The ins and outs of vacuum circuit breakers

It has been known for some 40 years that one of the most effective ways of interrupting an a.c. circuit is to do so by means of contacts in vacuum. Unlike all other interrupters there is no gas in the arc, only metal vapour which condenses very rapidly as the current falls to zero, giving a most predictable performance and a very fast rise of electric strength between opening contacts. During the last decade, high-power interrupters have been developed, and vacuum circuit breakers are commercially available. Their advantages are becoming increasingly apparent over a widening application