ACB (Air Circuit Breaker) - Electrical C & V


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17 March 2020

ACB (Air Circuit Breaker)

ACB (Air Circuit Breaker)

Air Circuit Breaker - Extremely important equipment in electric switch gear equipment. The main function of the breaker is to take the electrical load and supply it further. And in an unusual situation the power supply has to be disconnected from the load. Apart from this, we can also 'OFF' the power supply according to our needs.

ACB (Air Circuit Breaker)
ACB LV (low voltage) is used on the side. Its voltage capacity is up to 450 volt. And ampere capacities range from 800 Ampere to 10,000 Ampere. Mostly used in industries to distribute the load in PCC Panel.

Why is Breaker called Air Circuit Breaker?

Circuit breakers are of different types. Such as oil circuit breaker, vacuum circuit breaker, air blast circuit breaker, SF6 circuit breaker and oil circuit breaker. These breakers are named on the basis of the means of extinguishing the electric arc occurring during the time of make and break.

Just as the electric arc in the oil circuit breaker is extinguished by the oil, hence it is called oil circuit breaker. Air is the medium for extinguishing the electric arc in the air circuit breaker, hence it is called air circuit breaker.

Working of Air Circuit Breaker 

Breaker's job is to make and break the circuit. The air circuit breaker has fixed and moving contacts. The contact is made from Cadmium-silver alloy. The property of which produces good resistance against the electrical arc. This contact is when the breaker is in operation. That means make and break, then a heavy spark (electrical arc) is generated.

When the circuit breaker opens, first main contact opens. At the same time, Auxiliary Contact are engaged. When the main contact is open, when the arching contact is open, the spark is at the same time. Which will not affect the main contact.


Likewise, when the breaker is closed, then the first auxiliary contact is connected. After that the main contacts are connected. When the arching contact is connected, only the electric arc will be generated, which will not affect the main contact.

An arc chute is also installed in the breaker. The arc length increases the length of the spark. And produces resistance, which reduces the strength of the spark.

Air Circuit Breaker has protection such as over load, short circuit and earth fault, over under voltage. Which disconnect the circuit from the supply at the time of any fault.

Air circuit breakers are 3 poles and 4 poles. A 3 pole circuit breaker consists of three poles of three phases, while a 4 pole consists of 3 poles and a neutral with 4 poles.

What is MDO and EDO Breaker?

MDO Breaker -
MDO (Manually Operated Draw out) This type of breaker has to do spring chasing manually. Its operation is also done manually. It is cheaper than EDO in price.

EOD Breaker -
EDO (Electrically Operated Draw out) can break this type of breaker both electrically and manually. It has an electric motor for spring charging. That is why spring is charged. It can be operated anywhere and remotely. And D.G can also close it in auto under AMF system.

Air Circuit Breaker circuits

1 - Closing Circuit

2 - Tripping Circuit

3 - Spring Charging Circuit

4 - UV Release

5 - Indicating Circuit

1. Closing Circuit -
The Closing Circuit gives the breaker a command to close. The closing coil gets command from the anti pumping connector, then the breaker is closed.

The electrical and mechanical interlock must be clear before the closing coil receives the command. Should the trip circuit be healthy then the breaker will get the command and close.

2. Tripping Circuit -
The tripping circuit leads to a breaker trip. The Air Circuit Breaker has a tripping coil. This is called shunt release. Protection such as over load, short circuit meaning fault over voltage, under voltage in the breaker. If any abnormality is found in any of it, then the tripping coil is supplied. Which disconnects the breaker from the power supply.

3. Under voltage Release -
UV is released on the side of the closing and shunt coil. Which senses the voltage. Which is called UV Release. The breaker will not close until the coil is energized.

4. Spring Charging Circuit -
The spring charging circuit is in the EDO type breaker. It has a single phase motor. Which automatically charges after the breaker's operation. You can also charge it manually.

5. Indicating Circuit -
The breaker is in which position, we can easily know from the indications. For example, if the breaker is 'ON' it is usually red indication. 'OFF' will show a green indication, if a trip, it will show yellow indication. If the trip circuit is healthy indication then it is usually white.

Air Circuit Breaker parts- Outer Structure


1. Front Cover -
Front breaker is front facing. And what appears in front is called front cover. Most breaker makers like to see the front cover make it like this, because it is the front part of the breaker.

2. Arc extinguish chamber -
where resistance of electric arc is increased and extinguished.

3. Control circuit terminal -
Where the breaker tripping, closing indicator and control wire of interlock circuit are connected it is called control terminal.

4. Electric Trip Relay -
It can be called Heart of Breaker. Where we get protection Over current, short circuit, earth fault and instantaneous setting are done in this relay. It usually occurs in the pay percentage. The breaker trip will be according to the value we set.

5. Count- 
The count, how many times the breaker is operated, how many times the breaker is closed, we know from the count. By the way, the operation capacity of Air Circuit Breaker is from 4 to 5 thousand.

6. Closing button- 
By which the breaker gets the command of closing.

7. Charging handle- 
This is used to manually charge the spring of the breaker.

8. Name plate -
The name plate has the complete information about the breaker, such as amperage capacity, ka rating, voltage, pole, type details, we get the information from the name plate itself.

9. Caution mark - 
This is an indication of caution.

10. position indicator - 
Test and service are two positions in the breaker. In the breaker test or in the service, this is what we know from this indication.

11. Pushing / Drawing lever hole -
Its work is important. Having drawn the breaker out, it is a push button, only after pressing it, the draw out handley will go inside. In a way, it is a mechanical interlock.

12. Charging indicator -
This indicator shows the breaker's spring charge in the current state, not the breaker's spring charge.

13. Extension rail -
When moving from breaker to test and from service to test position in the breaker, then it is the movement on the extension rail itself. It is also called rack in, rack out.

14. Trip button -
where the breaker is tripped off.

15. ON / OFF indicator -
Used to indicate the current position of the breaker is closed or open.

16. Draw-out profile - 
The breaker which is rack in and rack out is called the draw out profile.

17. Main body profile -
The cover in which I have a body, I call it body profile.

18-Handle - 
Handle is used to rack out the breaker into the rack.

ACB Internal Structure - Air Circuit Breaker

1- Front cover                                                2- Electronic trip relay
3- Auxiliary switch                                        4- Arc extinguish chamber
5- Closing coil                                               6- ON / OFF indicator
7- Closing mechanism                                   8- Trip mechanism 
9- Trip coil                                                    10- Charging handle 
11- Charging indicator                                  12- Draw-out mechanism
13- Position indicator                                    14- Gear block
15- Draw-out cam                                         16- Extension rail
17- Closing spring                                         18- Movable shunt
19-CB conn. conductor                                 20- Load side conductor 
21- Draw-out conductor                                22 - Breaking spring 
23- Power supply side conductor                  24- Fixed contact 
25- Traveling contact                                    26- Draw-out main body

Air Circuit Breaker Maintenance

1- It is mandatory for any equipment to take permission from the first related department of maintenance.

2- Before starting the maintenance of the breaker, confirm that the panel is not completely isolated.

3- Take out the breaker from the service position so that you can work in this way.

4- Clean the entire breaker, clean old grease and dust thoroughly.
Do not use sand paper or emery paper to clean the contact of the breaker. Because they can remove the material of the contact.

5- Use a smooth cloth and CRC 2-26 to clean the old grease.

6- All the moving parts except the contact are greased using syn tho-lube 10 of LEACH or LIT HON ​​2 grease. Be careful not to over-grease, otherwise it is also a loss factor.

7- Mechanical parts are checked, if any damage is found, it is replaced.

8- The status of the current transformer (CT) is checked, its connection is checked.

9 - Control terminal terminalness and fuse stabilization in the breaker panel are investigated.

10- Check the spring and arc chute used in the breaker. Replace it if necessary.

11- After maintenance, the insulation resistance (IR) value is checked from the megger of 500 Volt. Between the line and load in the open position of the breaker, in the close position the phase is checked and the phase to phase is checked. The value of which should be more than 1 mega ohm.

The setting of the relay in the 12-Air circuit Breaker is checked according to our requirement and not.

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