Effect of low temperature on tree characteristics in silicone rubber with different power frequency

Electrical tree is one of the main reasons for long-term degradation of SiR cable accessories used in high voltage ac applications. In this paper, an investigation of electrical tree growth characteristics in SiR samples is reported. Ac voltage with frequency ranging from 50 to 200 Hz was applied between a pair of needle-plate electrodes to initiate electrical trees at temperature ranging from 30 to -100 °C. Both the tree structures and growth characteristics have been observed by using a digital microscope system. Three typical profiles of electrical trees, namely branch, bushbranch and pine branch tree, have been observed within the samples. The growth rate and accumulated damage have been employed to analyze the treeing process. It is observed that the high power frequency will lead to the occurrence of bush-branch tree and the low temperature will lead to the occurrence of pine branch tree. Meanwhile, the tree inception probability increases from 30 to -60 °C and then decreases fast. The high frequency will improve the tree inception probability under the same temperature. During the experiment, breakdown has occurred in some samples and the width of breakdown channels is related to the frequency.