Three-Parameter Weibull Distribution Curves for LIBV of Pressboard Samples Impregnated with Natural Ester and Mineral Oil

The studies presented in this paper were focused on comparative analysis of Weibull distribution curves determined for lightning impulse breakdown voltages of 1 mm thick pressboard samples impregnated with natural ester and mineral oil respectively. The analysis of the results was made using three-parameter Weibull distribution function with location parameter Vo (theoretical zero probability) meaning the threshold value of voltage below which breakdown does not happened. The curves obtained within the studies are in general similar in shape with some benefits in direction of curves connected with pressboard impregnated by natural ester liquid. Quantitatively the difference between the considered cases was found as very small (around 2 kV when comparing the Vo obtained). The reason for this may be the difference in electrical permittivity of pressboard impregnated by ester, which is a little bit higher in comparison with pressboard impregnated by mineral oil. The studies confirmed also that the applied three-parameter Weibull distribution is an excellent statistical tool for determination of threshold electrical strength of liquid-solid insulation systems.