Investigation of sensitivity of the ultra-high frequency partial-discharge detection technology for micro-crack in epoxy insulator in GIS

The ultra-high frequency(UHF)method has been widely used in a gas-insulated system(GIS)for partial-discharge detection,and many achievements have been realised.In addition,many studies based on artificial defects have been made to confirm its validity.Therefore,the UHF method is generally believed to be sufficiently effective for GIS monitoring.However,in practical application,the authors find that for some micro-crack discharge in GIS insulator,the UHF method has low sensitivity.To fully study the characteristics of the micro-crack discharge in the GIS insulator,an experiment is conducted in this study using an actual post insulator with a micro-crack defect.The current signal based on IEC 60270 standard and the radio-frequency electromagnetic signal is simultaneously measured for thorough analysis.The results show that some submillimetre crack defects may occur in the GIS insulator.Its discharge is mainly presented as glow discharge,and the discharge signal frequency usually cannot reach the UHF band;thus,it cannot be effectively detected by the UHF method.This study provides complementary information to the applicability of the UHF method and inspires further study of the GIS insulator and its monitoring technology.