Influence of accumulated surface charges on partial discharge activity at micro gap delamination in epoxy GIS spacer

In epoxy spacers in Gas Insulated Switchgear (GIS) under operating thermal or mechanical stresses, delamination would be initiated at electrode/epoxy interface leading to partial discharge (PD) activity. In this paper, PD activity for delamination at electrode/epoxy interface in SF₆ gas is measured and analyzed to clarify the effect of accumulated charges on the epoxy surface. The delamination gap length considered in this paper is 50 mum. The moment of delamination initiation in GIS is successfully simulated by applying sudden voltage to the electrode setup. The main results show that the charge accumulation has great effect on the PD generation rate. This effect is different between negative and positive PD as a result of the difference in initial electron generation mechanism. The measurement of surface potential and the change in PD inception voltage after PD activity enable to estimate the accumulated charge polarity. Consequently, the role of charge accumulation in PD activity is proposed based on the change in local electric field inside the delamination gap.