Establishment of Evaluation Method of Electrical Insulating Characteristics of External Interface and Discussion of Its Application to Field

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Electrical insulation characteristics of external interface between silicone rubber and air were studied, which was a typical interface of polymer insulators. Main results obtained are as follows.1. Behavior of water droplet on silicone rubber. A series of experiments were carried out under ac voltage application by using an optical system and a high-speed camera. The effect of water droplet vibration on electrical insulation capability was also investigated.(1) Water droplet became to vibrate more severely with increasing applied voltage. After it was extended in the direction of applied electric field, flashover occurred finally through the droplet.(2) Vibration frequency of an uncharged water droplet was double the frequency of the applied voltage. On the contrary, in the case of an artificially charged droplet, it was the same with that of the applied voltage.(3) The vibration had three mechanical resonance frequencies for each size of the water droplet in the range of the present study. Three modes of resonance were visually observed.(4) It was confirmed that flashover voltage was decreased as 65% as that at non-resonance when a water droplet vibrated severely at the mechanical resonance frequency.2. Measurement of leakage current flowing on silicone rubber surface under contaminated and wet conditions :(1) A measuring system was constructed and operation was confirmed. The system enabled measurement of conductive, dry-band arc and partial discharge components of leakage current separately and simultaneously.(2) Results of the accelerated salt fog tests showed that cumulative charge of leakage current was large in the order of conductive, dry-band arc and partial discharge components.(3) Specifications of salt fog test for silicone rubber sheet, which was able to be prepared more easily compared with rod-shaped silicone rubber, werer established by paying attention to the shapes of silicone rubber and electrodes.