Fire sprinkler abcb reference document - automatice fire sprinkler system
ABCB and SF6 CB
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Transcript of ABCB and SF6 CB
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AIR BLAST AND SF6
CIRCUIT BREAKERS
TYPES,CONSTRUCTION,WORKING,
ADVANTAGE AND DISADVANTAGE
By:
NIKUNJ AGARWAL
1009120055
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CONSTRUCTION OF ABCB:
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PRINCIPLE OF ARC QUENCHING:
Sequence of operation in ABCB
Contact close by spring pressure against reduced airpressure
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TYPES OF ABCB:
fig: cross flow ABCB
Axial-blast type or
single blast type:
Cross-blast type:
In this type of breaker the
air blast is directed along
the arc path. The fixed and
moving contacts are held
in the closed position by
spring pressure under
normal condition
In this type of breaker an
air blast is directed at right
angles to the arc.
The cross blast lengthens
and forces the arc into a
suitable chute (Arc
splitters) for arc extinction.
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Radial-blast type or double blast type:
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1.Elimination of fire hazard.
2.Cheap compared to oil circuit
breaker.
3.Arcing time is very less thereby
less burning of contacts.
4.Facility of high speed reclosure.
5.Suitable for frequent operation.
DisAdvantagesAdvantages
1.The air blast circuit breakers are very
sensitive, to the variations in the rate of
rise of restriking voltage
.
2.Maintenance is required for
compressor plant which supplies air
blast.3.Problem of current chopping.
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SULPHUR HEXAFLUORIDE SF6) CB: Sulphur Hexafluoride (SF6) gas is used as an arc quenching
medium.
SF6 has excellent insulating strength because of its affinity
for electrons.
Whenever a free electron collides with the neutral gas molecule
to form negative ion, the electron is absorbed by the neutral gasmolecule.
This property of SF6 is approximately 100 times as effective as
air in quenching arcs.
SF6 has excellent heat transfer by convection more effectivelythan the common gases.
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SF6 consists of 2 parts mainly:
The interrupter unit:
This consists of fixed contacts which comprise a set of currentcarrying fingers and an arcing probe. As the contacts move
further apart, the arc is extended and attenuated. It is finally
extinguished by the gas flow the high pressure to the low
pressure systems.
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The gas system:
The low and high pressure system are fitted with low pressurealarms and a set of lock-out switches which give a warning the
moment the gas pressure drops below a certain value
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PUFFERTYPESF6 :
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Simple construction, less
cost. SF6 gas is non
flammable, non toxic &chemical inert gas.
Same gas is recirculatedin the circuit.
Maintenance free C.B.
Ability to interrupt lowand high fault current.
Excellent Arc extinction.
o SF6 breakers are costly
due to high cost of SF6 .
o Sealing problems arise ,
Imperfect joints give rise
to leakage of gases
o After every operation SF6
gas has to be
reconditioned, so
additional equipment is
required.
Advantages Disadvantages