Main Differences Between Air Insulated Switchgear and Gas Insulated Switchgear

Air insulated switchgear and gas insulated switchgear are the two most common medium voltage switchgear types used in power distribution today.

Both AIS and GIS serve the same core purpose: they protect and control electrical circuits in substations and industrial networks. But they use different technologies to do this, so the right choice depends on your project's specific needs.

In fast-growing power markets, engineers and project managers need clear, practical guidance. This article compares AIS and GIS across design, performance, cost, and suitability, so you can make a confident decision for your next medium voltage project.

What Is Air Insulated Switchgear?

Air insulated switchgear(AIS) uses atmospheric air as the primary insulating medium between live components. This is the traditional approach to mv switchgear design. The components are housed inside a robust metal enclosed switchgear cabinet, and air fills the space between busbars, conductors, and contacts.

Modern AIS products have advanced significantly. This enclosed switchgear replaces harmful SF6 gas entirely with dry air or 99.99% pure nitrogen. As a result, it achieves zero global warming potential while maintaining full IEC compliance. The stainless steel enclosure uses laser-welding technology to reach an IP67 protection rating, making this RMU suitable for both indoor and outdoor environments.

Key Advantages of AIS:

• Eco-Friendly Insulation: This AIS uses no SF6, so it produces zero greenhouse gas emissions during operation or maintenance.

• Lower Initial Cost: Air insulated switchgear requires fewer specialist materials, so procurement and installation costs are lower.

• Wide Environmental Range: The IP67-rated metal enclosed switchgear resists moisture, dust, and corrosion in coastal and industrial conditions.

• Maintenance-Free Vacuum Technology: All conductive parts are sealed inside the enclosure, so routine maintenance is minimal.

• Modular Design: This ring main unit supports flexible combinations of circuit breaker and load switch modules, so it adapts to any project layout.

• Smart Grid Ready: Each RMU ships with a digital relay protection device and supports distribution automation integration.

Limitations of Air Insulated Switchgear:

• Larger Footprint: Because air has lower dielectric strength than SF6, AIS typically requires more clearance space between components.

• Performance in Extreme Cold: In very low temperature environments, certain insulation materials may need additional protection.

• Higher Voltage Applications: For voltage levels above 36kV, GIS generally offers a more compact and practical solution.

What Is Gas Insulated Switchgear?

Gas insulated switchgear(GIS) uses SF6 gas as the insulating and arc-quenching medium. SF6 is about five times heavier than air and has far superior dielectric strength. This allows GIS to pack all live parts into a much smaller enclosure. The result is a compact medium voltage switchgear solution for space-critical applications.

The SF6 ring main unit is a strong example of modern GIS design. This enclosed switchgear seals all busbars, switches, and live parts inside a 3.0mm-thick stainless steel chamber filled with SF6 gas at 1.4 bar pressure. It achieves an IP67 protection rating and a lifetime maintenance-free design. Furthermore, this mv switchgear supports fixed and expandable module combinations, so it fits a wide range of substation configurations.

Key Advantages of GIS:

• Extremely Compact: GIS saves up to 70–90% of the space required by conventional mv switchgear, so it is ideal for urban substations with limited footprint.

• Lifetime Maintenance-Free Sealing: All components are fully sealed inside the stainless steel chamber, so no scheduled maintenance is required.

• Superior Arc Performance: SF6 gas extinguishes electrical arcs more effectively than air, so GIS handles higher fault currents with greater reliability.

• Extreme Environment Adaptability: This gas insulated switchgear withstands brief water immersion, high humidity, and temperatures down to -40°C.

• Five-Prevention Interlocking: Every ring main unit integrates a complete interlock system that prevents all common operator errors.

• Smart Automation Integration: This RMU supports optional electric operating mechanisms and remote control, so it suits automated distribution networks.

Limitations of Gas Insulated Switchgear:

• Higher Initial Cost: The SF6 gas handling system and sealed enclosure add cost to the initial procurement budget.

• SF6 Environmental Concern: SF6 is a potent greenhouse gas. Leaks must be managed carefully to meet environmental regulations.

• Gas Monitoring Requirement: Operators must monitor SF6 pressure levels regularly to confirm the sealed system remains intact.

• Specialist Maintenance: When faults do occur inside GIS, repair requires specialist tools and trained technicians.

Technical Comparison: AIS vs GIS

Which Is Better, AIS or GIS?

Neither AIS nor GIS is universally better. Each technology suits different project conditions, and the right choice depends on your priorities.

Choose AIS if:

• Your project has more open space available, so a larger footprint is not a concern.

• Your team prioritizes environmental responsibility, because this enclosed switchgear eliminates SF6 entirely.

• Your budget is sensitive — AIS delivers strong performance at a lower upfront cost.

• Your site faces high humidity, coastal conditions, or dusty environments — the IP67-rated metal enclosed switchgear provides reliable protection.

• You need a practical and sustainable choice for rural substations, industrial parks, or urban distribution networks with standard-sized equipment.

Choose GIS if:

• Your project site has very limited space, so compact design is a priority.

• You need underground substations, high-rise buildings, or dense urban networks where footprint matters most.

• Your application demands high fault current capacity and superior arc performance.

• You need a fully sealed SF6 ring main unit that handles extreme weather and high humidity with minimal risk.

• Your automated distribution network requires remote control and SCADA integration.

In practice, both AIS and GIS can operate reliably in tropical climates, industrial zones, and fast-developing urban grids. The decision comes down to space, budget, environmental policy, and long-term operational goals.

Conclusion

Air insulated switchgear and gas insulated switchgear each bring clear strengths to modern power distribution. AIS offers an eco-friendly, cost-effective, and flexible solution for a wide range of projects. GIS delivers unmatched compactness and lifetime maintenance-free performance for space-critical applications.

Both medium voltage switchgear types meet IEC standards and support smart grid integration, so both are reliable choices for today's power networks.

Understanding the main differences between AIS and GIS helps engineers and procurement teams select the right ring main unit for each project. Whether you need a sustainable SF6-free RMU or a compact gas insulated enclosed switchgear, matching the technology to your site conditions leads to better performance and lower long-term costs.