Investigation and Cause Analysis on Frequent Zero?Sequence Current Alarms of 500?kV System in UHV Substation Caused by GIS Abnormal Contact Surface

For a 500?kV bus-coupler switch in an UHV substation, zero-sequence current alarms occurred during operation frequently . System power flow analysis indicated high-impedance contact points within the GIS. A series of inspections and tests were carried out on the 500?kV GIS, including visual inspection, SF? gas component analysis, GIS enclosure induced?current measurements, as well as displacement and stress analysis of vertical compensation units and GIS tee joints under temperature variation. Multiple potential causes were excluded through comprehensive analysis. Abnormal ablation was identified on contact surfaces of internal conductors during power?outage disassembly, the root cause of this abnormality was analyzed by simulation test and computational reasoning.