On the nature of surface discharges in silicone-gel: Prebreakdown discharges in cavities

Silicone gel is used to encapsulate power electronic circuits. The weakness of this insulation system is surface discharges which degrade silicone gel. In this paper, various features of surface discharge in gel are evaluated by analyzing the motion of cavities induced by discharges and by measuring dynamic potential distributions of surface discharges in gel. The results indicated that charges accumulated at the cavity surface contribute to retaining the cavity path. Temporal response of the potential at the cavity surface is explained using a classical capacitance model.