High resistance of surface fluorinated epoxy insulators to surface discharge in SF<inf>6</inf> gas

Our recent studies have indicated that direct fluorination can suppress surface charge accumulation of epoxy resin insulators and thus enhance the DC flashover performance. It was also confirmed that the fluorinated epoxy surface layer has a significantly improved resistance to corona discharge. Further, in this work, the degradation or tracking resistance to surface discharge and the AC flashover performance of the surface fluorinated epoxy insulator were investigated. A sheet sample/finger electrode arrangement was used in the AC flashover test in SF6 gas. The sample/electrode arrangement can keep the discharge along the same surface path for successive flashover tests, and thus can cause a lasting damage of the sample surface. Test results show that the fluorinated epoxy surface layer has a high degradation or tracking resistance, although direct fluorination only leads to a marginal increase in AC flashover voltage for the sample/electrode arrangement. The resistance improvement is mainly attributed to the formation of C-F bonds and the disappearance of conjugated double bonds in the surface layer by substitution and addition of fluorine atoms, as indicated by ATR-FTIR analysis. The marginal effect of the fluorination on AC flashover voltage is due to limited surface charge accumulation for the symmetrical sample/electrode arrangement during the short period between the partial discharge initiation and the occurrence of flashover.