Experimental investigation on magnetically controlled air arc oscillation characteristics for DC interruption

Abstract

Abstract With the development of the direct current (DC) power grid, the research of the forced current zero techniques in DC circuit breakers is of vital importance. Through applying an external alternating transverse magnetic field to an air arc confined by insulating walls, the arc can oscillate in a specific pattern, which is defined as ‘magnetically controlled arc oscillation’ in this article. The air arc oscillation characteristics are investigated through arc voltage spectrum analysis and arc motion captured by a high-speed camera. It can be found that the arc motion can be divided into a gliding process and a stretching process. The arc voltage oscillates at a particular frequency, which is nearly twice the magnetic field frequency. The basic arc oscillation pattern can be described from the aspects of arc voltage, arc column length and arc root velocity. Furthermore, this article proposes a DC breaking scheme based on the investigated magnetically controlled air arc oscillation characteristics. The forced current zero crossing point can be created in the resonant process between the oscillated air arc and the parallel-connected inductance-capacitance (LC) commutation path. Based on the proposed DC breaking scheme, interruption experiments are carried out, and it is observed that a current of 4.2 kA can be interrupted within several milliseconds. The feasibility of DC interruption based on magnetically controlled arc oscillation has been proved.