Method of effecting fast turbine valving for improvement of power system stability

Abstract

As an improved way of effecting fast valving of turbines of power system steam-electric generating units for the purpose of improving the stability of power transmission over transmission circuits to which their generators make connection .Iadd., .Iaddend.when stability is threatened by line faults and certain other stability endangering events, and in which intercept valves are rapidly closed on a momentary basis, the procedure of intercept valve closure is supplemented by simultaneously initiating turbine and steam supply source control programs, which (a) .[.being.]. .Iadd.bring .Iaddend.into effect a sustained reduction in turbine driving power via employment of measures which may include full closing of some or all control valves and/or employment of preprogrammed control valve repositioning, with provision to automatically divert high pressure steam to the condenser or to atmosphere as a way to prevent discharge of steam through high pressure safety valves. (b) bring into effect a rapidly executed process of reduction of rate of generation of steam within steam supply sources, and (c) initiate a control program that effects a predetermined degree of partial reopening of intercept valves early in the course of the generator rotor's first backward swing, following which intercept valves are further opened and control valve positions optionally revised in preprogrammed ways with the overall effect that in the period following the first forward swing the magnitude of turbine driving power is caused to hold below the value that applied prior to the event that initiated fast valving and to at most only briefly exceed a final sustained value that can be preset.

Based on the above, what I claim is: 
     
       1. In a steam-electric installation which incorporates .Iadd.an alternating current type generator driven by a compound type steam turbine incorporating control valves ahead of the high pressure turbine, and intercept valves ahead of the turbine or turbines that receive steam from the discharge of the high pressure turbine, which installation also incorporates a fossil fuel type steam generator equipped with .Iaddend.a reheater, .Iadd.and also one or more .Iaddend.power operated relief valves located ahead of the high pressure turbine, which are so controlled as to open and discharge steam to atmosphere when pressure ahead of the valve or valves exceeds a preset value that is less than that at which the turbine's high pressure safety valves are set to open, and to reclose when pressure falls below a preset value which exceeds normal operating pressure ahead of the turbine, .Iadd.the generator of .Iaddend.which installation .[.is part of.]. .Iadd.makes connection to .Iaddend.a power system which includes a plurality of prime mover driven generators, which generators are interconnected by a plurality of .Iadd.alternating current .Iaddend.transmission circuits, the method of employing fast .[.turbine.]. valving as a way to avoid development of system instability .[.as a consequence of stability endangering events of a type adapted to cause the generator of the said installation to experience a sudden at least momentary reduction of load,.]. which comprises the steps of, 1. providing within the turbine and steam generator control system, for response to a fast valving initiation signal input by bringing into effect preprogrammed jointly effected processes of, a. .Iadd.at least partial .Iaddend.intercept valve closure effected fast enough to have a favorable effect on generator rotor first swing stability, and control valve repositioning plus intercept valve reopening so effected as to cause turbine driving power subsequent to generator rotor first forward swing to hold below a preset value that is less than the driving power that applied prior to the event that brought about development of the signal,   b. runback of rate of steam production within the steam generator to a value that will cause termination of .[.the.]. .Iadd.whatever .Iaddend.discharge of steam through said power operated relief valves .[.that will.]. .Iadd.may .Iaddend.at first take place, with provision so that said runback is effected rapidly enough .Iadd.and is otherwise so executed as .Iaddend.to avoid overheating of the reheater,     2.   
     
     
       2.  providing in a preprogrammed manner so that .[.a fast valving signal is generated and transmitted as an input to the turbine and steam generator control system on the occurrence of certain types of events that endanger preservation of system stability..]. .Iadd.a. a fast valving signal is generated on the occurrence of system stability endangering events of a type that cause the said generator to experience a sudden at least momentary reduction of load,   b. the said fast valving signal is made available as an input to that portion of the turbine's control system that is adapted to bring into effect the said preprogrammed processes. .Iaddend. .[.2. The method of claim 1 wherein one of a plurality of pairs of coordinated preprogrammed processes of turbine and steam generator control will be selectively activated in dependence on the nature of the stability endangering event..]. .[.3. The method of claim 1 in which some but not all of the turbine's control valves are rapidly closed by valve actuator oil dumping..]. .[.4. The method of claim 1 in which half of the turbine's control valves are rapidly closed by valve actuator oil dumping..]. .[.5. The method of claim 1 in which one quarter of the turbine's control valves   
     
     
        are rapidly closed by valve actuator oil dumping..]. 6. In a steam-electric installation incorporating .[.a U.S. type.]. .Iadd.an alternating current type generator driven by a compound type steam turbine incorporating control valves ahead of the high pressure turbine, and intercept valves ahead of the turbine or turbines that receive steam from the discharge of the high pressure turbine, which installation also includes a reheater, and also a .Iaddend.once-through boiler, one or more power operated valves that are arranged so that when opened they provide a path by which steam can by-pass from a point ahead of the turbine to the flash tank of said boiler, .[.and from thence to the condenser,.]. which valves are subject to the control .[.ofa--  .Iadd.of .Iaddend.a control system which .[.causes.]. .Iadd.is operative under load conditions to cause .Iaddend.them to open when the pressure ahead of the valves exceeds a preset value which is less than that pressure that will cause discharge of steam through the turbine's high pressure safety valves, and are also so controlled as to close when pressure falls to a preset value that exceeds the normal operating pressure of the turbine, .Iadd.the generator of .Iaddend.which installation .[.is part of.]. .Iadd.makes connection to .Iaddend.a power system which includes a plurality of prime mover driven generators, which generators are interconnected by a plurality of .Iadd.alternating current .Iaddend.transmission circuits, the method of employing fast turbine valving as a way to avoid development of system instability .[.as a consequence of stability endangering events of a type adapted to cause the generator of the said installation to experience a sudden at least momentary reduction of load,.]. which comprises the steps of, 1. providing within the turbine and steam generator control system, for response to a fast valving initiation signal input by bringing into effect preprogrammed jointly effected processes, of a. .Iadd.at least partial .Iaddend.intercept valve closure effected fast enough to have a favorable effect on generator rotor first swing stability, and control valve repositioning plus intercept valve reopening so effected as to cause turbine driving power subsequent to generator rotor first forward swing to hold below a preset value that is less than the driving power that applied prior to the event that brought about development of the signal,   b. runback of rate of steam production within the steam generator to a value that will cause termination of .Iadd.whatever .Iaddend.discharge of steam through said steam by-pass valves .Iadd.may take place .Iaddend.with provision so that said runback is effected rapidly enough .Iadd.and is otherwise so executed .Iaddend.to avoid overheating of the reheater.     2. providing in a preprogrammed manner so that .[.a fast valving signal is generated and transmitted as an input to the turbine and steam generator control system on the occurrence of certain types of events that endanger preservation of system stability..].   a. a fast valving signal is generated on the occurrence of system stability endangering events of a type that cause the said generator to experience a sudden at least momentary reduction of load,   b. the said fast valving signal is made available as an input to that portion of the turbine's control system that is adapted to bring into   
     
     
        effect the said preprogrammed processes.  .[.7.  The method of claim 6 wherein one of a plurality of pairs of coordinated preprogrammed processes of turbine and steam generator control will be selectively activated in dependence on the nature of the stability endangering event..].  .[.8. The method of claim 6 in which some but not all of the turbine's control valves are rapidly closed by valve actuator oil dumping..].  .[.9. The method of claim 6 in which half of the turbine's control valves are rapidly closed by valve actuator oil dumping..].  .[.10. The method of claim 6 in which one quarter of the turbine's control valves are rapidly 
     
     
        closed by valve actuator oil dumping..].  11. In a steam-electric installation which .[.is part of.]. .Iadd.incorporates an alternating current type generator driven by a compound type steam turbine incorporating control valves ahead of the high pressure turbine, and intercept valves ahead of the turbine or turbines that receive steam from the discharge of the high pressure turbine, the generator of which installation makes connection to .Iaddend.a power system which includes a plurality of prime mover driven generators, which generators are interconnected by a plurality of .Iadd.alternating current .Iaddend.transmission circuits, the method of employing fast turbine valving as a way to avoid development of system instability .[.as a consequence of stability endangering events of a type adapted to cause the generator of the said installation to experience a sudden at least momentary reduction of load,.]. which comprises the steps of, 
     
     
       1. providing within the turbine's control system for response to a fast valving signal input by bringing into effect preprogrammed processes of, a. at least partial closure of the turbine's intercept valves,   b. partial intercept valve reopening, to the extent of at least 25 percent .[.brought to completion.]. .Iadd.on a flow basis, effected .Iaddend.within 1/2 second .[.of termination of closure, and.]. .Iadd.after the peak of the generator rotor first forward swing, with termination of fast opening occurring when the valves are still only part way open, .Iaddend.followed by more slowly effected full opening executed in a manner adapted to cause turbine driving power to hold below a preset value that is less than the driving power of the turbine at the instant of receipt of the said fast valving signal input,   2. providing in a preprogrammed manner so that .[.a fast valving signal is generated and transmitted as an input to the turbine and steam generator control system on the occurrence of certain types of events that endanger preservation of system stability..]. .Iadd. a. a fast valving signal is generated on the occurrence of system stability endangering events of a type that cause the said generator to experience a sudden at least momentary reduction of load,   b. the said fast valving signal is made available as an input to that portion of the turbine's control system that is adapted to bring into     
     
     
        effect the said preprogrammed processes. .Iaddend. 12. The process of 
     
     
        claim 11, in which intercept valves in step (1), are fully closed. 13. The process of claim 11 in which intercept valve reopening is initiated within 
     
     
        0.1 second of completion of the closing process. 14. The process of claim 11 in which partial intercept valve reopening carried out in step (2) is effected with oil supplied from accumulators, and is terminated by operation of valves of cam operated type, with cam position determined by 
     
     
        valve stroke. 15. The process of claim 11 in which fast partial intercept valve reopening, carried out in step 2, is effected by the transfer to the cylinder of each of the valve actuators, of a predetermined quantity of 
     
     
        oil contained within a second cylinder. 16. The process of claim 11 in which control valves are repositioned in a manner adapted to bring into effect a preset sustained degree of partial closure, with provision so that said process of partial closure is accomplished rapidly enough, and to an extent sufficient, to prevent an increase in steam pressure ahead of the turbine's intercept valves that would suffice to cause discharge of steam through safety valves located ahead of said intercept valves. .Iadd. 17. In a nuclear steam electric installation which incorporates an alternating current type generator that is driven by a compound type steam turbine in which steam received from a nuclear steam supply source passes through control valves into a high pressure turbine and is discharged as a mixture of steam and water into one or more moisture separators in which the bulk of the water is separated out and discharges into a drain system, and from there returns eventually to the nuclear steam supply source, and in which demoisturized steam is discharged from the moisture separator or separators into one or more reheaters from which it passes into one or more low pressure turbines, which it enters through intercept valves, which installation includes one or more by-pass valves that are arranged to open and discharge high pressure steam to the condenser when steam pressure ahead of the valves exceeds a preset value, and close when pressure falls below said preset value, the generator of which installation makes connection to a power system which includes a plurality of alternating current transmission circuits, the method of employing fast valving as a way to avoid development of system instability which comprises the steps of 1. providing within the turbine and steam generator control system, for response to a fast valving initiation signal input by bringing into effect preprogrammed jointly effected processes of, at least partial intercept valve closure effected fast enough to have a favorable effect on generator rotor first swing stability, and control valve repositioning plus intercept valve reopening so effected as to cause turbine driving power subsequent to generator rotor first forward swing to hold below a preset value that is less than the driving power that applied prior to the event that brought about development of the signal,   2. providing in a preprogrammed manner so that a. a fast valving signal is generated on the occurrence of system stability endangering events of a type that cause the said generator to experience a sudden at least momentary reduction of load,   b. the said fast valving signal is made available as an input to that portion of the turbine's control system that is adapted to bring into effect the said preprogrammed processes. .Iaddend..Iadd. 18. The method of claim 17 in which the process of control valve repositioning is so effected as to prevent an increase in steam pressure ahead of the turbine's intercept valves that would suffice to cause discharge of steam through safety valves located ahead of said intercept valves. .Iaddend..Iadd. 19. The method of claim 17 in which both the control and intercept valves of the turbine are at first fully closed, and, after closure, rapidly opened to a position at which the control valves have reached their preprogrammed new sustained position and the intercept valves have reached an equally open position on a flow basis, and providing thereafter to only slowly fully reopen the intercept valves under servo and/or rate of oil flow control. .Iaddend. .Iadd. 20. In a steam-electric installation which incorporates an alternating current type generator driven by a compound type steam turbine incorporating control valves ahead of the high pressure turbine, and intercept valves ahead of the turbine or turbines that receive steam from the discharge of the high pressure turbine, which installation also incorporates a fossil fuel type steam generator equipped with a reheater, and also one or more power operated relief valves located ahead of the high pressure turbine, which are so controlled as to open and discharge steam when pressure ahead of the valve or valves exceeds a preset value that is less than that at which the turbine's high pressure safety valves are set to open, and to reclose when pressure falls below a preset value which exceeds normal operating pressure ahead of the turbine, the generator of which installation makes connection to a power system which includes a plurality of prime mover driven generators, which generators are interconnected by a plurality of alternating current transmission circuits, the method of employing fast valving as a way to avoid development of system instability, which comprises the steps of,     1. providing the turbine and steam generator control system with a plurality of fast valving signal input channels, each of which, when it receives a signal, will bring into effect a different pair of preprogrammed jointly effected processes of a. intercept valve closure effected fast enough to have a favorable effect on generator rotor first swing stability, and control valve repositioning plus intercept valve reopening so effected as to cause turbine driving power subsequent to generator rotor first forward swing to hold below a preset value that is less than the driving power that applied prior to the event that brought about development of the signal,   b. runback of rate of steam production within the steam generator to a value that will cause termination of whatever discharge of steam through said power operated relief valves that may at first take place, with provision so that said runback is effected rapidly enough and is otherwise so executed to avoid overheating of the reheater,     2. providing in a preprogrammed manner so that a. a fast valving signal is generated on the occurrence of system stability endangering events of a type that cause the said generator to experience a sudden at least momentary reduction of load,   b. the said fast valving signal is selectively made available to one of the said plurality of fast valving signal input channels, in such manner that the pair of preprogrammed processes that will be activated will depend in a preprogrammed way on the nature of the stability endangering event. .Iaddend. .Iadd. 21. In a steam-electric installation which incorporates an alternating current type generator driven by a compound type steam turbine incorporating control valves ahead of the high pressure turbine, and intercept valves ahead of the turbine or turbines that receive steam from the discharge of the high pressure turbine, which high pressure turbine is of the partial admission type, and wherein there is provision to rapidly close at least half of the turbine's control valves by valve actuator oil dumping, the generator of which installation makes connection to a power system which includes a plurality of prime mover driven generators, which generators are interconnected by a plurality of alternating current transmission circuits, the method of employing fast valving as a way to avoid development of system instability which comprises, providing within the turbine's control system for response to a fast valving signal by bringing into effect preprogrammed processes of repositioning of both control and intercept valves, which include rapid closing of some but not all control valves effected with the benefit of valve actuator oil dumping. .Iaddend..Iadd. 22. The method of claim 20 in which half of the turbine's control valves are rapidly closed by valve actuator oil dumping. .Iaddend..Iadd. 23. The method of claim 20 in which one quarter of the turbine's control valves are rapidly closed by valve     
     
     
        actuator oil dumping. .Iaddend..Iadd. 24.  The method of claim 6 in which the steam by-pass valves which discharge to the flash tank are preprogrammed to open in response to the fast valving initiation signal, and wherein the process of valve opening would be designed to prevent a rise in or somewhat reduce steam pressure and would be followed by a process of progressive valve reclosing as pressure falls below a preset valve. .Iaddend..Iadd. 25. The method of claim 6 in which provision is made to allow flash tank steam to discharge to the condenser. .Iaddend.