Wormholes effect in flashover process of alumina filled epoxy resin surfaces in SF6

Alumina filled epoxy resin is important insulating material, which discharge characteristics are greatly determined by its material properties. In this paper, the surface flashover characteristics of the epoxy resin with various alumina contents (250- 400 phr) in 0.4 MPa SF6 are studied. The short-term and long-term withstand voltages and the application times are measured, and then the V-T characteristics are compared accordingly. The withstand voltage of the epoxy resin with certain alumina content decreases exponentially with time and the long-term withstand voltage is about 20-30% lower than the short-term withstand voltage. The discharge damages to alumina filled epoxy resin material are also studied through the carbonization traces and the microcosmic damage patterns. It is found that the epoxy resin with 350 phr alumina has the lowest short-term and long-term withstand voltages and most serious carbonizations according to the experimental results. The “wormholes” formation in the discharge and its effect in the flashover process are analyzed and discussed based on the carbonation traces and the microcosmic patterns. It is found that the flashover paths shift from creeping-discharge-based to bulk-breakdown-based due to wormholes effect with the increase of alumina content and the critical alumina content is about 300-350 phr.