In order to study the dielectric recovery performance of the SF₆ circuit breaker after the current zero (CZ), the magneto-hydro-dynamic (MHD) model of arc burning process was established for the structure of a 126 kV auto-expansion switch. Two methods of evaluating the post-arc dielectric recovery strength were established. The fist method is predicting the most likely area of post-arc electric breakdown according to the temperature and pressure distribution. Another method is based on the leader inception criterion, one can predicted the most likely breakdown path in the gap between two contacts and the breakdown voltage with the distribution of the critical breakdown electrical field determined by the temperature and pressure. The results about the post-arc breakdown voltage and electrical field distribution is essential for the evaluation of the performance of arc interruption. The simulation results can be used to estimate the possibility of breakdown and arc reburning after CZ. The influence of different factors on the strength recovery of the back-arc medium is studied by changing the current and the moving velocity of the contact. It is indicated that the higher current is conducive to the post-arc dielectric recovery, the influence of the contact moving velocity on the post-arc dielectric recovery needs to be analyzed by considering the specific switch structure.
 The established model in this thesis is valid and can be widely used in arc simulation and the evaluation of dielectric recovery. The results of this paper are significant for the application of new environmental gases in isolating switchgear and optimization design.
 

dielectric recovery,thermal interruption performance,leader inception criterion,high voltage switch