Air break circuit breaker

These circuit breakers employ high resistance interruption principle. The arc is rapidly lengthened by means of the arc runners and arc chutes and the resistance of the arc is increased by cooling, lengthening and spilitting the arc. The arc resistance increases to such an extent that the voltage drop across the arc becomes more than the supply voltage and the arc extinguished.

Air breaker circuit breakers are used in d.c circuits and a.c circuits upto 12 kV.

Magnetic field is utilized for lengthening the arc in high voltage air break circuit breaker.

The arc resistance is increased to such an extent that the system voltage cannot maintain the arc and the arc gets extinguished.

There are two set of contacts: Main contacts (1) and Arching contacts (2).

Main contacts conduct the current in closed position of the breaker. They have low contact resistance and are silver plated. The arching contacts (2) are hard, heat resistance and usually made of copper alloy. While opening the contact, the main contacts dislodge first. The current is shifted to the arching contacts. The arching contacts dislodge later and arc is drawn between them (3). This arc is forced upwards by the electromagnetic force and thermal action. The arc ends travel along the Arc Runner (Arcing horns). The arc moves upwards and is split by arc splitter plates (5). The arc is extinguished by lengthening, cooling, splitting etc. In some breakers the arc is drawn in the direction of the splitter by magnetic field.

Operating Mechanisms for Air Break Circuit Brreakers

The operating mechanisms are generally operating spring. The closing force is obtained from the following means:

a. Solenoid
b. Spring charged manually or by motor
c. Pneumatic

The solenoid mechanisms drive power from battery supply or rectifiers. The solenoid energized by the direct current gives the necessary force for the closing of the circuit breaker.

The springs used for closing operation can be charged either manually or by motor driven gears. At the time of closing operation the energy stored in the spring is released by unlatching of the spring and is utilized in closing of the circuit breaker.

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