Influence of corona discharge on the hydrophobic behaviour of nano/micro filler based silicone rubber insulators

Silicone rubber is one of the most used outdoor insulation materials in the last few decades due to its improved performance in contaminated and humid conditions. The improved performance of silicone rubber insulators is due to their hydrophobic nature however, the organic nature of silicone molecules makes them vulnerable to ageing and degradation. This paper aims at investigating the loss and recovery of hydrophobicity of four different silicone rubber micro/nanocomposites exposed to corona discharge. The samples were exposed to corona discharge generated by pin-plate electrode configuration under AC stress. A series of tests were performed to observe the impact of different electrode-sample gaps and for various periods of corona exposure. The hydrophobicity of samples was measured pre and post corona exposures at various intervals up to 72 hours. This time could confirm the hydrophobicity recovery process. Numerical simulations were also performed in COMSOL Multiphysics to investigate the electric fields along the sample surface at different electrode gaps. Experimental results showed that samples recovery time was proportional to the duration of exposure to corona discharge and inversely proportional to the electrode-sample gap. Among all, samples with 2.5% nano-silica as additive showed better hydrophobicity recovery. Simulation results showed that an increase in electrode gap resulted in decreased electric field intensity, hence supporting the experimental outcomes.