Influence of shed parameters on the aging performance of silicone rubber insulators in salt-fog

The paper presents the results of a study on the effect of shed design on the aging performance of silicone rubber (SIR) insulators in salt-fog. The experiments on a single shed design at 35 V/nun average stress and 0.25 S/m salt-fog conductivity level are reported. Shed diameter, location and inclination angle are the parameters investigated in the study. The low frequency harmonics of the leakage current, early aging period, equivalent salt deposit density (ESDD), and physical damage are used to evaluate the aging performance of various designs. Insulators having sheds with 100 mm diameter show a better performance than those having 80, 60 and 40 mm diameter sheds. The inclination angle of the sheds is shown to have a significant effect in reducing the leakage current to a very low value but simulation results using FEMLAB(R) show that a steep inclination angle results in field enhancement beneath the shed that may lead to corona damage of the shed. A cup shaped design for the shed is shown to have a low leakage current level and a low field enhancement beneath the shed.