Differences Between Air Insulated Switchgear (AIS) and Gas Insulated Switchgear (GIS)
The differences between Air Insulated Switchgear (AIS) and Gas Insulated Switchgear (GIS) are significant and impact various aspects of their design, operation, and maintenance. Below, we break down the key differences into several categories for a clearer understanding.
1. Ownership Costs
Ownership involves the total cost of acquiring and maintaining the equipment over its lifetime, typically around 30 years.
- GIS:
- Higher upfront costs, ranging from 10% to 40% more than AIS.
- Lower maintenance requirements, which reduce long-term costs.
- AIS:
- Lower initial investment.
- Higher maintenance demands, which can increase lifetime costs.
2. Maintenance Requirements
Maintenance is a crucial factor in determining the suitability of a switchgear system for specific applications.
- GIS:
- Requires minimal maintenance.
- Visual inspections are typically needed every 4+ years, depending on the manufacturer’s recommendations.
- Re-greasing is required only every 20+ years for most models.
- AIS:
- Demands more frequent maintenance, with visual inspections required annually or biannually.
- Each compartment needs thorough assessment, including cleaning, lubrication, vacuuming, and checking for copper corrosion.
- Maintenance is more labor-intensive compared to GIS, requiring approximately 4 hours per breaker every two years.
3. Operation
Operational simplicity and safety are essential considerations.
- GIS:
- Easier to maintain due to front access and built-in testing instruments.
- Arc flashes are rare, as all internal components are insulated.
- Cable compartments are isolated, preventing live part exposure.
- AIS:
- Requires careful operation, with more frequent manual interventions for inspection and maintenance.
4. Installation
Installation time and space requirements differ significantly between the two systems.
- GIS:
- Faster installation due to its compact and lightweight design.
- Occupies up to 35% less space compared to AIS.
- Installation time is reduced by approximately 30% compared to AIS.
- AIS:
- Requires more space due to air clearance for insulation.
- Installation takes longer and may involve additional steps.
5. Structural Design
The core structural differences lie in the insulation medium and breaker design.
- GIS:
- Uses SF6 gas for insulation, which is denser than air and offers excellent arc-extinguishing properties.
- Features sealed-for-life, mounted circuit breakers.
- AIS:
- Uses air as the insulating medium, requiring larger clearances to meet dielectric performance standards.
- Employs draw-out circuit breakers that can be removed for maintenance or troubleshooting.
6. Design Standards
Both AIS and GIS adhere to IEC standards (e.g., IEC 62271-1, IEC 62271-200, IEC 62271-100).
- AIS:
- Switching media include air, SF6, vacuum, or oil.
- GIS:
- Typically uses SF6 or vacuum as the switching medium.
7. Size
- GIS:
- Smaller, as multiple functions are integrated within a single gas tank, reducing overall dimensions.
- AIS:
- Larger, as it requires greater clearance distances for insulation.
8. Sensitivity to Pollution
- GIS:
- Highly resistant to environmental factors like humidity and pollution, thanks to its IP67-rated sealed design.
- AIS:
- Moderately sensitive to environmental conditions, with insulation exposed to air.
9. Cable Termination
- GIS:
- Requires specialized cable terminations to ensure proper insulation within reduced clearances.
- AIS:
- Compatible with standard cable terminations, making installation more straightforward.
10. Modularity
- GIS:
- Future expansions need to be considered during the initial design phase. Extensions may have limitations.
- AIS:
- Naturally modular, allowing easier and more flexible upgrades and extensions.
11. Gas Pressure Monitoring
- GIS:
- Requires monitoring for both switching devices and busbars with SF6 gas.
- AIS:
- May only require gas pressure monitoring for SF6-integrated switching devices.
Summary
Both GIS and AIS have their unique advantages and limitations:
- GIS is compact, requires less maintenance, and is better suited for environments where space and pollution resistance are critical.
- AIS is more cost-effective initially, easier to upgrade, and has simpler cable termination requirements.
Understanding these differences can help in selecting the right switchgear system based on project requirements and environmental factors.
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