Characteristic dynamic behavior of dc arc near graphite bar electrodes with short gap

Abstract

Periodic sawtooth patterns were observed for arc voltages of dc free burning air arcs between 16 mm diameter graphite bar electrodes with a gap length of 15 mm. Observation with a high-speed video camera showed that the sawtooth wave forms of the arc voltages were brought about by the dynamic motions of the arc spots on the electrodes. The anode spot showed a periodic movement on the electrode edge a few hundreds milliseconds after arc ignition, while no movement of the cathode spot was observed. The deflection of the arc column near the anode spot also showed a characteristic pattern during the periodic movement of the anode spot. In order to investigate the factors influencing the dynamic behavior of the arc column near the anode spot, the Lorentz force applied to the arc column near the anode spot was calculated by taking into account the flux induced by the current distributed inside the anode. It was pointed out that the dynamic behavior of the arc column near the anode spot was interpreted as caused by the Lorentz force.