Transition from the anodic arc phase to the cathodic metallic arc phase in vacuum at low DC electrical level

Contact material transfer during arcing in relays has been described in several papers. Transfer from the anode to the cathode has been attributed to the anodic arc phase, and opposite transfer from the cathode to the anode has been attributed to the cathodic arc phase. In a previous paper we showed that the transition from the anodic to the cathodic arc occurs when a break arc becomes longer than a critical arc length, independently from electrical and mechanical parameters. In this paper, we completed our work by using the same breaking apparatus (14 VDC, 40 A) equipped with an arc length control device. We showed that the transition from the anodic to the cathodic arc occurs always at the same critical arc length, independently from the opening speed and the ambient pressure. Through measurements of material transfer in vacuum, we have shown that a cathodic arc in the metallic phase can occur, i.e., that material transfer direction is independent of metallic and gaseous phases. Finally, we showed that it was possible to distinguish the transition from the anodic to the cathodic arc by observing the evolution of the arc spots on the rivets.