What is Air Blast Circuit Breaker?
In this Air blast circuit breaker, it uses a high-pressure air as the arc quenching medium. In this type of circuit breaker when the contacts are separated, high-pressure air is forced on the arc through a nozzle.
It cools the arc and the arcing products are blown away by the blast of the air. The chamber is filled with high-pressure air after the extinction of arc which prevents restrike.
Working
The compressed air is stored in a tank. When a fault occurs, the contacts are opened in a flow of arc and it is established by opening of blast valve. The high-pressure air blast cools the arc and sweeps away the ionized particles along with it.
This rapidly increases the dielectric strength of the medium between the contacts and prevents from reestablishing the arc. The arc is extinguished now and the current is interrupted.
Types of Air Blast Breakers
There are three types of Airblast circuit chambers used based on the flow of blast:
- Axial blast type
- Cross blast type
- Radial blast type
Axial Blast Air Circuit Breaker
Under normal conditions, the contacts are closed by spring pressure. The air reservoir is connected to the arcing chamber through an air valve.
When a fault occurs, the air valve opens. The high-pressure air entering the arcing chamber pushes away the moving contact and an arc is formed between the contacts. The high-pressure air flows along with the arc and sweeps away the ionized particles. Now the arc is extinguished.
Cross Blast Air Circuit Breaker
An air blast is directed at the right angle in this type. When the moving contact is separated an arc is formed between the contacts. The high-pressure cross blast forces the arc into a chamber called chute which consists of arc splitters and baffles.
The splitter is used to increase the length of the arc and the baffle is used for cooling purposes. Thus the arc is extinguished.
This type is suitable for interrupting high current up t0 100kA.
Radial Type Air Blast Circuit Breaker
In this radial type, the flow of air is longitudinal along the arc. Breaking by employing a double blast is called a radial blast circuit breaker. The air blast flows radially into space between the contacts.
The contacts are separated and an arc is formed between them. The air flows at a great speed axially along the arc. It causes the removal of heat and the arc is reduced to a value at current zero. Thus, the arc is extinguished. The flow of fresh air builds the dielectric strength between them.
Advantages of Air Blast Circuit Breaker:
- It eliminates the risk of fire
- Operating speed is high
- Requires less maintenance
- Suitable for frequent operation
- Short and consistent arcing time
- Cheap if using air as medium
Disadvantages of Air Blast Circuit Breaker:
- Air compressor needs to be maintained
- It produces a noise when the air is discharged
Conclusion
Airblast circuit breakers use compressed air or high-pressure air as an arc quenching medium. The high-pressure air blast is used to blow out the arc through a nozzle and push away the arcing products into the atmosphere. This type of circuit breaker is widely used in high voltage applications such as 245kV, 420kV, or more.
