Turbine Power Plant Automatic Control System

(1) "System And Method For Starting A Steam Turbine With Digital Computer Control" by Gerald E. Waldron, Ser. No. 247,885, filed Apr. 26, 1972, which relates to a digital start-up system where the start-up sequence is resumed "on the fly" after being taken out of automatic control.

(2) "System And Method For Operating A Steam Turbine With Digital Computer Control Having Automatic Startup Sequential Programming" by Juan J. Tanco, Ser. No. 247,598, filed Apr. 26, 1972, which relates to a digital system in which rotor stress and/or differential expansion is compared with predetermined limits in controlling the start-up of the turbine.

(3) "System And Method For Operating A Steam Turbine With Digital Computer Control And With Improved Monitoring Capability" by Donald J. Jones, Ser. No. 247,600, filed Apr. 26, 1972, which application is directed to a digital system for processing of monitored turbine operations during automatic start-up.

(4) "System And Method For Organizing Computer Programs For Operating A Steam Turbine With Digital Computer Control" by Robert Uran and Juan J. Tanco, Ser. No. 247,887, filed Apr. 26, 1972 and continued as Ser. No. 391,406, filed Aug. 24, 1973, which application is directed to an automatic start-up system wherein the turbine is started, synchronized in accordance with speed control signals which is governed by turbine parameters in a predetermined priority.

(5) "System And Method For Improved Steam Turbine Operation" by Robert L. Osborne, Ser. No. 331,738, filed Feb. 13, 1973, which is directed to a system where the steam flow to the turbine is controlled as a function of heat flow.

(6) "Anticipative Turbine Control" by Robert L. Osborne, Ser. No. 549,568, filed Feb. 13, 1973, which application is directed to a system where the speed and acceleration of the turbine is controlled as a function of predicted future heat transfer conditions.

The present invention relates to turbine power plants; and more particularly, to an improved system for controlling the dynamic operation of turbines automatically without operator intervention.

Turbine power systems typically include a high pressure (HP) turbine section where the steam is introduced directly from the steam generator. The steam from the HP turbine section after being reheated is introduced into a reheat turbine section, which in the case of fossil-fired steam generating systems is commonly termed the (IP) turbine section; and then into a low pressure turbine section before exhausting to the condenser. A rotor having an axial bore passes centrally through the turbine casings; and rotation of the rotor is achieved by passage of the steam over blades alternately affixed to the rotor and to the casing. The generator, which is affixed to the rotor, may be cooled by hydrogen has (H.sub.2).

The rotor of the HP turbine section may be typically in the order of 24 inches in diameter, for example, and the IP turbine section, includes a rotor which may be in the order of over forty inches in diameter. The IP rotor surface is replete with grooves and other irregularities, particularly where the turbine blades are affixed.

It is well known, that whenever the turbine is to undergo changes in speed, and the generator is to undergo changes in load, care must be taken lest damage be done either by thermal stresses, thermal expansion of adjacent parts of different rates, or by exceeding the capability of the generator. A turbine which undergoes thermal stress caused by uneven heat distribution in the rotors, tends to develop cracks at locations on the rotor most exposed to the widest and most frequent steam temperature variation. Also, such cracks will occur when the turbine is accelerated at too fast a rate when the turbine rotors are not of uniform temperatures.

The present invention is an improvement over the prior art system, as disclosed in U.S. patent application Ser. No. 408,962, which is a continuation of Ser. No. 247,887, filed by Theodore C. Giras and Robert Uran, on Apr. 26, 1972, entitled "System And Method For Starting, Synchronizing, And Operating A Steam Turbine With Digital Computer Control" and assigned to the assignee hereof, which is, in its entirety, hereby incorporated into the present application by reference. This referenced application, which discloses an automatic system for starting up a turbine includes certain details which form one part of the invention of the present system including the features of the related referenced applications (1) through (4) and shall be referred to hereinafter as the Giras application.

The Giras application includes an automatic start-up system for steam turbine power plant which controls the turbine under the thermal constraints of HP rotor stress from rolling off turning gear to synchronous speed, and the application of initial load. The system monitors plant conditions to inform the operation of dangerous conditions after the application of initial load. The Giras start-up system recognizes that the IP rotor is considered the most critical for speeds above the heat soak speed of approximately two-thirds synchronous speed when the rotor temperature is below 250.degree. F. The rotor metal is in a brittle state below 250.degree. F. which may result in the development of cracks in the event of excessive speeds.

In the Giras system, the turbine is prevented from exceeding the heat soak speed for a period of time based upon a time versus temperature curve, which must be conservatively estimated in order to protect the turbine. Specifically, the computation of this heat soak time, or time versus temperature curve, is based conservatively on the lowest of four calculated temperatures. A comparison is made between the calculated (1) the rotor volume average temperature which existed before opening the steam inlet valves, (2) the rotor volume average temperature at 2200 rpm's, (3) the first stage turbine metal temperature before opening the steam inlet valves. (4) and the first stage metal temperature at 2200 rpm's. When the heat soak speed has been reached, the amount of heat soak time is determined, based upon the lowest temperature selected from the above for a reheat steam temperature of 500.degree. F. Once the soak time is completed, a final check on the HP rotor volume average temperature is made before declaring that the heat soak is complete and allows the turbine to continue acceleration. In the event that the lowest of these temperatures is above 250.degree. F., the heat soak is considered unnecessary.

After the predetermined heat soak time is completed, the system accelerates the turbine to approximately 3300 rpm's at a rate which is determined by a calculated HP rotor strain which is compared to a selected rotor strain limit. After the system automatically transfers from throttle to governor valve control at 3300 rpm's the turbine is accelerated to synchronous speed. After the application of a minimum load, the system is supervisory only, that is, various parameters are monitored and appropriate messages are printed to assist the operator in the control of the turbine up to the desired load.

In the Giras application, the HP rotor surface thermal strain is proportional to the surface-to-volume average temperature differential and determines the acceleration of the turbine. A comparison of the present thermal strain value with previous thermal strain values determines the type of thermal transient that the rotor is undergoing, and selects the proper acceleration path to be followed. The rotor surface temperature is calculated as a function of the first stage HP steam temperature, the present heat transfer coefficient, and the history of the temperature of the rotor metal. The magnitude of the rotor strain is determined by the surface-to-volume average rotor temperature which is utilized to determine the rotor surface strain based on present and past history. The heat transfer coefficient is computed as a function of speed reaching its higher value in the speed mode at rated speed.

The system of the Giras application is advantageous in so far as it rotates to start-up of the turbine through the application of initial load; however, the heat soaking of the critical IP turbine rotor is based on a time versus temperature curve, which may result in an unnecessary elapsed time. With such elapsed heat soak time consecutively estimated, the HP rotor stress calculations provided sufficient thermal stress protection for automatic operation up to synchronous speed.

With respect to the calculation of HP rotor strain and various means for controlling the turbine in accordance with such strain, reference is made to U.S. Pat. No. 3,448,265, entitled "System And Method For Providing Steam Turbine Operation With Improved Dynamics", by William R. Berry, and assigned to the present assignee, in which there is discussed in detail the effects of thermal loading on permissible turbine operation, which is incorporated by reference herein for the purpose of indicating the background of certain aspects of the present invention. The referenced patent to Berry discloses an improved method of determining present rotor stress as a function of monitored HP turbine impulse chamber steam temperature, comparing the present stress with a predetermined stress limit, and deriving a control signal from such comparison, by which inlet steam to the HP turbine is controlled. In such a prior art system, the impulse chamber steam pressure at the HP turbine section may be further controlled by considerations of rotor bore loading or casing strain. The effects of thermal expansion and contraction of respective regions of the turbine are thus controlled as a function of calculated stress at such regions, which calculations are based upon the monitored inlet steam condition, centrifugal force loadings, and other input variables.

The Berry patent teaches that bore thermal stress calculations can be made for the reheat turbine by determining the rotor surface temperature in the inlet steam region of the reheat pressure section based upon the measured reheat inlet chamber steam temperature and the variable and lower heat transfer conductance of the reheat rotor surface in the same manner as the HP turbine.

Berry suggests that on-line rotor bore loading determinations can be eliminated in the event that a predetermined heat soak time is utilized in the start-up procedure. Berry mentions that the heat transfer conductance of the IP turbine is further determined as a predetermined function of the IP steam flow and IP steam density or pressure; that is

where W.sub.s = actual turbine speed, SF= IP steam flow, and P.sub.IP = IP steam pressure, and K.sub.(IS).sub..sbsb.i.sbsb.p is the heat transfer conductance of the IP rotor.

Another specific prior art example of turbine operation based upon considerations of rotor stress is disclosed in a patent to Zwicky, U.S. Pat. No. 3,446,224, issued May 27, 1969. This patent calculates rotor bore and surface stresses by means of temperature and speed measurements; and calculates safe stress margins, and applies the lowest of the surface or bore safe stress margin as either an acceleration reference signal or a load rate reference signal to control the acceleration and load of the turbine. Calculations of bore stress and bore temperature are made by periodically taking the inner casing steam temperature at three consecutive time intervals and multiplying by predetermined constants. Only the time intervals are varied according to the diameter of the rotor. In Moore, U.S. Pat. No. 3,561,216 issued Feb. 9, 1971, there is disclosed a rotor stress controlled system which calculates rotor stress in the same manner as the patent to Zwicky. In this patent, the rate of loading and the single-to-sequential transfer of the valves is governed by the highest stress of all the calculated thermal stresses. U.S. Pat. No. 3,577,733 issued to Manuel on May 4, 1971 discloses a method of loading a steam turbine and transferring between partial arc and full arc steam admission modes during loading while maintaining a constant rate of heating.

In each of the prior art examples, different systems are disclosed for preventing either cyclic variations in the temperature of the turbine rotors or for calculating rotor stress in order that a turbine may be operated without undue thermal strain. These patents recognize that the greatest thermal differences occur in the high pressure rotor because of differentials in steam temperature and small diameter of the rotor; and the patents to Berry and Zwicky suggest that such stress can be calculated with respect to the reheat turbine rotor as well as the high pressure turbine rotor by taking a longer time for heat conductance.

An automatic turbine control system which controls the turbine without operator intervention up to application of a desired operator entered load must be efficient in its operation; and take into consideration any undesirable conditions of operation that would tend to shorten the life of the component parts of the plant. In so doing the system should have versatility such that the undesirable conditions can be prevented, or rectified without interrupting turbine operation. In furtherance thereof, it is desirable that the system can increase or decrease the rate of loading in accordance with such conditions up to an operator entered medium.

The thermal stress of the rotors, both HP and IP should be considered for such a system, as well as the constraints of the electric generator. Also, such a system should control in real-time through all phases of its operation, with proper predictions of what will occur in the event the system is controlling the plant at a certain rate of increased load.

In determining the thermal stress of the IP turbine rotor, such a system should provide for the critical stress points that exist axially along the rotor as well as provide for different stresses for different types of blade mountings.

Broadly, the present invention relates to computer controlled system for controlling the operation of a turbine power plant from cold or hot start-up to the application of full megawatt load without the necessity of personal intervention. The system provides for accelerating the turbine from zero speed through heat soak speed and synchronous speed in accordance with the real-time thermal stresses in both the HP and IP rotor. During such control the system can vary the rate of acceleration by either stopping acceleration altogether, holding it constant, increasing it or decreasing it. In response to placing the generator on-line, the system varies the loading rate by either stopping further loading altogether, holding it constant, increasing it, or decreasing it in accordance with the generator capabilities as well as the HP and IP thermal constraints.

In one aspect, the system includes the determination of heat distribution in both an axial and radial direction for the IP rotor to account a stationary and moving blade.

FIG. 1 is a schematic block diagram of a typical turbine power plant operated in accordance with the principles of the present invention;

FIG. 2 is a schematic block diagram of a typical control system structure for embodying the principles of the present invention;

FIG. 3 is a schematic block diagram of an automatic turbine control system illustrating the overall organization of an automatic turbine start-up and loading rate control system of the present invention;

FIG. 4A and 4B is a flow chart of the automatic turbine control program POO of the system of FIG. 3;

FIG. 5A and 5B is a flow chart of the HP rotor stress program PO1 of the system of FIG. 3;

FIG. 6A and 6B is a flow chart of the reheat or IP rotor stress program P16 of the system of FIG. 3;

FIG. 7A, 7B and 7C is a flow chart of the rotor stress control program PO4 of the system of FIG. 3;

FIG. 8A and 8B is a flow chart of the heat soak program P14 of the system of FIG. 3;

FIG. 9A, 9B and 9C is a flow chart of the generator supervision program PO9 of the system of FIG. 3;

FIG. 10A and 10B is a flow chart of the speed demand and acceleration load/rate control program P07 of the system of FIG. 3;

FIG. 11 are curves illustrating the generator reactive capabilities;

FIG. 12A, 12B, 12C and 12D is a chart explaining the generator reactive capability curves;

FIG. 13 is a longitudinal sectional view of a typical IP turbine rotor, blading, and casing, the stress of which is controlled in accordance with the present invention; and,

FIG. 14 shows the portion of the IP rotor within the dashed lines 14--14 of FIG. 11 and illustrates the rotor heat flow determination in accordance with the present invention.

Referring to FIGS. 1 and 2, a large single reheat steam turbine 10 (FIG. 1) constructed in a well-known manner and operated by a control system 11 (FIG. 2) in a fossil electric power plant 12 in accordance with the principles of the invention is shown. As will become more evident through this description, other types of steam turbines and electric power plants can also be operated in accordance with the principles of the invention. The turbine 10 and its control system 11 and the electric power plant 12 are like those disclosed in the copending Giras application incorporated by reference herein.

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 sensed by a power detector 18. Typically, the generator 16 is connected through one or more breakers 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 turbo-generator speed changes would result.

After 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. The constant throttle pressure steam for driving the turbine 10 is developed by a stream generating system 17 which may be provided in the form of a conventional drum or once-through type boiler, for example, operated by fossil fuel such as pulverized coal, natural gas or oil.

In this case, the turbine 10 is of the multistage axial flow type and it includes a high pressure section 20, an intermediate pressure section 21, and a low pressure section 22. Each of the turbine sections may include a plurality of expansion stages provided by stationary vanes and an interacting bladed rotor connected to the shaft 14.

The turbine 10 in this instance employs steam chests of the double ended type, and steam flow is directed to the turbine steam chests (not specifically indicated) through four main inlet valves or throttle inlet valves TV1-TV4. Steam is directed from the admission steam chests to the first high pressure section expansion stage through eight 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 valve arrangement for large fossil fuel turbines.

In applications where the throttle valves have a flow control capability, the governor valves GV1-GV8 are typically all fully open during all or part of the startup process and steam flow is then varied by full arc throttle valve control. At some point in the start-up and loading process, transfer is normally and preferably automatically made from full arc throttle valve control to full arc governor valve control because of throttling energy losses and/or reduced throttling control capability.

In the partial arc mode, the governor valves are operated in a predetermined sequence usually directed to achieving thermal balance on the rotor and relatively 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 are jointly operated from time to time to define positions producing the desired total steam flow. After the governor valves GV1-GV4 have reached the end of their control region, i.e. upon being fully open or at some overlap point prior to reaching fully open positions, the 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 arcuately spaced about the 360.degree. periphery of the turbine high pressure casing.

In the described arrangement with throttle valve control capability, the preferred turbine start-up and loading method is to raise the turbine speed from the turning gear speed of about 2 rpm to about 80% of the synchronous speed under throttle valve control, then transfer to full arc governor valve control and raise the turbine speed to the synchronous speed, then close the power system breakers and meet the load demand with full or partial arc governor valve control.

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 23 which is associated in heat transfer relation with the steam generating system 17 as indicated by the reference character 24. With a raised enthalpy level, the reheated steam flows from the reheater system 23 through the intermediate pressure turbine section 21 and the low pressure turbine section 22. From the latter, the vitiated steam is exhausted to a condenser 25 from which water flow is directed (not indicated) back to the steam generating system 17.

To control the flow of reheat steam, one or more reheat stop valves SV are 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.

In the typical fossil fuel drum type boiler steam generating system, the boiler control system operates the boiler so that steam throttle pressure is controlled to be substantially constant or within a predetermined range of values. A throttle pressure detector 26 of suitable conventional design senses the steam throttle pressure for data monitoring and/or turbine or plant control purposes. If desired in nuclear or other plant applications, turbine control action can be directed to throttle pressure control as well as or in place of speed and/or load control.

In general, the steady state power or load developed by a steam turbine supplied with substantially constant throttle pressure steam is proportional to the ratio of first stage impulse pressure to throttle pressure. Where the throttle pressure is held substantially constant by external control, the turbine load is proportional to the first stage impulse pressure. A conventional pressure detector 27 is employed to sense the first stage impulse pressure for assigned control usage in the turbine control 11.

A speed detection system 28 is provided for determining the turbine shaft speed for speed control and for frequency participation control purposes; and can for example include a reluctance pickup (not shown) magnetically coupled to a notched wheel (not shown) on the turbo-generator shaft 14. In the present case, plurality of sensors are employed for speed detection.

Respective hydraulically operated throttle valve actuators 30 and governor valve actuators 31 are provided for the four throttle valves TV1-TV4 and the eight governor valves GV1-GV8. Hydraulically operated actuators 32 and 33 are also provided for the reheat stop and interceptor valves SV and IV. A high pressure hydraulic fluid supply 34 provides the controlling fluid for actuator operation of the valves TV1-TV4, GV1-GV8, SV and IV. A lubricating oil system (not shown) is separately provided for turbine plant lubricating requirements.

The inlet valve actuators 30 and 31 are operated by respective electrohydraulic position controls 35 and 36 which form a part of the control system 11. If desired, the interceptor valve actuators 33 can also be operated by a position control (not shown). Respective valve position detectors PDT1-PDT4 and PDG1-PDG8 are provided to generate respective valve position feedback signals which are combined with respective valve position setpoint signals SP to provide position error signals from which are generated the output control signals.

The setpoint signals SP are generated by a controller which also forms a part of the control system 11. The position detectors are provided in suitable conventional form, for example they may be linear variable differential transformers which generate negative position feedback signals for algebraic summing with the valve position setpoint signals SP.

The combination of an amplifier, converter, hydraulic actuator 30 or 31, and the associated valve position detector and other miscellaneous devices form a local analog electrohydraulic valve position control loop for each throttle or governor inlet steam valve as shown in the Giras application.

A description of the various control loops is included in the Giras application, the details of which form no part of the present invention.

Referring to FIG. 2, the programmed digital computer control system 11 operates the turbine 10 with improved dynamic performance characteristics, and can include conventional hardware in the form of a central processor 40 and associated input/output interfacing equipment such as that sold by Westinghouse Electric Corporation and described in detail in "Westinghouse Engineer", May, 1970, Volume 30, No. 3, pages 88 through 93. As will be apparent from the description hereinbelow, the control system of this invention may utilize, for performing the indicated calculations, any general purpose programmable computer, special purpose computer or microprocessors having real-time capability, in combination with the control apparatus illustrated in FIG. 1 and the required interface equipment, or equivalents thereof, as illustrated in FIG. 2. Also, it is to be understood that special purpose analog computer apparatus may be utilized for making the specific calculations required to practice this invention in controlling the operation of any particular turbine.

The interfacing equipment for the computer processor 40 includes a conventional contact closure input system 41 which scans contact or other similar signals representing the status of various plant and equipment conditions. Such contacts are generally indicated by the reference character 42 and might typically be contacts of mercury wetted relays (not shown) which are operated by energization circuits (not shown) capable of sensing the predetermined conditions associated with the various system devices. Status contact data is used in interlock lock functioning in control or other programs, protection and alarm system functioning, programmed monitoring and logging and demand logging, functioning of a computer executed manual supervisory control 43, etc.

The contact closure input system 41 also accepts digital load reference signals as indicated by the reference character 44. The load reference 44 can be manually set by the operation to define the desired megawatt generating level and the computer control system 11 of the present invention controls the turbine 10 to increase the load for supplying the power generation demand.

Input interfacing is also provided by a conventional analog input system 45 which samples analog signals from the plant 12 at a predetermined rate such as 15 points per second for each analog channel input and converts the signal samples to digital values for computer entry. The analog signals are generated by the power detector 18, the impulse pressure detector 27, the valve position detectors PDIV and PDRV, temperature detectors 46 and 37, and miscellaneous analog sensors 48, various steam flow detectors, other steam temperature detectors, miscellaneous equipment operating temperature detectors, generator hydrogen coolant pressure and temperature detectors, etc. A conventional pulse input system 49 provides for computer entry of pulse type detector signals such as those generated by the speed detector 28. The computer counterparts of the analog and pulse input signals are used in control program execution, protection and alarm system functioning, programmed and demand logging, etc.

Information input and output devices provide for computer entry and output of coded and non-coded information. These devices include a conventional tape reader and printer system 50 which is used for various purposes including, for example, program entry into the central processor core memory. A conventional teletypewriter system 51 is also provided and it is used for purposes including, for example, logging printouts as indicated by the reference character 52. Alphanumeric and/or other types of displays 53, 54 and 55 are used to communicate rotor strain, and other information as described hereinafter.

A conventional interrupt system 56 is provided with suitable hardware and circuitry for controlling the input and output transfer of information between the computer processor 40 and the slower input/output equipment. Thus, an interrupt signal is applied to the processor 40 when an input is ready for entry or when an output transfer has been completed. In general, the central processor 40 acts on interrupts in accordance with a conventional executive program. In some cases, particular interrupts are acknowledged and operated upon without executive priority limitaations.

Output interfacing is provided for the computer by means of a conventional contact closure output system 57 which operates in conjunction with a conventional analog output system 58 and with a valve position control output system 90. A manual control 49 is coupled to the valve position control output system and is operable therewith to provide manual turbine control during computer shutdown and other desired time periods.

Certain computer digital outputs are applied directly in effecting program determined and contact controlled control actions of equipment including the high pressure valve fluid and lubrication systems as indicated by the reference character 60, alarm devices 61 such as buzzers and displays, and predetermined plant auxiliary devices and systems 62 such as the generator hydrogen coolant system. Computer digital information outputs are similarly applied directly to the tape printer and the teletypewriter system 51 and the display devices 53, 54 and 55.

Other computer digital output signals are first converted to analog signals through functioning of the analog output system 58 and the valve position control output systems. The analog signals are then applied to the auxiliary devices and systems 62, the fluid and lubrication systems 60 and the valve controls 50 in effecting program determined control actions. The respective signals applied to the steam valve controls 35, 36 and 37 are the valve position setpoint signals SP to which reference has previously been made.

Referring to FIG. 3, the automatic turbine control system is included in and is part of the digital electrohydraulic (DEH) control system referred to at 70, one form of which is described in the copending Giras application incorporated by reference herein. The Giras application also includes the description of an automatic turbine start-up (ATS) system as previously described herein; and where certain details of the ATS system of the Giras application are common to or utilized in the system of the present invention, such details are described herein sufficient to enable an understanding of the system of the present invention.

A program POO referred to at 71 is controlled by the auxiliary synchronizer program of the basic DEH system referred to at 70. This program receives logical states from the basic DEH and controls the operation of each of the various subprograms of the automatic turbine control (ATC) system, periodically, as described in connection with FIGS. 4A and 4B. A program PO7 referred to at 72 provides an input to the basic DEH system 70 for controlling the speed demand of the turbine and the acceleration and rate of loading of the generator. The basic DEH system 70 provides an input to the program PO7 corresponding to the operator's load demand of the turbine generator. The program PO7 provides such speed, acceleration and loading rate under the constraints of the various subprograms PO1 through PO6, and PO8 through P16 as described.

In each of the flow charts for the programs are triangular blocks having a legand prefixed with a particular program designation, such as PO1 followed by the letter M and a number. Each triangular block represents a message given to the operator of the system either by typewriter or indicator light. In describing the programs, reference to the indicator blocks are omitted with the last of indication given following the description of the particular program.

A program PO1 referred to at 73 calculates the information relative to the high pressure rotor. Such calculations include the high pressure rotor surface temperature and the volume average temperature of the rotor and the effective temperature differential between the rotor surface and the rotor volume average temperature. Also, it calculates the stress limits for loading and the stress limits during wide range speed control. A program P16, referred to at 74 computes the IP rotor surface temperature, bore temperature, the volume average temperature, and the effective temperature difference between the IP rotor surface temperature and the volume average temperature. This program P16 also sets the IP rotor effective temperature difference limit.

A program PO4 which provides for rotor stress control is referred to at 75; and provides input to the program PO7 referred to at 72 for controlling the load upon the generator in accordance with the HP rotor stress and the IP rotor stress from the programs PO1 and P16.

A program P14 referred to at 77 which determines the length of time that the turbine will run at a constant heat soak speed is controlled by the IP rotor stress program P16 of block 74 and the HP rotor stress program PO1 of block 73. A program PO9 referred to at block 78 calculates and determines the various generator parameters which are utilized in the loading rate control of the turbine generator.

The remaining portions of the system are mentioned merely as to their general function with respect to the effective operation of the automatic turbine control system of the present invention, and the details of the remaining programs form no part of the present invention. For example, a program PO3 referred to at 79 checks all the conditions that hold the turbine unit from rolling off turning gear. A program PO5 referred to at 80 analyzes present vibration inputs from the turbine and takes action in accordance with a previously determined vibration trend.

A program PO2 referred to at 81 checks the temperature differences across the steam chest wall and controls the turbine to avoid extreme stresses caused thereby. A program P12 referred to at 82 controls the turbine in accordance with the difference between the LP exhaust pressure and the reheat steam temperature. A program PO6 referred to at 83 controls the turbine in accordance with any water detection and drain valve contingencies. A program P11 referred to at 84 checks the rotor position longitudinally in the casing and differential expansion to control the turbine under automatic turbine control. A program P10 referred to at 85 checks the gland steam, LP exhaust steam, and condenser vacuum in the automatic turbine control system. A program PO8 referred to at 86 checks the bearing metal and the oil temperature with respect to the automatic control of the turbine. A program P13 referred to at 87 scans the analog sensors that are provided for determining the HP rotor and IP rotor stress and determines whether or not there is a sensor failure that would prevent the proper operation of the ATC system; and finally program P15 functions to govern the sequence of the ATC system operation from turning gear through the heat soaking period to synchronization and control of the loading of the generator. For example, from the speed signal of the base DEH, it checks the actual speed, and from the program P14 it determines if the heat soak is complete, and appropriately sets the target speed to the next plateau at a rate determined by rotor stress. It provides for automatic synchronization at 3600 rpm, after reaching a certain speed; and when the breaker is initially closed, the rate index is set to a particular rate of loading depending on the present rotor stress.

Referring to the program PO0 in FIGS. 4A and 4B, which is operated every second by the synchronizer of the DEH system, initiates the operation of every other program PO1 through P16 shown in block form in FIG. 3. Prior to placing the automatic turbine control system in operation, the computer is operated for a period of two hours in order that all of the calculations which are made may be verified. During this time, the various sensors are checked for validity and appropriate messages printed out or indicator lights lit advising the operator of the condition of the system. In the event that any of the calculations associated with the HP stress are invalid, but those associated with the IP stress may be valid for exmple, then the automatic turbine control system will not control the turbine but merely be in a supervisory condition so that the operator may start the turbine, but ignore any information regarding the condition of the HP turbine. Although the flow charts of FIGS. 4A and 4B together with their appropriate legends are self-explanatory, with respect to many details, it should be pointed out that intially when the computer is turned on, the program is commenced at 90 to commence the two-hour time count of the computer. A flag referred to at 91, which is set by the base DEH system to indicate the beginning of the time period is recognized by the program; and if the flag is set, the "computer timeout" flag is cleared as denoted at 92, which is communicated to the base DEH system. Then the "operator automatic" flag is set and a two-minute counter is set to zero to begin a two-minute count prior to the (two-hour count previously mentioned to insure that various message writers and other peripheral equipment are in operation. Then each time that the program is run for the first two minutes, the two-minute counter is incremented by one second as shown at 93, and the program exits at 94. At the end of the two-minute period, the HP two-hour counter and the IP 2-hour counter are set to zero as shown at 95. During the two-minute period, the program is started each second at 96. During this period, various values are cleared in the system and various flags are set. For example, as shown at 97, "HP stress invalid" and "IP stress invalid flags" are set. As shown at 98, metal temperature counts that may be stored in the computer and differential expansion counts are set to zero as shown at 98; and all automatic turbine control "status light" flags as well as the "anticipated differential expansion" and "anticipated metal temperature" flags are cleared as shown at 99. At the end of the two-minute period, the program commences each second at block 100 and bypasses the previously described blocks to directly check at 101, whether the DEH has commanded the automatic control to be in control of the operation of the turbine at the end of the two-hour period. The program then checks at 102 through 105, various flags relating to the integrity and condition of the system. In the event such flags are set, appropriate messages are printed out as denoted by the legended triangles POOMO1 through POOMO6. For example, if the flag is set at 102, the message printed out advises the operator that a vital sensor is out of service. If the flag is set at 103, the operator is advised that a turbine trip condition exists. If the flag is set at 104, the operator is advised that the rotor stress calculations are invalid, and if the flag is set at 105, the operator is advised that the ATC system is not in control; because the operator has initiated such an action by making the actual load demand logical to the load. In the event that the operator has not pushed the button to put the ATC in control as shown at 101, the program checks to determine whether it is to be under turbine supervision; and if the operator has operated such a control as shown at 106, the program then checks other conditions as shown in blocks 107, 108, 109 and 110. Appropriate messages are printed out as indicated by triangular blocks POOMO7 and POOMO8. Thus, for the first two hours of computer operation, the ATC system will permit the operator to start up the system under an operator automatic condition with such system merely printing out the various values for supervisory purposes only and not for controlling the turbine. Referring to FIG. 4B, the program path at 111 at the output of blocks 109 and 112 (FIG. 4A) operate the subroutines PO1 through P16 periodically as shown in each of the appropriately legended blocks.

Referring to FIGS. 5A and 5B, the HP rotor stress program PO1, which is called every five seconds by the program PO0 utilizes in its calculations, various sensed inputs associated with the high pressure turbine. These include the first stage metal temperature, the first stage steam temperature, and the throttle steam temperature. After checking the time since start-up, and the various "invalid" flags, accomplished by the decision blocks within dashed line 113, the program PO1 checks the operating condition of the turbine generator at 114, 115 and 116 to determine whether it is on turning gear, wide range speed control, or whether the heat soak time is completed. At the beginning of the previously mentioned two-hour counting period, the high pressure rotor temperature is initialized with the value of the first stage metal temperature as shown at 117. Also, if the first stage metal temperature is less than 250.degree. as shown by dicision block 118, then the HP rotor effective temperature difference limit is set equal to the cold HP temperature limit, or in other words indicates to the system that this is a "cold"] In the event that the first stage metal temperature is greater than 250.degree., the temperature difference limit is set to equal a hot HP temperature limit, indicating a "hot" start. In the event that 115 indicates that the main breaker is open and the heat soak time is complete at 116, then the "hot" start limit is set at 120.

The system also provides for a high loading rate and a normal loading rate. An effective temperature differential limit for a high loading rate is different than the one for the normal loading rate, which permits the operator, for certain situations, to increase the load on the generator more rapidly than normal. This capability is shown at 121 and 122 when are controlled by a "high loading rate" flag as shown at 123. A five-minute counter is provided as shown at 125 which computes a heat transfer coefficient as shown at 126. Once the counter has run for the five-minute period, the computed heat transfer coefficient is held at its present value as shown at 127. In the event that the main breakers should open, the heat transfer coefficient is recomputed for the five-minute period. At the output of the blocks 119 and 120 which set the effective temperature difference limit to equal either a hot HP temperature or a cold HP temperature limit, a counter referred to at block 128 is reset to zero and the heat transfer coefficient is computed as shown at 130. The block 130 computes the heat transfer coefficient for wide range speed control whereas the block 126 computes the heat transfer coefficient for load control as hereinbefore described.

The HP rotor surface temperature and the rotor volume average temperature, and the effective temperature difference are computed at 131. The latest 15 values of the HP rotor effective temperature difference computed by the block 131 are updated as shown at 132 every minute as shown at 133. Also each minute, the updated table is used to extrapolate an anticipated value of the HP rotor effective temperature difference 15 minutes hence as shown at 134. The program then checks the present effective temperature difference with respect to the limit value of the system at 135 provided that the "HP stress invalid" is not set at 136, and an appropriate message is printed out.

In the present embodiment of the invention, there are four different throttle steam temperature sensors at different locations. The difference between these various input temperatures is checked at 137 to determine if such a difference is greater than 25.degree. F. Then, the main breaker is checked; and if it is open, the program returns. It it is closed, the load on the generator is then checked at 138, and if it is less than 20%, none of the throttle temperatures are stored and a five-minute counter in the system is reset to 300 seconds. A block 140 checks to determine if any of the throttle steam temperatures that are stored have a present value greater than 150.degree.. The system then checks at 141 to determine the number of stored throttle temperatures; and if the numbers stored are equal to or greater than six, the values are updated, which occurs at five-minute intervals, for the four throttle steam sensors in the system.

The formula used in computing the heat transfer coefficient by respective blocks 126 and 130 are as follows:

where C.sub.1-9 = heat transfer constants

N= speed in rpm

P= highest valve of condenser press #1, #2, and #3)

T= time in seconds after main breaker is closed

The HP rotor surface temperature is calculated to be the temperature of the first state steam at existing throttle steam temperature and pressure, and the volume average temperature 1)AVF(t) for the HP rotor is calculated in accordance with the following formula:

Next, the effective temperature difference between the rotor surface temperature T.sub.1 (t) and the volume average temperature T.sub.AVG (t) is in accordance with the following formula:

For extrapolating the fifteen-minute anticipated value T.sub.ANTICIP of the HP rotor effective temperature difference, T.sub.DIF, the following formula is used: ##EQU2## Where T.sub.DIF (t)= Present volue of RTR effective temp. diff.

T.sub.DIF (t-i)= Stored previoius ith value of RTR effective temp. diff.

The operator indications which are initiated by program PO1 include "HP Rotor Stress Invalid-Vidar out of service," "steam temperature difference exceeds 25.degree.," and "HP stress invalid calculation less than 2 hours," for example.

Referring to FIG. 6A and 6B, the IP rotor stress program P16 is operated every five seconds by the program PO0. That portion of the program within dashed lines 145 provides for the two-hour countdown similar to the previously described HP rotor stress program P01. The program P16 utilizes the temperature of the IP blade ring, the IP inlet steam temperature, and the IP exhaust steam temperature in its calculations. The program first checks the condition of the plant; that is, whether or not the turbine is on turning gear as shown at 146, the condition of the main breaker at 147, and whether or not the heat soak time of the turbine is complete at 148. Then, the IP rotor ambient steam temperature is computed at 150 and 151, and the ambient steam temperature and IP blade ring temperature is computed at 152 while the turbine is still on turning gear. If the main breaker is open, the IP rotor steam to surface heat transfer coefficient is computed at 153. The IP blade ring metal temperature is checked to determine if it is greater than 250.degree. F. minus a predetermined margin at 154. If it is less than 250.degree. F., the IP rotor effective temperature difference limit is set to be equal to a cold IP rotor temperature limit as shown at 155; and if it exceeds 250.degree. F., the IP rotor effective temperature difference limit is set equal to the hot IP rotor temperature limt at 156. The program P16 then computes the IP rotor surface temperature, the IP effective temperature difference as shown by action block 157. Each minute of operation, the anticipated value of the IP rotor effective temperature difference is extrapolated at 158, and the stored latest 15 values of the IP rotor effective temperature difference is updated at 160. After checking the validity of the IP stress at 161, the value of the present IP rotor effective temperature difference is checked at 162 with respect to the limit value which was previously set at either 155 or 156. The program then checks at 163 to determine whether the IP inlet steam temperature between the reheat stop valves differs more than 25.degree. F.

If the main breaker is closed as indicated at 147, after the computation of the IP rotor ambient steam temperature at 150, the IP rotor heat transfer coefficient as a function of steam flow is computed at 164. Then the high or low loading rate flag is checked; and depending on which is set, the IP rotor effective temperature differences limit is set to equal to IP "high load rate" temperature limit, or the "normal load rate" temperature limit. If the main breaker is closed as indicated at 165, the load is then checked to determine whether it is greater than 20%. If such load is less than 20%, the number of stored inlet steam temperature values is set to zero. If it is greater than 20%, then every five minutes the inlet steam temperature is stored, and then for the relevant sensor (FRS) the difference between the inlet steam temperature and any of the stored values is checked to determine if it exceeds 150.degree. F. Then, the number of stored inlet steam temperatures is updated at 167.

The IP rotor ambient steam temperature for the various conditions of the turbine is calculated by the following formula:

Where

T.sub.AO (t)= present temp. of steam entering seal strips (See FIG. 14)

t.sub.al (t).sub.1 T.sub.A2 (t)=) present ambient temp. at corresponding parts of FIG. 14

c.sub.9 through C.sub.17 = Cal. constants

T.sub.IP blade ring= IP blade ring metal temperature

T.sub.hot reheat stem = hot reheat stm temp (average value of 2 sensors)

T.sub.ip exh = ip exhaust stm temp.

T.sub.Al (t-1)= Previous iteration of grid point (l,l) (FIG. 14) temp.

K.sub.Al = Heat conductance of grid point (1,1) (FIG. 14) to ambient steam

G= stm flow rate

The IP rotor temperature including the surface temperature, intermediate segment temperature (as shown in FIG. 14), rotor bore temperature, rotor volume average temperature T.sub.ANG (t), and the rotor effective temperature difference T.sub.DIF (t) for the various types of grooves in the turbine rotor are calculated as shown at 157 according to the followng formulae:

where

C.sub.i,j =Heat conducting constants

T.sub.i,j (t)= Present temp. of the ith segment jth subsection

T.sub.i,j (t-1)= Previous temp. of above

V.sub.i,j = Volume of the ith segment jth subsection

V.sub.k = volume of the kth segment

C.sub.19 = Stress constants

L= number of segments

N= Present speed in rpm

The IP rotor steam to surface heat transfer coefficient H is computed at in accordance with the following formula:

where

H.sub.1, H.sub.2, and H.sub.3 = Heat Transfer Coef (see FIG. 14)

g-- stm flow rate (% of rated flow)

G= Cal. result from basic DEH when under load control mode

G= C.sub.3 P+ C.sub.4 N+ C.sub.5.sup.. P.sup.2 +C.sub.6.sup.. N.sup.2 + C.sub.7.sup.. P.sup.. N+ C.sub.8 when under speed control mode

C.sub.1 through C.sub.8 = Cal. constants

P= Highest value of condenser press (#1, #2, and #3)

N= Turbine Speed in rpm

The IP rotor heat conductance to ambient steam temperature K.sub.A1, K.sub.A2, and K.sub.A3 are calculated in accordance with the following formula:

h.sub.1, h.sub.2 = heat transfer Coef.

C.sub.19-22 = Cal. constants

The extrapolation of the IP rotor effective temperature difference as calculated at 158 is accomplished in accordance with the following formula: ##EQU6##

The operator indications initiated by program P16 are as follows:

Referring to FIG. 7, the program P04 referred to as the rotor stress control program, is placed into operation every thirty seconds and functions to command the speed demand and acceleration loading rate control program P07, in accordance with the previously described computations and logic of the HP rotor stress and IP rotor stress programs P01 and P16 respectively. Each time the program P04 is run, it first clears the various flags as indicated at 170; and then checks on the operational status of the turbine as indicated by blocks 171 and 172. In the event the HP stress invalid or the IP stress invalid flag is set, the program P04 checks determine whether the two-hour counter previously described has completed its countdown at 173. If such is the case, the first stage steam temperature rate of change is detected to determine if such change is greater than 300.degree. F. per hour at 174. If it is greater than such rate, block 175 determines if the turbine speed is greater than 600 rmp; and block 176 determines whether the speed is less than 3200 rpm. If the speed is less than 3200 rpm, block 177 checks the condition of the main breaker. In addition, a flag to hold the first stage temperature is set at 178, and the program P14 then sets the allowable increase or decrease load changes to zero as shown at 180.

When all conditions are met such that the turbine may be controlled by the ATC system, the program checks at 181 the condition of the main circuit breaker. If the circuit breaker is open indicating that the system is on wide range speed control, the absolute value of the present HP rotor effective temperature difference is compared with the HP limit value at 182. If the temperature difference is greater than the HP limit value, the "rotor stress hold" flag is set at 183. The program then checks at 184 the condition of the "rotor stress hold" flag, and the condition of the main breaker at 185. Then the absolute value of the present IP rotor effective temperature difference is compared with the IP limit value at 186; and if such temperature difference is equal to or greater than the IP limit value, a "rotor stress hold" flag is set at 187. After again checking the condition of the main breaker at 188, the allowable increase or decrease of any load change is set to equal zero at 180. Thus, under these conditions the system permits the turbine to be controlled at the present speed or load at which it is operating, but does permit a speed or rate increase. For other conditions, considering first the condition of the HP rotor, where the block 182 determines that the present temperature difference is less than the HP limit value, a block 190 determines whether or not the absolute value of the anticipated HP rotor effective temperature difference is equal to or greater than the HP limit value. Assuming that such anticipated temperature difference is equal, the absolute value of the present HP rotor temperature is checked at 191 to determine if the difference is greater than 85% of the HP limit value. If such is the case, then the program continues through the block 183 and the "rotor stress hold" flag is set as in the previous example. Assuming that the present temperature difference is less than 85% of the HP limit value, a flag "rotor stress reduce rate" in block 192 is set; and the program proceeds along the same path as described in the previous example.

Assuming that the anticipated HP rotor temperature difference is less than the HP limit value, a check is made at 193 to determine if the absolute value of the anticipated temperature difference is greater than 75% of the HP limit value. If such is the case, the flag is set at 192 for reducing the stress rate as in the preceding example. Assuming that such temperature difference is less than 75% of the HP limit value, the anticipated HP rotor effective temperature difference is then checked at 194 to determine if it is greater than 50% of the HP limit value. Thus, with the anticipated temperature difference being between 50 and 75% of the HP limit value, a flag for maintaining the same rate at 195 is set and the program proceeds, as in the preceding example. Should the value of the anticipated HP rotor temperature difference be less than 50% of the HP limit value, then the system checks at 196 to determine whether or not the present HP rotor effective temperature difference is greater than 90% of the HP limit value. If such is the case, the flag for maintaining the same rate is set at 195. In the event that the value of the present HP rotor temperature difference is less than 90% of the HP limit value, than a "rotor stress increase rate" flag at 197 is set for increasing the rate of speed of the turbine. However, the condition of the reheat or IP rotor overrides the previously given examples of the condition of the present and anticipated HP rotor stress. Thus, the program goes through a single path entering the block 184 to check the condition of the reheat or IP rotor on wide range speed control.

With respect to the IP rotor stress, after the appropriate flags have been set, as previously described in connection with the HP rotor stress, the system checks at 184 for the condition of the "rotor stress hold" flag. In the event that it is set, and the block 188 indicates that the main breaker is open, the allowable increase and decrease load change is set to zero at 180 without the necessity of checking the condition of the IP rotor stresses. However, in the event that the "rotor stress hold" flag is not set, the block 185 checks the condition of the main breaker, which for this situation is open, and the IP rotor effective temperature difference is compared with its limit value. In the event that the present IP rotor temperature difference is equal to or greater than its limit value, the "rotor stress hold" flag is set at 187 and the program exits as previously mentioned. However, in the event that the IP effective temperature difference is less than the limit value, the anticipated effective temperature difference is checked to determine whether it is equal to or greater than its limit value at 200. If such is the case, the present IP rotor temperature difference is checked at 201 to determine if it is equal to or greater than 85% of the limit value, and if such is the case, the "rotor stress hold" flag is set at 187. In the event that the present IP rotor temperature difference is less than 85% of the IP limit value, the "rotor stress reduce rate" flag is set at 202. In the event that the block 186 is negative indicating that the IP rotor temperature difference is less than the IP limit value, and a block 203 determines that the absolute value of the anticipated IP rotor effective temperature difference is equal to or greater than 75% of the IP limit value, the decision block 202 sets the "rotor stress rate" flag. Should such anticipated IP rotor temperature difference be less than 75% of the IP limit value, but greater than 50% of the IP limit value as shown at 204, then the "rotor stress increase rate" flag is set at 205. If such anticipated temperature difference is less than 50% of the IP limit value, but the absolute value of the present IP rotor temperature difference is equal to or greater than 90% of the IP limit value of 206, then the "rotor stress increase rate " flag is cleared at 205. In the event that the present IP rotor effective temperature difference is less than 90% of the limit value for the IP rotor, and the "remain at the same rate" flag has not been set by the HP stress comparison as previously mentioned, which is checked at 207, then the "rotor stress increase rate" flag is set at 208.

For load control of the turbine, a decision block 181 determines that the main breaker is closed. Then at decision block 210 it is determined whether or not the load is increasing and the HP rotor heating; or that the load is decreasing and the HP rotor is cooling. If either condition is occurring, then the logic previously described for the HP rotor in connection with wide range speed control is followed to set the appropriate flags for either holding the rotor stress, reducing the rotor stress rate, permitting the rate to remain the same, or increasing the rotor stress rate. However, in the event that the HP rotor is not heating or or cooling as decided at 210, then the program checks the present HP rotor effective temperature difference at 196 to determine whether or not to set the flag at 195 for causing the load rate remain the same, or set the flag for increasing the rotor stress rate at 197. For the IP stress, with the main breaker closed at 185, the heating and cooling of the IP rotor with the load increasing or decreasing is checked at 211. In the event that the load is increasing and the IP rotor heating, or the load decreasing and the IP rotor cooling, then the same values are checked as previously described in connection with the IP stress for wide range speed control. However, if such is not the case, then the value of the present IP rotor temperature difference is compared at 206 to either clear the rotor stress increase rate at 205 if the difference is equal to or greater than 90% of the IP limit value, or set the rotor stress increase rate at 208 if the flag for having the rate remain the same at 207 was not previously set by the HP stress comparison.

After setting the flags in connection with the previously described logic for load control, the indication that the main breaker is closed by the decision block 188 then causes a calculation of the allowable first stage steam temperature changes at the present HP rotor stress margin as indicated by decision block 212. Then, from the base DEH system (FIG. 2) the system determines the valve mode at 213. If the single valve mode flag is set indicating that the system is operating with full arc admission, then the allowable increase and decrease in load changes is calculated based upon the single valve characteristics as indicated at 214. In the event that the system is in the sequential or partial arc mode, then the allowable increase and decrease load changes based upon the sequential valve characteristics is calculated at 215. In the event that a flag "hold mode" is set from the program P07 hereinafter described as indicated at 216, then the program checks to determine if the stored target demand is greater than the load reference at 217. If such is the case, then the allowable load increase is set to zero at 218. If the target demand is less than the load reference, then the allowable load decrease is set to zero at 219.

In determining whether the load is increasing and the HP rotor is heating, or whether the load is decreasing and the HP rotor is cooling at 210, the first stage steam temperature is compared with the calculated rotor surface temperature. If the first stage steam temperature is greater than the calculated rotor surface temperature, the HP rotor is heating. If the first stage steam temperature is not greater than the calculated rotor surface temperature, the rotor is cooling. With respect to the determination for the IP rotor at 211, the IP rotor is heating if the calculated ambient steam temperature is greater than the calculated rotor surface temperature at grid point (1,2) (FIG. 14). If the calcualted ambient steam temperature is not greater than the calculated rotor surface temperature at such grid point, the IP rotor is cooling.

The allowable first stage steam temperature changes at the present HP rotor stress margin which are calculated at 212 are arrived at in accordance with the following formula:

where

T.sub.INCR -- Allowable Incr 1st Stage Stm Temp

T.sub.DECR -- Allowable Decr 1st Stage Stm Temp

T.sub.AVG (t)-- Present HP RTR Volume Average Temp

T.sub.U (t)-- Present HP RTR T.sub.U Temp

C.sub.10,N -- Stress Constants

T.sub.LIMIT -- Present HP RTR Effective Temp Diff Limit.

At 214, the allowable increase and decrease of the load based on single valve characteristics is calculated in accordance with the following formula:

where

M.sub.1 -- Slope of 1st Stage Steam Temp vs. MW Curve at rated throttle conditions.

The allowable increase and decrease load change based on the sequential valve characteristics calculated in the block 215 are in accordance with the following formula:

where

Lb.sub.rated -- % load at Break Point Of first Stage Stm Temp vs. MS Curve Under Rated Throttle Conditions

T.sub.RATED --]First Stage Temp at Above Break Point

LB.sub.Present -- % Load at Break Point of First Stage Stm. Temp vs. MW Curve Under Present Throttle Conditions

T.sub.BP -- First Stage Stm Temp at Above Break Point

L.sub.Present -- PRESENT % Load Reference

T.sub.Rl -- First Stage Stm Corresponding to Present % Load

T.sub.R2 -- First Stage Stm Temp Corresponding to LB.sub.Present % Load on Rated Throttel Condition Curve

M.sub.2 -- Slope of Upper Sector of first Stage Stm Temp vs. MW Curve at Rated Throttle Conditions

M.sub.3 -- Slope of Lower Sector of First Stage Stm Temp vs. MW Curve at Rated Throttle Conditions

T.sub.IMP -- Present First Stage Stm. Temp.

T.sub.INCR, T.sub.DECR -- From PO4.2

mw.sub.rated -- rated mw

mw.sub.incr -- allowable Incr Load in MW

mw.sub.decr -- allowable Decr Load in MW

The setting of the various flags for either holding the rotor stress, reducing the rate of rotor stress, increasing the rate or rotor stress, or governing the rate to remain the same, is utilized by the program PO7 for controlling the speed demand and acceleration and the load rate hereinafter described.

The operator indications initiated by program PO4 are as follows:

referring to FIG. 8, the heat soak program P14 is activated by the program P00 every 60 seconds. The program first determines whether or not the "heat soak complete" flag is set at 230, which is cleared by the program P16 each time it is run when the turbine is on turning gear. In the event that the "heat soak complete" flag is set, the program merely returns without further action. In the event that the "heat soak complete" flag is not set, the program then checks to determine the validity of the IP stress signal at 231. If the system shows in invalid signal, block 232 clears the "heat soak in progress" flag and the program exits. If the stress signals are valid, decision block 233 determines whether the "heat soak in progress" flag is set. If it is not set, decision block 234 determines whether the actual speed is less than the heat soak speed, which informs the system that the speed of the turbine has not yet reached 2200 rpm's approximately. If the actual speed is not less than the heat soak speed, the "heat soak in progress" flag is set as indicated by block 235. This same indicator 235 is also used to turn on or off the ATC status light indicating that a "heat soak" is in progress.

The system then checks at 236 to determine whether the IP rotor bore temperature is greater than 250.degree. F plus a predetermined margin. Then, if the IP metal temperature sensor failure flag at 237 is not set, the operator is so informed. If the sensor is out of service, decision block 238 then determines whether the operator has placed the "ATC in control". If not, a flag indicated at 239 is cleared which extinguishes the ability of the operator to override the ATC control. If the turbine system is in ATC control, then an indicator is set advising the operator to check the heat soak curve for sufficient soak time before attempting to override the ATC system. In the event that the operator has operated the override pushbutton as indicated by block 240, a panel light informing the operator that the heat soak has been terminated by operator override is lit. The "override permissive" flag is set at 241 for the base DEH system. Thus, in the event that the calculated IP rotor bore temperature is greater than 250.degree. F plus a margin, and the IP blade ring sensor has failed, the operator may override the ATC system, having been given the aformentioned warnings.

If 237 indicates that the IP blade ring temperature sensor has not failed, then the determination of whether the IP blade ring metal temperature is greater than 250.degree. F plus a predetermined margin is made at 242. If such is the case, the operator is informed that the heat soak is complete, and that the calculated rotor bore temperature is greater than a predetermined temperature and also that the IP blade ring temperature is greater than a predetermined temperature. Also, block 243 sets the "heat soak complete" flag for the other subprograms of the ATC system and clears the "heat soak in progress" flat at 244 for the appropriate ATC programs. However, in the event that the blade ring's metal temperature is less than 250.degree. F plus the predetermined margin, block 245 determines whether the remaining heat soak time is greater than zero. If it is greater than zero, the remaining heat soak time is incremented by 1 minute, as shown at 246; and if it is not greater than zero, a 10-minute counter C is checked at 247 to determine if it is less than 10 minutes. If the counter is less than 10 minutes, the counter is incremented by 1 minute at 248; and if it is not less than 10 minutes, the 10-minute counter C is set to zero at 249. The operator is also informed that additional heat soak time is required because the IP blade ring temperature is less than a predetermined temperature. The counter C is provided to inform the operator of this situation every 10 minutes.

The IP rotor bore temperature flag indicating that the temperature is less than 250.degree. F plus a margin, is utilized to provide the operator with an estimate for indication purposes only of the entire heat soak time that may be required. This is accomplished by estimating the required heat soak time at 250 and informing the operator of such time by the indicator hereinafter listed. Also, if the IP rotor bore temperature is less than 250.degree. plus the margin, the program checks at 251 whether the "Heat soak retimed" flag is set; and if the remaining heat soak time has not expired as indicated at 252, then the remaining heat soak time is incremented by 1 minute in block 253. The blocks 254, 255 and 256 provide the logic for checking and informing the operator by way of the appropriate indicator every 10 minutes that additional heat soak time is required in accordance with the required calculated rotor bore temperature.

The operator indications initiated by program P14 are as follows:

referring to FIG. 9, for the automatic control of the loading of the generator PO9, not only must the turbine conditions be checked and controlled, but also various operating parameters of the electrical generator itself. The program for supervising the conditions of the generator is initiated every 60 seconds by the program P00. The program enters at 260 and clears the "cooling gas temperature high" and "faulty hydrogen (hereinafter referred to as H.sub.2) system" flag. The system then determines whether or not the H.sub.2 cooler discharge temperature is less than 48.degree. C at 261. In this decision block, the highest value of up to 4 H.sub.2 cooler temperature sensors is utilized. If the temperature is equal to or greater than 48.degree. C, an indicator informs the operator that the H.sub.2 cooler discharge temperature is at its high limit. If it is less than the 48.degree. C, the indicator is cleared. The program then determines whether or not the H.sub.2 cooler discharge temperature is greater than 25.degree. C at 262. If the temperature is not greater than 25.degree. C, the operator is informed that the H.sub.2 cooler discharge temperature low limit equals a predetermined temperature; and if it exceeds such temperature, then such operator indication is cleared. For the decision block 262, the lowest value of up to 4 H.sub.2 cooler discharge temperature sensors are used. At 263, a check is made to determine whether or not the difference between the highest and the lowest generator stator coil gas discharge temperature is less than 8.degree. C. It is is less, the operator is informed that the maximum temperature difference between gas discharges exceeds the temperature limit; and if it is less than the maximum limit of 8.degree., then such indication is cleared.

Next the H.sub.2 pressure is checked in block 264 to determine if it is less than the maximum limit. If it is not less than the maximum limit, then an indicator informs the operator that there is a faulty H.sub.2 system, and a flag "faulty H.sub.2 system" is set at 265 for use in the program PO7, hereinafter described. A "cooling gas temperature high" flag at 266 is provided for use of the program PO7. The program then determines at 267 that the H.sub.2 pressure is greater than the minimum limit; if it is not, a flag is set at 268 that there is a "faulty H.sub.2 system" for use by the program PO7. The program PO9 then checks the purity of the hydrogen system; and if it is greater than 100% as indicated at 269, the program then determines at 270 whether or not the H.sub.2 side of the seal oil temperature is out of limit. If it is below 80.degree. or higher than 120.degree., an indication of this fact is given to the operator. In the event that the H.sub.2 purity is less than 90% but greater than 85%, an indication is given to the operator that the H.sub.2 purity is low. If it is less than 85%, then an indication is given that the H.sub.2 purity is very low, and a flag "faulty H.sub.2 system" for the program PO7 is set at 271.

The program then checks the air side of the seal oil temperature at block 272. If it is below 80.degree. F or greater than 120.degree. F, an indication is given to the operator that the air side seal oil temperature is out of limit. If the seal oil pressure minus the H.sub.2 pressure is not greater than 4 psig, as indicated at 273, then the operator is informed that the seal differential pressure is low and to correct the fault immediately or trip and purge the H.sub.2 system. Consequently, a "faulty H.sub.2 system" flag is set at 274 for the program PO7.

On the generator H.sub.2 panel, there are a number of annunciators which are closed for a respective alarm condition. The program checks at 275 if any of these generator annunciator contacts are closed; and if they are, an appropriate indication is made and a flag is appropriately set at 276 for the program PO7. The portion of the program within the dashed lines referred to at 277 is provided for generators that are water cooled and merely checks the status of the water pump and the water inlet and outlet temperatures to inform the operator accordingly at the various indicators. The exciter air temperature is checked at 278; and if it is greater than 52.degree. C, then the operator is appropriately informed, and a flag "cooling gas temperature high" is set for the program PO7. A similar check is made at 280 to determine if the exciter air temperature is less than 52.degree. C in another part of the exciter; and a similar flag at 281 is set for the program PO7. If the difference between the exciter air going out and the exciter air coming in is not less than 27.degree. C, as shown at 282, the operator is so informed. In block 283, each contact input from the voltage regulator equipment is interrogated to determine if any of the exciter controller contacts are closed. If such is the case, an appropriate flag "exciter monitor" is set at 284 for use by the program PO7. If the main breaker is not closed, as indicated at 285, the program returns. However, if the main breaker is closed, indicating that the system is on load rate control, the program calculates at 286, the expected and the limit of the generator stator coil discharge gas temperature rise. If the generator is water cooled, then the calculation would be of the H.sub.2 O temperature rise. The program then checks at 287 to determine whether the generator stator coil gas discharge temperature minus the H.sub.2 cooler output temperature is less than the calculated expected rise of the block 286. If it is not less than the calculated expected rise, the operator is informed. Then, if the generator stator coil has discharge temperature minus the H.sub.2 cooler output temperature is not less than the calculated rise limit as indicated at 288, the operator is also notified.

The expected generator stator coil discharge gas or H.sub.2 O temperature rise or the rise limit is shown for various types of generators in the chart of FIG. 10 under the appropriate heading. For determining the generator stator coil gas discharge temperature, the highest value of up to 12 temperature sensors for the generator stator coil gas is used; and the lowest value of up to four temperature sensors for the H.sub.2 cooler oil temperature is used.

The reactive capability of the generator is of prime importance in automatic load rate control. This generator capability must not be exceeded during the loading of the generator. In the present embodiment of the invention, the present H.sub.2 pressure is used to select an appropriate capability curve that is set from a possible maximum of four curve sets. A curve set consists of three circular arcs (see FIG. 11) with centers at C1, C2 and C3, and radii lengths of R1, R2 and R3, respectively. The circular arcs divide the positive megawatt side of the megavar (MVAR) less the megawatt (MW) plane into three different regions; namely, stator winding limiting region, stator core limiting region, and rotor winding limiting region.

The program first clears at 290, a flag which indicates to the system that a generator reactive capability is exceeded; and the megavolt ampere (MVA) vs. the frequency curve is also exceeded. Then, at 291 an MVA power factor (PF), and the allowable maximum MVA of the present frequency is calculated. The MVA, the power factor, and the allowable maximum MVA at the present frequency is calculated in accordance with the following formulae:

Where

MW = present megawatts reading

MVAR = present megavars reading

where

RMMVA = Rated MAX MVA

n = present speed in rpm

Then, decision block 292 checks as to whether the present MVA is less than the allowable maximum MVA. If it is not, the operator then is informed that the generator MVA vs. the frequency curve limit is exceeded; and a corresponding flag at 293 is set. The program checks at 294 if the H.sub.2 pressure is within operation limits, which is indicated by the setting of the flags 265 and 268. If it is not within operation limits, then the program returns. If it is within operation limits, then the appropriate generator capability curve set based on existing H.sub.2 pressure is selected in accordance with FIG. 11 at 295. If the MVAR is greater than zero, as indicated by 296, then 297 checks to determine whether the calculated lagging power factor is greater than the power factor value of the selected curve set. If 297 is negative, a rotor winding limiting sensor and radius for this region is set at 298. Then the distance between the generator operation point to the circular arc center of the selected limiting region of FIG. 11 is calculated at 299. If the selected region radius is not greater than the calculated distance, as checked by block 300, a flag "generator reactive capability exceeded" is set at 301, and an appropriate indication is given to the operator.

In the event that the MVAR is not greater than zero, block 302 checks to determine whether the calculated leading power factor is less than 95%. If it is less than 95%, the stator core limiting center and radius for this region is set at 303. If the MVAR is greater than zero; and the calculated lagging power factor is greater than the power factor value of the selected curve set, then the stator winding limiting center and radius for this region is set at 304. The distance from the generator operating point to the selected arc center of the appropriate limiting region on the MV-MVAR plane is calculated in accordance with the following formula:

where

X = Abscissa of the arc center on MW-MVARplane

Y = Ordinate of the arc center on MW-MVAR plane

The X and Y values should be initialized.

The operator indications initiated by program PO9 are as follows:

Referring to the FIGS. 12A and 12B, the program PO7 controls the speed demand and acceleration when the turbine power plant is on wide range speed control, and the load rate control when the circuit breaker is closed in accordance with information including the various flag conditions of the previously described programs. The speed demand and acceleration, and load rate control program PO7 is operated every second by the program P00.

The program first checks at 310 the several conditions thay may be detected by other programs that should institute a turbine trip. For example, and referring to FIG. 3, excessive vibration detected by the program 80, detection of water caused by the program 83, etc. In the event that there is such a condition and the turbine trip flag of 311 is not set, then the "trip turbine" flag is set for use by the program PO0 to reject from ATC to operator automatic control at 312. The operator is informed that the ATC system has requested a turbine trip. Then, the various contact outputs are caused for the various alarm and trip circuits. In the event there is no conditions requiring a turbine trip, the "trip turbine" flag is cleared at 313; and the contact outputs for the trip alarm and trip circuits are opened at 314.

Decision block 315 checks whether or not the system is on wide range speed or load control. In the event that it is on wide range speed control, checks are made at 316 and 317 to determine if the program P12 (FIG. 3) has set any conditions that would be injurious to the turbine blading. If so, an indicator informs the operator to reduce speed to avoid overheating the LT blades. After checking that the ATC system is in control at 318, a "reset target demand" flag is set and the stored target demand is made equal to the ATC target demand. The target demand speed is obtained from the program P12 (FIG. 3) and includes a speed of 605 rpm to which the turbine is run back when the actual speed is greater than 2150 rpm in the event that the steam conditions would cause dangerous overheating of the blades; and includes the heat soak speed to which the turbine would be run back if the actual speed is greater than 3550 rpm. Thus, if a run-back condition is required, depending upon the speed of the turbine from the program P12, the turbine blade reference is set equal to the ATC target demand in block 320 as previously described.

The main breaker is again checked at 321; and if it is open, block 322 checks to determine whether the actual speed is within .+-.7 rpm's of the DEH demand speed. The "hold speed" state is stored during each operation of the program; and if the "hold speed" flat at 337 is set, then the previously stored "hold speed" at 338 is updated. If the "hold speed" flag is set, then the difference between that flag and the stored previous state is checked at 339 and it is updated at 340. The "check speed" is then set equal to the actual speed at 341; and the program continues at 329 as previously described.

After the previously stored "hold speed" is updated at 338, and the validity of th HP and IP stress signals are determined to be valid at 342, the rotor stress control program inputs are checked for determining the proper rate of acceleration of deceleration in wide range speed control, and the proper load rate in megawatts per minute (hereinafter described) in load control. The computer memory has stored therein a rate index with information as follows:

The program PO7 then checks to determine if a flag for reducing the rotor stress rate at 343 or increasing the rotor stress at 344 is set. If block 343 is in the affirmative, the rate index is checked at 345 to determine if it is at the lowest acceleration or loading rate. In the event that the program PO4 does not indicate that the rotor stress should be either decreased or increased, a 3-minute reduce counter is set to 0 at 346, and a 3-minute increase time counter is set to 0 at 347. In the event that the rate index is at its lowest rate of equal to 1, then the flag for resetting the target damand is checked at 348. If the flag 348 is set, then it is cleared at 349, and the stored target demand is set to be equal to the DEH demand at 350 because the rate can go no lower than 1. If the block 348 is in the negative, then the program on wide range speed control follows through the previously described blocks 321 through 326. In the event that the rate index is not at its lowest rate, then block 351 checks to determine if the 3-minute reduce time counter is less than 180 seconds. If it is, then it is incremented at 352 by 1 second and the program continues through the previously described blocks 348, 349 and 350. If the 3-minute counter is at its maximum time, then it is set to equal 0 at 353. Also, the rate index is reduced by "one" in block 354 which reduces the acceleration rate of the turbine on wide range speed control. Accordingly, the loading rate of the turbine is also reduced if it is on load control.

If the "rotor stress increase" rate flag is set by the program PO4, the rate index is checked at 355 to determine if it is equal to the maximum rate or index 10. If it is, then the program proceeds to 348 as previously described; because the acceleration rate or the loading rate is at its maximum. If it is not at its maximum, the 3-minute increase time counter is checked to determine if the time has run out at 356. If it has not run out, then the 3-minute increase time counter is incremented by 1 second at 357. If it has run out, the counter is set to zero at 358 and the rate index is increased by "one" at 359.

Thus, the rotor stress control program PO4 controls the rate of acceleration or deceleration on speed control at 3-minute intervals; and the rotor stress control program PO4 controls the loading rate of the turbine at 3-minute intervals on load control. In the present embodiment of the invention, the system is structured so that the rate index is initialized at index 4.

After the rate index has been either reduced by "one" or increased by "one" in respective blocks 354 and 359; and the condition of the main breaker has been checked at 360, the automatic control acceleration rate is made equal to the rate index at 361 for wide range speed control and the turbine loading rate is made equal to the load rate index at 362. If the main breaker is open, the program continues to block 348 as previously described.

Assuming that the main circuit breaker is closed, the program provides for automatically increasing or decreasing, or holding the rate of increase the same of the megawatts per minute being generated by the turbine generator. The program enters at 310 and continues to 315 if there are no turbine trip conditions; and then clears the "hold load" flag at 370. In the event any of the other programs have detected a turbine conditions requiring a "load hold" at 371 then a flag 372 is determined by 273; and if such a condition exists, a "hold load" flag 374 is set. After checking the condition of the "override sensor hold" at 375; and either setting or not setting the appropriate flag of 376, the "hold load" flag is checked at 377. If the flag is set, a check is made at 378 to determine if the "hold load" flag is different from that stored during a previous program operation. If it is not set, the present "hold load" state is updated at 379. If the "hold load" flag is different from the stored previous state, then the stored previous state is also updated in 380. If the ATC is in control as determined by 381 from the base DEH system, the determination of whether or not the automatic dispatch system is in control is determined by flag 382. If ATC is not in control, the system merely returns. If the automatic dispatch (ADS) system is not in control then the stored target demand is set equal to the ATC target demand, and the target demand flag is reset for 383. Then the ATC target demand is set to be equal to the DEH load reference at 384. If the "hold load" flag is not different from the stored previous state, then the program continues to 321, which checks the condition of the main breaker.

Inasmuch as this portion of the program is concerned solely with load control, the main breaker is closed and the program checked, if the automatic dispatch system is in control at 385. If the operator enters a load demand that is equal to the DEH load, as indicated by 386, then the system sets a "load is equal to demand" flag 387. The "high loading rate" flag 388 is cleared for the program PO1 previously described. In the event that the ADS system is in control, a flag 389 is set to clear the "load equal to load demand".

Assuming that there is no "hold load" flag that is set, the block 342 checks to determine the validity of the HP or IP stress calculation and checks the flags for either reducing or increasing the rotor stress reduce rate 343 and 344 as previously described. The program then follows the paths given in connection with the description of the blocks 345-347 and 351-359 as previously described in connection with wide range speed control. The program then checks the condition of the main breaker; and the block 362 sets the turbine loading rate to be equal to the load rate index which was either decreased or increased at 354 or 359. The loading rate of the turbine is compared with the loading rate of the generator at 390; and if the turbine loading rate is greater, the automatic turbine control loading rate is set to be equal to the generator loading rate at 391. If the generator loading rate is not greater than the turbine loading rate, then the automatic turbine control loading rate is set to be equal to the turbine loading rate at 392. The program then continues at the decision block 348 as previously described.

The operator indications initiated by program PO7 are as follows:

Referring to FIG. 13, an IP turbine section 400 includes a rotor 401 having rotating blades 402 which are positioned to rotate relative to stationary blades 403 in response to the driving force of reheat steam entering intakes 404 and chamber 405. The steam exhausts through chambers 406 and conduits 407 to the low pressure turbine section.

The stationary blades 403 which are positioned between the rotating blades 402 are fastened to a blade ring 408. The temperature of the blade ring 408 is detected by a thermocouple 410 which extends at its sensing end into the blade ring 408 and at its outer end through casing 411. The outer end of the thermocouple 410 is adapted to be connected to the control system of the present invention. The rotor 401 has a bore 412 extending axially therethrough. The portion of the rotor 401 between dashed lines 14--14 illustrates that portion of the rotor for which the stress calculations are made in the present system.

Referring to FIG. 14, which shows in an enlarged form that portion of the IP turbine between dashed lines XIV--XIV of FIG. 13, bears similar reference numerals for similar parts thereof.

Referring to the fragmentary view of FIG. 14, the rotating blades 402 and 402' may be fastened to the rotor 401 in a well-known manner. In the present embodiment of the invention, stress calculations are described for either the well-known conventional "side entry" or T-root grooved blade fastenings. Opposite each rotating and stationary blade 402' and 403 of the IP rotor, there is an axial segment P extending radially inward from the surface of the rotor 401 to the bore 412 which is that area of the rotor between lines 415 and 416, which has different heat transfer coefficients and heat conductances therein. Although only one such area 415, 416 is shown in FIG. 14, the entire length of the rotor may be considered to have imaginary adjoining segments, each of which has similar characteristics with respect to varying points of conductance and heat transfer coefficients in each segment.

For example, for that area of the bore extending radially inward at opposite edges of the blades 402' and 403, the rotor is subjected to heat from the steam flowing at a rate G axially across the blades 402, 403 and 402', etc, and a portion of the steam flows in passageways 420, 421 and 422 around seal strips such as 423, which extend radially in close proximity to a peripheral surface 424 of the rotor 401 to provide an equalizing steam seal.

As is apparent from the fragmentary view of FIG. 14, the peripheral surface of the IP rotor is replete with irregularities which include grooves under the seal strips 423 as well as the peripheral extensions which fit into the base of the rotating blades 402 and 402' either by the "side entry" or "T-root" configuration. Because of these irregularities resulting in different diameters of the rotor at closely spaced axial intervals, the heat conductance is different for various portions of each of the individual segments such as that illustrated in the area between lines 415 and 416. Also, the conductance K takes different paths into the rotor in each one of the aforementioned radial segments. For example the conductance K.sub.A1, the heat travels substantially radially inward to grid point 1,1 and grid point 2,1. The heat conductance K.sub.A2 travels in a path indicated by the reference dashed line to a point 1,2 within the rotor 401 which point is axially spaced from the point 1,1. Heat also is conducted in the path K.sub.A3 in the blade 402' to a grid point 1,3. Heat transfer coefficient H.sub.1 from the space between the seal strips 423 through the conductance K.sub.A1 is as much as 10 times greater than the heat transfer coefficient H.sub.2 through the conductance paths K.sub.A2 and K.sub.A3. Thus, there is substantial heat flow axially in the rotor 401 as well as radially from the surface of the rotor to the bore 412. Such heat flow for each of the radial areas 415, 416 of the IP rotor travels from the grid point 1,1 towards 1,2 because the heat transfer coefficient is highest at the path 2,1. T.sub.A0 in the path 420 represents the actual ambient steam temperature; and is a function of the reheat steam inlet an the reheat steam exhaust after it leaves the IP turbine section. The temperature T.sub.A2 in the path 421 equals the temperature at grid point 1,1 and T.sub.AO. Therefore, the temperature T.sub.A2 can be obtained from T.sub.AO and the temperature T.sub.A1 beneath the seal strip 423 is the average.

The two-dimensional approach according to the present invention provides greater accuracy in determining the volume average temperature of the rotor. It has been found unnecessary to continue the two-dimensional calculation inwardly beyond the grid point 2,1 and 2,2 and 2,3. As the conduction path gets deeper into the rotor the calculations may then be confined merely to a single radial dimension rather than both the axial and radial which is adjacent the outer radial portions of the rotor. The details of calculating the various quantities used in the real-time determination of the rotor stress is apparent from the formulas set forth in connection with the program P16.

Appendix pages A1 through A71 is a program listing of the programs described herein including program P15.

To summarize broadly, the turbine power plant operation according to the present invention is controlled automatically from rolling of turning gear to the application of the desired megawatt loading in accordance with the real-time on line condition of the plant in the following manner.

The control system provides for storing a plurality of speed acceleration and loading rates in the computer. These rates range in increments from a predetermined minimum to a predetermined maximum; and the system at periodic intervals selects these rates in accordance with present and predicted plant conditions. For example, the system can either hold the rate of loading, at the present selected rate; decrease the rate of loading until the desired decreased rate is selected, and then hold at such decreased rate; increase the rate of loading to the desired rate, and the hold at such rate.

In starting up the turbine, after rolling off turning gear, the system selects a predetermined one of the stored rates of acceleration, provided plant conditions permit. The system then selects a stress limit for the HP turbine and the IP turbine, which limit may vary for the HP rotor depending on the temperature of the HP turbine when it rolled off turning gear and when it is under load, and for the IP rotor depending on whether it is heating or cooling. The effective temperature difference for both the HP rotor and the IP rotor is compared repetitively against its respective selected limit. Additionally, the anticipated effective temperature difference for a predetermined time in the future is also compared. Depending on such comparison both present and anticipated, the system provides for holding the stress, increasing the stress, or decreasing the stress. This command results in the rate of acceleration or loading to change incrementally in the required direction, or to remain the same.

Prior to synchronization and upon reaching heat soak speed, the turbine is held at such speed for a period of time depending on the calculated rotor bore temperature and the actual blade ring temperature of the IP turbine. The system compares these values periodically; and when both temperatures reach a predetermined value, the system is permitted to increase the speed of the turbine under the constraints of the HP and IP turbine rotor conditions as previously described.

Upon closing the circuit breaker, and after application of initial load the system, in response to the operator or other means requesting a target electrical load, changes its rate of loading periodically under the constaints of the HP and IP turbine rotors and the capabilities of the electric generator.

Briefly, the generator constraints which control the rate of loading includes the allowable maximum megavoltampers and the reactive capability of the generator. The capability curve of the generator is based on existing hydrogen pressure and a determination of whether the calculated lagging power factor is greater than the power factor value of a selected curve is made.

The IP rotor stress determination and bore temperature is calculated in two dimensions for greater accuracy.

It is understood that although a programmed digital computer having a central processor is disclosed in connection with the present invention, that hardwired digital or analog system or micro-processor may be used to perform the functions set forth herein. ##SPC1## ##SPC2## ##SPC3## ##SPC4## ##SPC5## ##SPC6## ##SPC7## ##SPC8## ##SPC9##