Air Circuit Breaker

Schneider Electric (NW&NT) air circuit breaker 

Air Circuit Breaker (ACB)

The type of circuit breaker, which operates in air (where air-blast as an arc quenching medium) at atmospheric pressure, is known to be an Air Circuit Breaker. Air circuit breaker has completely replaced by oil circuit breaker. In different countries, still it is a preferable choice to use an Air circuit breaker up to 15KV because, there is no chance of oil fire like in oil circuit breaker.

Construction of Air-Circuit Breaker

For Example of one of famous Circuit breaker, we explain the construction Schneider Electric NW

1- Shunt trip (MX2) or Under voltage trip device (MN)

2-Auxiliary control connection

3-Trip unit connection to overcurrent trip switch

4-Lifting tab

5-Cradle rejection kit

6-Cluster

7-Overcurrent trip switch (SDE2) or electric reset

8-Circuit breaker communication module

9-Overcurrent trip switch (SDE1)

10-Arc Chamber

11-Shunt Trip (MX1)

12-Auxiliary contact connection

13-Two blocks of four additional switches (OF) or combined "connected. closed "  switches (EF)

14-Block of four from C auxiliary contact (OF)

15-Shunt close (XF)

16-Ready to close contact (PF)

17-Charging Handle

18-Spring charging Motor(MCH)

19-Closing Push button

20-Opening push button

21-Operation counter

22-Trip unit

23-Electrical close pushbutton (BPFE)

24-Padlock attachment

25-Key interlock

26-Accessory cover

27-Push to reset on fault trip

28-Open / close indicator

29-Charged / discharged

30-Faceplate  

The working principle of Air Circuit Breaker:

The working principle of Air Circuit breaker is rather different from other types of circuit breaker. The main aim of circuit breaker is to prevent reestablishment of arcing after current zero where the contact gap will withstand the system recovery voltage. It does it same work, but in a different manner. During interruption of arc, it creates an arc voltage instead of supply voltage. Arc voltage is defined as the minimum voltage required for maintaining arc .The circuit breaker increases the voltage in three different ways:

Arc voltage can be increased by cooling arc plasma. As soon as the temperature of arc plasma motion of particle in arc plasma is reduced, more voltage gradient will be required to maintain the arc.

By splitting the arc into a number of series will increases the arc voltage.

Arc voltage can be increased by lengthening the arc path. As soon length of arc path is increased the resistance path will increase more arc voltage is applied across the arc path hence arc voltage is increased.

It is operated within voltage level up to 1 KV. It contains two pairs of contact. The main pair carries the current and the contact made of copper. An additional pair of contact is made of carbon. When the breaker is opened, the main contact opens first. During opening of the main contact, the arc contact remains in touch with each other. The arcing gets initiated when arc contacts are separated. The circuit breaker is obsolete for medium voltage.