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The Difference Between Air Insulated Switchgear and Gas Insulated Switchgear

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.