Air-blast circuit breakers utilize a blast of compressed air typically at a pressure of 25–75 bar, which is directed across the path to cool and eliminate the ionized gas, in other words the air-blast is employed as the quenching medium.
The air-blast cools the arc and sweeps away the arcing products to the atmosphere. This rapidly increases the dielectric strength of the medium between contacts and prevents the arc from re-creation. As a result, the arc is extinguished and flow of current is interrupted.
Air-blast circuit breakers can be classified depending upon the direction of air-blast in relation to the arc path into three types:
- Axial-blast circuit breaker: In this type the air-blast is directed along the arc path.
- Cross-blast circuit breaker: This type has the air-blast directed at right angles.
- Radial-blast circuit breaker: The air blast is directed radially.
Whilst air-blast circuit breakers are reliable and reasonably maintenance free, they tend to be very noisy in operation hence not a good choice for use in substations sites adjacent to built-up areas, they also require a reliable compressed air plant and have high dynamic loads. This increases the maintenance obligation in comparison with other types of arc interrupting circuit breakers. To overcome the problem of noisy operation, it is common to fit silencers to the exhaust systems of the circuit breaker. The use of a silencer will bring down the noisy level from approximately 120 dB to 90 dB.
Air-blast circuit breakers are used in high voltage applications up to 800 kV with fault currents of some 80 kA or more, nonetheless presently such breakers have been superseded by SF6 designs which are now available up to 800 kV.
Also read:
- Air Circuit Breakers: Features, Operation & Applications
- Switchgear Equipment
- 5 Causes of High-Voltage Switchgear Failures
- Key Factors to Consider In Substation Design
- Common Busbar Protection Schemes
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