Experimental Investigation of DC Switching Arcs in Molecular Gases at Small Currents

The behavior of an electric arc in molecular gases, particularly in hydrogen (H2) gas, is still not fully understood and lacks experimental investigations. In this work, we studied the arc behavior and presented experimental results of direct current (dc) switching arcs in nitrogen (N2) and hydrogen (H2) gases, focusing on small currents ranging between 2 and 16 A. The experiments were performed with graphite electrodes at atmospheric pressure and with a gap length of up to 2.8 mm. The arc voltage was measured at constant current and the arc length was estimated via processing of high-speed camera images. A relationship between the voltage and the length is introduced, which gives the average electric field. The comparative analysis of arc behavior in N2and H2indicates expected differences between both discharges. Erratic arc behavior, fast elongations, and higher electric fields are observed in H2. In N2, the average electric field at low lengths is higher than at higher lengths, whereas in H2, the field is constant regardless of arc length and the arc column is more constricted. Finally, an arc voltage–current model is presented for both gases and compared with experimental results.