circuit breakers classified by interrupting medium

8/17/2019 Circuit Breakers Classified by Interrupting Medium

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Square D - Powersub Vacuum Substat ionCircuit Breaker T ype FVR, 15 kV to 38 kV, 110kV to 200 kV BIL, Ampacit ies 600, 800, 1200,

2000, 3000, 3500, and 4000 Amperes,Interrupt ing Amperes 12 kA to 40 kA (RMS

Symmetrical)

h ttp ://e le ctrica l- en gine erin g- po rta l.com/circuit- brea kers- cla ssifie d- by- inte rru ptin g- me dium Jan ua ry 21, 2013

Circuit breakers classified by interrupting medium

A circuit breaker is def ined as “a mechanicalswitching device capable of making, carryingand breaking currents under normal circuit

conditions and also making, carrying andbreaking for a specified time, and breaking

currents under specif ied abnormal circuitconditions such as a short circuit”(IEEE Std.C37.100).

Circuit breakers are generally classifiedaccording to the interrupting medium used tocool and elongate the electrical arcper mitting interruption.

The circuit breaker types are:

• Air magnetic• Oil• Air blast• Vacuum• SF6 gas

Air magnet ic circuit breakers are limited to

older switchgear and have generally beenreplaced by vacuum or SF6 for switchgear applications. Vacuum is used f or switchgear applications and some outdoor breakers, generally 38 kV class and below. Air blastbreakers, used for high voltages (≥765 kV), are no longer manufactured and have beenreplaced by breakers using SF6 technology.

Oil circuit breakers have been widely used in the utility industry in the past but have been

replaced by other breaker technologies for newer installations. Two designs exist : bulk oi(dead-tank designs) dominant in the U.S.; and oil minimum breaker technology (live- tank

design). Bulk oil circuit breakers were designed as single-tank or three-tank mechanisms;generally, at higher voltages, three-tank designs were dominant.

Oil circuit breakers were large and required signif icant foundations to support the weightand impact loads occurring during operation.

Environmental concerns f orcing the necessity of oil retention systems, maintenancecosts, and the development of the SF6 gas circuit breaker have led to the gradualreplacement of the oil circuit breaker for new installations.

Oil circuit breaker develo ment has been relativel

http://electrical-engineering-portal.com/how-low-voltage-air-circuit-breaker-workshttp://electrical-engineering-portal.com/circuit-breakers-classified-by-interrupting-mediumhttp://electrical-engineering-portal.com/how-low-voltage-air-circuit-breaker-workshttp://electrical-engineering-portal.com/circuit-breakers-classified-by-interrupting-medium


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Oil circuit breakers

stat ic for many years. The design of the interrupter employs the arc caused when the contacts are partedand the breaker starts to operate. The electrical arcgenerates hydrogen gas due to the decomposit ion of the insulating mineral oil. The interrupter is designedto use the gas as a cooling mechanism to cool the arcand to use the pressure to elongate the arc through a

grid (arc chutes), allowing extinguishing of the arcwhen the current passes through zero.

Vacuum circuit breakers use an interrupter that is asmall cylinder enclosing the moving contacts under ahigh vacuum. When the contacts part, an arc isf ormed f rom contact erosion. The arc products areimmediately forced to and deposited on a metallicshield surrounding the contacts. Without anything tosustain the arc, it is quickly extinguished.

Vacuum circuit breakers are widely employed f or metal-clad switchgear up to 38 kV classThe small size of the breaker allows vertically stacked installations of breakers in a two-high conf iguration within one vert ical sect ion of switchgear, permitt ing signif icant savingsin space and material compared to earlier designs employing air magnetic technology.When used in outdoor circuit breaker designs, the vacuum cylinder is housed in a metalcabinet or oil-f illed tank for dead tank construction popular in the U.S. market.

Gas circuit breakers enerall em lo SF6 sulf ur

http://electrical-engineering-portal.com/comparison-between-vacuum-and-sf6-circuit-breaker


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Toshiba GSPF 245 HP GasCircuit Breaker - live t ank circuitbreakers with rated voltage of 245 kV. Each breaker consist of

three puf fer-type SF6interrupt ers, providing a high

level of insulat ions as well as anexcellent breaking capabilit y,

and a spring operat ingmechanism ensuring high

operat ional reliabilit y

hexaflouride) as an interrupting and sometimes as aninsulating medium. In “single puf f er”mechanisms, theinterrupter is designed to compress the gas during theopening stroke and use the compressed gas as atransfer mechanism to cool the arc and to elongate thearc through a grid (arc chutes), allowing extinguishing of the arc when the current passes through zero.

In other designs, the arc heats the SF6 gas and theresulting pressure is used f or elongating and interruptingthe arc. Some older two-pressure SF6 breakersemployed a pump to provide the high-pressure SF6 gasfor arc interruption.

Gas circuit breakers typically operate at pressuresbetween six and seven atmospheres. The dielectricstrength of SF6 gas reduces signif icantly at lower

pressures, normally as a result of lower ambient

temperatures. Monitoring of the density of the SF6 gas iscritical and some designs will block operation of thecircuit breaker in the event of low gas density.

Circuit breakers are available as live-tank or dead-tank designs. Dead-tank designs put the interrupter in agrounded metal enclosure. Interrupter maintenance is at

ground level and seismic withstand is improved vs. thelive-tank designs. Bushings are used for line and load connections which permitinstallation of bushing current transf ormers for relaying and metering at a nominal cost .

The dead-tank breaker does require additional insulating oil or gas to provide theinsulation between the interrupter and the grounded tank enclosure.

Live-tank circuit breakers consist of an interru ter

http://electrical-engineering-portal.com/sf6-gas-as-insulating-and-arc-quenching-medium


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Live t ank circuit breaker - designedfor a system voltage of 145kV, ashort circuit current up to 31.5kA

and a normal current rat ing of 2500amperes.

chamber that is mounted on insulators and is at linepotential. This approach allows a modular design asinterrupters can be connected in series to operate athigher voltage levels. Operation of the contacts isusually through an insulated operating rod or rotationof a porcelain insulator assembly by an operator atground level. This design minimizes the quantity of oil

or gas used f or interrupting the arc as no addit ionalquantity is required for insulation of a dead tankenclosure. The design also readily adapts to theaddition of pre-insertion resistors or gradingcapacitors when they are required. Seismic capabilityrequires special consideration due to the high center of gravity of the interrupting chamber assembly.

Interrupting t imes are usually quoted in cycles andare def ined as the maximum possible delay between

energizing the trip circuit at rated control voltage andthe interruption of the main contacts in all poles. Thisapplies to all currents f rom 25 to 100% of the ratedshort-circuit current.

Circuit breaker ratings must be examined closely.Voltage and interrupting ratings are stated at amaximum operat ing voltage rat ing, i.e., 38 kV voltage

rating f or a breaker applied on a nominal 34.5-kV circuit. The breakers have an operat ingrange designated as K factor per IEEE C37.06.

For a 72-kV breaker, the voltage range is 1.21, indicat ing that the breaker is capable of its f ull interrupting rating down to a voltage of 60 kV. Breaker rat ings need to be checkedfor some specif ic applicat ions. Applications requiring reclosing operation should bereviewed to be sure that the duty cycle of the circuit breaker is not being exceeded.

Some applications for out-of -phase switching or back- to-back switching of capacitor banks also require review and may require specif ic-duty circuit breakers to insure proper operation of the circuit breaker during fault interruption.

Reference: High-Voltage Switching Equipment by David L. Harris
http://standards.ieee.org/develop/wg/HVCB-WG_C37.06.html

circuit breakers classified by interrupting medium

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