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

In previous reports, pit formation in an artificial void has been discussed with the artificial void model which has been based on the Whitehead model. As a result, difference in surface discharge patterns in the artificial void was found to have a great effect on pit formation process. In this study, the further details am investigated, especially when the surface discharge pattern is Gleitbuschel. The pit formation processes are classified into two different types: degradation process of fatigue-failure-type in low voltage range and degradation process of early/random-failure-type in high voltage range. Assuming that the pit formation process in low voltage range is thermally activated degradation process of Arrhenius type, the activation energy is estimated to be 104.31 kJ/mol. This value is in good accord with activation energy for polymer bond scission caused by interaction with oxygen and ozone. Therefore, in low voltage range, oxidation reaction leads probably to the pit formation. In high voltage range, negative charges on the void surface have a sparse distribution. Furthermore, pit fort-nation occurs at an area on the void surface where negative charges accumulate. These results suggest that existing probability of structural defects at which a great deal of negative charges accumulates plays an important role in the pit formation process in high voltage range.