Phenomena and mechanism of electrical tree in silicone rubber

In this paper, room temperature vulcanized (RTV) silicone rubber (SiR) was employed as test sample to investigate the tree aging phenomena and mechanism of silicone rubber under commercial voltage. The structures and growth characteristics of electrical tree in SiR were observed by using a digital camera. A new parameter, the treeing proportion is introduced to describe the electrical tree propagation characteristics. Obtained results show that the tree channel of SiR composed of silicone compounds is non-conductive which is quite different from the conductive or semi-conductive carbonized channel within PE and XLPE. There are four kinds of electrical tree (few branch, branch, bush and mixed configurations) in RTV SiR under the commercial voltage, in which bush tree and branch tree take up a great proportion, and the probability of the appearance of bush tree increase with the applied voltage. In addition, three phases (initiation, rapid propagating and stagnation) of treeing propagation process are presented. The electrical tree propagates rapidly right after tree initiation, and the poor conductivity of electrical tree may have a great effect on the appearance of stagnation.