The insulator strength of the oil-immersed equipment is usually limited by surface flashover across the oil-solid surface. At the same time, the distributions of failure strengths have some statistical characteristics. In this paper, the flashover voltage electric strengths of several PMMA test samples are measured in transformer oil under nanosecond pulse voltage. Normal distribution is introduced to describe the statistical characteristics of the experimental data. The plot of the flashover dielectric strength on Weibull paper can also demonstrates the two-parameter Weibull distribution. The parameters of the distributions are presented and the more favorable distribution is discussed with the view of obtaining consistent results for the surface dielectric strength.
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