Surface Partial Discharge Characteristics of GIS Under AC and Superimposed Switching Impulse Voltage

The attachment of metal particles on the surface of insulators is a significant source of surface discharges and operational failures in gas insulated switchgear (GIS). This study systematically investigated the characteristics of surface partial discharge (PD) under both AC voltage and AC superimposed switching impulse voltage, verifying the feasibility of monitoring PDs during switching operations to detect surface defects within GIS. The development of surface PD under AC voltage can be categorized into three stages with relatively low discharge amplitudes observed in the initial two stages. Surface PDs can only be effectively measured using ultra-high frequency (UHF) and optical devices once PD progression becomes pronounced. When switching impulses with an amplitude of 2.2 times AC voltage were superimposed at various AC phases, sustained and high-amplitude PDs were induced following the impulses, even when the AC voltage remains below the PD inception voltage. Space and surface charge introduced by PDs under switching impulse distort the electric field, thereby triggering subsequent discharges. The amplitude and duration of PDs excited by superimposed impulse voltage are adequate for UHF detection. This finding suggests the potential for timely detection of surface defects in GIS by monitoring PD conditions during switchgear operation.