A coupled computational fluid dynamics and heat transfer model for accurate estimation of temperature increase of an ice-covered FRP live-line tool

Controlled laboratory tests validated a hypothesis that extremely light (~2-3 μg/cm²) levels of Equivalent Salt Deposit Density (ESDD) with no Non-Soluble Deposit (NSDD) can reduce voltage withstand capability of Fiberglass-Reinforced Plastic (FRP) hot sticks under cold-fog conditions near the freezing point, where the tool surfaces are fully wetted by the environment or alternately surrounded by fog. However, the source of moisture in flashovers at temperatures below -13 °C was not established. The mechanism of tool surface wetting was explored through coupled Computational Fluid Dynamics (CFD) and Heat Transfer mathematical equations for a FRP hot stick modeled in Commercial software, COMSOL Multiphysics. The results show that the flow of partial discharge current could be sufficient to raise the temperature of an iced pollution layer just below freezing, where the cold-fog flashover mechanism prevails.