Effect of ambient temperature on electrical treeing characteristics in silicone rubber

In this paper, electrical treeing was investigated in room temperature vulcanized (RTV) silicone rubber (SiR) over a range of ambient temperatures. An ac voltage with a frequency of 50 Hz was applied between a needle-plate electrode to initiate the electrical tree at different ambient temperatures. Both the structures and the growth characteristics were observed by using a digital microscope system. Obtained results show that the tree initiates from a single branch with a white gap. Four typical tree structures, namely branch, bush, pine branch and bush-pine mixed tree, were observed within the sample. The occurrence of tree structures changes with the increase of ambient temperature, in which branch tree takes up a great proportion at 30°C while bush tree becomes dominated as the temperature rises up to 90°C. Meanwhile, the cumulative inception probability within the same time decreases obviously with the increase of ambient temperature. The growth rate of the tree is closely related to the ambient temperature. It is suggested that the increase of vulcanization network density and elastic modulus with ambient temperature may have great influence on the treeing characteristics (including growth rate, fractal dimension and treeing proportion).