Vacuum arc transient behaviors and voltage characteristics in low-current DC interruption under rotating TMF

The objective of this work is to determine the relationship between the vacuum arc transient behaviors and voltage characteristics in low-current DC interruption under a rotating transverse magnetic field (TMF). An external rotating TMF was generated by two pairs of Helmholtz coils, set at right angles. The phase angle of alternating currents in the two Helmholtz coils was shifted by 90°. The rotating frequency was 230 Hz, with a peak flux density of 32 mT. The contact material was CuCr25 (25% Cr), with a diameter of 18 mm. The DC vacuum arc appearance was recorded by using a high-speed CCD video camera. The experimental results indicate that the voltage characteristics were closely related to the DC vacuum arc transient behaviors. In low-current DC interruption under a rotating TMF, vacuum arcs experienced two main stages of evolution, a constriction and motion stage and an unstable stage. The increase in the arc voltage, caused by the unstable state of the cathode spot group located at the edge of the contacts and the stretched state of the DC vacuum arc column, was the key for DC vacuum successful interruption under the rotating TMF. Moreover, the interruption characteristics of the DC vacuum arc were quite sensitive to the contact separation length and the rotating TMF flux density. The duration of the total interruption process decreased with the increase in the rotating TMF flux density, which mainly affected the duration of the constriction and motion stage in the DC vacuum interruption.