What is Air Circuit Breaker
In air circuit breakers the atmospheric pressure air s used as an arc extinguishing medium. the principle of high resistance interruption is employed for such type of breakers. The length of the arc is increased using arc runners which will increase its resistance in such a way that the voltage drop across the arc becomes mom than the supply voltage and the arc will he extinguished This type of circuit breaker is employed in both ac and d.c. type of circuits upto 12 kV. These are normally indoor type and installed on vertical panels. The lengthening of arc is done with the help of mangetic fields. Some typical ratings of this type of circuit breaker are 460V – 3.3 kV with current range 400 – 3503 A or 6.6 kV with current range 403-2400 A etc.
Air Circuit Breaker Construction
It consists of two sets of contacts
1) Main contacts
2) Arcing contacts
During the normal operation the main contacts are closed. They are having low resistance with silver plating. The arcing contact: are very hard, heat resistant. They are made up of copper alloy. Arc runners are provided at the one end of arcing contact. On the upper side arc splitter plates are provided.
Air Circuit Breaker Working Principle
Working As seen from the Fig the contacts remain in closed position during normal condition. Whenever fault occurs, the tripping signal makes the circuit Current breaker contacts to open. The arc is drawn in between the contacts When ever the arc is struck between the contacts, the surrounding air gets ionized. The arc is then cooled to reduce the diameter of arc core. While separating the main contacts are separated first. The current is then shifted to arcing contains. Later on the arcing contacts also start separating and arc between them is forced upwards by the electromagnetic forces and thermal action. The arc travels through the arc runners. Further it moves upwards and split by arc splitter plates. Due to all this finally the arc gets extinguished as the resistance of the arc is increased. Due to lengthening and cooling, arc resistance increases which will reduce the fault current and will not allow reaching at high value.
The current zero points in the ac. wave will help the arc extinction with increase in arc resistance the drop across it will go on increasing. Whenever arc leaves the contacts it is passed through arc runners with the help of blow out coils which provide a magnetic field due to which it will experience a force as given by electromagnetic theory (F = 131/). This force wilts assist in moving the arc upwards. The magnetic field produced is insufficient to extinguish the arc. For systems having low inductances arc gets extinguished before reaching extremity of runners because lengthening of arc will increase the voltage drop which is insufficient to maintain the arc.
For high inductance circuits if it is not extinguished while travelling through arc runners then it is passed through arc splitters where it is cooled. This will make the effective deionized by removing the heat from arc.
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