A breaker which used vacuum as an arc extinction medium is called a vacuum circuit breaker. In this circuit breaker, the fixed and moving contact is enclosed in a permanently sealed vacuum interrupter. The arc is extinct as the contacts are separated in high vacuum. It is mainly used for medium voltage ranging from 11 KV to 33 KV.
When an arc is opened by moving apart the contacts in a vacuum, an interruption occurs at the first current zero. With the arc interruption, their dielectric strength increases up to a rate of thousands time as compared to other breakers.The above two properties make the breakers more efficient, less bulky and cheaper in cost. Their service life is also much greater than any other circuit breaker, and almost no maintenance are required.
1. The arc is extinguished in a sealed container, and the arc and hot gas are not exposed. As an independent component, the arc extinguishing chamber is easy to install and debug.
2. The contact clearance is very small, usually about 10mm, with small closing power, simple mechanism and long service life.
3. The arc extinguishing time is short, the arc voltage is low, the arc energy is small, the contact loss is small, and the breaking times are many.
Strictly control the contact travel.The stroke of vacuum circuit breaker is relatively short. Generally, the contact stroke of vacuum circuit breaker with rated voltage of 10 ~ 15kV is only 8 ~ 12mm, and the contact over travel is only 2 ~ 3mm. If the contact stroke increases too much, excessive stress will be generated on the bellows after the circuit breaker is closed, causing damage to the bellows and destroying the vacuum in the sealed shell of the circuit breaker. Do not mistakenly think that a large opening distance is beneficial to arc extinguishing, and arbitrarily increase the contact travel of the vacuum circuit breaker.