Flashover characteristics of silicone rubber surface influenced by surface charge

A composite insulator using silicone rubber is widely applied to an outdoor insulator instead of a conventional porcelain insulator due to lightweight, easy handling and high pollution resistance of silicone rubber insulator. To understand DC surface insulating performances, the DC flashover inception voltages (FOIV) on silicone rubber sheet sample and porcelain insulator plate sample were measured under positive impulse voltage with or without DC prestressing. As the result, DC prestressing effect of silicone rubber sheet sample and porcelain insulator plate sample is same tendency as general DC prestressing effect under positive impulse voltage application with negative DC prestressing. But, under positive impulse voltage application with positive DC prestressing, FOIV of porcelain insulator plate sample showed a peak at DC prestressing of +20 kV. Moreover, surface resistivity of silicone rubber sheet sample is higher than that of porcelain insulator plate sample. In general, the impulse breakdown strength of insulating material increases under DC prestressing of same polarity. On the other hand, the impulse breakdown strength of insulating material decrease under DC prestressing of reverse polarity. From these result, due to the low surface resistivity of porcelain insulator plate sample, it is considered that FOIV decrease in spite of homo condition because the positive surface charge moves to the vicinity of the counter electrode and act as hetero charge.