One of the basic role of switchgear is protection, which is interruption of short-circuit and overload fault currents while maintaining service to unaffected circuits.
Switchgear also provides isolation of circuits from power supplies.
Switchgear is also used to enhance system availability by allowing more than one source to feed a load.
Circuit breakers with vacuum interrupters have minimal arcing characteristics (as there is nothing to ionize other than the contact material), so the arc quenches when it is stretched by a small amount (<2–8 mm). Near zero current the arc is not hot enough to maintain a plasma, and current ceases; the gap can then withstand the rise of voltage. Vacuum circuit breakers are frequently used in modern medium-voltage switchgear to 40,500 volts. Unlike the other types, they are inherently unsuitable for interrupting DC faults
Apr 4th, 2015
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