Why SF6 (sulfur hexafluoride) is used in high-voltage circuit breakers?

Sulfur hexafluoride, commonly known as SF6, is a type of inorganic, colorless, odorless, non-flammable, and extremely potent greenhouse gas. It is used across various sectors, including the electrical industry, where it is widely recognized for its high dielectric strength and thermal stability.

SF6 is an electron negative, inert, and heavy gas with excellent electric insulating and arc-quenching properties. These characteristics make it highly suitable for the construction and operation of high-voltage circuit breakers.

SF6 in Circuit Breakers

High-voltage circuit breakers, such as those used in power distribution networks, must reliably interrupt the flow of current and withstand high voltages without reigniting. SF6 gas is used in these circuit breakers due to its excellent insulation properties and its ability to extinguish an electric arc.

When an electric current passes through the air between unshielded conductors, it can create an arc. As SF6 is a heavier gas than air, it prevents this arcing by displacing the air around the conductors, effectively insulating them from each other and the surrounding equipment.

Advantages of SF6

The use of SF6 in circuit breakers offers several advantages:

1. High Dielectric Strength: SF6 has a dielectric strength roughly 2.5 times greater than air, making it an excellent insulator. This high dielectric strength allows SF6-filled equipment to be compactly designed and safely operated in high-voltage environments.
2. Arc Quenching: SF6 is superior to other media at interrupting electrical currents, due to its unique combination of properties. When an arc is formed, SF6 absorbs the energy, causing it to dissociate and form a dense cloud of SF6 ions. These ions impede the further flow of current and help to extinguish the arc.
3. Non-Toxic and Inert: SF6 is non-toxic and inert, making it safe to handle. The gas is stable, so it does not react with other substances or pose a risk of fire or explosion.
4. Low Maintenance: Equipment filled with SF6 requires less maintenance and is more reliable over time, reducing the overall operational and maintenance costs.