SF6 Circuit Breaker – Types, Construction, Working and Applications

Sf6 circuit breakers are used for their high interrupt capacity, compact design, and reliable performance these are important factors for modern electrical power systems especially in high voltage applications also SF6 gas is a potent greenhouse gas and is being made to reduce its usage and improve its environmental impact. In this article, we will study about SF6 Circuit Breaker and its functioning in detail.

Sulphur Hexafluoride

Sulfur hexafluoride (SF6) circuit breaker is a type of high-voltage electrical switchgear device. it is used for protecting electrical power systems from short circuits and overload conditions. These circuit breakers are commonly employed in medium to high-voltage power transmission and distribution systems.

Types of SF6 Circuit Breakers

There are two types of SF6 circuit breakers –

• Non-Puffer type
• Single Pressure puffer type
• Double Pressure puffer type

Non-Puffer SF6 Circuit Breaker

A non-puffer type SF6 circuit breaker is a type of high-voltage electrical circuit breaker used in power transmission and distribution systems to protect electrical equipment from short circuits and overloads. the reason this is called non-puffer because it does not depend on high-pressure gas blast to extinguish the electric arc during interruption.

Construction of Non Puffer SF6 Circuit Breaker

• The construction of the Non Puffer circuit breaker is simple based on the remaining types
• It consists of fixed and moving contacts both are hollow cylinder
• A stationary arc shield surrounds the contacts to control the arc.
• A mechanism used to open and close contacts
• SF6 gas is used as arc-quenching medium but does not create high-pressure blast.

Non-Puffer SF6 Circuit Breaker

Working of Non Puffer SF6 Circuit Breaker

• At the start the contacts are in closed position surrounded by SF6 and the electric current flows through them
• when any fault occur the mechanism activates and open the contacts
• as the arc separates an electric arc is formed
• SF6 gas surrounding the contacts absorbs the energy of the arc and quickly extinguishes it
• once the arc is extinguished contacts are fully opened interrupting the current flow
• After the extinction of arc and interruption of current, the gas moves out from the gas outlets and with the suitable methods, the gas gets recombined and reconditioned for further use.

Single Pressure SF6 Circuit Breaker

In the SF6 circuit breaker the SF6 gas is stored at a high pressure around 20 BA in a pressure vessel. The contacts are opened and closed by the movement of the operating rod.

Construction of single pressure SF6 Circuit Breaker

• The single pressure type SF6 circuit breaker has more complex construction compared to non puffer
• It consists of high pressure SF6 reservoir, puffer chamber, and an arc-quenching nozzle.
• fixed and moving contacts are placed inside the puffer chamber.
• An operating mechanism is used to open and close the contacts.
• The high pressure SF6 gas is stored in reservoir and released into puffer chamber when needed.

Working of single pressure SF6 Circuit Breaker

• During normal condition the high pressure SF6 gas is contained in the reservoir and the contacts are closed.
• When any fault occurs the operating mechanism opens the contacts and at same time a valve releases a controlled amount of SF6 gas from the reservoir into the puffer chamber.
• Rapid release of SF6 gas generates high-pressure flow creates blast effect, cooling and quenching the arc.
• Arc is extinguished, and the contacts are fully opened.

Single pressure SF6 circuit breaker contact are closed

Single pressure SF6 circuit breaker contact are open

Double Pressure SF6 Circuit Breaker

In Double pressure SF6 circuit breakers the gas is stored at two different pressure levels: high pressure (around 20 bar) and low pressure (around 3-4 bar). This design provides better control over the release of SF6 gas during circuit breaker operation.

Construction of Double Pressure SF6 Circuit Breaker

• The double pressure puffer type SF6 circuit breaker is more advanced design.
• It includes two pressure chambers a high-pressure chamber and a low-pressure chamber.
• The fixed and moving contacts are placed inside the high-pressure chamber.
• An operating mechanism is used to open and close the contacts.
• A valve controls the flow of SF6 gas between the two chambers.

Double Pressure SF6 Circuit Breaker

Working of Double Pressure SF6 Circuit Breaker

• During normal operation the high-pressure chamber contains the SF6 gas and the contacts are closed.
• When a fault occurs the operating mechanism opens the contacts and the valve allows a controlled amount of SF6 gas to flow from the high pressure chamber to the low pressure chamber.
• When the gas flows into the low pressure chamber it undergoes expansion. which cools the gas and generates a high velocity flow.
• The expanding and cooling SF6 gas extinguishes the arc by rapidly quenching it.
• The contacts are fully opened interrupting the current flow.

Properties of SF6 Circuit Breaker

Physical Properties

• High Dielectric Strength: SF6 has excellent insulating properties
• Heavy Gas: SF6 is heavier than air which helps in enclosing the arc during operation.
• Chemical inertness: SF6 is non flammable and chemically stable.

Chemical Properties

• Non Toxic: SF6 is non toxic and not risky for health when used in circuit breaker
• Chemically Stable: it does not react with materials that are present in electrical equipment
• Arc Quenching: SF6 effectively quenches electrical arcs that prevents further damage to the circuit.

Electrical Properties

• Excellent Insulator
• High Thermal Conductivity
• Low Arc Energy: It requires less energy to extinguish arcs which reduces wear and tear.

Maintenance of SF6 Circuit Breaker

• Maintenance of SF6 circuit breaker is essential to ensure working it properly
• Check regular gas leakage
• Check mechanical components
• Lubricate the moving parts
• Test the control circuits
• Replace the worn out components

Advantages of SF6 Circuit Breaker

• High dielectric strength
• Compact design
• Good performance
• Long service
• Low maintenance
• Good arc quenching properties
• Suitable for high voltage
• Less environmental impact

Disadvantages of SF6 Circuit Breaker

• Emits green house gas if not properly handled
• Costly
• Risk of gas leaks
• Complex recycling process

Difference between SF6 Circuit Breaker and Vacuum Circuit Breaker

Property	SF6 Circuit Breaker	Vacuum Circuit Breaker
Arc Quenching	Good	Good
Medium	SF6 gas	Vacuum
Environmental impact	Releases green house gases	Environmental friendly
Maintenance	regular maintenance	less maintenance
Cost	High	Low
Capacity	High voltage	Medium Voltage
Leakage Risk	more risk	No leakage risk

Applications of SF6 Circuit Breakers

• Power Transmission and Distribution: SF6 circuit breakers are commonly used in high-voltage power systems to protect transformers, circuit lines, and other critical equipment.
• Industrial Plants: They are used in industrial facilities to protect electrical equipment from short circuits and overloads.
• Railways: SF6 circuit breakers are used in railway electrification systems to ensure reliable power distribution.
• Substations: SF6 circuit breakers are employed in substations to control and protect the electrical grid.
• Power Generation: SF6 circuit breakers can be used in power generation facilities for generator protection.
• Renewable Energy: They are used in renewable energy systems like wind farms and solar power plants.

Conclusion

SF6 circuit breakers are essential component in high voltage electrical systems that offers good properties like they have high dielectric strength and arc quenching ability. However it is essential to maintain environment friendly it has environmental concerns associated with SF6 gas emission. SF6 gas is a green house gas and its release into the atmosphere contributes to climate change. to reduce this impact we have to responsibly handle, monitor and recycle the SF6 gas components are important. as technology advances there are many alternatives that can replace SF6 circuit breakers but it is a valuable and effective solution if we handle it care and environmental friendly.

FAQs on SF6 Circuit Breaker

1. How does an SF6 circuit breaker work?

SF6 circuit breakers work by using the properties of SF6 gas to rapidly cool and extinguish electric arcs that occur during circuit interruption.

2. Are SF6 circuit breakers environmentally friendly?

SF6 circuit breakers are not environment friendly because of SF6 has green house gas properties but if we maintain and handle good we can minimize the impact

3. How often should SF6 circuit breakers be maintained?

Regular maintenance which include gas leakage checks and inspections is necessary for SF6 circuit breaker

4. Can SF6 circuit breakers be replaced with eco friendly alternatives?

We replace it with good alternatives it is possible but depends on cost and application.

5. What safety precautions are needed when working with SF6 circuit breakers?

Proper safety measures like training and personal protective equipment must be followed to make sure the personnel safety during SF6 circuit breaker maintenance.