Study on tree propagation from an artificially-simulated tree channel by partial discharges

In attempt to clarify partial discharge (PD) and tree propagation, PD's in artificially-simulated tree channel in low-density polyethylene (LDPE) were investigated. Before tree propagation from the tip of artificial channel, PD pulses formed pulse train which tended to start and cease with a positive pulse. After a few hours of voltage application, new tree channels were formed at the tip of artificial channel. The propagated trees were divided into two types (type A and type B). In type A propagation, PD pulses formed pulse trains which have a tendency to start and ceased with a negative pulse. In type B propagation, several PD pulses occurred in every half cycle and did not pulse train. The diameter and number of the propagated tree in type B are larger than those in type A. Furthermore, when new tree channels were formed at the pin tip a few tens of minutes after the type B propagation, the PD pattern was similar to that of an actual tree initiation from the pin tip without void. These results suggests that PD characteristics are closely related to the type of the tree propagation from the artificial channel.