An air circuit breaker (ACB) is a type of circuit breaker that uses compressed air to extinguish the electric arc formed during the interruption of an electrical circuit. It is commonly used for protecting electrical circuits and equipment from over currents, short circuits, and other electrical faults.
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Here are some key features and characteristics of air circuit breakers:
Arc Interruption: When an electrical fault occurs, an arc is formed due to the flow of current. The ACB utilizes compressed air to blow out or quench the arc, thereby interrupting the current flow. The compressed air helps in cooling and deionizing the arc, making it easy to extinguish.
Ratings: Air circuit breakers are available in various current ratings to suit different applications. They can handle high current levels, typically ranging from hundreds of amperes to several thousand amperes.
Tripping Mechanism: ACBs incorporate a tripping mechanism to detect overcurrents or faults in the electrical system. The tripping mechanism may be based on thermal, magnetic, or electronic principles, depending on the specific design and application requirements.
Protection Functions: Air circuit breakers provide various protection functions, such as overcurrent protection, short circuit protection, ground fault protection, and earth leakage protection. These functions help safeguard electrical equipment and prevent damage caused by electrical faults. There are three coils in ACB Overcurrent coil, overvoltage coil & shunt coil. These coils are operates as per there name.
Settings and Adjustability: ACBs offer flexibility in terms of their settings and adjustable parameters. For example, they may have adjustable tripping thresholds, time delays, and other settings that can be tailored to meet specific requirements.
Durability: Air circuit breakers are known for their robust construction, making them suitable for demanding environments. They are designed to withstand high electrical and mechanical stresses, ensuring reliable operation over an extended period.
Maintenance: ACBs generally require regular maintenance to ensure proper functioning. This includes periodic inspection, cleaning, lubrication, and testing of the breaker mechanisms. The compressed air system also needs maintenance, such as monitoring air pressure and checking for leaks.
It's worth noting that while air circuit breakers have been widely used in the past, modern electrical systems often utilize other types of circuit breakers, such as vacuum circuit breakers or molded case circuit breakers, which offer additional advantages like compactness, better insulation, and higher interrupting ratings.
Construction & Working of ACB:
An air circuit breaker consists of a set of contacts, an operating mechanism, and an arc-extinguishing chamber. The contacts are made of copper or other suitable materials to carry the current. The operating mechanism controls the opening and closing of the contacts, and the arc-extinguishing chamber helps extinguish the electric arc that forms when the contacts separate.
The ACB is equipped with a trip unit, which is a protective device that detects abnormal electrical conditions such as overcurrent or short circuit faults. The trip unit monitors the current flowing through the circuit breaker and initiates the opening of the contacts when a fault is detected.
During normal operation, the contacts of the ACB are closed, allowing the current to flow through the circuit. The trip unit continuously monitors the current levels and remains in a standby mode.
If an overcurrent or short circuit fault occurs in the circuit, the current level exceeds the predetermined threshold set by the trip unit. The trip unit detects this abnormal condition and sends a signal to the operating mechanism.
Upon receiving the signal from the trip unit, the operating mechanism activates and initiates the opening of the contacts. The contacts start separating, creating an arc between them.
The arc-extinguishing chamber plays a crucial role in extinguishing the electric arc. It contains a set of arc chutes or plates designed to create a longer path for the arc and facilitate its cooling and interruption. The arc chutes or plates utilize the principle of arc quenching, such as magnetic blowout or arc splitting, to extinguish the arc.
As the arc is extinguished, the contacts are fully separated, breaking the circuit and interrupting the flow of current. This prevents further damage to the circuit and connected equipment.
After the fault is cleared, and the system is restored to a normal condition, the operating mechanism can be manually or automatically activated to close the contacts. Once the contacts are closed, the circuit is reestablished, and the ACB is ready for normal operation again.
There are some setting on ACB which is help to trip the MCB.
1. Continuous Amp(Ir) :
This setting is used to vary amp rating of breaker. You can adjust this setting by 20℅ to 100℅. This setting is used when your load is too low.
when your load is 600 Amp then it is costly or difficult to change breaker. So you can use this setting to minimize breaker capacity.
For Example: 1000 amp ACB who's this setting is set on 60℅ then this ACB will become 600 Amp breaker instead of 1000 Amp.
2. Long Time Delay:
This setting is used to pass inrush current through ACB without tripping.
Sometimes motors are taking large amount of current to start. At that time if current goes above capacity of ACB then this setting allow time to pass the extra capacity current. You can adjust this setting from 2.2 Sec to 27 Sec
For Example: 1000 Amp capacity ACB is trip when current goes above 1000 Amp but if you set this setting on 7 sec then ACB will allow 7 sec to pass that extra current through ACB. After 7 sec if current decrease then ACB will not trip and current is increased then ACB is trip.
3. Short Time Pickup:
This setting is used to trip ACB during short circuit. You can set the value of short circuit current in times ( from 1.5 time to 10 times).
For Example: when you set this setting on 3 that means 3 time of 1000. When short circuit happen in line & current will increase upto 3000 Amp then ACB will not trip. But when short circuit current goes upto or above 3001 Amp then ACB will trip.
4. Short Time Delay:
This setting used to provide time delay to trip ACB after short circuit happen. You can set this setting from 0.05 sec to 0.18 sec.
For Example: when you set this setting on 0.5 sec then ACB will trip after 0.5 sec of short circuit.
5. Instantaneous Pickup:
For Example: when you set this setting on 6 times then ACB will trip at 6000 Amp current flow instantly. There is a no time delay for this setting.
6. Ground Faulty Pickup:
There are three types of ground fault as per time delay which are 0.1, 0.2 & 0.4.
This setting is used to trip ACB when ground fault occurs. ACB is trip on what amount current is grounded.
For Example: when you set this setting on 0.4 and 20℅ then ACB will trip in 4 sec when 20℅ of current is ground.
nice information sir
ReplyDeleteVery well explained
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