Influence of thermal aging time on electrical tree initiation of silicone rubber

Power cable operating at high temperature over a long period would influence the electrical performance of silicone rubber (SIR) in the new types of extra-high voltage prefabricated cable accessories. Through tests, we revealed the relationship between thermal aging time (0~1 000 h) at 90°C and the characteristics of electrical tree aging: the electrical tree initiation voltage increases and then decreases with time; the thermal aging time greatly affects the characteristics of electrical trees, for instance, as the thermal aging develops, the proportion of pine-like trees firstly decreases and then increases, the proportion of bush-like trees firstly increases and then decreases, while the proportion of branch-like tree keeps low; the maximum discharge capacity firstly decreases and then increases with aging time. Further analysis combined with experiments of differential scanning calorimetry (DSC) and equilibrium swelling, it is concluded that the breakdown of cross-linking network in SIR causes all the changes mentioned above. Hence we should pay more attention to the thermal aging of SIR in operation.