what are SF6 circuit breakers?

SF6 Circuit Breaker: Types, Working Principles, and Construction| Electronicsinfos

SF6 circuit breakers are a type of circuit breaker that uses sulfur hexafluoride (SF6) gas as the arc extinguishing and insulating medium. They are commonly used in high-voltage electrical power systems, including substations and power transmission networks.

SF6 circuit breakers are known for their excellent dielectric properties, high thermal conductivity, and efficient arc quenching capabilities.

Sf6 circuit breaker diagram

Purpose Of SF6 circuit breaker

The main purpose of an SF6 circuit breaker is to interrupt the flow of electrical current in a circuit. when a fault or abnormal condition occurs, such as an overload or short circuit, the SF6 circuit breaker detects the fault current and initiates the opening of its contacts.

As the contacts open, a high-pressure SF6 gas is released into the interrupting chamber. The released gas creates a flow path for the fault arc and extinguishes it.

There are different designs available for interrupters including

Types of SF6 Circuit Breakers

Single Interrupter SF6 Circuit Breaker
Two Interrupter SF6 Circuit Breakers
Three Interrupter SF6 Circuit Breakers

Single Interrupter SF6 Circuit Breaker

This type of circuit breaker consists of one interrupting unit in a single housing. It is commonly used for low-voltage applications.

Two Interrupter SF6 Circuit Breakers

In this design, two interrupting units are housed in a single enclosure. This type of circuit breaker is typically used for medium-voltage applications.

Three Interrupter SF6 Circuit Breakers

Three interrupting units are contained within a single enclosure in this type of circuit breaker. It is employed for high-voltage applications, typically in substations and power transmission systems.

Working Principles of SF6 Circuit Breaker

SF6 circuit breakers operate based on the principle of the self-blast technique. When a fault occurs, the high-pressure SF6 gas is rapidly released. The released gas creates a flow path for the arc and increases its length.

As the arc lengthens, the voltage across the contacts increases, and the current decreases to the point where the arc is extinguished. During normal operation, the circuit breaker contacts are closed, and the SF6 gas provides excellent insulation and extinguishing properties.

When a fault occurs, a control circuit detects the fault current and initiates the opening of the circuit breaker contacts.

Construction of SF6 Circuit Breaker

The construction of an SF6 circuit breaker involves several key components including

Interrupting Unit
Arc Interrupting Chamber
Operating Mechanism
Insulation
Auxiliary Systems

Interrupting Unit of SF6 Circuit Breaker

The interrupting unit consists of Three contacts including

Fixed Contact
Moving Contact
Arcing Contact

Fixed Contact

The fixed contact is a stationary part of the circuit breaker that remains in position during normal operation.

Moving Contact

The moving contact is connected to the operating mechanism and can be opened or closed as needed. It moves to create or break the electrical connection with the fixed contact.

Arcing Contact

The arcing contact is designed to withstand and control the arc generated during fault interruption. It helps to elongate the arc and facilitate effective arc quenching.

Arc Interrupting Chamber

SF6 Gas
Nozzle
Arc Chutes

SF6 Gas

SF6 gas is used as the arc extinguishing and insulating medium within the arc interrupting chamber. It is stored in a high-pressure reservoir and circulated through the circuit breaker during operation.

Nozzle

The nozzle directs the flow of SF6 gas towards the arc. it enhances the cooling and elongation of the arc.

Arc Chutes

The arc chutes are designed to provide a controlled path for the fault arc. They help to cool and deionize the arc.

Operating Mechanism

Manual / Motor Mechanism
Spring Mechanism

Manual/Motor Mechanism

The operating mechanism controls the opening and closing of the circuit breaker contacts. It can be manually operated or motor-driven.

Spring Mechanism

A spring mechanism provides the required force for closing the contacts. it stores energy for the opening operation. The spring mechanism helps to ensure a quick and efficient response during fault conditions.

Insulation

Insulating Materials

Various insulating materials, such as epoxy or porcelain, provide insulation. These materials help to maintain the necessary electrical clearances and prevent flashovers or electrical leakage.

Auxiliary Systems

Control and Protection System

SF6 circuit breakers are equipped with a control and protection system. It monitors various parameters, such as fault currents, operating voltage, and temperature. This system helps detect faults and ensure the circuit breaker's proper functioning.

Gas Monitoring System

some circuit breakers use a gas monitoring system. It continuously monitors the gas pressure and quality. it allows for timely maintenance and gas refilling.

Advantages of SF6 Circuit Breakers

High dielectric strength
Rapid arc extinguishing
Low maintenance required
Long service life
chemically stable
non-toxic
non-flammable

Sf6 circuit breaker ratings

Rated Voltage

SF6 circuit breakers are rated for voltage levels, such as 72.5 kV, 145 kV, 245 kV, 420 kV etc.

Rated Current

The rated current of an SF6 circuit breaker is 630 A, 1250 A, 2000 A, and higher

Conclusion

SF6 circuit breakers are vital components in electrical power systems. Understanding the types, working principles, and construction of SF6 circuit breakers helps select and operate these devices.

As technology advances, SF6 circuit breakers continue to be essential in maintaining electrical infrastructure's safety and reliability.