PD breakdown process of fatigue-failure-type in a micro gap

In this paper, we made an artificial void model which was base on the Whitehead abc model and investigated partial discharge (PD) degradation of fatigue failure type in the micro gap. Maximum discharge magnitudes of PD in the micro gap and negative charge distributions on its surface were constant regardless of application time. On the other hand, PD degradation area spread according to the passage of time; it was eventually in accord with the negative charge distribution. PD pulses in the micro gap also increased with application time. Interestingly, the time dependence of the PD pulses was similar to the spread property of the PD degradation area. The following is suggested as reasons of this similarity. 1) PD activities increase due to field enhance caused by space charge effect. 2) It is easy to generate PD in the micro gap because PD degradation area promotes the injection of initial electrons required for PD generation. Assuming that the PD breakdown is thermally activated degradation process of Ahrenius type, the activation energy required for the pit formation is estimated. These values agree with an activation energy required for polymer bond scission caused by interaction with oxygen and ozone (85∼125 kJ/mol). Therefore, oxidation reaction probably leads to the PD breakdown of fatigue-failure-type.