High-Current Vacuum Arc Mode Transition of a Horseshoe-Type Axial Magnetic Field Contact With Long Contact Gap

The objective of this paper is to determine the high-current vacuum arc mode transition diagram of a horseshoe-type axial magnetic field (AMF) contact with long contact gap. Drawn arc experiments were carried out in an L-C discharging circuit. Horseshoe-type contacts with contact material of CuCr50 and contact diameter of 120 mm were arranged in a demountable vacuum chamber. Full contact gap was 60 mm. The experiment current level ranged from 4 to 40 kA, stepped by 4 kA. Prospective arcing time was set as 2, 5, and 9 ms, respectively. The evolution of vacuum arc behavior was observed using a high-speed camera. Nonsynchronous evolution phenomenon of twin parallel arc columns was observed. With current level ranged from 24 to 40 kA, the maximum nonsynchronous duration transiting from small-gap constricted column mode to diffuse column mode, from diffuse column mode to diffuse arc mode, and from diffuse arc mode to multicathode-spot arc mode were 0.98, 1.09, and 1.55 ms, respectively. The nonsynchronous duration in various vacuum arc modes was determined as well. Summarizing all arc mode transition points in the experiment, a vacuum arc mode transition diagram of the horseshoe-type AMF contact was proposed. Boundary of uncontrollable arc region was determined, which could provide criteria of maximum arcing contact gap design. Besides, an effective arcing region was defined according to distribution of AMF and arc behaviors, in which AMF on the contact surface plane was higher than 75%Baxial-max.