What Is an SF6 Gas Circuit Breaker?

In an electrical system, electrical discharges caused by low-resistance connections between ground or different phases are called arcs. Circuit breakers are used to extinguish these arcs. Different types of circuit breakers are produced depending on the medium in which the arc extinguishing process takes place.

One of these types is the SF6 gas circuit breaker. So, what is an SF6 gas circuit breaker?

SF6 gas, which is an electronegative gas, is used to interrupt electrical arcs occurring at contacts. SF6 gas circuit breakers, which have a wide range of applications, provide superior arc extinguishing performance compared to oil and air-based systems. They are mostly used in indoor installations, which is why their size is compact.

How Does an SF6 Gas Circuit Breaker Work?

The operating principle of SF6 circuit breakers is based on compressing sulfur hexafluoride gas via a piston in the moving contact and directing it toward the arc area.

Under 1.5–6 bar pressure, SF6 gas reduces the opening distance between contacts thanks to its insulating properties. Once compressed, the arc is cooled and the medium between contacts loses conductivity, becoming an insulator, thus extinguishing the arc.

Electronegative fluorine ions capture electrons in the arc zone, limiting current flow. SF6 gas also rapidly dissipates heat, quickly reducing temperature. Its dielectric strength is higher than that of compressed air.

Features of SF6 Gas Circuit Breakers

SF6 circuit breakers are classified according to their insulation type:

• Gas-insulated types used from 36 kV up to 500 kV
• Air-insulated types used from 72.5 kV up to 420 kV

Advantages of SF6 Gas Circuit Breakers

• Lower loss factor compared to oil
• No fire or explosion risk since decomposition products are non-explosive
• Not affected by environmental atmospheric changes
• High thermal conductivity allows rapid heat dissipation
• Fast arc cooling due to low insulation distance
• Dielectric strength is approximately three times higher than air at the same pressure
• Does not react with minerals
• SF6 gas is colorless, odorless, non-toxic, and non-flammable
• Low risk level
• Compact size and cost-effective
• High mechanical strength
• Can be re-pressurized and reused

SF6 circuit breakers have a low accident risk in operation, but gas leakage prevention and periodic maintenance are required.

SF6 Circuit Breakers and Greenhouse Effect

SF6 gas is a greenhouse gas and has been identified as harmful to the ozone layer, which has led to restrictions in its use. In case of leakage, it can cause environmental harm.

Manufacturers are working to reduce leakage and minimize emissions in order to comply with environmental regulations.