Tree characteristics in silicone rubber/SiO2 nanocomposites under low temperature

Silicone rubber (SiR) has been widely used in XLPE cable accessories because of its excellent electrical and mechanical properties. The electrical tree is a serious threat to SiR insulation and it can even cause the insulation breakdown. Addition of nanoparticles into SiR can improve the insulating properties compared with undoped material. The effect of nanoparticles on tree characteristics at temperatures above 0 °C has been widely researched. However, the effect under low temperature has not been researched. In this paper, electrical treeing process in SiR/SiO₂ nanocomposites was investigated over a range of low temperatures. The samples were prepared by mixing nano-SiO₂ into room temperature vulcanized (RTV) SiR, with the content of 0, 0.5, 1.0, 1.5 and 2.0 wt% respectively. The experiment temperature ranges from -30 °C to -90 °C. AC voltage with a frequency of 50 Hz was applied between a pair of needle-plate electrodes to initiate the electrical tree at different experiment temperatures. Both the tree structures and the growth characteristics were observed by using a digital microscope system. The experiment results indicated that both nanoparticles and low temperature are important factors of the treeing process in SiR/SiO₂ nanocomposites. The distribution of tree structures depends on the content of nanoparticles and temperature. Nano-SiO₂ can repress the tree growth effectively and the optimum content with the lowest tree growth speed is 1.5 wt%. Crystallization caused by the changing temperature also influences the treeing process.