Influence of H<inf>2</inf>O molecules on electrical tree initiation in silicone rubber

Abstract

Silicone rubber (SiR) has various excellent characteristics, and is widely used in various apparatus as insulating material. However, tree initiation processes and degradation phenomena in SiR are not clear. The investigations of tree initiation processes at high electric field region are very important. In this paper, the effect of H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O on electrical tree initiation voltage will be examined. Three kinds of samples were tested; untreated SiR, SiR treated by vacuum heating, and SiR impregnated with liquid water after vacuum heating treatment. The tree initiation voltage of SiR treated by vacuum heating was higher than that of untreated SiR. It is considered that the tree initiation voltage is increased by removing gaseous H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O molecules. However the tree initiation voltage of SiR impregnated with liquid water after vacuum heating was higher than that of SiR treated by vacuum heating. These results seem to contradict each other. We consider that the tree initiation voltage is increased by presence of liquid H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O. It is suggested that the states of H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O molecules included in the free volume have a large effect on ac tree initiation in SiR.