What 5p20 1e323r

1.

WHAT IS MEAN BY 5P20? The difference is the purpose for which the CT core is used. 5p20 means that there will be error of 5% when the primary current is 20 times. For example, if the ct is 1000/1 , then in case of fault, when the fault current is 20000 A, then the secondary current is 20 A +/- 5%. This means that the ct knee point is very high, and the CT is linear over a wide range of current. Further, when there is fault, the accuracy is not that important. A fault current of 20 KA or 21 KA may not matter much. What is important is the CT should not saturate so that the protection acts. In metering core, the opposite is true. When normal running, we want accuracy so that billing can be done. However, since accurate meters are very sensitive to over currents, we do not want that a high fault current to through the meter, otherwise it will get damaged. inaccuracy for a fraction of second will not really matter. We want the CT to saturate at high current so that the meter is safe. That is the reason why Vk only is mentioned in protection class.

2.

WHAT IS CT BURDEN IN ELECTRICAL ENGINEERING? CT (current transformer) Burden is the maximum load that the CT secondary can drive (e.g. meters or protection relays) Why do you care about burden when ordering current transformers? The burden is the termination impedance of the measuring instrument. The measuring instrument can be an analog or digital energy meter, a data logger or a recorder. All instruments that use a current transformer to measure line current must terminate the CT with a resistance (impedance in same case which means there is some inductance involved). A CT supplier should be given the burden when ordering. Technically, the total burden for a CT is the internal winding resistance, the connecting lead resistance and the measuring instrument input resistance. Some Ct's are installed a long distance from the measuring instrument and the connecting leads can have a resistance as much as 0.002 ohms per foot (both ways because the current makes a complete round trip). This resistance will cause an error if not taken into .

3.

INSTRUMENT SECURITY FACTOR OR ISF OF CURRENT TRANSFORMER Instrument Security Factor is the ratio of Instrument Limit Primary Current to the rated Primary Current. Instrument Limit Current of a meteringCurrent Transformer is the maximum value of primary current beyond whichCurrent Transformer core becomes saturated. Instrument Security Factor of CT is the significant factor for choosing the metering Instruments which to be connected to the secondary of the CT. Security or Safety of the measuring unit is better, if ISF is low. If we go through the example below it would be clear to us. Suppose one Current Transformer has rating 100/1A and ISF is 1.5 and another Current Transformer has same rating with ISF 2. That means, in first CT, the metering core would be saturated at 1.5X100 or 150 A, whereas is second CT, core will be saturated at 2X100 or 200A. That means whatever may be the primary current of both CTs, secondary current will not increase further after 150 & 200A of primary current of the CTs respectively. Hence maximum secondary current of the CTs would be 1.5 & 2.0 A. As the maximum electric current can flow through the instrument connected to the first CT is 1.5A which is less than the maximum value of electric current can flow through the instrument connected to the second CT i.e. 2A. Hence security or safety of the instruments of first CT is better than later. Another significance of ISF is during huge electrical fault, the short circuit current, flows through primary of the CT does not affect destructively, the measuring instrument attached to it as because, the secondary current of the CT will not rise above the value of rated secondary current multiplied by ISF Accuracy imit Factor or ALF of Current Transformer For protection current transformer, the ratio of accuracy limit primary current to the rated primary current. First we will explain, what is rated accuracy limit primary current? Broadly, this is the maximum value of primary current, beyond which core of the protection CT or simply protection core of of a CT starts saturated. The value of rated accuracy limit primary current is always many times more than the value of instrument limit primary current. Actually CT transforms the fault current of the electrical power system for operation of the protection relays

connected to the secondary of that CT. If the core of the CT becomes saturated at lower value of primary current, as in the case of metering CT, the system fault will not reflect properly to the secondary, which may cause, the relays remain inoperative even the fault level of the system is large enough. That is why the core of the protection CT is made such a way that saturation level of that core must be high enough. But still there is a limit as because, it is impossible to make one magnetic core with infinitely high saturation level and secondly most important reason is that although the protection care should have high saturation level but that must be limited up to certain level otherwise total transformation of primary current during huge fault may badly damage the protection relays. So it is clear from above explanation, rated accuracy limit primary current, should not be so less, that it will not at all help the relays to be operated on the other hand this value must not be so high that it can damage the relays. So, Accuracy Limit Factor or ALF should not have the value nearer to unit and at the same time it should not be as high as 100. The standard values of ALF as per IS - 2705 are 5, 10, 15, 20 & 30. 4.

KNEE POINT VOLTAGE OF CURRENT TRANSFORMER This is the significance of saturation level of a CT core mainly used for protection purposes. The sinusoidal voltage of rated frequency applied to the secondary terminals of Current Transformer, with other winding being open circuited, which when increased by 10% cause the exiting current to increase 50%. The CT core is made of CRGO steel. It has its won saturation level. The EMF induced in the CT secondary windings is E2 = 4.44φfT2 Where, f is the system frequency, φ is the maximum magnetic flux in Wb. T2 is the number of turns of the secondary winding. The flux in the core, is produced by excitation current Ie. We have a non – liner relationship between excitation current and magnetizing flux. After certain value of excitation current, flux will not further increase so rapidly with increase in excitation current. this nonliner relation curve is also called B – H curve. Again from the equation above, it is found that, secondary voltage of a Current Transformer is directly

proportional to flux φ. Hence one typical curve can be drawn from this relation between secondary voltage and excitation current as shown below, It is clear from the curve that, Linear relation between V & Ie is maintained from point A & K. The point ′A′ is known as ′Ankle Point′ and point ′K′ is known as ′Knee Point′.

In Differential and Restricted Earth Fault (REF) protection scheme, accuracy class and ALF of the CT may not ensure the reliability of the operation. It is desired that, Differential and REF relays should not be operated when fault occurs outside the protected transformer. When any fault occurs outside the Differential Protection zone, the faulty current flows through the CTs of both sides of Electrical Power Transformer. The both LV & HV CTs have magnetizing characteristics. Beyond the Knee Point, for slight increase in secondary emf a large increasing in excitation current is required. So after this knee point excitation current of both Current Transformers will be extremely high, which may cause mismatch between secondary current of LV & HV Current Transformers. This phenomena may cause unexpected tripping of Power Transformer. So the magnetizing characteristics of both LV & HV sides CTs, should be same that means they have same knee point voltage Vk as well as same excitation current Ie at Vk/2. It can be again said that, if both knee point voltage of current transformer and magnetizing characteristic of CTs of both sides of Power Transformer differ, there must be a mismatch in high excitation currents of the CTs during fault which ultimately causes the unbalancing between secondary current of both groups of CTs and transformer trips.

So for choosing CT for Differential Protection of Transformer, one should consider Current Transformer PS Class rather its convectional protection class. PS stands for protection Special which is defined by Knee Point voltage of current transformerVk and excitation current Ie at Vk/2. Why CT secondary should not be kept open The electrical

power system load current always

flows

through

current

transformer primary; irrespective of whether the Current Transformer is open circuited or connected to burden at its secondary.

If CT secondary is open circuited, all the primary current will behave as excitation current, which ultimately produce huge voltage. Every Current Transformer has its won Non – Linear magnetizing curve, because of which secondary open circuit voltage should be limited by saturation of the core. If one can measure the rms voltage across the secondary terminals, he or she will get the value which may not appear to be dangerous. As the CT primary current is sinusoidal in nature, it zero 100 times per second.(As frequency of the electric current is 50Hz). The rate of change of flux at every current zero is not limited by saturation and is high indeed. This develops extremely high peaks or pulses of voltage. This high peaks of voltage may not be measured by conventional voltmeter. But these high peaks of induced voltage may breakdown the CT insulation, and may case accident to personnel. The actual open – circuit voltage peak is difficult to measure accurately because of its very short peaks. That is why CT secondary should not be kept open.

The formula for calculating the knee point voltage of a PS Class CT is: Vkp > K * If (r) (Rct + Rb) where, Vkp = The minimum Knee Point Voltage of the CT K = Safety factor, generally taken as 2 If (r) = Maximum Anticipated fault current, as reflected on the CT Secondary side = Maximum anticipated primary fault current /CT Ratio Rct = Secondary Winding Resistance of the CT Rb = Two way lead burden of the wires from CT Secondary to the relay

CIRCUIT BREAKER A circuit breaker is an automatically operated electrical switch designed to protect anelectrical circuit from damage caused by overload or short circuit. Its basic function is to detect a fault condition and interrupt current flow. Unlike a fuse, 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 large switchgear designed to protecthigh voltage circuits feeding an entire city. For other uses, see Circuit breaker (disambiguation). Part of a series on Electrical wiring Regulation of Electrical Installations  BS 7671  IEC 60364  Canadian Electrical Code (CEC)  National Electrical Code (NEC)

Wiring Methods Cable tray  Electrical conduit  Knob and tube wiring 

Circuit Breakers and Devices AFCI ELCB  GFCI / RCD  Receptacles / Sockets  Sulfur Hexafluoride  

Electrical Distribution



 Bus bar Distribution board  Switchgear  Switchboard  Transformer

Wiring by Region or Country   

Hong Kong North America United Kingdom

Contents 

1 Origins



2 Operation



3 Arc interruption



4 Short-circuit current



5 Standard current ratings for Europe



6 Types of circuit breakers o

6.1 Low-voltage circuit breakers

o

6.2 Magnetic circuit breakers

o

6.3 Thermal magnetic circuit breakers

o

6.4 Common trip breakers

o

6.5 Medium-voltage circuit breakers

o

6.6 High-voltage circuit breakers

o

6.7 Sulfur hexafluoride (SF6) high-voltage circuit breakers

o

6.8 Hybrid Switchgear Modules

o

6.9 Disconnecting circuit breaker (DCB)

o

6.10 Carbon dioxide (CO2) high-voltage circuit breakers



7 Other breakers



8 See also



9 References



10 External links Origins[edit] An early form of circuit breaker was described by Thomas Edison in an 1879 patent application, although his commercial power distribution system used fuses.[1] Its 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 by Brown, Boveri & Ciein 1924. Hugo Stotz, an engineer who had sold his

company, to BBC, was credited as the inventor on DRP (Deutsches Reichspatent) 458329.[2] Stotz's 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 circuit 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 s, and various forms using 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 Dam project use eight series breaks and pressurized oil flow to interrupt faults of up to 2,500 MVA, in three cycles of the AC power frequency.[3] Operation[edit] 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. 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. The trip solenoid that releases the latch is usually energized by a separate battery, although some high-voltage circuit breakers are selfcontained with current transformers, protective relays and an internal control power source. Once a fault is detected, s 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 s, although some of the energy required may be obtained from the fault current itself. Small circuit breakers may be manually operated, larger units have solenoids to trip the mechanism, and electric motors to restore energy to the springs. The circuit breaker s must carry the load current without excessive heating, and must also withstand the heat of the arc produced when interrupting (opening) the circuit. s are made of copper or copper alloys, silver alloys and other highly conductive materials. Service life of the s is limited by the erosion of

material due to arcing while interrupting the current. Miniature circuit breaker (MCB) and molded-case circuit breaker (MCCB) are usually discarded when the s have worn, but power circuit breakers and high-voltage circuit breakers have replaceable s. 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 s can again withstand the voltage in the circuit. Different circuit breakers use vacuum, air, insulating gas or oil as the medium the arc forms in. Different techniques are used to extinguish the arc including: 

Lengthening / deflection of the arc



Intensive cooling (in jet chambers)



Division into partial arcs



Zero point quenching (s open at the zero current time crossing of the ACwaveform, effectively breaking no load current at the time of opening. The zero crossing occurs at twice the line frequency, i.e. 100 times per second for 50 Hz and 120 times per second for 60 Hz AC)



Connecting capacitors in parallel with s in DC circuits.

Finally, once the fault condition has been cleared, the s must again be closed to restore power to the interrupted circuit. Arc interruption[edit] Low-voltage MCB uses air alone to extinguish the arc. Larger ratings have metal plates or non-metallic arc chutes to divide and cool the arc. Magnetic blowout coils or permanent magnets 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.[4] 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. Vacuum circuit breakers have minimal arcing (as there is nothing to ionize other than the material), so the arc quenches when it is stretched a very small amount (<2–3 mm). Vacuum circuit breakers are frequently used in modern medium-voltage switchgear to 38,000 volts.

Air circuit breakers may use compressed air to blow out the arc, or alternatively, the s 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. Short-circuit current[edit] 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). When electrical s open to interrupt a large current, there is a tendency for an arc to form between the opened s, 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 additional 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. In air-insulated and miniature breakers an arc chute structure consisting (often) of metal plates or ceramic ridges cools the arc, andmagnetic blowout coils deflect the arc into the arc chute. Larger circuit breakers such as those used in electrical power distribution may use vacuum, an inert gas such as sulfur hexafluoride or have s immersed in oil to suppress the arc. The maximum short-circuit current that a breaker can interrupt is determined by testing. 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. In a worst-case scenario the breaker may successfully interrupt the fault, only to explode when reset. MCB used to protect control circuits or small appliances may not have sufficient interrupting capacity to use at a board; these circuit breakers are called "supplemental circuit protectors" to distinguish them from distribution-type circuit breakers.

Standard current ratings for Europe[edit] 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 maximum current that the breaker is designed to carry continuously (at an ambient air temperature of 30 °C). 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, 100 A,[5] and 125 A (Renard series, slightly modified to include current limit of British BS 1363 sockets). The circuit breaker is labeled with the rated current in amperes, but without the unit symbol "A". Instead, the ampere figure is preceded by a letter "B", "C" or "D", which indicates the instantaneous tripping current — that is, the minimum value of current that causes the circuit breaker to trip without intentional time delay (i.e., in less than 100 ms), expressed in of In: Type

Instantaneous tripping current

B

above 3 In up to and including 5 In

C

above 5 In up to and including 10 In

D

above 10 In up to and including 20 In

above 8 In up to and including 12 In K

For the protection of loads that cause frequent short duration (approximately 400 ms to 2 s) current peaks in normal operation. above 2 In up to and including 3 In for periods in the order of tens of seconds.

Z

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. For example, a 22/10 rating. 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.” Common meter pack ratings are 22/10, 42/10 and 100/10.[6] Types of circuit breakers[edit] Front of a 1250 A air circuit breaker manufactured by ABB. This low voltage power circuit breaker can be withdrawn from its housing for servicing. Trip characteristics are configurable via DIP switches on the front . 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 circuit breakers[edit] Low-voltage (less than 1,000 VAC) types are common in domestic, commercial and industrial application, and include: 

MCB (Miniature Circuit Breaker)—rated current not more than 100 A. Trip characteristics normally not adjustable. Thermal or thermal-magnetic operation. Breakers illustrated above are in this category.

There are three main types of MCBs: 1. Type B - trips between 3 and 5 times full load current; 2. Type C - trips between 5 and 10 times full load current; 3. Type D - trips between 10 and 20 times full load current. In the UK all MCBs must be selected in accordance with BS 7671. 

MCCB (Molded Case Circuit Breaker)—rated current up to 2,500 A. Thermal or thermal-magnetic operation. Trip current may be adjustable in larger ratings.



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. These circuit breakers are often installed in draw-out enclosures that allow removal and interchange without dismantling the switchgear. Large low-voltage molded case and power circuit breakers may have electric motor operators so they can trip (open) and close under remote control. These may form part of an automatic transfer switch system for standby power. Low-voltage circuit breakers are also made for direct-current (DC) applications, such as DC for subway lines. Direct current requires special breakers because the arc is

continuous—unlike an AC arc, which tends to go out on each half cycle. A direct current circuit breaker has blow-out coils that generate a magnetic field that rapidly stretches the arc. Small circuit breakers are either installed directly in equipment, or are arranged in a breaker .

Inside of a circuit breaker The 10 ampere DIN rail-mounted thermal-magnetic miniature circuit breaker is the most common style in modern domestic consumer units and commercial electricaldistribution boards throughout Europe. The design includes the following components: 1. Actuator lever - used to manually trip and reset the circuit breaker. Also indicates the status of the circuit breaker (On or Off/tripped). Most breakers are designed so they can still trip even if the lever is held or locked in the "on" position. This is sometimes referred to as "free trip" or "positive trip" operation. 2. Actuator mechanism - forces the s together or apart. 3. s - Allow current when touching and break the current when moved apart. 4. Terminals 5. Bimetallic strip. 6. Calibration screw - allows the manufacturer to precisely adjust the trip current of the device after assembly.

7. Solenoid 8. Arc divider/extinguisher

Magnetic circuit breakers[edit] Magnetic circuit breakers use a solenoid (electromagnet) whose pulling force increases with the current. Certain designs utilize electromagnetic forces in addition to those of the solenoid. The circuit breaker s are held closed by a latch. As the current in the solenoid increases beyond the rating of the circuit breaker, the solenoid's pull releases the latch, which lets the s open by spring action. Some magnetic breakers incorporate a hydraulic time delay feature using a viscous fluid. A spring restrains the core until the current exceeds the breaker rating. During an overload, the speed of the solenoid motion is restricted by the fluid. 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 bying the delay feature. Ambient temperature affects the time delay but does not affect the current rating of a magnetic breaker Thermal magnetic circuit breakers[edit] 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. 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. Common trip breakers[edit] Three-pole common trip breaker for supplying a three-phase device. This breaker has a 2 A rating When supplying a branch circuit with more than one live conductor, each live conductor must be protected by a breaker pole. To ensure that all live conductors are interrupted when any pole trips, a "common trip" breaker must be used. 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. Two-pole common trip breakers are common on 120/240-volt systems where 240 volt loads

(including major appliances or further distribution boards) span the two live wires. Three-pole common trip breakers are typically used to supply three-phase electric power to large motors or further distribution boards. Two- and four-pole breakers are used when there is a need to disconnect multiple phase AC—or to disconnect the neutral wire to ensure that no current flows through the neutral wire from other loads connected to the same network when workers may touch the wires during maintenance. Separate circuit breakers must never be used for live and neutral, because if the neutral is disconnected while the live conductor stays connected, a dangerous condition arises: the circuit appears de-energized (appliances don't work), but wires remain live andRCDs don't trip if someone touches the live wire (because RCDs need power to trip). This is why only common trip breakers must be used when neutral wire switching is needed. Medium-voltage circuit breakers[edit] 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. Air-break circuit breakers replaced oil-filled units for indoor applications, but are now themselves being replaced by vacuum circuit breakers (up to about 40.5 kV). Like the high voltage circuit breakers described below, these are also operated by current sensing protective relays operated through current transformers. The characteristics of MV breakers are given by international standards such as IEC 62271. Medium-voltage circuit breakers nearly always use separate current sensors and protective relays, instead of relying on built-in thermal or magnetic overcurrent sensors. Medium-voltage circuit breakers can be classified by the medium used to extinguish the arc: 

Vacuum circuit breakers—With rated current up to 6,300 A, and higher for generator circuit breakers. These breakers interrupt the current by creating and extinguishing the arc in a vacuum container - aka "bottle". Long life bellows are designed to travel the 6 to 10 mm the s must part. These are generally applied for voltages up to about 40,500 V,[7] which corresponds roughly to the medium-voltage range of power systems. Vacuum circuit breakers tend to have longer life expectancies between overhaul than do air circuit breakers.



Air circuit breakers—Rated current up to 6,300 A and higher for generator circuit breakers. Trip characteristics are often fully adjustable including configurable trip thresholds and delays. Usually electronically controlled, though some models aremicroprocessor controlled via an integral electronic trip unit. Often used for main power distribution in large industrial plant, where the breakers are arranged in draw-out enclosures for ease of maintenance.



SF6 circuit breakers extinguish the arc in a chamber filled with sulfur hexafluoride gas.

Medium-voltage circuit breakers may be connected into the circuit by bolted connections to bus bars or wires, especially in outdoor switchyards. Medium-voltage circuit breakers in switchgear line-ups are often built with draw-out construction, allowing breaker removal without disturbing power circuit connections, using a motoroperated or hand-cranked mechanism to separate the breaker from its enclosure. Some important manufacturer of VCB from 3.3 kV to 38 kV are Eaton, ABB, Siemens, C&S Electric Ltd., Jyoti and BHEL. High-voltage circuit breakers[edit] Main article: High-voltage switchgear Electrical power transmission networks are protected and controlled by high-voltage breakers. The definition of high voltage varies but in power transmission work is usually thought to be 72.5 kV or higher, according to a recent definition by the International Electrotechnical Commission (IEC). High-voltage breakers are nearly always solenoid-operated, with current sensing protective relays operated throughcurrent transformers. In substations the protective relay scheme can be complex, protecting equipment and buses from various types of overload or ground/earth fault. High-voltage breakers are broadly classified by the medium used to extinguish the arc. 

Bulk oil



Minimum oil



Air blast



Vacuum



SF6



CO2

Some of the manufacturers are ABB, General Electric, Eaton, Tavrida Electric, Alstom, Mitsubishi Electric, Pennsylvania Breaker, Siemens, Toshiba, Končar HVS, BHEL, CGL, Square D (Schneider Electric) and Becker/SMC (SMC Electrical Products). 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 AC circuit breakers are routinely available with ratings up to 765 kV. 1,200 kV breakers were launched by Siemens in November 2011,[8] followed by ABB in April the following year.[9] 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 high-voltage direct current circuit breaker uses DC transmission lines rather than the AC transmission lines that dominate as of 2013. An HVDC circuit breaker can be used to connect DC transmission lines into a DC transmission grid (which is more efficient than an AC transmission grid), thereby making it possible to link renewable energy sources and even out local variations in wind and solar power.[10] Sulfur hexafluoride (SF6) high-voltage circuit breakers[edit] Main article: Sulfur hexafluoride circuit breaker A sulfur hexafluoride circuit breaker uses s surrounded by sulfur hexafluoride gas to quench the arc. They are most often used for transmission-level voltages and may be incorporated into compact gas-insulated switchgear. In cold climates, supplemental heating or de-rating of the circuit breakers may be required due to liquefaction of the SF6 gas. Hybrid Switchgear Modules[edit] Main article: Hybrid switchgear modules A hybrid switchgear is one that combines the components of traditional air-insulated switchgear (AIS) and SF6 gas-insulated switchgear (GIS) technologies. It is characterized by a compact and modular design, which encomes several different functions in one module. Disconnecting circuit breaker (DCB)[edit]

72.5 kV carbon dioxide high-voltage circuit breaker The disconnecting circuit breaker (DCB) was introduced in 2000[11] and is a highvoltage circuit breaker modeled after the SF6-breaker. It presents a technical solution where the disconnecting function is integrated in the breaking chamber, eliminating the need for separate disconnectors. This increases theavailability, since open-air disconnecting switch main s need maintenance every 2–6 years, while modern circuit breakers have maintenance intervals of 15 years. Implementing a DCB solution also reduces the space requirements within the substation, and increases the reliability, due to the lack of separate disconnectors.[12][13] In order to further reduce the required space of substation, as well as simplifying the design and engineering of the substation, a fiber optic current sensor (FOCS) can be integrated with the DCB. A 420 kV DCB with integrated FOCS can reduce a substation’s footprint with over 50 % compared to a conventional solution of live tank breakers with disconnectors and current transformers, due to reduced material and no additional insulation medium.[14] Carbon dioxide (CO2) high-voltage circuit breakers[edit] In 2012 ABB presented a 75 kV high-voltage breaker that uses carbon dioxide as the medium to extinguish the arc. The carbon dioxide breaker works on the same principles as an SF6 breaker and can also be produced as a disconnecting circuit breaker. By switching from SF6 to CO2 it is possible to reduce the CO2 emissions by 10 tons during the product’s life cycle.[15] Other breakers[edit] Residual current circuit breaker with overload protection

The following types are described in separate articles. 

Breakers for protections against earth faults too small to trip an over-current device: 

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. In the United States and Canada, -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).



Earth leakage circuit breaker (ELCB)—This detects earth current directly rather than detecting imbalance. They are no longer seen in new installations for various reasons.



Autorecloser—A type of circuit breaker that closes automatically after a delay. These are used on overhead power distribution systems, to prevent short duration faults from causing sustained outages.



Polyswitch (polyfuse)—A small device commonly described as an automatically resetting fuse rather than a circuit breaker.

See also[edit] 

Power system protection



Residual current device



Earth leakage circuit breaker



Earthing system



Domestic AC power plugs and sockets



Arc-fault circuit interrupter



Insulation monitoring device



Circuit Total Limitation (CTL)



Network protector



Circuit breaker



Remote racking system

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Sulfur hexafluoride circuit breaker

References[edit] 1. Jump up^ Robert Friedel and Paul Israel, Edison's Electric Light: Biography of an Invention, Rutgers University Press, New Brunswick New Jersey USA,1986 ISBN 0-8135-1118-6 pp.65-66 2. Jump up^ "1920-1929 Stotz miniature circuit breaker and domestic appliances", ABB, 2006-01-09, accessed 4 July 2011 3. Jump up^ Charles H. Flurscheim (ed), Power Circuit Breaker Theory and Design, Second Edition IET, 1982 ISBN 0906048702 Chapter 1 4. Jump up^ B. M. Weedy, Electric Power Systems Second Edition, John Wiley and Sons, London, 1972, ISBN 0-471-92445-8 pp. 428-430 5. Jump up^ http://bonle.en.alibaba.com/product/50348671/51680889/Switch/MCB ___MCCB.html 6. Jump up^ http://www.claytonengineering.com/training/myweb6/Module11/Output /ImportantConcepts.html 7. Jump up^ A few manufacturers now offer a single-bottle vacuum breaker rated up to 72.5 kV and even 145 kV. Seehttp://www3.interscience.wiley.com/journal/113307491/abstract?CRETR Y=1&SRETRY=0 Electrical Engineering in Japan, vol 157 issue 4 pages 13-23 8. Jump up^ "Siemens launches world's first 1200kV SF6 Circuit Breaker". Retrieved 14 November 2011. 9. Jump up^ "ABB to develop ultra high voltage circuit breaker". Retrieved 14 August 2012. 10. Jump up^ "High Voltage DC Switch Enables Supergrids for Renewable Energy, MIT Technology Review". Retrieved 19 July 2013. 11. Jump up^ "Applications of Disconnecting Circuit Breakers, Michael Faxå, p.1". Retrieved 9 July 2012. 12. Jump up^ "HPL Disconnecting Circuit Breaker". Retrieved 9 July 2012. 13. Jump up^ "Disconnecting Circuit Breakers, Buyer’s and Application Guide, p. 10". Retrieved 9 July 2012. 14. Jump up^ "362 – 550 kV Disconnecting Circuit Breaker with FOCS: Small, smart and flexible, p.1". Retrieved 3 July 2013.

15. Jump up^ "Switzerland : ABB breaks new ground with environment friendly high-voltage circuit breaker.". Retrieved 7 June 2013. 

BS EN 60898-1. Electrical accessories — Circuit breakers for over-current protection for household and similar installations. British Standards Institution, 2003.