Splitting of vacuum arc column in transverse magnetic field contacts at intermediate-frequency

Splitting of vacuum arc at intermediate frequency (400-800Hz) 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 2 mm in a single-frequency circuit. With high-speed photography the arc appearances at different arc currents from 3.3 kA-rms to 10 kA-rms at intermediate frequencies were characterized. 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 rotated 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. Furthermore, the generations of the split arcs almost have the same features. The split arc formed in the opposite (retrograde) direction, contrary to the Ampere rule. The velocity of split arc is related to the motion direction and the generation position. According to the observation of the split arc at different frequencies, a conclusion can be drawn that the split arc is more likely to occur when the arc almost fills half of the contact surface. The motion direction and the velocity of arc column were studied. Finally, the formation of a split arc was discussed.