Partial discharge and light emission from tree channels in LDPE

In attempt to clarify partial discharge (PD) and tree propagation, PDs in an artificially-simulated tree channel in low-density polyethylene (LDPE) were investigated. We observed a PD pulse sequence under the condition where the maximum PD number per half cycle was one. PD took place in several consecutive cycles and ceased for several cycles (PD pulse train). In this paper, we focus attention on the polarity of PD pulses in a train. After a few hours of voltage application, a new tree channel was formed at the tip of artificial channel. Before the tree inception, the polarity of first and last PD pulses tended to be positive. It is expected that negative. Space charges around the pin-tip inhibit negative PD pulse. After the tree inception, a pulse train tended to start and cease with a negative pulse. This implies that factors which affect PD occurrence (for example, space charge) changes with tree inception.