Permissible Electrical-Field Intensities in the Cast Epoxy Insulation of a 6- to 110-kV Switchgear

Abstract

The method of choice of the working intensity of the electrical field in the cast epoxy insulation of a 6- to 110-kV switchgear taking into account its dimensions, structure, and basic operational factors is studied. The volt–time characteristics of the electrical strength of the cast epoxy insulation corresponding to a low probability of the breakdown at the different intensity of the partial discharges are analyzed. It is shown that the distribution of the electrical strength of the cast insulation under the short-term and long-term action of the commercial-frequency voltage is well described by the Weibull law and the influence of the dimensions on the electrical strength is specified by the “active” volume of the dielectric—the area where the electricalfield intensity makes up no less than 85% of the maximum in the clearance. The estimation of the permissible field intensities in the cast insulation of a 10- to 35-kV switchgear with various degrees of the field inhomogeneity and intensities of the partial discharges is given.