Electrical Tree Characterization in Silicone Rubber Under Different Numbers of Lightning Impulse Shot

Silicone Rubber (SiR) is widely used for high voltage cable accessories fabrication for AC and DC power system network as it stands for extensive range of voltage and temperature used. In addition, it also deals with excellent electrical and mechanical properties. However repetitive pulse voltage such as lightning and switching from converter become one of the main threats to the SiR cable jointer. In this paper, the electrical tree behavior under lightning impulse (LI) voltage was investigated. LI voltage stressed was applied to the needle electrode to initiate the electrical tree growth. The magnitude of LI was 15, 20, 25 and 30kV under 1000 numbers of shot. Electrical tree growth behavior was observed and analyzed under room temperature. The results reveal that tree inception appeared at 20kV LI with less number of shot than 15kV. However, the tree length propagates rapidly at 25kV and 30kV just under one shot of LI voltage. The electrical tree length propagates rapidly with the increase of LI magnitude voltage as well as the deterioration area disseminates. At 15, 20 and 25kV, the electrical tree length increased with the increasing numbers of shot and eventually start to saturate at 400 LI shot. However, there is abruptly increment of electrical tree length under 30kV LI voltage at initial LI shot and tend to be saturated starting at 800 LI shot. In the other hand, the increasing numbers of shot at 15, 20 and 25kV LI voltage tend to change the tree structure from branch type to bush type tree however at 30kV LI voltage, the tree structure appeared 100% in pine branch tree formation within 1000 numbers of LI shot.