What is an Air Circuit Breaker? Working Principle & Applications

A circuit breaker is the one device in switchgear that operates during any abnormal fault condition in an electrical system i.e. overcurrent, earth fault, and short circuit, thus isolating a faulty electrical circuit from the healthy electrical circuit.

Switchgear is switching equipment used in an electrical system for various applications. The general specifications of the circuit breaker are operating voltage, nominal current, making capacity, breaking capacity, and the duty cycle.

Circuit breakers can also be operated manually or from a remote location as per requirement in an electrical system.

Circuit breakers are made for various voltage and current ratings depending on is applications. Circuit breakers are classified according to arc quenching medium for extinguishing arc during the opening of a breaker.

Classification of Circuit Breakers

Features	ACB	MOCB	ABCB	VCB	SF6
Voltage Range LV: <1000 V, MV: 1KV to 33KV HV: 33 to 220KV, EHV: ≥440 KV	LV	MV	MV HV EHV	MV	MV HV EHV
Construction IMC- internal metal clad GIS – Gas insulated OPC – outdoor porcelain clad IK – indoor Kiosk	IMC	IMC OPC	IK OPC	IMC IK GIS	IMC OPC GIS
Maintenance	less	maximum	less	Nil	less
Contact life Max – 100 short circuits	less	less	more	maximum	more
Explosion possibilities	less	maximum	less	Nil	less
Fire Hazard	less	maximum	Nil	Nil	Nil
Capacitor switching NS- not suitable, S – suitable	NS	NS	S	S	S
Repeated operation NS- Not suitable, S – Suitable	S	NS	S	S	S

What is Air Circuit Breaker?

An air circuit breaker consists of fixed and moving contacts that are enclosed in an arc chute chamber having air as an arc quenching medium.

These circuit breakers are usually used for low voltage applications (up to 1000 V). Its current rating ranges from 500 amps to 10000 amps.

Air Circuit Breaker (ACB) Construction

A low voltage Air Circuit Breaker (ACB) has compact construction. All poles of an ACB having fixed and moving contacts are housed in an arc chute assembly. These breakers can be operated both electrically and mechanically through a triggering mechanism.

These breakers are provided with rack-in and rack-out features with sliding and guide rail assembly. Push buttons are mounted on ACB for its manual operations.

ACBs are also provided with inbuilt CTs, relay, and trip unit provisions.

Working Principle

The air circuit breaker employs a high resistance interruption method for arc extinction.

Resistance of the arc is rapidly increased to a high value during the opening of a circuit breaker in fault or normal operating condition such that source voltage becomes incapable to maintain arc voltage.

Arc Resistance Ra can be increased by many methods such as

1. Cooling the arc
2. Lengthening the arc
3. Reducing the cross-section of the arc
4. Splitting the arc

Types of Air Break Circuit Breaker

1. Plain Break Type ACB or Cross-Blast ACB
2. Magnetic Blowout Type ACB
3. Magnetic Blowout Type ACB
4. Magnetic Blowout Type ACB

Applications of Air Circuit Breakers

1. Air Circuit Breakers are mainly used for Low voltage and Low/high current applications.
2. Air Circuit Breakers are used mostly in indoor low to medium-voltage electrical installations such as Power control cubicles & Motor control cubicles.
3. Air Circuit Breakers are preferred for applications where there is a high risk of fire hazards as ACBs have a very short arcing time.
4. Air Circuit Breakers are used for motor & capacitor starting and protection applications as they are most suitable for frequent and high-speed operations.    
5. Air blast type circuit breakers are widely used in railways electrifications

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