The Air Blast Industrial Circuit Breaker

 

Air blast industrial circuit breaker are used today from 11 to 1100 KV for a range of applications. They offer several advantages: faster operations, suitability for related operation, auto-reclosure, unit type multi-break construction, simple assembly, and modest maintenance. A compressor plant is necessary to maintain high air pressure in the receiver. Air blast industrial circuit breakers are used for interconnected lines as well as lines in which rapid operation is desired.

Construction of the Air Blast Industrial circuit breaker

In the air blast industrial circuit breaker (also called a compressed air circuit breaker), high pressure air is forced on the arc through a nozzle at the instant of contact separation. The ionized medium between the contacts is blown away by the blast of the air. After the arc extinction, the chamber is filled with high pressure air, which prevents re-strike. In some low capacity industrial circuit breakers, the isolator is an integral part of the industrial circuit breaker. The industrial circuit breaker opens and immediately after that the isolator opens, to provide an additional gap.

Two Types of Air Blast Industrial Circuit Breakers

Air blast industrial circuit breakers are classified according to the type of air blast around the contacts for arc extinction. They are: 1) Axial-blast air industrial circuit breakers and 2) Cross blast air industrial circuit breakers.

    1. Axial-blast Industrial Circuit Breaker: This type of an industrial circuit breaker consists of fixed and moving contacts that are held in closed position by spring pressure under normal conditions. The air reservoir is connected to the arcing chamber through an air valve. This valve remains closed under normal conditions but opens automatically by tripping impulse when a fault occurs in the system.

 

When a fault occurs, the tripping impulse causes the opening of the air valve which connects the circuit breaker reservoir to the arcing chamber. The high pressure air entering the arcing chamber pushes away the moving contact against the spring pressure.

The moving contact is separated and an arc is struck. At the same time, high pressure air blast flows along the arc and takes away the ionized gases along with it. Consequently, the arc is extinguished and current flow is interrupted.

    1. Cross Blast Air Industrial Circuit Breaker: In this type of industrial circuit breaker, an air blast is directed at right angles to the arc. The cross-blast lengthens and forces the arc into a suitable chute for arc extinction.

 

When the moving contact is withdrawn, the arc is struck between the fixed and moving contacts. As a result, the high pressure cross blast forces into a chute consisting of arc splitters and baffles. The splitters serve to increase the length of the arc as the baffles provide improved cooling. The result is that the arc is extinguished and flow of current is interrupted. Since the blast pressure is the same for all currents, the inefficiency at low currents is eliminated. The final gap for interruption is great enough to give normal insulation clearance so that the series isolating switch is not necessary.