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Difference between Air Circuit Breaker and SF6 Circuit Breaker
A circuit breaker is an electrical switching device that can open or close an electric circuit either normally or in case of fault. Therefore, a circuit breaker is one of the major component of an electrical power system or wiring system.
A circuit breaker is usually equipped with a control mechanism which enable it to operate automatically in case of abnormal conditions in the circuit. Since the different electrical systems operate at different voltage and current levels. Therefore, according to system voltage and current, there are various types of circuit breakers available such as MCB (Miniature Circuit Breaker), ACB (Air Circuit Breaker), OCB (Oil Circuit Breaker), VCB (Vacuum Circuit Breaker), SF6 Circuit Breaker, etc.
Go through this post to get a clear understanding of how Air Circuit Breakers (ACB) are different from SF6 circuit breakers. Here, you will also learn the basics of air circuit breaker (ACB) and SF6 circuit breaker.
What is Air Circuit Breaker?
The type of the circuit breaker in which air is used as the arc quenching medium is known as air circuit breaker or ACB.
An air circuit breaker (ACB) is generally used in low voltage applications, where the supply voltage is less than 450 volts. Therefore, the air circuit breakers are widely used in the distribution panels.
The air circuit breakers are suitable to provide short-circuit protection and overcurrent protection to the electric circuits over 600 amperes to 10 kilo-amperes. The primary advantages of the air circuit breakers are high performance, long life and easy to install.
What is SF6 Circuit Breaker?
A type of circuit breaker that uses a pressurized Sulphur Hexafluoride (or SF6) gas for arc quenching is known as SF6 circuit breaker or Sulphur Hexafluoride circuit breaker.
The Sulphur Hexafluoride (SF6) gas has superior insulating and arc quenching properties as compared to oil and air. The SF6 circuit breakers are widely used in electrical power stations and substations for switching and protection of electric circuit up to 800 kV.
This circuit breaker is suitable for very high voltages because the SF6 gas used is highlyelectronegative and has a strong tendency of absorbing the free electrons that cause arc between the contacts while opening the circuit. Also, the SF6 gas is a non-flammable, non-toxic, colorless and odorless gas, which is a chemically stable and inert gas.
The SF6 circuit breakers are generally used in power generating plants and receiving substations for switching and protection of high voltage circuits.
Difference between ACB and SF6 Circuit Breaker
The function of both ACB (Air Circuit Breaker) and SF6 circuit breaker is the same, i.e. switching and protection. However, there are several difference between them that are listed in the following table −
| Basis of Difference | ACB | SF6 Circuit Breaker |
|---|---|---|
| Definition | A circuit breaker that uses air as the arc quenching medium is called air circuit breaker or ACB. | A circuit breaker that uses SF6 (Sulphur hexafluoride) gas for quenching the arc is called SF6 circuit breaker. |
| Applicable voltage range | ACB is used in low voltage circuits, where the voltage is less than 450 volts. | SF6 circuit breaker is used in high voltage circuits, where voltage is upto 800 kV. |
| Arc quenching medium | Air is used as the arc quenching medium. | SF6 (Sulphur hexafluoride) gas is used as arc quenching medium. |
| Current range | Current ranting of ACB is ranging from 600 A to 10 kA. | SF6 circuit breakers have high current rating, around 4 kA to 40 kA. |
| Arc development | Arc developed in ACB is high. | In SF6 circuit breakers, the arc development is relatively less. |
| Need of arc chute | ACB necessarily requires an arc chute. | There is no need of arc chute in an SF6 circuit breaker. |
| Short circuit breaking capacity | The short circuit breaking capacity of an air circuit breaker is very low. | SF6 circuit breakers have comparatively higher short circuit breaking capacity. |
| Cost of quenching medium refilling | There is no refilling cost of the arc quenching medium, as air is available for free. | SF6 circuit breakers involve significantly high refilling cost of SF6 gas. |
| Current | ACB uses both inside and outside | In SF6 circuit breaker, current |
| transformer installation | installation of current transformer. | transformer is installed outside the circuit breaker. |
| Protection relays installation | Most of ACBs involve internal installation of protection relays. | In case of SF6 circuit breaker, the protection relays are externally installed. |
| Installation | ACB involves less difficult installation. | The installation of Sf6 circuit breaker is extremely complicated. |
| Cost | Air circuit breaker is less expensive. | SF6 circuit breakers are comparatively more expensive. |
| Application | ACBs are commonly used in low tension distribution panels. | SF6 circuit breakers are used in high tension systems such as generating pants, switchyards, etc. |
Conclusion
The most significant difference between these two circuit breakers is in their arc quenching medium, where the ACB uses air for quenching the arc while SF6 circuit breaker uses Sulphur hexafluoride gas as the arc quenching medium.
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