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For other uses, see Circuit breaker (disambiguation). Circuit breaker switchgear A 2 pole miniature circuit breaker
Four 1 pole circuit breakersA circuit electrical switchboard manufacturer breaker is an automatically-operated electrical switch designed to protect an electrical electrical switchboard manufacturer circuit from damage caused by overload or short circuit. electrical switchboards manufacturer Its basic function is to detect a fault condition electrical switchboards and, by interrupting breakers electrical switchboard manufacturer continuity, to immediately discontinue electrical flow. electrical switchboard manufacturer Unlike a fuse, which operates once and electrical switchboard manufacturer then has to be replaced, a circuit breaker can be reset (either manually or electrical switchboard manufacturer automatically) to resume normal electrical switchboard manufacturer breakers operation. Circuit breakers are made electrical switchboard manufacturer in varying sizes, from electrical switchboard manufacturer small devices that protect an individual household appliance electrical switchboard manufacturer up to large switchgear electrical switchboard manufacturer designed to protect high voltage electrical switchboard manufacturer circuits feeding an breakers entire city.
Contents electrical [hide]* 1 Origins * 2 Operation * 3 Arc interruption * 4 Short circuit breakers current * 5 Standard current ratings * 6 Types of circuit breake o 6.1 Low voltage circuit breakers o 6.2 Magnetic circuit breaker o 6.3 electrical electrical switchboard manufacturer Thermal magnetic circuit breaker o 6.4 Common trip breakers o 6.5 Medium-voltage circuit breakers o 6.6 High-voltage circuit breakers electrical switchboard manufacturer o 6.7 Sulfur hexafluoride (SF6) high-voltage circuit-breakers electrical s * 7 Other breakers electrical switchboard manufacturer * 8 See also * 9 References
* 10 External breakers links[edit] OriginsAn early form of circuit breaker was electrical switchboard manufacturer described by Thomas Edison in an 1879 patent application, electrical switchboard manufacturer although his commercial power electrical switchboard manufacturer distribution system electrical switchboard manufacturer used fuses.[1] Its purpose was to protect lighting electrical switchboard manufacturer circuit wiring from breakers accidental short-circuits and overloads.
[edit] OperationAll circuit breakers electrical switchboard manufacturer have common electrical switchboard manufacturer features in their operation, although details vary electrical switchboard manufacturer substantially depending on the voltage class, current rating and type of the circuit breaker.The circuit breaker must breakers detect a fault electrical switchboard manufacturer condition; in low-voltage circuit breakers breakers this is usually done within the breaker electrical switchboard manufacturer enclosure. Circuit electrical> breakers for large currents electrical switchboard manufacturer or high voltages are usually arranged with pilot devices to sense a fault current and to operate the trip opening mechanism. The trip electrical switchboard manufacturer solenoid that releases electrical switchboard manufacturer the latch is usually energized by a separate battery, although electrical some high-voltage circuit breakers are self-contained with current transformers, protection relays, and an internal breakers electrical switchboard manufacturer control power source.Once a fault is electrical detected, contacts within the circuit breaker must open to interrupt the electrical circuit; some mechanically-stored energy (using something such as springs or compressed air) contained within electrical breaker is used to separate the contacts, although some of the energy required breakers may be obtained from the fault current itself. electrical Small circuit breakers may be manually operated; larger units have solenoids to trip the mechanism, and electrical electric motors to restore energy to the springs.
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The circuit breaker contacts must carry the load current without electrical switchboard manufacturer excessive heating, electrical and must also withstand the heat of the arc produced when interrupting the circuit. Contacts are made of copper or copper alloys, silver alloys, breakers and other materials. Service life of the contacts is limited by the erosion due to interrupting the arc. Miniature and molded Panel Boards case circuit breakers are usually electrical switchboard manufacturer discarded electrical when the contacts are worn, but power circuit breakers and high-voltage circuit breakers have replaceable contacts.electrical When a current is breakers 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 electrical switchboard manufacturer withstand the voltage in the circuit. Different circuit breakers use vacuum, air, insulating gas, or oil as electrical 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(Contacts open at the zero current time crossing of the AC waveform, effectively breaking no electrical switchboard manufacturer load electrical current at the time of opening. The zero crossing occures at twice the line frequency i.e. 100 times per second for electrical 50Hz ac and 120 times per second for 60Hz ac )
* Connecting capacitors in parallel with contacts in Panel Boards DC circuits electrical switchboard manufacturer Finally, once the fault condition has been cleared, electrical the contacts must again be closed to restore power to the electrical switchboards manufacturers interrupted circuit.
[edit] Arc interruptionMiniature low-voltagecircuit breakers use air alone to extinguish the arc. Panel Boards Larger ratings will have metal plates or non-metallic arc chutes to electrical switchboard manufacturer divide and cool the arc. Magnetic blowout coils cpe switchboards deflect the arc into the arc chute.In larger ratings, oil circuit breakers rely upon vaporization of some of the oil to blast a jet of oil through the arc.[2]Gas (usually sulfur hexafluoride) circuit breakers electrical switchboard manufacturer sometimes stretch the arc using a magnetic field, electrical switchboard manufacturer and then rely upon the dielectric strength of the sulfur hexafluoride (SF6) to quench the stretched arc.Vacuum circuit breakers have minimal arcing (as there is nothing to ionize other than the contact material), electrical switchboard manufacturer so the arc quenches when it is stretched a very small amount