Evaluation of current interruption performance with axial magnetic field at current peak and current zero of vacuum circuit breakers

This study investigates the influence of an axial magnetic field on current interruption performance of vacuum interrupters. The authors focused on axial magnetic flux densities at current peak and current zero of an alternating short-circuit current. An axial magnetic flux density at current peak is commonly understood to be important to stabilize arc plasma between electrodes. The authors considered that an axial magnetic field at current zero was also important since the magnetic field would retain residual charged particles between electrodes which degraded the insulation recovery of vacuum interrupters. A three-dimensional finite element analysis code was used to estimate the magnetic flux density of an axial magnetic field electrode. In order to control the magnetic flux density at current peak and current zero, the depth of the central cavity and the height of the coil arm of a cup-shaped electrode were adjusted. Current interruption performance of the test electrode was examined through a short-circuit test. The data was evaluated by comparing interruption region as functions of arcing time and interrupting current. The result suggests that too strong axial magnetic fields at current peak and/or at current zero are not preferable to have a better interruption performance.