Question

Which of the following is NOT an advantage of air blast circuit breakers? 
1. High speed operation is achieved. 
2. The stability of the system can be well maintained
3. There is no possibility of air leakages at the pipe fittings
4. This type of circuit breaker is almost maintenance free. 

Answer 1

Correct Answer - Option 3 : There is no possibility of air leakages at the pipe fittings

Option 3 'There is no possibility of air leakages at the pipe fittings' is NOT an advantage of air blast circuit breakers.

Concept:

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

 

Advantages:

• High speed operation is achieved. 
• Almost maintenance free. 
• The stability of the system can be well maintained

 

T here 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.