Experimental Investigation of Arc Ignition Modes of Vacuum Arc Under Transverse Magnetic Field

The drawn vacuum arc transitions from the rupture of the molten metal bridge. The initial arc has a significant influence on the temperature and heat distribution on the contact surface, and it greatly affects the whole arcing process. In this paper, arc ignition modes of vacuum arc under transverse magnetic field (TMF) were investigated in a demountable vacuum chamber with spiral-type and wan-type TMF contacts. By using a high-speed camera, multiple-point arc ignition (MPAI) mode was observed, which was different from the common single-point arc ignition (SPAI) mode. The MPAI mode observed can be subdivided into three categories: 1) stable mode; 2) mode with varying number of initial arc columns; and 3) mode with initial columns close to each other. The relationship between the number of initial arc columns and some parameters, such as initial arc voltage, initial arc current, was investigated. Simulation was carried out to compare the difference of magnetic force between MPAI mode and SPAI mode. It was shown that, unlike SPAI mode, arcing with MPAI mode has a stage in which the multiple arc columns gradually combine into one and keep motionless for a long time. Additionally, in most cases the total diameters of arc columns in MPAI mode are larger than that in SPAI mode. The occurrence of MPAI mode and the influence on the subsequent motion of arc was also discussed.