Protection techniques for a back-up electric power system

• US 7,521,822 B2
• Filed: 05/07/2007
• Issued: 04/21/2009
• Est. Priority Date: 05/07/2007
• Status: Active Grant

• Current Assignee: Cummins Power Generation IP, Inc. (Cummins Incorporated)
• Original Assignee: Cummins Power Generation IP, Inc. (Cummins Incorporated)
• Inventors: Lorenz, Rick A.
• Primary Examiner(s): PALADINI, ALBERT WILLIAM
• Application Number:
  US11/800,749
• Publication Number:
  US 20080277945A1
• Time in Patent Office: 715 Days
• Field of Search: 307 64- 66
• US Class Current: 307/64
• CPC Class Codes: H02H 7/06 for dynamo-electric generators; for synchronous capacitors
• CPC Class Codes: H02J 7/00308 Overvoltage protection
• CPC Class Codes: H02J 7/0031 using battery or load disconnect circuits H02J9/002 takes precedence
• CPC Class Codes: H02J 9/06 with automatic change-over , e.g. UPS systems

Abstract

One embodiment of the present application is directed to a protection technique for a back-up electric power generation system. This system includes an electric power generator, generator control circuitry, electrical output sensors to provide one or more corresponding signals, electrical switching equipment to selectively couple the generator to an electrical load, and electric power feeder conductors to route electric power from the generator to the switching equipment. The control circuitry is responsive to the sensor signals to determine if a shut-down condition exists as a function of a protection profile determined for the system. This profile may account for damage thresholds of the generator, the feeder conductors, and the electrical switching equipment for each of a number of different combinations of level and duration of electrical output as represented by the sensor signals.

Claims

1. A method, comprising:

operating a back-up electrical power system including a power generator and a power transfer switch with a first input coupled to the generator by feeder conductors and a second input coupled to a utility power source;

providing electrical power to an electrical load from the generator through the transfer switch;

monitoring electrical output of the generator during the providing of the electric power to the electrical load;

from the level and duration of the electrical output, determining a shutdown condition from a protection profile for the back-up electrical system, the protection profile corresponding to a relationship between the level and the duration of the electrical output, the protection profile representing the lowest damage threshold for the generator, the feeder conductors, and the transfer switch at each of a number of different combinations of the level and the duration of the electrical output; and

in response to the shutdown condition, halting operation of the generator.

2. The method of claim 1, which includes maintaining the electrical continuity of the feeder conductors to the generator and the transfer switch during the halting of the generator.

3. The method of claim 1, wherein the electrical output corresponds to electrical current provided by the generator and the protection profile is representative of an overcurrent protection curve.

4. The method of claim 1, wherein the electrical power is provided in a three phase form with a neutral conductor and the monitoring of the electrical output includes sensing a neutral electrical current through the neutral conductor and a ground electrical current through to an electrical ground of the generator.

5. The method of claim 4, which includes stopping operation of the generator if at least one of the neutral electrical current and the ground electrical current exceeds a threshold.

6. The method of claim 1, which includes configuring the transfer switch to route electricity from the utility power source to the electrical load in response to the shutdown condition.

7. The method of claim 1, wherein a protective device is provided between the generator and the transfer switch and further comprising changing state of the protective device to provide an electrical discontinuity between the generator and the transfer in response to the shutdown condition.

8. The method of claim 1, wherein the generator is one of multiple generators structured to operate in parallel to provide electricity to the transfer switch and each of the multiple generators is selectively coupled to a common power bus by a circuit switch device.

9. A method, comprising:

operating a back-up electrical power system including a power generation subsystem with an electric power generator and control circuitry, and a power transfer switch with a first input electrically coupled to the generator by one or more feeder conductors and a second input electrically coupled to a utility power source;

supplying electrical power from the generator to the transfer switch;

monitoring electrical output of the generator during the supplying of the electric power;

determining a shutdown condition with the control circuitry; and

in response to the shutdown condition, halting operation of the generator while maintaining electrical continuity between the generator and the transfer switch.

10. The method of claim 9, wherein electrical output includes electrical current, and the determining of the shutdown condition includes comparing the electrical current to an overcurrent protection profile for the back-up electrical system, the protection profile corresponding to a relationship between overcurrent level and overcurrent duration, the protection profile representing the lowest damage threshold for the generator, the feeder conductors, and the transfer switch at each of a number of different combinations of the overcurrent level and the overcurrent duration of the electrical output.

11. The method of claim 9, wherein the determining of the shutdown condition includes detecting one or more of a ground fault, an overvoltage condition, and an undervoltage condition.

12. The method of claim 9, wherein the electrical power is provided in a three phase form with a neutral conductor and the monitoring of the electrical output includes sensing a neutral electrical current through the neutral conductor and a ground electrical current through to an electrical ground of the generator.

13. The method of claim 12, which includes stopping operation of the generator if at least one of the neutral electrical current and the ground electrical current exceeds a threshold.

14. The method of claim 9, which includes configuring the transfer switch to route electricity from the utility power source to the electrical load in response to the shutdown condition.

15. An apparatus, comprising:

a back-up electric power generation system including;

an electric power generator;

generator control circuitry;

one or more electric output sensors to provide one or more sensor signals to the control circuitry representative of electric output of the generator;

electrical switching equipment to selectively couple the generator to an electrical load;

electric power feeder conductors to route electric power from the generator to the switching equipment; and

the control circuitry being responsive to the one or more sensor signals to determine if a shutdown condition exists as a function of an overcurrent protection profile, the overcurrent protection profile being representative of an overcurrent damage threshold of the generator, the feeder conductors, and the electrical switching equipment for each of a number of different combinations of overcurrent level and overcurrent duration, the control circuitry being structured to generate an output signal, the generator being responsive to the output signal to halt operation.

16. The apparatus of claim 15, further comprising an internal combustion engine mechanically coupled to the generator to provide rotary power thereto.

17. The apparatus of claim 16, wherein the control circuitry includes means for regulating generator operation that is responsive to rotational speed of the engine.

18. The apparatus of claim 15, wherein the generator is one of multiple generators coupled in parallel and each connected to a common power bus by a circuit switch and the electrical switching equipment is a transfer switch structured to select between the generator and one or more other power sources.

19. The apparatus of claim 15, wherein the electrical switching equipment includes a circuit switch.

20. The apparatus of claim 15, further comprising means for protecting the back-up electric power generation system in response to one or more of a ground fault, an overvoltage condition, and an undervoltage condition.

21. The apparatus of claim 15, wherein the generator includes three outputs of different phase and is coupled to a neutral conductor and further includes a first current sensor to detect electrical current flow through the neutral conductor and a second current sensor to detect electrical ground current.

22. The apparatus of claim 15, wherein the electrical switching equipment includes a transfer switch to route electricity from a utility power source to the electrical load in response to the shutdown condition.