Mapping of Discharge Channels in Void Creating Effective Partial Discharge Area

This paper describes a novel approach to understanding partial discharge (PD) dynamics and mapping of the discharge channels in a void. During long term PD exposure, discharges develop inside channels within a void, leading to a variation in the discharge area on the void wall as well as a clustering effect. In this paper, the development of a method for identifying localized changes in the dielectric structure, through the detection of dispersed channels with reduced resistivity which occur due to multichannel discharges, is described. Discharge spots in selected ranges of surface resistivity, occurring due to the energetic impact of PD, are mapped. This mapping shows both the distribution of local centers on the surface of the specimen, characterized by a reduced value of surface resistivity. Furthermore, during aging tests this surface resistivity exhibited a progressive reduction by four orders of magnitude, justifying the occurrence of an effective discharge area in the void source. This additionally impacts PD pattern modulation and can be a possible initiation of the formation of cross channels in the bulk isolation which, in the long term, can lead to complete discharge.