Investigation and Analysis of Hidden Danger in a 220kV GIS Isolation Switch

This paper takes an example of a partial discharge online monitoring system discovering suspended discharge signals inside GIS. Firstly, the presence of internal discharge is determined through SF6 gas composition analysis. Secondly, combined with acoustic imaging positioning, X-ray detection, UHF, and ultrasonic partial discharge to locate the discharge signal, it is determined that the position of the suspended discharge signal is at the connection part between the fork of the isolation switch transmission part and the moving contact rod of the switch. Finally, through disassembly inspection and verification of the fault location, it is found that there are a large amount of white dust and obvious discharge traces in the corresponding position of B-phase, and the root cause of the defect is analyzed to be that the size of the connection between the B-phase shift fork head is smaller than the normal phase, resulting in low contact pressure between the spring and the moving contact rod, poor contact, and ultimately suspended discharge. At the same time, the same manufacturer and model of equipment with the same type of defects are introduced, providing guidance for the troubleshooting methods of this type of defect hidden danger.