Seal Oil Temperature Control Method and Apparatus

The invention relates to turbine generators, and more specifically to gland seals for preventing or minimizing both the escape of hydrogen gas from a generator and the ingress of moisture and air into the generator. In particular, the present invention relates to a system for controlling temperatures of seal oils supplied to generator gland seals to reduce or minimize temperature differences between the oils that can create thermal differential expansion in the generator shaft.

A typical generator arrangement will include a shaft which transmits torque from a turbine to rotate a rotor in the generator to generate electricity. The rotor shaft also extends from the other side of the generator (often referred to as the exciter side) for support by a bearing. Generally, within the generator, an environment is provided which includes a gas such as hydrogen or helium for better heat conduction and reduced windage losses. On the shaft side which transmits the torque (turbine side) as well as the shaft side which provides support (exciter side), seals are provided for preventing escape of the gas, and also for preventing ingress of moisture or air to the interior of the generator. The seals may be in the form of a gland seal which directs two flows of oil toward and along the shaft. One flow of oil (hereinafter the hydrogen-side seal oil) will flow along the shaft toward the generator to prevent the escape of hydrogen to the outside atmosphere. Another flow (air-side seal oil) flows outwardly toward the bearing to prevent access of air or moisture into the generator. Since the oils tend to absorb hydrogen, air and moisture, the oil feed systems are separate, thereby preventing release of hydrogen to the outside atmosphere, and maintaining a high hydrogen purity within the generator. For best operation, the temperatures of the air-side seal oil and hydrogen-side seal oil should be maintained at or near the same temperature, and should be kept within 4.degree. F. If the oils are not at or near the same temperature, the seal ring can become distorted or non-uniformly thermally altered, thereby producing vibrations as the shaft rotates. Ring distortions can produce a rubbing between the shaft and the ring of the seal, which can in turn generate localized heating of the shaft causing it to bend and producing vibrations. Thus, it is essential to maintain the air-side seal oil and hydrogen-side seal oil at or near the same temperature.

Currently, two methods are available for temperature control of the hydrogen- and air-side oils. In one method, separate manual controls of cooling water to a cooler for the hydrogen-side oil, and a cooler for the air-side oil are utilized to control the respective oil temperatures. However, manual control requires constant adjustment to maintain the same or approximately the same temperatures of the two oils. Constant adjustment is necessary due to the continued variations in the flow rates and temperatures of the seal oil, as well as flow rates and temperatures of the cooling water supplied for controlling the temperatures. Thus, constant attention of an operator is required.

In a second method, individual automatic temperature controllers are provided for each cooler, with the temperature controllers set at the same temperature. The use of two controllers also requires adjustments to ensure that the temperatures are similar, since as the cooling water temperature varies, the desired flow response to a particular temperature deviation will also vary. In addition inherent system deviations make it difficult to maintain a small temperature differential. A major problem and expense involved with the use of separate controls is due to the requirement that the temperature control is finely tuned such that each system accurately responds to the set temperature, with the two controllers having a combined tolerance which ensures the required minimal temperature differential.

Thus, a system for providing seal oils to a gland seal ring is needed which can accurately and economically control the temperatures to reduce or minimize temperature differentials between the oils. Preferably, such a system should eliminate the need for constant adjustment as is the case with manual control or separate individual controllers. In addition, it is desirable to reduce the cost associated with precise and accurate independent control of the two flows.

In accordance with the present invention, a system for supplying seal oil to the hydrogen-side and air-side of a gland seal is provided which can reduce or minimize the temperature difference between the seal oils. The system utilizes the temperature of one of the seal oils as a reference, and controls the temperature of the other seal oil in response. Since one of the oils is utilized as a reference, a separate accurate control of the reference oil is not necessary as variation in the reference oil temperature is accommodated by a corresponding adjustment by the temperature control of the other seal oil. Thus, the need for constant adjustment, and the need for extremely accurate and precise controllers for two separate systems is not necessary.

It is therefore an object of the present invention to provide a seal oil feeding system which can provide seal oils to a seal such as a gland seal, with the oils fed at or near the same temperature.

It is a further object of the present invention to provide a temperature control system for providing seal oils having minimal temperature differences, in which continual adjustment of the temperature controls is not necessary.

It is another object of the present invention to provide a temperature control for seal oils for providing seal oils having small temperature differences, in which precise and accurate temperature controls for each seal oil are not necessary.

It is yet another object of the present invention to provide a system for feeding seal oils having little or no temperature differences, in which the temperature of one of the seal oils is utilized as a reference for controlling the temperature controls of a second seal oil.

These and other objects and advantages of the present invention will be apparent from the following detailed description when read in conjunction with the drawings.

FIG. 1 is a sectional view of a gland seal and bearing structure to which the present invention pertains.

FIG. 2 is a schematic of conventional hydrogen-side and air-side oil flow systems.

FIG. 3A is a schematic of the air-side and hydrogen-side oil temperature control system in accordance with the present invention.

FIG. 3B shows a modification of the temperature control system of FIG. 3A.

FIG. 4 shows an engineering schematic of the hydrogen- and air-side oil systems utilizing the temperature control system of FIG. 3A.

FIG. 1 illustrates a cross sectional view of the seal and bearing structure provided on larger generators (i.e., those in which the internal gas pressure of the hydrogen or other gas is in the range of 30-75 psi). The generator shaft 1 will either transmit torque from a turbine to the generator rotor on the turbine side, or will support the rotor on the exciter side opposite that of the turbine. A bearing 2 is provided for supporting the shaft, with the areas 10 outside of the bearing exposed to ambient air. The gland seal arrangement is shown generally at 12, and is in the form of an annular ring which directs fluid toward and along the shaft to form a seal between the air and moisture of the external atmosphere (10) and the internal atmosphere of hydrogen gas 14. A bearing and a gland seal are provided on both the exciter and turbine sides of the hydrogen generator, to support the shaft and to seal the hydrogen atmosphere within the generator. The gland seal does not support the shaft weight, but does support its own weight on the shaft.

Basically two flows of seal oils are provided to respective inlets 16,18 of the gland seal. The flow through inlet 16 adjacent the generator or hydrogen-side will be referred to as the hydrogen-side seal oil, while the flow to inlet 18 will be referred to as the air-side seal oil. The gland seal includes channels 16a, 18a for directing the respective seal oils to a gland seal ring 20, which in turn directs the oils toward the shaft via channels 15,17 formed in the annular gland seal ring. The channels 15,17 feed the oil to annular grooves which extend about the shaft to supply oil to the shaft.

The seal oils are directed toward the shaft causing the oils to flow along the shaft as indicated by the arrows shown on the shaft 1. The hydrogen-side oil is prevented from entering into the generator by a labyrinth seal ring 34, which typically takes the form of a brass ring having a radial clearance of approximately 0.010-0.020 inches. After flowing along the shaft, the hydrogen-side oil is directed to a drain as indicated by flow 30. The air-side oil is directed toward the bearing 2, and is drained as shown at 32. U-shaped babbitts 36 are provided, which are formed of a lead, tin or other soft material, such that if contact should occur between the shaft and the gland seal, the wear on the shaft will not be as great. The babbitt thus presents a softer surface than the gland seal ring 20, (which typically is bronze) and has a higher hardness and melting point than the material of the babbitt. The hydrogen-side oil thus flows through channels 16a, 17 and groove 26, toward and along the shaft, and is drained as shown at 30. The hydrogen-side oil blocks hydrogen from escaping from the interior of the generator. The hydrogen- and air-side oils are fed at substantially equal pressures to prevent mixing of the oils. Thus, air or moisture absorbed by the air-side oil is maintained away from the generator interior, and hydrogen absorbed by the hydrogen-side oil is maintained away from the external atmosphere.

The air-side seal oil is directed toward and along the shaft, is drained at 32, and prevents access of moisture and air into the interior of the generator. Float oil is also directed to a channel 19 which serves to apply pressure to the gland seal ring 20 for aiding in reducing any resultant, side forces on the gland seal ring. The flow to channel 19 may be of a pressure which is greater than that of the oils at 16,18, but generally it is sufficient to utilize an oil pressure which is the same as that of the oils 16,18 and typically the oil supplied at 19 will be from the same source as that of the air-side seal oil fed to the seal at 18. The float oil serves to compensate for the gas pressure of the generator interior which applies an axial outward force on the gland seal ring.

As mentioned earlier, it is extremely important to minimize the temperature differences between the hydrogen-side seal oil and the air-side seal oil. The temperature differences should be, at most, 4.degree. F. If the temperature differences are not minimized, the non-uniform thermal expansion of the gland seal ring can cause vibrations and damage the generator shaft. For example, if the hydrogen-side oil is hotter than the air-side, gland seal ring portions adjacent the hydrogen-side will be enlarged relative to the air-side, which can result in vibrations due to rubbing of the gland seal ring (or more particularly, the babbitt associated with the ring), which in turn causes localized heating and bending of the shaft.

FIG. 2 illustrates a feed system for the hydrogen- and air-side seals in accordance with the existing method or system. As shown in FIG. 2, a seal on the generator shaft will include an air-side seal oil directed toward the generator shaft as shown at 40, and a hydrogen-side seal oil feed as shown at 42. A pair of pressure sensors 44,46 are provided for operation of a pressure equalizing valve 48, such that the pressure of the air-side and hydrogen-side seal oils are the same. After passing over the generator shaft, the hydrogen-side oil drains from the gland seal (30, FIG. 1) to a defoaming tank 50. The defoaming tank slows the oil velocity and provides a large oil surface area which allows hydrogen bubbles to escape from the oil.

The air-side seal flows (32) oil from the gland seal to a common drain 52 with the bearing lubrication oil return as shown at 51. The bearing oil and air-side seal oil are returned to a loop seal tank 54 where oil vapors (and possible traces of hydrogen) are drawn off by a loop seal vapor extractor. The loop seal tank provides an interface with the main lubrication system of the generator, receiving oil from the air-side of the gland seal and from the bearings (via drain 52), with oil returning to the lubrication system as shown at 53. Loop seal tank 54 provides a source of oil for the air-side seal oil 58 via line 56. Thus, in the conventional system, the loop seal tank receives the hot air-side and bearing oil, allows excess to return (53) to the main lube oil system, and passes hot oil through pump 58 for cooling by the cooler 60.

The air-side oil from loop seal tank 54 is then pumped through a cooler 60 which includes water inlet and outlet ports 62 for supplying cooling water for controlling the temperature of the oil. After passing through a filter 64, the oil proceeds to the generator shaft as shown at 40.

Additional lines 66,68 are provided for maintaining an appropriate supply of oil in the hydrogen-side oil system. In particular, a float valve device 70 is provided in a regulating tank 72 which opens when the level of oil is low to receive oil from the flow line 66. An additional float valve 74 is provided which opens when the level is high to release oil through the line 68 to the suction side of the air-side seal oil pump. A bypass line 76 is provided with a bypass regulator 78 for maintaining the pressure of the air-side seal oil, such that it is maintained sufficiently above the hydrogen gas pressure in the generator during normal operation and typically the oil pressure will be maintained at 12 psi above the hydrogen gas pressure. To achieve the desired pressure differential, a sensor 75 senses gas pressure in the headspace of the defoaming tank, and sensor 77 senses pressure of the air-side oil, with the valve 78 controlled to maintain the oil pressure 12 psi above the gas pressure.

The hydrogen system feeds oil from the regulator tank 72 to a pump 80 which supplies pressurized oil for feeding through the cooler 82 and filter 84, and then through equalizing valve 48 for feed to the generator shaft as shown at 42. A pump bypass regulator (not shown) may also be provided to allow part of the pump not needed by the pressure equalizing valves to return to the suction side of the pump. The hydrogen-side cooler includes flow passages 86 for feeding of water, with the water feed rate controlled to control the cooling of the oil. In the prior art system, a manual control of the cooling water to the hydrogen and air-side coolers can be utilized for adjusting the temperatures in the air-side and hydrogen-side seal oil systems. However, it is often difficult to control the temperatures to minimize the temperature differences utilizing manual control, and constant operator attention is necessary.

Alternatively, individual temperature controllers have been provided which are set at the same temperature. However, with the individual controllers, deviations in the accuracy of the individual systems can cause the temperatures to deviate from the set temperature. More significantly, even where the temperature controllers are accurate, the systems will fluctuate due to varying flow rates and water coolant temperatures, with the oil and hydrogen seal oil temperatures deviating from the set temperature until the controller is able to adjust the coolant flow rates in an attempt to bring the oil temperatures to the set temperature. In addition, existing systems require separate coolers for controlling temperatures to be similar and below a maximum temperature (typically 120.degree. F. maximum).

In accordance with the present invention, separate finely tuned controllers and/or coolers are not necessary for both the hydrogen-side and the air-side oil systems. Constant manual control of individual systems can also be eliminated. Most significantly, the temperature differences can be consistently minimized as compared to the prior art systems, even though the control is simplified from a hardware and operational perspective.

FIGS. 3A and 3B illustrate the present invention in which separate control of the air-side and hydrogen-side oils is not utilized, but rather a differential temperature control system is utilized for controlling the hydrogen-side oil temperature, utilizing the air-side oil temperature as a reference. In particular, a sensor 100 is provided which senses the temperature of the air-side oil being fed to the gland seal and sends a signal indicative of the temperature to a differentiator 102. A temperature sensor 104 is also provided which provides the differentiator 102 with a signal indicative of the temperature of the hydrogen-side seal oil being fed to the gland seals. The differentiator 102 then provides a signal as shown at 103 to a valve controller 105 which then controls cooling of the hydrogen-side oil.

The hydrogen-side oil flows from a pump along passage 106 and is fed into the cooler at 108 and is cooled by the cooler 110, and is then fed out of the cooler at 112 through a three-way valve 114 and toward the gland seals. A bypass line 116 is provided which provides for mixing of cooled and uncooled oil to control the oil temperature fed to the gland seals. The three-way valve 114 controls the proportion of the mixing. The valve controller 105 thus provides a signal to a control or actuator 120 for the valve 114 to vary the mixing to adjust the hydrogen-side oil temperature to the reference temperature of the air-side oil. Thus, where the temperature of the hydrogen-side oil is sensed to be greater than that of the air-side oil, the three-way valve 114 reduces or eliminates the flow through 116, such that an increased proportion of the flow through the valve 114 is from the cooler outlet 112. Where the temperature is lower than that of the reference temperature, the valve 114 is controlled to increase the flow from the bypass 116.

Since the temperature control system utilizes the air-side oil as a reference, separate accurate controlling of the air-side oil is not necessary. In accordance with another aspect of the present invention, Applicants have recognized that, since separate control of the air-side oil is not necessary, a separate cooler for the air-side oil is not necessary, and the air-side system can simply utilize oil from the lube system which has been cooled in the main system. Most significantly, the temperature difference is more consistently minimized, since the system is not as subject to the fluctuations of two independently controlled systems.

In addition to these advantages, in the FIG. 3A system a more immediate and predictable response can be provided by the mixing of cooled and uncooled oil, since it is the mixing of oil which is provided for controlling the temperature, in contrast to the prior art system which controls the feed rate of the cooling water to the cooler. Often the cooling water temperature varies widely, and it is therefore difficult to predict the effect of a change in the water flow rate on the cooling of the oil. With the FIG. 3A system, the flow rate through the cooler can be maintained substantially constant. Another advantage of the FIG. 3A system resides in the ability to maintain a high water flow rate through the cooler, such that the formation of deposits within the cooler is reduced, thereby prolonging the life and efficient operation of the cooler.

An alternative embodiment of the control is shown in FIG. 3B. In the FIG. 3B arrangement, the bypass 116 and three-way valve are eliminated, and the temperature is controlled by controlling the flow rate of water through the cooler. While the FIG. 3B system does not provide the advantages associated with the oil mixing mentioned above, it is still advantageous over the prior art systems in eliminating the temperature controls and coolers for the air-side seal oil, and in providing a more consistent minimized temperature difference between the hydrogen-side and air-side seal oils. In the FIG. 3B arrangement, a control or actuator 220 receives a signal from a valve controller (similar to that shown at 105 in FIG. 3A), which, in response to a temperature difference signal from a differentiator (102), controls operation of the outlet valve 222 of the cooler 210, thereby controlling the flow rate of water through the cooler, and thus controlling the temperature of the hydrogen-side oil passing from the cooler as shown at 226.

FIG. 4 illustrates the bypass arrangement of FIG. 3A in slightly greater detail. As shown in FIG. 4, the air-side pump will generally include a pair of seal oil pumps (SOP1, SOP2) driven by AC motors with an emergency seal oil pump (ESOP) driven by a DC motor. The fluid is pressurized on the hydrogen-side by an AC motor driven oil pump (HSOP). Thus, as shown in FIG. 4, the temperature of oil passing from filters 250,252 then is sensed by temperature sensors 100,104 to produce a signal to the control unit 102,105 which will include circuitry for differentiating the temperature signals and producing a valve control signal based upon the difference between the temperature signals. The controller 102,105 will thus produce a signal to a valve controller 120 which controls the mixing of cooled and uncooled oil by three-way valve 114. Appropriate valving is provided to maintain the air- and hydrogen-side seal oils at the same pressure, and at a pressure which is approximately 12 psi above the hydrogen gas pressure in the generator.

An important aspect of the present invention, as shown in FIG. 4, resides in the use of the lube oil as the main feed source into the air-side system as shown at 260. Since a separate precise control of the air-side oil is not necessary, oil cooled from the main lubrication system can be utilized without the need for a separate cooler. The loop seal tank is connected to the air-side oil tank as shown at 262, but only for use as a back up oil supply. In particular, the oil from the loop seal tank is supplied at a lower pressure than the lube oil such that the loop seal oil generally does not enter the system unless the lube oil pressure fails. Check valves 262,266 are provided for preventing backflow of the oil. Thus, in accordance with the present invention, the lube oil is fed directly to the air-side oil system, with the hot loop seal oil utilized as a back-up or emergency flow. In contrast, in the prior art system, hot oil is fed to supply the air-side oil system from the loop seal tank, with the oil cooled by a separately controlled cooler in the air-side system. In the prior art systems, the back-up system utilized lube oil fed directly to the gland seals (i.e. at 42,40--FIG. 2), thus requiring additional hardware for providing an appropriately pressurized flow to the gland seal as an emergency back-up.

Still referring to FIG. 4, suitable isolation valves 349,353,355,358,361,353,356, and 359 are provided to isolate various portions of the pump systems to allow for maintenance or repairs. Check valves are provided at 354,357,360 and 363 to prevent backflows. Bypass relief valves 342,380, 381 and 382 are provided to feed any excess pumping fluid pressure back to the suction side of the pumps. A pressure regulator 364 controls the pressure of the air-side oil fed to the generator seal. Pressure equalizing valves 310,317 ensure that the oils fed to the gland seals are at the same pressure. A valve 370 is provided for connecting the air-side to a turbine control system which will detect the oil pressure, and shut off the turbine generator where oil pressure is insufficient. The hydrogen-side oil is thus fed to the gland seals as indicated at 330,332 and the air-side oil is fed to the gland seals as shown at 334. Note that the air side feed 334 is split (not shown) to feed a pair of gland seals, one on each side of the generator.

Oil draining from the hydrogen-side of the seals is drained as shown at 390, to a regulator tank 391. Oil from the generator bearings is collected by the loop seal tank as indicated at 234,235, with oil from the regulator tank (231) and the air-side drain collected as shown at 236. Alternatively, if desired, the tank drain could be fed to the air-side system rather than the loop seal tank. A level indicator LI provides a meter indication to an operator, and a level sensor LS sounds an alarm and/or causes actuation of a drain valve 231 when the tank level is too high. A solenoid 392 can be provided to admit oil from the air-side system when the level sensor indicates the level in the regulator tank is low. A vent 232 is also provided to prevent build-up of excess gas pressure in the regulator tank. Oil from the regulator tank is then fed back to the hydrogen side pump through shut off or isolation valve 337, which connection is shown as broken for clarity in the figure.

The present invention provides improved temperature control such that the temperature difference between the air-side and hydrogen-side seal oils can be consistently minimized. In addition, the need for constant manual control or separate precise and accurate temperature controllers is eliminated. Thus, seal oils having the same or nearly the same temperatures can be provided to a gland seal which advantageously prevents damage to the generator shaft and associated gland seal which can be caused by thermal differential expansion of the shaft, while also reducing costs associated with operator supervision or capital outlay of independent control systems.