Introduction

In the field of high-voltage power transmission, gas-insulated switchgear (GIS) has become a key technology for ensuring reliable power supply in areas with limited space or harsh environments. Although environmental concerns are growing, sulfur hexafluoride (SF₆) continues to dominate as the insulating gas for GIS due to its excellent insulating properties, superior arc-quenching capabilities, and long service life. While the industry is actively developing more environmentally friendly alternatives, SF6 remains the performance benchmark, ensuring the safe, compact, and stable operation of global power grids.

What is Gas-Insulated Switchgear (GIS)?

Gas-Insulated Switchgear (GIS) is a high-voltage electrical system that uses sulfur hexafluoride (SF6) gas or eco-friendly alternatives (like dry air or g₃ gas) to insulate live components in a sealed, metal-enclosed structure. Unlike traditional air-insulated switchgear (AIS), GIS is ultra-compact, highly reliable, and ideal for urban substations, data centers, and harsh environments (e.g., offshore wind farms).

Key Advantages of GIS

Gas-insulated switchgear (GIS) is an advanced gas-insulated system that replaces air with pressurized SF6 or eco-friendly gases to achieve superior performance in high-voltage applications. Unlike conventional switchgear, this gas-insulated switch gear technology offers:

Compact Design

• 70% smaller footprint than AIS

High Reliability

• Sealed construction prevents contamination from dust, moisture, or pollution

Enhanced Safety

• No exposed live parts, eliminating electrical hazards

Low Maintenance

• Maintenance intervals extend up to 25 years due to enclosed design

Environmental Adaptability

• Operates reliably in extreme conditions (e.g., deserts, coastal areas)

Smart Monitoring

• Built-in sensors for real-time gas pressure, temperature, and discharge detection

Why is SF6 the gas of choice for GIS?

SF6 (sulfur hexafluoride) remains the preferred insulating medium for gas-insulated switchgear solutions due to its unmatched properties:

• Superior Insulation– 3× stronger than air at the same pressure
• Excellent Arc Quenching– Extinguishes arcs 100x faster than air
• Chemical Stability– Non-flammable and non-reactive
• Compact Design Enabler– Enables compact gas-insulated switchgear designs (70-80% smaller footprint)

1 Exceptional Dielectric Strength

SF6 gas delivers exceptional dielectric strength – 3× higher than air at the same pressure. This property is critical for gas-insulated switchgear (GIS), enabling:

• Compact HV Designs – Equipment size reduced by 70% vs air insulation
• Higher Voltage Capacity– Supports 800kV+ transmission systems
• Stable Performance– Unaffected by humidity/pollution (unlike air insulation)

2 Superior Arc Quenching

SF6 gas provides superior arc quenching – 100× faster than air, critical for protecting gas-insulated switchgear (GIS) during faults:

• Ultra-Fast Extinction– Quenches arcs in <10ms (vs air’s ~100ms)
• No Re-Ignition – Prevents secondary arcs due to high thermal conductivity
• Minimal Damage– Reduces contact erosion, extending equipment lifespan

SF6 decomposes during arcing but 95% recombines automatically after cooling.

3 Chemical Stability

SF6 in switchgear exhibits exceptional chemical stability, making it ideal for SF6 gas-insulated switchgear (GIS):

• Non-Flammable & Non-Toxic– Safe for enclosed electrical systems
• No Degradation– Maintains insulation properties for 30+ years
• Minimal Reactivity– Resists corrosion even at high temperatures (up to 500°C)

Unlike air-insulated systems, SF6 gas-insulated switchgear remains unaffected by moisture, dust, or oxidation.

Key advantages comparison

4 Low Operating Pressure

Gas-insulated switchgear (GIS) operates at low pressure (0.4–0.6 MPa) while maintaining superior insulation, a key advantage for GIS substation deployment:

• Safety – Reduced vessel stress vs high-pressure systems
• Leakage Control– Easier to maintain hermetic seals
• Efficiency– Lower compression energy vs traditional air-insulated designs

At just 20% of air-insulated pressure, SF6 delivers 3× higher dielectric strength.

5 Effective Heat Transfer

Gas-insulated switchgear (GIS) achieves effective heat transfer through pressurized SF6 gas circulation, critical for GIS substation reliability:

• Enhanced Cooling – SF6’s thermal conductivity is 2-3× higher than air
• Temperature Uniformity – Prevents hot spots in GIS substation enclosures
• Compact Design– Enables higher current ratings in smaller spaces

Modern gas-insulated switchgear combines forced convection and optimized gas flow paths for maximum heat dissipation.

6 Self-Healing Property

SF6 in switchgear exhibits a unique self-healing property – when decomposed by arcing, 95% of molecules automatically recombine after cooling. This ensures:

• Long Gas Lifespan– No frequent refilling needed
• Consistent Performance– Maintains dielectric strength over decades
• Low Maintenance– Reduces operational costs for gas-insulated substations

7 Non-Corrosive Nature

SF6 gas in gas-insulated switchgear (GIS) exhibits non-corrosive properties, making it ideal for long-term use in gas-insulated systems:

• No Oxidation– Protects copper/aluminum contacts from degradation
• Material Compatibility– Safe with metals and insulating components
• Extended Lifespan – Ensures 30+ years of reliable operation

Unlike air, SF6 prevents oxidation even in humid environments, a key advantage for gas-insulated switchgear in coastal areas.

Conclusion

SF6 remains the performance benchmark for GIS, offering outstanding insulation strength, rapid arc quenching capability, stable chemical properties, and a compact design. It ensures safe and reliable power supply in various complex and harsh environments. Although its high global warming potential poses environmental challenges, the scientific and reasonable management and use of SF6 remain an important task for the industry until alternative technologies are fully mature. Chuanli will continue to leverage advanced engineering technology and environmental sustainability principles to provide high-performance, sustainable GIS solutions for global power grids.