today circuit breaker

8/2/2019 Today Circuit Breaker

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By:Chandramohan S. JhaClass :- 7th EERoll no :- 26.


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Circuit Breakers

Definition

Mechanical switching devices capableof making, carrying and breakingcurrents under normal and abnormal


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Circuit breakers Elements

Main Contact

Insulation between main contacts


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Types of Circuit breakersAir-Blast Circuit breakerOil Circuit Breakers SF6 Circuit breakers Vacuum Circuit Breakers


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Principles of Operation

Moving contact made of copper rod

Fixed contact made of spring-loadedcopper segments to exert pressure onmoving contact and to make goodcontact


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Circuit Breakers Requirements

Opens & closes in shortest possibletime

Conducts rated current.

Withstands thermally & mechanicallyany short circuit.


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Does not create over voltages duringcircuit opening

Easy to maintain.

Not very expensive

CONTINUE


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Principles of OperationOn opening moving contact moves

rapidly.

An electric Arc is formed.

The intensity of the arc depends on thecurrent been interrupted.


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The gas in the chamber sweeps the arcwhich is cooled.

Circuit opening is achieved if the arcdoes not re-ignite


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Oil Circuit breakerHeat from the arc breaks some oil to

form gases mostly hydrogen.

The high pressure of the gas blows outthe arc

Cold oil flows onto the arc which is

extinguished. Used in low and medium voltages up

to 110 kV.


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Air-Blast Circuit breakerAir is compressed in reservoir up to 14

atmospheric pressure. The compressed air is released anddirected towards the arc at high

velocityThe arc is then extinguishedUsed for 110 kV and above


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SF6 Circuit breaker

Sulfur Hexa Flouride (SF6) gas is usedunder pressure.It has high electric strength and

outstanding arc quenchingcharacteristics.It is an electro-negative gas. It means

that the free electrons are attracted tothe gas and are not free to move to

sustain the arc.


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SF6 Circuit breakerSF6 Breakers are smaller than air-blast

breakers.

Temperature of up to 30,000 K areexperienced in breakers.

SF6 breakers are used from lowvoltage system and up to 1300 kV


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Vacuum Circuit breakerInterruption chamber is vacuumed.No gas which is ionized to form the

arc.An arc is formed from the vaporized

contact material.

The choice of the contact material iscrucial


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Vacuum Circuit breakerVery small damage to contacts (life up

to 30 years). Small mechanical energy required for

tripping.

Widely used in low voltageapplications


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References:-

Power systemby:V.K.Mehta

Electrical Power Systemby: C.L.WADHWA

S.G.P.D. by: S. S.Rao


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ThankYou..

today circuit breaker

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