abcb and sf6 cb

8/14/2019 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

abcb and sf6 cb

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