Air Break Circuit Breaker (ACB)

Construction of Air Break Circuit Breaker :

• There are two sets of contacts. Main contacts and arcing contacts.
• Main contacts conduct the current in closed position of the breaker.
• They have low contact resistance and are silver-plated.
• The arcing contacts are hard heat resistant and are usually of copper alloy.
• Arcing horns and arc splitters are used to increase the length of arc.

• Figure(a) shows the construction details of air break circuit breaker in closed position while Figure(b) shows the air break circuit breaker in open position.

Operation of Air Break Circuit Breaker :

• In air break circuit breaker the contact separation and arc extinction take place in air at atmospheric pressure.
• As soon as the fault occurs the trip circuit gives command to circuit breaker and the contacts are opened.
• While opening the contact the main contact dislodge first. The current shifted to the arcing contacts.
• The arcing contacts dislodge later and arc is drawn between them.
• The arc core is conducting path of plasma. The surrounding medium contains ionised air.
• This arc is forced upward by the electromagnetic force and thermal action. The arc travels along the arcing horns.
• The arc moves upwards and is split by are splitter plates as shown by the arrow.
• By cooling the arc, the diameter of arc core is reduced. The arc is extinguished by lengthening, cooling and splitting.
• The arc resistance is increased to such an extent that the system voltage cannot maintain the arc and the arc gets extinguished at current zero of A.C. wave.