System and method employing a digital computer with improved programmed operation for automatically synchronizing a gas turbine or other electric power plant generator with a power system

• US 4,031,407 A
• Filed: 07/31/1972
• Issued: 06/21/1977
• Est. Priority Date: 12/18/1970
• Status: Expired due to Term

• Current Assignee: Westinghouse Electric Company LLC (Brookfield Asset Management Incorporated)
• Original Assignee: Westinghouse Electric Company LLC (Brookfield Asset Management Incorporated)
• Inventors: Reed, Terry J.
• Primary Examiner(s): Schaefer, Robert K.
• Assistant Examiner(s): Smith, William J.
• Application Number:
  US05/276,343
• Time in Patent Office: 1,786 Days
• Field of Search: 307/85, 307/86, 307/87, 415/17, 317/27, 290/1
• US Class Current: 307/87
• CPC Class Codes: H02J 3/42 with automatic parallel connection when synchronisation is achieved

Abstract

A gas turbine power plant is provided with an industrial gas turbine which drives a rotating brushless exciter generator coupled to a power system through a breaker. One or more of the turbine-generator plants are operated by a hybrid digital computer control system during sequenced startup, synchronizing, load and shutdown operations. The program system for the computer and external analog circuitry operate in a multiple gas turbine control loop arrangement. Automatic synchronization is achieved with a hybrid subsystem which includes the programmed computer and external phase detection circuitry. An automatic synchronization program for the computer is divided into rough speed and voltage matching, fine speed matching and breaker closure subprograms.

Claims

1. A system for operating an electric power plant comprising an electric generator, a prime mover for driving said generator, a circuit breaker for connecting the electric output of said generator to an external power system, a plant control system including means for controlling prime mover motive fluid flow, said control system including a digital control computer, means for detecting the generator speed and the external system frequency, means for determining a computer representation of the magnitude and rate of change of generator output and external system phase difference as a function of time, means for generating a first electric signal representative of the phase difference between the generator and system waveforms, the last named determining means finely determining said phase difference representation in accordance with a computer representation of said phase difference signal after the slip frequency is reduced below a predetermined value, the last named determining means roughly determining said phase difference representation in accordance with representations of the generator speed and external system frequency until the slip frequency is reduced below said predetermined value, said control system providing a loop for controlling prime mover speed in response to a speed reference means for operating said computer within said speed control loop at least to generate said speed reference representation at least during startup operations, means for operating said computer to modify said speed reference representation as a function of said phase difference representation, means for operating said computer to generate a breaker closure command when said phase difference representation reaches a predetermined condition, and means for operating said breaker in response to said closure command.

2. The operating system as set forth in claim 1 which further comprises means for exciting said generator, means for detecting and comparing said generator and the external system voltages, means for operating said computer to determine a representation of said compared voltage values, and means for operating said generator excitation means as a function of said voltage comparison representation and for generating said breaker closure command when said phase difference and voltage comparison representations both reach predetermined conditions.

3. The operating system as set forth in claim 2 which further comprises means for generating a second electric phase difference signal in a similar manner to but phase displaced from said first defined electric signal, and means for operating said computer to determine the direction of change of the phase difference between said first and said second phase difference signals.

4. The operating system as set forth in claim 2 which further comprises an analog input system having a plurality of input points cooperatively associated with said computer, means for operating said computer to scan said plurality of analog input points in said analog input system at a predetermined frequency, and means for operating said computer to preempt a plurality of predetermined analog input system points for input of said phase difference signal at time points within the analog scan cycle when said phase difference representation determination changes from rough to fine speed matching.

5. The operating system as set forth in claim 4 wherein at least three of said analog input points are preempted for said phase difference signal input and which further comprises means for operating said computer to determine the slip between two of the phases difference signal inputs and to check the validity of the slip determination between one of the two phase difference signal inputs previously utilized and another phase difference signal input.

6. The operating system as set forth in claim 3 which further comprises an analog input system having a plurality of input points cooperatively associated with said computer, means for operating said computer to scan said plurality of analog input points in said analog input system at a predetermined frequency, and means for operating said computer to preempt at least four analog input points for said two phase difference signal inputs with at least three of said points assigned to said first signal and at least one point assigned to said second signal.

7. The operating system as set forth in claim 6 wherein the analog points are successive points in the analog scan.

8. The operating system as set forth in claim 6 wherein four analog points are preempted, said first signal is assigned to the first two analog points, said second signal is assigned to the third analog point, and said first signal is assigned to the fourth analog point.

9. The operating system as set forth in claim 1 wherein the electric power plant is a gas turbine plant, said prime mover comprises a gas turbine, said motive fluid flow controlling means includes means for controlling and operating a fuel system which supplies fuel for combustion in a combustion element of said gas turbine, and said speed reference means is employed in said fuel system control and operation.

10. The operating system as set forth in claim 2 wherein the electric power plant is a gas turbine plant, said prime mover comprises a gas turbine, said motive fluid flow controlling means includes means for controlling and operating a fuel system which supplies fuel for combustion in a combustion element of said gas turbine, and said speed reference means is employed in said fuel system control and operation.

11. The operating system as set forth in claim 4 wherein the electric power plant is a gas turbine plant, said prime mover comprises a gas turbine, said motive fluid flow controlling means includes means for controlling and operating a fuel system which supplies fuel for combustion in a combustion element of said gas turbine, and said speed reference means is employed in said fuel system control and operation.

12. A method for automatically operating an electric power plant within a power system, the steps of said method comprising operating a prime mover to drive an electric generator, determining for a digital control computer a representation of generators and system frequencies and a time function representation of a generator and system phase difference signal, using the computer in a speed control loop to determine the flow of motive fluid to the prime mover, operating the computer to effect automatic synchronization by determining the speed control loop operation as a function of the frequency representation until the slip frequency becomes less than a predetermined value and as a function of the phase difference signal representation after the slip frequency becomes less than the predetermined value, operating the computer to command closure of a circuit breaker to couple the generator to the system when the phase difference signal representation reaches a predetermined condition, and operating the breaker in response to the closure command.

13. The method as set forth in claim 12 wherein the method steps further include operating the computer to determine a representation of detected generator and system voltage values, operating the computer to control the operation of an excitation system of the generator as a function of the voltage representation, and generating the breaker closure command when the phase difference signal and voltage representations reach respective predetermined conditions.

14. An automatic electric power plant synchronization system for an electric power plant generator driven by a prime mover comprising a circuit breaker for connecting the electric output of the generator to an external power system, a control system including a digital control computer for determining the speed of the prime mover, means for detecting the generator speed and the system frequency, means for generating an electric signal representative of the phase difference between the generator and system waveforms, means for determining a computer representation of the magnitude and rate of change of generator and system phase difference as a function of a computer representation of the generator speed and system frequency when the slip frequency exceeds a predetermined value and as a function of a computer representation of the phase difference signal when the slip frequency is less than the predetermined value, means for operating said computer to determine the operation of said speed control system as a function of said phase difference representation, means for operating said computer to generate a breaker closure command when said phase difference representation reaches a predetermined condition, and means for operating said breaker in response to said closure command.

15. The synchronizing system as set forth in claim 14 which further includes an excitation system for the generator, means for detecting the generator and system voltages and for operating said computer to determine a representation of a comparison between the voltage values, and means for operating said generator excitation system as a function of said voltage comparison representation and for generating said breaker closure command when said phase difference and voltage comparison representations both reach predetermined conditions.

16. The synchronizing system as set forth in claim 15 which further includes means for generating a second electric signal in a similar manner to but phase displaced from said first defined electric signal, and means for operating said computer to determine the direction of change of the phase difference between said first and said second phase difference signals.

17. The synchronizing system as set forth in claim 15 which further includes an analog input system having a plurality of input points cooperatively associated with said computer, means for operating said computer to scan said plurality of analog input points in said analog input system at a predetermined frequency, and means for operating said computer to preempt a plurality of predetermined analog input system points for input of said phase difference signal at time points within the analog scan cycle when said phase difference representation determination changes from rough to fine speed matching.

18. The synchronizing system as set forth in claim 14 which further includes means for operating said computer to permit the generation of the breaker closure command only when the slip frequency is valued between predetermined maximum and minimum values.

19. The synchronizing system as set forth in claim 14 which further includes means for operating said computer to determine a desired prime mover speed matching change in the speed reference as a function of the difference between determined slip frequency and a desired synchronization slip frequency.

20. The synchronizing system as set forth in claim 16 which further includes means for operating said computer to determine whether a raise or lower matching speed action is needed as a function of said first and second phase difference signals.

21. The synchronization system as set forth in claim 18 which further includes means for operating said computer to raise said prime mover speed reference by a predetermined amount if the slip frequency persists below said minimum slip frequency for an excessive time period.

22. The synchronization system as set forth in claim 14 which further includes means for operating said computer to raise said prime mover speed reference by a predetermined amount if the slip frequency persists below said predetermined value for an excessive time period.

23. The synchronization system as set forth in claim 14 which further includes means for operating said computer to calculate the breaker closure command time from predetermined characteristics including the slope of said phase difference signal input, and means for cyclically running said operating means to obtain updated valuation of said phase difference signal input and progressively more accurate breaker closure command time calculations until the breaker closure command time arrives.

24. A system as set forth in claim 23 wherein the closure command time calculations are allowed to be updated until a predetermined time point is reached prior to the last projected breaker closure command time.

25. The synchronization system as set forth in claim 24 which further includes means for operating said computer to set a breaker close time count when a final updated time to breaker closure command has been calculated and to downcount the close time count to zero at which time said breaker closure command is immediately issued.

26. An automatic electric power plant synchronization system for an electric power plant generator driven by a prime mover comprising a circuit breaker for connecting the electric output of the generator to an external power system, a control system including a digital control computer for determining the speed of the prime mover, means for determining a computer representation of the magnitude and rate of change of the generator and system phase differences as a function of time, means for operating said computer to determine the operation of said speed control system as a function of said phase difference representation, means for operating said computer to permit the generation of a breaker closure command only when the slip frequency is valued between predetermined maximum and minimum values, means for operating said computer to generate said breaker closure command when said phase difference representation reaches a predetermined condition, and means for operating said breaker in response to said closure command.

27. An electric power plant synchronization system for an electric power plant generator driven by a prime mover comprising a circuit breaker for connecting the electric output of the generator to an external power system, a control system including a digital control computer for determining the speed of the prime mover, means for determining a computer representation of the magnitude and rate of change of generator and external system phase differences as a function of time, means for operating said computer to determine the operation of said speed control system as a function of said phase difference representation, means for operating said computer to raise the prime mover speed reference by a predetermined amount if the slip frequency persists below a predetermined value for an excessive time period.

28. An automatic electric power plant synchronization system for an electric power plant generator driven by a prime mover comprising a circuit breaker for connecting the electric output of the generator to a power system, a control system including a digital control computer for determining the speed of the prime mover, means for determining a computer representation of the magnitude and rate of change of generator and external system phase differences as a function of time, means for operating said computer to determine the operation of said speed control system as a function of said phase difference representation, means for operating said computer to calculate the breaker closure command time from predetermined characteristics including the slope of said phase difference signal input thereto, and means for cyclically running said operating means to obtain updated valuation of said phase difference signal input and progressively more accurate breaker closure command time calculations until the breaker closure command time arrives.

29. A method for operating a digital computer to automatically synchronize a generator driven by a prime mover with a power system, the steps of said method comprising determining a representation of generator and system frequencies and a time function representation of a generator and system phase difference signal, determining prime mover speed control action as a function of the frequency representation until the slip frequency becomes less than a predetermined value and as a function of the phase difference signal representation after the slip frequency becomes less than the predetermined value, and determining a breaker close command when the phase difference signal representation reaches a predetermined condition.

30. The method as set forth in claim 29 further comprising the steps of detecting generator and system voltage values, determining a representation of detected generator and system voltage values, determining generator excitation control action as a function of the voltage representation, and permitting the breaker closure command only if the voltage representation satisfies predetermined conditions.

31. The method as set forth in claim 30 further comprising the step of enabling the generation of the breaker closure command only if the slip frequency is between predetermined maximum and minimum values.

32. The method as set forth in claim 30 further comprising the step of generating a prime mover speed raise control command if the slip frequency persists below a predetermined value for an excessive time period.