Evaluation of Creeping Flashover Characteristics of Dielectric-coated Vacuum Interrupter in Air

A vacuum interrupter used for high voltage distribution system must have enough insulation strength in air in order not to breakdown along an external surface of a vacuum interrupter. Coating dielectric substances on sealing parts of a vacuum interrupter provides both compactness and high insulation strength of a vacuum interrupter. In this paper, we investigated feasibility of the vacuum interrupter coated with dielectric substances. Before coating, we determined an optimal range of thickness and length of dielectric substances coated on the vacuum interrupter by simple field analysis. It was found that two cases showed high insulation performance; coating dielectric substances in a certain range of thickness and length, and a use of the dielectric substances which have high dielectric constant. It also turned out that the optimal coating could improve insulation strength by at most two times. After determining the condition of coating, we performed flashover tests for actual vacuum interrupters partially coated with dielectric substances and obtained flashover voltages. We found that coating dielectric substances increased the flashover voltages by approximately 1.3 times.