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Slide 1 :
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PRESENTATION ON AIR CIRCUIT BREAKER
PRESENTED BY
DIBYENDU CHAKRABORTY
CALCUTTA UNIVERSITY
DEPARTMENT OF APPLIED PHYSICS |
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Slide 2 :
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TYPES OF CIRCUIT BREAKER(ON THE BASIS OF ARC EXTINCTION) CIRCUIT BREAKER OIL CIRCUIT BREAKER AIR CIRCUIT BREAKER VACUUM CIRCUIT BREAKER SF6 CIRCUIT BREAKER AIR BREAK TYPE AIR BLAST TYPE (AIR IS USED AS DIELECTRIC MEDIUM) |
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Slide 3 :
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ARC FORMATION ,EXTINCTION &ROLL OF DIELECTRIC MEDIUM EXTINCTION
i> High Resistance
Interruption
a) Lengthening
the arc
b) Splitting of arc
c) cooling of arc
ii> Low resistance
Or
Zero point-
-interruption FORMATION
Separation of contact
leads produces
i> Thermal
Ionization
ii> Ionization by
Collision
iii> Thermal
Emission
from Surface of
Contacts
iv> Secondary
Emission from
Contact Surface
v> Field Emission
at Contact
Surface
vi> Photoemission
ROLL OF DIELECTRIC MEDIUM
i> Coolant Medium
ii> At current zero, deionizing the
space between contacts by
introducing unionized
medium
iii> Increasing the dielectric
strength of the contact space to
such an extent that the arc
does not continue after current
zero (If dielectric strength of
gap is less than the restriking
voltage then voltage may
reestablished the arc )
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Slide 4 :
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REASONS FOR USING AIR AS DIELECTRIC MEDIUM Air is used as dielectric medium for arc extinction(Dielectric strength-0.3-0.4 MVm-1)
Dielectric strength of air increases with in increase in pressure
It provides adequate insulation between the contacts and from each contacts to earth.
Thermal and Chemical stability of dielectric
Non-inflammability
High thermal conductivity
Cheapest and easily available
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Slide 5 :
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AIR BREAK CIRCUIT BREAKER AIR BREAK CIRCUIT BREAKER PLANE BREAK TYPE MAGNETIC BLOW-OUT TYPE ARC- CHUTE TYPE Contacts are horn shaped
Initially arc strikes across shortest distance between 2 horns
Driven upwards by convection of heated air & interaction of electric field
Air flows down to upwards
Result- lengthening & cooling of arc Arc horns act as previous
Magnetic field blows out arc into arc-chutes
Arc-chutes lengthen the arc
Air flows down to upwards
Result- lengthening & cooling of arc
Arc extinguishes within an confined area Main contacts & auxiliary contacts are provided
Auxiliary contacts close before & open after main contacts
The arc-chutes made by steel divides arc
When arc comes contact with steel it cools down *** Air is used at atmospheric pressure in all Air Break Circuit Breakers |
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Slide 6 :
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AIR - BLAST CIRCUIT BREAKER
AIR- BLAST CIRCUIT BREAKER AXIAL-BLAST AIR CIRCUIT BREAKER RADIAL-BLAST AIR
CIRCUIT BREAKER CROSS-BLAST AIR
CIRCUIT BREAKER |
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Slide 7 :
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APPLICATION AREA & DISCUSSION Air break type
Area:
Both in D.C.&A.C. , up to 12kV & 2okA
Placed in indoor, control of power station auxiliaries and industrial plants.
Advantages:
They do not require compressor, oil
Free from fire & explosion hazards
Disadvantages:
Less efficient for lengthening & deionizing action at high currents
Bulky
Not suitable in modern power system Air blast type
Area:
11kV to1100kV
placed in out door
Advantages:
High speed of operation
Negligible maintenance
Elimination of fire hazarded
Reduced size
Disadvantages:
Require air compressor of correct pressure, clean & dry
Largest installation & costly
Air leakages at the pipe fittings
Drastic effect on small current & problem of current chopping arises leading to serious overvoltage
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