Feb 11, 2026
AIS vs. GIS: Which Substation Technology Is Right for You?
Summary: Every new electrical substation design must account for insulation. Either air or a specialized gas can insulate the equipment against arcing. The two options must be carefully considered during a new substation's early design phase.
An electrical substation is essentially a traffic coordinator within a certain section of the power grid. A substation accepts high-voltage electricity from power plants and transforms it into lower voltages that can be safely utilized in homes and businesses. Without the substation, you do not have a viable grid accessible for daily use.
With that said, all electrical substations are not identical. They are not all built in the same way and with the same technologies. When engineers first begin design work on a new substation, there are plenty of things to consider. Chief among them is insulation. The two most common designs are Air-Insulated Substations (AIS) and Gas-Insulated Substations (GIS).
The two technologies perform exactly the same job. Yet they do it in unique ways. Engineers work diligently to figure out the best technology for each new project in order to avoid unnecessary costs, project delays, and future maintenance headaches.
The Primary Difference Between AIS and GIS
AIS and GIS substations can differ in several ways. Yet at the core is one primary difference rooted in insulation. Note that the type of insulation engineers are concerned about has nothing to do with keeping facilities warm in the winter and cool in the summer. Rather, engineers need to insulate against electricity.
In a high-voltage setting, electricity wants to arc (or jump) to other grounded objects. This cannot be allowed to happen. Therefore, engineers must insulate all electrified objects to ensure no arcing occurs. The electricity within each object must stay in it. How does that apply to AIS and GIS?
AIS – AIS technology relies on air as the primary insulator. Air's ability to prevent arcing is limited, so the equipment in an AIS substation needs to be spaced properly. There must be enough space between components to prevent arcing.
GIS – A GIS substation relies on a specialized gas within electrified components. Sulfur hexafluoride (SF₆) is a common choice. It is much more effective at preventing arcing than plain air, allowing equipment to be situated much closer together inside a sealed environment.
Carefully considering the needs of a new substation can help point engineers in the right direction during the early design stage. Neither technology is always better than the other. Both have their applications.
4 Factors for Comparison
Designing a new electrical substation is no easy task. Neither is deciding between AIS and GIS technologies. The rule of thumb in our industry is to look at key factors for comparison. Here are four such factors:
1. The Substation Footprint
The greatest impact of the AIS vs. GIS decision is observed in the footprint of the eventual substation. Because AIS relies on air to prevent arcing, an AIS design requires a lot of space. An outdoor substation with large towers and plenty of space between them is an AIS substation. The design is common in suburban and rural areas where engineers have plenty of land to work with.
GIS substations are comparatively smaller. They are considered compact for the simple fact that they can effectively operate in a footprint that is 70-90% smaller that an AIS footprint.
If engineers have plenty of land to work with, they may go with the standard AIS design. But GIS is often the best choice when land is limited. GIS substations are the preferred design in already crowded urban environments.
2. Short- and Long-Term Costs
Engineers need to always consider the budget when designing and planning for a new electrical substation. They look at both the initial investment and the long-term cost over about 30 years. For comparative purposes:
Short-Term Savings – AIS technology is significantly less expensive. Therefore, the initial investment is comparatively low. Between simpler equipment, industry standards, and no shortage of contractors able to do the work, AIS is definitely the cheaper option. GIS can cost up to 2.5 times more.
Long-Term Costs – While AIS is cheaper initially, it is not in the long run. GIS actually saves money over the long term thanks to easier maintenance, lower property taxes, fewer site preparation and maintenance needs, etc.
For engineers, the real trick is forecasting long-term costs. It is important to know if the savings generated by a GIS substation are substantial enough to warrant a higher initial investment.
3. Substation Maintenance and Reliability
Engineers are not designing substations just for the here and now. A station should last decades, potentially outliving the engineers behind it. Enter maintenance and reliability. Engineers need to think about what future engineers and technicians will have to deal with.
AIS technology is high-maintenance technology. Because equipment is outdoors, it is exposed to everything the environment throws at it. AIS installations require routine inspections and regular cleaning. The bill adds up quickly.
On the other hand, a GIS installation can go 10-20 years without significant maintenance. Equipment is sealed in closed environments, protecting it against environmental influences. For all intents and purposes, a GIS substation is a set-it-and-forget-it installation.
4. Sustainability and Environmental Impacts
Over the last 20 years or so, engineers have designed new substations with sustainability and environmental impacts in mind. It is part of a broader effort to prioritize protecting the planet for future generations. And as the world consumes ever more electricity, there is always the risk that building more substations will negatively affect the planet.
AIS is considered the more sustainable choice where building materials are concerned. Plastics are pretty much out of the question in an electrical substation, and insulating with air eliminates the risk of any harmful chemicals escaping into the environment.
The big concern with GIS is the insulating gas. SF₆ is classified as a greenhouse gas. So GIS systems are designed to be sealed for life. Yet there is always the risk that sealed environments will fail and the gas will escape.
Both AIS and GIS technologies accomplish the same thing. But they are different enough that engineers need to consider them carefully when designing new substations. It is all part of what goes into keeping the modern world humming along with sufficient power.
FAQs
Can GIS equipment be installed indoors?
Absolutely. One of the big advantages of GIS is that substations can be deployed inside new buildings or even basements.
Which technology is easier to scale?
In terms of scaling up, AIS is easier to work with. Adding new equipment on available land is fairly easy. GIS is more rigid and modular by design.
Which technology lasts longer?
Both have a 30-40-year lifespan. However, GIS components are less susceptible to damage because they are in a sealed environment.
Is GIS gas toxic?
SF₆ and other gas is used in GIS systems are nontoxic to humans. They are also non-flammable and chemically stable. But many are greenhouse gases.
Is it possible to mix the technologies?
Yes. Hybrid Substations (H-GIS) relies on GIS tech for the switchgear and AIS for everything else. Hybrid substations are a great middle-ground option.
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