Resistance of surface fluorinated epoxy resin to corona discharge in SF<inf>6</inf> gas

Abstract

Our previous results have shown that direct fluorination can modulate surface electrical properties and suppress surface charge accumulation of epoxy insulators, and thus has potential applications for improving the flashover performance of epoxy spacers in gas-insulated equipment. In this study, to investigate the resistance of the fluorinated epoxy surface layer to partial discharge in SF 6 gas, surface fluorinated epoxy samples together unfluorinated (virgin) ones were corona treated using a multi-needle-to-plate electrode system. ATR-IR analyses and SEM surface and cross section images show that the corona discharge caused the chemical modification and chain scission at some weak points in the fluorinated layer and the crosslinking reaction, and thus led to the formation of nodules on the corona treated fluorinated surface. However, the corona treatment did not change the fluorinated layer thickness. In contrast with this, severe degradation, most likely in the form of etching, occurred for the virgin surface layer during the same treatment. Measurements of surface potential decay and water contact angle indicate that the corona discharge obviously reduced surface conduction of the fluorinated sample, and rendered the surface conduction insensitive to humidity although the corona treatment almost did not change surface wettability of the fluorinated sample. On the contrary, the measurements show that surface conduction of the virgin sample increased and became sensitive to humidity after the corona treatment.