A breaker is normally used to break a circuit. while breaking the circuit, the contact terminals will be separated. At the time of separation an air gap is formed in between the terminals.
Due to existing current flow the air in the gap is ionised and results in the arc. various mediums are used to quench this arc in respective CB’s. but in VCB the medium is vacuum gas. since the air in the CB is having vacuum pressure the arc formation is interrupted. VCB’s can be used upto 11kv.