Breakdown between dielectric coated electrodes in compressed gases with metallic particle contamination

摘要

Metallic particle contamination can play a crucial role in compressed gas insulated apparatus. The application of a dielectric coating to an electrode surface should hamper the charging of a metallic particle and hence increase the lift off field at which particle motion commences. The effect of dielectric coatings (polyurethane, epoxy and anodized oxide layers) on the particle lift off field has been previously reported.1 The authors have extensively explored the effect of anodized oxide coatings on lifting field and breakdown between plane parallel aluminum electrodes in compressed sulphur hexafluoride gas. Some experiments have also been performed in nitrogen. In general anodized oxide coatings produce the following results under 60 Hz voltages: (a) The lifting field for the various metallic particles is increased by a factor of two or more if the lower electrode is anodized. (b) The coating thickness, the size, shape and material of the particle do not appear to have a significant influence on the lifting field. (c) The lifting field increases with gas pressure and this increase is more noticeable with thicker (> 100 μ) anodized oxide layers. (d) The lifting field in sulphur hexafluoride gas is higher than in nitrogen.