Systems and methods for monitoring and protecting an electric power generator

Patent metadata

Field	Value
Publication number	US-10288688-B2
Application number	US-201514807339-A
Country	US
Kind code	B2
Filing date	Jul 23, 2015
Priority date	Jul 24, 2014
Publication date	May 14, 2019
Grant date	May 14, 2019

Abstract

Protection of an electrical generator includes determining a rotor and stator components using rotor and stator electrical signals, calculating a unbalance and/or differential component using the stator and rotor components, and determining a stator or rotor fault based on the unbalance and/or differential component. Further, the faulted phase and/or zone of a stator fault may be determined using the stator positive sequence voltage and negative sequence current.

First claim

What is claimed is:

1. A system for protecting an electric power generator having a stator, a rotor, and a plurality of current transformers (CTs) and transducers, the system comprising:
a first input configured to receive an analog signal from a first transducer indicative of a rotor current associated with the rotor of the electric power generator;
a second input configured to receive an analog signal from a first CT indicative of a stator current associated with at least one stator phase of the electric power generator; and
a protection module configured to:
determine a rotor current value based on the analog signal from the first transducer indicative of the rotor current during an unbalanced condition;
determine a negative-sequence stator current value based on the analog signal from the first CT indicative of the stator current during the unbalanced condition;
determine a stator-rotor current difference, wherein the stator-rotor current difference comprises a difference between the determined rotor current value and the determined negative-sequence stator current value;
determine that the stator-rotor current difference exceeds a threshold fault current value; and
report a turn fault.

2. A system for protecting an electric power generator, comprising:
a first input configured to receive a rotor electrical characteristic associated with a rotor of an electric power generator;
a second input configured to receive at least one stator electrical characteristic associated with at least one stator phase of the electric power generator; and
a protection module configured to:
determine a rotor electrical value based on the received rotor electrical characteristic during an unbalanced condition;
determine a negative-sequence stator electrical value based on the received at least one stator electrical characteristic during the unbalanced condition;
determine a stator-rotor differential value, wherein the stator-rotor differential value comprises a difference between the determined rotor electrical value and the determined negative-sequence stator electrical value;
determine that the stator-rotor differential value exceeds a threshold fault value; and
report a fault.

3. The system of claim 2 , wherein the protection module is further configured to:
determine a turn fault value of the electric power generator based on the determined stator-rotor differential value; and
report the determined turn fault value.

4. The system of claim 2 , wherein the fault comprises a stator turn fault.

5. The system of claim 2 , wherein the fault comprises a rotor turn fault.

6. The system of claim 2 , wherein the fault comprises an internal series fault.

7. The system of claim 2 , wherein the at least one stator electrical characteristic comprises at least one of a terminal current and a neutral side current,
wherein the rotor electrical characteristic comprises a field current associated with field windings of the rotor,
wherein the determined rotor electrical value includes a rotor phasor with a rotor phasor frequency that is approximately twice an operating frequency of the generator, and
wherein the determined stator electrical value includes a stator phasor with a stator phasor frequency that is approximately equal to the operating frequency of the generator.

8. The system of claim 2 , wherein the protection module is further configured to:
normalize the rotor electrical value and the negative-sequence stator electrical value by multiplying one of the rotor electrical value and the negative-sequence stator electrical value by a constant associated with a turn ratio;
match a frequency of the determined rotor electrical value and a frequency of the determined negative-sequence stator electrical value by multiplying at least one of the determined rotor electrical value and the determined negative-sequence stator electrical value by a rotating vector with a rotating frequency that corresponds to an operating frequency of the electric power generator;
match a phase angle of the determined rotor electrical value and a phase angle of the determined negative-sequence stator electrical value by adjusting the phase angle of at least one of the determined rotor electrical value or the determined negative-sequence stator electrical value by a phase angle adjustment value; and
determine the stator-rotor differential value based on the magnitude of a difference between a plurality of phasors of the ratio-matched electrical values, the frequency-matched electrical values, and the phase angle-matched electrical values.

9. The system of claim 8 , wherein matching a frequency of the determined rotor electrical value and a frequency of the determined negative-sequence stator electrical value further comprises multiplying the determined rotor electrical value by a first rotating vector having a first rotating frequency and multiplying the determined negative-sequence stator electrical value by a second rotating vector having a second rotating frequency, and
wherein a magnitude of the frequency difference of the first rotating frequency and the second rotating frequency approximately equals the operating frequency of the generator.

10. The system of claim 2 , further comprising determining the phase location of a stator phase fault comprising:
determining a positive-sequence voltage based on the at least one stator electrical characteristic;
determining a negative-sequence current based on the at least one stator electrical characteristic;
determining a phase angle difference between the positive-sequence voltage and the negative-sequence current; and
determining a phase location of the stator phase fault based on the determined phase angle difference of the positive-sequence voltage and the negative-sequence current.

11. The system of claim 10 , wherein the protection module is configured:
to determine that the stator phase fault is on an A-phase when the determined phase angle difference between the positive-sequence voltage and the negative-sequence current advanced by 90 degrees is between 0 degrees and +120 degrees;
to determine that the stator phase fault is on an C-phase when the determined phase angle difference between the positive-sequence voltage and the negative-sequence current advanced by 90 degrees is between +120 degrees and −120 degrees; and
to determine that the stator phase fault is on a B-phase when the determined phase angle difference between the positive-sequence voltage and the negative-sequence current advanced by 90 degrees is between −120 degrees and 0 degrees.

12. The system of claim 10 , wherein the negative-sequence electrical value comprises a negative-sequence current, and wherein the stator-rotor differential value is determined based on the negative-sequence current of the at least one stator electrical characteristic and on a field current of the at least one rotor electrical characteristic.

13. The system of claim 12 , wherein the stator-rotor differential value, I OP , is calculated according to:
I OP =|I 2 +N SF *I F *1∠−Θ C |

where
I 2 corresponds to the negative-sequence current based on the at least one stator electrical characteristic with an adjusted frequency equal to a base frequency of the system
N SF corresponds to a stator field ratio value,
I F corresponds to the field current with an adjusted frequency approximately equal to the base frequency of the system, and
Θ C corresponds to a shift in the field current.

14. The system of claim 13 , wherein the base frequency of the system is the electrical frequency of the stator current.

Assignees

• Schweitzer Engineering Lab Inc

Inventors

• Kasztenny Bogdan Z
• Fischer Normann
• Finney Dale S
• Taylor Douglas I

Classifications

• H02H7/06

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

• H02H3/083

  for three-phase systems · CPC title

• G01R31/343 Primary

  in operation · CPC title