Severity diagnosis and assessment on defects in GIS based on partial discharge detection

In complex high voltage components local insulation defects can cause partial discharges (PD), especially in highly stressed gas insulated switchgear (GIS) these PD affected defects can lead to major blackouts. PD detection is recognized as one of the most effective and most important methods of insulation condition assessment in GIS. In this paper, we designed a scheme to diagnose and assess the severity levels of the PD provoked by defects in GIS. With the application of gradually increased voltage, long-term tests were conducted on a well-established 252kV GIS experiment platform to observe the entire evolution process of PD from its very initiation till the eventual flashover. Ream-time measurement was undertaken during the tests to capture the trend curve of as a result of test time, including the scatter plot, histogram, grey-scale map, etc. The results indicate that PD initiated by defects in GIS can be classified into three severity levels, namely, petty discharge, medium discharge, and threatening discharge. Moreover, on the basis of the features of phase distribution and the corresponding spectra, a procedure based on k-means cluster analysis are proposed to diagnosis and assess severity of PD automatically.