Electroluminescence in water-treed XLPE

Electroluminescence (EL) occurs in initiation phase of electrical tree and is considered to be a probe of the degradation of polymer insulating materials. On the other hand, under existence of water, water treeing takes place when subjected to a high electric field. Water tree provides a starting point of electrical tree, and therefore is responsible for the final breakdown of power cables with polymeric insulation. We studied the EL characteristics of XLPE with a water-treed region after drying process, and compared with those in virgin XLPE. The dried water-treed XLPE has higher EL activity, namely lower EL inception voltage and higher light intensity. We considered that EL is caused by the process in micro cavity of sub-micron size, namely by collision impact of electrons accelerated in that spaces. The experimental results above suggest that electron acceleration is emphasized by increase of microvoids in water-treed region. Additionally, it can be considered that luminescence center in dried water-treed XLPE is different from that in virgin XLPE.