Heat Transfer of Electrical Contact in Vacuum Interrupter: A Simulation Study

The heat transfer, in solid to liquid to vapor phase-transitions of the copper contacts in the initial breaking stage of vacuum interrupter, were empirically approximated, mathematically modeled, theoretically analyzed in classic hydrodynamics and simulated by numerically solving the analytically derived equations.The influence of Joule heating on the physical events, including the melting of solid contact, formation/evolution/rupture of liquid Cu-bridge, and diffusion of Cu-vapor, was investigated.The simulated results show that the hottest spot locates at the waist of liquid-Cu bridge, at which the cylindrical column rapidly shrinks into a dumbbell and ruptures, accompanied by spontaneously evaporation, diffusion and spreading of the Cu-vapor.Before the cathode spot forms, the Cu-vapor density reaches 1.091×10²⁵ m^-3 at the center of the micro-spots, decreasing rapidly because of diffusion between the electrodes.In addition, an increase of the load current significantly shortens the rupture time.