Surface Flashover of Water Repellant Insulators under Moist Conditions

A study was conducted to determine how surface moisture can lower the flashover strength of insulation, with particular reference to out-door high voltage insulation. Since water repellant greases are used to prevent flashover under moist, contaminated conditions, and since new insulator materials will have improved water repellancy, the study concentrated on surface wetting effects. Studies were made of droplet growth during fog for several surfaces. Flashover studies showed that near threshold, flashover occurred by means of droplet deformation in the electric field. Rough agreement was obtained with a simple theory. The study provided further support for the development of hydrophobic coatings for outdoor insulation.