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Difference between SF6 and Vacuum Circuit Breaker (VCB)
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.
In this article, we will highlight all the differences between vacuum circuit breaker (VCB) and SF6 circuit breaker. But, before going into the differences, let's start with some basic information about VCB and SF6 circuit breakers.
What is VCB?
VCB stands for Vacuum Circuit Breaker. A vacuum circuit breaker (VCB) is the type of circuit breaker which uses vacuum between the electrodes as the arc quenching medium.
The vacuum circuit breakers are mainly used in medium voltage applications, where the supply voltage ranges from 11 kV to 33 kV. In the VCB, the contacts of the circuit breaker are enclosed in a completely sealed vacuum cylinder. When the contacts are separated due to vacuum between the contacts, no arc is produced.
The major advantages of a vacuum circuit breaker are no emission of gas in atmosphere, little maintenance required, no danger of fire, longer life, silent operation, etc.
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 circuits upto 800 kV.
This circuit breaker is suitable for very high voltages because the SF6 gas used is highly electronegative 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.
SF6 circuit breakers are generally used in power generating plants and receiving substations for switching and protection of high voltage circuits.
Difference between VCB and SF6 Circuit Breaker
The function of both vacuum circuit breaker (VCB) and SF6 circuit breaker is the same. However, there are several differences between VCB and SF6 circuit breaker that are listed in the following table −
| Basis of Difference | VCB | SF6 CB |
|---|---|---|
| Full Form | VCB stands for Vacuum Circuit Breaker. | SF6 CB stands for Sulphur Hexafluoride Circuit Breaker. |
| Definition | A circuit breaker which uses vacuum as the arc quenching medium is called vacuum circuit breaker or VCB. | A circuit breaker that uses SF6 (Sulphur Hexafluoride) gas as the arc quenching medium is known as SF6 circuit breaker. |
| Voltage range | VCB is used for medium voltage range from 11 kV to 33 kV. | SF6 circuit breakers are applicable for high voltage range from 11 kV to 800 kV. |
| Arc quenching medium | Vacuum acts as the arc quenching medium in VCB. | SF6 circuit breaker has Sulphur hexafluoride (SF6) gas as the arc quenching medium. |
| Pressure of quenching medium | The pressure of vacuum in VCB is maintained at 10-2 torr to 10-6 torr in a vacuum chamber. | The pressure of SF6 gas is maintained at 1500 torr to 1875 torr. Which is very high as compared to pressure of vacuum in VCB. |
| Development of arc | A very low arc is developed in a VCB while the circuit is opened. | The arc developed in SF6 circuit breaker is slightly higher than VCB. |
| Refilling cost | For VCB, there is no refilling cost of quenching medium because vacuum in the vacuum chamber stay intact for long duration. | SF6 circuit breaker involves very high refilling cost of SF6 gas. |
| Suitability | Vacuum circuit breakers are largely suitable for indoor applications. | SF6 circuit breakers are mainly suitable for outdoor applications, but they can be used for indoor applications as well. |
| Maintenance | Vacuum circuit breakers require rare maintenance. | SF6 circuit breakers require periodic maintenance. |
| Short circuit breaking capacity | The short circuit breaking capacity of vacuum circuit breakers is extremely high. | The short circuit breaking capacity of SF6 circuit breakers is high but less than that of a VCB. |
| Installation | The installation of vacuum breakers is relatively less difficult. | SF6 circuit breakers involve extremely complicated installation. |
| Cost | The cost of VCB is comparatively low. | SF6 circuit breakers are comparatively expensive. |
| Applications | Vacuum circuit breakers (VCB) are mainly used in medium voltage range circuits for switching and protection such as in high voltage induction motor circuits, primary distribution stations, etc. | SF6 circuit breakers are used in high voltage applications like high tension (HT) power control centers (PCC), transmission substations, etc. |
Conclusion
Both SF6 circuit breakers and VCBs are widely used in electrical substations. The most significant difference between these two circuit breakers is that the SF6 circuit breaker uses Sulphur hexafluoride gas as the arc quenching medium, whereas VCB uses vacuum as the arc quenching medium.
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