Surface flashover phenomena at vacuum/oil interface

Summary form only given. The present paper presents experimental results of oil/solid and vacuum/solid interface flashover studies under varying experimental conditions, viz. (i) effect of input dV/dt: 50 to 400 kV/μs, (ii) angle of spacer: +70° to -70° and (iii) thickness of spacer: 1 to 3 mm. In a hollow insulator, the inner surface is a vacuum/solid interface and the outer surface of the insulator represents an oil/solid interface. Transformer oil and PMMA are used as oil and solid medium respectively. A statistical distribution of the flashover voltage for oil/solid interface has been done with N=10 samples. Even though the Weibull distribution is used in the case of spark gaps and different insulation breakdown studies, the present study is an exception and follows a normal distribution within 99% confidence limits. This may be due to the randomness in breakdown voltage due to inherent non-uniformity in the presence of a spacer in the uniform gap regime.