1. AIR CIRCUIT BREAKER

2. TYPES OF CIRCUIT BREAKER (ON THE BASIS OF ARC EXTINCTION)
OIL CIRCUIT BREAKER
AIR CIRCUIT BREAKER
AIR BREAK TYPE
VACUUM CIRCUIT BREAKER
(AIR IS USED AS DIELECTRIC MEDIUM)
SF6 CIRCUIT BREAKER
AIR BLAST TYPE

3. ARC FORMATION ,EXTINCTION &ROLL OF DIELECTRIC MEDIUM
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
EXTINCTION
i. High Resistance
Interruption
a) Lengthening
the arc
b) Splitting of arc
c) cooling of arc
ii. Low resistance Or
Zero point-
-interruption
ROLL OF DIELECTRIC MEDIUM
i. Coolant Medium
ii. At current zero, de-ionizing 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 )

4. REASONS FOR USING AIR AS DIELECTRIC MEDIUM
Air is used as dielectric medium for arc extinction(Dielectric strength 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

5. AIR BREAK CIRCUIT BREAKER

6. 1. Main Contacts: low resistance (Silver Plated) 2
1.Main Contacts: low resistance (Silver Plated) 2. Arcing Contacts: High resistance (copper alloy)

7. TYPES OF AIR BREAK CIRCUIT BREAKERS
PLANE BREAK TYPE
MAGNETIC BLOW-OUT TYPE
AIR BREAK CIRCUIT BREAKER
ARC- CHUTE TYPE

8. PLAIN BREAK 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

9. MAGNETIC BLOW OUT TYPE 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

10. ARC-CHUTE TYPE 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

11. AIR BLAST CIRCUIT BREAKER

12. Requires an auxiliary compressed air system (about 15kg/cm2 ).
At opening time compressed air admitted to the arc extinction chamber.
It pushes away the moving contact.
Air is released through nozzle to produce high velocity jet.
Dielectric strength increases in high pressure.
Then air blast takes away the ionization gases along with it and assists arc extinction.

13. TYPES OF AIR BLAST CIRCUIT BREAKERS
AXIAL-BLAST AIR CIRCUIT BREAKER
AIR BLASTCIRCUIT BREAKER
RADIAL-BLAST AIR CIRCUITBREAKER
CROSS-BLAST AIR CIRCUIT BREAKER

14. AXIAL BLAST TYPE

15. RADIAL BLAST TYPE

16. CROSS BLAST TYPE

17. 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

18. ThanQ