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【 ACB 】| All you need to know about Air Circuit Breaker

October 21, 2019

【 ACB 】| All you need to know about Air Circuit Breaker

What is ACB – Air Circuit Breaker?

Air Circuit Breaker (ACB) is electronic equipment that is used for the protection of electric circuits from short circuits or overcurrent. The ACB operates at atmospheric pressure in air. ACB is used in the switching mechanism and protection of the electrical system. 

Working Principle of Air Circuit Breaker

When a fault occurs in a circuit, the first main contacts of ACB are separated and current of the circuit is shifted to another contact termed as arching contact. The arcing contacts get disconnected and the arc is pulled away from the contacts. With the phenomena of electromagnet effect the arc is moved upward. The arc runner allows the arc ends to travel with itself. With the movement of arc runner, arc is allowed to move upward and the connection is split in this way.

The current keeps on flowing when the circuit is open so there is a need to extinguish the electrical arc to prevent it from reformation. Different dielectric materials like oil or gases are used and for Air circuit breakers, atmospheric air as a dielectric is used.

The air act as a resistance to the arc. Air acts as an insulator and forces arc to extinguish faster. It also prevents the arc to reform when it reaches zero, in case of alternating current, during its change in cycle. For high voltage applications like electrical substations, pressurized air is used so that circuit breakers can be used in those high voltage applications. In high voltage applications, pressurized air as a dielectric is used as it has a higher value of dielectric constant than atmospheric air. 

Air Circuit Breaker Function

Functions of Air Circuit Breaker are:

  • It opens or closes a circuit automatically or manually.
  • Open circuit automatically when a fault take place such as over current, short circuit, earth fault, over frequency, reverse power, etc.
  • It dampens the arcing in case of overloading

Type of ACB

Plain Break type ACB:

  • Plain ACB is the simplest form of the air circuit breaker. Their point of contact is in the shape of 2 horns. In this type of circuit, the arc of the breaker extends from one tip to the other tip.

Magnetic Blowout Type ACB:

  • Magnetic blowout ACBs are the breakers that are used where the voltage capacity is up to 11KV. The arc in this type of circuit gets extended by the current in blowout coils which produce a magnetic field to produce extension in the arc.

Air Chute ACB:

  • In this type of ACB, the main contacts are made up of copper. The current is conducted in closed positions of the contacts. Their contact resistance is very low. Their contacts are silver-plated. They are solid and heat resistant. 

Air Blast Circuit Breaker

  • These types of circuit breakers are used for heavy voltages of 245kV, 420kV or more. They have further categories:
    • Axial Blast Breaker
    • Axial Blast with Sliding Moving Contact

Application of ACB

Some of the applications of Air Circuit Breakers are:

  • ACB is used for the protection of industrial plants and electrical machines such as capacitors, generators, and transformers, etc.
  • ACB is mainly used in plants where there is a risk of fire or explosion.
  • ACB is also used in NGD and Electricity Sharing System
  • They are also used for controlling power station auxiliaries
  • Also used in Low/High Current and voltage applications
  • Also used in maintaining the switchgear and indoor medium voltage.

Drawback of Air-Break Circuit Breaker

Some of the drawbacks of ACB are:

  • Inefficiency at low current when the electromagnetic field is weak.
  • The chute of breaker is not less efficient in its lengthening action at high currents, instead, the movement of the arc into the chute of breaker tends to become slower.

Ratings of ACB

Air circuit breakers come in with different ratings as different circuits utilize different current and voltage ratings. However the standard ratings of the ACB’s lie in the range of 400A to 1600A. Similarly, another class of ACB lies in 2000A to 5000A rating. The standard current ratings of the ACB are these however, the voltage, the physical ratings of the ACB vary from manufacturer to manufacturer.

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