Air Circuit Breaker (ACB) : Construction, Operation, Types & Applications

Air Circuit Breaker (ACB) : Construction, Operation, Types & Applications

Table of Contents 

What is a Circuit Breaker?
Air Circuit Breaker
Construction of Air-Circuit Breaker
Principle of Operation of Air Circuit Breaker
Types of Air Circuit Breaker

Plain air circuit breaker or Cross-Blast Air Circuit Breaker:
Air Chute Air Break Circuit Breaker
Magnetic Blowout Type Air Break Circuit Breaker
Air Blast Circuit Breaker:

Axial blast breaker
Axial blast with sliding moving contact

What is a Circuit Breaker?

A circuit breaker is a device, which can
Make or break a circuit manually or by remote control under normal conditions.
Break a circuit automatically under fault conditions (like over current, Short circuit, etc).
Make a circuit manually or by remote control under the fault conditions.
A circuit breaker is used for switching mechanism and protection of the system. Other associated devises and components are also used for this purpose associated with circuit breakers like fuses, relays, switches etc. Circuit breakers are widely used in industries as well as power system for controlling and protection of different parts of the circuit like switch gears, Transformers, Motors, Generators/Alternator etc., which leads the system stable and reliable.
There are different types of air circuit breakers available in the market and we will discuss one by one in detail.

Air Circuit Breaker
The type of circuit breaker, which operates in air (where air-blast as an arc quenching medium) at atmospheric pressure, is known to be an Air Circuit Breaker. Air circuit breaker has completely replaced by oil circuit breaker. In some countries, still it is a preferable choice to use an Air circuit breaker up to 15KV because, there is no chance of oil fire like in oil circuit breaker.

Construction of Air-Circuit Breaker
The following fig shows the main and external parts of an ACB. Low Voltage, Current Limiting Air Circuit Breaker and Selective (Non-Current Limiting) Air Circuit Breaker).

Circuit Breaker External labels (Rated Current and Voltage = 1000A, 415V)

  1. OFF button (O)
  2. ON button (I)
  3. Main contact position indicator
  4. Energy storage mechanism status indicator
  5. Reset Button
  6. LED Indicators
  7. Controller
  8. “Connection”, “Test” and “isolated” position stopper (the three-position latching/locking mechanism)
  9. User-supplied padlock
  10. Connection “,” Test “and” separation “of the position indication
  11. Connection (CE) Separation, (CD) Test (CT) Position indication contacts
  12. Rated Name Plate
  13. Digital Displays
  14. Mechanical energy storage handle
  15. Shake (IN/OUT)
  16. Rocker repository
  17. Fault trip reset button

The following fig shows the Internal Construction of Air Circuit Breaker

( Low Voltage Current Limiting Air Circuit Breaker and Selective (Non-Current Limiting) Air Circuit Breaker)

    1.   Sheet Steel Supporting Structure

    2.   Current Transformer for Protection Trip Unit

    3.   Pole Group insulating box

    4.   Horizontal rare terminals

    5a. Plates for fixed main contacts

    5b. Plates for fixed arcing Contacts

    6a. Plates for Main moving contacts

    6b. Plates for Moving Arcing contacts

    7.   Arcing Chamber

    8.  Terminal box for fixed version – Sliding Contacts for withdrawable version

    9.   Protection Trip Unit

    10. Circuit breaker Closing and Opening Control

    11. Closing Springs

Principle of Operation of Air Circuit Breaker
The working principle of Air Circuit breaker is rather different from other types of circuit breaker. The main aim of circuit breaker is to prevent reestablishment of arcing after current zero where the contact gap will withstand the system recovery voltage. It does it same work, but in a different manner. During interruption of arc, it creates an arc voltage instead of supply voltage. Arc voltage is defined as the minimum voltage required for maintaining arc .The circuit breaker increases the voltage in three different ways:

1)  Arc voltage can be increased by cooling arc plasma. As soon as the temperature of arc plasma motion of particle in arc plasma is reduced, more voltage gradient will be required to maintain the arc.
2) By splitting the arc into a number of series will increases the arc voltage.
3) Arc voltage can be increased by lengthening the arc path. As soon length of arc path is increased the resistance path will increase more arc voltage is applied across the arc path hence arc voltage is increased.

It is operated within voltage level up to 1 KV. It contains two pairs of contact. The main pair carries the current and the contact made of copper. An additional pair of contact is made of carbon. When the breaker is opened, the main contact opens first. During opening of the main contact, the arc contact remains in touch with each other. The arcing gets initiated when arc contacts are separated. The circuit breaker is obsolete for medium voltage.

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