Dynamics of arc phenomena at closure of electrical contacts in vacuum circuit breakers

Dynamic phenomena accompanying electrical contacts closure in vacuum circuit breakers-are considered as consecutive singes, including breakdown, touch, penetration, restitution, bridging and arcing at bouncing. The hybrid mathematical model is elaborated to describe dynamics of the arc und forces acting in contact gap. It includes experimental oscillograms of current, voltage and contact displacement and nonlinear equations for arc, anode and cathode temperature fields and contact motion. Experiments are carried out using a standard vacuum circuit breaker with laser sensors for measurement of contact gap. The special difference path method techniques was applied to take into account oscillations of a fixed contact. The axisymmetrical Stefan problem with WO free boundaries corresponding to melting and evaporation interfaces is solved to find dynamics of contact evaporation. It is shown theoretically and confirmed experimentally that in the range of high current the force of metallic vapour pressure at arcing in vacuum is comparable with magnetic repulsion force and should he taken into consideration. Two mechanisms of vapour pressure formation and evolution are discussed, which occur due to explosion of micro-asperities at contact touch or due to arcing after bridge rupture at contact bouncing.