A partial discharge fault of 220 kV GIS isolation switch is introduced.Suspended discharge is found in the isolation switch via ultra-high frequency and ultrasonic partial discharge detection.In order to further determine the cause of discharge,the isolation switch is disassembled for factory inspection.It shows the fault is brought about due to unqualified dimensions of arm box drive shaft plug and upper end slot of insulation torsion bar and poor contact of parts,which leads to the suspended discharge,and the corresponding prevention and treatment countermeasures are put forward.
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