Abstract
The investigations into the degradation phenomena and the electric breakdown mechanisms in electrical insulating materials are very important to improve the long term reliability of the power apparatuses. Silicone rubber (SiR) has various excellent characteristics, and is widely used in various apparatus as insulating material. For example, SiR is used in cable joint of power transmission system. However, tree initiation process and degradation phenomena in SiR are not clear. It is commonly accepted that water in SiR influences its electrical insulating characteristic. In this paper, we reported the influence of H2O gas molecules and liquid water impregnation on electrical tree initiation in SiR. The followings are the main observations. 1. Removal of gaseous H2O molecules from SiR by vacuum heating treatment increases tree initiation voltage of SiR. We consider there is a possibility that gaseous H2O molecule forms the hydrogen bond with oxygen of the Si-O bond, and weakens the Si-O bond. This idea was qualitatively supported by a simulation where electric charge distribution and bond distance was calculated by “GAMESS”. 2. Liquid H2O absorption by liquid water impregnating treatment increases tree initiation voltage of SiR. We consider that liquid H2O removes the acceleration space for electron, and also relaxes the high electric field.
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