Comparison of the Dynamic and Static Measurements of Hydrophobicity of Silicone Rubber Affected by Partial Discharges and Moisture

Silicone high-voltage insulators are widely used in humid climatic conditions, such as fog or rain. Water droplets on the insulator surface lead to partial discharges, which reduce hydrophobicity of the silicone rubber. It is important to consider the combined effect of discharges and moisture. This work evaluates the hydrophobicity of a silicone rubber sample exposed to a short-term corona discharge for 3 minutes, followed by immersion in a 4% NaCl solution for several weeks. The effect is compared to immersion in water without prior exposure to corona discharge. The contact angle and dynamic runoff of water were measured during the experiments. The dynamic measurement shows that water flows off undamaged samples in less than a second, while after 360 hours of immersion in the solution, the flow time increases more than fivefold. Additionally, the area where water does not flow at all increases more than twice. However, static measurement using the sessile drop method shows no significant effect.