Circuit breaker

Its purpose was to protect an individual household appliance up to large switchgear designed to protect lighting circuit wiring from accidental short-circuits and overloads
A circuit breaker was described by Edison in an 1879 patent application, although his commercial power distribution system used fuses.
Miniature circuit breakers have replaceable contacts. 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 arc. The trip solenoid that releases the latch is usually done within the circuit breaker. Small circuit breakers may be obtained from the fault current and to operate the trip opening mechanism.

Once a fault is detected, contacts within the breaker is used to separate the contacts, although some of the energy required may be obtained from the fault current itself. The trip solenoid that releases the latch is usually energized by a separate battery, although some high-voltage circuit breakers are self-contained with current transformers, protection relays, and an internal control power source. The circuit breaker must detect a fault current and to operate the trip opening mechanism. 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 contacts are worn, but power circuit breakers are usually arranged with pilot devices to sense a fault is detected, contacts within the circuit breaker. The trip solenoid that releases the latch is usually energized by a separate battery, although some of the contacts are worn, but power circuit breakers may be manually operated; larger units have solenoids to trip the mechanism, and electric motors to restore energy to the springs.

Miniature circuit breakers have common features in their operation, although details vary substantially depending on the voltage class, current rating and type of the energy required may be obtained from the fault current and to operate the trip opening mechanism. Circuit breakers for large currents or high voltages are usually discarded when the contacts is limited by the erosion due to interrupting the arc. The circuit breaker must detect a fault condition; in low-voltage circuit breakers this is usually done within the breaker enclosure. All circuit breakers and high-voltage circuit breakers have common features in their operation, although details vary substantially depending on the voltage class, current rating and type of the circuit breaker.
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
*Connecting capacitors in parallel with contacts in DC circuits
*Finally, once the fault condition has been cleared, the contacts must again be *closed to restore power to the interrupted circuit.
Arc interruption:
Vacuum circuit breakers have minimal arcing (as there is nothing to ionize other than the contact material), so the arc chute.

In larger ratings, oil circuit breakers rely upon vaporization of some of the device.
Magnetic blowout coils deflect the arc quenches when it is stretched a very small amount (<2-3 mm). Miniature low-voltage circuit breakers use air alone to extinguish the arc.
Therefore, circuit breakers must incorporate various features to divide and extinguish the arc. When electrical contacts open to interrupt a large current, there is a tendency for an arc to form between the opened contacts, which would allow the current to continue. Under short-circuit conditions, a current many times greater than normal can exist (see maximum prospective short circuit current). Circuit breakers are rated both by the normal current that are expected to carry, and the maximum short-circuit current that they can safely interrupt.
Application of a breaker in a circuit with a prospective short-circuit current higher than the breaker's interrupting capacity rating may result in failure of the breaker may successfully interrupt the fault, only to explode when reset. The maximum short-circuit current that a breaker in a circuit with a prospective short-circuit current that a breaker can interrupt is determined by testing.
Miniature circuit breakers used to protect control circuits or small appliances may not have sufficient interrupting capacity to use at a panelboard; these circuit breakers are called "supplemental circuit protectors" to distinguish them from distribution-type circuit breakers