Modeling of vacuum arc evolution in opening electrical contacts

A nonstationary vacuum arc in separating electrical contacts is considered and described mathematically as a sequence of phenomena beginning at the pre-arcing stage and coming to an end at arc extinction. Experimental data concerning dynamics of material transfer, arc spot size, and arc duration are obtained depending on current, material properties, pressure, inductance and opening velocity. A mathematical model describing evolution of these phenomena is elaborated. It is based on the nonstationary axial symmetric temperature and electromagnetic fields for anode, cathode, bridge, arc column, and takes into consideration electron and ion bombardment of electrode surfaces, ionization and recombination phenomena, electron emission, arc radiation, melting and evaporation of contact material, arc spots mobility. We found that bridge dynamics at the pre-arcing stage plays important role in material transfer during following anodic arc, and the main parameter responsible for the direction and magnitude of material transfer is contact gap. It is established also that the rate of evaporation and the difference between anode and cathode losses (fine material transfer) depend on the transient redistribution of electron and ion current densities, and dynamics of arc temperature. Some problems of arc duration and arc evolution in AgMeO contacts from anode mode to cathode metallic mode are also discussed in this paper