AIR CIRCUIT BREAKERS
Air Circuit Breakers (ACB’s) are used for medium and low voltages. In air circuit breakers, the interrupting contacts are situated in air instead of any other medium. The arc produced is chopped into number of small arcs by the arc-chute as it rises due to heat and magnetic forces.
In such circuit breakers high resistance principle is employed for effective arc extinction. The arc is lengthened by means of the arc runners and arc chutes thus increasing the resistance. Arc resistance can be increased in the following ways:
1. Cooling: When the temperature is decreased by cooling the voltage required to maintain the ionization of the air increases which in turn increases the resistance.
2.Lengthening: As the length of the arc increases the resistance also increases.
3.Splitting: An appreciable voltage is absorbed at the two contact surfaces so that on splitting of an arc into a number of small arcs in series the voltage available for the actual arc column is reduced.
Figure shows a typical construction of an air circuit breaker. It consists of two sets of contacts viz. Main Contact and Arcing Contact. The arc chute is used for arc extinction process. When fault occurs in the system, the main contacts are separated initially, the current then shifts towards the arcing contacts. The arcing contacts also separates now drawing an arc between them. This arc is then moved up by arc chutes along the arc runner. The arc moves upwards and is split by the arc splitter plates. The ac is then extinguished by the high resistance method as illustrated above.
Application:
This type of circuit breaker is used for mainly medium and low voltages and low breaking capacity. they become more bulky, the arc chute design more complex and the cost will be much higher as the voltage and breaking capacity increases .
The ACB are usually applied for control of power station auxiliaries and industrial plants switchgears. They are also used for control of motor loads and furnaces where repeated switching are to be performed, where OCBs are not performed.
Air Circuit Breakers (ACB’s) are used for medium and low voltages. In air circuit breakers, the interrupting contacts are situated in air instead of any other medium. The arc produced is chopped into number of small arcs by the arc-chute as it rises due to heat and magnetic forces.
In such circuit breakers high resistance principle is employed for effective arc extinction. The arc is lengthened by means of the arc runners and arc chutes thus increasing the resistance. Arc resistance can be increased in the following ways:
1. Cooling: When the temperature is decreased by cooling the voltage required to maintain the ionization of the air increases which in turn increases the resistance.
2.Lengthening: As the length of the arc increases the resistance also increases.
3.Splitting: An appreciable voltage is absorbed at the two contact surfaces so that on splitting of an arc into a number of small arcs in series the voltage available for the actual arc column is reduced.
Figure shows a typical construction of an air circuit breaker. It consists of two sets of contacts viz. Main Contact and Arcing Contact. The arc chute is used for arc extinction process. When fault occurs in the system, the main contacts are separated initially, the current then shifts towards the arcing contacts. The arcing contacts also separates now drawing an arc between them. This arc is then moved up by arc chutes along the arc runner. The arc moves upwards and is split by the arc splitter plates. The ac is then extinguished by the high resistance method as illustrated above.
Application:
This type of circuit breaker is used for mainly medium and low voltages and low breaking capacity. they become more bulky, the arc chute design more complex and the cost will be much higher as the voltage and breaking capacity increases .
The ACB are usually applied for control of power station auxiliaries and industrial plants switchgears. They are also used for control of motor loads and furnaces where repeated switching are to be performed, where OCBs are not performed.
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