Influence of Absorbed Gas in Silicone Rubber on Electrical Tree Initiation

Silicone rubber (SiR) has various excellent characteristics. The use of SiR is increasing as an insulating material of cable joint in power transmission line in recent years. In SiR, the electrical tree initiation voltage is increased by vacuum evacuation, and it decreases with time after air is again impregnated. In polyethylene, it is known that electrical tree initiation voltage is increased by SF6 impregnation. In this paper, we will report the influence of SF6 impregnation on electrical tree initiation characteristic in SiR with and without vacuum evacuation. Without vacuum evacuation, the electrical tree initiation voltage of SF6-impregnated specimen is a little higher than that of untreated specimen. With vacuum evacuation, the electrical tree initiation voltage of SF6-impregnated specimen is a little lower than that of air reimpregnation. In SiR, unlike in polyethylene, the increase of the electrical tree initiation voltage by SF6 impregnation is not clear.