What is air circuit breaker and its applications?

What is air circuit breaker and its applications?
Air circuit breaker

What is Air Circuit Breaker?

Air circuit breaker is one of the most common used CB in domestic and industrial loads. The miniature circuit breaker (MCB) in your home electricity box is Air CB.

In the previous article, we discussed overcurrent protection devices. To safeguard an electrical system or device from overcurrent and electrical short circuit different devices are in use. We discussed fuses, Circuit breakers, and relays. In this article, we will discuss Circuit breakers further and specifically air circuit breakers.

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Construction

Circuit breakers (CBs) have some main components such as frame, operating mechanism, contacts, Arc Extinguisher, and trip units. The detail will be included in our next article.

The air breaker is a type of circuit breaker in which arc initiates and extinguishes in static air. The air breakers are rated for low voltages. Due to high performance, durability, easy installation, and maintenance the air breakers are very common to use.

How Air Circuit Breaker works

The air CB consists of two pairs of contacts. Contacts 1, usually called the main pair carries the current at normal load. Contact 2, also called the second pair is the arcing contact. Contact 1 is made of copper metal and contact 2 is made of carbon. When the circuit breaker opens, the main pair i.e. contact1 opens first while the arcing contacts are still connected with each other. When current flows through a low resistive path through the arcing contact. It heats up and the contacts detach from each other. During this process arcing initiates. Due to electromagnetic and thermal effects, the arcs move upward and fit in the chute. Where in chute the arc becomes colder and extinguishes at zero current.

Types of Air CB

There are three types of Air CB. These types are common in use for low voltages. Each type is discussed below.

  • Plain Break Type

In this type of breakers, the main points of contacts are made in the shape of two horns. During the operation, the arc extends from one tip to another. These types are most commonly in use.

  • Magnetic Blowout Type

In this type of circuit breaker, the arcing is providing with help of a magnetic field. These are normally used for rated voltage up to 11KV.

  • Air Chute Air CB

In this type of circuit breaker, the main contact is made up of copper. It conducts current in closed positions. The contacts are silver plated and have low contact resistance. The arcing contacts are made of copper alloy and they resist heating up.

Applications of Air Breaker

  • Air CBs are used in power generation station auxiliaries and other industrial plants. It safeguards electrical equipment from overcurrent and short circuit.
  • It can be used in both AC and DC circuits rated up to 12 KV.
  • Air CBs offers high resistance power by expanding, splitting & cooling.
  • Sometimes this type of breaker is used in the electricity sharing system.

Circuit breaker parameters

Each breaker is defined with rating current in AMP, Short circuit current in KA, curve type and the operating voltage. The rated current is the maximum current that the breaker could withstand in normal conditions. Short circuit current is the maximum short current that the breaker can clear its represented as Ics.

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What causes a circuit breaker to go bad?

CBs are like any electrical device, Has life time and rated current. If the current passing through the CB exceed the rated current, then the breaker trips. But in case of large currents due to large short circuit faults, the breaker may trip but will not be usable any more and then the breaker go bad.

Another reason which makes circuit breaker go bad is loosen connection which causes arc fault. Some breakers don’t detect the arc fault then goes bad. In this case although the CB went bad it won’t trip, but it will cause another fault called phase loss, this is because the bad phase of the CB will not connect.

bad circuit braker due to loosen connection
bad circuit braker due to loosen connection