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 N₂ and H₂ indicates 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.