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04.06.2014
A circuit breaker is an automatically operated electrical switch designed to protect an electrical circuit from damage caused by overload or short circuit.
An early form of circuit breaker was described by Thomas Alva Edison in an 1879 patent application, although his commercial power distribution system used fuses.[2] Its purpose was to protect lighting circuit wiring from accidental short-circuits and overloads. All 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.
The circuit breaker must detect a fault condition; in low-voltage circuit breakers this is usually done within the breaker enclosure. Once 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 (opening) the circuit.
Zero point quenching (Contacts open at the zero current time crossing of the AC waveform, effectively breaking no load current at the time of opening. Finally, once the fault condition has been cleared, the contacts must again be closed to restore power to the interrupted circuit. Gas (usually sulfur hexafluoride) circuit breakers sometimes stretch the arc using a magnetic field, and then rely upon the dielectric strength of the sulfur hexafluoride (SF6) to quench the stretched arc. Air circuit breakers may use compressed air to 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 after the mechanism has been tripped, depending upon age and construction of the device.
Circuit breakers are rated both by the normal current that they are expected to carry, and the maximum short-circuit current that they can safely interrupt. Under short-circuit conditions, a current many times greater than normal can exist (see maximum prospective short circuit current). In air-insulated and miniature breakers an arc chute structure consisting (often) of metal plates or ceramic ridges cools the arc, and magnetic blowout coils deflect the arc into the arc chute. 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. International Standard IEC 60898-1 and European Standard EN 60898-1 define the rated current In of a circuit breaker for low voltage distribution applications as the current that the breaker is designed to carry continuously (at an ambient air temperature of 30 °C). For the protection of loads that cause frequent short duration (approximately 400 ms to 2 s) current peaks in normal operation. For the protection of loads such as semiconductor devices or measuring circuits using current transformers. In the United States, Underwriters Laboratories (UL) certifies equipment ratings, called Series Ratings (or “integrated equipment ratings”), using a two-tier rating.
Many different classifications of circuit breakers can be made, based on their features such as voltage class, construction type, interrupting type, and structural features. Low voltage power circuit breakers can be mounted in multi-tiers in low-voltage switchboards or switchgear cabinets. The characteristics of Low Voltage circuit breakers are given by international standards such as IEC 947. Large low-voltage molded case and power circuit breakers may have electrical motor operators, allowing them to be tripped (opened) and closed under remote control.
Low-voltage circuit breakers are also made for direct-current (DC) applications, for example DC supplied for subway lines. Small circuit breakers are either installed directly in equipment, or are arranged in a breaker panel.
The 10 ampere DIN rail-mounted thermal-magnetic miniature circuit breaker is the most common style in modern domestic consumer units and commercial electrical distribution boards throughout Europe. Calibration screw - allows the manufacturer to precisely adjust the trip current of the device after assembly. Magnetic circuit breakers use a solenoid (electromagnet) whose pulling force increases with the current.
Thermal magnetic circuit breakers, which are the type found in most distribution boards, incorporate both techniques with the electromagnet responding instantaneously to large surges in current (short circuits) and the bimetallic strip responding to less extreme but longer-term over-current conditions. When supplying a branch circuit with more than one live conductor, each live conductor must be protected by a breaker pole. Two and four pole breakers are used when there is a need to disconnect the neutral wire, to be sure that no current can flow back through the neutral wire from other loads connected to the same network when people need to touch the wires for maintenance. Medium-voltage circuit breakers rated between 1 and 72 kV may be assembled into metal-enclosed switchgear line ups for indoor use, or may be individual components installed outdoors in a substation. Vacuum circuit breakers—With rated current up to 3000 A, these breakers interrupt the current by creating and extinguishing the arc in a vacuum container. Medium-voltage circuit breakers may be connected into the circuit by bolted connections to bus bars or wires, especially in outdoor switchyards.


Electrical power transmission networks are protected and controlled by high-voltage breakers.
Some of the manufacturers are ABB, GE (General Electric) , Tavrida Electric, Alstom, Mitsubishi Electric, Pennsylvania Breaker, Siemens, Toshiba, Koncar HVS, BHEL, CGL, Square D (Schneider Electric). Due to environmental and cost concerns over insulating oil spills, most new breakers use SF6 gas to quench the arc.
Circuit breakers can be classified as live tank, where the enclosure that contains the breaking mechanism is at line potential, or dead tank with the enclosure at earth potential. High-voltage circuit breakers used on transmission systems may be arranged to allow a single pole of a three-phase line to trip, instead of tripping all three poles; for some classes of faults this improves the system stability and availability.
A sulfur hexafluoride circuit breaker uses contacts surrounded by sulfur hexafluoride gas to quench the arc.
Residual-current device (RCD, formerly known as a residual current circuit breaker) — detects current imbalance, but does not provide over-current protection. Residual current breaker with over-current protection (RCBO) — combines the functions of an RCD and an MCB in one package. Earth leakage circuit breaker (ELCB) — This detects earth current directly rather than detecting imbalance.
Polyswitch (polyfuse) — A small device commonly described as an automatically resetting fuse rather than a circuit breaker.
Circuit Breaker — ist: eine Uberstromschutzeinrichtung eine Comicfigur von Marvel ein Pseudonym des Musikers Richie Hawtin eine Volatilitatsunterbrechung, ein Begriff aus dem Aktienwesen. Contact us with a description of the clipart you are searching for and we'll help you find it. Its basic function is to detect a fault condition and, by interrupting continuity, to immediately discontinue electrical flow. A modern miniature circuit breaker similar to the ones now in use was patented by Brown, Boveri & Cie in 1924. Circuit breakers for large currents or high voltages are usually arranged with pilot devices to sense a fault current and to operate the trip opening mechanism.
Small circuit breakers may be manually operated; larger units have solenoids to trip the mechanism, and electric motors to restore energy to the springs.
Contacts are made of copper or copper alloys, silver alloys, and other highly conductive materials. 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. Larger ratings will have metal plates or non-metallic arc chutes to divide and cool the arc. Vacuum circuit breakers are frequently used in modern medium-voltage switchgear to 35,000 volts.
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.
Larger circuit breakers such as those used in electrical power distribution may use vacuum, an inert gas such as sulphur hexafluoride or have contacts immersed in oil to suppress the arc. 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 to safely interrupt a fault. The commonly-available preferred values for the rated current are 6 A, 10 A, 13 A, 16 A, 20 A, 25 A, 32 A, 40 A, 50 A, 63 A, 80 A and 100 A[5] (Renard series, slightly modified to include current limit of British BS 1363 sockets). These circuit breakers are often installed in draw-out enclosures that allow removal and interchange without dismantling the switchgear. Special breakers are required for direct current because the arc does not have a natural tendency to go out on each half cycle as for alternating current. The thermal portion of the circuit breaker provides an "inverse time" response feature which provides faster or slower response for larger or smaller over currents respectively.
To ensure that all live conductors are interrupted when any pole trips, a "common trip" breaker must be used. Separate circuit breakers must never be used for disconnecting live and neutral, because if the neutral gets disconnected while the live conductor stays connected, a dangerous condition arises: the circuit will appear de-energized (appliances will not work), but wires will stay live and RCDs will not trip if someone touches the live wire (because RCDs need power to trip). Air-break circuit breakers replaced oil-filled units for indoor applications, but are now themselves being replaced by vacuum circuit breakers (up to about 35 kV).
These are generally applied for voltages up to about 35,000 V,[7] which corresponds roughly to the medium-voltage range of power systems. Trip characteristics are often fully adjustable including configurable trip thresholds and delays.
Medium-voltage circuit breakers in switchgear line-ups are often built with draw-out construction, allowing the breaker to be removed without disturbing the power circuit connections, using a motor-operated or hand-cranked mechanism to separate the breaker from its enclosure. They are most often used for transmission-level voltages and may be incorporated into compact gas-insulated switchgear.


In the United States and Canada, panel-mounted devices that combine ground (earth) fault detection and over-current protection are called Ground Fault Interrupter (GFI) breakers; a wall mounted outlet device or separately enclosed plug-in device providing ground fault detection and interruption only (no overload protection) is called a Ground Fault Circuit Interrupter (GFCI).
These are used on overhead power distribution systems, to prevent short duration faults from causing sustained outages.
Electrical accessories — Circuit breakers for over-current protection for household and similar installations. 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. 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.
Service life of the contacts is limited by the erosion of contact material due to arcing while interrupting the current.
Different circuit breakers use vacuum, air, insulating gas, or oil as the medium in which the arc forms.
This condition can create conductive ionized gases and molten or vaporized metal which can cause further continuation of the arc, or creation of additional short circuits, potentially resulting in the explosion of the circuit breaker and the equipment that it is installed in. In a worst-case scenario the breaker may successfully interrupt the fault, only to explode when reset.
The circuit breaker is labeled with the rated current in amperes, but without the unit symbol "A". This rating means that the meter pack has a 22 KAIC tenant breaker, feeding a 10 KAIC loadcenter with 10 KAIC branches, where KAIC stands for "Thousand Ampere Interrupting Capacity". A direct current circuit breaker will have blow-out coils which generate a magnetic field that rapidly stretches the arc when interrupting direct current. Most breakers are designed so they can still trip even if the lever is held or locked in the "on" position. These may either contain two or three tripping mechanisms within one case, or for small breakers, may externally tie the poles together via their operating handles.
Like the high voltage circuit breakers described below, these are also operated by current sensing protective relays operated through current transformers. Vacuum circuit breakers tend to have longer life expectancies between overhaul than do air circuit breakers. Usually electronically controlled, though some models are microprocessor controlled via an integral electronic trip unit. High-voltage breakers are nearly always solenoid-operated, with current sensing protective relays operated through current transformers. In cold climates, supplemental heating or de-rating of the circuit breakers may be required due to liquefaction of the SF6 gas. Circuit breakers 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. 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. Therefore, circuit breakers must incorporate various features to divide and extinguish the arc. As the current in the solenoid increases beyond the rating of the circuit breaker, the solenoid's pull releases the latch which then allows the contacts to open by spring action. Often used for main power distribution in large industrial plant, where the breakers are arranged in draw-out enclosures for ease of maintenance. Some types of magnetic breakers incorporate a hydraulic time delay feature using a viscous fluid. Three-pole common trip breakers are typically used to supply three-phase electric power to large motors or further distribution boards.
Medium-voltage circuit breakers nearly always use separate current sensors and protective relays, instead of relying on built-in thermal or magnetic overcurrent sensors. The delay permits brief current surges beyond normal running current for motor starting, energizing equipment, etc. Short circuit currents provide sufficient solenoid force to release the latch regardless of core position thus bypassing the delay feature. Follow Electrical Technology on Google+, Facebook , Twitter , Instagram , Pinterest & Linkedin to get the latest updates or subscribe Here to get latest Engineering Articles in your mailbox.
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