CIRCUIT BREAKERS:PLAIN BREAK TYPE AND MAGNETIC BLOWOUT TYPE

PLAIN BREAK TYPE

The plain break type is the simplest type of air-break circuit breaker. The contacts are made in the shape of two horns, as illustrated in Fig. 19.4. The arc initially strikes across the shortest distance between the horns. Then it is driven steadily upward by the convection currents which are caused by heating the air during arcing. The arc extends between the horns. This results in lengthening and cooling of the arc.

The arc interruption process is relatively slow. It limits the application of these circuit breakers to 500 V and low-power circuits.

MAGNETIC BLOWOUT TYPE

This type of circuit breaker extinguish the arc by means of a magnetic blast. It is limited to circuits up to 11 kV. The arc is subjected to the action of a magnetic field set up by coils

connected in series with the circuit being interrupted (Fig. 19.5). These coils are called blowout coils because they help blow out the arc magnetically. The arc is magnetically blown into arc chutes where the arc is lengthened, cooled, and extinguished.

The breaking action becomes more effective with heavy currents. This results in higher breaking capacities for these breakers.

The arc chute is an efficient device for quenching the arc in air. It performs the following interrelated functions:

1. It confines the arc within a restricted space.

2. It provides control of the movement of the arc to ensure extinction occurs within the device.

3. It cools the arc gases to ensure extinction by deionization.