PD-induced surface degradation of insulation embedded cavities: microscopic investigation

With the aim of developing defect-based life models (i.e. life models in which breakdown is explicitly associated with a partial discharge-induced damage growth from a defect beyond a critical level), ageing tests were carried out in the lab on XLPE sandwich specimens containing artificial cavities. PD activity taking place in the cavities was continuously monitored during ageing. The behavior of discharge repetition rate and amplitude were extracted from the monitoring records. The modification of the cavity surface at various ageing times was investigated using microscope observation. Brownish solid byproducts, having oxygen containing moieties, were found covering uniformly the entire area of the cavity surface. After the byproduct was wiped off, degradation pits were observed. The variation of PD repetition rate and amplitude, as well as the relevant PD patterns, could be related to the modification of the cavity surface.