The core of high voltage power system--SF6 circuit breaker

Overview

SF6 circuit breaker is a high-voltage switchgear that uses sulfur hexafluoride (SF6) gas as arc extinguishing and insulating medium. It is known as the core of high-voltage power grid. With its unique arc extinguishing ability and stable efficiency, it is widely used in various power systems and transmission and distribution networks. It is a key equipment to ensure the safe operation of the power grid. It is mainly divided into high voltage of 72.5kV and above and medium voltage of 3.6kV~72.5kV. The core function of SF6 circuit breaker is to quickly cut off fault current and protect power grid equipment from short circuit or overload damage.

一. What is an SF6 circuit breaker?

SF6 circuit breaker is a high-voltage switchgear that uses sulfur hexafluoride (SF6) gas as an insulating and arc-extinguishing medium. It is mainly used to quickly cut off fault currents in circuits (such as short circuits or overloads) to prevent damage to power grid equipment. Its operating voltage range covers 3.6kV to 800kV and is widely used in medium-voltage, high-voltage and ultra-high-voltage power systems.

二. How does the SF6 circuit breaker work?

1. Principle: The role of SF6 gas

Insulating medium: The insulation strength of SF6 gas is 2 to 3 times that of air, which can effectively isolate live parts under high voltage conditions.

Arc extinguishing medium: SF6 molecules have strong electronegativity and can quickly absorb arc energy to achieve microsecond arc extinguishing.

Stability: After decomposition at high temperature of the arc, 99% of SF6 gas can be quickly recombined without residual pollutants.

2. The whole process of arc extinguishing

Contact separation: The fault current triggers the circuit breaker to operate, and the contacts are quickly separated and an arc is generated.

Gas compression: The operating mechanism drives the piston to compress the SF6 gas, forming a high-speed airflow blowing towards the arc to reduce the degree of ionization.

Energy absorption: SF6 molecules capture free electrons, suppress the arc from continuing, quickly extinguish the arc, and achieve current disconnection.

Insulation recovery: After the arc is extinguished, the SF6 gas immediately restores the insulation strength to prevent the arc from reigniting and ensure that the circuit is completely disconnected.

三. Core structure and components of SF6 circuit breaker

1. Arc extinguishing chamber

Material: high temperature resistant ceramic or epoxy resin.

Design: compressed gas type (single pressure and double pressure) or self-energy arc extinguishing structure, suitable for different current levels.

2. Gas system

Gas chamber: sealed cavity filled with SF6 gas (rated pressure 0.4~0.6MPa).

Pressure monitoring: density relay monitors gas pressure in real time and triggers lockout or alarm signal.

3. Operating mechanism

Spring energy storage mechanism: economical and reliable, suitable for medium voltage system.

Hydraulic/pneumatic mechanism: large output torque, used for high voltage and large capacity circuit breakers.

Intelligent electric mechanism: integrated sensor, support remote opening and closing control.

4. Insulation support structure

Porcelain column type: standard design, strong anti-pollution ability.

Composite insulator type: silicone rubber jacket reduces weight and has better explosion-proof performance.

四. Advantages of SF6 circuit breakers

1. Super strong breaking capacity: can cut off short-circuit current up to 80kA, far exceeding ordinary vacuum circuit breakers.

2. Super long mechanical life: mechanical life up to 10,000 operations, and can meet 2,000 full-capacity breaking, maintenance-free cycle up to 20 years.

3. Compact design: SF6's high insulation makes the equipment volume 40% smaller than air-insulated circuit breakers, saving substation space.

4. Super strong adaptability: fully sealed structure, can operate stably in -30°C to +40°C, high humidity or dusty environment. Maintenance-free cycle up to 20 years.

五. Future technological innovation of SF6 circuit breakers

1. SF6 alternatives

Mixed gas: SF6/N₂ or SF6/CF4 mixed gas, reducing SF6 consumption and GWP by 30%~50%.

2. SF6-free alternatives:

Dry air circuit breaker: commercialized in the medium voltage field (≤40.5kV), GWP=0.

Vacuum circuit breaker + environmentally friendly gas: under development in the high voltage field (such as C5-FK gas).

3. Recovery and regeneration technology

SF6 recovery device: gas with a purity of ≥99.9% can be recycled to reduce operation and maintenance costs.

Decomposition treatment: high-temperature arc or plasma technology decomposes SF6 into harmless sulfur and fluoride.

4. Intelligent upgrade

Condition monitoring system: built-in sensors monitor gas density, contact wear, mechanical vibration, and predictive maintenance.

六. Application scenarios of SF6 circuit breakers

High-voltage transmission network: used in 500kV and above substations to protect transformers and transmission lines.

Urban power grid: integrated in GIS (gas insulated switchgear), suitable for urban substations with limited space.

New energy power station: booster station for power plants and photovoltaic power stations, withstanding frequent start-stop operations.

Industrial power system: incoming line protection for high current loads such as steel plants and chemical plants.

Conclusion

SF6 circuit breakers are the core protection devices of current high-voltage power systems due to their efficient breaking capacity. In the future, the industry is accelerating its transition to environmentally friendly technologies. With the development of technology, safer and cleaner gases will emerge. Lugao Power Co., Ltd. will combine performance with environmental protection and actively embrace innovation to meet the challenges and opportunities of energy transformation. Choose LUGAO to get customized SF6 circuit breaker solutions to provide efficient, reliable and sustainable protection for your power system!