SF6 Circuit Breaker Operation

Study Notes

SF6 Circuit Breaker

Operation Principle

SF6 circuit breaker uses Sulphur Hexafluoride (SF6) gas as the insulating and arc quenching medium
The breaker consists of fixed and moving contacts, arc shields, and a gas system
When the breaker is closed, the moving contact touches the fixed contact, allowing current to flow
When the breaker is opened, the moving contact separates from the fixed contact, creating an arc
The SF6 gas is used to quench the arc, allowing the breaker to extinguish the fault current

Arc Quenching

Arc quenching is the process of extinguishing the electrical arc that forms when the circuit breaker is opened
SF6 gas has excellent arc quenching properties due to its high dielectric strength and ability to absorb free electrons
The SF6 gas is released from the arc chamber and flows through the nozzle, creating a high-velocity gas flow that cools the arc and extinguishes it
The arc quenching process is facilitated by the use of arc shields, which help to constrict the arc and increase the gas flow velocity

Advantages

High dielectric strength, allowing for compact design and reduced size
Excellent arc quenching properties, enabling fast and reliable fault current interruption
Low maintenance requirements due to the closed gas system and lack of moving parts
High reliability and long lifespan
Environmentally friendly, as SF6 is a non-toxic and non-flammable gas

Limitations

SF6 is a potent greenhouse gas, with a global warming potential (GWP) of 22,800
SF6 circuit breakers are generally more expensive than air-blast or oil-filled circuit breakers
Specialized equipment and training are required for handling and maintenance
SF6 gas can be contaminated by moisture and air, reducing its effectiveness and requiring regular testing and maintenance

Gas Handling

SF6 gas is stored in cylinders or gas carts
Gas handling equipment, such as gas reclaimers and filling devices, are used to handle and manage the SF6 gas
Regular gas testing and analysis are required to ensure the gas meets the required purity and moisture levels
SF6 gas must be handled and stored according to safety guidelines and regulations to prevent accidents and environmental harm

SF6 Circuit Breaker

Operation Principle

SF6 gas is used as insulating and arc quenching medium in SF6 circuit breakers
Breaker consists of fixed and moving contacts, arc shields, and a gas system
Closing the breaker allows current to flow, while opening it creates an arc that is quenched by SF6 gas

Arc Quenching

Arc quenching is the process of extinguishing the electrical arc when the circuit breaker is opened
SF6 gas has high dielectric strength and absorbs free electrons, making it an excellent arc quenching medium
High-velocity gas flow cools and extinguishes the arc
Arc shields constrict the arc and increase gas flow velocity to facilitate quenching

Advantages

High dielectric strength allows for compact design and reduced size
Fast and reliable fault current interruption due to excellent arc quenching properties
Low maintenance requirements due to closed gas system and lack of moving parts
High reliability and long lifespan
Environmentally friendly due to non-toxic and non-flammable properties of SF6 gas

Limitations

SF6 is a potent greenhouse gas with a global warming potential (GWP) of 22,800
SF6 circuit breakers are generally more expensive than air-blast or oil-filled circuit breakers
Specialized equipment and training required for handling and maintenance
SF6 gas can be contaminated by moisture and air, reducing its effectiveness

Gas Handling

SF6 gas is stored in cylinders or gas carts
Gas handling equipment, such as gas reclaimers and filling devices, are used to handle and manage SF6 gas
Regular gas testing and analysis are required to ensure gas meets required purity and moisture levels
SF6 gas must be handled and stored according to safety guidelines and regulations to prevent accidents and environmental harm

Description

Learn about the operation principle of SF6 circuit breakers, including the use of Sulphur Hexafluoride gas as an insulating and arc quenching medium. Understand how the moving and fixed contacts work together to allow and interrupt current flow.