Influence of degradation on electroluminescence in polyethylene

Electrical treeing is responsible for the breakdown of power cables with polymeric insulation. Electroluminescence (EL) and the degraded region are observed in the initiation phase of the electrical tree before partial discharge starts. The degraded region has a larger number of microvoids and polar groups than the normal region dose. We studied the EL characteristics of PE (XLPE and LDPE) with the degraded region, and compared them with those in virgin PE. The specimen with the degraded region has higher EL activity, namely lower EL inception voltage and higher light intensity. We considered that EL is caused by the process in a micro cavity of sub-micron size, namely by collision impact of electrons accelerated in that space. These results suggest that electron acceleration is emphasized by the increase of microvoids in the degraded region.