Vacuum
circuit breaker
When two current carrying contacts are separated in a vacuum module, an arc
is drawn between them. An intensely hot spot or sparks are created at the instant
of contact separation from which metal vapor shoot off, constituting plasma.
The amount of vapour in the plasma is proportional to the rate of vapour emission
from the electrodes, hence to the arc current. With alternating current arc,
the current decreases during a portion of wave and tends to zero. Thereby the
rate of vapour emission tends to zero and the amount of plasma tends to zero.
Soon after natural current zero, the remaining metal vapour condenses and the
dielectric strength builds up rapidly, and restriking of arc is prevented.
This principle is used in vauum circuit breakers
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