SF6 Circuit Breaker

SF6 Circuit Breaker

What is SF6 circuit breaker ?

• A Circiuit breaker is an equipment which can
• Make or Break a circuit either manually or automatically under normal condition.
• Break a circuit under abnormal, short-circuit, overload condition or any other fault
• A circuit breaker in which current carrying contacts operate in SF6 (Sulphur Hexafluoride) is known as SF6 Breaker
• SF6 Breaker made from 72-800 Kv with interruption current is 20-63 KA and rated current of 1200-12000 A

Why SF6 Gas?

• High Electro-Negativity
• High Dilelectric strength
• Low Liquification Temperature
• Good Arc Quenching

Types of SF6 Breaker

• Single Interruptor SF6 Breaker (upto 245 KV)
• Two Interruptor SF6 Breaker (upto 420 KV)
• Three Interruptor SF6 Breaker (upto 800 KV)

Overview of an Arc in Circuit Breaker

• During Separation of contacts, due to large fault current and High current Density at the contact region , the surrounding medium ionises and thus a conduction medium is formed.
• This is called Arc.

Principle of Arc Quenching

• Factors responsible for Arc
• Potential Difference between the Contacts
• Ionized Particles between the contacts
• By removing any of these, Arc can be quenched.

Arc Resistance 

• Factors affecting Arc Resistance
• Degree of Ionisation
• Length of the Arc
• Cross-sectional area of Arc

Physical & Chemical Properties of SF6:

• Chemically inert
• Non-toxic
• Non-corrosive
• Non-flammable
• Odourless
• Electrical Insulator

Advantage of SF6 Breaker

• Simple Construction, Less Cost
• Same Gas is recirculated in SF6 CB
• Maintenance Free CB
• Ability to interrupt Low and High Fault cittent
• Excellent Arc Extinction

Disadvantage of SF6 CB:

• Arced SF6 gas is poisonous
• Contribute to man-made green-house effect
• Continuous Monitoring Devices are required
• Special facility is required for transportation of  the SF6 gas

Limitation:

• 100% SF6 gas is more hazardous
• Experiments suggests-69% SF6 and 3% N2 gas misture is better in circuit beaker and Non-Hazardous