Influence of Over-voltage Caused by Chopping Current on Electric Field Distribution in Vacuum Interrupter
A transient circuit model for the vacuum circuit breaker switching three-phase inductive motor is established and the steep-fronted over-voltages waves caused by chopping current are calculated. Discrete Fourier transform (DFT) is introduced to decompound the step-front transient over-voltage. Several main frequency components are obtained, which are regarded as boundary excitation. The differential equations of transient field are deduced, in which conductivity gamma is taken into account due to existence of plasma and metal gas between contacts, contact and shield. FEM is adopted to calculate the electric field in the vacuum interrupter and superposition of power frequency voltage and over-voltage of chopping current is regarded as boundary excitation, in which Delaunay method of mesh generation is introduced to discrete the solved region. Potential distribution curves at representative time are shown, which are compared with the one in the static field