Experimental investigation on the expansion speed of cathode spots in high-current triggered vacuum arc

Cathode spots (CSs) expansion speed in the initial expansion stage in high-current triggered vacuum arc was investigated experimentally. Experiments were conducted with butt contacts in a demountable vacuum chamber. Alternating current with frequency of 50Hz and peak value of 3kA~11kA was used. Images of CSs were photographed with a high-speed digital camera with exposure time of 2 microseconds. The influence of arc current rise rate and axial magnetic field (AMF), which was supplied by external magnetic field coil, on CSs expansion speed was mainly investigated. Experimental results indicated that, in the initial expansion stage, as the arc current increased linearly, CSs expansion speed was nearly a constant, which was proportional to the current rise rate. Experimental results also showed that CSs expansion speed decreased with the increase of AMF flux density.