At the moment of vacuum circuit breaker breaking, due to the existence of the capacitance between the two contacts, the insulation breakdown between the contacts causes a vacuum arc.

Due to the shape and structure of the contact, the vacuum arc column rapidly diffuses to the vacuum area outside the arc column.

When the interrupted current is close to zero, the temperature and pressure of the arc between the contacts drop sharply, making the arc unable to continue to be maintained and extinguished. Within a few μs after the arc is extinguished, the withstand voltage level of the vacuum gap between the two contacts quickly recovers.

At the same time, the contacts have reached a certain distance, which can withstand a high recovery voltage.

Therefore, after the general current crosses zero, the arc will not reignite and be broken. This is the principle of its arc extinguishing.

Third, the principle of arc extinguishing of high-voltage drop-out fuse

In the occasion of high voltage and high current, the switch usually uses more complicated methods and structures to extinguish the arc, but the high-voltage drop-out fuse only needs a very simple hose to achieve the arc extinguishment smoothly and well. The main reasons are: first, The high voltage drop fuse current is not very large. The arc generated is not very large. Second, air is used to extinguish the arc. This is the same as the arc extinguishing principle of the MCB. It’s just a different structure.