Application of vacuum circuit-breaker to clear faults with delayed current zeros

In medium-voltage systems short-circuit currents with delayed zero crossings can occur either in the proximity of a concentrated generation or when switching off large high-voltage motors, or both. For two typical system configurations it is shown theoretically that vacuum circuit-breakers are well suited to clear under these conditions, provided they can withstand the high peak currents associated with such faults and their contact configuration can withstand prolonged arcing. The theoretical considerations are backed by tests. However, it will be necessary to investigate the conditions of each application to determine the actual stress upon the circuit-breaker