Surface resistance and hydrophobicity of HTV silicone rubber in the presence of salt-fog

Silicone rubber used to fabricate insulators can provide long-term and satisfactory service even under polluted and wet conditions. This is due to its long-term hydrophobic surface properties. The hydrophobic surface inhibits the formation of a continuous water film and the flow of leakage current along the surface. This mitigates against the initiation of dry band arcings that lead to flashover. In the present study, high temperature vulcanized (HTV) silicone rubber rods were subjected to accelerated wetting in salt-fog and immersion in a saline solution. A dc voltage is applied to the specimens to measure the surface resistance. Some of the influencing parameters on the surface resistance are studied. These include: 1. The duration of the exposure to the salt-fog without electric stress, 2. The duration of the exposure to combined salt-fog and ac electric stress, and 3. The specimen length. The contact angle and the surface roughness are measured and correlated with the corresponding surface resistance.