Polar Coordinate Pattern Approach to Partial Discharge on Floating Electrode Defect in GIS

This paper proposes a polar coordinate pattern approach to characterize the floating electrode defect in gas-insulated metal-enclosed switchgear (GIS). A 220-kV GIS bus bar cavity is taken as an object to design the physical model of the floating electrode defect. The partial discharge (PD) development process is studied when the applied voltage is gradually increasing. The phase-resolved partial discharge (PRPD) patterns and the polar coordinate patterns at different voltage levels are accessed through phase-resolved pulse sequence (PRPS) data in the ultrahigh-frequency (UHF) measurement. The proposed polar coordinate pattern approach does not use the traditional positive half-cycle and negative half-cycle analysis method in the PRPD pattern. It uses the clustering results to analyze the characteristics of the PD. It can be concluded that there are several advantages to the polar coordinate pattern. First, in the polar coordinate pattern, the phase is in a head-to-tail arrangement, so the observation of the PD phase characteristics can be more intuitive. Second, the polar coordinate pattern makes the calculated phase median, amplitude median, and centroid meaningful. With the voltage increasing, the variation law of the phase median and centroid can be observed. Third, the discharge parameters, which are based on the quadrant and statistical theory and the cosine similarity proposed in this paper, are from a new point of view. They can make a clear description of the characteristics of the floating electrode defect quantitatively, which can be distinguished from other insulation faults. Additionally, the continuous mode and phase mode at different voltage levels measured by acoustic detection are obtained to further demonstrate the PD development process. The acoustic results agree with the UHF measurement results. The efficiency and rationale of the polar coordinate pattern are further verified. (C) 2017 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.