Incipient leakage current fault detection apparatus and method

• US 6,421,618 B1
• Filed: 12/28/1998
• Issued: 07/16/2002
• Est. Priority Date: 12/28/1998
• Status: Expired due to Term

• Current Assignee: General Electric Company
• Original Assignee: General Electric Company
• Inventors: Claus, Bernhard Erich Hermann, Chbat, Nicolas Wadih, Redinger, Kristofor Lynn, Kliman, Gerald Burt, Yazici, Birsen
• Primary Examiner(s): Hilten, John S.
• Assistant Examiner(s): VO, HIEN XUAN
• Application Number:
  US09/222,276
• Time in Patent Office: 1,296 Days
• Field of Search: 702/58, 702/57, 702/59, 361/42, 361/43, 361/44, 361/63, 361/45, 324/509, 324/512, 324/522, 324/500
• US Class Current: 702/58
• CPC Class Codes: G01R 31/343 in operation
• CPC Class Codes: G01R 31/346 Testing of armature or field windings
• CPC Class Codes: G01R 31/52 Testing for short-circuits, leakage current or ground faults

Abstract

A leakage sensor determines a signal representative of a neutral-to-ground leakage current or voltage from the neutral point of an electric machine of an associated electrical system. A processor uses the sensed signal to determine incipient faults in at least one component of the electrical system.

Claims

1. An apparatus for predicting incipient faults in an electrical system including an electric machine, comprising:

a leakage sensor determining a neutral-to-ground leakage signal representative of current or voltage between a neutral point of the machine and an electrical ground; and

a processor receiving the leakage signal, extracting at least one component of the leakage signal, and using the extracted signal component to predict incipient faults in at least one portion of the electrical system.

2. The apparatus of claim 1 further including at least one machine voltage sensor sensing at least one machine voltage selected from the machine voltage group consisting of at least one line-to-neutral voltage V_LN of the machine, and at least one line-to-line voltage V_LL of the machine, wherein the processor normalizes the extracted signal component to the at least one machine voltage yielding a representative leakage impedance and examines the representative leakage impedance over time to predict the incipient faults.

3. The apparatus of claim 1 further including at least one machine voltage sensor sensing at least one machine voltage selected from the machine voltage group consisting of at least one line-to-neutral voltage V_LN of the machine, and at least one line-to-line voltage V_LL of the machine, wherein the processor calculates a common mode voltage from the at least one machine voltage, normalizes the extracted signal component to the common mode voltage yielding a representative leakage impedance, and examines the representative leakage impedance over time to predict the incipient faults.

4. The apparatus of claim 1 wherein the processor extracts a dc signal component of the leakage signal, and trends the dc signal component over time to predict the incipient faults.

5. The apparatus of claim 1 further including at least one machine voltage sensor sensing at least one machine voltage selected from the machine voltage group consisting of at least one line-to-neutral voltage V_LN of the machine, and at least one line-to-line voltage V_LL of the machine, wherein the processor extracts a dc signal component of the leakage signal, uses the dc signal component and the at least one machine voltage to determine a representative dc leakage impedance, and examines a quantity proportional to the representative dc leakage impedance over time to predict the incipient faults in a dc portion of the electrical system.

6. The apparatus of claim 1 wherein the processor extracts an ac signal component of the leakage signal, and trends the ac signal component over time to predict the incipient faults.

7. The apparatus of claim 1 further including at least one machine voltage sensor sensing at least one machine voltage selected from the machine voltage group consisting of at least one line-to-neutral voltage V_LN of the machine, and at least one line-to-line voltage V_LL of the machine, wherein the processor extracts an ac signal component of the leakage signal, uses the ac signal component and the at least one machine voltage to determine a representative ac leakage impedance, and examines a quantity proportional to the representative ac leakage impedance over time to predict the incipient faults in an ac portion of the electrical system.

8. The apparatus of claim 1 wherein the processor extracts ac and dc components of the leakage signal, and separately trends the ac and dc components over time to predict the incipient faults.

9. The apparatus of claim 1 wherein the processor extracts a resistive component of the leakage signal and uses the resistive component to predict the incipient faults.

10. The apparatus of claim 9 wherein the processor extracts the resistive component of the leakage signal along an axis identified by a predetermined angle obtained from evaluating a neutral-to-ground voltage under good operating conditions of the electrical system.

11. The apparatus of claim 9 further including at least one machine voltage sensor sensing at least one machine voltage selected from the machine voltage group consisting of at least one line-to-neutral voltage V_LN of the machine, and at least one line-to-line voltage V_LL of the machine, wherein the processor calculates a common mode voltage from the at least one machine voltage, and wherein the processor extracts the resistive component by tracking a portion of the leakage signal which is in phase with the common mode voltage.

12. The apparatus of claim 9 further including at least one machine voltage sensor sensing at least one machine voltage selected from the machine voltage group consisting of at least one line-to-neutral voltage V_LN of the machine, and at least one line-to-line voltage V_LL of the machine, wherein the processor extracts the resistive component by varying the leakage signal until a single line voltage of the at least one machine voltage is minimized.

13. The apparatus of claim 1 wherein the processor extracts the extracted signal component at a predetermined frequency and trends the extracted signal component over time to predict the incipient faults.

14. The apparatus of claim 13 wherein the predetermined frequency comprises a predetermined frequency of the machine or a predetermined frequency of another portion of the electrical system.

15. The apparatus of claim 1 further including at least one machine voltage sensor sensing at least one machine voltage selected from the machine voltage group consisting of at least one line-to-neutral voltage V_LN of the machine, and at least one line-to-line voltage V_LL of the machine, wherein the processor extracts the extracted signal component at a predetermined frequency, uses the extracted signal component and the at least one machine voltage to determine a representative leakage impedance, and examines a quantity proportional to the representative leakage impedance over time to predict the incipient faults.

16. The apparatus of claim 1 wherein the processor derives fundamental components of the leakage signal and the at least one machine voltage to localize the incipient faults and substantially exclude outside interference sources from the prediction of the incipient faults.

17. The apparatus of claim 1 wherein the processor uses an inner product to extract an amplitude of a dc component of the leakage signal or an amplitude and a phase of at least one ac component of the leakage signal.

18. The apparatus of claim 17 wherein the processor further uses a decorrelating matrix to extract the amplitude of the dc component of the leakage signal or the amplitude and the phase of the at least one ac component of the leakage signal.

19. The apparatus of claim 1 wherein the processor predicts the incipient faults using the extracted signal component or a representative impedance based trending, such that the extracted signal component or the representative impedance H is monitored for any increase by

computing at least one of the following equations:

20. The apparatus of claim 19 wherein the processor further evaluates at least one of the following corresponding equations:

21. The apparatus of claim 19 wherein the processor further evaluates at least one of the following corresponding equations:

22. The apparatus of claim 1 wherein the processor determines the incipient faults using fault log based analysis, such that type, frequency and rate of fault logs are trended for a particular unit and used to incipiently predict the approach of a fault occurrence based on the processor evaluating at least one of the following equations:

23. An apparatus for predicting an incipient fault in an electrical system including an electric machine, comprising:

a leakage sensor determining a neutral-to-ground leakage signal representative of current or voltage between a neutral point of the machine and an electrical ground; and

a processor periodically receiving the leakage signal, normalizing the leakage signal to a machine voltage yielding a representative leakage impedance, and examining a resulting plurality of data points of the representative leakage impedance over time to predict the incipient fault.

24. The apparatus of claim 23 wherein the processor averages the data points;

forms the averaged data points into overlapping windows; and

in each window, uses the averaged data points to estimate regression model parameters and uses the regression model parameters to forecast a time at which the incipient fault will occur.

25. The apparatus of claim 24 wherein, the processor preprocesses the data points to reduce transient effects and noise prior to averaging the data points.

26. The apparatus of claim 25 wherein, the processor preprocesses the data points by median trimming the data points.

27. The apparatus of claim 24 wherein the processor determines an accuracy of the forecasted time.

28. The apparatus of claim 27 wherein the processor determines the accuracy by using the regression model parameters to determine a variance or confidence region of the forecasted time.

29. An apparatus for predicting an incipient fault in an electrical system including an electric machine, comprising:

a leakage sensor determining a neutral-to-ground leakage signal representative of current or voltage between a neutral point of the machine and an electrical ground; and

a processor receiving a plurality of data points of the leakage signal over time to predict the incipient fault by

averaging the data points;

forming the averaged data points into overlapping windows; and

in each window, using the averaged data points to estimate regression model parameters and using the regression model parameters to forecast a time at which the incipient fault will occur.

30. The apparatus of claim 29 wherein, the processor preprocesses the data points to reduce transient effects and noise prior to averaging the data points.

31. The apparatus of claim 30 wherein, the processor preprocesses the data points by median trimming the data points.

32. The apparatus of claim 29 wherein the processor determines an accuracy of the forecasted time.

33. The apparatus of claim 32 wherein the processor determines the accuracy by using the regression model parameters to determine a variance or confidence region of the forecasted time.

34. An apparatus for detecting incipient failure in an electrical system, the apparatus comprising a processor for using fault log based analysis, such that fault logs are created to include type, frequency and rate of fault and are trended for the electrical system to incipiently predict the approach of a failure by evaluating at least one of the following equations:

35. An apparatus for predicting incipient faults in an electrical system, comprising:

a current sensor sensing a current of the electrical system;

a processor trending the current to predict incipient faults in at least one component of the electrical system by computing at least one of the following equations;

36. The apparatus of claim 35 wherein the processor further computes at least one of the following corresponding equations:

37. The apparatus of claim 35 wherein the processor further computes at least one of the following corresponding equations:

38. An apparatus for predicting incipient faults in an electrical system, comprising:

a current sensor sensing a current of the electrical system;

a voltage sensor sensing at least one voltage of the electrical system;

a processor receiving input signals representing the leakage current and the at least one voltage, using the input signals to calculate a representative impedance, and trending the representative impedance to predict incipient faults in at least one component of the electrical system by computing at least one of the following equations;

39. A method for predicting incipient faults in an electrical system including an electric machine, comprising:

determining a neutral-to-ground leakage signal representative of current or voltage between a neutral point of the machine and an electrical ground; and

processing the leakage signal by extracting at least one component of the leakage signal and using the at least one extracted signal component to predict incipient faults in at least one portion of the electrical system.

40. The method of claim 39 wherein the at least one extracted signal component is a dc signal component of the leakage signal, an ac signal component of the leakage signal, a resistive component of the leakage signal, or an extracted signal component at a predetermined frequency.

41. The method of claim 39 wherein the processor uses an inner product to extract an amplitude and a phase of at least one ac component of the leakage signal.

42. The method of claim 39 wherein the processor uses an inner product to extract an amplitude of a dc component of the leakage signal.

43. A method for predicting an incipient fault in an electrical system including an electric machine, comprising:

determining a neutral-to-ground leakage signal representative of current or voltage between a neutral point of the machine and an electrical ground; and

periodically normalizing the leakage signal to a machine voltage yielding a representative leakage impedance and examining a resulting plurality of data points of the representative leakage impedance over time to predict the incipient fault.

44. The method of claim 43 wherein examining a resulting plurality of data points comprises:

averaging the data points;

forming the averaged data points into overlapping windows; and

in each window, using the averaged data points to estimate regression model parameters and using the regression model parameters to forecast a time at which the incipient fault will occur.

45. The method of claim 44 further including determining an accuracy of the forecasted time by using the regression model parameters to determine a variance or confidence region of the forecasted time.

46. A method for predicting an incipient fault in an electrical system including an electric machine, comprising:

determining a neutral-to-ground leakage signal representative of current or voltage between a neutral point of the machine and an electrical ground; and

predicting the incipient fault by

averaging a plurality of periodically determined data points of the leakage signal over time;

forming the averaged data points into overlapping windows; and

in each window, using the averaged data points to estimate regression model parameters and using the regression model parameters to forecast a time at which the incipient fault will occur.

47. The method of claim 46 wherein further including determining an accuracy of the forecasted time by using the regression model parameters to determine a variance or confidence region of the forecasted time.

48. A method for detecting incipient failure in an electrical system using fault log based analysis, such that fault logs are created to include type, frequency and rate of fault and are trended for the electrical system to incipiently predict the approach of a failure by evaluating at least one of the following equations:

49. A method for predicting incipient faults in an electrical system, comprising:

sensing a current of the electrical system;

trending the current to predict incipient faults in at least one component of the electrical system by computing at least one of the following equations;