Air Blast Circuit Breaker 1

7/24/2019 Air Blast Circuit Breaker 1

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AIRBLAST CIRCUIT BREAKER


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These type of breakers employ air blast as the

quenching medium.The contacts are opened by air blast produced

by the opening of blast valve. The air blast cools the arc and sweeps away the

arcing products to the atmosphere. This rapidly increases the dielectric strength of

the medium between contacts and preventsfrom re-establishing the arc.

So the arc is extinguished and the ow ofcurrent is interrupted.

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Introduction


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ClassifcationTypes of "ir blast circuit breaker

#$%. "xial-blast type#!%.&ross-blast type#'%.(adial-blast type


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1) Axial-blast type:-

)n which the air-blast is

directed along the arc path as

shown in *ig.

,


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directed at right angles to the

arc path as shown in *ig.

Types o Air blast circuitbreaker

2)Cross-blast type:-


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directed radially as shown

in *ig

Types o Air blast circuitbreaker

(3)adial-blast type:-


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1) Axial blast Air blast circuitbreaker


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The fixed and moving contacts are held in closed position with the help of spring pressure.

There is an air reservoir connected to the arcing chamber through an air valve. The air

valve control the flow of air into the arcing chamber. The valve is closed under normalconditions.

When a fault occurs a tripping impulse is produced which causes opening of the air valve.

Since the air valve connects the air reservoir and the arcing chamber, a high pressure air

enters to the arcing chamber.

This air pushes away the moving contact against the spring pressure. The moving contact

is separated and an arc is struck. At the same time high pressure air blast flows along the

arc and takes away the ionised gases along with it. Conseuently the arc is extinguished

and current flow is interrupted.

The contact seperation reuired for arc extinction is very small generally !".#$ or so %.

This small gap may sometimes inadeuate clearence for the normal sevice voltage.

Therefore an isolating switch is included as a part of this C&.

This switch opens immediately after the fault interruption to provide necessary clearence

for insulation.

Axial blast Air blast circuit breaker


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2)Cross-blast air breaker


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When the moving contact is withdrawn, an arc is struck between the fixed andmoving contacts. The high pressure cross'blast forces the arc into a chute

consisting of arc splitters and baffles.

The splitters serve to increase the length of the arc and baffles give improved

cooling. The result is that arc is extinguished and flow of current is interrupted.Since blast pressure is same for all currents, the inefficiency at low currents is

eliminated.

The final gap for interruption is great enough to give normal iusulation clearance

so that a series isolating switch is not necessary.

Cross-blast air breaker


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The risk of fire is eliminated.

The arcing products are completely removed by the blast

The growth of dielectric strength is so rapid that final contact gap needed for arc

extinction is very small. This reduces the si(e of device.

The arcing time is very small due to the rapid build up of dielectric strength between

contacts

)ue to lesser arc energy, A&C& are very suitable for conditions where freuent

operation is reuired

The energy supplied for arc extinction is obtained from high pressure air *

independent of the current to be interrupted

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Ad!anta"es


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Air has relatively inferior arc extinguishing properties.

Air blast circuit breakers are very sensitive to the variations in the rate of

restriking voltage.

Considerable maintenance is reuired for the compressor plant which

supplies the air blast .

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#isad!anta"es


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The air blast circuit breakers are finding wide applications in high voltageinstallations. +aority of the circuit breakers for voltages beyond ""- k

are of this type.

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Application

Air Blast Circuit Breaker 1

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