Deterioration of silicone rubber for polymer insulators by corona discharge and effect of fillers

This paper describes deterioration phenomena and mechanisms on silicone rubber housings of the polymer insulators by corona discharges. The corona discharge was observed on the trunk portion the insulator tested in a fog chamber. Nitric acid and ozone generated by the corona discharge were recognized on that trunk portion, which was discolored and became whitish. The discolored area was expanded with test period. Surface conditions and mechanical properties of six kinds of the silicone rubber containing ATH (Alumina Tri-Hydrate) and CaCO₃ (Calcium Carbonate) as fillers, were investigated after immersion in 1 N nitric acid for 96 hours. As a result, weight loss of test pieces containing CaCO₃ and ATH fillers was more than those solely containing ATH. Cracks were observed on the surface of two specimens containing CaCO₃ filler, and not observed on that not containing CaCO₃ filler. This shows the cracks on the surface due to corona discharges are depending on the kind of the filler. The careful survey on the deterioration of the housing rubber due to the corona discharge should be done when we select the housing materials for the polymer insulators