Vacuum Breaker for High DC Current: Experimental Performances and Operational Limits

This paper presents a new method to assess the performances of vacuum circuit breakers (VCBs) for high DC based on the measurement of the energy dissipated in the contacts before the opening of the breaker. This energy is given by the product of the closed-contact resistance times the specific energy (I ² t) flowing through the breaker. The results of an extensive experimental campaign on VCB prototypes, customized for special applications in the field of thermonuclear fusion, are reported in this paper, showing that, whenever the energy dissipated before the opening exceeds a threshold, the probability of VCB restrike increases. It is also demonstrated that vacuum tubes need initial training at low current prior to the operation at full performance.