Partial Discharge Characteristics of Typical Insulation Defect under AC and Impulse Superimposed Voltage in SF6 Gas

Partial discharge (PD) in SF 6 gas-insulated apparatuses will cause unexpected failure. In this paper, a test platform capable of generating AC and impulse superimposed voltage with controllable phase is built. Surface defect, free particle, void defect and floating potential defect models are designed and tested. The PD behaviors of the four typical insulation defects under AC and standard switching impulse superimposed voltages are experimentally investigated in SF 6 gas. When the AC voltage is 90% PD inception voltage (PDIV), the standard switching impulse with amplitude of about twice the PDIV is superimposed on 90° of the AC voltage. Results show that PDs under AC voltage can be excited after switching impulse. There are obvious differences in partial discharge characteristics of different insulation defects after switching impulse. The duration of AC PDs excited by switching impulse is differences for the four typical insulation defects. These results are meaningful findings for rationalizing epoxy insulation while maintaining its reliability.