Comparison of AIS and GIS switchgear in medium voltage power distribution – Taili Electric reference
Medium voltage (MV) switchgear is one of the most important parts of a power distribution system. It protects equipment, maintains service continuity, and ensures safe operation. But when it comes to selecting switchgear, should you choose Air-Insulated Switchgear (AIS) or Gas-Insulated Switchgear (GIS)?
The answer depends on cost, footprint, features, environment, and long-term maintenance. In this article, we take a closer look at the differences, use cases, and technical data that matter to contractors and end-users.
1. What is MV Switchgear?
MV switchgear generally operates from 3.3 kV up to 36 kV, used in utilities, industrial plants, commercial complexes, and infrastructure projects. It houses components such as circuit breakers, busbars, relays, and disconnectors.
- AIS (Air-Insulated Switchgear) uses ambient air as the insulation medium.
- GIS (Gas-Insulated Switchgear) uses SF₆ (sulfur hexafluoride) or new eco-friendly gases in a sealed chamber.
2. Space and Installation Requirements
- AIS requires large clearance distances due to the lower dielectric strength of air (~3 kV/mm). Moisture and pollution further reduce this.
- GIS uses SF₆ gas with dielectric strength ≥ 9 kV/mm, allowing compact design.
Key fact: GIS can save up to 60% footprint compared to AIS above 10 kV.
3. Cost Considerations
| Aspect | AIS (Air-Insulated) | GIS (Gas-Insulated) |
| Initial cost | Low to medium | High (1.5–2.5× higher) |
| Civil works | Simple, less demanding | Requires precision & tightness |
| Land requirement cost | Higher (more space needed) | Lower (compact footprint) |
| Long-term O&M cost | Higher (frequent maintenance) | Lower (sealed design, less aging) |
4. Features and Maintenance
- AIS advantages: easy to access and expand, simple installation and repair, flexible modification.
- AIS disadvantages: components exposed to dust, humidity, wildlife → faster aging, requires routine cleaning.
- GIS advantages: compact and sealed → long service life, minimal maintenance, high reliability.
- GIS disadvantages: difficult to modify once installed, requires SF₆ handling.
Taili Electric AIS switchgear inspection at workshop
5. Typical Applications
- AIS: rural or industrial sites, factories needing flexibility, projects with lower budgets.
- GIS: urban substations, metro stations, airports, polluted/coastal environments, projects requiring high reliability.
6. Technical Parameters (Typical)
| Parameter | AIS (IEC Standard) | GIS (IEC Standard) |
| Rated Voltage | up to 36 kV | up to 36 kV (some to 72.5 kV) |
| Rated Current | up to 4000 A | up to 3150 A |
| Short-circuit withstand | up to 63 kA (1s) | up to 40 kA (1s) |
| Dielectric strength | ~3 kV/mm (air) | ≥ 9 kV/mm (SF₆ gas) |
| Typical service life | 25 years (with maintenance) | 30–40 years (sealed design) |
7. Environmental Considerations
- AIS: no greenhouse gases, but larger footprint.
- GIS: uses SF₆, strict leakage control needed.
- Future trend: Eco-GIS using alternative gases (dry air, C4-FN mixtures).
8. Checklist Before You Decide
- Do you have enough land for AIS, or is your site space-constrained?
- Is initial cost more critical, or long-term reliability?
- What are the environmental conditions?
- Are maintenance resources available locally?
- How strict are regulations on SF₆ in your country?
9. Conclusion
There is no one-size-fits-all answer.
- Choose AIS if you want low upfront cost, flexibility, and easy maintenance.
- Choose GIS if your project faces space constraints, pollution risks, or requires high reliability.
Taili Electric has experience delivering both AIS and GIS switchgear solutions worldwide, supporting contractors and utilities to balance technical needs, land use, and life-cycle costs.
Author's Note
This article was prepared based on IEC standards and project experience by the Taili Electric technical team. With four factories and global project references, Taili Electric offers customized MV switchgear solutions.
