Entire process of surface discharge of GIS disc-spacers under constant AC voltage

Surface contamination on the disc-spacers is one of the main threats to the safe operation of gas insulated switchgear(GIS)insulation.The authors’research has confirmed the phenomena of intermittent discharge of such defects under AC constant voltage and concluded that long-intermittent discharge may be the cause of sudden flashover failure of GIS.To explore the characteristics of the process from the partial discharge(PD)inception to the breakdown of surface discharge under constant AC voltage,a 126 kV GIS test platform was built and long-term uninterrupted detection was carried out in this study.By processing the discharge data of the entire process,distribution characteristics of phase-resolved PD and N-V spectra and the trend of discharge repetition rate,discharge amplitude(maximum,mean,standard deviation)and discharge time interval(maximum,mean,standard deviation)were obtained.The results indicate that:there are two typical stages in the entire process of surface discharge under constant voltage and both discharge characteristics and risk of breakdown of those two stages are different obviously.Furthermore,based on the electro-chemical aging theory and space charge effects,the long-intermittent characteristics of solid insulation discharge are explained.