Multiple generator ground fault detection

Patent metadata

Field	Value
Publication number	US-10333291-B2
Application number	US-201816106567-A
Country	US
Kind code	B2
Filing date	Aug 21, 2018
Priority date	Sep 25, 2017
Publication date	Jun 25, 2019
Grant date	Jun 25, 2019

Abstract

Detection and protection against electric power generator stator ground fault conditions in multiple-generator high-impedance grounded installations is provided herein. In one embodiment, a generator protection element may block a determination of a fault using third harmonic voltages when the third harmonic voltage from the generator is less than a factor of the maximum third harmonic voltage from all of the generators on the common bus. A tripping subsystem may issue a trip command based upon detection of a stator ground fault condition.

First claim

What is claimed:

1. A system, comprising:
a generator configured to generate electrical energy for an electric power delivery system, in electrical communication with common bus for providing the electrical energy to the common bus;
an intelligent electronic device (IED), comprising:
a generator monitoring subsystem configured to measure a neutral voltage value and a terminal voltage value of the generator;
a stator ground fault detection subsystem in communication with the generator monitoring subsystem and configured to determine a stator ground fault using a neutral voltage and terminal voltage value from the generator monitoring subsystem, and to block a determination of the stator ground fault when a factor of the third harmonic voltage from the generator is less than a maximum third harmonic voltage from another generator in electrical communication with the common bus;
a tripping subsystem configured to issue a trip command based upon satisfaction of the stator ground fault detection and absence of the block; and,

an electrical interrupter configured to securely and selectively interrupt an electrical connection between the generator and the electric power generation and transmission system based on the trip command.

2. The system of claim 1 , wherein the stator ground fault detection subsystem is further configured to block the determination when a communication channel is faulty.

3. The system of claim 1 , wherein the stator ground fault detection subsystem is further configured to block the determination when a stator ground fault is detected using fundamental measurements.

4. The system of claim 1 , wherein the stator ground fault detection subsystem is configured to determine whether a total number of generators electrically connected to the common bus is greater than one.

5. The system of claim 1 , wherein the stator ground fault detection subsystem is configured to receive an input indicating that the generator and another generator are electrically connected to the common bus.

6. The system of claim 1 , wherein the stator ground fault detection subsystem is configured to select the factor based at least in part on a number of total generators electrically connected to the common bus.

7. The system of claim 1 , wherein the stator ground fault detection subsystem is configured to receive a user input indicating the factor to be used.

8. The system of claim 1 , wherein the stator ground fault detection subsystem is configured to:
calculate a ratio of a generator neutral third harmonic voltage value and the generator third harmonic voltage value; and
when the ratio is less than a predetermined threshold, determining the stator ground fault is present.

9. A method of monitoring an electrical generator using a generator protection element, comprising:
measuring a neutral voltage and a terminal voltage of a generator;
determining a generator third harmonic voltage value using the neutral and terminal voltages;
calculating a ratio of a generator neutral third harmonic voltage value and the generator third harmonic voltage value;
when the ratio is less than a predetermined threshold, determining a stator ground fault condition;
blocking the stator ground fault detection based at least in part on:
a factor of the generator third harmonic voltage value being less than a maximum third harmonic voltage value from another generator in electrical communication with a common bus of the generator;
a communication channel of the bus being not healthy;
a fundamental ground fault protection system detecting a fault on the generator; or
any combination thereof; and

issuing a trip command based upon the declared stator ground fault condition.

10. The method of claim 9 , wherein the predetermined threshold is associated with a percentage of windings to be protected on the electrical generator using the generator third harmonic voltage.

11. The method of claim 9 , comprising blocking the stator ground fault detection based at least in part on a total number of generators on the common bus.

12. The method of claim 9 , comprising receiving a user setting indicating the factor.

13. An intelligent electronic device (IED) for monitoring a generator on a common bus of an electric power delivery system, comprising:
a memory;
a processor operatively connected to the memory, wherein the processor is configured to execute instructions stored on the memory to cause the processor to:
receive voltage measurements of the generator;
determine that a stator ground fault has occurred based on the voltage measurements;
determine a biasing factor associated with a likelihood that the stator ground fault has occurred at the generator;
receive at least one other biasing factor associated with a likelihood that the stator ground fault has occurred on an at least one other generator on the common bus;
determine an order in which to trip a circuit breaker of the generator and an at least one other circuit breaker of the at least one other generator based at least in part on the biasing factor and the at least one other biasing factor; and
send a signal to cause the circuit breaker of the generator to trip based on the order.

14. The IED of claim 13 , wherein the processor is configured to execute instructions stored on the memory to cause the processor to block the determination that the stator ground fault has occurred when a communication channel between the generator and another generator is not healthy.

15. The IED of claim 13 , wherein the processor is configured to execute instructions stored on the memory to cause the processor to block the determination that the stator ground fault has occurred when another ground fault protection system of the generator has detected a fault.

16. The IED of claim 13 , wherein the processor is configured to execute instructions stored on the memory to cause the processor to receive an input indicating that the generator and another generator are electrically connected to the common bus.

17. The IED of claim 13 , wherein the processor is configured to execute instructions stored on the memory to cause the processor to trip the circuit breaker of the generator before the at least one other circuit breaker is tripped when the biasing factor indicates that the generator has a higher likelihood of having the stator ground fault than the at least one other generator.

18. The IED of claim 13 , wherein the processor is configured to execute instructions stored on the memory to cause the processor to determine the biasing factor based at least in part on a ratio of a third harmonic neutral voltage of the generator to a third harmonic generator voltage of the generator and a ratio of a neutral voltage of the generator to a positive sequence voltage of the generator.

19. The IED of claim 13 , wherein the processor is configured to execute instructions stored on the memory to cause the processor to determine the biasing factor using the equation:
BIAS=⅔*32 S+ ⅓*87 V 31

where 32S is a value that indicates the direction of the stator ground fault and 87V31 is a value that indicates the likelihood the stator ground fault is within the windings of the generator.

20. The IED of claim 19 , wherein the processor is configured to execute instructions stored on the memory to cause the processor to determine 87V31 using the equation:

87
⁢
V
⁢

Assignees

• Schweitzer Engineering Lab Inc

Inventors

• Chowdhury Ritwik
• Finney Dale S

Classifications

• H02H3/52

  responsive to the appearance of harmonics · CPC title

• H02H3/16

  responsive to fault current to earth, frame or mass (with balanced or differential arrangement H02H3/26 {; monitoring earth connection H02H5/105}) · CPC title

• H02H7/26

  Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured (locating faults in cables G01R31/08) · CPC title

• H02H7/06 Primary

  for dynamo-electric generators; for synchronous capacitors · CPC title

• H02H1/0007

  concerning the detecting means (in general G01R or other subclasses of G01; reed switches H01H71/2445) · CPC title