AIR CIRCUIT BREAKER BASIC INFORMATION AND TUTORIALS

What Are Air Circuit Breakers And How Does Air Circuit Breaker Works?

The usual construction of an air circuit breaker makes use of two fixed terminals mounted one above and the other in a vertical plane, which, when the breaker is closed, are bridged under heavy pressure by a bridging member operated by a system of linkages.

Auxiliary and arcing contacts close before and open after the main contacts. The arcing contacts are easily renewable. The breaker is held closed by a latch which may be tripped electrically or mechanically.

Modern breakers are trip-free.

Many breakers use a solid bridging member with spring-mounted self-aligning contacts. The contact surfaces are made of silver so that oxidation will not cause excessive resistance and overheating.

Arcing contacts of modern breakers use a silver-tungsten or copper-tungsten alloy which is arcresistant. The secondary contacts, where used, are usually of copper or silver alloy.

Barriers between poles are generally furnished with breakers on ac and dc circuits 250 V and above, and special arc chutes, quenchers, or deionizing chambers are also used throughout the available lines of air circuit breakers.

These devices are made in different forms by different manufacturers and serve to improve the interrupting performance of the breaker and to shorten the arcing time.

Air-insulated high-voltage electrical equipment is generally covered by standards based on assumed ambient temperatures and altitudes. Ambient temperatures are generally rated over a range from –40°C to +40°C for equipment that is air insulated and dependent on ambient cooling.

At higher altitudes, air density decreases, hence the dielectric strength is also reduced and derating of the equipment is recommended. Operating (strike distances) clearances must be increased to compensate for the reduction in dielectric strength of the ambient air.

Also, current ratings generally decrease at higher elevations due to the decreased density of the ambient air, which is the cooling medium used for dissipation of the heat generated by the load losses associated with load current levels.