Relationship between surface discharge of Polbuschel-type in an artificial void and pit formation

In previous reports, pit formation in a micro-gap has been discussed using an artificial void model which has been made based on the Whitehead model. As a result, a difference in surface discharge patterns in the micro-gap was found to have an effect on pit formation processes. In this study, further details are investigated, especially when the surface discharge pattern is Polbuschel-type. The pit formation processes are classified into two different types: fatigue-failure-type degradation process at low voltage and random-failure-type degradation process at high voltage. At low voltage, the oxidation reaction probably leads to pit formation. To investigate the pit formation process at high voltage, local field strength around a tip of a surface discharge is calculated using an analysis model. The result suggests that a surface discharge of Polbuschel-type makes possible instantaneous breakdown of a polymer. Therefore, pit formation at high voltage is probably governed by a surface discharge causing instantaneous breakdown of the polymer.