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.

What is Air Circuit Breaker

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

FeaturesACBMOCBABCBVCBSF6
Voltage Range
LV: <1000 V,
MV: 1KV to 33KV
HV: 33 to 220KV,
EHV: ≥440 KV
LVMVMV HV EHVMVMV HV EHV
Construction
IMC- internal metal clad
GIS – Gas insulated
OPC – outdoor porcelain clad
IK – indoor Kiosk
IMCIMC OPCIK OPCIMC IK GISIMC OPC GIS
MaintenancelessmaximumlessNilless
Contact life
Max – 100 short circuits
lesslessmoremaximummore
Explosion possibilitieslessmaximumlessNilless
Fire HazardlessmaximumNilNilNil
Capacitor switching
NS- not suitable, S – suitable
NSNSSSS
Repeated operation
NS- Not suitable, S – Suitable
SNSSSS

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.

Components of Air Circuit Breaker

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.

Air Circuit Breaker (ACB) Construction

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.

Working Principle of Air Circuit Breaker

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
Air Break Circuit Breaker Graph

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
Air Chute Circuit Breaker, Image Courtesy: Codrey

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
Electrical Air Circuit Breaker

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What is an Air Circuit Breaker? Working Principle & Applications

 
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