Systems and methods for monitoring and protecting an electric power generator

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.

15. The system of claim 13 , wherein the base frequency of the system is the electrical frequency of the rotor.

16. The system of claim 13 , wherein the stator field ratio value is calculated based on the negative-sequence stator current and the field current during normal generator operating conditions.

17. The system of claim 13 , wherein an operating electrical value is calculated based on the negative-sequence current of the at least one stator electrical characteristic and a field current of the rotor electrical characteristic; and

wherein a restraining electrical value is calculated based on the negative-sequence current of the at least one stator electrical characteristic and a field current of the rotor electrical characteristic.

18. The system of claim 17 , wherein the operating electrical value, I OP , is calculated according to:

I OP =||I 2(Nom) |−N SF ·|I F(2×Nom) ||

where

I 2 corresponds to the negative-sequence current,

N SF corresponds to a stator field ratio value, and

I F corresponds to the field current with an adjusted frequency approximately equal to twice the operating frequency of the generator.

19. A non-transitory computer readable medium for protecting an electric power generator comprising instructions, that when executed by a processor, cause the processor to perform operations for determining a fault value, comprising:

receiving a rotor electrical characteristic associated with a rotor of an electric power generator;

receiving at least one stator electrical characteristic associated with at least one stator phase of the electric power generator;

determining a rotor electrical value based on the rotor electrical characteristic during an unbalanced condition;

determining a negative-sequence stator electrical value based on the at least one stator electrical characteristic during the unbalanced condition;

determining a stator-rotor unbalance or differential value, wherein the stator-rotor unbalance or differential value comprises a difference between the determined rotor electrical value and the determined negative-sequence stator electrical value;

determining that the stator rotor unbalance or differential value exceeds a threshold fault value; and

reporting a turn fault.

20. The computer readable medium of claim 19 , wherein reporting a turn fault comprises:

determining a fault value of the electric power generator based on the determined stator-rotor differential value; and

reporting the determined fault value.

21. A method for protecting an electric power generator comprising:

receiving a rotor electrical characteristic associated with a rotor of an electric power generator;

receiving at least one stator electrical characteristic associated with at least one stator phase of the electric power generator;

determining a rotor electrical value based on the rotor electrical characteristic during an unbalanced condition;

determining a negative-sequence stator electrical value based on the at least one stator electrical characteristic during the unbalanced condition;

determining a stator rotor unbalance or differential value, wherein the stator-rotor unbalance or differential value comprises a difference between the determined rotor electrical value and the determined negative-sequence stator electrical value;

determining that the stator rotor unbalance or differential value exceeds a threshold fault value; and

reporting a turn fault.

22. The method of claim 21 , wherein reporting a turn fault comprises:

determining a turn fault value of the electric power generator based on the determined stator-rotor differential value; and

reporting the determined turn fault value.