High current interruption in vacuum circuit breakers

A great number of interruption experiments were made in a vacuum chamber with the contact materials Cu, CuCr (50/50) and AgWC. The currents to be interrupted varied from 2.5 to 32 kA. The rate of change of current and recovery voltage were kept at a fixed value immediately after current zero. Many reignitions of the dielectric type were observed but only a few of the thermal type. No evidence of strong anode spot melting was found. At 5 to 10 /spl mu/s after post arc current, a "second" post arc current also appeared