Arc Cooling by an External Magnetic Field in Low-Voltage DC Switching

The effects of an external magnetic field on the interruption of dc switching arcs are intensively studied and considered in the design of commercial products. However, these effects are not fully understood yet. This paper presents an investigation of these effects through experimental and numerical methods. The experiments were conducted using a dc switch apparatus with controlled contact opening speed, 10-500 mm/sec, interrupting a resistive load current of up to 45 A with an applied voltage of up to 75 V. The switching arc is exposed to a uniform external magnetic field of 40 mT generated by a pair of Helmholtz coils. The arcing events are analyzed to determine the arc’s length, diameter and column conductivity. The experimental results show that, for a given voltage and current, the duration of the arc is reduced by a factor of 5 to 25 for the range studied because of a reduction of conductivity. Simulation results show that the magnetic field increases air flow velocity in the arc plasma which enhances mixing and cooling. The combined experimental and simulation results show that the external magnetic field effectively enhances arc cooling, leading to a significant reduction in arc conductivity and duration.