What is Air Circuit Breaker : Working & Its Applications

A circuit breaker is one kind of electric device, used to break any circuit manually otherwise through remotely under normal circumstances. The main function of a circuit breaker or CB is to break a circuit in some fault conditions like a short circuit, over-current, etc. Generally, a circuit breaker switches or protects the system. Some devices are associated with circuit breakers such as relays; switches, fuses, etc are also used for the same purpose. The applications of circuit breakers mainly include power systems and industries for protecting as well as controlling various parts in the circuit namely transformers, switch gears, motors, alternators, generators, etc. There are different kinds of circuit breakers used in industries where the air circuit breaker is one type. This article discusses an overview of the air circuit breaker.

What is Air Circuit Breaker?

Air Circuit Breaker (ACB) is an electrical device used to provide Overcurrent and short-circuit protection for electric circuits over 800 Amps to 10K Amps. These are usually used in low voltage applications below 450V. We can find these systems in Distribution Panels (below 450V). Here in this article, we will discuss the working of Air Circuit Breaker.

Air Circuit Breaker
Air Circuit Breaker

An air circuit breaker is a circuit operation breaker that operates in the air as an arc extinguishing medium, at a given atmospheric pressure. There are several types of air circuit breakers and switching gears available in the market today that are durable, high-performing, easy to install and maintain. The air circuit breakers have completely replaced oil circuit breakers.

Air Circuit Breaker Construction

The construction of an air circuit breaker can be done by using different internal and external parts like the following.

The external parts of ACB mainly include the ON & OFF button, an indicator for the position of the main contact, an indicator for the mechanism of energy storage, LED indicators, RST button, controller, rated nameplate, handle for energy storage, displays, shake, fault trip rest button, rocker repository, etc.

Construction of ACB
Construction of ACB

The internal parts of ACB mainly include supporting structure with steel sheet, the current transformer used to protect the trip unit, pole group insulating box, horizontal terminals, arcing chamber, trip unit for protection, terminal box, closing springs, CB opening & closing control, plates to move arcing and main contacts, plates for fixed main & arcing contacts.


Working Principle

  • The air circuit breaker working principle is different as compared with other kinds of CBs. We know that the basic function of CB is to stop the restoration of arcing wherever the gap between contacts will resist the recovery voltage of the system.
  • The air circuit breaker also works the same but in a different way. While interrupting an arc, it makes an arc voltage in place of the voltage supply. This voltage can be defined as the least voltage which is necessary to maintain the arc. The voltage supply can be increased in three different ways by a circuit breaker.
  • The arc voltage can be enhanced through cooling arc plasma.
  • Once the temperature of arc plasma and particle motion is reduced, then additional voltage gradient will be necessary to keep the arc. The arc voltage can be increased by splitting the arc into several series
  • Once the arc path is increased then Arc voltage can also be increased. As soon arc path length is enhanced then the path of resistance will also increase the arc voltage which is used across the arc path thus arc voltage can be increased.
  • The range of operating voltage is upto 1KV. It includes two sets of contact where the major pair uses the current as well as the contact made with copper. Another pair of contact can be made with carbon. Once the circuit breaker is opened, the first major contact unlocks.
  • While opening the major contact, the arc contact stays connected. Whenever arc contacts are divided then arcing gets started. The circuit breaker is outdated for average voltage.

Air Circuit Breaker Working

Air circuit breakers operate with their contacts in free air. Their method of arc quenching control is entirely different from that of oil circuit-breakers. They are always used for the low-voltage interruption and now tends to replace high-voltage oil breakers. The below-shown figure illustrates the principle of air breaker circuit operation.

Air Circuit breakers generally have two pairs of contacts. The main pair of contacts (1) carries the current at normal load and these contacts are made of copper metal. The second pair is the arcing contact (2) and is made of carbon. When the circuit breaker is being opened, the main contacts open first. When the main contacts opened the arcing contacts are still in touch with each other.

As the current gets a parallel low resistive path through the arcing contact. During the opening of the main contacts, there will not be any arcing in the main contact. The arcing is only initiated when finally the arcing contacts are separated. Each of the arc contacts is fitted with an arc runner which helps.

The arc discharge moves upward due to both thermal and electromagnetic effects as shown in the figure. As the arc is driven upward it enters the arc chute, consisting of splatters. The arc in the chute will become colder, lengthen, and split hence arc voltage becomes much larger than the system voltage at the time of operation of an air circuit breaker, and therefore the arc is extinguished finally during the current zero.

The air brake circuit box is made of insulating and fireproof material and it is divided into different sections by the barriers of the same material. At the bottom of each barrier is a small metal conducting element between one side of the barrier and the other. When the arc, driven upwards by the electromagnetic forces, enters the bottom of the chute, it is split into many sections by the barriers, but each metal piece ensures electrical continuity between the arcs in each section, the several arcs are consequently in the series.

The electromagnetic forces within each and every section of the chute cause the arc in that section to start the form of a helix, as shown above, figure (b). All these helices are in series so that the total length of the arc has been greatly extended, and its resistance is abundantly increased. This will affect the current reduction in the circuit.

Figure (a) shows the development of the arc from the time it leaves the main contacts until it is within the arc chute. When the current next ceases at a current zero, the ionized air in the path of where the arc had been being in parallel with the open contacts and acts as a shunt resistance across both the contacts and the self-capacitance C, shown in the below figure with red as a high resistance R.

When the oscillation starts between C and L as described for the idealized circuit breaker shown in Figure below, this resistance damps the oscillation heavily. Certainly, it is usually so heavy that the damping is critical, the oscillation cannot then take place at all, and the restriking voltage, instead of appearing as a high-frequency oscillation, rises dead-beat to its eventual value of peak generator voltage. This is shown below the lower waveform.

Idealized CB with Waveforms
Idealized CB with Waveforms

Types of Air Break Circuit Breaker

The air circuit breakers are mostly of four types and are widely used for maintaining the indoor medium voltage and switch gears of the home.

  • Plain Break Type ACB or Cross-Blast ACB
  • Magnetic Blowout Type ACB
  • Air Chute Air Break Circuit Breaker
  • Air Blast Circuit Breaker

Plain Break type Air Break Circuit Breaker

Plain brake air circuit breakers are the simplest form of air breakers. The main points of contacts are made in the shape of two horns. The arc of these circuit breakers extends from one tip to the other. This kind of circuit breaker is also known as cross blast ACB. The arrangement of this can be done through a chamber (arc chute) which is surrounded by the contact.

The chamber or arc chute helps in achieving cooling and it is made with refractory material. The arc chute contains walls inside and it is separated into small compartments using metallic separation plates. These plates are arc splitters where each compartment will work as a mini-arc chute.

The first arc will divide into a sequence of arcs so that all arc voltages will become higher as compared with the system voltage. These are used in low voltage applications.

Magnetic Blowout Type Air Break Circuit Breaker

Magnetic blowout air circuit breakers are used in voltage capacity up to 11KV. The extension of the arc can get by the magnetic field provided by the current in blowout coils.

This kind of circuit breaker provides magnetic control over the arc moment to create arc extinction in the devices. So, this extinction can be controlled through a magnetic field that is supplied by the flow of current within blowout coils. The connection of blow-out coils can be done in series through the circuit being disrupted.

As the name suggests, these coils are called ‘blow out the coil’. The magnetic field does not manage the arc which is made in the circuit breaker, however, it shifts the arc into arc chutes wherever the arc is cooled and extended accordingly. These types of CBs are utilized up to 11kV.

Air Chute Air Break Circuit Breaker

In the air chute air break circuit breaker, the main contacts are usually made up of copper and conduct current in closed positions. Air chute air break circuit breakers have low contact resistance and are silver plated. The arcing contacts are solid, resistant to heat, and are made up of copper alloy.

This circuit breaker includes two kinds of contacts like main & arcing or auxiliary. The designing of main contacts can be done with copper as well as silver plates which have less resistance & conduct the current within the closed location. Other types like arcing or auxiliary are designed with copper alloy because they are heat resistant.

These are used to avoid harming the main contacts because of arcing & they can be simply changed once required. While operating this circuit breaker, both the contacts are opened after & before closed the main contacts in the circuit breaker.

Air Blast Circuit Breaker

These kinds of circuit breakers are used for 245 KV and 420 KV system voltages & even more, particularly where quick breaker operation is necessary. The benefits of this circuit breaker as compared to oil type are listed below.

  • Fire hazard cannot be caused
  • The speed of breaking is high throughout the operation of this circuit breaker.
  • Arc quenching is faster throughout the operation of this breaker.
  • The arc duration is similar for all the values of currents disruptions.
  • Once the arc duration is less, so less amount heat can be realized from arc to contacts therefore the contact’s service life turns longer.
  • The maintenance of system stability is well maintained because it depends on the operation speed of the circuit breaker.
  • It needs less maintenance as compared to oil type circuit breaker.
  • The types of air blast circuit breakers are three types like an axial blast & an axial blast with a sliding moving contact & cross blast.

Air Circuit Breaker Maintenance

ACBs work like circuit protection devices for an extensive range of low voltage applications up to 600V AC like UPS, generators, mini power stations, MCCB distribution boards, etc and their sizes range from 400A to 6300A otherwise larger.

In this circuit breaker, nearly 20% of failures in the power distribution system occur due to less maintenance, tough grease, dust, corrosion & frozen parts. So maintenance of circuit breaker is the ideal choice to ensure consistent operation as well as expand the lifetime.

The air circuit breaker maintenance is very important. For that, it should be turned off first, and then separated from both faces by opening the required electrical isolator. The circuit breaker should be worked at this no isolated condition for restricted and distant areas in every year. The circuit breaker must be worked electrically from restricted and isolated after that mechanically from restricted. This kind of process will make the breaker more consistent by detaching any outside layer developed among sliding faces.

Air Circuit Breaker Testing Procedure

Circuit Breaker Testing is mainly used to check each switching system operation as well as the programming of the complete tripping construction. So, testing is very essential for any kind of circuit breaker to ensure secure and consistent performance. As compared to other devices, performing testing is more challenging.

When a malfunction occurs in a circuit breaker then it can lead to a short circuit within the coils, incorrect behavior, damage the mechanical connections, etc. Thus, circuit breakers need to test regularly to overcome all these faults.

Different types of tests performed in circuit breaker mainly include mechanical, thermal, dielectric, short circuit, etc. The routine tests of a circuit breaker are a trip test, insulation resistance, connection, contact resistance, overload tripping, instantaneous magnetic tripping, etc.

How Testing can be Performed?

For testing a circuit breaker, different kinds of test equipment are used to verify the condition of the circuit breaker in any power system. This testing can be performed through different test methods as well as kinds of testing equipment. The testing devices are analyzer, micro ohmmeter, primary injection tester with high current, etc. There are some benefits of circuit breaker testing like the following.

  • The performance of the circuit breaker can be enhanced.
  • The circuit can be checked on load or offload.
  • Recognizes requirement of maintenance
  • Issues can be avoided
  • Early indications of faults can be identified


The advantages of an air circuit breaker include the following.

  • High-speed re-closures facility
  • Used for frequent operation
  • Need less maintenance
  • High-speed operation
  • Fire risk can be eliminated not like in oil circuit breakers
  • Consistent and short arcing time, so burning of contacts is less


The disadvantages of air circuit breaker include the following.

  • A drawback of the arc chute principle is its inefficiency at low currents where the electromagnetic fields are weak.
  • The chute itself is not necessarily less efficient in its lengthening and de-ionizing action than at high currents, but the arc movement into the chute tends to become slower, and high-speed interruption is not necessarily obtained.

Applications of Air Circuit Breakers

Air Circuit Breakers are used for controlling the power station auxiliaries and industrial plants. They offer protection to industrial plants, electrical machines like transformers, capacitors, and generators.

  • They are mainly used for the protection of plants, where there are possibilities of fire or explosion hazards.
  • The air brake principle of the air breaker circuit arc is used in DC circuits and AC circuits up to 12KV.
  • The air circuit breakers have high resistance power that helps in increasing the resistance of the arc by splitting, cooling, and lengthening.
  • An air circuit breaker is also used in the Electricity sharing system and NGD about 15kV

Thus, this is all about Air Circuit Breaker (ACB), its working, and its applications. We hope that you have got a better understanding of this concept. Furthermore, any doubts regarding this concept or to implement any electrical and electronic projects, please give your feedback by commenting in the comment section below. Here is a question for you, what is the function of ACB?

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