Effects of mechanical stress on treeing growth characteristics in HTV silicone rubber

Tensile and compressive stress, produced by the spring clamp device and the banding force after the expansion of silicone rubber stress cone, can affect the electrical properties of silicone rubber in the cable accessories. Electrical tree, one of the main electrical aging phenomena, is supposed to be related to the mechanical stress. In this paper, the treeing growth characteristics considering the tensile and compressive stress were investigated by the pin-plane electrode system respectively. The tensile rate of silicone rubber ranged from 0% to 30%, while the compressive rate varied from 0% to 50%. The results indicate that both the tensile stress and compressive stress affect the treeing propagation characteristics. The appearance probability of bush tree increases and it becomes the main tree structure at higher tensile rate, while branch tree turns into the main tree structure at higher compressive rate. Electrical tree initiation probability becomes higher and the initial time tends to be shorter under the tensile stress, while they show an opposite tendency under the compressive stress. Under tensile stress, the tree length, fractal dimension and accumulated damage become lager as the tensile rate increasing, which indicates that the higher tensile rate accelerates the treeing process. However, under the compressive stress, the treeing growth process shows a converse trend, which demonstrates that the higher compressive rate retards the electrical tree growth.