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Estimation of Endurance Coefficient of Insulating Material under Uniform and Non-Uniform Fields by Damage Equalization Method

In high voltage insulation system, the insulation will be undergoing various stresses and the life of the insulation will be different from uniform fields when stressed by a divergent field. In this paper, dc breakdown experiments at different step stresses are conducted using needle-plane and plane-plane electrode systems. Using the data from the breakdown tests, assessment of life of the insulating material can be done by estimating the voltage endurance coefficient (n) and accumulated damage. Stepped-stress damage equalization method (SSDEM) is used for estimating the life of the insulating material used. Interesting results on the role of uniform and non-uniform field on endurance coefficient is reported which in turn shows the effect of divergent and uniform stress on the life of the insulation. Furthermore, in this study, a numerical model is developed to estimate the electric field around the tip of the needle electrode using a semi-empirical equation of nonlinear conduction under steady state DC. Spherical geometry system is used for solving the differential equations numerically. The results show the developed numerical model can predict the Poisson's field when conduction is field dependent.