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Effect of Local Arc Discharge on Hydrophobicity Decrease of Silicone Rubber Surface: -Investigation on Hydrophobicity Change by Measuring Water Drop Velocity and Surface Analysis-

Various methods have been proposed to evaluate hydrophobicity of silicone rubber used for sheds of polymeric insulators. CIGRE WG D1.14 has proposed Dynamic Drop Test (DDT) method to evaluate the hydrophobicity changes of the materials. In this paper, we measured static contact angle, hydrophobicity class in spray method, and drop velocity of water droplets, in order to observe the change in hydrophobicity of silicone rubber surface suffered to local arc discharge at DDT. Because of the hydrophobicity decreases due to the local arc discharge, the water droplet changes from a spherical to a water film. In particular, changes of initial state in hydrophobicity can be observed by measuring the drop velocity of water droplets. And the correlation was confirmed with the cumulative charge of local arc discharge. Therefore, the water drop velocity was effective for the evaluation of hydrophobicity change.