Breaker.docx

1、BreakerCircuit breakerFrom Wikipedia, the free encyclopediaFor other uses, seeCircuit breaker (disambiguation).It has been suggested thatOil Circuit Breakerbemergedinto this article. (Discuss)Proposed since April 2016.Part of a series onElectrical wiringRegulation of electrical installations BS 7671

2、 IEC 60364 Canadian Electrical Code (CEC) National Electrical Code (NEC)Wiring methods Armored cable Cable tray Electrical conduit Knob-and-tube wiring Multiway switching Thermoplastic-sheathed cableCircuit breakersand devices AFCI ELCB GFCI / RCD Receptacles / Sockets Sulfur Hexafluoride SwitchElec

3、trical distribution Bus bar Distribution board Switchgear Switchboard TransformerWiring by region or country Hong Kong North America United Kingdom v t eCircuit BreakerElectronic symbolAn air circuit breaker for low-voltage (less than 1,000 volt) power distribution switchgearA two-pole miniature cir

4、cuit breakerFour one-pole miniature circuit breakersMolded-case circuit breakerAcircuit breakeris an automatically operatedelectricalswitchdesigned to protect anelectrical circuitfrom damage caused byovercurrent or overloadorshort circuit. Its basic function is to interrupt current flow afterprotect

5、ive relaysdetect afault. Unlike afuse, which operates once and then must be replaced, a circuit breaker can be reset (either manually or automatically) to resume normal operation. Circuit breakers are made in varying sizes, from small devices that protect an individual household appliance up to larg

6、eswitchgeardesigned to protecthigh voltagecircuits feeding an entire city. The generic function of a circuit breaker,RCDor afuse, as an automatic means of removing power from a faulty system is often abbreviated to ADS (Automatic Disconnection of Supply).Contentshide 1Origins 2Operation 3Arc interru

7、ption 4Short-circuit 5Standard current ratings 6Types of circuit breakerso 6.1Low-voltage circuit breakerso 6.2Magnetic circuit breakerso 6.3Thermal magnetic circuit breakerso 6.4Common trip breakerso 6.5Medium-voltage circuit breakerso 6.6High-voltage circuit breakerso 6.7Sulfur hexafluoride (SF6)

8、high-voltage circuit breakerso 6.8Disconnecting circuit breaker (DCB)o 6.9Carbon dioxide (CO2) high-voltage circuit breakers 7Other breakers 8See also 9References 10External linksOriginseditAn early form of circuit breaker was described byThomas Edisonin an 1879 patent application, although his comm

9、ercial power distribution system usedfuses.1Its purpose was to protect lighting circuit wiring from accidental short circuits and overloads. A modern miniature circuit breaker similar to the ones now in use was patented byBrown, Boveri & Ciein 1924. Hugo Stotz, an engineer who had sold his company t

10、oBBC, was credited as the inventor on DRP (Deutsches Reichspatent) 458392.2Stotzs invention was the forerunner of the modern thermal-magnetic breaker commonly used in household load centers to this day. Interconnection of multiple generator sources into an electrical grid required development of cir

11、cuit breakers with increasing voltage ratings and increased ability to safely interrupt the increasing short circuit currents produced by networks. Simple air-break manual switches produced hazardous arcs when interrupting high currents; these gave way to oil-enclosed contacts, and various forms usi

12、ng directed flow of pressurized air, or of pressurized oil, to cool and interrupt the arc. By 1935, the specially constructed circuit breakers used at theBoulder Damproject use eight series breaks and pressurized oil flow to interrupt faults of up to 2,500 MVA, in three cycles of the AC power freque

13、ncy.3OperationeditAll circuit breaker systems have common features in their operation. Although details vary substantially depending on the voltage class, current rating and type of the circuit breaker.The circuit breaker must detect a fault condition; inlow voltagecircuit breakers this is usually d

14、one within the breaker enclosure. Circuit breakers for large currents or high voltages are usually arranged withprotective relaypilot devices to sense a fault condition and to operate the trip opening mechanism. The tripsolenoidthat releases the latch is usually energized by a separatebattery, altho

15、ugh some high-voltage circuit breakers are self-contained withcurrent transformers,protective relays, and an internal control power source.Once a fault is detected, the circuit breaker contacts must open to interrupt the circuit; some mechanically stored energy (using something such as springs or co

16、mpressed 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. Small circuit breakers may be manually operated, larger units havesolenoidsto trip the mechanism, andelectric motorsto restore energy to th

17、e springs.The circuit breaker contacts must carry the load current without excessive heating, and must also withstand the heat of the arc produced when interrupting (opening) the circuit. Contacts are made of copper or copper alloys, silver alloys and other highly conductive materials. Service life

18、of the contacts is limited by the erosion of contact material due to arcing while interrupting the current. Miniature and molded-case circuit breakers are usually discarded when the contacts have worn, but power circuit breakers and high-voltage circuit breakers have replaceable contacts.When a curr

19、ent is interrupted, anarcis 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 usevacuum, air,insulating gas, oroilas the medium the arc forms in. Differen

20、t techniques are used to extinguish the arc including: Lengthening or deflecting the arc Intensive cooling (in jet chambers) Division into partial arcs Zero point quenching (contacts open at the zero current time crossing of theACwaveform, effectively breaking no load current at the time of opening.

21、 The zero crossing occurs at twice the line frequency; i.e., 100 times per second for 50Hz and 120 times per second for 60Hz AC.) Connectingcapacitorsin parallel with contacts inDCcircuits.Finally, once the fault condition has been cleared, the contacts must again be closed to restore power to the i

22、nterrupted circuit.Arc interruptioneditLow-voltage miniature circuit breaker (MCB) uses air alone to extinguish the arc. These circuit breakers contain so-called arc chutes, a stack of mutually insulated parallel metal plates which divide and cool the arc. By splitting the arc into smaller arcs the

23、arc is cooled down while the arc voltage is increased and serves as an additional impedance which limits the current through the circuit breaker. The current-carrying parts near the contacts provide easy deflection of the arc into the arc chutes by a magnetic force of a current path, althoughmagneti

24、c blowoutcoils orpermanent magnetscould also deflect the arc into the arc chute (used on circuit breakers for higher ratings). The number of plates in the arc chute is dependent on the short-circuit rating and nominal voltage of the circuit breaker.In larger ratings, oil circuit breakers rely upon v

25、aporization of some of the oil to blast a jet of oil through the arc.4Gas (usuallysulfur hexafluoride) circuit breakers sometimes stretch the arc using a magnetic field, and then rely upon thedielectric strengthof the sulfur hexafluoride (SF6) to quench the stretched arc.Vacuumcircuit breakers have

26、minimal arcing (as there is nothing to ionize other than the contact material), so the arc quenches when it is stretched a very small amount (less than 23mm (0.0790.118in). Vacuum circuit breakers are frequently used in modern medium-voltage switchgear to 38,000 volts.Air circuit breakers may usecom

27、pressed airto blow out the arc, or alternatively, the contacts are rapidly swung into a small sealed chamber, the escaping of the displaced air thus blowing out the arc.Circuit breakers are usually able to terminate all current very quickly: typically the arc is extinguished between 30 ms and 150 ms

28、 after the mechanism has been tripped, depending upon age and construction of the device. The maximum current value and let-through energy determine the quality of the circuit breakers.Short-circuiteditCircuit breakers are rated both by the normal current that they are expected to carry, and the max

29、imum short-circuit current that they can safely interrupt. This latter figure is theampere interrupting capacity(AIC) of the breaker.Under short-circuit conditions, the calculated maximumprospective short circuit currentmay be many times the normal, rated current of the circuit. When electrical cont

30、acts open to interrupt a large current, there is a tendency for anarcto form between the opened contacts, which would allow the current to continue. This condition can create conductive ionized gases and molten or vaporized metal, which can cause further continuation of the arc, or creation of addit

31、ional short circuits, potentially resulting in the explosion of the circuit breaker and the equipment that it is installed in. Therefore, circuit breakers must incorporate various features to divide and extinguish the arc.The maximum short-circuit current that a breaker can interrupt is determined b

32、y testing. Application of a breaker in a circuit with a prospective short-circuit current higher than the breakers interrupting capacity rating may result in failure of the breaker to safely interrupt a fault. In a worst-case scenario the breaker may successfully interrupt the fault, only to explode when reset.Typical domestic panel circuit br