Dielectric Strength Improvement by Higher Frequency AC Conditioning

We discuss the effects of AC conditioning with higher frequency on the dielectric strength in vacuum. We have confirmed that multiple breakdowns occur in a half cycle of AC voltage application in the AC conditioning process. It is considered that the multiple breakdowns are triggered by metal vapor due to the previous breakdown in the same half cycle. Such breakdowns can not be attributed to a micro protrusion on the electrode surface. Therefore, multiple breakdowns are considered not effective, but harmful for conditioning. In this paper, we carried out the AC conditioning with the higher frequency than the commercial power frequency in the sphere-plane electrode system. We experimentally confirmed that the conditioning effect is improved by increasing the frequency of AC conditioning in the sphere-plane electrode system, where multiple or harmful breakdowns were suppressed during AC conditioning. These results suggest the feasibility of higher frequency AC conditioning for the dielectric strength improvement in vacuum.