Method and system for monitoring partial discharge in gas-insulated apparatus

• US 20060132144A1
• Filed: 12/16/2005
• Published: 06/22/2006
• Est. Priority Date: 12/16/2004
• Status: Active Grant

• Current Assignee: Hitachi, Ltd.
• Original Assignee: Japan AE Power Systems Corporation
• Inventors: Kato, Tatsuro, Endo, Fumihiro, Moriyama, Tomohiro
• Granted Patent: US 7,388,384 B2
• Time in Patent Office: Days
• US Class Current: 324/536
• CPC Class Codes: G01R 31/085 in power transmission or distribution lines, e.g. overhead
• CPC Class Codes: G01R 31/1254 of gas-insulated power appliances or vacuum gaps testing switches G01R31/327; detecting electrical or mechanical defects in encased switchgear H02B13/065

Abstract

A gas-insulated apparatus is equipped inside with multiple sensors for sensing a partial discharge signal caused by a foreign substance, and a frequency analyzing section for analyzing the frequency of the sensed partial discharge signal. A defect type judging section estimates the defect type of the foreign substance from the signal obtained through the frequency analysis or from the voltage phase distribution of partial discharge synchronized with the frequency of the voltage applied to the gas-insulated apparatus, and a location determining section estimates the defect location and signal intensity from the multiple partial discharge signals. A defect size calculating section estimates the defect size for each defect type from the signal intensity and field distribution at the defect location. Dielectric breakdown risk evaluation is performed based on the defect size and type, and the insulation failure risk is diagnosed from the partial discharge.

Claims

1. A method of monitoring partial discharge in a gas-insulated apparatus and diagnosing failure condition by sensing the partial discharge signal caused by defect, where defect size being estimated based on the signal intensity of the sensed partial discharge signal and the field distribution at the location of the defect deduced from the structural dimension of the gas-insulated apparatus.

2. A method of monitoring partial discharge in a gas-insulated apparatus according to claim 1, wherein the field distribution at the location of the defect is based on conductor surface field strength in case the defect is a protrusion, field strength of the field component along spacer surface in case the defect lies on the spacer, and tank-bottom field strength in case the defect is a free one.

3. A method of monitoring partial discharge in a gas-insulated apparatus according to claim 1, wherein the field distribution at the location of the defect is based on field strength and field unevenness factor in case the defect is a protrusion.

4. A method of monitoring partial discharge in a gas-insulated apparatus according to claim 1, wherein defect location is determined from multiple sensed partial discharge signals and the signal intensity, discharge level at the location of the defect, is calculated from the signal attenuation between the defect location and partial discharge signal sensors.

8. A method of monitoring partial discharge in a gas-insulated apparatus according to claim 1, wherein breakdown probability is calculated from the estimated defect size and anticipated lightning surge, disconnecting switch surge, switching surge, and overvoltage level upon one-line ground failure and its occurrence ratio, all of which total is then regarded as the breakdown probability of the gas-insulated apparatus to calculate the risk of breakdown.

9. A method of monitoring partial discharge in a gas-insulated apparatus according to claim 1, wherein the risk of breakdown and breakdown time are estimated based on the dielectric breakdown characteristic of the estimated defect type and size in long time operation.

5. A method of monitoring partial discharge in a gas-insulated apparatus and diagnosing failure condition by sensing the partial discharge signal caused by defect, where the frequency of the sensed partial discharge signal being analyzed and defect type of the defect being estimated based on the analyzed waveform of the frequency analysis or from the voltage phase distribution of the partial discharge synchronized with the frequency of the voltage applied to the gas-insulated apparatus, and also defect location and signal intensity being estimated based on the multiple partial frequency signals, and then defect size being estimated for each estimated defect type based on the signal intensity and field distribution at the defect location.

6. A method of monitoring partial discharge in a gas-insulated apparatus according to claim 5, wherein the signal intensity of the partial discharge signal is the maximum frequency component of the analyzed waveform converted into a signal intensity of a predetermined reference frequency.

7. A method of monitoring partial discharge in a gas-insulated apparatus according to claim 5, wherein the field distribution at the defect location is obtained from the correlation, predetermined for each defect type, between the defect location, conductor surface field strength and field unevenness factor.

10. A partial discharge monitoring system of a gas-insulated apparatus equipped with multiple sensors for sensing the partial discharge signal caused by defect, comprising a frequency analyzing section for analyzing the frequency of the sensed partial discharge signal, a defect type judging section for estimating defect type of the defect based on the analyzed waveform of the frequency analysis or from the voltage phase distribution of the partial discharge synchronized with the frequency of the voltage applied to the gas-insulated apparatus, a location determining section for estimating defect location and signal intensity based on the partial frequency signal from multiple sensors, and a defect size calculating section for estimating defect size for each estimated defect type based on the signal intensity and field distribution at the defect location.

11. A partial discharge monitoring system of a gas-insulated apparatus according to claim 10, which is further equipped with a risk evaluating section for evaluating risk based on the defect size estimated by the defect size estimating section and a check result displaying section for displaying the check result of the risk as well as maintenance guidance.

12. A partial discharge monitoring system of a gas-insulated apparatus according to claim 10, wherein, if the defect is judged to be a protrusion or one caught on a spacer surface by the defect type judging section, the size of metallic container of the gas-insulated apparatus is converted into a predetermined reference size and the signal intensity of the partial discharge signal is converted based on the converted size.