Effect the Numbers of Lightning Impulse Shot on Electrical Tree Growth in Silicone Rubber

Recently, silicone Rubber (SiR) is preferable for high voltage cable accessories manufacture for AC and DC power system network application. It is because it stands for oxidization, wide range of voltage and temperature used as well as offers with superb electrical and mechanical properties. However, repetitive and high-frequency pulse voltages from lightning and switching in high voltage direct current (HVDC) converters pose significant threats to SiR cable joints. In this paper, the electrical tree growth behavior under lightning impulse (LI) voltage was studied. LI voltage was stressed to the needle electrode to initiate the electrical tree growth. The magnitude of LI was 15, 20, and 25kV under 800 numbers of shot. Electrical tree propagation was perceived and analyzed under room temperature. The results indicate that the electrical tree length propagates proportionally with the increase of LI magnitude voltage as well as the increment of tree width. At 15, 20 and 25kV, the electrical tree length increased with the increasing numbers of shot and eventually attain the steady state at 400 LI shot. In addition, the increasing numbers of shot at 15, 20 and 25kV LI voltage tend the tree formation change from branch type to bush type tree.