Effect of Moisture Distribution on Surface Flashover of Oil–Paper Insulation: Fundamental Phenomena, Statistical Behavior

Abstract

Moisture in oil–paper insulation has a great influence on insulation performance, and moisture distribution is always uneven. In this study, the distribution of surface flashover channel position and surface flashover time of oil–paper insulation under dc voltage and different moisture distributions were examined by statistical methods. The experimental results of surface flashover positions were fit by normal, lognormal, gamma, and Weibull distributions, and the goodness of fit was evaluated by correlation coefficient and Kolmogorov–Smirnov (K–S) testing. The results showed that the distributions of flashover positions under different moisture distributions were the best fit by Normal distribution. A hypothesis test results of the double sample <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${t}$ </tex-math></inline-formula> -test showed that, at a significance level of 0.01, the mean value of flashover position under uneven moisture distribution was significantly different from that of a uniform distribution, and that flashover tended to high moisture areas. Using the same method, the distribution of surface flashover time met the Lognormal distribution, and the average value of surface flashover time, under uneven moisture distribution, was significantly lower than that under the uniform distribution. The shifting of flashover position and a significant decrease in flashover time were directly attributed to the electric field distortion caused by uneven moisture distribution. The induction effects of moisture on the statistical characteristics of surface flashover were obtained, which was of great significance in evaluating the harm of partial dampness.