Influence of surface modification by direct fluorination on dielectric flashover characteristics in vacuum

The surface flashover phenomena of insulating materials in vacuum greatly weakens the overall performance of vacuum-dielectric system, which seriously limits its development. The improvement of surface flashover characteristics of insulators in vacuum becomes a significant challenge for the development of high voltage electrical equipment. In this paper, we report a simple and convenient way to achieve the high surface flashover performance of low density polyethylene (LDPE) and alumina ceramics (Al₂O₃) in vacuum based on direct fluorination technique. The direct fluorination of test samples was performed in a fluorination apparatus for different time of 30, 60, and 90min by using F₂/N₂ mixture of 12.5% F₂ with the pressure and temperature keeping constant as 0.1MPa and 55°C. Then the surface flashover characteristics of LDPE and Al₂O₃ at different fluorination time was investigated. The results show that for LDPE samples fluorinated with 30 and 60min, the hold-off voltage increased by 21.9% and 34.1% than the virgin sample. However, the hold-on capability decreased apparently for the case of 90min fluorination. However for Al₂O₃ samples, direct fluorination had little influence on the surface flashover characteristics. This research could make a contribution to understand the influence of direct fluorination on dielectric flashover characteristics in vacuum.