Question

In air-blast circuit breakers, the pressure of the air is of the order of:
1. 100 mm Hg
2. 1 kg / cm²
3. 20 kg / cm² to 30 kg / cm²
4. 200 kg / cm² to 300 kg / cm²

Answer 1

Correct Answer - Option 3 : 20 kg / cm² to 30 kg / cm²

Air Blast Circuit breakers:

• The second ‘air’ based circuit breakers are air blast circuit breakers.
• In this type, a high-pressure air-blast is used as an arc extinguishing medium. In case of a fault, the air-blast, controlled by a blast valve, will open the contacts and also cools the arc.
• The arc and the arching products are swept into the atmosphere, which rapidly increases the dielectric strength of the medium.
• As a result, the restriking of the arc is prevented. The arc is extinguished consequently and the flow of current is completely interrupted.
• These are finding their best applications in systems at 132 kV and above (up to 400 kV) with breaking capacity up to 7,500 MVA and above.
• The pressure of the air is of the order of 20 kg / cm2 to 30 kg / cm2

There are three types of air blast circuit breakers based on the direction of the air-blast in relation to the arc. They are:

1.  Axial Blast Type
2. Cross Blast Type
3. Radial Blast Type

 

In axial-blast circuit breakers, the air-blast flows in the same direction as the arc.

The high-pressure air-blast will push the moving contact away, opening the circuit and also pushes the arc along with it.

The air-blast in cross-blast type circuit breakers is perpendicular to the arc path and in radial-blast type circuit breakers, it is directed radially.