The characteristic features of recovery of the breakdown strength of vacuum switching devices after interruption of high currents

The relevant effects determining the recovery period are discussed. Metal vapor and residual charge at early times after current extinction reduce the breakdown strength. Metal droplets play only a secondary role obviously. The drawing of liquid protrusion out of the molten contact surfaces will be a mechanism in case of high field strength at the contact surfaces. The knowledge about the breakdown processes has to be improved, especially concerning the effect of delayed breakdowns.