17-12-2012, 11:16 AM
AIR CIRCUIT BREAKER
1AIR CIRCUIT.pptx (Size: 511.72 KB / Downloads: 35)
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
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
AIR BLAST CIRCUIT BREAKER
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.