program 1110 is executed to align the DEH system 1100 to existing plant conditions. Finally, the controller reset lamp 1820 on the operator's panel 1130 as shown in FIG. 18 is turned on and the DEH system 1100 is ready to restart. A flow chart of the stop/initializer program is shown in FIG. 30.
When the operator presses the CONTROLLER RESET button, thus acknowledging the fact that the DEH system is operational again, all periodic programs begin to execute regularly and the control system tracks to the existing plant conditions. Operation from this point on is identical in all respects to normal execution of the DEH control system programs.
13. VISUAL DISPLAY PROGRAM
Visual display of numerical information which resides in memory has been a traditional function of control computer systems. This feature provides communication between the operator and the controller, with both display and changing of internal information usually available. Continuous display of a quantity provides visual indication of trends, patterns and dynamic response of control system variables; periodically updated values of the displayed quantity are entered into the windows so that fast changes may readily be observed by operating and technical personnel.
The DEH control system has provision for visual display of six important control quantities through dedicated individual pushbuttons. In addition, complete valve status (i.e. position) may be displayed through a group of appropriate pushbuttons; all remaining control system variables, parameters or constants may be displayed through another pushbutton, in conjunction with keyboard-entered dictionary addresses which select the desired quantity for display.
The visual display program 1134 as shown in FIG. 8 is connected with the panel interrupt program 1156 and the auxiliary synchronizer program 1114. The visual display program 1134 controls the display windows 1138 with a reference window 1852 and a demand window 1854. The demand window 1854 and the reference window 1852 are also shown in FIG. 18 as part of the operator's panel 1130. By pressing an appropriate button such as the reference button 1856 a reference value will be displayed in the reference window 1852 and a demand value will be displayed in the demand window 1854. Similarly, for example, if a valve position limit display button 1858 is pressed a valve position limit value will be displayed in the reference window 1852 and the corresponding valve variable being limited is displayed in the demand window 1854. Upon pressing the load rate button 1858 the load rate will be displayed in the reference window 1852. In addition, a keyboard 1860 has the capability through an appropriate program to select virtually any parameter or constant in the DEH system 1100 and display that parameter in the reference window 1852 and the demand window 1854. Referring now to FIG. 31 a table of the display buttons and their functions is given in greater detail. In FIG. 32 a block diagram of the visual display program system is shown. FIG. 33 shows a block diagram of the execution of a two-part visual display function.
14. ANALOG SCAN PROGRAM
In order to carry out its function, a computer control system must be provided with input signals from the process or plant variables which are to be controlled. However, the vast majority of real process variables (for example pressure, temperature and position) are analog or continuous in their natural form, whereas the organization and internal structure of computers is digital or discontinuous in nature. This basic difference in information format between the controller and the controlled process must be overcome with interfacing equipment which converts process signals to an appropriate computer numerical value.
A device which can accomplish this function is the analog-to-digital (A/D) converter. The A/D converter provides the interface between plant analog instrumentation and the digital control system. Normally the analog signal as picked up from a transducer is in the millivolt or volt range, and the A/D converter produces an output bit pattern which may be stored in computer memory. A/D converters can only convert a limited number of analog inputs to digital form in a given interval of time. The usual method of stating this limit is to indicate the number of points (analog inputs) which can be converted in 1 sec. Thus, the A/D converter used in the DEH system has a capacity of 40 pps. Since the total number of analog inputs to the DEH system maybe as high as 224, depending on the type of turbine to be controlled and the control system options selected, most of these must be scanned at a reduced frequency.
The nature of the plant variables which represent the analog inputs, and the sampling frequency of control programs using these inputs, are normally considered when one determines the scanning frequency of various analog input signals. In the DEH system, the control programs execute once a second and the primary analog signals used by the control system are generated megawatts, impulse pressure, throttle pressure, turbine speed and valve position. Since each of these variables may change a significant amount in a few seconds, all of these are scanned once a second. On the other hand, the majority of the analog inputs to the ATS program are temperatures which require minutes before significant changes in them may be observed. Consequently, all temperatures in the DEH system are scanned once a minute. The ATS program also requires a group of vibrations, which are scanned once every 5 sec, and a group of miscellaneous variables which are scanned once every 10 sec.
A timing diagram, or scan-frequency chart, is shown in FIG. 35 to indicate the complete analog scanning system for an end-bar-lift turbine having two throttle valves and two governor valves. The scanning pattern has been designed so that the A/D converter and the DEH computer system have an approximately uniform distribution of activity. A close look at FIG. 35 will indicate that once every 15 sec the analog scan system performs what is known as a SPAN/ADJUST operation. The purpose of this is to adjust the analog input bit patterns to account for drift in the A/D converter electronic circuitry and to account for the frequency variations, since the A/D converter operates on a voltage to fequency conversion principle.
The analog scan program 1116, shown in FIG. 8 periodically scans all analog inputs to the DEH system 1100 for control and monitoring purposes. The function of the analog scan program 1116 is performed in two parts. The first part of the analog scan program 1116 comprises the scanning of a first group of analog inputs. Values of scanned inputs are converted to engineering units and the values are checked against predetermined limits as required for computations in the DEH computer.
The second part of the function of the analog scan program 1116 comprises the scanning of the analog inputs required for the automatic turbine startup program as shown in FIG. 8. Conversion and limit-checking of this latter group of inputs is performed by another program. The automatic turbine startup program is shown in FIG. 8 as the ATS periodic program 1140, the ATS analog conversion routine 1142 and the ATS message writer program 1144.
15. LOGIC TASK
A functional organization diagram of the ANALOG SCAN task is shown in FIG. 34. The AUX SYNC task bids the ANALOG SCAN program every 1/2 sec. The ANALOG SCAN task then selects the appropriate group of inputs to be scanned, according to the timing diagram of FIG. 35, and calls the analog input handler portion of the Monitor. This handler triggers the A/D converter hardware to scan these points and suspends the ANALOG SCAN task until the bid patterns are available. The handler then restarts the ANALOG SCAN task, which converts the input bit patterns to engineering units, does appropriate limit-checking and makes logical decisions, and then exists until the next call from the AUX SYNC task, 1/2 sec later. Referring now to FIGS. 36 and 37, a block diagram representing the operation of the logic task 1110 is shown. A contact input from the plant wiring 1126 triggers the sequence of events or interrupt program 1124 which calls upon the plant contact closure input subroutine 1150 which in turn requests that the logic program 1110 be executed by the setting of a flag called RUNLOGIC 1151 in the logic program 1110. The logic program 1110 is also run by the panel interrupt program 1156 which calls upon the panel task program 1112 to run the logic program 1110 in response to panel button operations. The control task program 1020 in performing its various computations and decisions will sometimes request the logic program 1110 to run in order to update conditions in the control system. In FIG. 38, the functioning of the logic program 1110 is shown. FIG. 39 shows a more explicit block diagram of the logic program 1110.
The mechanism for actual execution of the LOGIC program is provided by the AUX SYNC task, which runs every 1/10 sec and carries out the scheduled and demand bidding of various tasks in the DEH system. AUX SYNC checks the state of the RUNLOGIC flag and, if it is set, bids the LOGIC task immediately. Thus, the maximum response time for LOGIC requests is 1/10 sec; on the average the response will be much faster than this.
In order to allow immediate rerunning of the LOGIC task should system conditions require, the LOGIC program first resets RUNLOGIC. Thus any other program may then set RUNLOGIC and request a bid which will be carried out by the AUX SYNC program within 1/10 sec. There are two major results of the LOGIC task: the computation of all logic states necessary for proper operation of the DEH system, and the processing of all status and monitor lamp contact outputs to inform the plant control system and operating personnel of the state of the DEH system.
The logic program 1110 controls a series of tests which determine the readiness and operability of the DEH system 1100. One of these tests is that for the overspeed protection controller which is part of the analog backup portion of the hardwired system 1016 shown in FIG. 6. Generally, the logic program 1110 is structured from a plurality of subroutines which provide the varying logic functions for other programs in the DEH program system, and the various logic subroutines are all sequentially executed each time the logic program is run.
LOGIC CONTACT CLOSURE OUTPUT SUBROUTINE
The logic task 1110 includes a subroutine called a logic contact closure output subroutine 1910 (FIGS. 36 and 37) therein. The logic contact closure output subroutine 1910 updates all the digital outputs to the status lamps and contacts 1128 for transmission thereto. The logic program 1110 handles a great number of contact outputs thereby keeping the output logic states of the DEH computer current. In addition, certain logical variables, which are normally set by the PANEL task, must be aligned by the LOGIC task with conditions as they exist instant by instant in the power plant. To do these functions in-line for each contact output in the LOGIC task would take considerable core storage to accommodate the individual situations. Thus, the logic contact closure output subroutine 1910 reduces the total storage requirements otherwise required for the logic program 1110.
MAINTENANCE TEST
In order to take advantage of the full flexibility, adjustability and dynamic response of the DEH system 1100 a maintenance test system 1810 is provided, a logic flow chart of which is shown in FIG. 40. The maintenance test program 1810 allows an operator to change, adjust or tune a large number of operational parameters and constants of the DEH system 1100. The constants of the DEH system 1100 can therefore be modified without extensive adjustment or reprogramming. An operator is able to optimize the DEH system 1100 from the control panel 1130 as shown in FIGS. 17 and 18 which allows for an essentially infinite variability in the choice of constants. Great flexibility and control is therefore available to an operator.
In addition, the maintenance test program 1810 of FIG. 40 allows an operator to use a simulation mode for operator training purposes.
TURBINE SUPERVISION OFF LOGIC
COMPUTER SET MANUAL LOGIC
When the DEH system is in automatic control, it is possible for certain conditions to occur which require transfer to manual operator control. One of these is the case in which the maintenance test switch is moved to the test position. Even though a wired connection places the control in manual operation, the DEH LOGIC program sets a contact output requesting transfer to manual as a backup. The second situation occurs when the turbine is on automatic speed control and all speed input signals fail, as determined by the speed selection program in the CONTROL task. This speed channel failure will also require transfer to manual operation by a contact output from this LOGIC task.
FIG. 42 shows a flow chart of a transfer to manual operation subroutine.
STM is the logical variable to switch to turbine manual control, and is set by the maintenance test contact input (OPRT) or the speed channel failure variable (SPFT) while on speed control (i.e. the main breaker (BR) is not set). A call to the LCCO subroutine is then made.
BREAKER LOGIC
The state of the main circuit breaker which connects the generator to the power system determines a primary control strategy of the DEH system. When the breaker is open, the DEH system is on speed control and thus positions the throttle and governor valves to maintain speed demand as requested by the operator, an automatic startup program, or an automatic synchronizer. When the breaker is closed, the DEH system is on load control and thus positions the governor valves to maintain load demand as requested by the operator or by an automatic dispatching system.
The function of the breaker logic program is to detect changes in the state of the main breaker and take the appropriate action. When the breaker opens, it is necessary to reset the breaker flip-flop to place the DEH control system on speed control; in addition, both the REFERENCE and DEMAND are set to synchronous speed, and the speed integral controller is reset to zero. The control system will then position the governor valves to maintain synchronous speed. When the breaker closes and the unit is synchronized to the line, the breaker logic program must set the breaker flip-flop to place the DEH system on load control; in addition both the REFERENCE and DEMAND are set to pick up an initial megawatt load so that the turbine does not tend to motor. The control system will then position the governor valves to maintain this initial load.
Referring again to FIG. 1, upon synchronization of the turbine system 10 with a power grid, not shown, the governor valves GV1 through GV8 must allow sufficient steam to flow through the turbine system 10 to overcome turbine system losses. Otherwise, upon synchronization of the generator 16 with other generators in the power grid by closing the breakers 17, the turbine system 10 would as already indicated have a tendency to motor. The DEH control system 1100, in order to prevent motoring and subsequent damage to the low pressure turbine section 24, automatically opens the governor valves GV1 through GV8 such that a predetermined load is picked up by the generator 16 upon synchronization.
The value of the initial megawatt pickup is defined as MWINIT upon synchronization is entered from the keyboard 1860 in FIG. 18 and is typically set at about 5% of the rating of the turbine-generator 10. In the load control system 1814, as shown in FIG. 43, the actual megawatt pickup is modified by a factor which is the ratio of the rated throttle pressure to the existing throttle pressure at synchronization. This factor is utilized by the DEH system 1100 in maintaining approximately the same initial megawatt load pickup whether the turbine system 10 is synchronized at rated throttle pressure or at some lower or even higher throttle pressure. A second condition must be handled by the breaker logic program to properly position the governor valves in picking up initial load. This concerns the fact that the governor valves just prior to synchronizing will be at some small position necessary to maintain synchronous speed. Then immediately after synchronization the initial megawatt pickup must be added to the existing valve position. Since the existing position is coputed by the speed control program and the new position will be computed by the load control program, then an equivalent load position must be computed from the existing speed position. Reference is made to Appendix 3 for details on the Breaker Logic Program.
MEGAWATT FEEDBACK LOGIC
Megawatt feedback is one of the two major loops used on turbine load control to maintain the governor valves at the correct position. The other feedback is impulse pressure; between these two loops it is possible to adapt the computer outputs to account for valve non-linearities and to assure that the megawatt setting in the reference window is actually being supplied by the turbine/generator.
The megawatt feedback logic places the megawatt loop in service on request from an operator's panel pushbutton, providing all permissive conditions are satisfied, and removes the loop from service from the operator's panel pushbutton or when any condition exists which requires removing the megawatt feedback. Placing the loop in service or removing it is done bumplessly, so that the governor valves remain at the same position. In addition, the REFERENCE and DEMAND values are automatically adjusted to agree with the new state of the DEH control system.
Referring to FIG. 46, a block diagram of the megawatt feedback loop is shown in greater detail than in FIG. 7. It should be noted that the speed compensated reference 1087, at the input of multiplication function 1086, is multiplied by the megawatt compensation 1089. The multiplication of the signals instead of a differencing provides an additional safety feature since the loss of either of the signals 1087 or 1089 will produce a zero output rather than a runaway condition.
IMPULSE PRESSURE FEEDBACK LOGIC
Impulse pressure feedback is the other of the two major loops used in the turbine load control to maintain the governor valves at the correct position. The impulse pressure feedback logic places the impulse pressure feedback loop in service on request from an operator's panel pushbutton, providing all permissive conditions are satisfied, and removes the loop from service on request from the operator or when any condition exists which requires removing impulse pressure feedback. Placing the loop in service or removing it is done automatically and bumplessly, so that the governor valves remain at the same position.
The impulse pressure feedback logic is shown in greater detail in FIG. 47. With a digital computer, bumpless transfer is achieved without the use of elaborate external circuitry because of the digital computational nature of the machine. A value can be computed instantaneously and inserted in the integrator 1218 of the proportional plus reset controller subroutine 1068 as shown in FIG. 11. In the preferred embodiment of the Digital Electro-Hydraulic control system 1100, the proportional plus reset controller 1168 is utilized by the following functions: the megawatt feedback loop 1091, the impulse pressure feedback loop 1816 and the speed feedback loop made up of the rated speed reference 1074, the compare function 1076 and the actual turbine speed function 1076.
SYNCHRONIZER LOGIC
During the process of accelerating a turbine on automatic speed control, the normal steps of operation may be summarized as follows: latch and roll the turbine on throttle control, accelerate to near synchronous speed, transfer to governor valve control, accelerate to synchronous speed, and synchronize the turbine with the power system. Most turbines are brought on the line with conventional automatic synchronizing equipment which carefully matches turbine conditions with power system conditions before automatically closing the main generator breaker.
The DEH control system 1100 provides an interface with synchronizing equipment by turning over supervision of the turbine reference and demand to the automatic synchronizer, which provides raise and lower pulses to the DEH system via contact inputs. Each pulse will raise and lower the turbine speed reference one rpm, thus providing the mechanism for adjusting the turbine speed to the power system. Provision has been made in the DEH system to allow selection of the auto sync mode through a pushbutton on the operator's panel or from an automatic turbine startup program, while the auto sync mode may be rejected by simply pressing the OPER AUTO pushbutton on the panel. The automatic synchronizer (auto sync) logic program detects those conditions concerned with auto sync, and sets all logical conditions accordingly. The turbine 10 operates in accordance with actions generated by the DEH control program in response to the synchronizer signals. FIG. 48 shows a flow chart of the automatic synchronizer logic program.
Because of the extreme accuracy of the ATS program 1141 in controlling the speed of the turbine 10 synchronization can be and preferably is performed without external automatic synchronizer equipment.
AUTOMATIC DISPATCH LOGIC
During the process of operating a turbine on automatic load control, the normal method of changing load is by entering new values of load demand from the keyboard, as described in the operating instructions. Then by using the GO and HOLD pushbuttons in conjunction with the load rate pushbutton, the operator may supervise the loading on the turbine which is actually carried out by the DEH system of control programs. This will result in the desired load being supplied to the power system by the turbine/generator.
Another method of supervising load on the turbine is through use of a remote automatic dispatching system. By turning over supervision of the turbine reference to an ADS operating mode, which provides raise and lower pulses whose width determines the requested load change, the DEH control system allows the turbine loading to be coordinated by a central dispatching office which can allocate total utility load on an economic basis to all units in the power system. Provision has been made in the DEH system to allow selection of the automatic dispatch mode through a pushbutton 1870 (FIG. 18) on the operator's panel; in addition, the ADS mode may be rejected by simply pressing the operator automatic pushbutton on the panel. The automatic dispatch logic program detects those conditions concerned with ADS, and sets all DEH states accordingly. A flow chart for the automatic dispatch logic program is shown in FIG. 49. It is triggered into operation on demand for automatic dispatch in order to interface the remote data with the DEH system.
AUTOMATIC TURBINE STARTUP (ATS) LOGIC
Modern methods of starting up turbines and accelerating to synchronous speed require careful monitoring of all turbine metal temperatures and vibrations to assure that safe conditions exist for continued acceleration. Until recently, these conditions have been observed by plant operators visually on various panel instruments. However, all of the important variables are rarely available from the plant instrumentation, and even if they were, the operator can not always be depended upon to make the right decision at a critical time. In addition to these factors, it is impossible to instrument the internal rotor metal temperatures, which are extremely important for indicating potentially excessive mechanical stresses.
To improve the performance at startup, automatic turbine accelerating programs have been written and placed under computer control. Such programs monitor large numbers of analog input signals representing all conceivable turbine variables, and from this information the program makes decisions on how and when to accelerate the unit. In addition, these programs numerically solve the complex heat distribution equations which describe temperature variations in the critical rotor metal parts. From these thermal computations it is possible to predict mechanical stresses and strains, and then to automatically take the proper action in the acceleration of the turbine.
The DEH system has such an automatic turbine startup program available as an optional item. Besides supervising the acceleration as described above, the program provides various messages printed on a typewriter to keep the operator informed as to the turbine acceleration progress. In addition, a group of monitor lamps are operated to indicate key points in the startup stages and to indicate alarm or contingency conditions. The automatic turbine startup logic program detects those conditions concerned with this DEH feature and sets all logical states accordingly.
REMOTE TRANSFER LOGIC
In the DEH turbine control system philosophy, the operator has overall authority in a control system hierarchy which has three general states: manual operation, operator automatic control, and remote automatic control. The manual operating mode is a contingency state which is used only when the computer is not available, as when the software control system is being tuned or modified. The operator automatic mode is the normal operating state during which speed/load demand and all other operating data are entered and displayed from the keyboard by the operator. Remote automatic control modes are those in which speed/load demand and rate are supervised from a source outside the basic DEH system.
In order to allow the DEH system 1100 to provide for automatic turbine operation from an independent source or a remote location, a remote transfer logic program shown in flow chart form in FIG. 51 is provided. In the preferred embodiment of the DEH system 1100, the available remote modes place the DEH system under control of the external automatic synchronizer system, the external automatic dispatching system or the automatic turbine startup system which is implemented within the DEH computer. An operator has the capability of choosing whichever mode is permissible and desired at a particular moment.
16. PANEL TASK
The DEH Operator's Panel is the focal point of turbine operation; it has been designed to make use of the latest digital techniques to provide maximum operational capability. The Operator's Panel provides the primary method of communicating information and control action between the operator and the DEH Control System. This is accomplished through a group of pushbuttons and a keyboard (which together initiate a number of diverse actions), and two digital displays (which provide the operator with visual indication of internal DEH system numerical values).
When pressed, any of the buttons on the Operator's Panel provide momentary action during which a normally-open contact is connected to an electronic diode matrix. Operation of a button energizes a common computer interrupt for the Operator's Panel and applies voltage to a unique combination of 6 contact inputs assigned as a pushbutton decoder. The diode matrix may be used to identify up to 60 pushbuttons. When a button is pressed, the associated interrupt is read within 64 .mu.sec, and the corresponding contact inputs scanned and stored in computer memory as a bit pattern for further processing.
Each of the buttons on the panel are backlighted. When a button is pressed and appropriate logical conditions exist, the lamp is turned on to acknowledge to the operator that the action he initiated has been carried out. Should the proper logical conditions not be set, the lamp is not turned on. This informs the operator that the action he requested cannot be carried out.
A few of the buttons are of the digital push-push type which when pushed once initiate an action, and when pushed again suppress that action. Some of these buttons also contain a split lens which indicates one action in the upper half of the lamp and another (usually opposite) action in the lower lens. In addition, certain button backlights are flashed under particular operating circumstances and conditions.
The buttons and keys on the Operator's Panel may be grouped in broad functional groups according to the type of action associated with each set of buttons. A brief description of these groups follows:
1. CONTROL SYSTEM SWITCHING--These buttons alter the configuration of the DEH Control System by switching in or out certain control functions. Examples are throttle pressure control and impulse pressure control.
2. DISPLAY/CHANGE DEH SYSTEM PARAMETERS--These buttons allow the operator to visually display and change important parameters which affect the operation of the DEH system. Examples are the speed and load demand, high and low load limits, speed and load rate settings, and control system tuning parameters.
3. OPERATING MODE SELECTION--This group of buttons provides the operator with the ability to select the turbine operating mode. Examples are permitting an Automatic Synchronizer or an Automatic Dispatch System to set the turbine reference, or selecting local operator automatic control of the turbine (which includes hold/go action).
4. VALVE STATUS/TESTING/LIMITING--This group of buttons allows valve status information display, throttle/governor valve testing, and valve position limit adjustment.
5. AUTOMATIC TURBINE STARTUP--This group of buttons is used in conjunction with a special DEH program which continuously monitors important turbine variables, and which also may start up and accelerate the turbine during wide-range speed control.
6. MANUAL OPERATION--These buttons allow the operator to manually control the position of the turbine valves from the Operator's Panel. The DEH PANEL task has no direct connection with this group of buttons.
7. KEYBOARD ACTIVITY--These buttons and keys allow numerical data to be input to the DEH system. Such information may include requests for numerical values via the display windows, or may adjust system parameters for optimum performance.
The panel task 1112 responds to the buttons pressed on the operator's panel 1130 by an operator of the DEH control system 1100. The control panel 1130 is shown in FIGS. 17 and 18. Referring now to FIGS. 52 and 53, the interactions of the panel task 1112 are shown in greater detail. Pushbuttons 1110 are decoded in a diode decoding network 1912 which generates contact inputs to activate the panel interrupt program 1156. The panel interrupt program scans the contact inputs and bids the panel task 1112 whereby the pressed button is decoded and either the panel task 112 carries out the desired action or the logic task 1110 is bid or the visual display task 1134 is called to carry out the desired command.
17. CONTROL PROGRAM
Automatic control of turbine speed and load requires a complex, interacting feedback control system capable of compensating for dynamic conditions in the power system, the boiler and the turbine-generator. Impulse chamber pressure and shaft speed from the turbine, megawatts from the generator, and throttle pressure from the boiler are used in the controlled operation of the turbine.
In addition to the primary control features discussed above, the DEH system also contains provisions for high and low load limits, valve position limit, and throttle pressure limit; each of these can be adjusted from the Operator's Panel. A number of auxiliary functions are also available which improve the overall turbine performance and the capabilities of the DEH system. Brief descriptions of these follow:
1. Valve position limit adjustment from the Operator's Panel.
2. Valve testing from the Operator's Panel.
3. Speed signal selection from alternate independent sources.
4. Automatic instantaneous, and bumpless operating-mode selection from the Operator's Panel.
5. A continuous valve position monitor and contingency-alert function for the operator during automatic control.
6. A digital simulation and training feature which allows use of the Operator's Panel and most of the DEH system at any time on manual control, without affecting the turbine output or valve position. This powerful aid is used for operator and engineer training, simulation studies, control system tuning or adjustment, and for demonstration purposes.
In order to achieve these objectives, the CONTROL task is provided with analog inputs representing the various important quantities to be controlled, and also is supplied with contact inputs and system logical states.
The control program 1012 and related programs are shown in greater detail in FIG. 54. In the computer program system, the control program 1012 is interconnected with the analog scan program 1116, the auxiliary sync program 1114, the sequence of events interrupt program 1124 and the logic task 1110. FIG. 55 shows a block diagram of the control program 1012. The control program 1012 accepts data from the analog scan program 1116, the sequence of events interrupt program 1124 and is controlled in certain respects by the logic program 1110 and the auxiliary synchronizing program 1114. The control program 1012, upon receiving appropriate inputs, computes the throttle valve TV1-TV4 and the governor valve GV1-GV8 outputs needed to satisfy speed or load demand.
The control program 1012 of the DEH control system 1100 functions, in the preferred embodiment, under three modes of DEH system control. The modes are manual, where the valves GV1-GV8 and TV1-TV4 are positioned manually through the hardwired control system and the DEH control computer tracks in preparation for an automatic mode of control. The second mode of control is the operator automatic mode, where the valves GV1-GV8 and TV1-TV4 are positioned automatically by the DEH computer in response to a demand signal entered from the keyboard 1130, of FIG. 18. The third mode of control is remote automatic mode, where the valves GV1-GV8 and TV1-TV4 are positioned automatically as in the operator automatic mode but use the automatic turbine startup program 1141 or an automatic synchronizer or an automatic dispatch system for setting the demand value.
VALVE POSITION LIMIT FUNCTION SUBROUTINE
Referring now to FIGS. 56 and 56a, a block diagram of the valve position limit function subroutine 1950 is shown in detail. A speed control signal is limited by limit function 1952 which is controlled by the valve position limit function 1954 (VPOSL); similarly the governor valve speed signal (GVPOS) signal is limited by limiting function 1956. The valve position limit function 1954 may be raised by a raise function 1960 and lowered by a lower function 1958.
VALVE CONTINGENCY FUNCTION
A valve contingency function 1964 is shown in the flow chart of FIG. 58. In the automatic control mode, the valve contingency function subroutine 1964 continuously checks for discrepancies between the positions of the governor valves GV1 to GV8 called for by the DEH controller system 1100 and the actual valve positions sensed by a linear variable differential transformer LVDT of FIG. 4. If the discrepancy between the sensed and actual positions exceeds a predetermined value set on the keyboard 1860 of the operator's panel 1130, shown in FIG. 18, a valve status lamp 1966 warns the operator of this discrepancy situation. The valve contingency subroutine 1964 interfaces with the process and the operator through the analog scan program 1116 and the operator's panel 1130 of FIG. 8.
SPEED SELECTOR FUNCTION
When operating a steam turbine, the single most important variable which must be controlled is shaft speed. During load operation, speed regulation is necessary to help the power system maintain line frequency. During wide-range speed control, precise speed control is doubly important to bring the unit to synchronous speed and to overcome critical speed points at which excessive vibrations may cause a turbine trip. To accomplish such demanding control objectives, it is necessary to provide high-accuracy speed input signals to the control system so that exact valve position outputs may be computed by the speed controllers.
The DEH Control System has three independent speed signals available; these are used to achieve the precision required in speed control. The first of these (which is called the digital speed) is generated by a magnetic pickup, shaped and counted by specially-designed electronic printed circuitry, and passed on to the DEH Control System in the form of a digital numerical value. The second speed signal (which is called the analog speed) is generated by an identical independent magnetic pickup, processed in the analog packup circuitry for use there, and passed on to the DEH system as an analog input. The third speed signal (which is called the supervisory speed) is also generated by its own magnetic pickup, processed by supervisory instrumentation methods, and passed on to the DEH Control System as an analog input.
Referring now to FIG. 59, a block diagram of the DEH speed instrumentation and computation interface is shown. A digital counting and shaping circuit 2010 described in the copending Ruether application Ser. No. 412,513, referred to supra, generates the highly accurate digital signal. The digital shaping and counting circuitry 2010 includes a magnetic pickup, a shaping and counting circuit which passes the data to the DEH computer in the form of a digital numerical value. The second or analog speed signal is generated by high accuracy analog processing circuitry 2012. The third or supervisory signal is generated by analog supervisory instrumentation processing circuitry 2014 and transmitted to an analog to digital converter 2016 with the signal from the high grade analog processing circuitry 2012.
The speed selection function determines which of these available speed inputs should be used in the DEH Control System. If the speed selection process concludes that the digital speed is reliable, then under all circumstances it is used as the controlling speed signal because it is the most accurate. If the selection process concludes that the digital speed is unreliable, the analog speed is used as the controlling speed signal since it is of acceptable accuracy. If neither the digital nor the analog speed signal is reliable, the speed selection function must disable the speed feedback control loop, because the supervisory speed is not of acceptable accuracy for controlling turbine speed response.
Although the supervisory speed is unacceptable for control requirements, it performs a valuable role in helping to determine which of the two speeds, digital or analog, is to be used in the DEH system. The speed selection accomplishes this by using a two-out-of-three logical error detection process to deduce the status of the digital and the analog speed signals. If either becomes unreliable, logical states are set which will turn on appropriate monitor lamps on the Operator A Panel. In addition, if a switch is made from the digital to the analog speed signal, or vice versa, while on load control, appropriate bumpless transfers are made with respect to the turbine reference and valve position outputs.
If both the digital and the analog speeds become unreliable, the speed selection function makes a more serious decision as to what control action to take. Thus, if the turbine is on wide-range speed operation, the DEH system must transfer to manual control and stop all speed control computations; this is necessary because the speed feedback information is unreliable. However, if the turbine is on load control, the DEH system simply opens the speed feedback loop bumplessly and continues on automatic control. This is acceptable because the speed feedback is simply a trim factor during load operation.
In the digital speed circuitry there are actually two numerical outputs, each of which is accurate in certain ranges. The quantity ICOURSE is a low-range course value which is appropriate from 0 to about 1600 rpm, while the quantity of IFINE is a high-range vernier value which is appropriate from about 1600 to 4500 rpm. Thus, the speed selection function must determine which of these values to use in its two-out-of-three comparison with the remaining speed signals. The final result of the speed selection process is the value WS which is used by all other programs in the DEH system. The digital signal from the digital shaping and counting circuitry 2010 passes through a speed channel interrupt 2018 to a speed channel decoding program 2020 as shown in FIG. 59. In this speed counting program 2020 an output quantity designated ICOURSE is the low range course value used from about 0 to 1600 rpm, while the IFINE quantity is the high range fine value used between about 1600 to 4500 rpm.
An analog to digital converter 2016 makes both the high precision analog signals from the analog processing circuitry 2012 and the supervisory circuitry 2014 available to the analog scan program 1116 which in turn provides the represented speed values available to the speed selection program 2022. The speed selection program 2022 compares the digital speed value and the high grade analog speed value with the supervisory analog speed value in order to determine whether both the digital value and the high grade analog value are accurate or whether there is any discrepancy between the two. The supervisory speed value is generally not accurate enough for speed control. Therefore, the speed selection program 2022 makes use of the supervisory speed value to determine which of the high grade speed values is accurate if they are not equal.
The digital speed value from the digital shaping and counting circuitry 2010 is used as the reference WS at 1076 if it is found to be accurate enough for control purposes. The high grade analog speed value from the analog processing circuitry 2012 is utilized if the digital speed value is not accurate enough for control purposes. If either of the high grade signals becomes unreliable, appropriate monitor lamps on the control panel 1130 alert an operator to this fact.
If both the high grade analog and the high grade digital speed values become unreliable and if the DEH system 1100 is on wide range speed control then a transfer takes place to the manual mode of control. However, if the turbine system 10 is on load control, the DEH system 1100 opens the speed feedback loop bumplessly and continues on automatic control with the remaining feedback loops intact.
SELECT OPERATING MODE FUNCTION
Input demand values of speed, load, rate of change of speed, and rate of change of load are fed to the DEH control system 1100 from various sources and transferred bumplessly from one source to another. Each of these sources has its own independent mode of operation and provides a demand or rate signal to the control program 1020. The control task 1020 responds to the input demand signals and generates outputs which ultimately move the throttle valves TV1 through TV4 and/or the governor valves GV1 through GB8.
With the breaker 17 open and the turbine 10 in speed control, the following modes of operation may be selected:
1. Automatic synchronizer mode--pulse type contact input for adjusting the turbine speed reference and speed demand and moving the turbine 10 to synchronizing speed and phase.
2. Automatic turbine startup program mode--provides turbine speed demand and rate.
3. Operator automatic mode--speed, demand and rate of change of speed entered from the keyboard 1860 on the operator's panel 1130 shown in FIG. 18.
4. Maintenance test mode--speed demand and rate of change of speed are entered by an operator from the keyboard 1860 on the operator's control panel 1130 of FIG. 18 while the DEH system 1100 is being used as a simulator or trainer.
5. Manual tracking mode--the speed demand and rate of change of speed are internally computed by the DEH system 1100 and set to track the manual analog back-up system 1016 as shown in FIG. 6 in preparation for a bumpless transfer to the operator automatic mode of control.
With the breaker 17 closed and the turbine 10 in the level mode control, the following modes of operation may be selected:
1. Throttle pressure limiting mode--a contingent mode in which the turbine load reference is run back or decreased at a predetermined rate to a predetermined minimum value as long as a predetermined condition exists.
2. Run-back mode--a contingency mode in which the load reference is run back or decreased at a predetermined rate as long as a predetermined condition exists.
3. Automatic dispatch system mode--pulse type contact inputs are supplied from an automatic dispatch system to adjust turbine load reference and demand when the automatic dispatch system button 1870 on the operator's panel 1130 is depressed.
4. Operator automatic mode--the load demand and the load rate are entered from the keyboard 1830 on the control panel 1130 in FIG. 18.
5. Maintenance test mode--load demand and load rate are entered from the keyboard 1860 of the control panel 1130 in FIG. 18 while the DEH system 1100 is being used as a simulator or trainer.
6. Manual tracking mode--the load demand and rate are internally computed by the DEH system 1100 and set to track the manual analog back-up system 1016 preparatory to a bumpless transfer to the operator automatic mode of control.
The select operating mode function responds immediately to turbine demand and rate inputs from the appropriate source as described above. This program determines which operating mode is currently in control by performing various logical and numerical decisions, and then retrieves from selected storage locations the correct values for demand and rate. These are then passed on to the succeeding DEH control programs for further processing and ultimate positioning of the valves. The select operating mode function also accommodates switching between operating modes, accepting new inputs and adapting the DEH system to the new state in a bumpless transfer of control.
Various contact inputs are required for raise and lower pulses, manual operation, maintenance test, and so forth; these are handled by the SEQUENCE OF EVENTS interrupt program and the PLANTCCI subroutine, which performs a contact input scan. In addition, certain panel pushbuttons affect the operating mode selection; these are handled by the PANEL INTERRUPT program and the PANEL task, which decode and classify the pushbuttons pressed. The LOGIC task then checks all permissive conditions and current control system status, and computes the appropriate logical states for interpretation by the CONTROL task and the SELECT OPERATING MODE program.
Referring now to FIG. 61, a block diagram is shown illustrating the select operating mode function 2050. Contact inputs from plant wiring 1126 activate the sequence of events interrupt program 1124 which calls the plant contact input subroutine 1150, to scan the plant wiring 1126 for contact inputs. Mode pushbuttons such as automatic turbine startup 1141, automatic dispatch system 1170 and automatic synchronizer 1871 activate the panel interrupt program 1156 which calls the panel program 1112 for classification and which in turn calls upon the logic program 1110 to compute the logic states involved. The logic program 1110 calls the control program 1020 to select the operating mode in that program.
In FIGS. 61A and 61B a flow chart of the select operating mode logic is shown. As one example of mode selection referring to a path 2023, after a statement 7000, provisions are made for a bumpless transfer from an automatic or test mode to an operator mode. The bumpless transfer is accomplished by comparing the computer outputs and the operator mode output signals for the governor valve GV1-GV4 positions. The DEH system 1110 inhibits any transfer until the error between the transferring output and the output transferred is within a predetermined deadband (DBTRKS). Bumpless transfer is accomplished by the DEH control system 1100 by comparing output from one mode of control of the governor valves GV and the throttle valves TV and the same output from another output mode controlling the same parameters. The flow chart of FIGS. 61A and 61B shows mode selection for a complete system. In a hardwired or analog control system, the analog parameter output, to be transferred to must continuously track the parameter output to be transferred from. This tracking method is expensive and cumbersome since it has to be done continuously and requires complex hardware. However, in a digital system, such as the DEH control system 1100, the equating of the two parameter outputs need be performed only on transfer. Therefore, great economy of operation is achieved.
SPEED/LOAD REFERENCE FUNCTION
In the DEH turbine controller, the speed/load reference is the central and most important variable in the entire control system. The reference serves as the junction or meeting place between the turbine speed or load demand, selected from any of the various operating modes discussed in the last section, and the Speed or Load Control System, which directs the reference through appropriate control system strategy to the turbine throttle and governor valves to supply the requested demand. FIG. 62 is a diagram which indicates the central importance of the reference in the DEH control system.
The speed/load reference function increments the internal turbine reference at the selected rate to meet the selected demand. This function is most useful when the turbine is on Operator Automatic, on the AUTOMATIC TURBINE STARTUP program, or in the Simulator/Trainer modes. This is because each of these control modes requests unique rates of change of the reference, while the remaining control modes, such as the Automatic Synchronizer and the Automatic Dispatch System, move the reference in pulses or short bursts which are carried out in one step. The Runback and Throttle Pressure contingency modes use some of the features of the reference function, but they bypass much of the subtle reference logic in their hurry to unload the turbine.
For these modes which request movement of the reference at a unique rate, the reference function must provide the controlled motion. Not only must the rate be ramped exactly, but the logic must be such that, at the correct time, the reference must be made exactly equal to the demand, with no overshoot or undershoot. In addition, the reference logic must be sensitive to the GO and HOLD states, and must start or stop movement instantly if requested to do so. Finally, the reference system must turn off the GO and HOLD lamps, if conditions dictate, by passing on to the LOGIC task the proper status information to accomplish this important visual indication feature.
FIG. 63 is a plot of the reference as it moves to meet a given demand, both in the increasing and decreasing direction. The slope of the reference curve is the rate selected by the controlling mode. A key point in the reference system is the detection of the instant in time when the reference is within one increment of the demand; this increment is the step size associated with the selected rate, taken each second by the CONTROL task whose sampling interval is once a second. For example, an acceleration rate of 120 rpm per min yields an incremental speed step size of 2 rpm each sec, while a load rate of 30 MW per min yields an incremental load step size of 0.5 MW each sec. Thus when the reference approaches to within this step size of the demand, then the reference system immediately sets the internal reference to the demand. This condition is indicated by the step jumps at the 12-sec and the 21-sec points in time on the graph of FIG. 63. Special logical and numerical decisions are required to detect these points.
The decision breaker function 1060, of FIG. 7, is identical to the speed/load reference function 1060, of FIG. 62. A software speed control subsystem 2092 of FIG. 62, corresponds to the compare function 1062, the speed reference 1066 and the proportional plus reset controller function 1068, of FIG. 7. The software load control subsystem 1094, of FIG. 62, corresponds to the rated speed reference 1074, the turbine speed 1076, the compare function 1078, the proportional controller 1080, the summing function 1972, the compare function 1082, the proportional plus reset controller function 1084, the multiplication function 1086, the compare function 1090, the impulse pressure transducer 1088 and the proportional plus reset controller 1092, of FIG. 7. The speed/load reference 1060 is controlled by, depending upon the mode, and automatic synchronizer 1080, the automatic turbine starter program 1141, and operator automatic mode 1082, a manual tracking mode 2084, a simulator/trainer 2086, an automatic dispatch system 2088, or a run-back contingency load 2090. Each of these modes increments the speed/load reference function 1060 at a selected rate to meet a selected demand. A typical demand/reference rate is shown in FIG. 63 drawn as a function of time.
SPEED CONTROL FUNCTION
The speed control function positions the throttle and governor valves to achieve the existing speed reference with optimum dynamic and steady state response. This is accomplished by using individual proportional-plus-reset controllers for throttle and governor valve speed control, as shown in FIG. 64. The speed error between the turbine speed reference and actual speed drives the appropriate controller, which then reacts by positioning the proper valves to reduce the speed error to zero. The speed controller outputs are low-limit checked against zero and high-limit checked against the quantity HLS, which is a keyboard-entered constant set at 4200 rpm. This prevents the controllers from reaching a reset-windup condition which may inadvertently occur in odd circumstances. The speed controller output is then suitably ranged from 0 to 100 percent and sent downstream as the quantity SPD in the CONTROL task to the THROTTLE and GOVERNOR VALVE programs.
LOAD CONTROL FUNCTION
The load control function positions the governor valves to achieve the existing load reference with optimum dynamic and steady state response. This is accomplished with a feedforward-feedback control system strategy designed to stabilize interactions between the major turbine-generator variables: impulse chamber pressure, megawatts, shaft speed and valve position. FIGS. 65 and 65A show the control system which satisfies these objectives.
The main feedforward path is represented by the turbine load reference value (REFDMD), which is computed by the operating mode selection function described earlier. The feedforward variable (REFDMD) is compensated with two feedback trim factors to account for frequency (speed) participation and megawatt mismatch. The speed compensation is provided by a proportional feedback loop in which the droop regulation gain (GR1) is adjusted to yield rated megawatts correction for a 180 rpm speer error. This speed feedback factor (X) is then summed with the turbine load reference (REFDMD) to produce the speed-corrected load reference (REF1).
A special feature which has been incorporated in the speed feedback loop is a software speed-deadband; this non-linear function filters out high-frequency low-amplitude noise on the speed input signal, thus keeping the load control system from responding to such meaningless information. The width of the speed deadband may be adjusted from the keyboard by setting the appropriate value into the constant SPDB. Another special feature of the speed deadband is the method of implementing this function in comparison with most standard control systems. The common way to incorporate the speed deadband in previous systems is to allow speed errors greater than the width of the deadband to enter the control system completely. This has been found to shock many systems into oscillatory conditions which may have undesirable effects. In the DEH Control System the speed error, when it is larger than the deadband, is smoothly entered into the speed compensation factor by a linear relationship. Thus the shock effect of a sudden speed error is removed completely.
The megawatt feedback loop provides a trim correction signal which is applied to the speed-compensated load reference (REF1) in a product form to yield the speed-and-megawatt corrected load reference (REF2). An additional highly desirable feature of megawatt feedback in the DEH system is that with it the reference and demand display windows on the Operator's Panel are calibrated in actual megawatts when the loop is in service. A proportional-plus-reset controller is used to reduce megawatt error to zero, with the loop providing a feedback factor (Y) which floats around unity (1.9) in performing its corrective action. As usual, high and low limits are provided to prevent reset windup and to bound the range of megawatt compensation.
The load reference (REF2), now corrected for speed and megawatt errors, becomes the set point for the impulse pressure cascade feedback loop or the direct demand for valve position, depending on whether the impulse pressure loop is in or out of service. REF2 is multiplied by a ranging gain (GR3) to convert to impulse pressure set point (PISP) in psi. If the loop is in service, then a proportional-plus-reset controller is implemented to drive the impulse pressure error to zero; as always, high and low limits restrict the range of variation of the controller to eliminate the possibility of reset windup. The final governor valve set point (VSP), whether it is generated by the feedback loop or directly from the load reference (REF2), is then converted into a percent valve demand (GVSP) by suitable ranging and is sent downstream in the control task to the THROTTLE and GOVERNOR VALVE programs.
The load control function block diagram shown in FIGS. 65 and 65A is an expansion of the load control, shown in FIG. 7, incorporating the speed loop subroutine and proportional control of function diagram of FIG. 13.
THROTTLE VALVE CONTROL FUNCTION
The throttle valve control function (FIG. 66) computes the correct value of the throttle valve analog output at all times. When the DEH system is on automatic control, this analog output actually positions the throttle valves; when the DEH system is on manual control, this analog output tracks the backup system preparatory to transfer to automatic control.
To accomplish its objective, the throttle valve control function must interrogate various turbine logical and numerical states, and proceed to act on the outcome of these decisions. There are five distinct situations which must be detected by these logical and numerical interrogations. A brief description of these follow; refer to Figure for the method of performing these tests and the major actions taken.
1. The turbine is unlatched and in neither throttle nor governor valve control. During this time the throttle valves are held closed by the throttle valve control function.
2. The turbine is latched and in positive throttle valve control while the DEH system is in wide-range speed control. During this time the throttle valve control function accepts the output of the speed controller (SPD) and positions the throttle valves accordingly.
3. The DEH system is in a transition period, transferring from throttle to governor valves during wide-range speed control. For this interval of time, the throttle valves are still in positive control and the throttle valve control function continues to accept the speed controller output (SPD) and positions the throttle valves accordingly.
4. The DEH system remains in the transition period of transferring from throttle to governor valve control, but now the governor valves are in positive control. During this time the throttle valve control function drives the throttle valves to the wide-open position with a throttle valve bias integrator (TVBIAS), which has a constant input (BTVO) incrementing the integrator.
5. The transition period is over and the transfer from throttle to governor valve control is complete; the turbine is now on either wide-range speed control or on load control after having been synchronized with the power system. During this time the throttle valve control function keeps the throttle valves wide open.
GOVERNOR VALVE CONTROL FUNCTION
The governor valve control function (FIG. 67) computes the correct value for the governor valve analog output at all times. When the DEH system is on automatic control, this analog output actually positions the governor valves; when the DEH system is on manual control, this analog output tracks the backup system preparatory to transfer to automatic control.
To accomplish its objective, the governor valve control function must interrogate various turbine logical states and proceed to act on the outcome of these decisions. There are five distinct situations which must be detected by these logical interrogations. A brief description of these follows; refer to Figure for the method of performing these tests and the major action taken.
1. The turbine is unlatched and in neither throttle nor governor control. During this time the governor valves are held closed by the governor valve control function.
2. The turbine is latched and in positive throttle valve control while the DEH system is in wide-range speed control. During this time the governor valve control function drives the governor valves wide open with a governor valve bias integrator (GVBIAS).
3. The DEH system is in a transition period, transferring from throttle valve to governor valve control during wide-range speed operation. For this interval of time, the governor valve control function drives the governor valves to the closed position with the governor valve bias integrator (GVBIAS). The governor valve control function then waits for a decrease in turbine speed and for the Analog Backup System to track the computer outputs.
4. The DEH system remains in the transition period but now the governor valves are in positive control during wide-range speed operation. During this time the governor valve control function accepts the output of the speed controller (SPD) and positions the governor valves accordingly.
5. The main generator circuit breaker is closed and the DEH system is in load control. During this time the governor valve control function accepts the output of the load control system (GVSP) and positions the governor valves accordingly.
TURBINE OPERATION SIMULATION
In order to allow operators to become proficient in the operation of the DEH system 1100 without risking damage to a multimillion dollar turbine-generator system 10 a simulation subroutine 2110, in FIG. 64, is provided during speed control. A similar subroutine 2111 (FIG. 65) is provided for simulation of the turbine-generator system dynamics during load control.
BUMPLESS TRANSFER
A flow chart path (FIG. 67) allows for the smooth and bumpless transfer from governor valve control to throttle valve control and vice versa. A function 2102 tests whether a governor valve bias integrator GVBIAS has reached zero. By forcing the DEH system 1100 to wait until the governor valve bias integrator GVBIAS has reached zero a bumpless transfer from governor to throttle valve control and vice versa is effectuated. Other bumpless transfer features are considered elsewhere herein.
18. DEH DATALINK
A DEH DATALINK shown in FIG. 8 allows the DEH control system 1100 to communicate with other computers such as a plant computer. In the preferred embodiment, the communication is initiated by the other computer, the plant computer. The DEH DATALINK waits for requests to send or receive information. In the operation of the DEH DATALILNK any core location can be interrogated and numerous setpoint values can be changed. The format of the DATALINK is such that information as to a starting address in the memory 214, and a code indicating the number of words to be interrogated or changed. The following eight-bit control words are used for DATALINK transmission and reception.
For an absolute starting address in core to transmission words are used indicating the number of transmission words in one transmission. In the sequencing charts 8-bit numbers are represented by the following symbols:
ADD:First half of absolute core address
REF:Second half of absolute core address
WDS:Number of transmission words
W1, W2, . . . :Transmitted information
LIC:Checksum
The checksum is the binary sum of all 8-bit numbers of a data transmission with any remainder truncated. The hardware for the DEH DATALINK is operated asynchronously. A message can be transmitted at any time from the plant computer. The interrupt program 1124 is provided so that the plant computer can be serviced immediately.
FIG. 76a shows a DATALINK between two computers. A modem 2510 transmission system, available through the Bell Telephone Company, is shown for data transmission. The sequence of events interrupt program 1124 directs the computer 210 to execute one or more instructions in a sequence thereby interrupting any program running in the computer 210. When the interrupt program 1124 has finished, the computer 210 returns to complete the program which it was previously executing.
A DATALINK task shuttles any received data words into an input buffer in the memory 214 and thereby through the action of the central processor 212 generates the checksum which is compared with a received checksum. The data from the DEH system is transmitted and a checksum calculated at both the plant computer and the DEH computer 210. If a mistake is found an alarm interrupt is generated and a control word indicating an error is sent back and no further action is taken. The plant computer or requesting computer must then send the same message again for a second reply. If the interrupt program receives a proper message request, a DEH DATALINK task is energized again. A complete program of the DATALINK system is to be found in the appendices.
G. ANALOG BACKUP SYSTEM
The analog backup portion of the DEH Control System provides a second means, independent of the digital portion, of controlling the turbine valves. In the event of a failure in the digital portion, or during certain maintenance modes of operation, the Analog Backup System generates the signals necessary to control the valves, and thus the turbine.
While the digital portion of the control system is in service and in control of the turbine (the Operator Automatic mode), the analog system tracks the digital control signals. If the digital portion fails, or manual operation is selected, the DEH Control System transfers to the Analog Backup System without a change in valve positon (bumpless transfer). When the analog portion is supplying the control signals (the Turbine Manual mode), the operator controls valve position using the "manual" pushbuttons on the Operator B Panel.
In addition to tracking and positioning capabilities, the Analog Backup System provides protection circuits. This protection capability is used during contingency conditions, and duplicates similar protection circuits. This protection capability is used during contingency conditions, and duplicates similar protection provided by the digital portion of the DEH Control System. Thus, the operator is provided with an effective means of operating the turbine during a contingency condition or during maintenance or testing of the system.
Modes Of Operation
In the Turbine Manual mode of operation, the operator controls the turbine using the Analog Backup System. The mode of operation (Operator Automatic or Turbine Manual) of the DEH ControlSystem is determined by the state of a flip-flop (the Turbine Manual flip-flop). When this flip-flop is reset, the Analog Backup System is controlling the turbine (Turbine Manual mode). When the Turbine Manual flip-flop is set, the Digital Controller is controlling the turbine (Operator Automatic mode) and the Analog Backup System is tracking the Digital System.
If the Analog Backup System is in control, the operator must press the OPER AUTO button on the Operator B Panel to transfer to the Operator Automatic mode of operation (flip-flop is set). At the same time, however, a permissive generated by the digital portion must be maintained. If an internal failure in the digital portion causes the permissive to be absent, the DEH Control System remains in Turbine Manual even if the OPER AUTO button is pressed.
The Turbine Manual flip-flop can be reset (the DEH Control System goes from the Operator Automatic to the Turbine Manual mode) in several ways. If the operator presses the TURBINE MANUAL button on the Operator B Panel, the DEH Control System is placed in the Turbine Manual mode. Also, a contact closure generated by the digital portion (indicating a failure in the digital portion) causes the system to be placed in the Turbine Manual mode. In the event of a power supply failure in the digital portion, a contact closure is generated which resets the Turbine Manual flip-flop (Turbine Manual mode).
H. AUTOMATIC TURBINE STARTUP PROGRAMS--FUNCTIONAL DESCRIPTION
AUTOMATIC TURBINE STARTUP PROGRAM FOR FOSSIL UNITS
A digital computer is a powerful tool for achieving a better and more efficient control of a turbo-generator unit. To take advantage of the computer's ability to scan, memorize, calculate, make decisions and take executive actions, the computer program should go further than the operating instructions, normally provided with each turbine, by scanning additional parameters if necessary, determining the trends in the parameter changes and performing computations beyond the capacity and duties of a human operator.
The general objective of the starting and load changing recommendatios is the protection of the turbine parts against thermal-fatigue cracking caused by internal temperature variations. In the large turbines of present design the critical element is the H.P. rotor due to its relatively large diameters and high number of temperature variations at the first stage zone produced during startups and load changes. The operating procedures provided with each turbine, in the form of charts, assume that the machine is normally passing from one steady state to another, during a transient period, and the transition between the two selected states should be performed in a determined time to keep the thermal stresses below the allowable limit.
With the help of the computer, the thermal stresses in the rotor can be calculated minute by minute based on the actual temperature at the first stage provided by a thermocouple. The assumption that the turbine was in a steady state condition is not necessary. Once the thermal stress (or strain) is calculated, it can be compared with the allowable value, and the difference used as the index of the permissible first stage temperature variation, translated in the computer program as a variation of speed or load or rate of speed or load change.
Using the memory of the computer, values of some parameters can be stored for use in the estimation of their future values or rate of change, which in turn are used to take corrective measures before alarm or trip points are reached. Such is the case with metal temperature differentials and differential expansions.
Bearing vibration is another of the parameters for which the computer capacity is used in making logical decisions. Each bearing is under close supervision and when one of the vibrations reaches an alarm limit, its behaviour is studied and a decision is made according to the estimated future value of the vibrations, and whether it is an increasing, steady or decreasing function. A priority system is also inserted due to the possibility that two or more bearings may be in a different stage of alarm.
Under the approach used in the program, the rotor stress (or strain) calculations, sub-program P#01, and its decision-making counterpart, sub-program P#04, are the main controlling sections. They will allow the unit to roll with relatively high acceleration until the anticipated value of strain or other controlling parameters predict that limiting values are to be reached in the near future. Then a lower rate is selected and, if the condition persists, a speed hold is generated.
The following describes the Automatic Turbine Start-Up Program (ATS) in the DEH-P2000 Controller. The ATS program employs general concepts including the rotor stress control concepts described in the aforementioned Berry patent. In providing automatic control and monitoring, the ATS provides improvements over the Berry patent and earlier control systems in which digital computers have been used to provide supervisory startup control over analog EH controls.
The ATS Program is stored and executed in the same Central Processing Unit (CPU) as the basic DEH programs. Both programs work directly together by means of shared core locations. They also share the same input/output hardware and software, which is needed to communicate with the outside world, i.e., to read and operate contacts. The ATS Program is capable of rolling the turbine from turning gear to synchronous speed and application of initial load. It will check the pre-roll conditions, determine if a soak period is required, transfer from throttle valve (TV) to governor valve (GV) operation, check the presynchronizing conditions and allow the automatic synchronizer to put the unit on line or otherwise allow synchronization to occur, i.e. under accurate speed loop control.
During the operation of the turbine, whether during the acceleration period or under load, the computer will monitor the various parameters of the turbine, compare their values with limit values and print messages to inform the operator about the conditions of the machine to guide him in the operation of the unit.
The modes of operation are ATS Control and ATS Supervision. If both the "turbine auto-start" and the "turbine supervision off" pushbuttons are not backlighted the ATS Program is in ATS Supervision and messages are printed out. Pressing the "turbine auto-start" button brings the ATS Program into ATS Control. Pressing the "turbine supervision off" button stops the messages from being printed out while the ATS Programs are still running. If the "turbine supervision off" button is pushed a second time, all current alarm messages and all subsequent messages are printed
The computer performs the following evaluations and control actions:
(a) Every minute prior to rolling off turning gear, the program checks and compares with allowable limits, the following parameters: Throttle temperature, differential expansions, metal temperature differentials, vacuum, exhaust temperatures, eccentricity, bearing metal temperatures, drain valve positions.
(b) Requests a change in throttle steam conditions to match inpulse chamber steam temperature to metal temperature within -100 .degree. and +200.degree. F.
(c) Allows the turbine to roll off turning gear.
(d) Sets the target speed and selects the acceleration in the DEH controller.
(e) Determines the heat soak time at 2200 RPM and counts it down.
(f) Accelerates the turbine to 3300 RPM at controlled rates.
(g) Commands the DEH controller to transfer from throttle to governor control.
(h) Accelerates the turbine to synchronous speed.
(i) Allows the Automatic Synchronizer and DEH Controller to put the turbine on the line and apply minimum load.
(j) Calls for a "Load hold" at initial load if required by the thermal conditions of the turbine.
Under ATS Supervision, the function of the computer is limited to monitoring the various parameters and generating appropriate messages to assist the operator in the control of the turbine. The strain calculation is continuously performed to advise the operator about the thermal condition of the rotor. It is the operator's responsibility to match steam and metal temperatures, set demands, select rates of speed and load changes, determine the heat soak requirements and take all the necessary sequential steps to bring the turbine up to speed and load it.
All programs are called periodically and will run to completion unless preempted by a higher priority program. Program P15 determines the appropriate action to be performed in a sequential operational order. Programs P01 through P14 check the turbine and generator parameters. They compute rotor temperatures and strain at impulse chamber zone; they calcualte anticipated metal temperature differentials and differential expansions. Depending on the mode of operation these programs generate new DEH demands or holds.
PROGRAM LIST
P01 Determination of rotor thermal conditions.
P02 Periodic computation and supervision of anticipated steam chest wall, bolt flange temperature differentials and differential expansion.
P03 Supervision of turning gear operation.
P04 Control of rotor stress at first stage.
P05 Supervision of eccentricity and vibration.
P06 Turbine metal temperature supervision.
P07 Control of EH speed reference.
P08 Supervision of bearing temperatures.
P09 Supervision of generator.
P10 Supervision of gland seal, turbine exhaust and condenser vacuum conditions.
P11 Supervision of drain valves and computation in of anticipated differential expansion.
P12 Supervision of LP exhaust tempertures.
P13 Sensor failure action.
P14 Computation and timing of heat soak time.
P15 Acceleration sequence.
In order to improve the performance of a turbine 10 at startup and thereby decrease startup time and allow the turbine 10 to go to line at the earliest possible moment without undesired adverse effect on turbine life, the DEH system 1100 includes an automatic startup program. The automatic turbine startup and monitoring programs 1140, 1141, 1142 monitor large numbers of analog signals representing various turbine parameters including bearing, coolant, steam temperature, bearing vibration, speed valve phases, and others included in the input/output signal list in Appendix 5. In addition, the automatic startup programs 1140, 1141, 1142 calculate complex heat distribution equations which describe temperature variations in critical metal parts of the steam turbine 10 as generally considered in the aforementioned Berry patent. The automatic turbine startup program 1141 types out the variables and associated warnings through ATS periodic program 1140, ATS conversion routine 1142 and the message writer 1144 on the logging typewriter 1146.
The ATs automatic startup program 1141 is able to control the speed of the turbine generator 10 to well within a maximum deviation of 1 rpm over tens of minutes. Because of the extreme accuracy with which the ATS program 1141 can hold the speed of the turbine generator 10, a prefrred method for synchronization in the present embodiment is the use of manual synchronization of the generator 16 to the line. The automatic dispatch system as shown in FIG. 49 sends signals to the ATS program 1141 thereby allowing the ATS program to hold the speed of the turbine generator system 10 to well within 1 rpm. By the use of simple lamps to indicate the differential phase between the generator 16 and the line an operator is conveniently able to manually synchronize the system.
A more common approach, in the prior art, is the use of conventional automatic synchronizer equipment. However, because of the high degree of accuracy which the ATS program 1141 controls the turbine generator 10 the present system is easily synchronized without conventional automatic synchronizer equipment.
PROGRAM P01
DETERMINATION OF THE ROTOR THERMAL CONDITIONS
This program runs periodically to calculate and update the temperature of the H.P. rotor at the first stage zone, based on the temperature of its environment. Heat Transfer coefficient, rotor temperatures, temperature differentials, and rotor strain are calculated. The results are invalid if the rotor temperature has not been calculated continuously for at least 2 hours i.e. if the program was not running or the revelant sensor not in service. Then the ATS control mode cannot be entered, only STS Supervision is possible.
Program Sequence
If the analog signal to frequency (A/F) converter is out of service the rotor stress program is initialized with the actual first stage metal temperature.
If it did not run one cycle the variable values used in the program to start the calculations would be misleading.
If the unit is on turning gear (TG) the "HEAT SOAK COMPLETE" indicator is cleared to allow the calculation and timing of heat soak to be initiated.
The HP first stage metal and IP metal temperatures before opening the valves (bov) to be used in the heat soak calculation program are set equal to the present metal temperatures, this being an updating process that occurs only when the unit is on TG. Until the unit has been synchronized these temperatures are not changed since the heat soak calculation is based only on initial metal temperature values.
If the unit is not on TG, the variable N used to calculate the heat transfer coefficient is set equal to actual speed, otherwise it will be N=0.
The first stage metal temperature will determine if the turbine will go through a cold or hot start procedure. Rotor strain limits as well as rotor (surface-volume average) temperature are chosen based on the above temperature.
The heat transfer coefficient H will be computed as a function of speed reaching its higher value in the speed mode at rated speed. (See FIG. 1). Once the breaker is closed H will increase linearly as a function of time reaching its maximum value after five (5) minutes. The heat coefficient algorithms for speed and load modes are:
H.sub.speed =12.4 (1000+N).sup.2.times.10.sup.-6 N=RPM H.sub.Load =262+(12.3.times.Time Counter).
The rotor surface temperature is calculated as a function of the first stage steam temperature, the present heat transfer coefficient, and the rotor metal temperature's history. The magnitude of the rotor stress is determined by the rotor (surface-volume average) temperature which is stored in memory to be used by program P04 to analyze the rotor conditions based on present and past history. If the computer has been running after initialization for two (2) hours or more the rotor temperature calculation will be considered valid. Rotor strain, which is a direct function of the rotor temperature, is then calculated, compared to the selected limit and printed out if it is found to exceed the limit.
Principal steps accomplished in this program are:
1. Set:
(a) 1st stage metal temperature b.o.v.
(b) rotor strain limits
(c) rotor (surface-volume average) temperature limits
2. Calculate:
(a) heat transfer coefficient (H)
(b) rotor (surface-volume average) temperature
(c) rotor strain
3. Store and Update:
(a) latest 15 values of rotor volume average every 1 min.
(b) latest 15 values of rotor (surface-volume average) every 1 min.
PROGRAM P02
Computation and supervision of anticipated steam chest wall, bolt flange temperature differentials and differential expansion. This program runs every 1 minute to calculate the anticipated steam chest wall temperature difference in both chests. The actual generator and governor end differential expansion are compared against limits to determine the best course of action.
Program Sequence
The "SKIP NO PART OF P02" indicator is used to avoid errnoeous calculations of the anticipated temperature differentials when this program runs for the first time. This is accomplished by setting this indicator when the programs are initialized Likewise "P13" sets this indicator in order to avoid misleading actions and messages when at least one of the thermocouples used in this part of the program is out of service.
This program will calculate the 5 MINUTES ANTICIPATED STEAM CHEST WALL TEMPERATURE DIFFERENTIAL as a linear interpolation for a 5 minute period from the latest stored temperature difference and the one stored one minute before. The algorithms used is T.sub.A =T.sub.j +5(T.sub.j -T.sub.j-1). The heating/cooling limit for the ANTIC. (IN-OUT) WALL TEMP. DIFF. is +150. A speed or load hold is generated by ANTIC. METAL COND REQUIRE HOLD indicator.
The GENERATOR END and GOVERNOR END differential expansion input is checked against the alarm and trip limits resulting in different actions taken by program P07.
Generator End: If the input exceeds the ALARM limit the DIFF. EXP. SPD HOLD indicator is set. This results in a speed or load hold.
If the input exceeds the TRIP limit the "DIFF. EXP. TRIP" indicator is set and a tripping action is initiated.
Governor End: Two diffrent actions are taken when the alarm limits are exceeded.
If the rotor is short the "DIFF. EXP. INCR SPEED RATE" indicator is set in order to increase the ACCELERATION which will result in an increase of the heat transfer coefficient. Therefore the rotor will heat faster counteracting the cause that generated the alarm.
If the rotor is long the "DIFF. EXP. SPD. HOLD" indicator. This results in a speed or load hold. If the TRIP limit is exceeded the "DIFF. EXP. TRIP" indicator is set and a tripping acton is initiated.
Any of the conditions analyzed will set the "DIFF. EXP. OF NORMAL" indicator which will prevent the turbine from rolling off turning gear (REF to P03), if the turbine is on turning gear.
In the Figures, there are shown the GENERATOR END and GOVERNOR END differential expansion non-contacting sensors in relationship to the thrust bearing and turbine elements for the rotor long and rotor short relative position. A representation of the supervisory recorder scale and the pointer movement in relation to the sensors and shaft position are shown. FIG. 3 shows the alarm and trip limits in relation to the pointer movement in the supervisory recorder scale.
PO2
Principal steps accomplished in this program are:
1. Calculate the:
a. 5 MIN. anticipated steam chest wall temperature differential
b. 5 MIN. anticipated HP & IP (flange-bolt) temperature differential.
2. Compares against limits the:
a. anticipated HP & IP (flange-bolt) temperature differential
b. anticipated steam chest wall differential
c. governor end present differential expansion
d. generator end present differential expansion.
Action Taken
Generator End
exceed alarm short--speed/load hold
exceed alarm long--speed/load hold
exceed trip--short or long--turbine trip request
Governor End
exceed alarm--short--accelerate
exceed alarm--long--speed/load hold
exceed trip--short or long--turbine trip request.
PROGRAM PO3
Supervision of turning Gear Operation
All conditions that would hold the unit from rolling-off turning gear are checked. Messages will guide the operator on how to obtain the allowable mismatch between the impulse chamber steam and metal temperatures.
Program Sequence
This program runs to completion only if the unit is on turning gear. The minimum allowable throttle steam temperature at the existing pressure is checked against the actual throttle steam temperature (TST).
In the event of low TST the minimum allowed TST necessary to avoid steam condensation is printed-out.
If the TST is too high in respect to the rotor the TST will have to be decremented.
The two above mentioned conditions will prevent an automatic roll-off turning gear. The computer estimates what the first stage steam temperature would be when the valves open, as a function of the actual throttle steam temperature and pressure.
The expected temperature mismatch between the expected or anticipated first stage steam and metal temperature is checked. If the mismatch is out of specified limits a message will tell the operator what the first stage steam temperature should be to fall within limits and therefore permit the roll-off as soon as the inlet conditions are adjusted accordingly.
The following conditions checked and flagged in another program have to be within limits before a roll-off is allowed.
The above listed conditions will be alarmed by setting a common indicator for P15.
PROGRAM P04
Control Of Rotor Stress At First Stage
Since the rotor surface thermal stress (or strain) is proportional to the surface-to-volume average temperature differential calculated in P01, this is the parameter selected to determine the acceleration. By comparing the present value with previous values, the program finds the type of thermal transient the rotor is undergoing, and selects the path to be followed. An extrapolated value is also calculated and compared with the allowed value, according to this difference.
Program Sequence
If the turbine is off turning gear, latched, and the periodic programs have been running for 2 hours or more we proceed to:
1. Calculate the 15 minute anticipated rotor (surface-volume average) temperature.
2. To set permissive indicators for the P07 periodic program that will hold, reduce or increase turbine speed.
If the turbine is in turning gear and latched but the periodic programs have not been running for 2 hours or more we proceed to:
1. Store and update the latest ten values of 1st stage steam temperature to calculate the temperature gradient.
2. Hold speed by means of P07 if the 1st stage steam temperature rate of change is >300.degree./hr. and turbine speed is >600 RPM.
An increase in speed or load rate will be requested making use of the "ROTOR STRESS INCREASE RATE" indicator if,
1.1 The load is increasing and the rotor heating or,
1.2 The load is decreasing and the rotor cooling, the anticipated (surface-volume average) temperature difference is less than 50% of specified limit, and the present difference is less than 90% of the same limit.
2.1 The load is increasing and the rotor cooling.
2.2 The load is decreasing and the rotor heating, and the present (surface-volume average) temperature is less than 90% of limit.
3.1 In speed mode the motor is cooling, the anticipated difference is less than 10% of limit, and the present difference is less than 90% of limit.
4.1 In speed mode the rotor is heating, the anticipated difference is less than 50% of limit and the present difference is less than 90% of limit.
A reduction in speed or load rate will be requested making use of the "ROTOR STRESS REDUCE RATE" indicator, if
1.1 The load is increasing and the rotor heating, or
1.2 The load is decreasing and the rotor cooling, or
1.3 In speed mode the rotor is heating and the anticipated difference larger than the limit and the actual difference less than 85% of limit, or
The anticipated difference larger than 75% of limit.
Finally the remaining action, a speed or load hold will be requested making use of the "ROTOR STRESS HOLD" indicator which is set when
2.1 The load is increasing and the rotor heating
3.1 The load is decreasing and the rotor cooling and
(a) the present temperature difference is larger than the limit or
(b) the anticipated temperature difference is larger than the limit and the present temperature difference is large than 85% of limit.
PROGRAM P05
Supervision Of Eccentricity and Vibration
This program analyzes present vibration inputs and takes action in accordance with the previously determined vibration trend.
Program Sequence
The program starts by clearing the vibration trip and vibration alarm indicators. If the turbine speed is below 600 rpm it checks for eccentricity. If the eccentricity is below the alarm limit, the high eccentricity indicator is cleared and the program is completed. Otherwise it prints "high eccentricity" and sets the high eccentricity indicator. If the turbine speed is larger than 600 rpm it proceeds to set alarm limits as a function of turbine speed. Below 2400 rpm the vibration alarm limit will be 8 mils. Above 3200 rpm it will be 5 mils. Between 2400 and 3200 rpm the vibration alarm will be a linear function to speed.
All vibration inputs to the computer are checked. This is done by as many loops as vibration inputs. Each loop represents one input as is referenced by an index number, according to the bearing number.
A trip is requested if a vibration input is equal to or higher than 10 mils. Tables are used to record the vibration values of each input. As more than one input may be in alarm at the same time, separate loops must be used. Also each input may be in a different stage of alarm requiring a speed hold or a change of speed to correct the vibration. Therefore, a priority system is necessary. Top priority is the decreasing mode, next is the hold condition and third the increasing mode of speed reference. Thus, a decrease is always checked before a hold or increase is called for by the conditions in the other vibration inputs. By applying the described method the following is accomplished for each bearing:
Vibration Trend
The program scans each vibration input in sequential order and determine if a vibration alarm condition exists. The alarm limit is decreased slightly to avoid an unstable alarm condition that would occur in the event of an input signal with ripple and/or noise. If a decrease or increase condition has not been set previously the program makes sure that the speed is not going to be held within the blade resonance range. If this is the case the program continues with the next sensor.
Otherwise, making use of counter "B" the program stores the present vibration level (VIB).sub.o for use one minute later and continues the scanning process. Once a minute has elapsed the following is executed.
1. If .delta.VIB>0 the expected vibration 5 minutes later is computed by (VIB).sub.+5 =(VIB).sub.o +((VIB).sub.+1 -(VIB).sub.o).times.5
1. If (VIB).sub.+5 .gtoreq.TRIP LIMIT speed is reduced by 200 rpm. If (VIB).sub.+5 <TRIP LIMIT the (VIB).sub.o is replaced by the present vibration level and the process described is repeated again.
2. If .DELTA.VIB .ltoreq.0 the program keeps updating (VIB).sub.o, (VIB).sub.+1 and calculating .DELTA.VIB until the alarm condition is cleared or until 15 minutes has elapsed. The latter would indicate that the vibration has been descreasing steadily for 15 minutes, as a result an increase in speed of 200 rpm will be requested.
The speed change is accomplished by making the SPEED REFERENCE equal to the VIBR. SPEED REF. in program P07.
The VIB SPEED REF is decreased or increased by 200 RPM every time the conditions mentioned before are satisfied.
To make sure that the SPEED REFERENCE is only decreased or increased in steps of 200 RPM the VIBR. SPEED REF CHANGE NOT PERMITTED indicator is cleared only when the PRESENT TURBINE SPEED=SPEED REF.
PROGRAM P06
Turbine Metal Temperature Supervision
The temperature difference across the steam chest wall has to be maintained within limits to avoid extreme stresses.
Temperature sensors in the base and cover of the HP or HP-IP turbine will monitor its temperature. A difference larger than 100.degree. F. denotes presence of water and the unit should be tripped to avoid further damage.
Program Sequence
This program monitors and alarms on metal conditions of the steam chest walls, cylinder bolt-flange (in single case units), and cover-base cyliner differentials. When limits are reached speed or load holds are requested.
A trip is requested if the cover-base temperature difference indicates presence of water induction. In this program:
1. Limits are compared to:
a. both steam chest (outer wall-inner wall) temperature difference.
b. (flange-bolt) temperature.
c. (cover--outer cylinder base metal) temperature.
2. Indicators are set to:
a. hold speed if temperature diffentials are above limits.
b. request ATS rejection if the (flange-outer cylinder base metal) temperature is >100 and the load is 20% or the load is <20% and the drain valves are open.
PROGRAM P07
Control OF DEH Speed Reference
This is the speed controlling or action program. It sets DEH speed DEMAND which is used by the DEH speed control programs when in ATS control. Acceleration rates are also selected by checking permissive set by other programs.
Program Sequence
Trip conditions requested by other programs will reject the ATS program.
Vibration Trip (P05)
Met. Temp. Trip (P06)
Diff. Exp. Trip (P02)
Brg. Metal Temp. Trip (P08)
Any of the five (5) sensors listed below will also make this program reject ATS.
1. differential expansion sensor (P13)
2. first stage metal temperature sensor (P13)
3. first stage steam temperature (P13)
4. reheat steam temperature (P13)
5. vibration sensor failed high and an adjacent vibration sensor failed high or is in an alarm condition (P13).
If there is at least one bearing with a vibration level above the ALARM limit and the unitis not on the line and the turbine is not changing speed (turbine not accelerating or decelerating) the program will make sure that the speed hold to be generated will not fall in the blade critical regions designated by "X" and "Y" in the flow chart.
If the turbine is dwelling at a blade resonance speed a new speed reference is generated which will decrease the speed to a lower level out of the resonant region. To avoid another reference change request due to the same cause the "VIBR. SPEED REF CHANGE NOT PERMITTED" is set, which will make the program go through a different path.
If in ATS mode the DEH demand will be changed to satisfy the new desired speed called by this program or by P05.
As soon as the demand is within .+-.7 RPM of the reference a new speed change will be permitted (if a request exists) by clearing the "VIBR. SPEED REF. CHANGE NOT PERMITTED" indicator. Lights are turned on and off accordingly.
With reference to connector (a) in the P07 flow chart, once the vibrator alarm is cleared indicators or flags set by other programs are scanned and new flags (to determine the type of message to be printed out) will be set. Following is a list of indicators scanned.
If the first stage steam temperature sensor fails messages requesting a hold because of rotor stresses are inhibited.
If the turbine is not dwelling at a blade resonance speed, a speed hold is requested (i.e. "SPEED HOLD" ind.) and continues per 3.1 of this program description.
With reference to connector (C)in the PO7 flow chart, if a speed hold other than vibration was requested, with the turbinwe in speed mode (i.e. breaker open) and not dwelling at blade resonance, speed messages indicating the type of speed hold are output.
The speed hold is accomplished by making the DEH DEMAND equal to the instantaneous REFERENCE.
If it is dwelling in or going through a blade resonance frequency zone the turbine will continue to accelerate toward the next speed reference plateau set by the Acceleration Sequence (P15) program before a hold.
If a speed hold was not requested and the first stage steam temperature sensor did not fail, the rotor stress program PO4 will decrease or increase the present acceleration rate one step down or up at the maximum rate of one step every 3 minutes according to the standard acceleration index table.
Present and anticipated differential expansion increase the acceleration rate at a maximum rate of one step every 5 minutes.
Acceleration rate changes will be carried on within the standard or allowable limit which are represented by index 1 through 9 (refer to P07-3).
If a rate request change would allow the present rate to exceed the allowable limits the request and corresponding messages will not be acknowledged.
Once a rate is selected, the DEH DEMAND will be made equal to the target speed reference set by the Acceleration Sequencing program P15. This is accomplished by means of a jump to connector (f) in P07-2.
Going back to connector (c) we will notice that if the turbine is in a hold speed condition and in load control relevant messages will be printed out.
PROGRAM P08
Supervision of Bearing Temperature
This program monitors the lube oil in and out of cooler temperature, the bearing metal temperature, and the bearing oil header pressure.
Program Sequence
Two different low and high oil out of cooler limits are used. If the turbine is running (speed or load mode) a higher pair of limits are used.
If the turbine is accelerating the oil will increase in temperature therefore if the oil temperature is below the low limit but the turbine is accelerating no action is required from the operator. All journal and thrust bearing metal temperatures are checked against two limits.
If any one of the bearing metal temperatures exceeds 210.degree. F. an indicator is used to request a speed or load hold by means of program P07.
If any of these temperatures exceeds 225.degree. F., a trip request is generated. The bearing oil pressure is monitored continuously, nevertheless the only action taken is a hold if the unit is in the roll-off turning gear routine. The oil returning to the lube ol cooler should be kept below 170.degree. F., otherwise the program will put out a message indicating this alarm condition.
Summarizing in a table like format the following are the different steps and actions that this program takes care of:
1. It compares against limits:
a. the oil temperature out of cooler in turning gear
b. the oil temperature out of cooler out of turning gear
c. each metal bearing temperature (trip and alarm)
d. the bearing oil pressure
e. the oil temperature to cooler
2. It sets indicators that will:
a. hold roll-off T.G. if, the lube oil temperature is too cold, or the lube oil pressure is too low
b. hold speed or load if any bearing temperature exceeds the alarm limit
c. request a turbine trip if any bearing temperature exceeds the trip limit.
PROGRAM P09
Supervision of Generator
The generator cooling and sealing system and exciter cooling system are monitored by this program. Calculations are run continuously to determine if the generator stator coil temperature rise is within calculated limits.
Program Sequence
The generator cooling gas or water is monitored and a roll-off turning gear hold or a prior to synchronizing hold is generated if the cooling fluid exceeds a fixed high limit. A similar action is taken with the exciter cooling air.
The allowable coolant expected temperature rise is continuously calculated as a function of the coolant pressure (if it is a gas), the instantaneous or present stator current (I.sub.SA) and the nominal stator current (I.sub.S). Its limit is a sole function of the gas pressure (if gas cooled). Messages will tell the operator if the temperature rise trend is larger than expected. This will give him enough lead time to take a corrective action. Hydrogen pressure and purity are closely monitored, as well as seal oil pressures (air and hydrogen side).
The latter conditions will prevent the synchronization ion program to run. This means that the unit will go on a speed hold until these conditions are cleared.
Principal steps accomplished in this program are:
1. Calculate the:
a. expected generator stator coil coolant discharge temperature rise.
b. generator stator coil coolant temperature rise limit.
c. present generator stator coil coolant discharge temperature rise.
d. present exicter air temperature rise.
2. Compares against limits the:
a. coolant inlet temperature.
b. present generator stator coil coolant discharge temperature rise.
c. exciter coolant air.
d. exciter previously calculated temperature rise.
e. hydrogen and air side seal oil pressure and temperature.
f. hydrogen pressure.
g. seal pressure difference
3. It checks the running status of the
a. air side seal oil back-up pump.
b. hydrogen side seal oil pump.
PROGRAM P10
Supervision of Gland Seal, Turbine Exhaust And Condenser Vacuum Conditions
This program monitors temperatures and pressures in the LP exhaust and temperature differences in the seal LP gland system. Exhaust spray operation is monitored and HP sealing steam temperature are also monitored.
Program Description
The following conditions, which are monitored by this program will not allow the P15 program to carry on the roll-off turning gear operation if the:
1. HP gland seal steam is too cold
2. LP gland seal steam temperature is too high (3500.degree. F.)
3. difference between the metal and the sealing steam temperatures in the HP sealing area is too great (+ 200.degree. F. max.)
4. LP exhaust steam temperature is larger than the allowable limit for the sprays.
If the LP exhaust pressure is larger than 5 inches of Hg Absolute this program will request a speed or load hold carry on by P07 as usual.
Turbine operation experience recommends that the LP exhaust sprays be open between 600 RPM and 10 percent load. This is properly monitored by this program. Commands to take corrective actions are given to the operator by printed message.
PROGRAM P11
Supervision Of Drain Valves And Computation Of Anticipated Differential Expansion
This program can be considered an extension of P02. The anticipated differential expansion in one or both ends is calculated and appropriate actions determined. Drain valves position are monitored and commands to open and close them (generated in accordance with speed and loading conditions as well as recommendation emanated of the recent water prevention operating procedures) are given.
Program Sequence
The GOVERNOR END AND GENERATOR END anticipated (desired) differential expansion is checked against the alarm and trip limits resulting in different actions taken by P07. The present temperature is calculated by a desired anticipation algorithm T.sub.A =T.sub.-5 +5 (T.sub.-5 -T.sub.-6).
Governor End. Two different actions are taken when the alarm limits are exceeded.
If the rotor tends to become shorter the "ANTIC. DIFF. EXP. RATE" indicator is set in order to increase the acceleration which will result in an increase of the heat transfer coefficient. Therefore the rotor will heat faster counteracting the trend toward a shorter rotor. If the rotor tends to become longer the "ANTIC. DIFF. EXP. SPEED HOLD" indicator is set resulting in a speed or load hold made effective by P07.
Generator End. A speed or load hold is accomplished through program P07 when the "ANTIC. DIFF. EXP. SPEED HOLD" indicator is set as a result of an anticipation to a rotor long alarm condition. p If on speed control, the drain valves are opened if not already open.
If on load control at less than 20% load, the drain valves are opened. If load is greater than 20%, the drain valves are closed.
PROGRAM P12
Supervision of LP Exhaust Temperatures
This program provides additional checks and calculations for a turbine with Building Block 73 to prevent overheating of the low pressure blades.
The temperature in the last row of blades is a direct function of the exhaust or condenser pressure. Therefore the LP exhaust pressure is used as the sensible index to determine low pressure blade conditions.
Program Sequence
To determine if the low pressure end is exceeding preestablished limits a straight linear approximation of Operating Curve #CT-22596B, attached, is being used.
The intersection of these two (2) straight lines has been selected to be at 1.92 in. HgAbs., and its respective equations are:
1. For full speed--no load
If cond. press. abs. <1.92-TEMP 1=1000-(80.times.cond. press. abs.)
If cond. press. abs. >1.92-TEMP 1=1150-(160.times.cond. press. abs.)
2. For 5% of MAX. GUAR. LOAD
If cond. press. abs.<1.92-TEMP 2=1023-(33.3.times.cond. press. abs.)
If cond. press. abs.>1.92-TEMP 2=1150-(100.times.cond. press. abs.)
If the reheat temperature does not fall below the curve for FULL SPEED - NO LOAD (see curve #CT22596B) or in other words if reheat temperature is larger than TEMP 1 an indicator named "VACUUM" is set to be used in the acceleration program P15. Its function is to hold turbine speed before the speed demand is moved up to the next higher level.
SPEED MODE
If the turbine is not on the line but close to rated speed two actions would be taken:
1. If there is not any bearing vibrating above the alarm limit the program will wait 4 minutes before advising the operator to reduce speed (if in OPER. AUTO) or decrease speed to the next lower step if it was not decreased already within the last 15 minutes. If speed was decreased already the program will wait 15 minutes total before advising the operator to go to OPER AUTO and place the turbine in turning gear.
2. If there is a bearing vibration above the alarm limit the operator will be advised to reduce speed (if in OPER AUTO).
In ATS the turbine speed will be brought down to the next lower step by program P15 making use of the "SPEED REF" indicator. In any case after 15 minutes total the operator will be advised to go to OPER AUTO and turning gear.
LOAD MODE
No action will be taken if the load applied is larger than 5%. If it is less than 5% and the reheat temperature does not fall below the curve for 5% of MAX. GUAR. LOAD (curve #CT-22596B) or in other words if reheat temperature is larger than TEMP. 2 the operator will be advised to increase load to avoid overheating the LP blades.
PROGRAM P13
Sensor Failure Action
This program monitors the converted ATS analog input values for detection of sensor failures, and initiates special actions (i.e. rejects ATS) for correct system response if a sensor failure is detected.
Program Sequence
This program can be distinctly divided into two parts. The main purpose of the first part is scanning all converted analog inputs for detection of sensor failures.
If an input is not reliable the program determines if the action has already been completed for this failure.
If action is complete it determines if action was completed while not in ATS mode. If this is true and the ATS mode was just selected (in the last 5 sec.) the sensor failure conditions must be reevaluated for possible further action.
Otherwise, no further action is taken. If action was not completed, then the failure has just occurred or it occurred previously but has remained incompleted because of an outstanding sensor failure override that has been requested (to allow a substitution) has not been satisfied. This condition will light the "OVERRIDE SENSOR HOLD" pushbutton on the operator's panel.
If the failure has just occurred (within the last 5 seconds since previous monitoring) a sensor failure message is printed (P13M11), a contact closure is sent to a plant alarm and the required sensor failure action is initiated as well as any required sensor value substitutions if a sensor failure override is not required for the particular sensor in scan.
If the failure is not new and subsequent action is pending a sensor failure override by the operator, a substitution is made if the operator pushed the "OVERRIDE SENSOR HOLD" pushbutton. Otherwise, no further action is taken until the pushbutton is pressed.
The second part of P13 monitors key sensors for failures which have more serious consequence to the ATS programs than actions initiated in the first part. This action results in, Reverting to OPERATOR AUTO from ATS mode if
1. a differential expansion sensor failed.
2. a vibration sensor failed high and an adjacent vibration sensor failed high or is in an alarm condition.
3. the first stage metal temperature sensor failed.
4. the reheat steam temperature sensor failed.
5. the first stage steam temperature sensor failed.
Substitutions
Depending on the sensor type a direct or reference substitution will be applied. In the substitution table, each substitutable sensor is listed with its predefined substitution sensors with the latter listed in accordance with substitution priorities.
Direct Substitution
This occurs when either the last previous valid value of the failed sensor is used or some preassigned fixed value is inserted for the failed sensor.
The oil out of cooler temperature and the bearing oil pressure are in this class.
Reference Substitutions
This is based on a table of other sensors whose value may be used for the analog input of the failed sensor. Thus, if the left steam-chest inner-temperature sensor fails, the right steam-chest inner-temperature is used in its place, providing that this sensor has not also failed. However, if it too has failed, the next sensor specified in the list is used. If no valid substitute is listed, then no replacement will be made for the original sensor which failed.
Priorities
There is a priority system applied to the order in which failed sensors are monitored for substitution action. Further, certain sensors i.e. vibration, differential expansion, first stage temperature and reheat temperature are classed as nonsubstitutable and processed separately for sensor failure control action.
PROGRAM P14
Calculation And Timing Of Heat Soak Time
This program will compute the necessary soak time based on the more critical temperature in the first stage. It will keep track of the time and allow the start-up sequence control program P15 to continue as soon as the computed time has expired.
Considerations
The soaking time necessary to bring the rotor volume average temperature above 250.degree. F. is accomplished between 2200 and 2400 rpm. This speed is chosen as a compromise between soaking temperature and rotor velocity which generates undesirable centrifugal stresses.
The IP rotor is considered the most critical rotor. The energy absorbed by the rotor as a function of rotor temperature is represented by ENERGY versus TEMPERATURE curve (FIG. 2) obtained by the Charpy test method.
The transition point (A) which corresponds approximately to 50% of the ductile fracture falls in the 250.degree. F. zone for the IP rotor material. For the Lp this transition point is below freezing.
The computation of the heat soak time is based conservatively on the lowest of four (4) temperatures listed below for the combined and separate HP-IP case.
COMBINED HP-IP
Rotor volume average temperature b.o.v. (1)
Rotor volume average temperature present
First stage metal temperature b.o.v.
First stage metal temperature present
SEPARATE HP-IP
IP metal temperature b.o.v.
IP metal temperature present
First stage metal temperature b.o.v.
First stage metal temperature present
The b.o.v. temperatures are updated only when the unit is on turning gear. Once the unit rolls-off turning gear the updating process stops (See P01).
Three indicators or flags are used in order to select the appropriate path in the program.
"HEAT SOAK COMPLETE" indicator which is cleared in P01 only when the unit is on turning gear, determines if P14 will run. It is set when all thermal operating conditions have been satisfied.
"SOAK TIME PERMITTED" indicator. It is used as a means of determining the validity of message P14M1 (HEAT SOAK DELAY, SPD LO). This message is printed only when the soak time speed is lower than recommended and the reheat steam temperature is larger than 500.degree. F. The heat soak time calculation is based on that temperature.
(1) b.o.v. stands for BEFORE OPENING THE VALVES.
"RETIME" indicator. The selection of the heat soak temperature and the heat soak temperature calculation is done only when the unit is on turning gear and the first time this program runs to completion. This indicator will bypass the calculation portion of the program every time but the first time.
Program Sequence
When the soak time speed has been reached the lowest metal temperature is selected and the heat soak computed unless it is a hot start (lowest temperature 250.degree. F.) in which case heat soak is considered unnecessary.
The countdown of the heat soak time will start as soon as the reheat temperature goes above 500.degree. F.
If for any reason the reheat temperature goes below 500.degree. F. the countdown will stop until the reheat temperature is reestablished. Once the soak time has timed out a final check on the rotor volume average temperature is done (it should be 250.degree. F.) before declaring that the heat soak cycle has been completed and allowing the turbine to continue acceleration.
PROGRAM P15
Acceleration Sequence
This program runs continuously, however, its actions are only accepted by the DEH if on ATS Control. In a normal start-up this program brings the turbine from turning to synchronous speed and turns the DEH Controller REFERENCE to the AUTOSYNCHRONIZER.
If the starting sequence is interrupted by a hold requested by any of the monitoring programs, it will resume its logical sequence where it was interrupted.
P15-1
The program will be in ATS Control when a flag set in the DEH Logic Program is set. This flag is set when not in loading mode, not in OPER. AUTO, and when the "SENSOR FAILURE REJECT ATS" indicator, (which is set by the SENSOR FAILURE ACTION program) is clear.
If in speed control and not in TG (turning gear) the VALVE POSITION LIMIT will be run up if it is set at less than 95%.
None of the conditions questioned in the vertical line between the questions IS TURB. ON T.G. will be affirmatively answered.
For study purposes we will assume that the unit is in TG and the ATS control P.B. has been pushed. Refer to P15-4.
If the unit is latched and in ATS control P03 flags are cleared. This is done to make sure that the latest PRE-ROLL conditions are being checked.
The "E" flag, set when the program has been overriden or the pre-roll completed successfully, is now not set, therefore, when P03 has completed successfully the pre-roll check out, an ACC RATE of 200 RPM/MIN. and a TARGET speed of approximately 605 RPM is selected.
The turbine now will accelerate at the selected rate until the selected target speed is reached.
By now the "E" flag has been set. The program will jump to repeatedly select the target speed until the turning gear disengages. If no HOLD has been requested by the monitoring programs the turbine will continue to accelerate until a speed larger than 580 RPM has been reached. At this point a new target speed between 2200 and 2400 RPM is selected.
The acceleration rate by now could have been increased by P07 which will every 3 minutes recognize an increase or decrease request by P04 which looks at the rotor stress computation and determines the course of action.
P15-3
Once the turbine has reached HEAT SOAK SPEED (2200 to 2400 RPM) the program will come down the same path until P14 sets the "HEAT SOAK COMPLETION" indicator. Then a new target speed of the order of 3300 RPM is selected and the turbine accelerates now at the present acceleration rate. This rate is being updated every 3 minutes as a result of the rotor stress calculation.
Again the turbine will accelerate to reach the new target speed. In the next step the transfer from throttle valves to governor valves occurs. Prerequisites are that all vibration levels be below the alarm limit and that the cooler steam chest inner temperature be larger than the throttle temperature at existing pressure. This is to avoid water condensation on the chest walls once the transfer is accomplished. We must remember that when in governor valve control the pressure in the steam chest is equal to the throttle pressure. "D" flag is set above 3260 RPM when:
1. there is not any vibration alarm
2. there has been a vibration alarm override.
Once "D" flag is set and the correct throttle temperature is achieved, the transfer is initiated.
If the throttle temperature is too cold the recommended throttle temperature is recalculated and printed out every 10 minutes.
Also, every 10 minutes a message indicating the cause of the transfer delay is output. Once the transfer has been initiated the system will have 2 minutes to complete it. If it has not been completed in 2 minutes this will be indicative of a malfunction and a message requesting the operator to take control will be printed out with the latter frequency.
The time counter is shown as counter "J" in this program.
P15-1
The unit should now be in GOV. CONTROL, therefore, the transfer is completed and a message indicating this condition is printed out.
The next time the program runs, a new target speed reference (equals synchronous speed) will be selected and the acceleration continued until the turbine speed is within synchronization range (SYNCHRONOUS SPEED.+-.50 RPM). At this point the pre-synch check out starts.
P15-2
Indicator A, B and C are used to run this part of the program in a certain sequence.
It is desirable that the (surface-volume average) temperature differential in the rotor be less than 75% of the allowable limit before the unit is synchronized.
If the latter is not so the program will proceed only if the rotor average temperature is larger than the first stage steam temperature. If this second condition is not met the operator will have to override the program in order to complete the automatic start-up.
Otherwise the OPERATOR AUTO mode will have to be selected to make use of the remaining synchronizing monitor sequence. The program continues checking conditions that should have been accomplished by the operator beforehand. These are:
The exciter field breaker should be unlocked.
The generator main breaker should be unlocked.
The voltage regulator switch is in the "OFF" position.
Vibration and generator system conditions are checked before the program determines if the base adjuster and voltage adjuster have been prepositioned to the rated voltage, no load position. These will be prepositioned by motor operators which are actuated by a contact closure when the exciter field breaker is opened.
The exciter field breaker is closed by a contact closure output from the DEH controller. This contact reopens after 10 seconds. Successively the program checks if the:
1. exciter field breaker has closed.
2. base adjuster is at rated no load setting.
3. voltage adjuster is at rated no load setting.
4. voltage regulator switch is in the "ON" position.
5. voltage regulator is "ON".
6. auto-synchronizer is in AUTOMATIC. This should have been set by the operator beforehand.
Messages indicating the discrepancies with the programmed logic are printed out. Finally the program will instruct the DEH controller to go in AUTO SYNC. mode allowing the automatic synchronizer to change the reference signal in the DEH.
A generator excitation system schematic is shown in FIG. 2.
Once the breaker closes a message dependent on the present rotor stress is printed out advising the operator on the most desirable loading rate.
ATS Control At Any Speed Level
This program will catch the unit on the fly and resume the start-up sequence setting the reference at the next higher reference step (600, 2200, 3300, or 3600 RPM).
I. SUMMARY
Improved turbine and electric power plant operation is realized through the disclosed turbine startup, synchronizing, and load control systems and methods. Improved turbine and plant operation and management also results from the disclosed turbine monitoring and operator interface systems and methods. The improvements stem from advances in functional performances, operating efficiency, operating economy, manufacturing design and operating flexibility and operating convenience.
The present system supplements, expands and improves over the prior art. In doing so, the present system includes specialized programs for suppressing noise in the reference, demand and sensed parameter signals of the turbine-generator system; the programs are broken down into a series of master task programs and other programs for better utilization of the digital computer; a special program which monitors all of the programs and detects computing, addressing and transmitting errors therein increases the reliability, safety and flexibility of the system. Panel monitoring, information transmission and warning systems greatly increase the usefulness, ease-of-operation and inherent reliability of the present system. A breaker open interrupt program indicating the loss of load connected to the generator prevents any overspeed condition from becoming serious. A stop and initialization program automatically readies the digital computer for immediate service after any computer or turbine stop or loss of power thereto, either instantaneous or long term. A logic program in the present system provides the capability for maintenance testing of logic functions; monitoring analog and digital speed failure; increasing turbine supervision capabilities, expanding manual control capabilities of the computer allowing an operator to work in conjunction with the automatic operation of the turbine generator system with the digital computer. The logic program also including hold and suspend systems; governor and throttle valves control interlock systems; turbine latching logic programs; breaker logic programs; throttle pressure control logic programs; megawatt feedback logic; impulse pressure feedback logic; speed feedback logic; automatic synchronizer logic; automatic dispatch system logic; automatic turbine startup logic and remote transfer logic.
The control program of the present system includes the capability of time updating any function in the computer; limiting the position of predetermined valves in the turbine system; testing any valve in the system, checking for contingency conditions such as inoperativeness of any program or hardware; being able to select various speed control functions and various hardware therein for high reliability; selecting a series of operating modes in both load and speed modes of operation, providing speed and load reference functions with flexibility to change these during operation, switching between the speed control function and the load control functions during the automatic operation of the DEH system providing governor valve control functions and peripheral functions, such as, lags and nonlinear characterization of characteristics in the turbine-generator system.
The present system also has an elaborate programming system for better communications between an operator and the digital computer through use of special panel task program. The panel programs include a button-decoding program, a control switching system, a display system for displaying a vast number of system parameters of the turbine generator system, a system for changing during operation most parameters and constants in the digital computer with great ease and rapidity, a capability to select a great number of operating modes, a system for checking the status of predetermined valves in the system and display devices therefor, a testing system for predetermined valves in the system, a limiting provision for limiting the position of predetermined valves in the system. In addition the panel programs provide for the control of automatic turbine startup programs; the control of the digital computing system through the use of a series of manual buttons, switches, toggles, etc.; the program capability of monitoring keyboard activity for failsafe and improper operation thereby preventing operator mistakes from resulting in improper signals and signaling means for warning an operator of any improper commands or mistakes in his operation of the keyboard, panels etc.
APPENDIX 3
DEH SYSTEM PROGRAMS
In this section the DEH system programs are described in the following order:
Interrupt Programs and Subroutines
Logic Programs
Operator's Panel Programs
Control Programs
PRESET SUBROUTINE
The CALL statement to PRESET provides the linking mechanism for all variables and parameters except the sampling interval (DT). This quantity is referenced in the PRESET program through a COMMON statement which defines the location of DT in the proper block COMMON area labeled DELTA. The PRESET program size is 108 words and the data pool size is 19 words; this requires a total storage of 127 words. The program is normally linked separately and loaded into the computer through the tape reader. The core area assigned to PRESET is from (26B0 to 273F).sub.16 ; this is 90.sub.16 (144.sub.10) locations; this allows 17.sub.10 words spare for future changes or modifications. The first executable location in PRESET is at 26B2.sub.16 and the subroutine requires the library function SAT: for argument transfer handling. PRESET is not a reentrant subroutine and therefore can be called only from the CONTROL task.
PLANTCCI SUBROUTINE
The PLANTCCI subroutine scans all contact inputs to the DEH system and sets full-word logical images of these in designated COMMON areas. The subroutine may be called by the SEQUENCE OF EVENTS program, the COMPUTER STOP/INITIALIZE task, or the AUXILIARY SYNCHRONIZER task. The PLANTCCI subroutine sets lockout prior to running and releases lockout after execution; this allows it to be called from any other program in the DEH system.
The PLANTCCI subroutine is desined so that it has COMMON areas which receive the full-word logical images of the contact input states. The DEH system has four channels of contact inputs; each channel contains 14 bits, thus yielding 56 contacts which must be scanned. Channels 2 and 3, covering the 28 contacts D029 through D056, are assigned to the AUTOMATIC TURBINE STARTUP program; these images are stored in the TACOMCCI COMMON area. Channels 4 and 5, covering the 28 contacts D057 through D084, are assigned to the basic DEH Control System; these images are stored in the ALPHA COMMON area.
The PLANTCCI subroutine is defined by the FORTRAN statement:
SUBROUTINE PLANTCCI
Three counters are first initialized: J counts from 1 to 28 for each group of 28 contacts assigned to the AUTOMATIC TURBINE STARTUP program and the basic DEH system; K counts from 0 to 4 to transfer to each of the contact input channel instructions; L counts from 1 to 2 to identify first the automatic turbine startup contacts and then the basic DEH contacts.
The program executes an Input to or Output from the Accumulator (IOA) assembly language instruction to input through the accumulator the contacts on channel 2. These are saved in a temporary location (IDUMMY) which has been equivalenced with the bit variable (ICCI). A simple FORTRAN DO loop then executes through steps 0 to 13, setting the proper full-word core location to the state of the corresponding contact.
The program repeats this pattern for channels 3, 4 and 5. Prior to returning, the subroutine bids the LOGIC task to run so that the DEH system status may be updated as a consequence of any contact changes. However, should the LOGIC task have been running just prior to PLANTCCI, this bid will be ignored by the Monitor. To guarantee that the LOGIC task runs, the variable RUNLOGIC is also set true, the AUXILIARY SYNCHRONIZER task then detects RUNLOGIC within 1/10 sec and it bids the LOGIC task.
SPDLOOP SUBROUTINE
The SPDLOOP subroutine is designed so that it has access to all quantities through COMMON references. The parameters WR, HLF, GR1, and SPDB are referenced through the DELTA COMMON block; the variables REFDMD, WS, X , and REF1 are accessed through the EPSILON COMMON block. The subroutine structure is given by the FORTRAN statement:
SUBROUTINE SPDLOOP
The subroutine computes the speed error, checks the magnitude of this with a deadband value, converts the result to an equivalent megawatt speed correction factor, and checks against a high limit before returning to the CONTROL task.
The SPDLOOP programs size is 49 words and the data pool size is 10 words; this requires a total storage of 59 words. The program is normally linked separately and loaded into the computer through the tape reader. The core area assigned to the program is from (2FC2 to 2FFF).sub.16 ; this is 3E.sub.16 (62.sub.10) words, allowing a few spare. The first executable location in SPDLOOP is at location 2FC4.sub.16 and the subroutine requires the library function ABS to evaluate the absolute value of speed error. SPDLOOP is not a reentrant subroutine and thus can be called only from the CONTROL task.
AUXILIARY SYNCHRONIZER (AUX SYNC) TASK
The program first checks the CONTROLLER RESET pushbutton on the DEH Operator's Panel; if the button is backlighted, the operator has not acknowledged computer return from a power failure or an out-of-sync condition. When the button is pressed, the AUX SYNC task proceeds to carry out its functions.
The program checks three counters for timing. IVPL is incremented in 1/10 sec steps as long as the VALVE POSITION LIMIT RAISE or LOWER buttons are pressed. CADSUP is similarly incremented as long as the Automatic Dispatch System (ADS) raise contact input is set. CADSDOWN is incremented while the ADS lower contact input is set. Finally, if the RUNLOGIC variable is set, AUX SYNC bids the LOGIC task to run.
The program then initiates a FORTRAN DO loop to check for normal execution of the DEH system periodic tasks. Each entry in the array ICOUNTER is incremented and tested against its maximum count (IMAX). If ICOUNTER has expired, it is reset to zero and transfer is made to appropriate portions of the remaining program. Otherwise the next counter is examined in the same way until all have been tested; at this time the AUX SYNC task exits until the next bid from the Monitor.
When the first ICOUNTER expires, the CONTROL task is bid and a flag (ISCAN) is set for further action in both the AUX SYNC and the ANALOG SCAN tasks. When the second ICOUNTER expires, logical decisions are made on ISCAN and INTSCAN to set up the necessary information to properly execute the ANALOG SCAN task. This task and the FLASH task are then bid to run.
When the third ICOUNTER expires, the AUTOMATIC TURBINE STARTUP (ATS) task is bid. In addition, the VISUAL DISPLAY task is bid if no key entry is being made on the Operator's Panel keyboard. The PLANTCCI subroutine is called if the constant PERCCI has been set non-zero from the keyboard to request a periodic contact input scan. Finally, when the fourth ICOUNTER expires the ATS MESSAGE WRITER task is bid.
The AUX SYNC program communicates with the various counters, flags and variables in the DEH system through the COMMON areas BETA, DELTA, ZETA and THETA. The program size is 135 words, the data pool size is 36 words, and the task header size is 9 words, for a required minimum storage of 180 locations. AUX SYNC is linked as a separate task and is loaded into the computer through the tape reader. The core area assigned to the task is from (14E0 to 149F).sub.16 ; this is C0.sub.16 (192.sub.10) locations, thus allowing some room for expansion.
CCO TEST TASK
The CCO TEST task is assigned priority level 1 and can be bid from the Programmer's Console only. The program first checks invalid entries for ITF, ICCO1 and ICCO2; if invalid, the CCO TEST request is ignored. For valid inputs, the program selects the set or reset pattern for the contact outputs according to the value of ITF, and computes the number of contacts to be sent out according to the values of ICCO1 and ICCO2. A FORTRAN DO loop then ranges through this group, computing the output register and selecting from a table of masks (MTABLE), the proper mask to output each contact. After all contacts have been sent out the CCO TEST task exists.
Use Of CCO Test For Analog Outputs
To use the CCO TEST task for analog outputs it is necessary to understand the hardware and software organization of the DEH system. A total of 32 words of contact and analog outputs are available, with 16 of these assigned to the contact outputs discussed above and the remaining 16 assigned to analog outputs. During initialization of the DEH software system, the Monitor variable PCREG is set to 32 to indicate the total number of contact output registers for use by the CO handler of the Monitor. In addition, the Monitor table PCOCTRL, which is 32 words long, was initialized with the hardware description of the 16 contact output words, followed by the hardware description of the 16 analog output words. This in effect makes the analog output words look like contact output words, and essentially doubles the length of the contact output list. The analog outputs can be considered to be contact outputs starting at C225 and continuing to C448.
However, the analog output printed circuit cards are not the same as the contact output printed circuit cards. Whereas each word of contact outputs has 14 bits associated with it and thus 14 contact outputs, each word of analog output has only 11 bits associated with it. Thus the 11 low-order bits look like contact outputs but the 3 high-order bits are essentially dummy or psuedo outputs.
A description of the analog output words in contact output terminology suitable for use with the CCO TEST task is given in the following table. As an example of setting an analog output, suppose it is desired to set maximum voltage on output word 22; this means it is necessary to set bits 0 through 10 on this word, which in turn means set equivalent contacts C253 through C263 as shown in the table.
SEQUENCE OF EVENTS INTERRUPT PROGRAM
A flow chart for the SEQUENCE OF EVENTS INTERRUPT program is shown in FIG. 23. A call is made to the PLANTCCI subrouting to do the contact scanning; return then is to the Monitor interrupt handler indirectly through location 00DF.sub.16 (0023.sub.10) in the Monitor zero table. The program size is 13 words and the data pool size is 1 word for a required storage of 14 location. The program is normally linked seprately and loaded into the computer through the tape reader. The SEQUENCE OF EVENTS INTERRUPT program has been assigned to core area (0020 to 003F).sub.16 ; this is 20.sub.16 (32.sub.10) locations, thus providing some spares.
The sequence of events interrupt is number 2 in the total list of interrupts in the DEH system. The Monitor interrupt transfer table (INTB) must be initialized to contain the location of the SEQUENCE OF EVENTS INTERRUPT program. The table entry is at 0327.sub.16 ; the value 0020.sub.16 must be entered in this location. Normally, this is done with a special SYMBOLIC ASSEMBLY program which defines all interrupt locations, and which is loaded after complete debugging of the DEH system in the field.
BREAKER OPEN INTERRUPT PROGRAM
A call is made to the contact output handler to send a zero analog output to the governor valves. Return is made to the Monitor interrupt handler indirectly through location 00DF.sub.16 (0223.sub.10) in the Monitor zero table. The program size is 17 words and the data pool size is 5 words for a required storage of 22 locations. The program is normally linked separately and loaded into the computer through the tape reader. The BREAKER OPEN INTERRUPT program has been assigned to core area (116A to 117F).sub.16 ; this is 16.sub.16 (22.sub.10) locations, thus allowing a few spares.
The breaker open interrupt is number 37 in the total list of interrupts in the DEH system. The Monitor interrupt transfer table (INTB) must be initialized to contain the location of the BREAKER OPEN INTERRUPT program. The table entry is at 034A.sub.16 ; the valve of 116A.sub.16 must be entered in this location. Normally this is done with a special SYMBOLIC ASSEMBLY program which defines all interrupt locations, and which is loaded after complete debugging of the DEH system in the field.
TASK ERROR PROGRAM
A contact output is set to switch the turbine to manual control. A time delay of 1/10 sec is then initiated to avert a race condition and to give the analog backup system enough time to switch; after this delay, the contact requesting manual is reset so that automatic control may be selected after the TASK ERROR problem is solved. Return to the Monitor error handler is made indirectly through the C register.
The TASK ERROR program size is 25 words and the data pool size is 5 words for a required storage of 30 words. The program is normally linked spearately and loaded into the computer through the tape reader. The TASK ERROR program is assigned core area (3FE0 to 3FFF.sub.16 ; this is 20.sub.16 (32.sub.10) locations, thus providing a few spares.
TURBINE TRIP INTERRUPT PROGRAM
A call is made to the contact output handler to set a zero analog output to the throttle and governor valves. Return is made to the Monitor interrupt handler indirectly through location 00DF.sub.16 (0223.sub.10) in the Monitor zero table. The program size is 17 words and the data pool size is 8 words for a required storage of 25 locations. The program is normally linked separately and loaded into the computer through the tape reader. The TURBINE TRIP INTERRUPT program is assigned to core area (14A0 to 14DF).sub.16 ; this is 40.sub.16 (64.sub.10) locations, thus allowing some spares.
The turbine trip interrupt is number 34 in the total list of interrupts in the DEH system. The Monitor interrupt transfer table (INTB) must be initialized to contain the location of the TURBINE TRIP INTERRUPT program. The table entry is at 0347.sub.16 and the value 14A0.sub.16 must be entered in this location. Normally this is done with a special SYMBOLIC ASSEMBLY program which defines all interrupt locations, and which is loaded after complete debugging of the DEH system in the field.
PANEL INTERRUPT PROGRAM
A scan of the panel contact inputs (which are on channel 0) is performed with an IOA instruction. The high-order bits are then masked out so that the six contacts on bits 0 through 5 remain to identify the pushbutton pressed. This information is then stored in location IPB in the BETA COMMON area, the PANEL task is bid, and return is made to the Monitor interrupt handler indirectly through location 00DF.sub.16 (0223.sub.10) in the Monitor zero table. The program size is 18 words and the data pool size is 3 words for a required storage of 21 words. The program is normally linked separately and loaded into the computer through the tape reader. The PANEL INTERRUPT program has been assigned core area (1480 to 149F).sub.16 ; this is 20.sub.16 (32.sub.10) locations, thus allowing a few spares for growth.
The panel interrupt is number 33 in the total list of interrupts in the DEH system. The Monitor interrupt transfer table (INTB) must be initialized to contain the location of the PANEL INTERRUPT program. The table entry is at 0346.sub.16 and the value 1480.sub.16 must be entered in this location. Normally this is done with a special SYMBOLIC ASSEMBLY program which defines all interrupt locations, and which is loaded after complete debugging of the DEH system in the field.
VALVE INTERRUPT PROGRAM
The VALVE TEST CLOSEPB is interrogated to determine if it was the pushbuttom released. If so, the pushbutton flag is reset and the contact output holding the throttle valve in a test close position is reset. If not, the VALVE TEST OPENPB is interrogated to determine if it was the pushbottom released. If so, the pushbuttom flag is reset and the test analog output (TESTAO) is checked to determine if it has been reduced to zero. If not, no further action is taken since the test is not completed. But if the test analog output is zero, then the counter (NVTEST) indicating which valve was being tested is reset to zero and the contact output connecting this test signal to the governor valve servo amplifier is reset.
If neither the CLOSEPB nor the OPENPB has been released, then the VALVE INTERRUPT program concludes that it was a VALVE POSITION LIMIT RAISE or LOWER pushbutton; therefore, both of these are reset and return is made to the Monitor interrupt handler indirectly through location 00DF.sub.16 (0223.sub.10) in the Monitor zero table. The VALVE INTERRUPT program size is 62 words and the data pool size is 18 words for a required storage of 80 locations. The program is normally linked separately and loaded into the computer through the tape reader. The VALVE INTERRUPT program is assigned to core area (0040 to 009F.sub.16 ; this is 60.sub.16 (96.sub.10) locations, thus providing some room for growth.
The valve interrupt is number 35 in the total list of interrupts in the DEH system. The Monitor interrupt transfer table (INTB) must be initialized to contain the location of the VALVE INTERRUPT program. The table entry is at 0348.sub.16 and the valve 0040.sub.16 must be entered in this location. Normally this is done with a special SYMBOLIC ASSEMBLY program which defines all interrupt locations, and which is loaded after complete debugging of the DEH system in the field.
STOP/INITIALIZE TASK
Although recovery from a power failure is the most common situation in which the STOP/INITIALIZE task will be called on, there is another case during which a precautionary note is necessary. This is the situation in which the SYNCH DISABLE button has been pressed on the CPU maintenance panel to allow special software debugging or reloading to proceed. When SYNCH DISABLE is pressed, the computer outputs are immediately disconnected by special hardware circuitry and the manual backup system holds the turbine at the existing state. Thus, for all intents and purposes the SYNCH DISABLE is identical to a power failure.
However, when return is to be made from SYNCH DISABLE, the following four-step procedure must be carried out at the CPU maintenance panel:
1. Press STOP button.
2. Press RESET button.
3. Press RUN button.
4. Press RESET button.
This will guarantee an orderly restart procedure as described above and minimize the time necessary to place the DEH system on automatic control.
An output instruction is executed to restore the digital speed channel interrupt system, after which all contact and analog outputs are reset by a FORTRAN DO loop which calls the Monitor handler (M:CCO). Then all DEH COMMON areas containing counters or logical variables are reset, thus concluding the clean-up stage of restarting.
In the initializing phase, certain counters in the BETA COMMON are set as follows: ICOUNTER3 is set to 5 so that the AUX SYNC task will then bid the turbine acceleration and supervising task in a fashion to uniformly distribute computer duty cycle; IPBX is set to 1 so that the VISUAL DISPLAY task will begin displaying the turbine REFERENCE; and NOMINS is set to 1 so that the duty cycle task, if it is initiated, will measure DEH duty cycle over 1 min intervals. A call is made to the PLANTCCI subroutine so that a contact input scan is activated; this is subroutine in turn bids the LOGIC task which aligns the DEH Control System to the existing state of the plant. Finally, the CONTROLLER RESET lamp is turned on with a contact output and the logical variable CRESETPB is set. This inhibits the AUX SYNC task from executing any periodic programs until the operator presses the CONTROLLER RESET pushbutton; when he does this, the PANEL task resets CRESETPB, thus allowing AUX SYNC to bid all periodic tasks in the normal pattern.
The STOP/INITIALIZE task is 81 words long, its data pool size is 17 words, and the header size is 9 words for a required storage of 107 locations. STOP/INITIALIZE is linked as a separate task and loaded into the computer through the tape reader. The core area assigned to the task is (2F40 to 2FC1).sub.16 ; this is 82.sub.16 (130.sub.10) locations, thus providing spare area for additional functions which may be needed.
VISUAL DISPLAY TASK
The VISUAL DISPLAY TASK IN ON PRIORITY LEVEL 8 and is normally bid by the AUX SYNC task every 1 sec; however, when the operator requests a new display quantity, then VISUAL DISPLAY will be bid initially by the PANEL task.
A description of the display pushbuttons is given in FIG. 31 where there is also included the value of the counter (IPBX) which identifies these buttons to the appropriate DEH programs. Since more of the display pushbuttons in FIG. 31 are dedicated to a single quantity, the programming mechanism to accomplish this function is straight-forward. However, the general DEH parameter display requires a coded address to access the proper quantity in the various COMMON areas. This coding is necessary because the format of the displayed variable may be logical, integer or real (floating point); in addition, the variable may reside in the base DEH area, and thus exist in all systems, or it may reside in the AUTOMATIC TURBINE STARTUP area, and thus be an option which may or may not exist in all systems.
To accommodate these various situations, a dictionary addressing scheme has been designed which will provide access to every combination of variables. In this scheme all addresses are composed of four digits, each of which may validly range from 0 through 9. The most significant digit is coded to indicate the desired variable format (logical, integer or real) and the storage area (base DEH or ATS). The three least significant digits simply point to the relative location of the variable in either the base DEH or the ATS COMMON area.
The following table lists the address structure. The symbols XXX represent relative location in COMMON area and are completely catalogued in the dictionary portion of the operating instructions. The remaining most significant digit and its definition are tabulated.
Under normal conditions, the program is bid once a second by the AUX SYNC task. However, when the operator presses a panel pushbutton to request a new display, a separate path to the VISUAL DISPLAY task is taken. The pushbutton generates a panel interrupt which is serviced by the Monitor; this results in the PANEL INTERRUPT program being executed, and after decoding the pushbuttom pressed the PANEL program runs. The PANEL task responds by setting appropriate flags and counters, and then bids the VISUAL DISPLAY task.
Whether called from the AUX SYNC or the PANEL task, the VISUAL DISPLAY program performs its functions the same way. It first checks the appropriate flags and counters previously set, decodes these, selects the proper numerical value from core storage, and then manipulates this value to the correct form. Then the VISUAL DISPLAY task sets up a contact output pattern for the number to be displayed and gates this to the display hardware.
The VISUAL DISPLAY program first reacts to a group of variables which have been set by the PANEL task, and then VISUAL DISPLAY creates another group of variables which will place the proper values in the windows. Concerning those variables generated by the PANEL program, IPBX indicateswhich display pushbutton has been pressed as shown in FIG. 31. INDEX1 and INDEX3 are flags which indicate special action; INDEX1 means a VALVE STATUS or PROGRAM DISPLAY pushbutton has been pressed and thus both display windows should be cleared preparatory to additional keyboard entries; INDEX3 indicates a dedicated pushbutton has been pressed and new values for the dedicated variable are being entered from the keyboard. DATENTRY and DADR are flags associated with changing DEH system constants while INDEX2 is a relative location in a COMMON area indicated by the symbols XXX in the above table.
The DEH system state (BR) is necessary when displaying REFERENCE in order to place the MW or SPEED message in the left-most windows. The state ATS is required when displaying REFERENCE and ACCELERATION RATE since these quantities are set by the ATS program, rather than from the keyboard, when the turbine is being accelerated by computed values from ATS. The state GC is necessary when displaying VALVE POSITION LIMIT since the limited quantity depends on whether the turbine is on throttle or governor control. The DEH system variables, such as REFERENCE, DEMAND, RATES and LIMITS are accessed from appropriate COMMON areas through the use of INDEX2.
ANALOG SCAN TASK
The ANALOG SCAN task is assigned priority level B.sub.16 (11.sub.10) and is bid by the AUX SYNC task every 1/2 sec.
The ANALOG SCAN task communicates with other parts of the DEH system through various COMMON areas. The BETA COMMON contains the variable FLGWRD which is set by the Monitor analog handler to indicate that the A/D converter is out of service. The converted base DEH system analog inputs are stored in the GAMMA COMMON area, while DELTA contains the arrays SLOPE and BINT for conversion of inputs to engineering units. Additional logic states are accessed via ZETA COMMON, while the ATS analog inputs and control words are located in TAAI and TAADBUF.
The program first checks the value of ISCAN, which is set by the AUX SYNC program to indicate whether to scan base DEH inputs or ATS inputs. These groups are each scanned on alternate 1/2 sec; the AUX SYNC task arranges the timing so that 1/2 sec prior to bidding the CONTROL task, the ANALOG SCAN task is directed to scan the inputs necessary for the control system. The following 1/2 sec, while the CONTROL task is running, the AUX SYNC task arranges the timing so that the ANALOG SCAN task will scan a group of ATS inputs. This is done by setting ISCAN=0 for base DEH inputs and ISCAN=1 for ATS inputs.
When ISCAN=0, the Monitor analog handler is called to scan the 15 base DEH inputs. The handler must be provided with a list of control words, one per input, which defines the hardware configuration of each input which are stored in ADBUF1. The P2000 Monitor Reference Manual, TP043, describes the format and function of each bit in these words, but essentially these bits define the channel, bit, multiplexer word and A/D gain setting for each input.
When the A/D converter completes the scanning of these inputs, the raw bit patterns are stored in a temporary buffer (VALBUF). The scan program then executes a FORTRAN DO loop to process these inputs. The two inputs MW and PI are checked for sensor failure against absolute low and high limits, and appropriate action is initiated if either failure occurs.
The remaining 10 base DEH inputs represent governor and throttle valve demand from the analog backup system and the digital system, and the actual LVDT position of each governor and throttle valve. These inputs are not converted but are kept in their raw form until used by the appropriate program. The reason for this is that these quantities are used much less frequently than the above inputs. In addition, the format of these inputs in engineering units is a percent value from 0 to 100; consequently, there is not much advantage to their conversion. However, these values are checked for low sensor limit, and if this occurs, they are set to zero. A portion of the instructions to do this work are written in Assembly language to reduce the program size. The inputs for the valve demands are stored in array ITVGV and the LVDT inputs are stored in array ITVGVSS.
The last action taken in this part of the ANALOG SCAN program is to check the A/D converter. The Monitor analog handlers set the variable FLGWRD if the A/D converter cannot be adjusted to the existing plant conditions; if this flag is set, the converter is said to be out of service and all feedback loops must be removed from the control system.
The variable ISCAN is reset to zero and a GO TO statement is executed; the transfer point depends on the value of INTSCAN, which is incremented once a second and runs from 1 to 10 before being reset back to 1. INTSCAN values 1, 3, 6 and 8 represent intervals of time when no additional work need be done, as can be seen on the timing chart of FIG. 2. INTSCAN values of 2 and 7 (thus being 5 sec apart) transfer to statement 200. Here a second counter (ISPAN) is incremented in steps of 1; when ISPAN=3, this represents a 15 sec interval and thus a SPAN/ADJUST call must be made. As this is done, the counter ISPAN is set back to zero.
When INTSCAN=9, it is time to call for a group of temperature analog inputs; these are scanned in groups of 10, and there are 6 such groups. Thus, the counter NSYNC1 is incremented from 1 to 6 to indicate to the ATS conversion program which group has been input at this time. Also, the variable NSYNC2 is set to -1 to indicate that temperatures are coming in now. Finally, J is a pointer to the proper control words in the ATS COMMON area ITAAI.
When INTSCAN=4, the ATS miscellaneous inputs which are scanned every 10 sec will be input. Statement 400 sets J to the proper pointer and sets NSYNC2=-2 to indicate this fact.
When INTSCAN=5 or 10, transfer is to statement 500 which sets up J to point to the ATS 5 sec vibration inputs. A flag (BIDATSCV) is also set at this point so that the ATS CONVERSION task may be bid further on in this program (note that this conversion task is bid every 5 sec). Finally, the Monitor analog handler is called with the proper pointer to control word tables and buffer areas where the raw bit patterns are stored for the appropriate group of ATS inputs.
The ANALOG SCAN task size is 335 words, its data pool size is 89 words, and its header is 9 words for a required minimum storage of 433 locations. ANALOG SCAN is linked as a separate task and loaded into the computer through the tape reader. The core area assigned to ANALOG SCAN is (16DO to 188F).sub.16 ; this is 11CO.sub.16 (448.sub.10) locations, which allows a few spares.
LCCO SUBROUTINE
The subroutine is called only by the LOGIC task and thus is not reentrant. Arguments to the LCCO subroutine include three variables which indicate the appropriate action to be taken, and a pointer to a table of contact output words and bits which define the hardware connections for the quantities which must be set or reset.
The LCCO subroutine is designed so that a call from the LOGIC task provides a list of the variables necessary to evaluate whether or not contact outputs should be actuated and, if so, whether they should be set or reset. Not all calls to LCCO involve the logical pushbutton state; in those cases this argument (LVIPB) is a dummy which satisfies the calling sequence but accomplishes no other significant action. An exclusive-OR test is made on LV and LVX; if they are alike, no further action is taken. If they are different, this means contact outputs must be actuated.
The LCCO program size is 68 words and the data pool size is 92 words for a required storage of 160 locations. The program is normally linked separately and loaded into the computer through the tape reader. The core area assigned to LCCO is (18DO to 196F).sub.16; this is AO.sub.16 (160.sub.10) locations, which is exactly that required by the subroutine.
LOGIC TASK
The LOGIC task is assigned priority level 9 and is bid by the AUX SYNC program on demand by other tasks in the DEH system.
Its size is 1092 words, its data pool size is 147 words, and its header is 9 words for a required storage of 1248 locations. LOGIC is linked as a separate task and loaded into the computer through the tape reader. The core area assigned to LOGIC is (1970 to 1E5F).sub.16 ; this is 4F0.sub.16 (1264.sub.10) locations, which allows a few spares. The LOGIC task is organized as a series of small subprograms which are executed sequentially and which address themselves to particular aspects of the total DEH Control System logical operation. The subprograms are in some cases quite simple, as when monitor lights are turned on or off, and in other cases they are quite complex, as when it is necessary to account for many permissive conditions to allow feedback loops to be put into service.
Flip-Flop Function
The flip-flop is a basic building block of most logic systems, whether the system be of hardware or of software construction. A flip-flop is essentially a memory element which may be set or reset by other logical elements to achieve a desired result. The flip-flop has two input terminals, one for setting and one for resetting (or clearing), and one output terminal, which indicates the state of the flip-flop.
The operation of the flip-flop is as follows. A logically true signal at the set terminal results in a logical true signal at the output terminal, while a logically true signal at the reset terminal produces a logical false signal at the output terminal. Simultaneous logically true signals at both the set and reset terminals yield a logical false signal at the output terminal, thus providing the reset terminal with precedence over the set terminal. Simultaneous logically false signals at both the set and reset terminals yield no change at the output terminal; that is, the output stays at whatever state it had been, thus providing the memory feature of the flip-flop.
The flip-flop function has been incorporated into the DEH system with a FORTRAN FUNCTION statement, thus allowing evaluation of the flip-flop element anywhere in the LOGIC task as an in-line statement.
OPC Test/24 V Monitor Lamps
The OPC TEST and 24 V monitor lamps indicate the status of these systems to the operator. The OPC (Overspeed Protection Controller) is part of the analog backup portion of the DEH system. It continually compares turbine speed with an overspeed set point; should the turbine overspeed, then the backup system immediately provides a large bias to close the governor valves, thus cutting off steam flow and arresting the overspeed condition. The state of the OPC system is controlled from a three-position key-lock switch on the DEH Operator's Panel. Normally, the key-switch is in the mid-position which places the OPC system in service as described above.
Under certain conditions, however, it is desirable to run the turbine at a speed greater than the overspeed set point; this is usually done during initial startup as part of the turbine acceptance. During such times it is necessary to disable the OPC system and to provide a monitor light to indicate the special overspeed test. This is accomplished by switching the key-switch to the right position; the analog OPC system is then disabled and a contact input is sent to the DEH logic system to turn on a monitor lamp located above and to the right of the key-switch. When the overspeed test is completed, the switch is returned to the off position; this enables the OPC system and resets the contact input to the DEH LOGIC task, which then turns off the monitor lamp.
The 24 V monitor lamp is to indicate a failure in the 24 V power supply to the DEH system. The failure is detected by special circuitry in the analog backup system, which switches to an alternate supply and sets a contact input to the DEH system. The LOGIC task then turns on the 24 V monitor lamp which is located on the Operator A Panel. When the power supply problem is corrected, the contact input is reset and the LOGIC task turns off the monitor lamp.
The program to control these monitor lamps consists simply of two calls to the LCCO subroutine with the proper arguments to indicate the required action.
Maintenance Test
The MAINTENANCE TEST system is activated by a two-position key-lock switch on the Operator's Panel. The function of this switch is to allow tuning or adjusting of certain constants in the DEH Control System, or to allow operation of the DEH system in a simulation mode for training purposes. When such tests are to be performed, the maintenace test key is moved to the right position; this immediately switches the turbine to manual control by a wired connection and sets a contact input to the DEH system. The LOGIC task then reacts in three ways: first, a contact output is set which turns on a monitor lamp above and to the right of the maintenance test switch; second, another contact output is set which requests transfer to manual as a backup to the wired connection; and third, the manual-tracking portion of the DEH Control System is disabled.
When the maintenace test action is completed and the test switch returned to the off position, the LOGIC task resets the two contact outputs to turn off the maintenance test lamp and to release the request for manual control. In addition, this part of the program enables the manual-tracking system by resetting the turbine REFERENCE and DEMAND to zero and allowing the normal control programs to run.
Analog/Digital Speed Failure Monitor Lamps
The analog and digital speed failure monitor lamps indicate the status of the analog and digital speed channel inputs to the DEH system. The speed signals supplied by these two channels are generated by independent magnetic pickups and are compared, with the aid of a supervisory instrument speed signal as a third input, in a speed selection system in the CONTROL task. The result of this selection process is passed on to the LOGIC task by the variables ANASPDF and DIGSPDF, which when set, indicate failure of the particular speed input and when reset, indicate valid speed signals. The LOGIC task then places the corresponding monitor lamps in the proper state. The program to control these monitor lamps consists simply of two calls to the LCCO subroutine with the proper arguments to indicate the required action.
ANASPDF is the status of the analog speed channel as determined by the speed selection process, while ANASPDFX is the last value of ANASPDF. DIGSPDF is the status of the digital speed channel as determined by the speed selection process described above, while DIGSPDFX is the last value of DIGSPDF.
Turbine Supervision Off Logic
The logical state (TSOFF) may be set by either the panel pushbutton represented by TURBSPOF or the the A/D converter out of service as given by VIDAROS as shown in FIG. 41. The pushbutton state (TURBSPOF) is generated by the PANEL task while VIDAROS is generated by the ANALOG SCAN task. A call to the LCCO subroutine is then made to update the pushbutton lamp status.
Operation Automatic Logic
The state of manual or automatic operation of the DEH system is actually determined by circuitry in the analog backup system, and the DEH programs simply respond to these states. When the DEH system is in manual control, the analog backup system ignores the computer output signals and positions the valves according to its up/down counter circuitry. Conversely, when the DEH system is in automatic control, the analog backup system uses the computer outputs to position the valves and adjusts its up/down counter to track the computer outputs.
When transfer is made to manual, either by pushbutton or computer request, the analog backup system opens contacts carrying the computer outputs to the valves and simultaneously closes contacts carrying backup system outputs to the valves. In addition, a contact input is sent to the DEH system LOGIC task indicating manual operation. When transfer is made to automatic control by pressing the OPERATOR AUTOMATIC pushbutton, and assuming that the computer system is tracked and ready for automatic, the analog backup system opens contacts carrying its own signals to the valves and simultaneously closes contacts carrying the computer outputs to the valves. The operator automatic logic thus merely updates internal computer variables to the state of manual or automatic control as determined by the backup system.
In updating the DEH system programs to the existing control state, the internal operator automatic variable (OA) is set to the logical inverse of the manual contact input represented by TM. Then a decision is made to determine if the system has just been switched to automatic by comparing OA and its last value (OAX). If automatic has just occurred, ready tracking flags are reset; if not, no action is taken. In either case, the last value (OAX) is set to the current automatic state (OA) for use in the next bid of the LOGIC task.
Go Logic
When the DEH system is on operator automatic control, the turbine speed/load (DEMAND) is entered from the keyboard. The operator then may allow the turbine reference to adjust to the demand by pressing the GO pushbutton. When the operator does this, the GO lamp is turned on and logical states are set to begin moving the reference in the CONTROL task. When the reference equals the demand, the GO lamp is turned off. The GO logic detects the various conditions affecting the GO state and sets the status and lamp accordingly. The GO pushbutton (GOPB), which is updated by the PANEL task, is the set signal for the GO flip-flop. The reset or clear signal, which will override the set signal, can occur from a number of different conditions as follows: the HOLD pushbutton (HOLDPB) as updated by the PANEL task, a computed hold condition (HOLDCP) as set by the CONTROL or LOGIC tasks, the DEH system not being in operator automatic control (OA) or in the maintenance test condition (OPRT) (during which the system may be used as a simulator/trainer), or the condition in which the reference has reached the demand and the CONTROL task sets the GOHOLDOF state to clear the GO lamp.
Hold Logic
When the DEH system is an operator automatic control, the turbine speed/load (DEMAND) is entered from the keyboard. The operator may then inhibit the turbine reference from adjusting to the demand by pressing the HOLD pushbutton. When the operator does this, the HOLD lamp is turned on and logical states are set to prohibit the reference from moving in the CONTROL task. The HOLD logic detects the various conditions affecting the HOLD state and sets the status and lamp accordingly.
The HOLD pushbutton state (HOLDPB), which is set by the PANEL task, or the hold state (HOLDCP) computed by the CONTROL or LOGIC tasks, acts as the set signal for the HOLD flip-flop. The reset or clear signal, which will override the set signal, can occur from a number of different conditions as follows: the DEH system not being on operator automatic control (OA) or in the maintenance test condition (OPRT) (during which the system may be used as a simulator/trainer), the GO flip-flop being set and thus overriding the HOLD state, or the condition in which the reference has reached the demand and the CONTROL task sets the GOHOLDOF state to clear the HOLD lamp. The HOLD logic program then resets the computed hold state (HOLDCP) and the GOHOLDOF state, so that they may be used in future decisions by the CONTROL and LOGIC tasks.
Governor Control Logic
Control of turbine steam flow with the governor valves is required during speed and load control. Normally governor control is initiated when the turbine has been accelerated to near synchronous speed, after which the unit is brought up to synchronous speed, synchronized and then loaded with the governor valves as the normal mode of operation.
The governor control logic detects turbine latch and unlatching conditions, transfer from throttle valve to governor valve control, and manual operation of the governor valves. When any of these conditions occur, the governor logic must align the DEH system to the appropriate governor control state.
The governor control flip-flop (GC) may be set by a number of conditions, the most common of which occurs on automatic control when the operator presses the transfer TV/GV pushbutton (TRPB). Assuming that the governor valves are at their maximum open position as indicated by GVMAX and that the automatic turbine startup mode (ATS) is not selected, then the governor flip-flop will be set. An alternate path for setting this flip-flop occurs if the automatic turbine startup program (ATS) requests transfer via the logical variable ATSTRPB. In addition, when the throttle valves reach about 90 percent position, a contact input (THI) is activated by the analog backup system, and this contact sets the GC flip-flop. This last case occurs when the turbine is a manual control. Finally, the governor control flip-flop is reset when the turbine latch contact input (ASL) is released.
Following the GC flip-flop, a decision is made to determine if the system has just switched to governor control by comparing GC with its last state (GCX). If transfer has just occurred, the turbine speed (WS) at this instant is saved as WSTRANS, the speed at throttle/governor valve transfer. This value is used in the CONTROL task for a special valve position control logic decision. The last operation in the governor control program is to call the LCCO subroutine to update the GC lamp.
Throttle Valve Control Logic
Control of turbine steam flow with the throttle valves is required when the turbine is initially rolled and during speed control up to the point of transfer to governor valve control. After this the throttle valves are kept wide open during normal operation. The throttle control logic detects turbine latch and unlatching conditions, transfer from throttle to governor valve control, and manual operation of the throttle valves. When any of these conditions occur the throttle logic must then align the DEH system to the appropriate throttle control state.
The throttle control state (TC) is simply the logical inverse of the governor control state (GC) when the turbine is latched. However, the throttle control lamp flip-flop (TCLITE) may be set by either TC or by manual operation (TM) while the throttle valves are below 90 percent open as indicated by the contact input (THI) not being set. The TCLITE flip-flop is reset by the contact input (THI) indicating throttle valves wide open or by the turbine latch contact input (ASL) not set.
The throttle control logic also indicates that the transfer from throttle to governor valve state (TRTVGV) is underway when governor control (GC) exists but the throttle valves are not yet wide open. In addition, the transfer complete state (TRCOM) is set when the throttle valves are wide open on governor control as indicated by THI. Finally, the program sets various contact outputs to pass this information on to the plant and operating personnel by calling the LCCO subroutine.
Turbine Latch Logic
Before the turbine can be rolled and accelerated, it must be mechanically latched; this means the hydraulic fluid system must be prepared to move the throttle and governor valves, and a series of safety features as described in the turbine instruction book must be satisfied. After the turbine is latched, if unlatching should occur at any future time during speed or load control, then the control system must trip the turbine and close all valves immediately. The turbine latch logic detects latching or unlatching, and instantly sets the turbine reference and the control system to the proper states. A decision is made to determine if the turbine has just unlatched by comparing the current latch state (ASL) with the last state (ASLX). If unlatched has just occurred, then the DEH turbine reference given by REFDMD, the demand given by ODMD, and the speed integral controller given by RESSPD are immediately reset to zero. If the turbine has not unlatched, then a decision is made to determine if the turbine has just latched by a similar comparison of ASL and ASLX. If the unit has just latched, the DEH reference (REFDMD) and demand (ODMD) are set to the existing speed so that the control system may "catch the unit on the fly" should it be decelerating. The speed integral controller (RESSPD) is set to a zero value, from which point the control system will act to control the throttle valves.
Breaker Logic
The necessary and sufficient condition which must be satisfied when transferring from speed to load control is that the governor valve analog output must remain constant. This may be expressed as:
The computed values for these outputs may be written by referring to FIG. 43. This diagram shows the path taken by the CONTROL program on initial load control, when the megawatt and impulse pressure feedbacks are out of service, and on speed control prior to breaker closing. The expressions for the two governor valve analog outputs given in Equation (1) above follow.
These may be substituted into Equation (1) and solved for the governor valve position (GVPOS) in terms of the governor valve speed position (SPD) and ranging gains (GR7 and GR8).
The required position (GVPOS) may in turn be related to the governor valve set point (GVSP) and the governor valve characterization curve. This relationship follows.
POS(2) and SP(2) are points on the valve characterization and represent the slope of the first segment of the curve. Substitution of Equation (3) into (2) and solution for GVSP yields the required set point for correct valve position.
Referring to the load control system an expression for the governor valve set point can be written in terms of additional computed quantities as follows:
VSP is the governor valve set point in psi and GR4 is a ranging constant to convert to percent position. Substitution of Equation (5) into (4) produces the necessary value of VSP.
Note that immediately after synchronizing, the impulse pressure loop is out of service. In this case, then the governor valve set point (VSP) in psi is identical to the impulse pressure set point (PISP) in psi. This is given below.
Substitution of Equation (7) into (6) yields the required value of PISP.
Now the impulse pressure set point (PISP) can be related to the megawatt set point (REF2) as follows:
GR3 is a ranging gain which converts megawatts to psi. Substitution of Equation (9) into (8) allows computation of REF2.
Note that at the instant of synchronization, the megawatt feedback loop is out of service and that the speed error is essentially zero (otherwise the unit would not have been synchronized). Thus, the expression for the turbine reference is:
Substitution of Equation (11) into (10) yields the desired result:
Equation (12) thus gives the required value which must be set into the turbine reference when the main breaker closes to maintain governor valve position on transfer from speed to load control. When this is added to the throttle-pressure modified initial megawatt pickup discussed above, the DEH Control System will make a smooth transfer from speed to load control with no potential motoring action by the turbine.
As shown in FIG. 44, the main generator breaker contact input (MGB) sets the breaker flip-flop (BR), while loss of either MGB or the latch contact input (ASL) resets the BR flip-flop. Then a test is made to determine if the breaker just closed by comparing BR with its last state (BRX) as indicated by the leading edge of the BR pulse. If the breaker just closed, then the initial megawatt pickup (MWINIT) modified by throttle pressure ratio is computed as discussed above, the equivalent load governor position as given in Equation (12) is computed, and these are added together to form the new load REFERENCE and DEMAND.
If the breaker did not close, then BR and BRX are tested to see if the breaker opened as indicated by the trailing edge of the BR pulse. If this is the case, the turbine REFERENCE and DEMAND are set to synchronous speed, and logical flags set to rerun the LOGIC task to update the DEH system status. The final operation in the program then is to set the last states (MGBX and ASLX) to the current values of MGB and ASL for succeeding bids of the LOGIC task.
Throttle Pressure Control Logic
Control of throttle pressure in a fossil fired power plant is primarily a function of the boiler control system. Traditional turbine control practice is to react defensively to throttle pressure variations such that protection of the turbine is guaranteed. The DEH Control System is designed to detect throttle pressure below a set point and to runback the turbine reference at a preselected rate until the throttle pressure condition is corrected. For this purpose, the throttle pressure detector 112 of FIG. 1, transmits a signal to the DEH computer which is compared to a predetermined pressure set by keyboard 1816 entry on the Operator's Panel 1130. The throttle pressure control logic allows the throttle pressure controller to be placed in service or to be taken out of service by the operator when the turbine is on automatic control. In addition, this logic will automatically remove the loop from service under certain contingency conditions or when the turbine is in speed control.
With reference to FIG. 45, the throttle pressure control flip-flop (TPC) may be set by the throttle pressure pushbutton (TPCPB) on the Operator's Panel or by the analog backup system having its throttle pressure controller in service prior to transfer to automatic control; this latter case is given by the last state (MANTPCX) of the contact input (MANTPC) being set while in manual control. The TPC flip-flop is reset by a number of conditions; the panel pushbutton (TPCPB) when the loop is in service, breaker (BR) open, manual operation (TM), throttle pressure transducer failure (TPTF) which is a contact input from the backup system, the analog-to-digital converter out of service (VIDAROS), or an attempt to put the loop in service when the existing throttle pressure (PO) is below the set point (POSP). After evaluation of the TPC flip-flop, the program calls the LCCO subroutine to place the throttle pressure contact outputs in the correct state. Then the last values of the manual control and throttle pressure circuit are updated.
Megawatt Feedback Logic
To place the loop in service bumplessly, it is necessary to maintain constant governor valve position while inserting the magawatt proportional-plus-reset controller in the control system computations. This means that the integrator in this controller must be instantly set to the proper value, the reference must be reset to that value which will yield no change in governor valve position, and proper account must be taken of the speed feedback effect at the instant of putting the loop in service. A derivation of the equations necessary to guarantee these conditions follows.
REF2 is effectively the governor valve set point which must remain fixed in placing the loop in service, REFDMD is the turbine reference, X is the speed feedback effect and REF1 is the speed modified reference. When the loop is placed in service, the proper values of Y, the megawatt feedback factor, and RESMW, the megawatt integrator, must be computed, and REFDMD then readjusted to produce exactly the same value for REF2 to yield bumpless transfer. The necessary and sufficient condition for bumpless transfer then is that REF2 before and after the switching must be identical, as shown in Equation (13).
The value of REF2 before the switch is retained in computer memory, whereas the expression for REF2 after the loop is in may be determined result follows.
Immediately after the switch, the value of REF1 must equal the existing analog input representing megawatts (MW), so that the integrator sees a zero error. Thus, an equation for this condition is:
Substituting Equations (13) and (15) into (14) and solving for the required value of the megawatt factor (Y) and therefore the megawatt integrator output (RESMW) yields the following result:
Finally, to guarantee that the transfer will be bumpless the new vaue of REFDMD must be computed as follows.
Substituting Equation (15) into (17) and solving for REFDMD completes the required derivation.
The steps in the computation may be summarized: compute the new value of Y and RESMW from Equation (16), compute the new value of REFDMD from Equation (18), set the megawatt integrator last input (RESMWX) to zero, and place the loop in service.
To remove the megawatt loop from service bumplessly, a similar set of computations must be followed. The necessary and sufficient condition for bumpless transfer is to retain a constant value for REF2 as follows.
The value of REF2 before the switch is retained in computer memory, whereas the expression for REF2 after the switch may be determined as given below.
Immediately after the switch, the value of REF1 must equal the value of REF2 before the switch, since the megawatt loop is now out of service.
Finally, to guarantee the bumpless transfer, the new value of the reference REFDMD must be computed to satisfy Equation (19).
Substituting Equation (19) into (20) and solving for REFDMD yields the final result.
Thus to take the megawatt loop out of service, the reference is reset to the value given in Equation (21) and the monitor lamp indication is reset.
The megawatt pushbutton, represented by MWIPB and updated by the PANEL program, sets the megawatt flip-flop (MWI), while this flip-flop may be reset by a number of conditions as follows: the main breaker (BR) open; a megawatt transducer failure (MWTF), which is a contact input set by the analog backup system; a valve position limit condition as indicated by VPLIM; an analog input failure (AIFAILMW) of the megawatt feedback signal as set by the ANALOG SCAN program; or the analog-to-digital converter out of service (VIDAROS). After evaluation of the megawatt flip-flop, decisions are made to determine if the megawatt loop has just been put into service or just taken out of service, assuming that the main breaker (BR) is closed. If the loop has just been put in, as indicated by the leading edge of the MWI pulse, then the bumpless transfer computations listed in Equations (16) and (18) are executed. If the loop has just come out of service, as indicated by the trailing edge of the MWI pulse, then the bumpless transfer computation listed in Equation (21) is executed. In both cases a call to the LCCO subroutine is made to place the megawatt lamp and two status contact outputs for the megawatt loop in the proper state.
Impulse Pressure Feedback Logic
To place the impulse pressure loop in service bumplessly, it is necessary to maintain the governor valves constant while inserting the impulse pressure proportional-plus-reset controller in the control system computations. This means that the integrator in the controller must be instantly positioned at the proper value. Depending on whether the megawatt feedback loop is in service at this time, one of the following two sets of derivations will be appropriate.
GR3 is a ranging constant which converts the megawatt reference value (REF2) to an impulse pressure set point (PISP) while IPI is the impulse pressure flip-flop. The analog input (PI) is the actual impulse pressure at the instant of placing the loop in service, RESPI is the impulse pressure integrator, and VSP is the governor valve set point. When the loop is put in service, both the integrator values (RESMW and RESPI) must be instantly recomputed to hold the governor valve set point (VSP) constant. Thus to remain bumpless, the following expression must hold.
The value of VSP before the switch is retained in computer memory, whereas after the loop is in service, the value of VSP will be given by the integrator (RESPI). Therefore this integrator output must be instantly set to the value of VSP.
The additional requirement is that the impulse pressure set point (PISP) be identical to the existing impulse pressure analog ouput at the instant of switching so that the integrator sees a zero error. This is satisfied as follows.
The computed value for PISP now may be written to determine what changes must be made to the megawatt integrator.
The value of REF2 in turn may be determined in terms of REF1, which does not change when the impulse pressure is switched in since REF1 is upstream of the megawatt loop.
Substituting Equations (23) and (24) into (25), and remembering that the megawatt correction factor (Y) and the megawatt integrator output (RESMW) are equal, the new value which must be given to RESMW may be solved for as follows: ##EQU2## The steps in the computation to place impulse pressure feedback into service when the megawatt loop is already in service may be summarized: compute the new value of the impulse integrator from Equation (22), set the last value of the impulse integrator input (RESPIX) to zero, compute the new value of the megawatt integrator from Equation (26), and place the loop in service.
To remove the impulse pressure feedback from service bumplessly, a similar set of computations must be followed. The necessary and sufficient condition is to hold the value of VSP constant as follows:
The value of VSP before the switch will be retained in computer memory, whereas the value of VSP after the switch can be determined when the loop is out.
The set point (PISP) can in turn be computed as follows:
Finally, REF2 may be determined from REF1 which does not change since it is upstream of the megawatt integrator.
Substituting Equations (27), (28) and (29) into (30), and remembering that the megawatt correction factor (Y) and the megawatt integrator (RESMW) are equal, the new value which must be given to RESMW may be solved for as follows: ##EQU3## The steps in the computation to remove the impulse pressure feedback from service when the megawatt loop is in service are to compute the new value of the megawatt integrator from Equation (31) and then place the loop out of service.
The above set of computations hold for switching the impulse pressure loop while the megawatt loop is in service. The situation is significantly different when the megawatt loop is out of service, since then the reference must be reset to maintain a bumpless transfer. To put the impulse pressure loop in service bumplessly, it is necessary, as always, to keep the governor valve set point constant.
Again, the value of VSP before the switch will be in computer memory. The remaining equations describing the system after the switch may be derived with results as follows: ##EQU4## Solving this set of equations for the new value of REFDMD yields the required condition.
Thus, to summarize, when placing impulse pressure feedback in service with the megawatt loop out of service, it is necessary to set the impulse integrator (RESPI) to the value given in Equation (32), reset the last input to this integrator (RESPIX) to zero, compute the new reference REFDMD from Equation (33), and place the loop in service.
The last case to cover is that of removing the impulse pressure loop when megawatt feedback is out of service. Once more the governor valves must remain constant to assure bumpless transfer, as indicated below.
As always, the value of VSP prior to the switch will be in computer memory. The set of equations describing the computations may be written as follows:
Solving this set of equations for the new value of REFDMD yields the required condition.
Thus, REFDMD is computed according to Equation (34), the impulse pressure loop is removed, and the transfer proceeds bumplessly.
The impulse pressure pushbutton, represented by IPIPB and updated by the PANEL program, sets the impulse pressure flip-flop (IPI), while a number of conditions may reset the flip-flop as follows: the main breaker (BR) open; a valve position limiting condition as indicated by VPLIM; an analog input failure (AIFAILPI) for the impulse pressure feedback signal as set by the ANALOG SCAN task; the analog-to-digital converter out of service (VISAROS); or a contact input (SIO) to set impulse pressure out of service when in the automatic dispatch system (ADS) mode. After evaulation of the impulse pressure flip-flop (IPI), decisions are made to determine if the loop has just been put into service or just taken out of service assuming that the main breaker (BR) is closed. If the loop has just come in, as indicated by "the leading edge of the IPI pulse, " then the bumpless transfer computations discussed and derived above and evaluated. If the loop has just come out, as indicated by "the trailing edge of the IPI pulse, " then again appropriate bumpless transfer conditions are evaulated as discussed above. An additional decision is made on MWI as to whether or not the megawatt feedback loop is in service. As derived above, the form of the bumpless transfer computations depends on the state of the megawatt loop. After all expressions are evaluated, calls are made to the LCCO subroutine to place the impulse pressure lamp and two status contact outputs in the proper state.
Speed Feedback Logic
The speed feedback loop is critically important when the turbine is on automatic speed control, and is of somewhat less importance on load control. Without speed feedback on automatic speed control, the DEH system must reject to manual operation, while on automatic load control the DEH system merely removes the speed feedback loop from service. The operator may place the speed loop back in service after it has been rejected by pressing the speed loop pushbutton, providing the speed inputs have in the meantime been corrected and are again valid.
Once the speed feedback loop is in service, the operator cannot take it out of service, since standard turbine control practice requires speed in service at all times if the input signals are valid. Thus when the loop is in service pressing the pushbutton is ignored. The only mechanism for taking the loop out of service is by automatic action of the DEH system programs when a speed transducer failure occurs. The speed feedback logic program responds to those conditions which will activate or deactivate the speed loop, whether the conditions be an operator pushbutton request or automatic rejection by the transducer failure.
Automatic Synchronizer Logic
The auto sync flip-flop (AS) may be set by the auto sync pushbutton (ASPB) or by the automatic turbine startup program request (ATSASPB), provided in both cases that the unit is on automatic control (OA), the breaker (BR) is open, the turbine is on governor control (GC), and the automatic synchronizer equipment permissive contact input (ASPERM) is set. Otherwise the AS flip-flop will be rest. Decisions are then made to determine if the AS flip-flop has just come on. If AS just came on, the temporary variable (T3) is set to indicate a remote control transfer for later logic programs. Then a call is made to the LCCO subroutine to set the auto sync lamp to the correct state; arguments in the call consist of the current state of AS, the last state (ASX), the auto sync pushbutton state (ASPB) which must be aligned with the AS flip-flop, and a pointer (N9) to a table of contact output words and bits which define connections to the auto sync lamp.
Decisions must be made in the auto sync logic program, when the AS mode has been selected, to detect whether the automatic synchronizing equipment is sending raise or lower pulses to the DEH system. Thus, if the leading edge of the ASUP contact input pulse has just come on, then the logical variable ASINC is set so that the CONTROL task may increment the turbine reference by one rpm. Similarly, if the leading edge of the ASDOWN contact input pulse has just come on, then the logical variable (ASDEC) is set so that the CONTROL task may decrement the turbine reference by one rpm. Finally, last values (ASUPX and ASDOWNX) are updated to the current states (ASUP and ASDOWN) in preparation for furtur bids of the LOGIC task.
Automatic Dispatch Logic
The automatic dispatch flip-flop (ADS) may be set by the automatic dispatch button (ADSPB), which is updated by the PANEL program, providing the unit is on automatic control (OA), the breaker (BR) is closed, and the automatic dispatch permissive contact input (ADSPERM) is set. Otherwise the ADS flip-flop will be reset. Decisions then are made to determine if the ADS flip-flop has just come on. If ADS just came on, the temporary variable (T3) is set to indicate a remote control transfer for later logic programs. Then a call is made to the LCCO subroutine to set the ADS lamp to the correct state; arguments in the call consist of the current state of ADS, the last state (ADSX), the automatic dispatch button (ADSPB) which must be aligned with the ADS flip-flop, and a pointer (N10) to a table of contact output words and bits which define connection to the ADS lamp.
Additional decisions must be made in the ADS logic program, when the ADS mode has been selected, to detect whether the ADS equipment is sending raise or lower pulses to the DEH system. Thus if the leading edge of the ADSUP contact input pulse has just come on, then a flip-flop (CADSUP) is set to start a counter which is handled by the AUX SYNC program. As long as the CADSUP is set the AUX SYNC will count in 1/10 sec increments, thus determining the length of time the raise pulse is on. When the trailing edge of the ADSUP contact input pulse is detected, this means the raise contact has been released; this then resets the CADSUP flip-flop and the AUX SYNC program will stop counting. Finally, a logical state (ADSINC) is set so that the CONTROL take may raise the turbine reference by an amount proportional to the CADSUP counter. Identical checks and logical decisions are made with respect to the ADS lower contact input (ADSDOWN), after which last values of both ADSUPX and ADSDOWNX are updated with the current state of ADSUP and ADSDOWN in preparation for future bids of the LOGIC task.
Automatic Turbine Startup Logic
As shown in FIG. 50, the automatic startup flip-flop (ATS) may be set by the pushbutton (AUTOSTAR), which is updated by the PANEL task, provided the turbine is on automatic control (OA), the main breaker (BR) is not closed, and the turbine supervision off pushbutton (TURBSPOF) has not been pushed. Otherwise the ATS flip-flop will be reset by the lack of any of these conditions or by the automatic startup program itself through the variable SSPROA if the program detects improper conditions for startup.
Decisions are then made to determine if the ATS flip-flop has just come on. If so, a temporary logical variable (T3) is set to indicate a remote control transfer for later logic programs. A decision is also made to determine if the ATS flip-flop has just gone off. If this is the case, then a group of logical variables used in the ATS program must be reset. In addition, certain DEH system conditions must be aligned properly; these include the auto sync pushbutton (ASPB), which may have been set by the ATS program, and the reference/demand windows on the DEH Operator's Panel, which may have been left in an unequal state by the startup program. These conditions are cleared by setting RUNLOGIC to request another bid of the LOGIC task. Finally a call is made to the LCCO subroutine to set the ATS lamp to the proper state. Arguments in the call are the current state of ATS, the last state (ATSX), the auto start pushbutton (AUTOSTAR) which must be aligned with ATS, and a pointer (N11) to a table of contact output words and bits which define the hardware connections to the ATS lamp.
Remote Transfer Logic
To transfer from operator automatic to a remote mode, the operator simply presses the appropriate pushbutton on the Operator's Panel. Then, assuming all permissive conditions as described elsewhere in this writeup are satisifed, the new mode will be selected with a bumpless transfer in which the turbine valves remain at the existing position. In addition, a lamp behind the pushbutton selected will be turned on and the lamp for the previous mode will be turned off. Conversely, in order to return from any remote mode to operator automatic, the operator simply presses the OPER AUTO pushbutton. The remote transfer logic program detects operating mode chages and updates the panel lamps according.
As shown in FIG. 51, the temporary logical variable (T3), which has been updated in earlier portions of the logic program, is checked to determine if any remote state has been selected. If so, the operator demand (ODMD) is set equal to the current reference (REFDMD), and logical flags are set to run the LOGIC task again to set the appropriate conditions in the DEH system. Then the status of the operator automatic lamp (OALITE) is determined since a remote control mode selection must result in turning off this lamp. Finally, a call to the LCCO subroutine is made to place this lamp in the proper state.
PANEL TASK
The PANEL task is assigned priority level C.sub.16 (12.sub.10) and is bid by the PANEL INTERRUPT program when a button is pressed.
FIG. 53 shows a block diagram of the major functions performed by the PANEL task. These include executing each of the button group functions discussed above, as well as additional decisions, checks, and bookkeeping necessary to properly perform the action requested by the operator.
Button Decode
The BUTTON DECODE program examines the button identification (IPB) provided by the PANEL INTERRUPT program, and transfers to the proper location in the PANEL task to carry out the action required by this button. The program also does some bookkeeping checks necessary to keep the panel lamps in the correct state. A total of 54 buttons can be decoded in the current version of the DEH PANEL task.
The identification of the last button (IPBX), which had been pressed and which has associated with it a visual display mode lamp, is stored in a temporary integer location (JJ) for later use in turning off the last lamp. Then the current button identification (IPB) is checked to determine if it represents the ENTER pushbutton; if so, a special logical variable ENTERPB is reset for later use should the ENTER button be pressed two or more consecutive times. This has been found to be a rather common operator error and is flashed as an invalid request. The program then simply executes a FORTRAN computed GO TO statement and transfers to the appropriate portion of the PANEL task.
Control System Switching
There are six buttons on the Operator's Panel which may switch control states of the DEH system. A brief description of each follows:
1. TRANSFER TV/GV--This button initiates a transfer from throttle valve to governor valve control during wide-range speed operation. The pushbutton has a split lens. When control is on the throttle valves, the upper half of the lens is backlighted. When the button is pressed, to transfer control, the entire lens is backlighted. At the completion of the transfer, only the bottom half of the lens remains on. Once the DEH system is on governor control, it stays in this mode until the turbine is tripped and relatched. At this time, it is again in throttle valve control.
2. IMPULSE PRESSURE FEEDBACK IN/OUT--This is a push-push button with split lens. It places the impulse pressure feedback loop in or out of service, with appropriate backlighting of the button lens.
3. MEGAWATT FEEDBACK IN/OUT--This is a push-push button with split lens. It places the megawatt feedback loop in or out of service, with appropriate back-lighting of the button lens.
4. SPEED FEEDBACK IN/OUT--This split lens button places the speed feedback loop in service in the DEH system. Normally the speed loop is always in service; however, when the DEH CONTROL task detects a speed channel failure condition in which all speed input signals are unreliable, the speed feedback loop is disabled and the speed channel monitor lamps turned on. When the speed inputs become reliable, the monitor lamps are turned off, thus indicating to the operator that he may place the speed feedback loop back in service. As long as the speed signals are reliable, the operator cannot take the speed loop out of service.
5. THROTTLE PRESSURE CONTROL IN/OUT--This is a push-push button with split lens which places the throttle pressure controller in or out of service, with appropriate backlighting of the lens.
6. CONTROLLER RESET--The button restores the DEH system to an active operating state after the computer has been stopped due to a power failure or hardware/software mainntenance.
The logical variable TRPB is set when the TRANSFER TV/GV button is pressed. The impulse pressure, megawatt, and throttle pressure logical states (IPIPB, MWIPB and TRCPB respectively) are set to the logical inverse of their previous state when the corresponding buttons are pressed. This is the mechanism which provides the push-push nature of these buttons. The logical variable SPIPB is set when the speed feedback button is pressed. Finally, each of these buttons initiate a bid for the LOGIC task by setting the RUNLOGIC variable prior to exit from the PANEL task.
The CONTROLLER RESET button is handled somewhat differnetly. The state CRESETPB is set by the STOP/INITIALIZE task, which does cleanup and initialization after a computer stop condition. Then CRESETPB is checked; if it is not set, the computer has been running, and thus the button pressed is ignored. If CRESTETPB is set, this means the computer had been stopped; CRESETPB is reset and the lamp behind the button is turned off. In addition, the PANEL task effectively presses the speed feedback button by setting the logical state SPIPB. This is done so that the DEH system restarts after a power failure or other computer stop condition with the speed feedback loop in service. The LOGIC task is requested to run by setting the RUNLOGIC state. The REFERENCE display button is also effectively pressed so that the display windows always start out in the same mode after a stop condition on the computer.
Display/Change DEH System Parameters
Eight buttons allow the operator to display or change various DEH system parameters. Six of these buttons are dedicated to the display or change of a single important parameter for each button. The remaining two buttons provide the ability to display or change a group of DEH system variables from each button. In addition, two special buttons (GO and HOLD) are intimately associated with one of the dedicated display/change buttons, and thus are also included in this discussion.
Before listing each of these buttons, a brief description of the display window mechanism is given. The DEH Operator B Panel contains two digital displays which are provided with five windows each. The left display, labeled REFERENCE, has two major functions. It either presents numerical information which currently exists in computer memory for the six dedicated buttons mentioned above, or it accepts address inputs from the keyboard for the two buttons assigned to display or change groups of DEH system variables. The right display, labeled DEMAND, also has two major functions. It either accepts keyboard inputs in preparation for changing any of the currently existing numerical information in computer memory for the six dedicated buttons mentioned above, or it presents currently existing information in computer memory for the two buttons assigned to display or change groups of DEH system variables.
Of the five windows in each digital, the leftmost is reserved for mnemonic characters. These characters combine to form a short message identifying the numerical quantity in the remaining four windows. The following table lists the 11 available messages and an explanation of each. The four right windows in each display provide the numerical digits 0 through 9 and a decimal point where appropriate.
A brief description of the eight buttons associated with display/change as well as the GO and HOLD buttons, follows:
1. REFERENCE--This button initiates a display or change of the DEH reference and demand for speed or load operation. When the turbine is on operator automatic control, new demand values may be entered from the keyboard. However, when the turbine is in a remote operating mode such as automatic synchronizer, dispatch or ACCELERATION program, the demand cannot be changed from the keyboard. Any attempt to do so is flashed as an invalid request.
2. ACCELERATION RATE--This button initiates a display or change of the acceleration rate used on wide-range speed operation. When the turbine is on operator automatic control, this value is entered by the operator, and may be changed from the keyboard. However, when the turbine is being accelerated by an AUTOMATIC STARTUP program, the displayed value is the rate selected by this program and cannot be changed from the keyboard. Any attempt to do so is flashed as an invalid request.
3. LOAD RATE--This button initiates a display or change of the load rate used on operator automatic control. This value may be displayed or changed at any time.
4. LOW LIMIT--This button is an optional feature which initiates a display or change of the low load limit used on all automatic load control modes. This value may be displayed or changed at any time.
5. HIGH LIMIT--This button is an optional feature which initiates a display or change of the high load limit used on all automatic load control modes. This value may be changed at any time.
Each of these buttons have high or low limits, whichever is appropriate, associated with them when changes are to be made in the values discussed above. Violation of these limits from a keyboard entry is flashed as an invalid request and the entry is ignored. More details of these limits are discussed in a later section where the KEYBOARD program is described.
6. VALVE POSITION LIMIT--This button initiates a display of the governor valve position limit and the quantity being limited. Change or adjustment of the valve position limit is accomplished by raise/lower buttons (described in a later section where the valve buttons are discussed). Any attempt to enter values from the keyboard in this display mode is flashed as an invalid request.
7. VALVE STATUS--This button initiates a display of the status (position) of the turbine throttle and governor valves. Thus, this button is associated with a group of DEH system variables. A description of the steps necessary to carry out this display function is given in later paragraphs (where the valve buttons are discussed).
8. TURBINE PROGRAM DISPLAY--This button initiates a display or change of any DEH system parameter not otherwise addressable with one of the unique buttons described above. These variables include pressures, temperatures, control system tuning constants, and calculated quantities in all parts of the DEH system. A dictionary is provided so that the address of such quantities may be entered from the keyboard. Further discussion of these points is given in later paragraphs where the keyboard is described.
9. GO--This button initiates a special DEH CONTROL program to adjust the turbine reference. The program ultimately positions the valves on operator automatic control. The reference then moves at the appropriate load or acceleration rate until the reference and demand are equal. The updated reference value is continually displayed in the REFERENCE windows so that the operator may observe it changing to meet the demand, which is displayed in the DEMAND windows.
10. HOLD--This button interrupts the reference adjustment process described above, and holds the reference at the value existing at the moment the HOLD button is pressed. In order to continue the adjustment process on the reference, the operator must press the GO button.
A brief description of the steps necessary to display or change any of the first six variables discussed above follows; description of cases 7 and 8 are withheld until a later section. When the operator wishes to display or change any of the DEH dedicated system parameters, he must execute a sequence of steps which result in the desired action. The steps are listed as follows:
1. The operator presses the appropriate button; the DEH programs display the current value of the parameter in the reference windows while the demand windows are cleared to allow for possible keyboard entry.
2. If the operator wishes only to observe the parameter value, then he does nothing else. The value remains in the reference windows until some new button is pressed.
3. If the operator wishes to change the parameter, he types in on the keyboard the new value which he desires. This is displayed in the DEMAND windows, but will not yet be entered into the DEH programs.
4. If the operator is satisfied with the new value as it appears in the demand windows, he may enter the new quantity into the DEH operating system by pressing the ENTER button. The ENTER button is described in more detail in a later section on the keyboard.
5. If for any reason the operator is not satisfied with the value as it appears in the demand windows, he may press the CANCEL button. The CANCEL button will be described in more detail in a later section on the keyboard. This removes the number from the DEMAND windows and allows the operator to begin a new sequence for the parameter.
6. Assuming that the operator is satisfied with the number and that he presses the ENTER button, the new value of the parameter appears in the REFERENCE window and the DEMAND window is cleared. This is an acknowledgment that the DEH programs have accepted the number and are using the new value from that point on.
7. If for any reason the numerical value entered into the DEH system violates preprogrammed conditions (such as high limits less than low limits), the entire operation is aborted and the INVALID REQUEST lamp is flashed.
The above description of data manipulation is modified somewhat when the operator wishes to display or change the turbine reference and demand. Both of these quantities are displayed when the reference button is pressed. During wide-range speed control, the left REFERENCE display contains the turbine speed reference value, while the right DEMAND display contains the turbine speed demand. During load control the REFERENCE display contains the turbine load reference while the demand display contains the turbine load demand.
Since the reference and demand control the turbine valves directly, it is essential that the operator have a unique handle on these quantities so that he may start or stop reference changes quickly and easily. This is accomplished by use of the GO and HOLD buttons in conjunction with the reference button. The GO and HOLD buttons control two reference states in the DEH system, which indicate whether the reference and demand are equal or unequal. When these quantities are equal, both the GO and HOLD backlights are off. When these quantities are unequal, either the GO or the HOLD lamp is on. If the GO light is turned on, the reference is changing to meet the demand value at the selected rate. Should the operator wish to stop the reference adjustment process, he simply presses the HOLD button. The HOLD button then backlights and holds the reference at its current value. When the operator wishes to start the reference moving again, he must press the GO button, which then backlights and enables the reference to adjust to the proper value.
The sequence of steps for displaying or changing the reference follows:
1. The operator presses the reference button. The DEH programs display the current value of reference in the left windows and the current value of demand in the right windows.
2. If the operator wishes to change the demand, he types the new value on the keyboard. This is displayed in the DEMAND windows, but is not yet entered into the DEH programs.
3. If the operator is satisfied with the new value, he presses the ENTER button. This places the new demand value in the DEH programs and turns the HOLD lamp, assuming that the new demand satisfies certain limit checks to be described shortly. If these conditions are not met, the INVALID REQUEST lamp is flashed, the new value is ignored, and the original value is returned to the DEMAND windows.
4. If the operator is not satisfied with the new value (set in Step 3), he simply presses the CANCEL button. The DEH programs then ignore this value and return the original value to the DEMAND windows.
5. If a new demand is finally entered and the HOLD lamp comes on, the operator may start the reference adjusting to this new demand by pressing the GO button. The HOLD lamp is turned off, the GO lamp is turned on, and the reference begins to move at the selected rate toward the demand.
6. At any time, the operator may inhibit the reference adjustment by pressing the HOLD button. He may then restart the reference adjustment by pressing the GO button.
7. When the reference finally equals the demand both the GO and HOLD lamps will be turned off.
Each of the eight display buttons set the integer pointer (IPBX) to its assigned value and the appropriate panel lamps are turned off and on. IPBX is then checked by the VISUAL DISPLAY task, which selects the numerical values from computer memory and displays then in the windows.
The TURBINE PROGRAM DISPLAY button also resets a few logical states in preparation for keyboard entries. These are discussed in later paragraphs on the keyboard description. The remote control modes AS, ADS and ATS for the Automatic Synchronizer, Dispatch System and TURBINE STARTUP program are checked, along with the manual control state (TM) if the maintenance test switch (OPRT) is not set. All of these modes exclude the possibility of the GO and HOLD buttons being active, so these buttons are ignored in these states and the PANEL program simply exits. However on operator automatic control, the HOLD button state (HOLDPB) is set, or the GO button state (G0PB) is set. In the latter case, HOLDPB is also reset. The LOGIC task is requested to run by setting the RUNLOGIC variable, and the program then exits.
Operating Mode Selection
There are five buttons which may be used to select the turbine operating mode. When any of these are pressed, they initiate major operating changes in the DEH Control System, assuming the proper conditions exist for the mode selected. A brief description of these buttons follows:
1. OPERATOR AUTOMATIC (OPER AUTO)--This button places the turbine in automatic control with the operator providing all demand, rate, and set point information from the keyboard. If the turbine had been previously in manual control, the OPER AUTO lamp must be flashing to indicate that the DEH system is ready to accept automatic control; otherwise pressing the OPER AUTO button is ignored. If the turbine had been in one of the remote control modes listed below, then pressing the OPER AUTO button rejects the remote and returns automatic control to the operator.
2. AUXILIARY SYNCHRONIZER (AUTO SYNC)--This button allows automatic synchronizing equipment to synchronize the turbine generator with the power system by indexing the speed demand and reference with raise/lower pulses, in the form of contact inputs.
3. AUTOMATIC DISPATCHING SYSTEM (ADS)--This button allows automatic dispatching equipment to operate the turbine generator by setting the load demand and reference. A number of dispatching options are available, including raise/lower pulses, raise/lower pulse-width modulation, and analog input values to set the reference.
4. AUTOMATIC TURBINE STARTUP (TURBINE AUTO START)--This button allows a special computer program to automatically start up and accelerate the turbine during wide-range speed control. The program may reside in the DEH computer or it may exist in another computer in the plant or at a remote location.
5. COMPUTER DATA LINK (COMP DATA LINK)--This optional button allows another computer, either in the plant or at a remote location, to provide all demand, rate, and set point information to the DEH system.
The OPER AUTO button resets the remote mode button states (ASPB, ADSPB and AUTOSTAR) for Automatic Synchronizer, the Automatic Dispatch System, and the AUTOMATIC TURBINE STARTUP program, respectively. Since the operator automatic state (OA) is merely the logical inverse of the turbine manual state (TM), the PANEL task cannot actually set OA, but can only request the LOGIC task to run, but setting the RUNLOGIC variable. The LOGIC program then determines whether or not operator automatic is accepted by the manual backup system.
The remote buttons set their corresponding pushbutton states after which RUNLOGIC is set. As in the case of operator automatic, the LOGIC task then determines if the requested mode will be accepted.
The data link button is handled somewhat differently; this is a push-push button whose stae (DLINK) is given the logical inverse of its previous value at statement 14. The new state is then interrogated in order to determine whether to turn the button backlight on or off, after which the program exits.
Valve Status/Testing/Limiting
Nine buttons on the Operator's Panel are used for displaying valve status, testing the throttle and governor valves, and displaying or changing the valve position limit. Some of these buttons are used in more than one of these areas. A brief description of the three buttons associated with display of valve status follows:
1. VALVE STATUS--This button initiates a display of the status (position) of the turbine throttle and governor valves.
2. TV--This button provides the mechanism for the throttle valve status (position) to be displayed.
3. GV--This button provides the mechanism for the governor valve status (position) to be displayed.
In order to display valve status, the operator must execute the following sequence of steps:
1. Press the VALVE STATUS button, which then backlights.
2. Press either the TV or the GV button, depending on which group of valves are to be displayed; the TV or GV lamp then lights.
3. On the keyboard, press the key corresponding to the number of the valve to be displayed; this valve then appears in the left windows.
4. Press the ENTER button. The DEH programs then place the valve position in percent in the right windows, and continually update this value as the valve position changes.
5. If the valve number entered on the keyboard in Step 3 is out of range of the existing valves on the turbine, the INVALID REQUEST lamp is flashed and both display windows are cleared. The operator then should press the CANCEL button, and begin again at Step 3.
A brief description of the four buttons associated with valve testing follows:
1. VALVE TEST--This button initiates a sequence of steps which results in throttle/governor valve testing.
2. TV--This button indicates that the turbine throttle valves are to be tested.
3. CLOSE--This button provides the mechanism for gradually closing the governor valve associated with the throttle valve to be tested.
4. OPEN--This button provides the mechanism for gradually opening the governor valve associated with the throttle valve which has just been tested.
To understand the need for valve testing, one must realize that steam turbines have two sets of valves for control of steam flow. The throttle valves are located upstream in the steam flow path and the governor valves are downstream.
Under most turbine operating conditions, the throttle valves are wide open and the governor valves assume the correct position to control steam flow. However, the throttle valves must always be prepared to close instantly in case a contingency occurs which requires a mandatory trip of the turbine. If either or both of the throttle valves remain open under such an emergency condition, the possibility of severe damage to the turbine and power plant is very high.
In order to demonstrate that the throttle valves are operable, the valve test feature is made available. Essentially this feature allows the operator to close the throttle valves for a few seconds to assure their operational availability during contingencies. However, in certain steam chest arrangements, a complication arises in the incorporation of a throttle valve test function. With normal steam flow through the throttle valve, mechanical forces acting on the throttle valve mechanism are so large that it is physically impossible to reopen the valve and thus verify its operational availability. To overcome this problem, it is necessary to close the governor valve on the same side of the turbine (in small incremental steps) so that load on the turbine is not upset to any great degree. When the governor valve is essentially closed and steam flow cut off, the throttle valve forces are negligible and the throttle valve may be test-closed and reopened to verify its operation. Finally, the governor valve must then be opened incrementally to return it to the conditions prior to the test.
In order to carry out a throttle valve test, the operator must execute the following sequence of steps:
1. Press the VALVE TEST button, which then backlights; the VALVE STATUS lamp also backlights if it is not already on.
2. Press the TV button, which then backlights.
3. On the keyboard, press the key corresponding to the number of the throttle valve to be tested. This number then appears in the left windows.
4. Press the ENTER button. The DEH programs then place the governor valve position, corresponding to the throttle valve being tested, in the right windows. This value is continually updated as the test proceeds.
5. Should the valve number entered on the keyboard in Step 3 be out of range of the existing valves on the turbine, the INVALID REQUEST lamp is flashed and both display windows are cleared. The operator then presses the CANCEL button and begins again at Step 3.
6. Press and hold the CLOSE button. The DEH valve test system then closes the appropriate governor valve at a controlled gradual rate; the right display windows show the governor valve position as it decreases throughout this part of the test. The lamps behind the CLOSE and OPEN buttons turn on and remain on until the test is complete. When the governor valve is within 5 percent of its closed position, the throttle valve immediately closes and stays closed as long as the CLOSE button is held down.
7. Release the CLOSE button. The throttle valves opens, but the governor valve remains closed. Pressing the CLOSE button again quickly recloses the throttle valve, if another operational check is desired. As many reclosures as necessary may be carried out at this stage of the test.
8. Press and hold the OPEN button. The DEH valve test system then opens the appropriate governor valve at the same controlled gradual rate. The right display windows show the governor valve position as it increases continually throughout this part of the test. When the governor valve is returned to its original position, the lamps behind the CLOSE and OPEN buttons go out, thus indicating the completion of the valve test.
9. It is not necessary to hold down the CLOSE and OPEN buttons continuously during the valve test. They may be released at any time and the test will simply be suspended; then a short while later, the buttons may be pressed and held and the test will continue.
10. It is prefectly valid to use the other visual display buttons during the temporary suspension of a valve test. When it is desired to return to complete or continue the valve test, it is necessary only to press the VALVE TEST button. The DEH system then retrieves from memory all the information needed to continue the test (including the valve number and position of governor valve for the display windows) so that the test procedure may be continued from that point.
A brief description of the three buttons associated with the valve position limit display and change function follows:
1. VALVE POSITION LIMIT DISPLAY--This button initiates a display of the current value of the valve position limit setting in the left windows, and the DEH governor valve quantity being limited in the right windows.
2. VALVE POSITION LIMIT LOWER--This button is used to lower the valve position limit setting as long as the button is held down.
3. VALVE POSITION LIMIT RAISE--This button is used to raise the valve position limit setting as long as the button is held down.
The rate of adjustment of the valve position limit setting is controlled by a keyboard entered constant. As long as the raise or lower button is held down, the setting is varied at an exponential rate. In order to make small changes in the limit, the operator simply presses and holds the appropriate button for a few seconds and then releases the button. He may do this more or less continuously, and the value of the limit is displayed in the left windows. In order to adjust the valve position limit setting with the raise and lower buttons, it is first necessary to press the VALVE POSITION LIMIT DISPLAY button. If it is not pressed, the raise and lower buttons are ignored. The display button acts as a permissive for varying the limit setting.
The program sets the state VSTATUS for this button and sets the integer pointer IPBX to 8 for this visual display mode. The program handles the TV and GV buttons, respectively. The VSTATUS state is checked; if it is not set, the TV and GV buttons are ignored. Otherwise, the TV and GV logical states are set and the lamp behind the button pressed is turned on by a call to the contact output handler. The VALVE TEST button is processed and the manual control state (TM) is checked. If the turbine is in manual operation, the valve test cannot be carried out and the test button is ignored. However, in automatic control, the logical state VTESTPB is set and the lamp behind the button is turned on. Then the integer NVTEST representing the valve to be tested is checked. If the value is non-zero, a test has been previously started, so the test conditions are immediately set up from memory. This includes setting the TV button state and lamp, and setting the pointer INDEX2 equal to NVTEST so that the visual display of governor valve position in the right windows may be properly selected. Should the value of NVTEST be zero, the VALVE STATUS lamp is set. The system then waits for more keyboard information from the operator.
The VALVE POSITION LIMIT DISPLAY button is serviced; this requires setting the pointer IPBX to 6 for a visual display. The valve test button (VTESTPB) and the TV buttons must have been previously pressed, and the valve number which is to be tested (which is stored in location INDEX2) must be valid; otherwise the CLOSE or OPEN button is ignored. If these conditions are met, the open button state (OPENPB) is set if this button is pressed, while the close button state (CLOSEPB) is set if this is the button pressed. In addition, a contact output to actuate the governor valve closing circuitry is set if the CLOSE button is pressed. Finally, the valve being tested NVTEST is set equal to INDEX2.
The VALVE POSITION LIMIT RAISE and LOWER buttons are serviced. If the display pointer IPBX is not equal to 6, the VALVE POSITION LIMIT DISPLAY button has not been pushed; therefore, the raise and lower buttons are ignored. If IPBX equals 6, the appropriate state VPLRPB or VPLLPB is set and the program exits.
Automatic Turbine Startup
Five buttons are associated with the automatic turbine startup feature of the DEH system. A brief description of these buttons follows:
1. AUTOMATIC TURBINE STARTUP (TURBINE AUTO START)--This button allows a special computer program to automatically start up and accelerate the turbine during wide-range speed control.
2. TURBINE SUPERVISION OFF--This is a push-push button which controls the printout of messages from the turbine supervisory programs. Normally, the messages are always printed; the operator may suppress printing by pressing this button, which then backlights. Should the messages be desired later, then the button may be pressed again; the lamp is turned off and the supervisory messages are printed on the typewriter.
3. OVERRIDE ALARM--This button overrides certain alarm stops which the AUTOMATIC TURBINE STARTUP program may detect. When this happens, the program waits for operator action before proceeding with the acceleration. If the operator decides to continue the startup, he presses the OVERRIDE ALARM button.
4. OVERRIDE SENSOR HOLD--This button overrides certain analog input sensor stops, which the AUTOMATIC TURBINE STARTUP program may detect. When this happens, the program waits for operator action before proceeding with the acceleration. If the operator decides to continue the startup, he presses this button.
5. RETURN SENSOR TO SCAN--This button returns certain analog inputs to scan after their sensor has been repaired. Should a sensor fail, the AUTOMATIC TURBINE STARTUP removes the corresponding input from scan; when the sensor is detected valid again, this button is backlighted to notify the operator. He then presses the button to return the input to its normal scan.
Manual Buttons
Six buttons on the Operator's Panel are associated with manual operation of the turbine. Even though the DEH PANEL program does not interface directly with these buttons, a brief description of their function is given for completeness. In general, these buttons allow the operator to control the position of the turbine throttle and governor valves directly from the panel.
1. TURBINE MANUAL--This button places the turbine under manual control of the operator, with the transition from automatic being achieved essentially bumplessly.
2. TV LOWER--This button lowers, or decreases, the throttle valves at a fixed rate as long as the button is held down.
3. TV RAISE--This button raises, or increases, the throttle valves at a fixed rate as long as the button is held down.
4. GV LOWER--This button lowers, or decreases, the governor valves at a fixed rate as long as the button is held down.
5. GV RAISE--This button raises, or increases, the governor valves at a fixed rate as long as the button is held down.
6. FAST ACTION--This button opens or closes the throttle and governor valves, at a fast rate, in manual control. The FAST ACTION button must be held down at the same time as any of the TV or GV RAISE/LOWER buttons described above to achieve the fast action effect.
Keyboard Activity.
There are fourteen buttons associated with keyboard activity on the DEH Operator's Panel. Of this total, eleven are numerical keys; these include the integers 0 through 9 and a decimal point. Three additional buttons are available for use with the keyboard to aid in data display or change. A brief description of these buttons follows:
1. NUMERICAL BUTTONS 0 THROUGH 9--When the operator keys in numbers of these buttons, the corresponding values are displayed in the reference or demand windows, whichever are appropriate, for the function being performed. The values move from right to left in the windows as new keys are pressed, and both leading and trailing zeros are always displayed. If more than four numerical keys are pressed, the leftmost value in the windows is lost as the new value is entered in the right-most window, and the remaining values shift left one position.
2. DECIMAL POINT BUTTON--When the decimal point key is pressed, the PANEL program retains this information but does not yet display it. When the next numerical key is pressed, both the value and the decimal point appear in the right-most window. The decimal point is positioned in the lower left-hand corner of the window position. Should additional numerical keys be pressed, the decimal point moves one position to the left with the number with which it was originally entered. Should the decimal point be shifted out of the left-most window it is lost, and a new point may be entered.
3. ENTER--When this button is pressed, the PANEL program enters the value residing in the reference or demand windows, whichever is appropriate, into core memory and performs the correct action requested by the keyboard activity. This action may consist of visual display, parameter change, or intermediate steps in a sequence of operations as described in preceding sections.
4. CANCEL--When this button is pressed, the PANEL program clears both the reference and demand windows, deletes any intermediate values in computer memory, and aborts the entire sequence of operations which was canceled. The operator may then begin a new sequence of steps.
5. CHANGE--This button indicates a sequence of operations necessary to alter numerical values residing in the DEH system memory. The steps necessary to change parameters are described earlier.
The decimal point key and keys 0-9 are serviced to check the validity of the requested entry and to set the entry if it is valid. Among other checks, a check is made on the integer IPBX, which represents the visual display and change button which has been previously pressed. If this value equals 2, thus indicating the acceleration rate button has been pressed, and the Automatic Turbine Startup mode (ATS) is in control, all keyboard buttons are invalid. During the ATS mode the acceleration rate is controlled by the startup program, and thus may be visually displayed but cannot be changed from the keyboard.
Should the ATS state be satisfied, the pointer IPBX is checked to determine if it is equal to 6; if so, the keyboard entry is flashed as invalid because this represents the valve position limit display mode, which cannot use the keyboard. If this situation is all right, the valve test button state (VTESTPB) is checked; should VTESTPB be set and the valve being tested NVTEST is non-zero, the keyboard entry is invalid. This is because NVTEST indicates that some valve has already been selected for test, thus implying that no further keyboard activity is necessary.
Finally, some special tests are made if IPBX equals 1; this means the reference display mode has been selected. If this is the case, all remote control modes such as Automatic Synchronizer (AS), Automatic Dispatch System (ADS), and Automatic Turbine Startup (ATS), imply that the keyboard cannot be used during reference display. Thus these result in the INVALID REQUEST lamp being flashed. In addition, should the turbine be on manual control (TM) or unlatched (NOT ASL), and not in the maintenance test mode (OPRT), then keyboard activity is also invalid during reference display. All of these cases are invalid for keyboard entry because the turbine demand and reference are set by the remote mode or the manual tracking system. The only time that the operator may use the keyboard in the reference display mode is during operator automatic control or during the maintenance test condition in which the DEH system is being used as a simulator and trainer.
Should all of these test be passed properly, the logical state KEYENTRY is set and the numerical value in location KEY is checked. This is the keyboard button which has just been pressed, and must lie between 0 and 9 inclusive; otherwise, the entry is flashed as invalid. For a valid value of KEY, the program then places the new number in its proper position in the integer array (IW). This array has a place for each of the four window positions of the visual display and, as keyboard buttons are pressed, the entries move down one position in IW and the latest key is entered in the top position. The pointer ID maintains the proper position for each new key. Thus, if ID equals 0, this means there are no entries in the array IW. The value KEY is thus placed in the first position of IW. However, if ID is not zero, then a FORTRAN DO loop is executed to move the entries in IW down one position prior to entering the new value of key in the first position at statement 414. Then the value of the pointer ID is checked again; if it is less than 3, it is incremented by 1. If it is equal to 3, it retains that value. This is the mechanism used to accept more than four keyboard values with only the last four key entries being retained.
CONTROL TASK
General
The CONTROL task is assigned priority level D.sub.16 (13.sub.10) and is bid by the AUX SYNC task every 1 sec.
The CONTROL task size is 1759 words long, the data pool is 247 words long, and the header is 9 words for a required storage of 2015 locations. CONTROL is linked as a separate task and loaded into the computer through the tape reader. The core area assigned to CONTROL is (2740 to 2F3F).sub.16 ; this is 800.sub.16 (2048.sub.10) locations, thus allowing a few spares. The CONTROL task is organized as a series of relatively short subprograms, executed sequentially, and which address themselves to particular aspects of the general control system objectives.
Time Update Function
Most process control computers have the ability to synchronize with a real time station clock. Once this synchronization is made, the computer Monitor program continuously updates itself, usually every 1 sec, so that real time in hours, minutes and seconds in the computer is identical with real time on the station clock. Then any messages, alarms, or similar computer output to typewriters may be preceded with the time of occurrence for hardcopy record and analysis purposes.
However, should the computer stop for any reason, its time counters are immediately out of phase with the station clock. Thus when the computer returns to service, a mechanism must be provided to update the computer real time counters to the station clock. The TIME UPDATE function of the DEH CONTROL task provides this important feature by utilizing appropriate entries from the keyboard.
Since the time update mechanism requires keyboard entered values, it is necessary to switch to the maintenance test mode by using the key-lock switch on the Operator's Panel. This immediately switches the turbine to manual control and enables entry of values from the keyboard. At the end of the time update operation, the MAINTENANCE TEST key should be switched to the OFF position. The DEH system then tracks to the manual valve position in preparation for automatic control. As an example, assume that it is desired to update time to the value 3:27 PM. The following steps should be executed:
1. Move the MAINTENANCE TEST switch to the TEST position.
2. Press the TURBINE PROGRAM DISPLAY button; it will light.
3. Key in the address 3136 and press the ENTER button. The address appears in the left display windows.
4. Press the CHANGE button; it will light.
5. Key in the time value 1527 and press the ENTER button. The time appears in the right display windows and the CHANGE light is turned off.
6. Key in the address 3137 and press the ENTER button. The address appears in the left display windows.
7. Press the CHANGE button; it will light.
8. Key in the XUPDATE value of 1.0 and watch the station clock.
9. When the clock sweep second hand passes exactly through 3:27 PM, press the ENTER button. The right windows clear to zero and the CHANGE light is turned off.
10. Key in the address 2078 and press the ENTER button. The address appears in the left display windows and the computer real time appears in the right display windows. This value is continuously updated by the DEH CONTROL task TIME UPDATE program.
11. Move the MAINTENANCE TEST switch to the OFF position. It should be necessary to update time only when the computer has stopped; once this is done the DEH system keeps track of real time continuously. If it is desired to display computer time, Steps 2 and 10 above need only be executed.
Valve Position Limit Function
A valve position limit function is a traditional feature of turbine control systems. This function generally provides the operator with high limiting action on the final computer governor valve output to the servo actuator. It is most useful when the turbine is on automatic control, and allows the operator to override the automatic output if he feels a particular siutation justifies such action.
In the DEH Control System, the valve position limit feature is active on both speed and load control. The valve position limit is normally adjustable in both the rise and lower direction; when the governor valves are actually being limited by this function, the VALVE POSITION LIMIT DISPLAY button is flashed to alert the operator to the condition. The computed value (SPD) is the governor valve position set by the Speed Control System, while GVPOS is the governor valve position set by the Load Control System. Each output is high limited by the valve position limit (VPOSL) which is continuously adjustable by raise and lower push-buttons on the Operator's Panel.
When the valve position limit is adjusted with the raise or lower buttons, the rate of change of VPOSL is controlled by a keyboard entered constant (VPOSLINC), the valve position limit increment. The actual variation of VPOSL is a nonlinear function of the time in seconds which the raise or lower button is pressed and held. Basically, the valve position limit is incremented every 1 sec by an amount given by the expression (N * VPOSLINC), where N is the running number of consecutive seconds during which the raise or lower button is held down. Once the button is released, N is reset to zero and is counted up when either the raise or lower button is pressed again. By pressing and releasing these buttons, the operator may incrementally vary the valve position limit in a variety of ways.
When the raise or lower button is initially pressed, the PANEL INTERRUPT program decodes these buttons and bids the PANEL task. This program then sets logical states, if the proper conditions exist, to begin a time counter in the AUX SYNC task. The AUX SYNC task counts in 1/10 sec steps, as long as the raise or lower button is held down. Simultaneously, the CONTROL program runs every 1 sec and increments the valve position limit according to the count set by the AUX SYNC task.
When the raise or lower button is released, the valve interrupt is triggered. The Monitor then runs the VALVE INTERRUPT program, which resets the valve position limit logical states and time counter so that the valve position limit incremental action is no longer executed in the control task. Pressing the raise or lower button again repeats the cycle described.
A test is first made to determine if the limit is to be raised or lowered as indicated by raise pushbutton state (VPLRPB), or by a request from the AUTOMATIC TURBINE STARTUP (ATS) program through an equivalent raise logic state (ATSVPLPB-assuming that the limit VPOSL is below its maximum value VPOSLMAX). If the limit is to be raised, a temporary location is set to the incremental change (VPOSLINC). If the limit is not to be raised, a test is made to determine if the limit is to be lowered as indicated by the lower button state (VPLLPB). If so, a temporary location is set with the negative incremental change (VPOSLINC); if there is no lower action, the program moves on to the next stage.
If some changes is to be made in the limit, the program computes the incremental step as discussed above and adds this to the last value of VPOSL. Finally, tests are made to be sure that the limit does not exceed a maximum value (VPOSLMAX, a keyboard entered constant) or go below zero. The program then moves on to the next stage.
Valve Test Function
A valve test function is a traditional feature of turbine control systems. To understand the need for this function, it is necessary to realize that a steam turbine has two sets of valves for control of steam flow. The throttle valves are located first in the steam flow path and the governor valves follow. Under most turbine operating conditions, the throttle valves are wide open and the governor valves assume the proper position to control steam flow. However, the throttle valves must always be prepared to close instantly, in case a contingency occurs which requires a mandatory trip of the turbine. Should either or both throttle valves remain open under such emergency conditions, the possibility of severe damage to the turbine and the power plant is very high. Past experience shows that malfunctions in the electrical and mechanical trip detection systems, or physical binding of the throttle valve elements themselves, makes such a potentially disastrous situation occur occasionally.
In order to detect such malfunctions, a throttle valve test feature is always provided with turbine control systems. Essentially the test function allows the operator to close the throttle valves for a few seconds to assure their opertional availability during contingencies. Electric utility practices vary, but typically the throttle valves are periodically tested at times of relatively low load and stable power system conditions.
A complication can arise in the actual incorporation of a throttle valve test function. With normal steam flow through the turbine, the mechanical forces acting on the throttle valve mechanism are so large that it is physcially impossible to close and reopen the valve and thus verify its operational availability. To overcome this problem it is first necessary to close the governor valve(s) on the same side of the turbine in small incremental steps so that load on the turbine is not upset to any great degree. When the governor valve is closed and steam flow cut off, the throttle valve forces are negligible and the throttle valve may then be test-closed and reopened to verify its operation. Finally, the governor valve(s) must be opened incrementally to return it to conditions existing prior to the test.
In the DEH system, the valve test feature is arranged to accomplish the end functions discussed above. The incremental rate of closing and opening the governor valves is controlled by a keyboard entered constant (VTESTINC). Every 1 sec, the governor valve is moved by this amount, which is usually about 1 percent, until the governor valve reaches its proper position in the test sequence. The valve test program automatically carries out all steps in the procedure under control of the operator, who selects from appropriate panel pushbuttons the valve to be tested and the close/open portion of the governor valve excursion. The valve test need not be accomplished in one step, but rather the operator may stretch the test out over any reasonable time interval by simply releasing the close or open pushbuttons for a time and then pressing them again.
When the CLOSE or OPEN pushbutton is initially pressed, the PANEL INTERRUPT program decodes the pushbuttons and bids the PANEL task; the PANEL task program then sets logical states, if all permissive conditions exist, to activate the appropriate part of the test. The CONTROL task continually monitors these logical states and increments the governor valve at the proper time, closes the throttle valve, and keeps track of all necessary bookkeeping.
When the CLOSE or OPEN pushbutton is released, the VALVE INTERRUPT program resets the pushbutton logic states and either terminates the test or waits until the operator presses the proper pushbuttons to continue the test, whichever situation is appropriate. In FIG. 57, a block diagram shows interactions provided in the DEH system 1100 by the valve test function 1962. In the valve test execution, a check is first made to determine if the turbine is on manual control; if so a valve test cannot be carried out but some bookkeeping may be necessary to clean up computer conditions. These may have existed from an immediately preceding valve test on automatic control which was interrupted by transfer to manual control. Therefore, the test analog output (TESTAO) is checked to determine if it is non-zero. If so, this means that a valve test had been underway; thus TESTAO and the valve identification (NVTEST) are reset to zero and a call is made to the contact output handler to reset the test analog output voltage to zero.
If the turbine is on automatic control, the CLOSE pushbutton state (CLOSEPB) is interrogated. If it is set, the appropriate governor position, as determined from the linear variable differential transformer (LVDT) analog input in computer location IGVSS (INDEX2), is checked to see if it is within a deadband (CLOSEDB) of being closed. If it is not, the valve test increment (VTESTINC) is added to the current analog output (TESTAO) and the governor valve closed further. After a number of passes through this loop, the governor valve is esentially closed and a contact output is set to immediately close the corresponding throttle valve. As long as the CLOSE pushbutton is held down, the throttle and governor valves are held closed. When the CLOSE pushbutton is released, the VALVE INTERRUPT program resets the throttle valve contact output and thus allows the throttle valve to return to its normally open position. However, the governor valve remains closed because the test analog output (TESTAO) is still set.
A check is made to determine if the OPEN pushbutton has been pressed. If not, the program bypasses into the next section of the CONTROL task. However, if the OPEN pushbutton is pressed, this means that the governor valve test analog output must be removed at the incremental rate (VTESTINC). Thus, the valve (TESTAO) is checked to see if it is less than VTESTINC; if not, TESTAO is decremented by the amount (VTESTINC) and the cycle continued. Ultimately, TESTAO is reduced to a numerical value below VTESTINC, at which time TESTAO is reset to zero and the valve test is essentially completed. When the operator releases the OPEN pushbutton, the VALVE INTERRUPT program formally terminates the test by cleaning up logical states as described above.
Valve Contingency Function
In situations where the throttle and governor valves are asked to move very fast, such as the transfer from throttle to governor valve control or when load is changed at a high rate, the VALVE CONTINGENCY program flashes the valve status lamps for a few seconds. This is a normal situation which simply indicates that the valve servo actuator cannot move quite as fast as the DEH system has called for. The lamps flicker briefly and then go out when the LVDT signals catch up to the computer output.
The valve contingency function has a second feature which is executed during automatic control to alert the operator to situations during which the analog backup system 1016 is not tracking the DEH controller valve analog outputs. Under normal conditions, the backup system continuously tracks the computer outputs to assume control bumplessly at any time. However, in certain situations, when the automatic system makes fast valve movements, such as during throttle/governor transfer or large load changes at a high rate, the manual backup tracking system lags for a short interval of time. The valve contingency function indicates this conditin by flashing the MANUAL NOT TRACKING monitor lamp on the Operator A Panel. The tracking deadband is a keyboard entered constant for the throttle and governor valves individually; these are normally set at about 1 percent. While the MANUAL NOT TRACKING lamp is flashing, the operator must not transfer to manual control; otherwise, he may sustain a significant bump in the operating conditions and may even place the turbine in an unsafe operating state. In the preferred embodiment, the tracking deadband or discrepancy is a keyboard entered constant individually selectable for each throttle valve TV1, TV2, TV3, TV4 and each governor valve GV1 through GV8. The discrepancy values or deadbands are normally set at about 1%.
The valve contingency function interfaces with the remaining portions of the DEH Control System primarily through the appropriate analog inputs and keyboard entered constants discussed above. Otherwise the function is more or less self-contained.
In the VALVE CONTINGENCY program, all contingency states are reset and the manual control contact input (TM) is interrogated. If the turbine is on manual, nothing else is done in the contingency program. However, if the turbine is on automatic control, a FORTRAN DO loop is executed to evaluate the throttle and governor valve LVDT inputs with respect to the computer outputs. The throttle inputs are stored in the array ITVSS while the governor inputs are in array IGVSS. The throttle contingency deadband is at TVDB and the governor contingency deadband is at GVDB. If either contingency exists, the appropriate contingency state is set for flashing; otherwise no further action is taken.
A similar test is made for the manual not tracking situation. The throttle and governor valve analog outputs (ITVAO and IGVAO) are checked against the manual backup system outputs (ITVMAN and IGVMAN), with deadbands TVMANDB and GVMANDB respectively. If a discrepancy exits, the manual not tracking state is set for flashing; otherwise no action is taken and the program proceeds to the next section.
Speed Selection Function
An additional task which the speed selection function must accomplish is the bumpless transfer mechanisms necessary when the speed input signals are switched, and when all speed inputs fail. These bumpless transfers are incorporated only on load control, since speed switching then can be significant in affecting governor position and thus turbine load. During speed control, no noticeable effect of speed signal switching may be expected.
Consider first the case when the speed signal is to be switched from the digital to the analog channel, or from the analog to the digital channel. The portion of the Load Control System which will be affected by such a change includes essentially the speed feedback loop output (X, considered simply as a single block since the details are not important in this context), the turbine load reference (REFDMD), and the turbine speed modified load reference (REF1).
When the speed signal is switched, the factor X changes, in general, so it is necessary to change the reference (REFDMD) to avoid a bump in REF1 and ultimately in the valves. Suppose that the system has been using one of the two speed inputs (it is immaterial which one), and thus had been yielding a speed feedback factor (X.sub.1). Then the value of REF1 is given by:
Now the system switches to the other input and yields a speed feedback factor (X.sub.2). The corresponding value for REF1 is given in:
To yield a bumpless transfer, it is necessary to hold the value of REF1 constant, as indicated in the following expression:
Substituting Equations (35) and (36) into (37) and solving for the new value of REFDMD gives the proper condition for a bumpless transfer, as shown below:
Thus when the speed signal is switched, the speed selection function recomputes the new value of turbine reference according to Equation (38) and achieves the required bumpless transfer.
Consider next the situation in which both the digital and the analog signals fail, thus requiring the speed feedback loop to be disabled and taken out of service. Again this must be accomplished bumplessly so that the governor valves, and thus turbine load, do not change significantly. The value of the speed compensated reference when the speed loop (SPI) is in service is given by:
When the loop is taken out of service due to speed channel failure, the value of REF1 is computed from:
To yield a bumpless transfer, it is necessary to hold the value of REF1 constant as follows:
Substituting Equations (39) and (40) into (41) and solving for the new value of REFDMD gives the proper conditions to maintain a bumpless transfer, as shown below:
Thus, to satisfy the conditions for bumpless transfer with respect to the speed loop, the speed selection function must reset the reference as given in Equation (42) to maintain constant valve position and thus constant load during this interval. Brief consideration will now be directed to the two out of three logical error detection scheme used by the speed selection function. It must be realized first that the three speed signals will rarely, if ever, be exactly equal; thus, it is necessary to compare these signals with each other and check for a significant difference. The value of the allowable difference given by WSERROR and is a keyboard entered constant; should any two speeds differ in magnitude greater than WSERROR, then one or both of the speeds are faulty. The allowable speed error (WSERROR) is usually set about 100 rpm.
The speed selection process compares the three speeds and bases its logical conclusions on the results of this test. Since there are three differences (between the digital and the analog, the digital and the supervisory, and the analog and the supervisory), which may or may not be greater than WSERROR, then there are eight possible combinations which must be examined. Table 1 lists these combinations, the decision as to which speed to be used, and a comment on each situation. The column titles in Table 1 indicate "approximately equal", which means that the various speeds agree within WSERROR rpm. The letter Y in the table means YES they do agree, while the letter N means NO they do not agree.
The speed selection function simply compares the speed differences which exist every 1 sec (the sampling interval for the CONTROL task) and finds the corresponding entry in Table 1. Logical conditions are then set to carry out the appropriate action as indicated by the comments in Table 1, to assure proper control by the remaining parts of the DEH system.
FIGS. 60A and 60B show the flow chart for the SPEED SELECTION program. At statement 50, the digital course and fine speeds (WSCOURSE and WSFINE) are computed from the integer numerical values (ICOURSE and IFINE) provided by the digital speed channel circuitry. Then either the course or the fine value, depending on whether the course is greater than the switchover speed (WSWITCH, a keyboard entered constant set at 1650 rpm), is selected as the digital speed (WSDIG). At statement 52 all speed failure states are reset prior to the two out of three speed selection process; then comparisons of the three speed differences are made against the allowable difference (WSERROR). The results of this comparison yield an entry in Table 1 which is then acted upon.
At statement 53, the speed selection process has concluded that the digital speed is unreliable, and therefore sets the logical state (DIGSPDF) for further action later in this process. Similarly, just before statement 57, the analog speed has been found to be unreliable and its logical state (ANASPDF) is set for further action. Finally, at statement 57 all speeds have been found unreliable, thus requiring the speed channel failure logical state (SPTF) to be set as well as the digital and analog failure states (DIGSPDF and ANASPDF).
At statement 54, the selected speed, whether it be the digital or the analog, has been placed in a temporary location (TEMP). This value is now checked against a high limit (WSMAX) and a low limit (WSMIN), each of which are keyboard entered constants which normally have values about 4500 and 300 rpm, respectively. This checks against absolute limits which the selected speeds may have violated. In addition, if the breaker (BR) is open (thus indicating that the DEH system is in wide-range speed control) and the selected speed is below WSMIN, the turbine speed reference (REFDMD) is compared with a minimum speed reference (WSREFMIN), which is another keyboard entered constant usually set at 600 rpm. If the reference (REFDMD) is greater than WSREFMIN, this indicates the turbine is not rolling or the speed channel system is not functioning properly. In all of these latter cases, transfer is made to statement 57 where the speed channel failure states are set, which then switch the turbine to manual control through action in the LOGIC task.
For the large majority of times however, the selected speed is reliable and the program transfers to statement 58. The state of the breaker (BR) is checked; if it is open, no special action is taken other than transfer to statement 65 for final bookkeeping. If the breaker is closed, thus indicating load control, special logic decisions are made to determine if a speed channel failure or a speed signal switch has just occurred. If so, the appropriate speed bumpless transfer computations are made as indicated in Equations (38) and (42) above, and transfer is made to statement 65.
At statement 65, final bookkeeping checks are made for the speed selection function. Thus, if any of the logical conditions (SPIF, DIGSPDF or ANASPDF) have changed state in the current execution of the SPEED SELECTION program will respect to the last execution of this program, the LOGIC task is asked to run by setting the RUNLOGIC flag. The AUX SYNC task then bids the LOGIC task within 1/10 sec, thus providing the mechanism for aligning all monitor lamps and the speed feedback loop IN/OUT status. The program then proceeds to the next section of the CONTROL task.
Select Operating Mode Function
The SELECT OPERATING MODE program must distinguish between speed and load control by examining the state of the main generator circuit breaker. For wide-range speed control, the program flow chart is shown in FIG. 61A. The automatic synchronizer state (AS) is first interrogated; if it is the operating mode, the auto sync increase and decrease states (ASINC and ASDEC) are examined. These states are flip-flops which are controlled by the LOGIC task when the auto sync raise or lower contact inputs are set. The program carefully checks to see if both the increase and decrease states re set; if so, no action is taken. Otherwise a temporary location (TEMP) is set to +1 rpm or -1 rpm for each pass through the program during which the appropriate contact input is set. The turbine speed reference and demand are then incremented properly, the ASINC and ASDEC states are reset for the next time, and the program passes to the next stage of the CONTROL task.
If the automatic synchronizer is not the operating mode, then the Automatic Turbine Startup (ATS) stte is interrogated at sttement 4000 (FIG. 61A). If it is the operating mode, as determined by the LOGIC task, the turbine speed demand and rate are selected from this program via computer locations TASDMD and TASRATE. The rate is then checked against an absolute high limit (OARATMAX), which is a keyboard entered constant usually set at 800 rpm after which the program passes on to the next stage of the CONTROL task.
If the AUTOMATIC TURBINE STARTUP program is not the operating mode, the Operator Automatic (OA) state, and the Maintenance Test (OPRT) state are interrogated at statement 6000 (FIG. 61A). If either of these states are set, the turbine speed demand and rate are selected from the keyboard and the program proceeds to the next stage of the CONTROL task. Note that on Operator Automatic the keyboard values control the turbine, while in Maintenance Test the keyboard values simulate a turbine.
If neither Operator Automatic nor Maintenance Test is the operating mode, then the turbine is in Manual control and the SELECT OPERATING MODE program goes into the manual tracking mode at statement 7000. If the contact input (THI) is set, this means the throttle valves are wide open and the turbine is in speed governor control. Then the error between manual and computer governor valve outputs (IGVMAN and IGVAO) is multiplied by a gain factor (GR10) and saved in a temporary location. If the contact input (THI) is not set, then the turbine is in speed throttle control and the error between manual and computer throttle valve outputs (ITVMAN and ITVAO) is multiplied by a gain factor (GR5) and saved in a temporary location.
In either case, assuming the speed loop (SPI) is in service, the valve output error is checked against a speed tracking deadband (DBTRKS, which is a keyboard entered constant usually set at 1 percent) and the reference is checked against actual speed (WS) through a reference tracking deadband (DBTRKREF, which is also a keyboard entered constant usually set at 50 rpm). If both conditions are met, the READY state is set to indicate the DEH system is ready to assume automatic control. The READY state is detected by the FLASH task, which then flashes the OPER AUTO light to let the operator know that he may transfer to automatic control.
Finally, the gained valve position error in the temporary location (TEMP) is used to increment the reference (REFDMD), which is then checked against an absolute high speed limit (HLS). This is a keyboard entered constant which is normally set at 4200 rpm. The program then transfers to statement 15500 for some final bookkeeping checks.
When the SELECT OPERATING MODE program determines that the main generator circuit breaker is closed, thus indicating the turbine is on load control, transfer is made to statement 10000 which is shown in FIG. 61B. The Throttle Pressure Control (TPC) state is interrogated; if it is in service, then the actual throttle pressure (PO) is compared against a set point (POSP), which is a keyboard entered constant usually set at about 1600 psia. If the throttle pressure (PO) is above the set point (POSP), no further action is taken. But if PO is below POSP, then the governor valve position (GVSP) as called for by the computer is checked against a minimum governor valve set point (GVSPMIN). This is a keyboard entered constant usually set at about 25 percent. If GVSP is less than GVSPMIN, no further action is taken; but if GVSP is greater than GVSPMIN, then the throttle pressure limiting state (TPLIM) is set and the reference load rate is set to runback the reference at the rate TPCRATE, which is a keyboard entered constant usually set at 200 percents per minute. The program then transfers to statement 11500 for further bookkeeping computation.
If not throttle pressure contingency exists, the RUNBACK contact input (RB) is interrogated; if it is set, the load reference is runback at the rate (RBRATE, which is a keyboard entered constant set at about 100 percent per minute. Then at statement 11500 some bookkeeping details are taken care of. Thus if the Automatic Dispatch System (ADS) state has been in control when either a throttle pressure limit or runback condition occurred, this mode is rejected by resetting the automatic dispatch system pushbutton state (ADSPB) and setting th RUNLOGIC flag. Within 1/10 sec the AUX SYNC task bids the LOGIC task, which then realigns all states to the correct position. A second bookkeeping check is made at statement 11700 where th HOLD state is checked. If HOLD is reset, then it is set so that the operator has an indication of why the reference has been runback.
If no runback contingency exists, then the Automatic Dispatch System (ADS) state is interrogated at statement 1200. If it is the operating mode, the ADS increase and decrease states (ADSINC and ADSDEC) are examined. These are flip-flops which are controlled by the LOGIC task when the ADS increase and decrease contact inputs are set. The program carefully checks to see if both the increase and decrease contacts are set; if so no action is taken. Otherwise a temporary location (TEMP) is set to the ADS raise or lower pulse count (IADSUP or IADSDOWN). The AUX SYNC task keeps track of these pulse counts according to the conditions set up by the LOGIC task. However, a maximum ADS pulse-width is imposed on both the raise and lower pulses in the SELECT OPERATING MODE program by comparing their counts (IADSUP and IADSDOWN) with a limit (ADSMAXT), which is a keyboard entered constant usually set to 10 counts of 1/10 sec each (thus yielding a maximum pulse-width of 1 sec). After the pulse-width limiting action, at statement 12400 the turbine load reference and demand are incremented by an amount proprotional to the pulse-width; the proportionality factor (ADSRATE) is a keyboard entered constant usually set somewhere between 1 and 10 MW per sec of pulse-width. Finally, at statement 12600, various ADS counters and states are reset prior to moving on to the next stage of the CONTROL task.
If the ADS state is not set, then the select operating mode program checks the Operator Automatic (OA) state and the Maintenance Test (OPRT) state at statement 14000. If either of these states are set, then the turbine demand and rate are accepted from the keyboard and the program proceeds to the next stage of the CONTROL task. Note that in Operator Automatic the keyboard values control the turbine, while in Maintenance Test the keyboard values simulate a turbine.
If neither Operator Automatic nor Maintenance Test is the operting mode, then the turbine is in Manual control and the SELECT OPERATING MODE program goes into the Manual Load Tracking mode at statement 1500. The error between the manual and computer governor valve outputs (IGVMAN and IGVAO) is stored in a temporary location (TEMP) and compared against a load tracking deadband (DBTRKL), which is a keyboard entered constant usually set at about 1 percent. If the outputs agree within DBTRKL, then the READY state is set to indicate the DEH system is ready to assume automatic control. The READY state is detected by the FLASH task, which then flashes the OPER AUTO light to let the operator know that he may transfer to automatic control.
The valve output error is then gain multiplied by GR9 and added to the current reference (REFDMD), which is high-limit-checked against MWMAX, a keyboard entered constant usually set to about 120 percent of rated megawatts. REFDMD is also low-limit-checked against zero, thus assuring that the tracking scheme will not windup in either direction. Finally, a last check is made to determine if a voltage exists on the test analog output lines; if so, the READY state is reset so that transfer to automatic control is inhibited until this voltage is removed. This may be done by pressing the OPEN valve test pushbutton until the lights behind the OPEN and CLOSE pushbutton go out.
Speed/Load Reference Function
The GO state is checked; if GO is off, the HOLD state is checked. If HOLD is on and the demand and reference value (REFDMD) are equal, then the logical states (GOHOLDOF and RUNLOGIC) are set. This results in the LOGIC task being bid within 1/10 sec by the AUX SYNC task, which recognizes the RUNLOGIC state. The LOGIC task then turns off the HOLD flip-flop and lamp as requested by the GOHOLDOF state.
If the GO state is set back however, then this is the signal to allow the reference to move toward the demand. The magnitude of the difference between the reference and the demand is computed and stored in a temporary location. Then the magnitude of the incremental step size taken each second by the selected rate, as discussed above, is saved in another temporary location. These two temporary quantities are then compared and if the demand/reference difference in TEMP is greater than the incremental step size in TEMP1, this means the reference must continue to move closer to the demand. However, the governor valve position limiting state (VPLIM) is checked; if it is set and the demand is above the reference, then no movement is allowed in the reference. This is because the valve position limit function is operating and refuses to allow any increase in reference because this will attempt to increase the governor valve position beyond the limit.
If there is no valve position limiting action, then the reference is incremented by the incremental rate step size and the program transfers for final exit.
Eventually the reference will approach within the allotted boundary of the demand. Then the reference program immediately sets the reference equal to the demand. Finally, the state of the breaker (BR) is interrogated; if it is set, the program transfers for the Load Control System computations, while transfer is made for the Speed Control System computations if the breaker state (BR) is reset.
Speed Control Function
To provide the simulation and training feature, FIG. 64 shows an additional program path which will internally generate a simulated speed signal (SIMWS) in the Maintenance Test mode of operation. This is accomplished by feeding back the speed controller output (SPDSP) through a first order lag transfer function which approximates the turbine inertia response. This simulated speed then replaces the actual speed in developing a speed error during the Simulation/Training mode of operation.
All speed control system parameters, such as gains, reset times and limits, are keyboard entered constants which are available for tuning or adjustment during the Maintenance Test mode. These changes require transfer of the turbine control to manual operation.
Logical checks are made to determine whether the speed computations should be evaluated. Thus, if the speed inputs failed and are unreliable, then the speed loop (SPI) is taken out of service, and there is no speed information by which to control the turbine. In addition, if the overspeed speed protection circuit in the Analog Backup System is operating, as indicated by the contact input (OPCOP), this closes the governor valve and thus overrides the DEH Speed Control System; consequently in this case, no speed control computations are performed.
Assuming that neither of these situations exist, the speed error is calculated. If the system is in the Simulation/Training mode, this error is the difference between the reference and simulated speed; the speed error is the difference between the reference and actual speed in all other cases. Following this error computation, a decision is made as to whether the turbine is on governor or throttle control. Appropriate calls are then made to the PRESET subroutine to evaluate the proportional-plus-reset controller action for the throttle or governor valve. This subroutine takes care of evaluating the controller algorithm and the high/low limit checks to eliminate reset windup.
Load Control Function
As in the Speed Control System, all parameters in the Load Control System are keyboard entered constants, which may be tuned or adjusted in the Maintenance Test mode. As always, changes of this type require transfer to manual control for the adjustment, after which the DEH system will track and permit return to automatic control.
To provide the simulation and training feature disclosed previously, FIG. 65 shows additional program paths which internally generate simulated megawatt and impulse pressure signals (SIMMW and SIMPI) in the Maintenance Test mode of operation. These are accomplished by feeding back the load reference (REF2) and the valve set point (VSP) (through software) to first order lag transfer functions which approximate the generator and turbine responses. These simulated signals then replace the actual feedback in developing megawatt and impulse pressure errors during the Simulation/Training mode of operation.
A check is first made (FIG. 65A) to determine if a change has occurred in the throttle pressure limit state (TPLIM); if so the LOGIC task aligns all status variables accordingly. The LOAD CONTROL program next checks the speed transducer failure state (SPTF). If there is no failure, the speed feedback loop is evaluated with a call to the SPDLOOP subroutine; if there is a speed transducer failure, the speed feedback loop is bypassed and the speed compensation factor (X) is set to zero. Whichever is the case, the factor (X) is summed with the turbine load reference (REFDMD) to form the speed compensated load reference (REFI). A low-limit-check against zero is performed on REF1 to keep it from going negative, which is possible should a turbine overspeed condition result.
The LOAD CONTROL program then checks the maintenance test contact input (OPRT), which if set means the DEH system is being used as a simulator/trainer or control system tuning is underway. In either case, simulated megawatt and impulse pressure signals (SIMMW and SIMPI) are generated; if the turbine is not in this mode, then the simulated signals are set equal to the actual signals.
The state of the megawatt feedback loop (MWI) is checked; if the loop is out of service, the speed/megawatt compensated load reference (REF2) is simply set equal to the speed compensated load reference (REF1). But if the megawatt loop is in service, the megawatt error is computed and ranged to a per unit value by using the ranging gain (GR2), which is normally set at rated turbine generator megawatts. Then the PRESET subroutine is called to evaluate the megawatt proportional-plus-reset controller, including high/low limit checking. The result of this computation is the megawatt trim factor (Y), which is then applied to the speed compensated load reference (REF1) in a product relationship to form the speed/megawatt corrected load reference (REF2).
The speed/megawatt compensated load reference (REF2) is converted to an impulse pressure set point (PISP) by use of ranging gain (GR3). The state of the impulse pressure feedback loop (IPI) is then interrogated; if it is out of service the governor valve set point (VSP) is simply set equal to the impulse pressure set point (PISP) in psi. But if the impulse pressure loop is in service, then the impulse pressure error is computed and used as the driving signal for the proportional-plus-reset controller, which is evaluated by a call to the PRESET subroutine; this also does the high/low limit checking.
Finally, the governor valve set point (VSP) in psi is converted to a governor valve set point from 0 to 100 percent by use of the ranging gain (GR4), which is normally set at rated impulse pressure. The program then transfers to the final stages of the CONTROL task which actually compute the throttle and governor valve outputs.
Throttle Valve Control Function
The throttle control state (TC) is interrogated (FIG. 66); if it is set, this means the throttle valves are in positive control, and the program computes the throttle valve analog output from the speed controller value (SPD) and the keyboard entered ranging constant (GR6). However, if the throttle control state (TC) is not set, then the governor control state (GC) is checked. If it is not set, this means that the turbine is unlatched and that the throttle valves should be at their minimum position of completely closed. The program then computes the throttle valve analog output of zero.
If the governor control state (GC) is set, it is then necessary to determine if the throttle/governor transfer is complete by checking the TRCOM state. If TRCOM is not set, this means the transfer is still in progress; an additional check is made to determine if the governor valves have closed as indicated by GVMIN. If GVMIN is not set, then the throttle valves are still in positive control and the program computes the throttle valve analog output as required by the speed controller value (SPD) and the ranging gain (GR6).
Eventually the state GVMIN will be set to indicate that the governor valves are now in positive control. Then the throttle valve maximum position state (TVMAX) is questioned. If it is not set, then the throttle valve bias integrator (TVBIAS) is incremented by the bias constant (BTVO) and the throttle valve analog output set accordingly. In a short time the throttle valves are wide open; after this all logical states will be set to indicate this fact. Succeeding passes through the THROTTLE VALVE CONTROL program will then hold the throttle valve analog outputs wide open until the turbine is unlatched and tripped for some reason.
Governor Valve Control Function
The governor valve position, as set by the governor valve control function, is compared to (and high limited by) the valve position limit (VPOSL) at all times. This gives the operator the ability to override the control system at any time that he considers it necessary, and allows him to control the position of the governor valves from VALVE POSITION LIMIT RAISE and LOWER pushbuttons on the Operator's Panel. If the governor valves are limited by the valve position limit (VPOSL), the lamp behind the VALVE POSITION LIMIT DISPLAY pushbutton flashes, thus alterting the operator to the condition.
Various logical numerical checks are necessary to determine which of the five situations the turbine is currently in, on a second-by-second real time basis. Further, the actual governor valve analog output computation is made for each of these five situations, along with the valve position limit checking feature and additional bookkeeping computations necessary for coordination of the various DEH programs.
Considering the flow chart of FIG. 67 at statement 1200, the valve position limit state (VPLIM) is reset at each pass through the governor valve control program. Then the governor control state (GC) is interrogated; if it is not set, the throttle control state (TC) is checked. If throttle control (TC) is not set, this means the turbine is unlatched and the governor valve minimum state (GVMIN) is checked. If GVMIN is not set, then at statement 1270 all governor valve open states are reset and all governor valve close states, including GVMIN, are set. The program then transfers to statement 1320 for analog output computation and valve position limit checking to hold the governor valvess closed. Succeeding passes through the program will find the GVMIN state set and transfer directly to statement 1320.
If the turbine is latched, then the throttle control state (TC) is set. The governor valve control function finds itself at statement 1210, where the governor valve maximum state (GVMAX) is interrogated. If it is not set, then the governor valve bias integrator (GVBIAS) is incremented by the governor valve open-bias constant (BGVO), which is keyboard entered constant usually set at 10 percent to open the governor valves incrementally when the turbine is latched. The program then transfers to statement 1240 where the governor control state (GC) is again checked, since this point in the program may be reached from alternate paths. For the present situation, GC will not be set, thus leading to a check on whether the governor valve bias integrator (GVBIAS) has reached 100 percent and therefore have positioned the governor valves wide open. Assuming that GVBIAS has incremented up to 100 percent, all governor valve close states are reset and all governor valve open states are set, including GVMAX. The program then transfers to statement 1320 for analog output computation and valve position limit checking to hold the governor valves wide open. Succeeding passes through the program find the GVMAX state set at statement 1210 and transfer directly to statement 1320.
Each of the cases discussed above apply when the governor control state (GC) is not set. Once the throttle/governor transfer is initiated, however, this sets the governor control state (GC), in which case the GOVERNOR VALVE CONTROL program arrives at statement 1220. The state of the breaker (BR) is checked; if BR is set, this means the DEH system is on load control and the program transfers to statement 1340 for load computation of the governor valve analog outputs and valve position limit checking.
However, if the breaker (BR) is open and the DEH system still in speed control, the check of BR at statement 1220 finds it not set. Then the throttle/governor transfer complete state (TRCOM) is checked; assuming it has not yet been set, the governor valve closed state (GVMIN) is checked. Normally this will not be set at this point in time, thus requiring the governor valve bias integrator (GVBIAS) to be decremented by the governor valve close-bias constant (BGVC), which is a keyboard entered quantity normally set at 100 percent to instantly close the governor valves when the transfer from throttle to governor control is initiated.
The program then passes on to statement 1240 where the governor control state (GC) is checked again; since GC is set for the present discussion, then at statement 1260 the manual contact input (TM) is interrogated. If the turbine is in manual control at this time, the program transfers to statement 1270 for appropriate bookkeeping which will be described shortly. If the turbine is in automatic control, then the test at statement 1260 on the state of TM finds it not set and an additional test is made on whether the governor valve bias integrator (GVBIAS) has reached zero to indicate the governor valves are closed. If it has not, then the program cycles through this area until the GVBIAS value is zero. Normally this will take only a few passes since the closing bias constant (BGVC) will be quite large to achieve a fast, smooth throttle/governor valve transfer.
Once GVBIAS is zero, the GOVERNOR VALVE CONTROL program searches to determine if the turbine speed (WS) has dropped below the speed at transfer WSTRANS by an amount WSDIP, which is a keyboard entered constant usually set at 10 rpm. When this has occurred, and assuming that the analog backup system has followed the computer governor valve analog output as indicated by the manual not tracking state (MANOTRAK) the GOVERNOR VALVE CONTROL program transfer to statement 1270. All governor valve open states are reset and all governor valve close states, including GVMIN, are set and the program passes on to statement 1320 for computation of the governor valve analog output and valve position limit checking to hold the governor valves closed.
The setting of GVMIN at statement 1270 leads to execution of the LOGIC task, which then uses this information to generate the throttle/governor valve transfer complete state (TRCOM). Succeeding passes through the GOVERNOR VALVE CONTROL program at statement 1220 find TRCOM set and immediately transfer to statement 1380 for computation of the governor valve analog output and valve position limit checking to control turbine speed. The portion of the program at statement 1320 is that necessary to hold the governor valves at the value residing in the governor valve bias integrator (GVBIAS).
The computations necessary to position the governor valves on load control determine where the load control governor valve set point (GVSP) liess with respect to a nonlinear curve which characterizes the governor valve stroke mechanism. The result of this search positions GVSP along the abscissa of the curve, after which the actual valve position (GVPOS) is computed from analytical solution of points along the curve.
The computed governor valve position (GVPOS) is compared with the current valve position limit (VPOSL). If GVPOS is below VPOSL, no action is taken, if GVPOS is greater than VPOSL, then the valve position limiting state VPLIM is set, RUNLOGIC is set and the actual governor valve position GVPOS is reset to the value residing in VPOSL. The LOGIC and FLASH task perform their assigned functions of aligning the DEH system to these conditions and flashing the VALVE POSITION LIMIT DISPLAY lamp, respectively.
In the computations necessary to position the governor valves on speed control, the speed controller percent output (SPD), suitably ratioed to account for differences between the speed ranging gain (GR7) and the maximum ranging factor of 20.47, is checked against the current valve position limit (VPOSL). If the ratioed speed controller output is below VPOSL, no special action is taken; if VPOSL is violated, then the valve position limiting states (VPLIM and RUNLOGIC) are set to trigger the appropriate responses from the LOGIC and FLASH tasks. In addition the speed controller output (SPD) and the speed integrator (RESSPD) are reset to values consistant with VPOSL.
A FORTRAN DO loop is executed to make final checks on both the throttle and governor valve analog outputs. They are low-limit-checked to guarantee that they do not go below zero and high-limit-checked to guarantee that they do not go above the maximum analog output voltage pattern. Then, the analog output handler is called to output the computed throttle and governor valve patterns. Finally, the CONTROL task exits to the Monitor for the next bid 1 sec later.
First Order Lag Function
The first order lag transfer function is a more or less standard component of control systems. It provides an output signal which is a time delayed version of the input signal. The time constant T of the first order lag is a measure of the time delay in seconds produced by the lag. Approximately 5 T (i.e. five time constants) after the input makes a step change, the output has essentially reproduced this change.
The uses of the first order lag function vary somewhat. In some cases, it is valuable as a filter to smooth out random noise pulses or spikes in signals. In other cases, the first order lag is useful in simulating known response of various devices or portions of systems. This latter situation is the way in which the first order lag is used in the DEH application. When the MAINTENANCE TEST switch is moved to the TEST position; thus placing the DEH system in the simulation/training mode of operation, appropriate computer variables are sent into first order lag transfer functions. The output of these functions represents simulated analog inputs such as turbine speed, impulse pressure and megawatts.
In order to perform the mathematical function of a first order lag in a computer, it is necessary to use numerical techniques to approximate the function. A number of algorithms are available, each of which have certain advantages and disadvantages. Although the trapezoidal rule yields the most accurate first order lag response, it requires additional storage for past history of the input. For this reasons, the rectangular rule is used in the DEH system; it requires less storage and, though it is not as accurate as the trapezoidal rule, such accuracy is not required in the use of the first order lag in a simulator/trainer context.
The algorithm used by the DEH system to evaluate the first order lag is given by: ##EQU5## Definition of terms in Equation (43) follows:
To use the algorithm of Equation (43), the DEH system is organized so that the parameters (DT and T), the input variable (ZIN(N)), and the output variables (ZOUT(N)) and ZOUT(N-1) are in known COMMON areas of storage. The algorithm itself is programmed in the form of a FORTRAN STATEMENT function, so that use of the first order lag is restricted to the CONTROL task. To evaluate the lag transfer function, it is necessary only to write the statement function expression in-line at the appropriate place in the CONTROL task.
The first order lag is programmed as a FORTRAN STATEMENT function to minimize the overhead storage requirements that occur if programmed as a subroutine.
This statement expresses the algorithm of Equation (43), with some collecting of terms and substitution of 1.0 for the general sampling interval (DT), since the CONTROL task runs every 1 sec. The dummy arguments (ZIN,TDELAY and ZOUT) represent the input, the time delay and the output variables needed to evaluate the first order lag.
Nonlinear Characterization Function
The nonlinear characterization function provides an important feature for accommodating the nonlinear nature of process equipment. This function produces an output related in a nonlinear fashion to the input.
The form of the curve comprising the characterization function varies somewhat with the application and with the mechanism available for incorporating this feature in the control system. In some analog systems, the curve may have two or at most three segments to accomplish its function. In some highly sophisticated computer systems, the curve may have as many as eight or ten segments. The DEH Control System provides a nonlinear characterization function having five straight-line segments composed of six points describing the intersections of these segments. The slope of any segment may be positive, zero or negative, while the points defining the intersections of various segments may have any positive value. For the DEH application requirements, it is only necessary to work with curves in the first quadrant.
The nonlinear characterization function in the DEH system is used to describe the governor valve position-versus-stroke relationship on load control. Accurate representation of this curve allows operation of the DEH system in automatic control (with the megawatt and impulse pressure feedback loops out of service) to be effectively linearized. Megawatt load demand can be achieved quite closely on automatic control without the feedback loops, which may be out of service due to faults with the transducers, or due to other problems. Of course, with the loops in service, operation then is exactly aligned between load demand and actual megawatt load. The axis of ordinates POS and the axis of abscissa SP consist of six points each. These are all keyboard entered quantities which may be tuned or adjusted in the maintenance test mode of operation.
The program isolates the segment of the SP axis within which the input value (GVSP) lies. Having found this, the program then evaluates the output value (GVPOS) using the slop intercept form of a straight-line from analytical geometry considerations. The ratio of the difference between corresponding values of POS and SP yields the slope of that section. This slope is multiplied by the exact position within the I-th section, which is given by the difference between the current value of the input (GVSP) and the left end point (SP(I-1)). The resultant product is added to the intercept (POS(I-1)) for this section to yield the required governor valve position (GVPOS).
CCI SCAN MONITOR -- ANNUNCIATOR ALARM
The DEH system scans contact inputs on a demand basis. The scan is initiated by a change of state of any contact. This change triggers a sequence of events interrupt which in turn bids the CONTACT SCAN program. However under certain conditions such as may occur during initial plant startup when all wiring has not been completely checked out, high-frequency noise on a contact can result in the sequence interrupt being generated continuously. This activity essentially "captures" the computer and prevents the DEH programs from carrying out their normal functions.
In order to counteract such a condition, special logic detects high-frequency contact noise. Should this occur, the DEH system immediately switches from a demand scan to a 1/2 sec periodic contact scan, the sequence interrupt is disabled, and a contact output is set which triggers the DEH CCI SCAN MONITOR annunciator alarm. If this happens, the noisy contact input should be found and the field problem fixed. After this is done, the DEH system may be returned to its originally dessigned demand scan by entering a particular constant from the keyboard as follows:
1. Turn the MAINTENANCE TEST key to the TEST position; this switches the turbine to manual control.
2. Press the PROGRAM DISPLAY button, which then backlights.
3. Key in the address 3141 and press the ENTER buttons. The address appears in the left windows and the value 1.000 appears in the right windows.
4. Press the CHANGE button, which backlights. The right windows clear to zero.
5. Key in the value 0 and press the ENTER button. The CHANGE lamp goes out and the DEH CCI SCAN MONITOR annunciator is turned off.
6. Return the MAINTENANCE TEST key to the OFF position. The DEH system tracks the manual backup system preparatory to transfer to automatic control, which the normal demand scan being used.
DEH DIGITAL TREND UPDATE PROCEDURE
The digital trend feature provides the ability to print up to 19 DEH system variables. These quantities may be printed at one time, or they may be printed periodically at a controllable rate by setting certain constants from the keyboard. A brief description of the entry procedure follows:
1. Press the TURBINE PROGRAM DISPLAY button, which then backlights.
2. Key in address 3364 and press the ENTER button. The address appears in the left windows and a numerical value of 0000, 1.000, or 2.000 appears in the right windows, depending on the previous state of the digital trend.
3. Press the CHANGE button; the button backlights and the right windows are cleared.
4. Key in one of the following numerical values, depending on the desired results as listed.
0 -- Suppress the digital trend
1 -- Print the digital trend values one time
2 -- Print the digital trend values periodically at the frequency to be described below
5. Press the ENTER button. The CHANGE lamp goes out and the digital trend requested in Step 4 is carried out.
If a periodic trend has been requested, the time in seconds between printing of the values must be entered as follows:
1. Press the TURBINE PROGRAM DISPLAY button, which then backlights.
2. Key in address 3365 and press the ENTER button. The address appears in the left windows and the current value of the digital trend frequency appears in the right windows.
3. To alter the trend frequency, press the CHANGE button. The button then backlights and the right windows are cleared.
4. Key in the new digital trend frequency, in seconds, which will appear in the right windows.
5. Press the ENTER button. The CHANGE lamp goes out and the digital trend frequency requested is carried out.
A note on the frequency of the digital trend is appropriate. The IBM 735 typewriter prints out the 19 values requested, including real time and the address of each value, in about 40 sec. Therefore, this represents the minimum trend frequency; actually the frequency should be kept somewhere in the 120-300 sec range, which is about 2-5 min, or longer. However, it is not necessary to trend all 19 quantities which are available. If fewer quantities are trended, the frequency may be increased somewhat. Good practice would indicate 60 sec, (1 min) as the fastest trend frequency attempted.
The addresses of the 19, or less, quantities to be trended must be entered from the keyboard. The following presents the computer locations which must be given the addresses of the DEH quantities to be trended. In order to alter the variables in the digital trend, the following procedure must be carried out.
1. Press the TURBINE PROGRAM DISPLAY button, which then backlights.
2. Key in the trend location to be altered, as indicated in the following table. As an example, if the fourth variable is to be changed, then key in the number 3369; this appears in the left windows.
3. Press the ENTER button. The current value of the DEH quantity being trended in the fourth column will appear in the right windows.
4. Press the CHANGE button. The button backlights and the right windows are cleared.
5. Key in the address of the new DEH quantity to be trended in the fourth column.
6. Press the ENTER button. The CHANGE lamp is turned off and the new variable appears in the next print of the trend in column 4.
APPENDIX 4
DEH Analog Hardware Description
P2000 Computer System
ANALOG BACKUP SYSTEM
Throttle Valve Control (Applicable Only to Units with Steam Chest Inlet Configurations)
Throttle valves are used on wide-range speed control from turning gear to approximately 90 percent of rated speed. From this point to full rated speed, governor valves are used for control.
When the DEH Control System is in the Operator Automatic mode of operation, the control signal from the computer analog output card (TVAAZ1) is permitted to control the throttle valves, through the Servo/Linear Variable Differential Transformer (S/LVDT) Cards. The Analog Backup System tracks the computer output.
To accomplish this tracking, the analog comparator compares the TVAAZ1 signal to the output of digital-to-analog (D/A) converter (TVMAZ1). If TVAAZ1 exceeds TVMAZ1, the comparator generates a raise signal. This signal causes the up/down counter to count up at a preset rate and increase its digital output. The digital-to-analog (D/A) converter output (TVMAZ1) increases until it equals TVAAZ1. Thus the Analog Backup System continuously tracks signal TVAAZ1, when the DEH Control System is in the Operator Automatic mode.
When the DEH Control System is in the Turbine Manual mode of operation, the analog output (TVMAZ2) controls the throttle valves through the S/LVDT Cards; the computer output (TVAAZ2) is blocked. The auto/manual logic circuitry blocks the analog comparator output and allows the TV RAISE and TV LOWER pushbuttons on the Operator B Panel to control the up/down counter. Pressing the TV RAISE button causes the up/down counter to count up at a slow rate. If the FAST ACTION pushbutton is pressed at the same time however, a faster rate is selected. The up/down counter output is converted to an analog output and used to control the throttle valves (TVMAZ2). With the DEH Control System in the Turbine Manual mode, the digital portion tracks the analog output with a computer software program.
In summary, when the system is in the Operator Automatic mode, the Analog Backup System tracks the computer output. When the system goes to the Turbine Manual mode, the analog system output equals the computer output and the transfer is made without moving the throttle valves (bumpless transfer). While the system is in Turbine Manual, the TV RAISE and TV LOWER pushbuttons control the throttle valve position and the digital portion tracks the analog system output. If the system is put back in the Operator Automatic mode, the transfer is made without a bump.
Governor Valve Control
Governor valves are used for speed and load control. If there are separate valve actuators for each valve, the DEH Control System may be in either single valve or sequential valve operation.
There are two types of inputs to the S/LVDT Cards. One type is the sequential valve inputs (GV1AZ1, GV2AZ1); these signals are generated independently of the Analog Backup System. The second type of input (GV*AZ1) is the single valve input; this input is generated either by the computer GVAAZ2) or by the analog system (GVMAZ2).
When the system is in single valve operation (or when sequential valve operation is not supplied), the sequential valve inputs to the S/LVDT Cards are zero. The GV*AZ1 signal controls the governor valves. Except for the fact that the analog output is biased so that positive and negative values can be obtained, the governor valve control circuits are the same as the throttle valve control circuits previously discussed.
The Analog Backup System tracks the computer output (GVAAZ1) when the control system is in the Operator Automatic mode. The analog system is controlled by the GV RAISE and GV LOWER pushbuttons when the control system is in the Turbine Manual mode and the computer tracks the analog output. The control signal (GV*AZ1) goes to all S/LVDT Cards; all valves move the same amount at the same time.
When the control system is in sequential valve operation (and in the Operator Automatic mode), the sequential inputs (GV1AZ1, GV2AZ1) are controlled by the computer. The computer also sets the single valve input (GV*AZ1) to zero. The computer then uses the sequential inputs to individually control the governor valves.
If the control system transfers to the Turbine Manual mode while in sequential valve operation, the computer keeps the sequential valve input signals (GV1AZ1, GV2AZ1) constant. Bumpless transfer occurs since the governor valves do not move. When the transfer is complete, the operator can position the valves with the GV RAISE and GV LOWER pushbuttons. Pressing the GV RAISE pushbutton increases the output of the D/A converter (GVMAZ) and thus increases the single valve input signal (GV*AZ1). GV*AZ1 is summed with the sequential input signals (GV1AZ1 and GV2AZ1); this increases the output of the S/LVDT Cards, and opens all the valves by the same amount.
If the GV LOWER pushbutton is pressed, the single valve input signal (GV*AZ1) is decreased. This signal is summed with the sequential input signals, causes the decrease in S/LVDT Card output, and closes all the valves by the same amount. The up/down counter counts below its mid range and causes the D/A converter output (GVMAZ1) to go negative. This feature allows the valves to be closed, even though the sequential valve input remains constant.
The digital system continuously tracks the single valve input (GV*AZ1) with a computer software program. When transfer to Operator Automatic is initiated (by pressing the OPER AUTO pushbutton), transfer occurs without changing the valve position (bumpless transfer).
In summary, for units with individual servos, the governor valves can operate in either the single valve or sequential valve mode. In either case, the Analog Backup System tracks the computer generated single valve output signal when in Operator Automatic mode, and positions the valves when in Turbine Manual mode.
Overspeed Protection Control (OPC) System
The OPC system controls turbine overspeed in the event of a partial or complete loss of load and if the turbine reaches or exceeds 103 percent of rated speed. Turbine input power is a function of Intermediate Pressure (IP) exhaust pressure; a pressure transducer provides IP exhaust pressure. A three-phase watt transducer provides generated kW information. These quantities are compared; if they differ by a preset amount (adjustable with the OPC PRESSURE/KW COMPARISON SETPOINT switch on the Test and Calibration Panel from 20 to 100 percent), protection is required. OPC protection is also required if turbine shaft speed exceed 103 percent of rated speed. This information (in rpm) is supplied by another transducer. The signals from the transducers are checked against high and low reference voltages to determine when a transducer fails.
Partial Loss of Load
The IP exhaust pressure and the generated power are compared. When they differ by an adjustable amount, and neither transducer has failed, the close interceptor valve (CIV) flip-flop is set. This causes the interceptor valves to close in approximately 0.15 sec. If the generator breaker does not open, this condition is detected as a partial load loss. The interceptor valves remain closed for a period of time (0.4 to 1.6 sec); this time delay depends on the setting of the INTERCEPT VALVE CYCLE TIME switch on the Test and Calibration Panel. After the time delay, the CIV flip-flop is reset and the interceptor valves reopen. Closing the interceptor valves provides a momentary reduction in generator input and aids in achieving power system stability. This feature may be inhibited, if not required, by a jumper on the half-shell connectors.
Complete Loss Of Load
When the interceptor valves are closed and the generator breaker opens, this condition is detected as a complete load loss. When the generator breaker opens, the load drop anticipation (LDA) is set, requesting OPC action. All governor and interceptor valves are then rapidly closed. Load drop reset time is fixed at 10 sec. Both CIV and LDA load loss circuits are inoperable below 25 percent load as measured by IP exhaust pressure.
Overspeed Action
OPC action also occurs when turbine speed is equal to, or greater than, 103 percent of rated speed. Governor and interceptor valves are closed until the speed drops below 103 percent. The OPC system may be tested using the OPC key switch on the Operator B Panel. If the breaker is open and the key is turned to the OPC TEST position, a signal is generated; this signal indicates that the speed of the turbine is over 103 percent. The OPC system then closes the valves as though an actual overspeed condition had occurred.
Speed Channel System
Two speed channels are located in the Analog Backup System: an analog speed channel and a digital speed channel. The analog speed channel detects a system overspeed condition by comparing an analog speed signal to a reference voltage. The analog speed signal is also sent to the digital portion of the control system and to the rpm meter on the Operator B Panel. The digital speed channel shapes the input speed signal (analog) and uses a 36 kHz clock to convert the analog signal to a corresponding digital signal. This digital signal is then applied to circuits in the digital portion of the control system.
Throttle Pressure Control (TPC)
The TPC circuits provide a means (in Turbine Manual mode) of controlling minimum throttle pressure. If throttle pressure falls below a set point (adjustable on the Test and Calibration Panel from 20 to 100 percent of rated pressure), the governor valves are closed until throttle pressure increases to the set point. The TPC circuits cannot close the governor valves to less than 20 percent open. The TPC circuits can be placed in, or out, of service in two ways, as follows:
1. TPC IN/TPC OUT pushbutton on the Operator B Panel.
2. Digital controller.
A hardware flip-flop and associated contact closure input to the controller ensure that both the analog and digital systems are in the same state. A transducer failure or the generator breaker opening will put the TPC circuits out of service. The TPC circuits cannot be restored to service until the problem is corrected. Also, the TPC circuits cannot be placed in service at any pressure below the TPC set point.
Transducer Monitors And Status Contacts
The following Analog Backup System parameters are measured with transducers:
Inlet Pressure
Generator Electric Load
Analog Speed Channel
Throttle Pressure
The transducers are monitored for high signal and low signal failures.
The transducers for the first three parameters listed above are used in the OPC system. If any of these transducers fails, both the OPC MONITOR lamp and the appropriate failure lamp (on the Operator A Panel) light. If throttle pressure fails, only the THROT PRESS MONITOR lamp lights. When any transducer fails, a form C contact is activated. This contat provides a contact closure input to the digital section and also provides a contact for an external alarm.
Analog Backup System Schematic Description
General
The control and logic circuits for the Analog Backup System are shown on 18 drawings; these are numbered D01 through D18.
In general, analog signals are scaled for 0 to 10 Vdc representing 0 to 100 percent of the particular function. The signal can represent percent of valve position, pressure, megawatts, or any other similar signal. Analog signal names have a three or four letter prefix, followed by a Z1 and Z2. The "Z" indicates an analog signal; the "1" indicates that the signal is the original signal; the "2" indicates that the original signal has been processed by a circuit such as a mixing amplifier and may be inverted.
Logic level signal names have a three or four letter prefix followed by a Y1, Y2, X1 or X2. The Y designates the "yes" condition and the X designates the "no" condition. The "1" indicates the original logic signal and the "2" indicates a logic signal that has been inverted twice. A logical 1 is represented by a +15 V signal and indicates that the condition is true; a logical 0 is represented by ground (0 Vdc) and indicates that the condition is false.
Note
A four digit number/letter designation is associated with all signal names on the schematics (for example: 15B3). The first two digits indicate the drawing where the signal originates or is sent (D01 through 18). The second two digits indicate the zone coordinates on the drawing where the signal can be found. In the above example, the signal can be found on drawing D15, zone B3. All destinations or origins of all signals are given.
In the following descriptions, each of the schematics is discussed. The intent of these discussions is to point out the circuits shown on the schematics.
Manual Pushbuttons On Operator B Panel
The manual pushbutton circuit consists of a pushbutton and a Pushbutton Signal Conditioner (PSC) Card. When the pushbutton is pressed, card pins 3 and 4 are shorted. This action causes a +15 V output on card pin 5; the +15 V is equivalent to a 1. The signal conditioning circuit ensures that a good logical signal is sent to the analog section when a pushbutton is pressed.
Throttle Valve Tracking System (Drawing D04) (Applicable ONLY to Units with Steam Chest Inlet Configuration)
Details of the logic portion of the throttle valve tracking and manual control system are shown in this drawing. The essential elements of the throttle valve analog control system are shown in this drawing and also in drawings D05 and D06. The output to the throttle valve Servo/Linear Variable Differential Transformer (S/LVDT VP) Cards is generated by an up/down counter, digital/analog (D/A) converter, and an operational amplifier circuit.
In the quiescent state, the up/down counter has a 1 on pins 1 and 2. Input TVCUX1 on pin 2 is the raise signal; if this signal is 0, the counter counts upward at a rate determined by the clock rate signal (TVCKX1) applied to pin 8. A 0 is applied to pin 2 when the TV RAISE pushbutton on the Operator B Panel is pressed (TVIBY1 on NAND gate 3M is a 1), the system is in the Turbine Manual Mode (TM**Y1 on NAND gate 3M is a 1), and permissives are present.
When the DEH Control System is in the Operator Automatic mode (TM**X1 gate 3M, pin 14, is a 1), the Analog Backup System tracks the Digital Controller by increasing or decreasing the up/down counter output. Tracking for an increasing signal is accomplished with signal TI**Y1; this signal is generated by the tracking comparator (see the description for drawing D05). Two permissives must be present to enable the up/down counter, as follows:
1. The unit must be latched (ASL*Y1 gate 3M, pin 1, is a 1).
2. A high limit of 4500 counts must not have been reached (TVCHX1 gate 3M, pin 6, is a 1). TVCHX1 is determined by the signals at the input to NAND gates 3D.
Input TVCDX1 on pin 1 of the up/down counter is the decrease signal; if this signal is a 0, the counter counts downward at a rate determined by the clock rate signal (TVCKX1) applied to pin 8. A 0 is applied to pin 1 when the TV LOWER pushbutton is pressed, (TVDBY1 gate 3M, pin 5, is a 1), and the system is in the Turbine Manual Mode (TM**Y1 gate 3M, pin 4, is a 1).
When the system is in the Operator Automatic mode, the Analog Backup System tracks the Digital Controller. The system must be in the Operator Automatic mode (TM**X1 gate 3M, pin 38, must be a 1), and the comparator (see the description for D05) produces TD**Y1.
A decrease signal can also be generated by a turbine tripped condition (ASL*Y1 gate 3B, pin 28, is a 0). This causes the counter to run down to a 0000 output. The counter zero stop is provided by an Input Expander (IE) Card (3L) and a gate (3C); these set signal TVCLX1 (gate 3L, pin 16) to a 0. A 1.5 sec clock rate (CLM) is used so that the counter is in the zero position prior to relatching.
The throttle valves cannot be closed after the transfer to governor valves has occurred. When signal THI*X1 (gate 3B, pin 14) is a zero, the counter cannot count down and the throttle valves cannot be closed. Signals THI*X1 is described in the description for drawing D06.
The pulse-rate input, on pin 8 of up/down counter 3E, determines the rate at which the counter output changes.
Clock rate selection is detailed in the following table.
The X1 outputs of the up/down counter (pins 3 to 36) are connected to the input of the digital-to-analog (D/A) converter, card 3F on drawing D05. The counter output is in an Aiken code with a count range of 0 to 4500.
Throttle Valve Tracking System (Drawing D05) (Applicable ONLY to Units with Steam Chest Inlet Configuration)
The analog and transfer portions of the throttle valve control are shown on this drawing. The Relay 4 (RC4) Card (3K) selects the output from either the Analog Backup System (TVMAZ2) in the Turbine Manual mode, or from the Digital Controller (TVAAZ2) in the Operator Automatic mode. The selected output (TV*AZ1) is sent to the Servo/Linear Variable Differential Transformer (S/LVDT VP) Card, see drawing D06. Transfer of the relay is controlled by the input (pin 2, TM**X1); this signal is generated by circuitry on drawing D15. The relay is shown in the deenergized state (Turbine Manual mode).
The output from the up/down counter (see drawing D04) is the digital input to the D/A converter, card 3F, the digital input is converted to a 0 to -10 V analog signal (TVMAZ1). This signal is one input to the Mixing Amplifier 4 (MA4) Card (card 3J, pin 38). A +15 V bias is also applied to pin 37 upon loss of auto stop latch (ASL*X2, card 3K, pin 22, is a 1). The bias ensures that the output of the mixing amplifier (TVMAZ2) will be negative on loss of auto stop latch regardless of the level of the manual input signal (TVMAZ1).
The Digital Controller output is converted from digital to analog form with an Analog Output (AO) Card. The AO Card uses an 11 bit, resistance network as a voltage divider across a regulated -15 V source to generate a 0 to -10 V output TVAAZ1 (refer to computer system documentation for details). TVAAZ1 is applied to card 3H (MA4 Card) and a bias is applied upon loss of auto stop latch as described for the manual signal.
When the DEH Control System is in the Operator Automatic mode, manual tracking is accomplished by changing the up/down counter until TVMAZ1 equals TVAAZ1. The Analog Comparator 7 (AC7) Card (card 3G) generates increase (TI**Y1) and decrease (TD**Y1) signals for this purpose.
During the Operator Automatic mode, the Digital Controller monitors the Analog Backup System. If the Analog Backup System does not track the Digital Controller, the MANUAL NOT TRACKING AUTO lamp on the Operator A Panel is lit by the Digital Controller. Bumpless transfer from Turbine Manual to Operator Automatic is implemented by the Digital Controller tracking the Manual Backup System. Signals TV*AZ1, TVMAZ2, and TVAAZ2 (Analog Input (AI) (A211, A212, and A213) are used for this purpose.
Throttle Valve Servo's (Drawing D06) (Applicable ONLY to Units with Steam Chest Inlet Configurations)
The S/LVDT VP Cards for the throttle valves are shown on this drawing. The analog common signal (TV*AZ1, generated by circuitry shown on drawing D05) is applied to the S/LVDT VP Cards on pin 2. The valve test input (TV*TZ1) is generated by cards 3D and 4J (upper right corner of drawing D06) and applied to pin 2 of the S/LVDT VP Cards. TV*TZ1 is a -15 V signal, generated by a contact closure. When the unit is in the Turbine Manual mode, the input to gate 3D (TM**Y1) becomes a 1 and removes the -15 V valve test input by energizing the relay. Thus, if a valve test is in progress and the unit goes to the Turbine Manual mode, the valve test is immediately terminated and the throttle valves are opened.
When the throttle valves are opened more than 90 percent, it is necessary to inhibit the throttle valve manual up/down counter from counting down, so that the throttle valves cannot be closed. This is accomplished with signal THI*X1 which is generated by card 2Q. An indication of throttle valve position is sent to the Digital Controller (A214, A215, A216, and A217) from pin 10 of the S/LVDT VP Cards. The position signals (TV1PZ1 through TV4PZ1) are analog voltages with a range of 0 to 10 Vdc.
Governor Valve Tracking System (Drawing D07)
Details of the logic portion of the governor valve tracking and manual control system are shown in this drawing. The essential elements of the governor valve analog control system are shown in this drawing and also in drawings D08, D09 and D10. As previously described, the output to the governor valve S/LVDT VP Cards is generated by an up/down counter, D/A converter and an operational amplifier.
In the quiescent state, the up/down counter (card 4R) has a 1 on pins 1 and 2. Input GVCUX1 on pin 2 is the raise signal; if this signal is 0, the counter counts upward at a rate determined by the clock rate signal (GVCKX1) applied to pin 8. A 0 is applied to pin 2, in the Turbine Manual mode, when the GV RAISE pushbutton on the Operator B Panel is pressed (GVIBY1, gate 3Q, pin 40, is a 1), the system is in Turbine Manual mode (TM**Y1, gate 3Q, pin 38, is a 1), and permissives are present.
When the DEH Control System is in the Operator Automatic mode (TM**X1, gate 3Q, pin 1, is a 1), the Analog Backup System tracks the Digital Controller by increasing or decreasing the up/down counter output. Tracking for an increasing signal is accomplished with signal GI**Y1; this signal is generated by the tracking comparator (see the description for drawing D08).
Several permissives must be present to enable the up/down counter to count up, as follows:
1. A high limit of 4500 counts must not have been reached (GVCHX1, gate 3M, pin 6, is a 1). GVCHX1 is determined by the signals at the inputs to gates 3N (pins 9, 11, and 13) and 3R (pins 4, 5, and 36).
2. An OPC test must not be in progress (OPC*Y1, gate 3R, pin 33, is a 0).
3. A runback must not be in progress (RBO*Y1, gate 3R, pin 6, is a 0).
4. A throttle pressure limiting action must not occur (TPL*Y1, gate 3R, pin 13, is a 0).
Input GVCDX1 on pin 1 of the governor valve up/down counter is the decrease signal; if this signal is a 0, the counter counts downward at a rate determined by the clock rate signal (GVCKX1) applied to pin 8. A 0 is applied to pin 1 when the GV LOWER pushbutton is pressed (GVDBY1) in the Turbine Manual mode (TM**Y1), or when the tracking signal (GD**Y1) is present in the Operator Automatic mode (TM**X1), and the counter has not reached a count of 0000 (GVCLX1). Also, the loss of auto stop latch (ASL*X2), throttle pressure limiting (TPL*Y1), runback (RBO*Y1), and OPC action (OPC*Y1) generates a decrease signal.
Pin 8 of the up/down counter is the clock rate input. Clock CLA is used during fast action (FAST ACTION pushbutton on Operator B Panel is pressed), tracking, and throttle pressure limiting. Clock CLB is used during normal raise and lower action. Clock CLM is used during OPC action and when the turbine is tripped (loss of auto stop latch). The X1 outputs of the counter are connected to the input of the digital-to-analog (D/A) converter, card 4R on drawing D07. The counter output is in an Aiken code.
Governor Valve Tracking System (Drawing D08)
The analog and transfer portions of the governor valve control are shown on this drawing. The Relay 4 (RC4) Card 3K, selects the output from either the Analog Backup System (GVMAZ2) in the Turbine Manual mode, or from the Digital Controller (GVAAZ2) in the Operator Automatic mode. The selected output (GV*AZ1) is sent to the S/LVDT VP Card, see drawing D09. Transfer of the relay is controlled by signal TM**X1; this signal is generated by circuits on drawing D15. The relay is shown in the deenergized state (Turbine Manual mode).
The output from the up/down counter (see drawing D07) is the digital input to the D/A Converter, card 4Q; the digital input is converted to a 0 to -10 V analog signal (GVMAZ1). This signal is one input to Mixing Amplifier 4 (MA4) Card (card 3J, pin 33). A +15 V bias is also applied to pin 32 upon loss of auto stop latch (ASL*X2) or OPC action (OPC*Y1). The bias ensures that the output of the mixing amplifier (GVMAZ2) will be negative on loss of auto stop latch or OPC action, regardless of the level of GVMAZ1.
In Operator Automatic mode, the Digital Controller output is converted from digital to analog form with a governor valve Single Valve A/O Card. A 0 to -10 V signal (GVAAZ1) is generated. GVAAZ1 is applied to card 3H (MA4 Card) and a bias is applied upon loss of auto stop latch or OPC action as described for the manual signal.
When the DEH Control System is in the Operator Automatic mode, manual tracking is accomplished by changing the up/down counter (previously described) until GVMAZ1 equals GVAAZ1. The Analog Comparator (AC7) Card 3G generates increase (GI**Y1) and decrease (GD**Y1) signals for this purpose. Bumpless transfer from Turbine Manual to Operator Automatic is implemented by the Digital Controller tracking the Manual Backup system. Signals GV*AZ1, GVMAZ2, and GVAAZ2 (analog inputs A218, A219, and A220) are used for this purpose.
Governor Valve Servo's (Drawing D09)
A typical S/LVDT VP Card and some additional circuitry are shown on this drawing. The analog common signal (GV*AZ1, generated by circuitry shown on drawing D08) is applied to the S/LVDT VP Cards on pin 3. The sequential valve input (GVAZ1) is applied to pin 5. The valve test input (GVTZ1) is applied to pin 2. The Track Hold Amplifier (THA) Card generates the valve test input. During a valve test, the input to the THA Card is supplied by the Digital Controller GV Test Analog/Output Card. Note that, in this operation, the "A" contacts in the THA Card must be closed.
If the DEH Control System is rejected to the Turbine Manual mode of operation during a valve test, the operator can ramp the THA Card output to 0 Vdc using the OPEN button on the Operator B Panel (card 3R, pin 14). An Analog Comparator 8 (AC8) Card (card 2Q) ensures that the THA Card output cannot be ramped above 0 Vdc. The signal on pin 7 of card 2Q (VTIPY1) is present only when the THA Card output is less than 0 Vdc.
The GV ADD meter on the Operator A Panel receives its input from a Mixing Amplifier 4 (MA4) Card, shown on this drawing (card 2P). An AC8 Card (card 2Q) compares the mixed governor valve position signal (GVAGZ1) with a +2.0 reference voltage (RV04Z1). The resulting signal (GVOMY1) is used in the throttle pressure limiting circuitry shown on drawing D07. GVOMY1 is also used in the throttle pressure control circuitry shown on drawing D14.
Digital and Analog Speed Channels (Drawing D11)
Both the analog and the digital speed channels are shown on this drawing. The output of the analog speed channel cards (SPD*Z3) is checked against a high and a low limit; if either limit is exceeded, corresponding failure signals (SCFLY1 for low and SCFHY1 for high) are generated. SPD*Z3 is also compared to an overspeed set point (OSTPZ1) which is generated by a scaling amplifier (card 6C). The resulting signal (SPD*Y1) indicates when the speed is above the set point. If the speed is above the set point, and the Digital Controller has determined that no failure has occurred in the analog speed channel (CSCFX1), and the high limit has not been exceeded (SCFHX1), a signal (SMH*Y1) is generated for use by the Overspeed Protection Controller (OPC) circuitry (see drawing D12).
The analog speed channel signal is also applied to the rpm meter on the Operator A Panel, and to the Digital Controller. The controller uses the analog speed signal (SPD*Z6) in a two-out-of-three selection process to determine which speed channel is to be used. Circuitry for a portion of the digital speed channel is also shown on this drawing. The digital circuitry consists of a coarse channel (used for the entire speed range) and a fine channel (used only above 1600 rpm-synchronous speed).
The speed input (sine-wave frequency) is applied to Speed Channel A (SCA) Card 6Q. This card doubles and shapes the input and applies its output (through logic circuitry) to a Counter (CC) Card in the Digital Controller. The CC Card feeds a Register Comparator (RK) Card; the RK Card output is applied to the computer. This channel (coarse) works for the whole range of turbine speed; it has an accuracy of +10 rpm. A 0.1 sec time base is provided by a 36 kHz clock which is counted by another CC Card.
The fine channel counts the 36 kHz clock for a period of time dependent on the speed input. This method increases the accuracy to .+-.1 rpm at 3600 rpm (since the clock pulse might be missing). However, the fine channel can be used only above 1600 rpm. In both cases, the Digital Controller uses a software program to determine the speed channel used and the count.
Overspeed Protection Control--OPC (Drawing D12)
The OPC circuits are shown on this drawing. When the DEH Control System is on speed control, the overspeed protection signal (OPC*Y1, card 4F, pin 37) controls the governor valves using the SMH*Y1 signal (gate 4F, pin 40). This signal indicates that the speed is over 103 percent and is generated by circuitry shown on drawing D11. Note that, if an overspeed test is in progress, the overspeed protection signal (OPC*Y1) cannot be generated. OPC*Y1 closes the governor valves if the speed is above 103 percent.
When the DEH Control System is on load control, OPC*Y1 controls the governor using the Load Drop Anticipation signal (LDA*X1). LDA*Z1 is generated by HTL Latch 1 (HTLL1), pin 10. The latch is set when a mismatch exists between the kilowatt transducer signal and the OPC pressure transducer signal, and neither transducer has failed. The latch is reset 10 sec after the overspeed condition clears and the breaker is opened.
The transducer signals are compared with reference voltages (cards 4A and 4C) to determine sensor failure. The reference voltages for the OPC pressure transducer are -0.5 V and -5.5 V; the reference voltages for the kW transducer are -0.5 V and -10 V. The OPC pressure and kW transducer signals are also compared with an adjustable (from the Test and Calibration Panel) mismatch set point to determine the mismatch. Also, the kW transducer signal is compared with a reference set point to ensure that the load is greater than 30 percent before the LDA operates.
The Close Interceptor Valve latch (CIV--card 4H, pins 29 and 30) is set by the same signal (DAA*Y1) that sets the LDA latch. The CIV latch is reset when the breaker opens, after an adjustable time delay, or upon receiving a block CIV (BCIVX1) signal from the Digital Controller. The CIV*Y1 signal (card 4H, pin 6) energizes a relay shown on drawing D17. The relay contacts are wired externally to close the interceptor valves.
Throttle Pressure Control--TPC (Drawing D14)
The TPC circuits are shown on this drawing. The TPC latch (card 5E) indicates the status of the TPC system. If the latch is set, the output of the comparator which compares the throttle pressure signal (TPA*Z1) and the set point (TPSPZ1) is gated through gate 5C (pin 40). This causes the throttle pressure limiting signal (TPL*Y1) to be true. If the TPC latch is reset, TPL*Y1 is false. Signal TPL*Y1 closes the governor valves, as described in the Governor Valve Tracking System D07 description.
In the Turbine Manual mode of operation, the TPC latch is set when the TPC IN/TPC OUT pushbutton is pressed the first time. If this pushbutton is pressed again, the TPC latch is reset. In the Operator Automatic mode of operation, a contact closure from the Digital Controller (CTPCX1) sets the TPC latch. As long as the closure is maintained, the latch remains set; when the contact is opened, the latch is reset. A throttle pressure transducer failure (high or low) and the breaker opening also resets the TPC latch. Status contacts for TPC in service and TPC limiting are provided. A TPC in service contact is also provided to the Digital Controller. In addition, the Lamp Driver (LD) Cards and associated lamps (TPC IN/TPC OUT) are shown on this drawing.
THE P2000 COMPUTER SYSTEM
The preferred embodiment of the present invention is implemented using elements of the P2000 computer system designed and built by the Hagan/Computer Systems Division of Westinghouse Electric Corporation, Pittsburgh, Pennsylvania. Since many facets of the monitored and controlled system are affected by the nature of the computer system, at least a partial knowledge of the P2000 computer system will aid in reaching a full understanding of the invention.
FIG. 69 is a greatly simplified block diagram of the P2000 computer system. The system is designed around a central processing unit 200 having an addressable core memory 240. Each addressable location within the core memory contains 16 bits of data. In addition to the core memory 240, the P2000 system may be equipped with one or more disk or drum, high-speed, peripheral storage units 255. A variety of data input/output devices and options are available including an analog-to-digital converter input 260, contact closure inputs 270 and outputs 280, analog outputs 290, a variety of console display devices 250, and various input/output and interrupt options 230. A control unit 210 controls the operation of the central processing unit 200.
The arithmetic and logic portions of the P2000 computer system are shown in FIG. 70. Six system hardware registers P, B, C, G, E, and A are organized in such a way that their contents may be addressed as though they were part of the system core memory. A program address hardware register P is addressed as memory location zero. Two hardware index registers B and C are addressed as memory locations 1 and 2. A hardware shift code register G, the contents of which are used to control data shifting operations, is addressed as memory location 3. A hardware arithmetic accumulator A and a hardware extended arithmetic accumulator E (sometimes referred to as registers A and E) are respectively addressed as memory locations 5 and 4. Data may be transferred into or retrieved from these registers in the same manner that data may be transferred into or retrieved from any location within the system core memory, but at a higher rate of speed due to the hardware nature of these registers.
Arithmetic operations, such as addition, subtraction, multiplication and division are carried out by an adder 2009. Input data for this adder is presented by a data buffer register 2003 and by a memory read data register 2004. The particular operation which is carried out is determined by the contents of a function code register 2007, a mode register 2006, and a designator register 2005 which is sometimes referred to as register D.
When an instruction is to be executed, the address of that instruction is placed in the memory address register 2001. An address selector 2002 causes the contents of that location to be transferred into the function code register 2007 and into the mode register 2006. The function code register 2007 determines what is to be done, and the mode register 2006 together with the designator register 2005 determine how address computations are to be carried out. Data from the core memory is transferred into the memory read data register 2004. Additional data which is to be included in a computation is placed in the data buffer register 2003. The result of a computation is transferred back into core or into one of the hardware registers which occupy the six lowest addresses of the core memory. In the case of input/output instructions, the system hardware communicates directly with the input/output device or devices 2008. Data is transmitted either directly from register A to the input/output device or from the device to register A.
The designator register 2005 is loaded by special programming instructions so as to determine the mode of operation of the system. Bits of data may be placed in this register to lock out completely all types of interrupts. At the end of an arithmetic computation, the result of the computation (positive, zero, overflow, or carry) is indicated by bits within the designator register. The designator register is also used to aid in addressing. Bits may be set within the designator register to cause automatic post indexing using either the contents of index register B or the contents of index register C. When the system is operating with the designator register adjusted for post indexing using the contents of register C, for example, the contents of register C are added to the result of every address computation involving the use of the index register B.
The central processor of the P2000 system includes an executive monitor program package (FIG. 71B) which provides for the simultaneous handling of 16 different tasks. Each of the 16 tasks is assigned to a task (or priority) level between "O" and "F" (using hexadecimal numbers). These tasks are fully interruptable. Hence, if task "3" is runing at a time when a request for the execution of higher priority task "6" is received, the execution of task "3" is immediately suspended until the execution of task "6" is completed. The execution of task "3" is then recommended where it left off.
Bids for the execution of a program assigned to an executive task level may be placed by a program (for example, the program 2306) operating within a task level (in this case, the task level D.sub.16), by a program operating within the system interrupt level 2305 in response to an external interrupt EI or a service request interrupt SRI, or by a program operating under software lockout 2303. In every case, an executive program 2304 records the bid in the table shown in FIG. 71A. Each such bid is recorded within an "able" word bit whose position corresponds to the task level of the program for which the bid has been placed. For example, the seventh bit position within the "able" word (FIG. 71A) contains a "1" data bit indicating that a program within the seventh task level is bidding for execution. Program control is then transferred to a task scheduler program 2302. The task scheduler program 2302 examines the contents of the able word (FIG. 71A) and determines which is the highest priority task level that is bidding for execution by examining the bits in the able word one at a time. An active word (FIG. 71A) is also provided so that a particular task level may be disabled. If the bit corresponding to a task level in the active word is "0", then the task level is disabled and the programs assigned to that task level are not run. When software lockout is in effect, the program which is running runs at a software lockout priority level 2303 which is higher than the priority level of the remaining programs in the system 2301 and which may only be interrupted by an external interrupt coming in at the interrupt level 2305. When a program running under software lockout bids for execution of a task level, the task level bid is recorded in the able word (FIG. 71A) and then program control is returned to the program running under software lockout rather than to the task scheduler 2302. Only when software lockout is released does program control return to the task scheduler 2302.
The executive program which calls for the execution of individual task levels is called the executive scheduler or task scheduler 2302 (FIG. 71B). Within the scheduler are located two sets of tables containing one entry for each task level within the system. The first is called the Z:ORIG table 2301 in FIG. 71B and "Z:ORIG" in FIG. 73. Each entry in this table is the starting address of a task header 10/220 (FIG. 73). The address of the Z:ORIG table entry for a particular task is found by adding the task level number to the starting address "Z:ORIG" of the table. A typical task header is shown in FIG. 73 at 10/220. Each task header contains data which is loaded into the system hardware registers P, B, C, G, E, A, and D (register D is the designator register - see FIG. 70) at the time when the corresponding task is given program control. The first location within the task header is loaded into the system program counter register P and is the address of the location which immediately precedes a location containing the first executable command of the task level. For example, in FIG. 73, the first location in the task header contains the address of a location SPEXIT. When the scheduler calls for execution of this task, program control commences at location SPEXIT+1 within the core memory.
A second table within the scheduler is called the Z:START table (FIG. 73). Each entry in this table is the starting address of a register storage pool for a task. The register storage pool may be any group of seven consecutive core locations into which the data contents of the registers P, B, C, G, E, A, and D (see FIG. 70) may be placed when the execution of a task is interrupted. If the execution of a task is interrupted before the task runs to completion, the contents of these seven system registers are loaded into the task register storage pool. When execution of the task is restarted, the contents of the register pool are reloaded into "CORE" locations 0 through 5 and into the designator register. Execution of the interrupted task then automatically proceeds from the point of interruption.
In order to speed up the process of testing or of manipulating a single data bit within a 16 bit group of data bits occupying a core location, the system can include a bit mask table BITTBL. The table starting address is "BITTBL", but this starting address is occasionally referred to as "K:X1" by some system subroutines. The mask for a particular bit position with a group of 16 bits is found by adding a bit position number to the starting address of the bit mask table. Each bit within a group of 16 bits is assigned a bit position number between 0 and 15 or "F.sub.16 " (again using hexadecimal numbers). The right-most bit in a group is the bit position 0, and the left-most bit is the bit position 15 or "F.sub.16 ". Thus, the second location within the bit mask table contains the binary number "0000000000000100". This location contains a "1" in a bit position 2, and may be used to test or to manipulate the second bit position within any group of 16 bits. The following 2 bit manipulation commands are available within the P2000 system: AND and EXOR (exclusive OR). Any other logical operation may be carried out using logical combinations of these two commands.
When a program within the P2000 system wishes to call for the execution of a subroutine, the program usually executes a command:
Prior to executing this command, index register B contains the address of the last location in a register storage pool. The above command stores the contents of the seven system registers (P, B, C, G, E, A, and D) in the register storage pool and subtracts "7" from the contents of register B so that index register B contains the address of the location just preceding the pool. Program control is then transferred to the subroutine. The first executable subroutine statement must reside in the location having an address one greater than the address stored in the location X. The subroutine must take steps to preserve the address which is stored in index register B, since this address must be available when program control is returned to the calling program. If any arguments are to be transferred to the subroutine from the calling program, the addresses of these arguments are stored in the locations immediately following the SST instruction, and the subroutine calls upon a standard argument fetching subroutine which retrieves the argument addresses and transfers the addresses to the subroutine.
When a subroutine has run to completion, register B is reloaded with the address of the location just preceding the register storage pool. The following command is then executed:
This command reloads the system registers from the calling program pool and adds "7" to the address stored in register B. Program execution within the calling program then resumes automatically with register B again pointing to the last location within the register storage pool.
The program registers P, B, C, G, E, and A are stored in the register storage pool in the exact order in which they appear in the "CORE" memory in FIG. 70. The contents of the designator register D are stored in a seventh location in the pool just beyond that in which the contents of register A are stored.
If a core location contains a negative number, the number is a 15 bit binary number in two's complement form, and the left-most bit (bit position F) in the core location is a sign bit equal to "1". If a core location contains a positive number, the number is a 15 bit binary number in standard form, and the left-most bit is a sign bit equal to "0". Often when the contents of the core location are discussed, those contents are represented as a 4 digit hexadecimal number, and the sign bit is included as part of the first digit in the hexadecimal number. For example, a core location containing +1 is said to contain the hexadecimal number "0001.sub.16 "; a core location containing -1 is said to contain the hexadecimal number "FFFF.sub.16 ".
The executive scheduler within the P2000 system includes a software lockout provision for preventing a first program from interrupting the execution of a subroutine called by a second, lower priority program. Such an interruption can be undesirable. If the first program were allowed to interrupt the second and to call for execution of the same subroutine, data values relating to the second program and stored within the subroutine would be destroyed. A subroutine establishes software lockout by adding "1" to the present value of a software lockout counter having the symbolic name Z:SFL. Software lockout is in effect whenever the counter Z:SFL has a numeric value that is greater than 0. As long as software lockout is in effect, the executive scheduler accepts bids for the running of any task level but does not execute the bids until software lockout is "replaced"--that is, when Z:SFL equals 0. When a bid is received by the executive scheduler during software lockout, a call flag whose symbolic name is Z:CALL is set. The flag Z:CALL is set by adding "1" to the present value of the flag.
When the subroutine executed under software lockout has run to completion, index register B is loaded with the address of the calling program. Program control is then transferred to an executive software lockout release program whose symbolic address is stored in a location M:SFX. The executive software lockout release program subtracts 1 from the software lockout counter. If the counter then contains 0 count, the program checks the scheduler call flag Z:CALL. If the scheduler call flag indicates that task level bids have been received during the software lockout interval, program control is transferred to an executive scheduler task bidding routine. If the scheduler flag is not set, then no bids for the execution of other task levels were received during software lockout, and program control is returned by the standard subroutine exit procedure to the calling program.
Software lockout is used by many of the subroutines within the process control system. To simplify the discussion which follows, no mention is made of software lockout except in connection with the discussion of the CHKBID subroutine 10/1400 which has its own special software lockout release procedure.
The software lockout steps included in a program listing generally take the following form:
The "INC" step places software lockout in effect, and the JMP step is an executive call requesting the release of software lockout.
The analog-to-digital converters within the computer system are of the counter integration type. A typical converter is shown in FIG. 72A. The computer supplies channel, word, and bit selection signals to an analog input selector which connects one of a plurality of analog input signals to the analog-to-digital converter 265. A voltage-to-frequency converter 261 converts the incoming signal into a pulse train whose frequency is proportional to the magnitude of the incoming signal. A control 264 then allows the pulse train from the converter 261 to pass through a gate 262 to a counter 263 normally for exactly 1/60 of a second so that any 60 cycle noise pickup does not affect the result of the signal measurement (see FIG. 72B). The count upon the counter 263 is then transferred back to the central processor unit. This count is the digitized analog signal input value.
A typical system includes anywhere from 1 to 10 of these converters running in parallel. The executive handlers which control the operaton of these converters function by transmitting the necessary channel, word, bit, and gain figures to the converters at the request of other system programs. If a converter is busy, the program task level which is attempting to use the converter is automatically suspended until the converter is free.
In a typical analog scan application, analog signal input requests are transmitted to each of the converters in sequence until all of the converters are busy. A second request is then transferred to the first converter. Since this request may not be processed immediately, the task level containing the program which is attempting to retrieve analog signal data is suspended until the converters have finished retrieving the first set of data. At that time, the request to have the first converter input a second analog signal is processed, and simultaneously the result of the initial analog input request is returned to the calling program by the first converter. In a similar manner, each subsequent request to have a converter process an analog signal input causes the queried converter to return the result of an earlier request. After the last group of requests have been supplied to the converters, it is necessary to then make a final "dummy" request to the converters so that the converters are able to return the results of the last group of actual requests.
The system includes routines for handling contact closure inputs and outputs. Executive contact closure input handler routines check the status of contact closure inputs and maintain an accurate record of the status of each contact closure input within digital tables. A contact closure output handler alters the status of the system contact closure outputs at the request of any program within the system. This same handler routine is also able to service digital to analog outputs of the system. A typical digital-to-analog converter comprises a network of resistors which converts a binary number into an analog signal. Such a converter has a binary number input which is connected to an array of the system contact closure outputs and it has an analog signal output. By presenting appropriate data bits to the array of contact closure outputs, the contact closure output handler is able to generate any desired analog signal output. ##SPC5## ##SPC6## ##SPC7## ##SPC8## ##SPC9## ##SPC10##
APPENDIX 6
COMPUTER PROGRAM LISTING
The following computer program listing was compiled from a FORTRAN program and represents instructional information used in the DEH system in the digital computer to provide steam turbine operation including automtic startup, speed and load control, data monitoring, operator interface, etc. The listing represents an operative program system which substantially conforms to the system description presented elsewhere herein. ##SPC11## ##SPC12## ##SPC13## ##SPC14## ##SPC15## ##SPC16## ##SPC17## ##SPC18## ##SPC19## ##SPC20## ##SPC21## ##SPC22## ##SPC23## ##SPC24## ##SPC25## ##SPC26## ##SPC27## ##SPC28## ##SPC29## ##SPC30## ##SPC31## ##SPC32## ##SPC33## ##SPC34## ##SPC35## ##SPC36## ##SPC37## ##SPC38## ##SPC39## ##SPC40## ##SPC41##
Claims
We claim as our invention:
1. A digital electrohydraulic control system for a steam turbine having at least two throttle valves and a plurality of downstream governor valves, said control system comprising an automatic digital control for generating valve position signals to operate the valves and control the turbine speed and load in response to predetermined input signals, a manual backup control for generating control signals to operate the valves for speed and load control when the automatic control is nonoperational, said automatic control including means for generating a throttle valve test select signal, means for digitally generating at least one test signal for closing the governor valve or valves downstream from a throttle valve selected for test, means for generating signals to close and reopen the test throttle valve when the downstream governor valves are closed, means for enabling the governor valves to be reopened after the throttle valve test, and means for disabling said test closing signal generating means from operating if said backup control is operating the valves when a throttle valve test selection is made.
2. A turbine control system as set forth in claim 1 wherein said automatic digital control includes a digital computer to which the test select signal is applied and from which the governor valve test signal and the throttle valve close and reopen signals are generated.
3. A digital electrohydraulic control system for a steam turbine having at least two throttle valves and a plurality of downstream governor valves, said control system comprising means for digitally generating at least one test signal for closing the governor valve or valves downstream from a throttle valve selected for test, means for generating signals to close and reopen the test throttle valve when the downstream governor valves are closed, means for enabling the governor valves to be reopened after the throttle valve test and means for increasing or decreasing the test governor valve closure signal in incremental steps to enable said automatic speed and load control to open or close the nontest governor valves as the test path governor valves are closed or open and thereby control turbine speed or load during a throttle valve test.
4. A turbine control system as set forth in claim 3 wherein said automatic digital control includes a digital computer to which the test select signal is applied and from which the governor valve test signal and the throttle valve close and reopen signals are generated and from which valve position setpoint signals are generated, and an electrohydraulic position control for operating the governor and throttle valves in response to the position setpoint signals.
5. A turbine control system as set forth in claim 4 wherein said computer generates a single governor valve test signal which is applied to said electrohydraulic position control.
6. An electric power plant comprising a steam turbine and an electric generator coupled thereto, said turbine having a plurality of throttle and governor valves for controlling the flow of steam therethrough, a digital electrohydraulic control system for generating valve control signals to operate the valves and control the turbine speed and load in response to actual and demand turbine speed and load signals, a manual backup control for generating control signals to operate the valves for speed and load control when the automatic control is nonoperational, said automatic control including means for generating a throttle valve test select signal, means for digitally generating at least one test signal for closing the governor valve or valves downstream from a throttle valve selected for test, means for generating signals to close and reopen the test throttle valve when the downstream governor valves are closed, means for enabling the governor valves to be reopened after the throttle valve test, and means for disabling said test closure signal generating means from operating if said backup control is operating the valves when a throttle valve test selection is made.
7. An electric power plant as set forth in claim 6 wherein said automatic digital control includes a digital computer to which the test select signal is applied and from which the governor valve test signal and the throttle valve close and reopen signals are generated.
8. An electric power plant comprising a steam turbine and an electric generator coupled thereto, said turbine having a plurality of throttle and governor valves for controlling the flow of steam therethrough, a digital electrohydraulic control system for generating valve control signals to operate the valves and control the turbine speed and load in response to actual and demand turbine speed and load signals, a manual backup control for generating control signals to operate the valves for speed and load control when the automatic control is nonoperational, said automatic control including means for generating a throttle valve test select signal, means for digitally generating at least one test signal for closing the governor valve or valves downstream from a throttle valve selected for test, means for generating signals to close and reopen the test throttle valve when the downstream governor valves are closed, means for enabling the governor valves to be reopened after the throttle valve test, said automatic control further including means for increasing or decreasing the test governor valve closure signal in incremental steps to enable said automatic speed and load control to open or close the nontest governor valves as the test path governor valves are closed or opened and thereby control turbine speed or load during a throttle valve test.
9. An automatic digital electrohydraulic control system for a steam turbine having a plurality of throttle and governor valves, said control system comprising means for generating respective signals representataive of the turbine speed and load, an electrohydraulic control for positioning the throttle and governor valves in response to valve position signals, and means for digitally generating valve position signals in response to a turbine speed or load demand and the turbine speed and load signals, said digital generating means including a speed/load control for generating a speed or load reference to satisfy the demand, a throttle valve control and a governor valve control for generating the valve position signals during speed and load control, and means for logically determining in response to predetermined inputs whether the reference is to be coupled to said throttle valve control or said governor valve control during speed and load control, said governor valve control further including means for storing representations of at least six points on a valve position versus load characterization, means for generating a position representation interpolated from the stored characterization points in correspondence to the generated reference, and means for generating the governor valve position signals in correspondence to the position representations.
10. A control system as set forth in claim 9 wherein said digital generating means includes a digital computer which generates the valve position signals.
11. A control system as set forth in claim 10 wherein there is provided in said computer a speed/load control including means for generating GO and HOLD logicals in response to predetermined inputs, means for comparing the demand with the reference and for comparing the resultant difference with a predetermined incremental reference change value, means for changing the reference by the incremental amount if the GO logical is true and if the difference exceeds the incremental amount and for setting the reference equal to the demand if the incremental amount exceeds the difference.
12. An electric power plant comprising a steam turbine and an electric generator coupled thereto, said turbine having a plurality of throttle and governor valves for controlling the flow of steam therethrough, and an automatic digital electrohydraulic control system having means for generating respective signals representative of the turbine speed and load, an electrohydraulic control for positioning the throttle and governor valves in response to valve position signals, and means for digitally generating valve position signals in response to a turbine speed or load demand and the turbine speed and load signals, said digital generating means including a speed/load control for generating a speed or load reference to satisfy the demand, a throttle valve control and a governor valve control for generating the valve position signals during speed and load control, and means for logically determining in response to predetermined inputs whether the reference is to be coupled to said throttle valve control or said governor valve control during speed and load control, said governor valve control further including means for storing representations of at least six points on a value position versus load characterization, means for generating a position representation interpolated from the stored characterization points in correspondence to the generated reference and means for generating the governor valve position signals in correspondence to the position representations.
13. An electric power plant as set forth in claim 12 wherein said digital generating means includes a digital computer which generates the valve position signals.
14. A digital electrohydraulic control system for a steam turbine having at least two throttle valves and a plurality of downstream governor valves, said control system comprising means for generating respective signals representative of the turbine speed and load, an electrohydraulic control for positioning the throttle and governor valves in response to valve position signals, an automatic digital control for generating valve position signals to operate the valves and control the turbine speed and load in response to predetermined input signals, a manual backup control for generating control signals to operate the valves for speed and load control when the automatic control is nonoperational, said automatic control including means for digitally generating valve position signals in response to a turbine speed or load demand and the turbine speed and load signals, said digital generating means including a speed/load control for generating a speed or load reference to satisfy the demand, a throttle valve control and a governor valve control for generating the valve position signals during speed and load control, and means for logically determining in response to predetermined inputs whether the reference is to be coupled to said throttle valve control or said governor valve control during speed and load control, means for sensing when predetermined task errors are made by said digital generating means, and means for uncoupling said automatic control and for coupling the manual backup control to the valves when preselected ones of the task errors occur.
15. An electric power plant comprising a steam turbine and an electric generator coupled thereto, said turbine having a plurality of throttle and governor valves for controlling the flow of steam therethrough, and an electrohydraulic control system having means for generating respective signals representative of the turbine speed and load, an electrohydraulic control for positioning the throttle and governor valves in response to valve position signals, an automatic digital control for generating valve position signals to operate the valves and control the turbine speed and load in response to predetermined input signals, a manual backup control for generating control signals to operate the valves for speed and load control when the automatic control is nonoperational said automatic control including means for digitally generating valve position signals in response to a turbine speed or load demand and the turbine speed and load signals, said digital generating means including a speed/load control for generating a speed or load reference to satisfy the demand a throttle valve control and a governor valve control for generating the valve position signals during speed and load control, and means for logically determining in response to predetermined inputs whether the reference is to be coupled to said throttle valve control or said governor valve control during speed and load control means for sensing when predetermined task errors are made by said digital generating means, and means for uncoupling said automatic control and for coupling the manual backup control to the valves when preselected ones of the task errors occur.
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