Introduction

In power system construction, the selection of switchgear not only affects the safety and reliability of power supply but also directly impacts project investment, land use, and post-construction maintenance. Air-insulated switchgear (AIS) and gas-insulated switchgear (GIS) are the two most common solutions currently available, each with its own advantages and limitations. To make a reasonable choice under different spatial conditions, budget objectives, and environmental requirements, it is essential to first understand their characteristics and applicable scenarios. This article will provide a comprehensive comparison of the differences between AIS and GIS, offering guidance for your project decision-making.

What is AIS?

AIS (Air Insulated Switchgear) uses ambient air and insulators as the insulation medium, with exposed busbars. It’s suitable for less confined areas and offers cost-effective options for medium voltage systems.

Advantages of AIS

1. Lower Initial Cost: More affordable compared to GIS, no need for SF₆
2. Simple Structure: Proven and reliable technology with straightforward design.
3. Easy Maintenance: Accessible parts for frequent inspection and repairs.
4. Scalability: Modular design allows easy future expansion.
5. Environmentally Friendly: No greenhouse gas emissions (no SF₆).
6. Good Heat Dissipation: Open layout helps in better heat management.

Disadvantages of AIS

1. Large Footprint: Requires significant land area, inefficient in urban areas.
2. Environmental Sensitivity: Vulnerable to pollution, weather conditions, and animals.
3. Frequent Maintenance: Needs regular cleaning and inspections.
4. Lower Reliability: More prone to contamination and short circuits in harsh environments.
5. Safety Risks: Exposed components pose a higher risk of electric shock.
6. Noise Pollution: Switching operations create significant noise.

AIS Advantages vs. Disadvantages Table

What is GIS?

GIS (Gas Insulated Switchgear) utilizes SF₆ gas in sealed metal enclosures to insulate live components, making it suitable for high-voltage and space-constrained environments.

Advantages of GIS

1. Compact Design: Saves significant space (90% footprint reduction compared to AIS).
2. High Environmental Resistance: Sealed design protects against dust, humidity, and animals.
3. Low Maintenance: Maintenance-free for 10 years, fewer inspections needed.
4. High Reliability: Low failure rate, suitable for harsh environments.
5. Safety: Enclosed components reduce electrical shock risk and arc flash.
6. Noise Reduction: Metal enclosures reduce operational noise by 30%–50%.

Disadvantages of GIS

1. High Initial Cost: 1.5–2.5 times more expensive than AIS.
2. SF₆Gas Risks: Potential environmental and health risks due to SF₆
3. Complicated Fault Repairs: Internal faults require disassembly and specialized repairs.
4. Limited Flexibility: Difficult to retrofit or expand after installation.
5. Sensitive to Particle Contamination: Requires clean assembly conditions to prevent partial discharge.

GIS Advantages vs. Disadvantages Table

AIS vs. GIS: Key Differences

1. Space and Footprint

GIS: Occupies only 10%–30% of AIS footprint, supports compact 3D layouts, suitable for underground, multi-floor, or offshore sites.

AIS: Requires large outdoor areas, higher land cost, unsuitable for urban cores.

2. Cost

AIS: Low initial investment (about 40%–60% of GIS), but higher land and maintenance costs.

GIS: High initial investment (1.5–2.5× AIS), but saves on land, construction, and long-term O&M.

3. Environmental Impact

AIS: No SF₆ gas risk, but large footprint and environmental exposure.

GIS: SF₆ gas has high GWP, but compact and sealed against pollution.

4. Maintenance & Reliability

AIS: Easy to maintain, fast repairs, but exposed components are vulnerable to contamination and have higher failure rates.

GIS: Long maintenance cycle (10 years maintenance-free), low failure rate, but slow repairs requiring specialists.

5. Safety

AIS: Exposed high-voltage parts require strict protection measures.

GIS: Fully enclosed design prevents electric shock and arc flash, safer.

6. Applications

GIS: Best for urban areas, polluted industrial zones, high-voltage, and special facilities.

AIS: Best for suburban/rural areas with abundant land and medium-voltage systems, cost-effective.

When to Choose AIS vs. GIS?

Choosing between AIS and GIS is not a matter of right or wrong; it all depends on how you balance spatial considerations, budget, environmental conditions, and long-term operational goals.
If the site is spacious, the budget prioritizes upfront costs, and environmental conditions are relatively mild, AIS may be the more natural choice. It has a simple structure and is easy to maintain, making it ideal for medium-voltage projects in rural or suburban areas.
If the project is in a densely populated urban core area, a heavily polluted industrial zone, or a coastal region, or if the project has particularly high requirements for reliability and safety, GIS often has the advantage. It is compact, sealed, and environmentally resistant, with a long maintenance cycle, making it especially suitable for critical mission scenarios.
Many projects actually opt for a hybrid solution, leveraging the strengths of both AIS and GIS. For example, the core components use GIS to ensure performance, while the peripheral feeders use AIS to save costs, achieving both stability and flexibility.

Conclusion

Whether it’s AIS or GIS, there is no absolute superiority or inferiority; only the most suitable solution exists. AIS excels in low initial investment, simple structure, and ease of maintenance, while GIS stands out for its compact design, high reliability, and long lifespan. The key lies in conducting a comprehensive assessment based on the project’s spatial requirements, budget, environmental conditions, and operational needs. For certain specialized applications, a hybrid solution combining AIS and GIS is also worth considering, as it strikes a balance between performance and cost. By understanding the characteristics of both technologies, Chuanli can help you choose a reliable and cost-effective path for your power system.

FAQ

Is SF6 gas dangerous to humans?

Pure sulfur hexaluoride (SF₆) gas is non-toxic, but arcs decompose it into highly corrosive substances like hydrogen fluoride (HF) that can cause fatal injuries. In confined high-concentration environments, it also poses suffocation risks by displacing oxygen. Therefore, Gas Insulated Switchgear (GIS) mandates integrated leakage monitoring and purification recovery systems, while next-generation eco-insulating gases (g₃) will fully replace SF₆ by 2025 to eliminate these hazards.

How often does GIS need maintenance

GIS requires only annual basic inspections, with core gas chambers supporting maintenance-free operation for 10 years. However, high-corrosion environments (coastal/chemical zones) necessitate semi-annual checks. Modern intelligent GIS further enables proactive maintenance through real-time partial discharge monitoring.

Can an AIS substation be converted to a GIS substation?

AIS substations to GIS is technically feasible but subject to significant practical constraints: New seismic-resistant foundations must be poured to support heavy GIS modules (each cubicle weighs 3-5 tons), existing open busbars require replacement with gas pipelines (maintaining SF₆ explosion-proof clearances), and arc-extinguishing chambers must be integrated within confined spaces (110kV conversion costs >¥8 million per bay). Consequently, 70% of real-world cases adopt hybrid “GIS core + AIS feeders” solutions instead of full-station conversion.

What is the lifespan of AIS vs. GIS equipment?

The design lifespan of AIS reaches 30 years in dry, clean environments, but practical application is constrained by insulator aging (approximately 20 years) and salt fog/contamination (reducing longevity to ~15 years). In contrast, GIS achieves over 40 years through its fully sealed structure that shields against environmental degradation. When SF₆ gas purity exceeds 97%, GIS reliably operates beyond 50 years. For medium-high voltage projects (220kV+), GIS service life averages 60% longer than AIS systems.