Effects of low temperature on treeing phenomena of silicone rubber

In this paper, room temperature vulcanized (RTV) silicone rubber (SiR) was employed as test sample to investigate the relationship between electrical tree propagation characteristics and the low experiment temperature. Power frequency voltage was applied on the SiR specimens through the needle-plate electrode with the same radius of needle tips to initiate the electrical tree at different low experiment temperatures. Both the structures and growth characteristics of electrical tree in SiR were observed by using a digital camera and a microscope system. Obtained results show that electrical tree in RTV SiR is white gap tree channel which maybe composed of silicone compounds instead of carbonized channel in XLPE. Electrical tree in SiR all initiate from single branch, and the width of initiative single branch channel varies a lot with the electrical tree structure. The structure of at experiment temperature from 0 °C to -70 °C in RTV SiR can be classified into three categories, which are branch, bush and pine branch tree. The distribution of tree structures changes with the experiment temperature. At the temperature of -70 °C, pine branch tree take up a great proportion, however, bush tree becomes the dominant structure when the temperature rise up to -50 °C and -30 °C. All kinds of electrical tree grow rapidly in the first beginning of the treeing propagation, and this process lasts only a few minutes.