Influence of swarming pulsive micro discharge on tree degradation

Electrical treeing is one of the problems with insulating polymer materials. Therefore, much research of treeing has been carried out. One object of these researches is to investigate SPMD (swarming pulsive micro discharge). Pulse discharges decrease and disappear before tree initiation. It is considered that SPMD occurs by some factors in the void. In treeing degradation, discharges in the tree channel through the void occur. Therefore, there is a difference in the treeing process between the cases of occurrence of SPMD before tree initiation and no occurrence of SPMD. Comparing SPMD samples with the non-SPMD samples, the characteristics of treeing degradation are investigated in this study. The results are as follows: (1) Treeing samples are evaluated by SPMD using electric discharge statistics. In phase angles, φ5-φ15 and φ7-φ17, in which the difference between positive discharges and negative discharges is large, it is shown that the degree of SPMD in these phases is large. (2) The rate of tree growth of the SPNM samples is slower than that of the non-SPMD samples. (3) The density of tree channels of the SPMD samples is higher than that of the non-SPMD samples.