Method and apparatus for controlling excitation of a generator

• US 4,326,159 A
• Filed: 08/30/1979
• Issued: 04/20/1982
• Est. Priority Date: 08/01/1979
• Status: Expired due to Term

• Current Assignee: Hitachi Engineering Co.,Ltd (Hitachi, Ltd.), Hitachi, Ltd.
• Original Assignee: Hitachi Engineering Co.,Ltd (Hitachi, Ltd.), Hitachi, Ltd.
• Inventors: Aotsu, Hiroaki, Fukushima, Mamoru, Isono, Akira, Inayama, Tsutomu
• Primary Examiner(s): Hickey, Robert J.
• Application Number:
  US06/071,403
• Time in Patent Office: 964 Days
• Field of Search: 322/17, 322/19-25, 322/28, 322/37, 322/59, 322/61, 322/72, 322/75, 322/80, 361/20, 361/21
• US Class Current: 322/19
• CPC Class Codes: H02P 9/10 Control effected upon generator excitation circuit to reduce harmful effects of overloads or transients, e.g. sudden application of load, sudden removal of load, sudden change of load

Abstract

Voltage, current and field voltage of a generator connected to an electric power system are sampled at a predetermined period for analog-digital conversion and then led to a digital computer. In addition to computation for AVR, the computer computes from its input the generator output power, and also monitors the occurrence of a fault, the removal of the fault and variation in the generator output in the system. After the occurrence of a fault, the field excitation of the generator is intensified until the generator output power reaches substantially a peak value, but after the peak value is substantially passed by, the excitation is conversely depressed to a value below the level which is present before the fault occurs. When the generator output power recovers the value which is present before the fault occurs, the computer returns to deliver the AVR output.

Claims

1. A method for controlling the excitation of a generator connected to an electric power system by controlling its field in response to the generator voltage comprising the steps of:

increasing, when a fault occurs in the electric power system, the field excitation such that it exceeds a level which is present before the fault occurs during a time interval after the fault is removed until the internal phase angle of the generator substantially reaches a peak value; and

decreasing the field excitation such that it falls below said level after the interval phase angle has substantially passed through the peak value.

6. A method for controlling the excitation of the generator according to any one of claims 1 to 5, wherein determination of the amount of the decreased excitation depends on a lower limit of the generator output voltage.

2. A method for controlling the excitation of a generator connected to an electric power system by controlling its field in response to the generator voltage comprising the steps of:

increasing, when a fault occurs in the electric power system, the field excitation such that it exceeds a level which is present before the fault occurs during a time interval after the fault is removed until the internal phase angle of the generator substantially reaches a peak value; and

decreasing the field excitation such that it falls below said level during a time interval after the internal phase angle has substantially passed through the peak value until the generator output returns to substantially the same level as that present before the fault occurs.

3. A method for controlling the excitation of the generator according to claim 2, wherein a signal representative of the generator output power is used as a signal representative of the internal phase angle.

4. A method for controlling the excitation of the generator according to claim 2, wherein the time interval through which the excitation is decreased is determined in accordance with the generator output power which is present when the internal phase angle or generator output power substantially reaches a peak value.

5. A method for controlling the excitation of the generator according to claim 2, wherein the time interval through which the excitation is decreased is determined in relation with the generator output power which is present when the fault occurs and a time interval between occurrence of the fault and removal thereof.

14. A method according to claim 2, further comprising setting said field excitation at said level which was present before the fault occurs after said generator output returns to substantially the same level as that present before the fault occurs.

7. A method for controlling the excitation of a generator connected to an electric power system by controlling its field in response to the generator voltage comprising the steps of:

increasing, when a fault occurs in the electric power system, the field excitation such that it exceeds a level which is present before the fault occurs during a time interval through which the power transmission is effected at a power which is larger than the generator input by an amount which compensates for a decreased power in the power transmission due to the fault; and

decreasing the field excitation such that it falls below said level when said time interval has elapsed.

9. A method for controlling the excitation of the generator according to claim 7 or 8, wherein the time interval through which the excitation is decreased is determined in accordance with the generator output power which is present when the internal phase angle or generator output power substantially reaches a peak value.

10. A method for controlling the excitation of the generator according to claim 7 or 8, wherein the interval through which the excitation is decreased is determined in relation with the generator output power which is present when the fault occurs and a time interval between occurrence of the fault and removal thereof.

11. A method for controlling the excitation of the generator according to claim 7 or 8, wherein determination of the amount of the decreased excitation depends on a lower limit of the generator output voltage.

8. A method of controlling the excitation of a generator connected to an electric power system by controlling its field in response to the generator voltage comprising the steps of:

increasing, when a fault occurs in the electric power system, the field excitation such that it exceeds a level which is present before the fault occurs during a first time interval through which the power transmission is effected at a power which is larger than the generator input by an amount which compensates for a decreased power in the power transmission due to the fault; and

decreasing the field excitation such that it falls below said level during a second time interval after the first time interval has elapsed until the generator output returns to substantially the same level as that present before the fault occurs.

12. Apparatus for controlling the excitation of a generator comprising:

first means for detecting, at predetermined periods, voltage, current, and field voltage of the generator connected to an electric power system;

second means for converting an output of the first means into a digital output signal;

third means for carrying out a predetermined operation processing of the digital output signal of the second means within each of the predetermined periods in accordance with a stored program;

fourth means for storing the program;

fifth means for storing the digital output signal of the second means and an output of the third means;

sixth means for storing data to be used as reference values for examination; and

seventh means for controlling the field excitation of the generator by the output of the third means,

said third means including means for computing the generator output power from the voltage and current, delivering an output for intensifying the field excitation of the generator to a predetermined value, when a computation result from the present period is decreased below a computation result from an immediately preceding period by more than a predetermined value, and thereafter delivering an output for depressing the field excitation such that it falls below a value which is present immediately before the excitation is intensified to the predetermined value, when a computation result of the generator output power which falls below a computation result from an immediately preceding period is detected.

13. Apparatus for controlling the excitation of a generator comprising:

first means for detecting, at predetermined periods, voltage, current and field voltage of the generator connected to an electric power system;

second means for converting an output of the first means into a digital output signal;

third means for carrying out a predetermined operation processing of the digital output signal of the second means within each of the predetermined periods in accordance with a stored program;

fourth means for storing the program;

fifth means for storing the digital output signal of the second means and an output of the third means;

sixth means for storing data to be used as reference values for examination; and

seventh means for controlling the field excitation of the generator by the output of the third means,

said third means including means for computing the generator output power from the voltage and current, delivering an output for intensifying the field excitation of the generator to a predetermined value, when a computation result from the present period is decreased below a computation result from an immediately preceding period by more than a predetermined value, thereafter delivering an output for depressing the field excitation such that it falls below a value which is present immediately before the excitation is intensified to the predetermined value, when a computation result of the generator output power which falls below a computation result from an immediately preceding period is detected, and then delivering an output for stopping the output for depressing the field excitation, when the subsequent output power of the generator becomes substantially the same as the generator output power which is present before the output for intensifying the field excitation is delivered.