Generator rotor turn-to-turn fault detection using fractional harmonics

Patent metadata

Field	Value
Publication number	US-11316455-B2
Application number	US-202017003477-A
Country	US
Kind code	B2
Filing date	Aug 26, 2020
Priority date	Aug 28, 2019
Publication date	Apr 26, 2022
Grant date	Apr 26, 2022

Abstract

Detection and protection against electric power generator rotor turn-to-turn faults, rotor multi-point-to-ground faults, and rotor permanent magnet faults is provided herein. A fractional harmonic signal is used to determine the rotor fault condition. The fractional harmonic signal may be a fractional harmonic magnitude of the circulating current of one phase. The fractional harmonic may be a fractional harmonic magnitude of a neutral voltage. A tripping subsystem may issue a trip command based upon detection of a rotor turn-to-turn fault condition.

First claim

What is claimed:

1. A device for protecting an electric power generator for generating electrical energy for an electric power delivery system using a stator and a rotor, the device comprising;
a sensor component in electrical communication with an instrument transformer of the generator, the sensor component including a current signal output for providing current signals corresponding with the instrument transformer of the generator;
a processor;
a computer-readable storage medium in communication with the processor and the sensor component, comprising instructions that when executed by the processor cause the device to:
calculate a fractional harmonic of the signal output using the current signals as a circulating current magnitude at the fractional harmonic by:
calculating filter coefficients using a number of pole pairs of the rotor, a number of samples per cycle at a fundamental frequency, and a number of branches per phase of the stator, and;
calculating a circulating current magnitude using the filter coefficients;

compare the fractional harmonic to a predetermined threshold;
determine a rotor fault condition when the fractional harmonic exceeds the predetermined threshold for a predetermined time; and,
determine a protective action when the rotor fault condition is determined; and,

an output in communication with the computer-readable storage medium for effecting the determined protective action.

2. The device of claim 1 , wherein the instrument transformer is associated with a parallel branch of a single phase of the electric power generator.

3. The device of claim 1 , wherein the sensor component is in electrical communication with a plurality of instrument transformers of the generator and the sensor current signal output for providing current signals corresponding with the instrument transformers of the generator.

4. The device of claim 3 , wherein:
the generator comprises a multiple-phase generator;
the stator comprises a plurality of parallel branches for each phase; and
the current signal output comprises current signals from the parallel branches for each phase.

5. The system of claim 4 , wherein the fractional harmonic comprises the circulating current magnitude of the plurality of parallel branches at the first fractional harmonic for one phase of the multiple phases.

6. The system of claim 1 , wherein the fractional harmonic comprises the circulating current magnitude of a plurality of parallel branches at a first fractional harmonic.

7. The system of claim 6 , wherein the generator monitoring subsystem is configured to calculate the circulating current magnitude of the plurality of parallel branches using a finite impulse response filter.

8. The system of claim 7 , wherein the finite impulse response filter comprises a cosine filter with coefficients calculated as:

b
n

=

2

H
*
SPC

*

cos
⁡

(

2
⁢
π
*

1
H

*

g
SPC

)

where:
b n represents filter coefficients;

g
=

{

1
,
2
,
…
⁢

,

H
*
SPC

}

-
0.5

H
=

2
*

(

P
NBR

)

P represents the number of pole pairs of the rotor;
SPC represents the number of samples per cycle at a fundamental frequency; and,
NBR represents the number of branches per phase of the stator.

9. The system of claim 1 , wherein the current signal comprises a current through a generator neutral grounding transformer.

10. The system of claim 1 , wherein the current signal comprises a current through a secondary of a generator neutral grounding transformer.

11. The system of claim 1 , wherein the current signal comprises a stator branch neutral signal.

12. The system of claim 1 , wherein the rotor fault condition comprises a rotor turn-to-turn fault.

13. The system of claim 1 , wherein the rotor fault condition comprises a rotor double-point-to-ground fault.

14. The system of claim 1 , wherein the rotor fault condition comprises a rotor permanent magnet fault condition.

15. A method of detecting a rotor fault condition using available electric power signals from an electric power generator with a rotor and a stator, the method comprising:
receiving a current signal proportional to a current in a phase branch of the stator of the electric power generator;
calculating a fractional harmonic of the current signal as a circulating current magnitude at the fractional harmonic by:
calculating filter coefficients using a number of pole pairs of the rotor, a number of samples per cycle at a fundamental frequency, and a number of branches per phase of the stator, and;
calculating a circulating current magnitude using the filter coefficients;

comparing the fractional harmonic to a predetermined threshold;
determining a rotor fault condition when the fractional harmonic exceeds the predetermined threshold for a predetermined time;
determining a protective action when the rotor fault condition is determined; and,
effecting the determined protective action.

16. The method of claim 15 , wherein the current signal comprises a plurality of current signals proportional to a plurality of currents in a plurality of phase branches of the stator of the electric power generator.

17. The method of claim 16 , wherein the fractional harmonic comprises the circulating current magnitude at a first fractional harmonic.

18. A device for protecting an electric power generator for generating electrical energy for an electric power delivery system using a stator and a rotor, the device comprising;
a sensor component in electrical communication with an instrument transformer of the generator, the sensor component including a voltage signal output for providing voltage signals corresponding with the instrument transforme

Assignees

• Schweitzer Engineering Lab Inc

Inventors

• Alla Matchyaraju
• Chowdhury Ritwik
• Fischer Normann
• Finney Dale S
• Scharlach Rogerio

Classifications

• G01R31/62

  Testing of transformers · CPC title

• H02H7/06 Primary

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

• H02P9/02

  Details {of the control} · CPC title

• H02P9/006 Primary

  Means for protecting the generator by using control (control effected upon generator excitation circuit to reduce harmful effects of overloads or transients H02P9/10) · CPC title

• G01R31/346

  Testing of armature or field windings · CPC title