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1. Air Circuit Breaker (ACB) is used to provide Overcurrent and short-circuit protection. 
2. Air as an arc extinguishing medium.

Air Circuit Breaker Working

1. Air Circuit breakers generally have two pairs of contacts.
2.  The main pair of contacts (1) carries the current at normal load and these contacts are made of copper metal. 
3. The second pair is the arcing contact (2) and is made of carbon. 
4. When the circuit breaker is being opened, the main contacts open first. When the main contacts opened the arcing contacts(2) are still in touch with each other.
5.  As the current gets a low resistive path through the arcing contact. During the opening of main contacts, there will not be any arcing in the main contact. 
6. The arcing is only initiated when finally the arcing contacts are separated.
7. The each of the arc contacts is fitted with an arc runner. The arc discharge to move upward due to both thermal and electromagnetic effects as shown in the figure. As the arc is driven upward it enters in the arc chute, consisting of splatters.
8. The arc in the chute will become colder, lengthen and split, the arc is extinguished finally during the current zero.

Operation

Main contact are kept close and isolated against high spring force

Quick act trip by reverse spring

Arc contact close earlier and open earlier than main contact, cooling and spitting arc by arc chute

Closing coil operate on Dc power from rectifier and is engergised by closing relay operated by push

 

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