What is air-blast circuit breaker?
A high pressure air-blast is used as arc quenching medium. The contact are opened in a flow of a high pressure air established by opening the circuit breaker blast valve of pressurized air chamber.
The air blast cools the arc and sweeps away the arcing products to the open atmosphere. This rapidly increases the dielectric strength of the medium between contacts and prevent from re-establishing the arc. Consequently, the arc is extinguished and the flow of current is interrupted.
Air Blast Circuit Breaker working
In order to supply air to the air receiver, the air blast requires a separate compressed air system. When compressed air is needed for opening, it is allowed into the arc extinction chamber. The moving contacts are pushed away by it. As a result, the contacts are separated, aiding in arc extinction as the air blast also helps to remove the ionized gas from the area. The arc is put out by air blast within one or more cycles, and high-pressure air is injected into the arc chamber to stop restrikes.
Fig: Air Blast Circuit Breaker(Ref- studyelectrical.com)
The arc is put out by air blast within one or more cycles, and high-pressure air is injected into the arc chamber to stop restrikes. The sort of external extinguishing energy that the air blast circuit breakers use. The air blast circuit breakers fall under the category of external extinguishing type. High-pressure air is used to generate the energy needed to quench the arc without interrupting the flow of current.
Types of Air Blast Circuit Breaker
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| Types of air blast circuit breaker(Ref- circuitglobe.com) |
Axial blast circuit breaker- The air flow in an air blast circuit breaker is longitudinal along the arc, and it might be a single blast or double blast. Due to the air blast's radial flow into the nozzle or space between the contacts, double blast circuit breakers are also known as radial blast circuit breakers.
Cross blast circuit breaker- A blast from an arc is pointed at a right angle to the arc in this type of breaker. The image below shows a schematic illustration of the cross blast air circuit breaker's cross principle.
When operating in confined spaces, a moving contact arm draws an arc that is forced into the splitter plates by a transverse blast of air, lightening it to the point where it cannot restart after zero current.
Radial blast circuit breaker- In this type of circuit breakers the blast of air is directed to the ark.
Advantages of air-blast circuit breaker:
An air-blast circuit breaker has the following advantages over the oil circuit breaker.
➤ The risk of fire is limited.
➤ The high speed of operation is achieved.
➤ The arcing products are completely removed by the blast.
➤ The growth of dielectric strength is so rapid that the final contact gap needed for arc extinction is very small. This reduces the size of device.
➤ Arcing time is very small due to the rapid buildup of dielectric strength between the contacts so arc energy is less as a result less burning of contacts. So life of circuit breaker is increased.
➤ Air-blast circuit breakers are ideal for situations requiring frequent operation due to their lower arc energy.
➤ The energy supplied for arc extinction is obtained from high pressure air and is independent of the current to be interrupted.
Disadvantages of air-blast circuit breaker:
The following drawbacks are involved with using air as the arc quenching medium.
1. The extinguishing abilities of the air are comparatively poor.
2. These type circuit breakers are very sensitive to the variation in the rate of rise of restriking voltage.
3. Considerable maintenance is required for the compressor plant which supplies the air blast.
Application of air-blast circuit breaker:
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