Rain-induced triboelectric charging on silicone rubber: surface potential evolution and hydrophobicity loss

Abstract Unusual flashovers of composite insulators with low pollution levels under rainfall conditions have been observed in recent years, yet their mechanisms remain unclear. This study investigates the triboelectric charging of hydrophobic silicone rubber surfaces under simulated rainfall. Using a custom-built water dripping platform, the charge of sliding water drops was measured by both a Faraday cup and a fine tungsten-wire probe connected to a current amplifier, while the surface potential distribution was obtained through electrostatic voltmeter scanning. Results show that the charge of water drops changes from negative to positive along the sliding path, with the maximum positive potential appearing near the lower end of the specimen. This polarity separation arises from the competition between solid–liquid triboelectric charge transfer and surface charge retention mechanisms on the silicone rubber surface. The transient charging process is governed by a balance between triboelectric charging and surface charge dissipation, which is well described by an equivalent RC model. Additionally, the charge dissipation experiment confirms the exponential decay of both positive and negative surface potentials. A supplementary test reveals that water dripping for 2 min reduces the contact angle of silicone rubber by approximately 10°, indicating a decrease in hydrophobicity that may promote continuous conductive film formation and increase flashover risk under service conditions. These findings provide insights into the coupling of triboelectric charging, surface charge retention, and hydrophobicity degradation, contributing to the understanding of flashover mechanisms for composite insulators under wet conditions.