Coupled measurements of partial discharges activity and space charge in a polyethylene model sample under 50 Hz AC field

Coupled measurements of partial discharges activity and space charge have been realized in polyethylene model samples (HDPE-air gap-HDPE). A controlled charge has been introduced in the vicinity of the cavity. Partial discharges with or without space charge into the sample are measured. Experimental results show that space charge modifies the main characteristics of partial discharges: threshold, pulse-height and pulse-phase distributions. As regards space charge measurements, two kinds of charge have to be distinguished. The first type is accumulated onto the surfaces of the cavity and their effect is very short because they quickly disappear during the discharge activity. The second ones have a longer effect because they penetrate into the PE slabs during the charge generation process