Circuit Breakers ( ACB and VCB)

A circuit breaker is an automatically operated electrical switch designed to protect an electrical circuit from damage caused by overload or short circuit. Its basic function is to detect a fault condition and, by interrupting continuity, to immediately discontinue electrical flow. Unlike a fuse, which operates once and then has to be replaced, a circuit breaker can be reset (either manually or automatically) to resume normal operation. Circuit breakers are made in varying sizes, from small devices that protect an individual household appliance up to large switchgear designed to protect high voltage circuits feeding an entire city.

When a current is interrupted, an arc is generated. This arc must be contained, cooled, and extinguished in a controlled way, so that the gap between the contacts can again withstand the voltage in the circuit. Different circuit breakers use vacuum, air, insulating gas, or oil as the medium in which the arc forms.

 

Specifically we will look at the air circuit breaker (ACB) and vacuum circuit breaker (VCB). The selection process of the kind of circuit breaker that is required depends on the levels of current in the circuit. Why? Its simply because the higher the current, the farther the arcing distance.

ACBs may use compressed air to blow out the arc, or alternatively, the contacts are rapidly swung into a small sealed chamber, the escaping of the displaced air thus blowing out the arc however, VCBs have minimal arcing (as there is nothing to ionize other than the contact material), so the arc quenches when it is stretched a very small amount (<2–3 mm). VCBs are frequently used in modern medium-voltage switchgear to 35,000 volts.

VCBs are used to protect medium and high voltage circuits from dangerous electrical situations. Two electrical contacts are enclosed in vacuum. One is fixed, the other is movable. When it detects danger, the movable contact pulls away from the fixed contact thus interrupting the current. Arcing suppressed due to the contacts being in vacuum. This ensures the circuit remains open. As long as it is open, it will not be energized.