Motion and splitting of vacuum arc column in transverse magnetic field contacts at intermediate-frequency

Arc motion and splitting of vacuum arc at intermediate frequency (400-800 Hz) were investigated under transverse magnetic field (TMF). The experiment was performed on cup-type TMF contacts with contact diameter of 40 mm and a contact gap of 4 mm in a single-frequency circuit. With high-speed photography we characterized the arc appearance at different arc currents from 3.3 kA-rms to 10 kA-rms at intermediate frequencies. As arc current increases from 3.3 kA-rms to 10 kA-rms the arc appearance changes obviously. When current value is 3.3 kA-rms (current frequency 400-800 Hz), there is almost no splitting arc; when the current exceeds 5 kA-rms (current frequency 400-800 Hz), the arc rotates at a speed above 20 m/s, accompanied by an observable splitting arc. The splitting arc could be observed at different frequencies and the arc-voltage had no noises when splitting occurred. The motion direction and the velocity of arc column were studied. Finally, the formation of a split arc was discussed.