Air Circuit Breakers

 Air Circuit Breakers

Air circuit breaker is defined as a circuit breaker, in which the contacts open and close in air at atmospheric pressure. In general, the use of this type of circuit breakers is restricted to low voltage applications or high security installations where the risk of an oil fire or oil contamination of the environment is too high to be tolerated. Countries following the American practice used air circuit breakers almost exclusively for systems
up to 15 kV until the advent of the new vacuum and SF6 technologies.

The principles of arc interruption used in an air circuit breaker are rather different from those in any other type of circuit breaker. However, the objective is the same for both categories of the circuit breakers, i.e. to prevent the resumption of arcing after current zero by creating a situation wherein the contact gap will withstand the system recovery voltage; the air circuit breaker does this by creating an arc voltage in excess of the supply voltage. This can be achieved in three ways:

1- Intense cooling of the arc plasma, so that the voltage gradient is very high
2- Lengthening the arc path to increase the arc voltage
3- Splitting up the arc into a number of series arcs

Although these circuit breakers are considered obsolete for medium voltage applications, they continue to be preferred choice for high current rating in low voltage applications.