On the motion of high current switching arcs in vacuum and low pressure gas

Magnetically driven arcs in vacuum and low pressure gases are investigated at currents of several tens of kA. Arcs driven in a low pressure environment exhibit peak arc velocity of more than 100 km/s, exceeding those of comparable vacuum arcs by at least two orders of magnitude. The influences of current amplitude, gas pressure and the kind of gas fill on the arc velocity are investigated. A threshold behaviour concerning the minimum requirements for a nonstationary arc is found. An improved model is presented, which explains the observed peak arc velocities in vacuum and in gases.