Air Blast Circuit Breaker
These type of breakers employ ‘air blast’ as the quenching medium.The contacts are opened by air blast produced by the opening of blast valve.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 from re-establishing the arc.Consequently the arc is extinguished and the flow of current is interrupted.
An air blast circuit breaker has the following advantages over an oil circuit breaker:
- The risk of fire is eliminated
- The arcing products are completely removed by the blast whereas the oil deteriorates with successive operations;the expense of regular oil is replacement is avoided
- The growth of dielectric strength is so rapid that final contact gap needed for arc extinction is very small.this reduces the size of device
- The arcing time is very small due to the rapid build up of dielectric strength between contacts.Therefore,the arc energy is only a fraction that in oil circuit breakers,thus resulting in less burning of contacts
- Due to lesser arc energy,air blast circuit breakers are very suitable for conditions where frequent operation is required
- The energy supplied for arc extinction is obtained from high pressure air and is independent of the current to be interrupted.
- Air has relatively inferior arc extinguishing properties
- Air blast circuit breakers are very sensitive to the variations in the rate of restriking voltage.
- Considerable maintenance is required for the compressor plant which supplies the air blast
Air blast circuit breakers are finding wide applications in high voltage installations. Majority of circuit breakers for voltages beyond 110 kV are of this type.