Method and apparatus detecting shorted turns in an electric generator

1. A system for detecting one or more shorted rotor turns in a field winding of an electric generator, comprising:

an electrical tap for measuring a first voltage drop V f1 and a subsequent voltage drop V f2 across said field winding;

an electrical shunt for measuring a first current I f1 and a subsequent current I f2 entering said field winding;

an impedance-measuring circuit for determining a reference inductance L REF based on V f1 and I f1 and for determining a subsequent inductance L based on V f2 and I f2 ;

a memory circuit for storing L REF ; and

a data processing system for comparing L REF to said subsequent inductance L to determine whether L REF and said subsequent inductance L differ by more than a predetermined amount and for providing an alarm to indicate the presence of said one or more shorted rotor turns when L REF and said subsequent inductance L differ by more than said predetermined amount.

2. The system of claim 1 wherein said impedance-measuring circuit comprises circuitry for isolating harmonic components V 0 and I 0 and an associated harmonic frequency ω 0 using Fourier analysis and for determining L REF and L via a formula L=V o /(ω 0 *I o ).

3. The system of claim 1 wherein said impedance-measuring circuit comprises an inductance-measuring bridge.

4. The system of claim 1 wherein said impedance-measuring circuit is located onboard a spinning rotor of said electrical generator.

5. The system of claim 4 further including a telemetry circuit for transmitting data from said impedance-measuring circuit to a remote location.

6. A method for detecting one or more rotor turn shorts in a field winding of an electric generator, comprising the steps of:

taking a first measurement of a voltage V f1 across said field winding;

taking a first measurement of a current I f1 entering said field winding;

analyzing said first measurement V f1 and I f1 to isolate a harmonic component V o1 of V f1 and a harmonic component I o1 of I f1 and an associated harmonic frequency ω 01 ;

calculating a reference inductance L REF based on said first measurements;

taking a subsequent measurement of a voltage V f2 across said field winding;

taking a subsequent measurement of a current I f2 entering said field winding;

analyzing said subsequent measurement V f2 and I f2 to isolate a harmonic component V o2 of V f2 and a harmonic component I o2 of I f2 and an associated harmonic frequency ω 02 ;

calculating a subsequent inductance L based on said subsequent measurements;

comparing said reference inductance L REF to said subsequent inductance L to determine whether said reference inductance L REF and said subsequent inductance L differ by more than a predetermined amount; and

providing an alarm indication if said reference inductance L REF and said subsequent inductance L differ by more than said predetermined amount.

7. The method of claim 6 wherein said predetermined amount is a difference between L REF and L of about 5%.

8. The method of claim 6 wherein said harmonic component is a fundamental harmonic component.

9. The method of claim 6 further comprising the step of transmitting said alarm via telemetry to a remote location.

10. The method of claim 6 wherein said step of calculating a reference inductance L REF and said step of calculating a subsequent inductance L comprises using a formula L REF =V o1 /(ω 01 *I o1 ) and L=V o2 /(ω 02 *I o2 ), respectively.

11. A method of detecting a shorted rotor turn in a field winding of an electric generator, comprising the steps of:

determining a reference inductance L REF for said field winding at an initial time;

determining a second inductance L for said field winding at a time subsequent to said initial time;

comparing said reference inductance L REF to said second inductance L to determine whether said reference inductance L REF and said second inductance L differ by more than a predetermined amount; and

providing an alarm if said reference inductance L REF and said second inductance L differ by more than said predetermined amount.

12. The method of claim 11 wherein said predetermined amount is a difference between L REF and L of about 5%.

13. The method of claim 11 further comprising the step of transmitting said alarm via telemetry to a remote location.

14. The method of claim 11 wherein said step of calculating a reference inductance L REF and said step of calculating a second inductance L includes isolating harmonic components V 0 and I 0 with a harmonic frequency ω 0 and using the formula L=V o /(ω 0 *I o ).

15. The method of claim 14 wherein said harmonic component is a fundamental harmonic component.

16. The method of claim 11 wherein said step of calculating a reference inductance L REF and said step of calculating a second inductance L includes obtaining an indication of L REF and L from an inductance measurement bridge.

17. The method of claim 11 wherein said step of determining a reference inductance L REF and said step of determining a second inductance L comprises taking measurements from said field winding while said electrical generator is in operation.