Physical process of interrupting AC current in vacuum interrupter and mathematical evaluation of the interrupting capacity

Multi-cathode-spot AC arc extinguishing process in vacuum interrupters is shown. It is divided into 4 periods: arc transient state period; sheath developing period; metal vapor decaying period; and static state period. The first 3 stages are dynamic physical processes and their mathematical models are given. Residual resistance in sheath developing period and metal vapor density in metal vapor decaying period can be obtained by solving the mathematical equations and the two parameters are used to evaluate the interrupting capability of a vacuum interrupter. In the current interrupting process, if residual resistance keeps rising and metal vapor density is less than the critical one, the vacuum interrupter can interrupt the current successfully.