Air Circuit Breaker (ACB): Construction, Operation, Types, and Uses.

Air circuit breakers (ACBs) are essential devices used in electrical systems for short circuit and overcurrent protection. They play a critical role in maintaining the stability and reliability of the system. In this article, we will explore the construction, operation, types, advantages, and applications of air circuit breakers.

Table of Contents

1. What is a Circuit Breaker?
2. Air Circuit Breaker (ACB)
3. Construction of Air-Circuit Breaker
4. Principle of Operation of Air Circuit Breaker
5. Types of Air Circuit Breaker

• Plain air circuit breaker or Cross-Blast Air Circuit Breaker
• Air Chute Air Break Circuit Breaker
• Magnetic Blowout Type Air Break Circuit Breaker
• Air Blast Circuit Breaker

1. Advantages & Disadvantages of Air Blast Circuit Breaker
2. Application and Uses of Air Circuit Breaker

What is a Circuit Breaker?

A circuit breaker is a device used to make or break a circuit manually or by remote control under normal conditions. It also breaks a circuit automatically under fault conditions such as overcurrent or short circuit. The main purpose of a circuit breaker is to protect the electrical system and prevent damage to connected devices.

Circuit breakers are widely used in industries and power systems to control and protect various parts of the circuit, including switch gears, transformers, motors, and generators. They work in conjunction with other devices such as fuses, relays, and switches to ensure the safety and reliability of the system.

Air Circuit Breaker (ACB)

An air circuit breaker (ACB) is an electrical protection device used for short circuit and overcurrent protection. It operates in air at atmospheric pressure and uses air blast as an arc quenching medium. ACBs are commonly used in low voltage applications, up to 15kV, with amperage ratings ranging from 800A to 10kA.

ACBs have replaced oil circuit breakers in many applications due to their advantages, such as eliminating the risk of oil fire and being more compact in size. They are suitable for frequent operation and provide reliable protection for electrical systems.

Construction of Air-Circuit Breaker

The construction of an air circuit breaker consists of various components that work together to ensure its proper functioning. The main parts of an ACB include:

1. Main and Auxiliary Contacts: The ACB has two pairs of contacts — the main contacts, made of copper, carry the current, while the auxiliary or arcing contacts, made of copper alloy, prevent damage to the main contacts due to arcing.
2. Arc Chute: The arc chute is a chamber surrounding the contacts. It is made of refractory material and is designed to cool and extinguish the arc. The inner walls of the arc chute are shaped to force the arc into close proximity, allowing it to be quenched effectively.
3. Trip Unit: The trip unit is responsible for detecting faults and initiating the opening of the contacts. It consists of protective relays and sensors that monitor the current and voltage levels in the circuit.
4. Closing and Opening Mechanism: The closing and opening mechanism controls the operation of the ACB. It includes springs, solenoids, and mechanical linkages that ensure smooth and reliable switching.

Principle of Operation of Air Circuit Breaker

The principle of operation of an air circuit breaker is based on the creation of an arc voltage instead of the supply voltage during arc interruption. The ACB increases the voltage in three ways:

1. Cooling the Arc Plasma: By cooling the arc plasma, the temperature and motion of particles in the arc plasma decrease, requiring a higher voltage gradient to sustain the arc.
2. Arc Splitting: The arc is split into multiple series arcs, increasing the arc voltage.
3. Lengthening the Arc Path: By lengthening the arc path, the resistance of the arc path increases, resulting in a higher applied voltage and increased arc voltage.

When the ACB is opened, the main contacts open first, but the arcing contacts remain in contact. The arcing contacts separate, initiating the arc. The ACB uses these principles to ensure efficient arc interruption and protect the electrical system.

Types of Air Circuit Breaker

There are several types of air circuit breakers available in the market, each with its own design and operational characteristics. The common types of ACBs include:

1. Plain Air Circuit Breaker or Cross-Blast Air Circuit Breaker:

• This type of ACB uses an arc chute to quench the arc. The arc chute is divided into small compartments by metallic separation plates, ensuring effective arc extinction.

1. Air Chute Air Break Circuit Breaker:

• In this type, the ACB has main and auxiliary contacts. The auxiliary contacts prevent damage to the main contacts due to arcing and can be easily replaced when needed.

1. Magnetic Blowout Type Air Break Circuit Breaker:

• Magnetic blowout ACBs use blowout coils connected in series with the circuit being interrupted. The magnetic field generated by the coils helps control and extinguish the arc.

1. Air Blast Circuit Breaker:

• Air blast circuit breakers are used for high-voltage applications. They are further divided into axial blast breakers and axial blast with sliding moving contact breakers.

Each type of ACB has its own advantages and disadvantages in terms of arc interruption capability, size, maintenance requirements, and application suitability.

Advantages & Disadvantages of Air Blast Circuit Breaker

Air blast circuit breakers offer several advantages and disadvantages compared to other types of circuit breakers. Let’s explore them:

Advantages:

• Suitable for applications requiring frequent operation due to lower arc energy.
• Eliminates the risk of fire as there is no oil involved.
• Compact in size, thanks to the rapid growth of dielectric strength.
• Faster arc quenching and shorter duration of the arc.
• Stable operation and high-speed switching.
• Requires less maintenance compared to other types of circuit breakers.

Disadvantages:

• Requires an additional air supplier plant, increasing maintenance requirements.
• Possibility of air pressure leakage from air pipes junctions.
• Higher rate rise of re-striking voltage and current chopping.
• Relatively lower arc extinguishing properties compared to other mediums.

Application and Uses of Air Circuit Breaker

Air circuit breakers are widely used in various applications to provide protection and control in electrical systems. Some common applications of ACBs include:

• Protection of electrical machines, such as motors, transformers, and generators.
• Common protection for multiple electrical machines in a system.
• Electricity distribution systems up to 15kV.
• Low and high voltage and current applications.
• Industrial plants and commercial buildings.

ACBs are essential components in electrical systems, ensuring the safe and reliable operation of connected devices and protecting them from faults and overcurrent conditions.

In conclusion, air circuit breakers are critical devices used in electrical systems for short circuit and overcurrent protection. With their unique construction and operational principles, ACBs provide reliable and efficient arc interruption. The different types of ACBs offer advantages and disadvantages that make them suitable for various applications. Understanding the construction, operation, and types of air circuit breakers is essential for ensuring the safety and stability of electrical systems.