Electrical performance of RTV silicone rubber coating of different thicknesses on porcelain

A study of the effects of coating thickness of room temperature vulcanizing (RTV) silicone rubber on its electrical performance in salt-fog of 250 /spl mu/S/cm and 1000 /spl mu/S/cm at 0.5 kV/sub rms//cm is presented. Porcelain rods coated with RTV silicone rubber to a thickness from 0.17 to 0.99 mm were studied. The dependence of current pulse rate and cumulative number of current pulses on coating thickness were determined as a function of time of exposure to combined electric stress and salt-fog. The surface roughness and the total content of low molecular weight (LMW) silicone fluid in the coating were measured before and after the salt-fog test as a function of coating thickness. The effects of heating the RTV in an electric oven on the production and loss of LMW silicone fluid were investigated in order to elucidate the influence of the heat generated by dry band discharges. The loss of weight of RTV at high temperatures (370/spl deg/C) due to the decomposition of the alumina trihydrate filler into alumina and water was measured and found to be close to the theoretical value.