Abstract:The gas insulated switchgear is used in 220kV part of a 500kV new substation in Anhui Province. In the process of starting power transmission, The insulation breakdown causes equipment tripping during the start-up and power transmission, which seriously affects the normal order of power production. In order to thoroughly identify the fault and provide reference to avoid the gas insulated switchgear similar faults, the detailed process, fault diagnosis and reason analysis of insulation breakdown fault are introduced. After disassembly analysis of the faulty unit, it is analyzed from the view of internal discharge traces, insulation rod and basin insulator X-ray inspection, fault cell withstand voltage and partial discharge test, silver layer thickness detection, equipment size. Combining with internal sample powder test report, it is found out that the process control of the equipment manufacturing and assembly stage is not executed strictly, and metal particles inside are not completely cleaned, resulting in insulation breakdown after the device is powered. It is exposed that the gas insulated switchgear manufacturer do not strictly implement the relevant process control requirements, and the equipment operation and maintenance management unit required the manufacturer to take corresponding preventive measures to prevent similar failures of other equipment.