Mobility of Arc Roots on Copper and Steel Surfaces at Low DC Currents

We study by high-speed imaging, optical emission spectroscopy and finite element simulations the motion of electric arcs on copper and steel surfaces for direct currents (DC) between 5 and 20 A in the presence of external magnetic fields. With increasing external magnetic field, the arc immobility time decreases and the arc root velocity increases. This increase in arc mobility arises from the Lorentz force applied to the arc column and to the electrons and ions clouds that accumulate at the anode and cathode surfaces, respectively. With steel, the lines of the external magnetic field close into the bulk of the metal, leading to a reduced arc mobility. Finally, we discuss the importance of our findings for DC electromechanical switchgear at low currents.