Electrical generator damage protection apparatus and method with circuit breaker trip initiation

• US 5,701,070 A
• Filed: 08/04/1995
• Issued: 12/23/1997
• Est. Priority Date: 08/04/1995
• Status: Expired due to Fees

• Current Assignee: Cummins PowerGen IP, Inc. (Cummins Incorporated)
• Original Assignee: ONAN Corporation (Cummins Incorporated)
• Inventors: Schultz, Mark H.
• Primary Examiner(s): Stephan, Steven L.
• Assistant Examiner(s): Ponomarenko, Nicholas
• Application Number:
  US08/511,265
• Time in Patent Office: 872 Days
• Field of Search: 322/20, 322/24, 322/25, 322/27, 322/37, 322/58, 307/84, 307/87
• US Class Current: 322/37
• CPC Class Codes: H02H 3/0935 the timing being determined by numerical means
• CPC Class Codes: H02H 7/06 for dynamo-electric generators; for synchronous capacitors

Abstract

An electrical generator damage protection apparatus is provided. The protection apparatus includes a circuit breaker which opens and closes an electrical circuit in response to a breaker control signal. A controller is operatively coupled to the circuit breaker to generate the breaker control signal based upon periodically sensed current magnitudes output by a generator. This breaker control signal controls total current output by the generator over a predetermined time span to less than a generator damage curve. The generator damage curve corresponds to a maximum amount of total current which can be generated by the generator over the predetermined time span without damaging the generator. In addition, a electrical generator system having the protection apparatus is provided. Also, a method for protecting an electrical generator from damage with a breaker control signal which controls total current output by the generator over a predetermined time span to less than a generator damage curve is provided.

Claims

1. An electrical generator damage protection apparatus, comprising:

(a) a circuit breaker which opens and closes an electrical circuit in response to a breaker control signal; and

(b) control means, operatively coupled to the circuit breaker, for generating the breaker control signal based upon a periodically sensed current magnitudes signal which is output by a generator, the control means controlling a square of total current output by the generator over a predetermined time span to be a value less than a value on a generator damage curve, the generator damage curve corresponding to a maximum amount of total current squared which can be generatable by the generator over the predetermined time span without damaging the generator.

2. The electrical generator damage protection apparatus of claim 1 wherein the control means comprises means for generating an engine shutdown signal based upon the periodically sensed current magnitudes signal which is output by a generator such that the engine shutdown signal stops an engine providing rotational energy to the generator prior to damage occurring in the generator as a result of generating more than the maximum amount of total current over the predetermined time span.

3. The electrical generator damage protection apparatus of claim 2 wherein the control means comprises means for generating an electric power regulation stop signal based upon the periodically sensed current magnitudes signal which is output by a generator such that the electric power regulation stop signal stops regulation of electrical power generated by the generator when the engine shutdown signal stops the engine.

4. The electrical generator damage protection apparatus of claim 1 wherein the control means comprises means for generating a generator excitation stop signal based upon the periodically sensed current magnitudes signal which is output by a generator such that the generator excitation stop signal stops the generator from generating current prior to damage occurring in the generator as a result of generating more than the maximum amount of total current over the predetermined time span.

5. The electrical generator damage protection apparatus of claim 1 wherein the control means comprises means for generating the breaker control signal based upon at least two different phase current magnitudes signals which are output by a generator and which are periodically sensed during each sensing instance.

6. The electrical generator damage protection apparatus of claim 1 wherein the control means comprises means for generating the breaker control signal by iteratively performing the following damage protection steps:

(a) determining if a largest sensed phase current magnitude of a sensing instance is greater than 1.1 times a nominal current magnitude, then performing steps (b) through (f), otherwise perform steps (g) through (h);

(b) subtracting a nominal current from a largest sensed current to generate a normalized current value;

(c) squaring the normalized current value;

(d) adding the squared normalized current value to a long term time count;

(e) determining if the long term time constant is greater than an I² trip constant, then performing step (f), otherwise returning to step (a) to begin another iteration of the damage protection steps;

(f) setting the breaker control signal to instruct the circuit breaker to open the electrical circuit and returning to step (a) to begin another iteration of the damage protection steps;

(g) subtracting a time constant from the long term time count; and

(h) determining if the long term time constant is less than one, then setting the long term time constant to zero, otherwise returning to step (a) to begin another iteration of the damage protection steps.

7. The electrical generator damage protection apparatus of claim 6 wherein the control means damage protection steps further comprise the step of setting an over current warning on after the adding step (d).

8. The electrical generator damage protection apparatus of claim 6 wherein the control means damage protection steps further comprise the step of setting an over current warning off after the subtracting step (g).

9. The electrical generator damage protection apparatus of claim 6 wherein the control means damage protection steps further comprise the step of determining, prior to the adding step (d), if any of the sensed phase current magnitude of a sensing instance is greater than 4.4 times the nominal current magnitude, then setting the squared normalized current value to a fast trip value, otherwise continue to step (d).

10. The electrical generator damage protection apparatus of claim 6 wherein the control means damage protection setting step (f) further comprises determining if the largest sensed current magnitude is greater than 1.75 times the nominal current magnitude, then setting a fault flag to short circuit and a shutdown flag on, otherwise setting the fault flag to over current and the shutdown flag on.

11. The electrical generator damage protection apparatus of claim 6 wherein the control means damage protection setting step (f) further comprises setting an engine shutdown signal to instruct an engine providing rotational energy to the generator to stop prior to returning to step (a) to begin another iteration of the damage protection steps.

12. The electrical generator damage protection apparatus of claim 11 wherein the control means damage protection setting step (f) further comprises setting an electric power regulation stop signal to stop regulation of electrical power generated by the generator when the engine shutdown signal stops the engine prior to returning to step (a) to begin another iteration of the damage protection steps.

13. The electrical generator damage protection apparatus of claim 6 wherein the control means damage protection setting step (f) further comprises setting a generator excitation stop signal to instruct the generator to stop generating current prior to returning to step (a) to begin another iteration of the damage protection steps.

14. The electrical generator damage protection apparatus of claim 6 wherein the control means comprises means for setting the breaker control signal to instruct the circuit breaker to close the electrical circuit such that the control means is reset to subsequently continue iteratively performing the damage protection steps.

15. An electrical generator system, comprising:

(a) a generator to generate polyphase electrical power;

(b) a circuit breaker, operatively coupled to the generator, to open and close an electrical circuit for each electrical power phase in response to a breaker control signal, the electrical circuit having means for transmitting the electrical power to an external load;

(c) a current sensor, operatively coupled to the generator to periodically sense a magnitude of current for each electrical power phase during each sensing instance to generate a current magnitudes signal; and

(d) control means, operatively coupled to the circuit breaker and the current sensor, to generate the breaker control signal based upon the current magnitudes signal, the control means controlling a square of total current generated by the generator over a predetermined time span to be a value less than a value on a generator damage curve, the generator damage curve corresponding to a maximum amount of total current squared generatable by the generator over the predetermined time span without damaging the generator.

16. The electrical generator system of claim 15 further comprising an engine mechanically linked to the generator which provides rotational energy to the generator and wherein the control means comprises for generating an engine shutdown signal based upon the periodically sensed current magnitudes signal which is output by the generator such that the engine shutdown signal stops the engine from providing rotational energy to the generator prior to damage occurring in the generator as a result of generating more than the maximum amount of total current over the predetermined time span.

17. The electrical generator system of claim 15 further comprising an electric power regulator operatively coupled to the generator for regulating the generated electrical power and wherein the control means comprises for generating an electric power regulation stop signal based upon the periodically sensed current magnitudes signal which is output by the generator such that the electric power regulation stop signal stops regulation of the generated electrical power when the engine shutdown signal stops the engine.

18. The electrical generator system of claim 17 wherein the electric power regulator comprises a voltage regulator.

19. The electrical generator system of claim 17 wherein the electric power regulator comprises a current regulator.

20. The electrical generator system of claim 15 further comprising an excitation winding operatively coupled to the generator for generating electrical current and wherein the control means comprises for generating a generator excitation stop signal based upon the periodically sensed current magnitudes signal which is output by the generator such that the generator excitation stop signal stops the generator from generating current prior to damage occurring in the generator as a result of generating more than the maximum amount of total current over the predetermined time span.

21. The electrical generator system of claim 15 wherein the control means comprises for generating the breaker control signal by iteratively performing the following damage protection steps:

(a) determining if a largest sensed phase current magnitude of a sensing instance is greater than 1.1 times a nominal current magnitude, then performing steps (b) through (f), otherwise perform steps (g) through (h);

(b) subtracting a nominal current from a largest sensed current to generate a normalized current value;

(c) squaring the normalized current value;

(d) adding the squared normalized current value to a long term time count;

(e) determining if the long term time constant is greater than an I² trip constant, then performing step (f), otherwise returning to step (a) to begin another iteration of the damage protection steps;

(f) setting the breaker control signal to instruct the circuit breaker to open the electrical circuit and returning to step (a) to begin another iteration of the damage protection steps;

(g) subtracting a time constant from the long term time count; and

(h) determining if the long term time constant is less than one, then setting the long term time constant to zero, otherwise returning to step (a) to begin another iteration of the damage protection steps.

22. The electrical generator system of claim 21 wherein the control means damage protection steps further comprise the step of setting an over current warning on after the adding step (d).

23. The electrical generator system of claim 21 wherein the control means damage protection steps further comprise the step of setting an over current warning off after the subtracting step (g).

24. The electrical generator system of claim 21 wherein the control means damage protection steps further comprise the step of determining, prior to the adding step (d), if any of the sensed current magnitudes of the sensing instance is greater than 4.4 times the nominal current magnitude, then setting the squared normalized current value to a fast trip value, otherwise continue to step (d).

25. The electrical generator system of claim 21 wherein the control means damage protection setting step (f) further comprises determining if the largest sensed current magnitude is greater than 1.75 times the nominal current magnitude, then setting a fault flag to short circuit and a shutdown flag on, otherwise setting the fault flag to over current and the shutdown flag on.

26. The electrical generator system of claim 16 wherein the control means comprises means for setting the breaker control signal to instruct the circuit breaker to close the electrical circuit such that the control means is reset to subsequently continue iteratively performing the damage protection steps.

27. A method for protecting an electrical generator from damage with a breaker control signal which controls total current output by a generator over a predetermined time span to a value which is less than that on a generator damage curve, the generator damage curve being a maximum amount of total current which can be generated by the generator over the predetermined time span without damaging the generator, the method comprising iteratively performing the steps of:

(a) periodically sensing a current magnitude of each phase of generated electrical power of the generator during each sensing instance;

(b) determining if a largest sensed phase current magnitude of a sensing instance is greater than 1.1 times a nominal current magnitude, then performing steps (c) through (g), otherwise perform steps (h) through (i);

(c) subtracting a nominal current from a largest sensed current to generate a normalized current value;

(d) squaring the normalized current value;

(e) adding the squared normalized current value to a long term time count;

(f) determining if the long term time constant is greater than an I² trip constant, then performing step (g), otherwise returning to step (a) to begin another iteration of the damage protection steps;

(g) setting the breaker control signal to instruct the circuit breaker to open the electrical circuit and returning to step (a) to begin another iteration of the damage protection steps;

(h) subtracting a time constant from the long term time count; and

(i) determining if the long term time constant is less than one, then setting the long term time constant to zero, otherwise returning to step (a) to begin another iteration of the damage protection steps.

28. The method of claim 27 further comprising the step of setting an over current warning on after the adding step (e).

29. The method of claim 27 further comprising the step of setting an over current warning off after the subtracting step (h).

30. The method of claim 27 further comprising the step of determining, prior to the adding step (e), if any of the sensed phase current magnitude of a sensing instance is greater than 4.4 times the nominal current magnitude, then setting the squared normalized current value to a fast trip value, otherwise continue to step (e).

31. The method of claim 27 wherein the setting step (g) further comprises determining if the largest sensed current magnitude is greater than 1.75 times the nominal current magnitude, then setting a fault flag to short circuit and a shutdown flag on, otherwise setting the fault flag to over current and the shutdown flag on.

32. The method of claim 27 wherein the setting step (g) further comprises setting an engine shutdown signal to instruct an engine providing rotational energy to the generator to stop prior to returning to step (a) to begin another iteration of the damage protection steps.

33. The method of claim 32 wherein the setting step (g) further comprises setting an electric power regulation stop signal to stop regulation of electrical power generated by the generator when the engine shutdown signal stops the engine prior to returning to step (a) to begin another iteration of the damage protection steps.

34. The method of claim 27 wherein the setting step (g) further comprises setting a generator excitation stop signal to instruct the generator to stop generating current prior to returning to step (a) to begin another iteration of the damage protection steps.

35. The method of claim 27 further comprising the step of setting the breaker control signal to instruct the circuit breaker to close the electrical circuit when a reset sequence is initiated prior to subsequently iteratively performing steps (a) through (i).