Surface Degradation of HTV Silicone Rubber under the effect of low air Pressure

Polymeric insulators are widely accepted for the use of outdoor insulators in power transmission systems. When they are planted at the higher altitude regions the corona discharge activity can get accelerated due to the effect of low pressure. The corona discharge intensity under low air pressure can change the surface morphology of the insulator eventually leading to ageing which further leads to the insulator failure. In the present study high temperature vulcanized (HTV) silicone rubber samples were exposed to corona discharges under low pressure environment. The samples were kept in a pressure chamber and the internal pressure was varied between 100 kPa to 40 kPa by using a vacuum pump to setup an analogy with the higher altitude conditions. A point plane electrode system maintaining a gap distance of 5 mm between the sample and the needle tip was setup for corona discharge creation. The samples were exposed to corona discharges for 10 hours and the results show that discharge current increased with the decrease in pressure. Fourier transform infrared (FTIR) spectroscopy was carried out to observe the physico-chemical changes occurring on aged samples and the samples under decreasing pressure showed higher hydroxylation which promotes the surface deterioration eventually leading to ageing of the samples.