Download - 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
#$%. "xial-blast type#!%.&ross-blast type#'%.(adial-blast type
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1) Axial-blast type:-
)n which the air-blast is
directed along the arc path as
shown in *ig.
,
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)n which the air-blast is
directed at right angles to the
arc path as shown in *ig.
Types o Air blast circuitbreaker
2)Cross-blast type:-
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)n which the air-blast is
directed radially as shown
in *ig
Types o Air blast circuitbreaker
(3)adial-blast type:-
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1) Axial blast Air blast circuitbreaker
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The fixed and moving contacts are held in closed position with the help of spring pressure.
There is an air reservoir connected to the arcing chamber through an air valve. The air
valve control the flow of air into the arcing chamber. The valve is closed under normalconditions.
When a fault occurs a tripping impulse is produced which causes opening of the air valve.
Since the air valve connects the air reservoir and the arcing chamber, a high pressure air
enters to the arcing chamber.
This air pushes away the moving contact against the spring pressure. The moving contact
is separated and an arc is struck. At the same time high pressure air blast flows along the
arc and takes away the ionised gases along with it. Conseuently the arc is extinguished
and current flow is interrupted.
The contact seperation reuired for arc extinction is very small generally !".#$ 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