Numerical modeling to evaluate the withstand voltage of a HV vacuum interrupter

A model based on the area effect of breakdown has been developed that allows statistical evaluation of the withstand voltage of HV vacuum interrupters. The applicability of the model to show the breakdown properties in a model vacuum interrupter of gaps between the electrodes and between the electrode and the shield is demonstrated experimentally. This model makes possible the evaluation of the breakdown voltage of a vacuum interrupter through the relation between the breakdown probability and the effective area at a given voltage level. Weibull statistics are utilized to calculate the effective anode area from the distributions of the weak point on the anode and of the electric field on both anode and cathode. The model account for the polarity effect of breakdown and influence of field enhancement of the breakdown. It is also demonstrated that the model can predict the coaxial gap configuration in which the highest withstand voltage can be obtained for the AC stress. The model was applied to designing a 72/84 kV rating model vacuum interrupter