What is circuit breaker ?
A circuit breaker is an automatically-operated electrical switch designed to protect an electrical circuit from damage caused by overload or shortcircuit.
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 breaker 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.
Circuit breakers are usually able to terminate all current very quickly : typically the arc is extinguished between 30ms and 150ms after the mechanism has been tripped, depending up on the construction of the device.
Rated current.
International standard IEC 60898-1 and European standard EN 60898-1 define the rated current of the circuit breaker for household applications as the current that the breaker is designed to carry continuously (at an ambient temperature of 30°C).
The commonly-available preferred values for the rated current are 6, 10, 13, 16, 20, 25, 32, 40, 50, 63, 80 and 100 A.
Short circuit capacity.
It is the maximum power that can be interrupted with out CB failure or damage.
Methods of arc interruption.
Since switching almost gives rise to arcing, extinguishing such arcs assumes vital importance to prolong contact life. The following methods are employed :
· Lengthening of the arc till it extinguishes.
· Cooling the arc till it extinguishes.
· Division into partial arcs.
· Connecting capacitors in parallel with contacts in DC circuits.
· Zero point quenching.
· Use of vacuum.
· Use of air.
· Use of oil.
· Use of SF6.
Types of circuit breakers.
· Magnetic CB
· Thermal CB
· Thermo-magnetic CB
· High voltage CB
