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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.
OPERATION
When a fault is detected, contacts within the circuit breaker must open to interrupt the circuit. Some mechanically-stored energy using something such as springs or compressed air contained within the breaker is used to separate the contacts, although some of the energy required may be obtained from the fault current itself. The circuit breaker contacts must carry the load current without excessive heating, and must also withstand the heat of the arc produced when interrupting the circuit. 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. Different techniques are used to extinguish the arc including:
• Lengthening of the arc
• Intensive cooling (in jet chambers)
• Division into partial arcs
• Zero point quenching
Finally, once the fault condition has been cleared, the contacts must again be closed to restore power to the interrupted circuit.
CLASSIFICATION OF CIRCUIT BREAKER
1. Oil circuit breaker which employ some insulating oil.eg. transformer oil for extinction
2. Air blast circuit breaker in which hogh pressure air blast is used for extinguishing the arc.
3. Sulphur hexa fluoride circuit breaker in which SF6 gas is used for arc extinction.
4. Vacuum circuit breaker in which vacuum is used for arc extinction.