Detection, localization and interpretation of partial discharge

• US 8,126,664 B2
• Filed: 05/18/2006
• Issued: 02/28/2012
• Est. Priority Date: 05/20/2005
• Status: Active Grant

• Current Assignee: Hydro-Quebec (Province of Québec)
• Original Assignee: Hydro-Quebec (Province of Québec)
• Inventors: Cantin, Bruno, Bourgeois, Jean-Marc, Léonard, François, Roy, Yvan, Fournier, Daniel
• Primary Examiner(s): WACHSMAN, HAL D
• Application Number:
  US11/920,612
• Publication Number:
  US 20090177420A1
• Time in Patent Office: 2,112 Days
• Field of Search: 702/59, 702/58, 702/72, 702/76, 702/78, 702/79
• US Class Current: 702/59
• CPC Class Codes: G01R 31/1272 of cable, line or wire insulation, e.g. using partial discharge measurements locating faults in cables G01R31/083

Abstract

In order to detect, localize and interpret a partial discharge occurring in a partial discharge site along an electrical equipment, two measurement probes and a synchronization probe are installed along the electrical equipment. The measurement probes detect pulses travelling in the electrical equipment while the synchronization probe detects a phase angle in the electrical equipment and is usable for calibration purposes. A control unit receives the signals sensed by the probes and conditions them. Digital processing applied on the conditioned signals, involving their correlation, a time-frequency distribution and a form factor estimation, allows establishing a diagnosis indicating a detection of a partial discharge and its localization along the electrical equipment. A wideband magnetic probe may be provided for detecting the pulses traveling in the electrical equipment.

Claims

1. An apparatus for detecting, localizing and interpreting a partial discharge occurring in a partial discharge site along an electrical equipment, comprising:

two measurement probes and a synchronization probe installable along the electrical equipment so that pulses travelling in the electrical equipment are detectable by the measurement probes and a phase angle in the electrical equipment is detectable by the synchronization probe;

a control unit connecting to the measurement probes for receiving signals representative of the detected pulses, and connecting to the synchronization probe for acquiring a signal representative of the detected phase angle, the control unit having a circuit for selective conditioning of the received signals; and

a digital processing unit connecting to the control unit for acquiring the signals after selective conditioning as a function of the detected phase angle and driving the control unit, the digital processing unit having a correlation measuring module for measuring correlation of the acquired signals, a module for performing a time-frequency distribution of at least one of the acquired signals, a form factor estimating module for estimating a form factor corresponding to a ratio of a spectral bandwidth over a time length of a discharge pulse derived from the time-frequency distribution, and a diagnosis module configured for interpretation of the correlation and the form factor for generating a diagnosis indicative of a detection of a partial discharge and of a localization of the partial discharge along the electrical equipment based on the interpretation.

2. The apparatus according to claim 1, wherein the processing unit further comprises a candidate eliminating module eliminating candidates of diagnosis solutions corresponding to traces in the acquired signals derived from detected pulses having out-of-range propagation delays between the measurement probes.

3. The apparatus according to claim 2, wherein a threshold for delays considered being out-of-range by the candidate eliminating module is settable by a user.

4. The apparatus according to claim 2, wherein the control unit comprises a circuit for generating a test signal transmitted to the synchronization probe that injects the test signal in the electrical equipment, the digital processing unit being apt, from the acquired signals corresponding to pulses detected by the measurement probes caused by the test signal injected in the electrical equipment, to determine the propagation delay between the measurement probes, a threshold for delays considered to be out-of-range being set as a function of the propagation delay so determined.

5. The apparatus according to claim 1, wherein the processing unit further comprises a module for estimating a probability of error as a function of a ratio between a peak of a maximum of correlation among other correlation peaks, a warning signal indicative of a multiple probable candidates of diagnosis explanation being transmitted to the diagnosis module when the probability of error exceeds a preset threshold.

6. The apparatus according to claim 1, wherein the processing unit further comprises a module for detecting typical traces of radiation in the acquired signals, the processing being stopped and a radiation diagnosis being retained when a determination is made that the acquired signals correspond to radiation.

7. The apparatus according to claim 1, wherein the correlation measuring module provides the diagnosis module with a signal indicative of the polarities of the pulses in the acquired signals, a correlation factor of the correlated signals, a temporal trace portion of a higher amplitude discharge, and a temporal distance between a same discharge sensed by the measurement probes.

8. The apparatus according to claim 7, wherein the processing unit further comprises a module for estimating an equivalent bandwidth and a rise time of the higher amplitude discharge, both provided to the diagnosis module.

9. The apparatus according to claim 1, wherein the processing unit further comprises a clusterization module upstream of the correlation measuring module and the module performing the time-frequency distribution, for clusterizing the acquired signals into respective clusters and producing signatures characterizing the acquired signals in the clusters, the correlation and the time-frequency distribution being achieved on the signatures.

10. A method for detecting, localizing and interpreting a partial discharge occurring in a partial discharge site along an electrical equipment, comprising:

detecting pulses travelling in the electrical equipment using two measurement probes spaced from each other along the electrical equipment;

detecting a phase angle in the electrical equipment using a synchronization probe positioned along the electrical equipment;

performing a selective conditioning of signals representative of the detected pulses;

acquiring the signals after the selective conditioning as a function of the detected phase angle;

putting the acquired signals in correlation;

presenting at least one of the acquired signals in a time-frequency distribution;

estimating a form factor corresponding to a ratio of a spectral bandwidth over a time length of a discharge pulse derived from the time-frequency distribution; and

interpreting the correlation and the form factor to generate a diagnosis indicative of a detection of a partial discharge and of a localization of the partial discharge along the electrical equipment as a function of results from the interpretation of the correlation and the form factor.

11. The method according to claim 10, further comprising:

eliminating candidates of diagnosis solutions corresponding to traces in the acquired signals derived from detected pulses having out-of-range propagation delays between the measurement probes.

12. The method according to claim 11, further comprising:

generating a test signal transmitted to the synchronization probe that injects the test signal in the electrical equipment; and

determining the propagation delay between the measurement probes from the acquired signals corresponding to the pulses detected by the measurement probes caused by the test signal injected in the electrical equipment, a threshold for delays considered to be out-of-range being then set as a function of the propagation delay so determined.

13. The method according to claim 10, further comprising:

generating a test signal transmitted to the synchronization probe that injects the test signal in the electrical equipment; and

checking a configuration of the measurement probes as a function of the acquired signals corresponding to the test signal injected in the electrical equipment.

14. The method according to claim 10, further comprising:

estimating a probability of error as a function of a ratio between a peak of a maximum of correlation among other correlation peaks, a warning signal indicative of multiple probable candidates of diagnosis explanation being produced when the probability of error exceeds a preset threshold.

15. The method according to claim 10, further comprising:

detecting typical traces of radiation in the acquired signals, their processing being stopped and a radiation diagnosis being retained when a determination is made that the acquired signals correspond to radiation.

16. The method according to claim 10, wherein the diagnosis is also established based on a signal indicative of the polarities of the pulses in the acquired signals, a correlation factor of the correlated signals, a temporal trace portion of a higher amplitude discharge, a temporal distance between a same discharge sensed by the measurement probes, an equivalent bandwidth and a rise time of the higher amplitude discharge.

17. The method according to claim 10, wherein the form factor corresponds to the ratio of the spectral bandwidth over the time length of the discharge pulse in one of the acquired signals, the spectral bandwidth and the time length being estimated from a prevailing spectral line and a temporal marginal of the partial discharge provided in the time-frequency distribution.

18. The method according to claim 17, wherein the time-frequency distribution corresponds to a spectrogram, a Wigner-Ville transform, or to a wavelet transform of said at least one acquired signal.

19. The method according to claim 17, wherein the time-frequency distribution is first subjected to a time-frequency filtering prior to estimation of the form factor in order to remove background noise exhibiting a substantially constant spectral power in the time domain.

20. The method according to claim 10, further comprising:

interpolating the acquired signals before correlation.

21. The method according to claim 10, further comprising clusterizing the acquired signals into respective clusters and producing signatures characterizing the acquired signals in the clusters, the correlation and the time-frequency distribution being achieved on the signatures.

22. A wideband magnetic probe for detecting pulses traveling in an electrical equipment, comprising:

a removable clamp having a conductive loop forming a magnetic sensing circuit apt to surround a section of the electrical equipment in order to sense a signal representing a magnetic component of the pulses traveling in the electrical equipment;

a conductive shield covering and electrostatically insulating the conductive loop, the conductive shield being in open circuit at opposite ends of the clamp so that a gap appears between the ends of the clamp;

a connector closing the circuit of the conductive loop at the ends of the clamp where the gap is located when the clamp is installed around the electrical equipment; and

a connector for establishing an external electrical connection with the circuit of the conductive loop.

23. The wideband magnetic probe according to claim 22, further comprising an amplifier circuit integrated in the conductive shield and inserted in the conductive loop in order to filter and amplify the signal.

24. The wideband magnetic probe according to claim 23, wherein the amplifier circuit has a controlled gain.

25. An apparatus for detecting partial discharges in an electrical equipment, comprising:

a measurement probe and a synchronization probe installable along the electrical equipment so that pulses travelling in the electrical equipment are detectable by the measurement probe and a signal indicative of a phase angle in the electrical equipment is detectable by the synchronization probe;

a control unit connecting to the measurement probe for receiving signals representative of the detected pulses, and connecting to the synchronization probe for acquiring the signal indicative of the phase angle, the control unit having a circuit for selective conditioning of the received signals; and

a digital processing unit connecting to the control unit for acquiring the signals after selective conditioning as a function of an appraisal of the phase angle and driving the control unit, the digital processing unit having a clusterization module for clusterizing the acquired signals into respective clusters and producing signatures characterizing the signals in the clusters, a module for performing a time-frequency distribution of the signatures, a form factor estimating module for estimating a form factor corresponding to a ratio of a spectral bandwidth over a time length of a discharge pulse derived from the time-frequency distribution, a module for determining rise times of the signatures, and a diagnosis module configured for interpretation of the form factor and the rise times for generating a diagnosis indicative of a detection of partial discharges and producing a warning signal as a function of the diagnosis based on the interpretation.

26. A method for detecting partial discharges in an electrical equipment, comprising:

detecting pulses travelling in the electrical equipment using a measurement probe positioned along the electrical equipment;

detecting a signal indicative of a phase angle in the electrical equipment using a synchronization probe positioned along the electrical equipment;

performing selective conditioning of signals representative of the detected pulses;

acquiring the signals after the selective conditioning as a function of an appraisal of the phase angle;

clusterizing the acquired signals into clusters and producing signatures characterizing the signals in the clusters;

presenting the signatures in a time-frequency distribution;

estimating a form factor corresponding to a ratio of a spectral bandwidth over a time length of a discharge pulse derived from the time-frequency distribution;

determining rise times of the signatures;

interpreting the form factor and the rise times to generate a diagnosis indicative of a detection of partial discharges as a function of results from the interpretation of the form factor and the rise times; and

producing a warning signal as a function of the diagnosis based on the interpretation.

27. An apparatus for detecting partial discharges in an electrical equipment, comprising:

a measurement probe and a synchronization probe installable along the electrical equipment so that pulses travelling in the electrical equipment are detectable by the measurement probe and a signal indicative of a phase angle in the electrical equipment is detectable by the synchronization probe;

a control unit connecting to the measurement probe for receiving signals representative of the detected pulses, and connecting to the synchronization probe for acquiring the signal indicative of the phase angle, the control unit having a circuit for selective conditioning of the received signals; and

a digital processing unit connecting to the control unit for acquiring the signals after selective conditioning considering the phase angle and driving the control unit, the digital processing unit having a clusterization module for clusterizing the acquired signals into respective clusters and producing time signatures characterizing the signals in the clusters, a module for determining characteristic elements of the signatures based on predetermined analysis parameters, and a diagnosis module configured for interpretation of the characteristic elements for generating a diagnosis indicative of a detection of partial discharges and producing a warning signal as a function of the diagnosis based on the interpretation.

28. A method for detecting partial discharges in an electrical equipment, comprising:

detecting pulses travelling in the electrical equipment using a measurement probe positioned along the electrical equipment;

detecting a signal indicative of a phase angle in the electrical equipment using a synchronization probe positioned along the electrical equipment;

performing selective conditioning of signals representative of the detected pulses;

acquiring the signals after the selective conditioning considering the phase angle;

clusterizing the acquired signals into clusters and producing time signatures characterizing the signals in the clusters;

determining characteristic elements of the signatures based on predetermined analysis parameters;

interpreting the characteristic elements to generate a diagnosis indicative of a detection of partial discharges as a function of results from the interpretation of the characteristic elements; and

producing a warning signal as a function of the diagnosis.