Contents I. Introduction
Micro meter size cavities in solid insulating material would lead to partial discharge (PD) resulting in deterioration of the insulation performance. So far, there are many reports on PD in a single cavity in solid insulating material [1]–[13], while only a few report on PD in material with multi cavities. In this paper, we investigate discharge phenomena in micro cellular resin including multi cavities with micrometer order size by measuring partial discharge inception voltage (PDIV) and breakdown voltage (BDV). There is a time delay of discharge occurred in the small cavity due to the insufficient initial electron in the microsize cavity. X-ray irirradiation to the sample was carried out to resolve this problem. An X-ray module with 10 W output power was used to supply an initial electron to the cavity which minimizes the time lag of discharge occuring in the cavity [6].
