An air Circuit Breaker (ACB) is an electrical device used to provide Overcurrent and short-circuit protection for electric circuits over 800 Amps to 10K Amps. These are usually used in low voltage applications below 450V. We can find these systems in Distribution Panels (below 450V). Here in this article, we will discuss the working of Air Circuit Breaker. Air circuit breaker is circuit operation breaker that operates in the air as an arc extinguishing medium, at a given atmospheric pressure. There are several types of Air circuit breakers and switching gears available in the market today that is durable, high-performing, easy to install and maintain. The air circuit breakers have completely replaced oil circuit breakers.
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Air circuit breakers operate with their contacts in free air. Their method of arc quenching control is entirely different from that of oil circuit-breakers. They are always used for a low-voltage interruption and now tends to replace high-voltage oil breakers. The below-shown figure illustrates the principle of air breaker circuit operation.
Air Circuit breakers generally have two pairs of contacts. The main pair of contacts (1) carries the current at normal load and these contacts are made of copper metal. The second pair is the arcing contact (2) and is made of carbon. When the circuit breaker is being opened, the main contacts open first. When the main contacts opened the arcing contacts are still in touch with each other. As the current gets a parallel low resistive path through the arcing contact. During the opening of main contacts, there will not be any arcing in the main contact. The arcing is only initiated when finally the arcing contacts are separated. The each of the arc contacts is fitted with an arc runner which helps. The arc discharge to move upward due to both thermal and electromagnetic effects as shown in the figure. As the arc is driven upward it enters in the arc chute, consisting of splatters.
The arc in the chute will become colder, lengthen and split hence arc voltage becomes much larger than the system voltage at the time of operation of air circuit breaker, and therefore the arc is extinguished finally during the current zero.
The air brake circuit box is made of insulating and fireproof material and it is divided into different sections by the barriers of the same material, as shown above, figure (a). At the bottom of each barrier is a small metal conducting element between one side of the barrier and the other. When the arc, driven upwards by the electromagnetic forces, enters the bottom of the chute, it is split into many sections by the barriers, but the each metal piece ensures electrical continuity between the arcs in each section, the several arcs are consequently in the series.
The electromagnetic forces within each and every section of the chute cause the arc in that section to start the form of a helix, as shown above, figure (b). All these helices are in series so that the total length of the arc has been greatly extended, and its resistance is abundantly increased. This will affect the current reduction in the circuit.
Figure (a) shows the development of the arc from the time it leaves the main contacts until it is within the arc chute. When the current next ceases at a current zero, the ionised air in the path of where the arc had been being in parallel with the open contacts and acts as a shunt resistance across both the contacts and the self-capacitance C, shown in below figure with red as a high resistance R.
When the oscillation starts between C and L as described for the idealised circuit breaker shown in Figure below, this resistance damps the oscillation heavily. Certainly, it is usually so heavy that the damping is critical, the oscillation cannot then take place at all, and the restriking voltage, instead of appearing as a high-frequency oscillation, rises dead-beat to its eventual value of peak generator voltage. This is shown below the lower waveform.
The air circuit breakers are mostly of three types and are widely used for maintaining the indoor medium voltage and switch gears of the home.
Plain brake air circuit breakers are the simplest form of air breakers. The main points of contacts are made in the shape of two horns. The arc of these circuit breakers extends from one tip to the other.
Magnetic blowout air circuit breakers are used in voltage capacity up to 11KV. The extension of the arc can get by magnetic field provided by the current in blowout coils
In air chute air break circuit breaker, the main contacts are usually made up of copper and conduct current in closed positions. Air chute air break circuit breakers have low contact resistance and they are silver plated. The arcing contacts are solid, resistant to heat and are made up of copper alloy.
Air Circuit Breakers are used for controlling the power station auxiliaries and industrial plants. They offer protection to industrial plants, electrical machines like the transformers, capacitors, and generators.
Thus, this is all about Air Circuit Breaker (ACB), its working and applications. We hope that you have got a better understanding of this concept. Furthermore, any doubts regarding this concept or to implement any electrical and electronic projects, please give your feedback by commenting in the comment section below. Here is a question for you, what is the function of ACB?
Air Circuit Breaker (ACB) is an electrical device used to provide Overcurrent and short-circuit protection for electric circuits over 800 Amps to 10K Amps. These are usually used in low voltage applications below 450V. We can find these systems in Distribution Panels (below 450V). Here in this article, we will discuss the working of Air Circuit Breaker. Air circuit breaker is circuit operation breaker that operates in the air as an arc extinguishing medium, at a given atmospheric pressure. There are several types of Air circuit breakers and switching gears available in the market today that is durable, high-performing, easy to install and maintain. The air circuit breakers have completely replaced oil circuit breakers.
Air circuit breakers operate with their contacts in free air. Their method of arc quenching control is entirely different from that of oil circuit-breakers. They are always used for a low-voltage interruption and now tends to replace high-voltage oil breakers. The below-shown figure illustrates the principle of air breaker circuit operation.
Air Circuit breakers generally have two pairs of contacts. The main pair of contacts (1) carries the current at normal load and these contacts are made of copper metal. The second pair is the arcing contact (2) and is made of carbon. When the circuit breaker is being opened, the main contacts open first. When the main contacts opened the arcing contacts are still in touch with each other. As the current gets a parallel low resistive path through the arcing contact. During the opening of main contacts, there will not be any arcing in the main contact. The arcing is only initiated when finally the arcing contacts are separated. The each of the arc contacts is fitted with an arc runner which helps. The arc discharge to move upward due to both thermal and electromagnetic effects as shown in the figure. As the arc is driven upward it enters in the arc chute, consisting of splatters.
The arc in the chute will become colder, lengthen and split hence arc voltage becomes much larger than the system voltage at the time of operation of air circuit breaker, and therefore the arc is extinguished finally during the current zero.
The air brake circuit box is made of insulating and fireproof material and it is divided into different sections by the barriers of the same material, as shown above, figure (a). At the bottom of each barrier is a small metal conducting element between one side of the barrier and the other. When the arc, driven upwards by the electromagnetic forces, enters the bottom of the chute, it is split into many sections by the barriers, but the each metal piece ensures electrical continuity between the arcs in each section, the several arcs are consequently in the series.
The electromagnetic forces within each and every section of the chute cause the arc in that section to start the form of a helix, as shown above, figure (b). All these helices are in series so that the total length of the arc has been greatly extended, and its resistance is abundantly increased. This will affect the current reduction in the circuit.
Figure (a) shows the development of the arc from the time it leaves the main contacts until it is within the arc chute. When the current next ceases at a current zero, the ionised air in the path of where the arc had been being in parallel with the open contacts and acts as a shunt resistance across both the contacts and the self-capacitance C, shown in below figure with red as a high resistance R.
When the oscillation starts between C and L as described for the idealised circuit breaker shown in Figure below, this resistance damps the oscillation heavily. Certainly, it is usually so heavy that the damping is critical, the oscillation cannot then take place at all, and the restriking voltage, instead of appearing as a high-frequency oscillation, rises dead-beat to its eventual value of peak generator voltage. This is shown below the lower waveform.
The air circuit breakers are mostly of three types and are widely used for maintaining the indoor medium voltage and switch gears of the home.
Plain brake air circuit breakers are the simplest form of air breakers. The main points of contacts are made in the shape of two horns. The arc of these circuit breakers extends from one tip to the other.
Magnetic blowout air circuit breakers are used in voltage capacity up to 11KV. The extension of the arc can get by magnetic field provided by the current in blowout coils
In air chute air break circuit breaker, the main contacts are usually made up of copper and conduct current in closed positions. Air chute air break circuit breakers have low contact resistance and they are silver plated. The arcing contacts are solid, resistant to heat and are made up of copper alloy.
Air Circuit Breakers are used for controlling the power station auxiliaries and industrial plants. They offer protection to industrial plants, electrical machines like the transformers, capacitors, and generators.
Thus, this is all about Air Circuit Breaker (ACB), its working and applications. We hope that you have got a better understanding of this concept. Furthermore, any doubts regarding this concept or to implement any electrical and electronic projects, please give your feedback by commenting in the comment section below. Here is a question for you, what is the function of ACB?
Air Circuit Breakers (ACBs) are vital components in electrical systems, offering protection against overcurrents, short circuits, and other electrical faults. They are commonly used in industrial, commercial, and large-scale residential applications due to their robustness and ability to handle high currents. Understanding the settings of an ACB is crucial for ensuring the safety and efficiency of the electrical system. This blog post will delve into the key settings of ACBs and how to properly configure them.
What is an Air Circuit Breaker (ACB)?
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An Air Circuit Breaker (ACB) is an electrical device used to protect an electrical circuit from damage caused by overcurrent, overload, or short circuits. Unlike other circuit breakers that use oil, vacuum, or gas to quench the arc, ACBs use air as the medium to extinguish the arc during circuit interruption.
Key Settings of an Air Circuit Breaker
To effectively use an ACB, it’s important to understand the various settings that control its operation. These settings ensure that the breaker responds correctly to different electrical conditions, providing both protection and continuity of service.
1. Overcurrent Protection (Ir or Long-Time Setting)
- Purpose: Protects the circuit from prolonged overcurrent conditions that can cause overheating and damage.
- Setting: This is usually set as a percentage of the full load current (In). For example, if In is A, and Ir is set to 0.8, the breaker will trip if the current exceeds 800A for a prolonged period.
2. Short-Time Protection (Isd or Short-Time Setting)
- Purpose: Protects against short circuits that occur close to the breaker, typically within the distribution system.
- Setting: Isd is often set as a multiple of the Ir value. The delay time can be adjusted to allow for selective coordination with downstream devices.
3. Instantaneous Protection (Ii or Instantaneous Setting)
- Purpose: Provides immediate protection against very high fault currents, such as those caused by a direct short circuit.
- Setting: This is usually set as a multiple of the full load current (In), and the breaker will trip instantly when the current exceeds this setting. Common settings range from 2x to 10x In.
4. Ground Fault Protection (Ig or Ground Fault Setting)
- Purpose: Detects and responds to ground faults, which can cause serious damage and pose safety hazards.
- Setting: Ground fault protection settings are typically lower than short-time or instantaneous settings. The sensitivity can be adjusted based on the specific requirements of the installation.
5. Neutral Protection (In or Neutral Protection Setting)
- Purpose: Protects the neutral conductor in cases where it may carry unbalanced loads or faults.
- Setting: This setting ensures that the neutral current is monitored and that the breaker trips if the current exceeds a safe level.
6. Arc Flash Protection
- Purpose: Provides additional protection against arc flash incidents by reducing the time it takes for the breaker to trip in the event of a fault.
- Setting: Often, ACBs are equipped with sensors and settings to reduce arc flash energy by ensuring quick tripping in case of a fault.
How to Properly Set an ACB
Setting an ACB involves understanding the electrical system's characteristics and the protection requirements. Here’s a general approach:
1. Determine Full Load Current (In): Calculate the full load current based on the connected load and system voltage.
2. Set Long-Time Protection (Ir): Adjust the Ir setting based on the full load current, ensuring it provides adequate protection against prolonged overcurrent without nuisance tripping.
3. Adjust Short-Time and Instantaneous Settings (Isd and Ii): Configure these settings to allow for selective tripping, ensuring that only the affected circuit is disconnected during a fault.
4. Configure Ground Fault Protection (Ig): Set this to a level that provides protection against ground faults while avoiding false trips.
5. Test and Verify: After setting the ACB, it’s crucial to test the system to ensure that the settings provide the desired level of protection and that the ACB operates correctly under fault conditions.
Conclusion
Understanding and correctly setting an Air Circuit Breaker is essential for the safety and reliability of any electrical system. Properly configured ACB settings protect against a wide range of electrical faults, minimizing the risk of damage and ensuring continuous operation. Always consult the manufacturer’s guidelines and, if necessary, seek professional assistance when configuring ACB settings to match the specific needs of your electrical installation.