Selecting the right products for your next electrical project is important!

If you don’t know the key differences between AIS vs GIS medium voltage switchgear, it’s easy to just assume they are all more-or-less the same.

But what if we told you the medium voltage switchgear market is projected to reach $42.89 Billion by 2024 and one wrong decision could cost you your entire electrical system?

Here’s the reality…

AIS and GIS technology are two distinct types of medium voltage switchgear that have different performance characteristics, advantages, and disadvantages. Your selection of gas insulated or air insulated switchgear will impact everything from upfront capital costs to maintenance headaches later.

Medium voltage switchgear is a critical component of any electrical system and when choosing switchgear for medium voltage applications, your understanding of AIS vs GIS makes all the difference for the success of your project.

What you’ll learn:

• What is so special about air insulated switchgear?
• Why is gas insulated switchgear more expensive (but could be worth it)?
• The real performance numbers you need to know.
• Smart selection strategies for your next project.

What is so special about air insulated switchgear?

Air insulated switchgear, also known as AIS, uses atmospheric air as the primary insulation medium between live parts. This can make them seem like simpler technology – and they are, in many ways.

Air insulated switchgear is not new, and has a market share of 69.9% as of 2022. But it’s not just due to legacy applications keeping this technology alive. The design of AIS is relatively simple – electrical components are separated by air gaps within metal enclosures.

AIS makes use of the natural cooling and deionization characteristics of air to extinguish any arcs after a fault condition, before the problem spreads.

Major benefits of air insulated switchgear

• Lower cost upfront. AIS is typically 30-40% less expensive than GIS.
• Easier to maintain. All components are exposed and easily accessible.
• Quicker installation. Simpler design results in faster construction.
• Environmentally friendly. No greenhouse gases or complex disposal needs.

Air insulated switchgear requires significantly more space than GIS though, which is the primary drawback.

Why is gas insulated switchgear more expensive (but could be worth it)?

Gas insulated switchgear, also known as GIS, uses sulfur hexafluoride (SF6) gas as the insulation medium, which enables it to operate in a very different manner than AIS.

Gas insulated switchgear is unique in that the SF6 gas used is 5x more insulating than air. This allows manufacturers to cram much more switching capacity into a much smaller space.

Major benefits of gas insulated switchgear

• Compact design. Takes up 10-15% of the space required by an equivalent AIS design.
• More reliable. Sealed systems isolate the equipment from outside environmental factors.
• Longer lifespan. GIS equipment can last 50 years vs 25-30 years for AIS.
• Safer. Fully enclosed systems mitigate arc flash hazards.

Of course there is always a trade-off. GIS comes with higher initial purchase price and more complex specialized maintenance procedures are required. The SF6 gas is also a greenhouse gas, and this is an issue many organizations are trying to avoid these days.

The real performance numbers you need to know

In the real world, here are the things that really matter in day to day operations.

The maintenance cycles are the game changer…

• AIS maintenance: 1-2 year maintenance cycle with regular visual checks.
• GIS maintenance: 8-10 years between maintenance intervals with little to no intervention.

Yes, that is an 8X difference in maintenance requirements when you calculate operating costs over the life of the equipment.

Space requirements are equally drastic

The obvious benefit of a more compact GIS system is a smaller footprint. AIS substations require large facilities for safe operation, while GIS can be accommodated on rooftops, underground or in urban areas where space is at a premium.

Installation timelines also vary greatly

GIS units can be delivered pre-assembled and factory tested, which cuts on-site installation time in half compared to AIS. AIS requires more work to assemble and test on site, but utilizes simpler methods most technicians are familiar with.

Smart selection strategies for your next project

It’s not just about technical specifications though. The project site and your particular needs must also be considered.

Choose Air Insulated Switchgear if

• Budget is a primary constraint
• Space is not an issue in the installation area
• Your maintenance team only has standard electrical experience
• Environmental regulations/rules favor gas free products
• You need to quickly replace AIS equipment

Choose Gas Insulated Switchgear if

• Space is extremely constrained or high cost
• Planning for a 40+ year installation
• Environmental conditions are extreme (pollution, moisture, temp. variations)
• Reliability cannot be compromised
• Specialized GIS maintenance expertise is available

The hybrid approach is also gaining market share

Combination air and gas insulated switchgear can provide a middle ground for certain applications.

Installation and Lifecycle Considerations

One thing most people forget

Equipment lifetime cost of ownership is much more than the purchase price. Maintenance, downtime, and replacement must all be factored in to see the true economics.

AIS offers many advantages over time.

• Lower skill level required for maintenance personnel.
• Spare parts availability is higher.
• Troubleshooting and repair is easier.
• No gas handling or disposal requirements.

GIS offers many advantages over time.

• Minimal maintenance requirements
• More reliable results in lower unplanned outages
• Compact size allows for more capacity in future
• Better performance in harsh environments

Project timeline considerations must also be taken into account

AIS installations generally take longer than GIS because all equipment must be assembled on site. GIS arrives as a pre-built unit and testing can begin much sooner, which can save weeks or months on the construction schedule.

Environmental and Safety Factors

Environmental factors also must be considered.

AIS environmental benefits

• No greenhouse gas emissions involved
• Simpler to dispose of at end of life
• No special handling or monitoring of gases
• Easier to meet environmental compliance standards

GIS environmental concerns

• SF6 gas has high global warming potential
• Specialized disposal methods needed
• Gas leak detection and monitoring is required
• Growing regulatory concerns

Safety considerations also weigh in differently

AIS gives you visual access to components but larger safety clearances are required. GIS provides better arc flash mitigation but maintenance personnel must have specialized training.

Wrapping It Up

Gas insulated or air insulated medium voltage switchgear each have their place depending on the specific application and long term operational needs.

Air insulated switchgear remains the more cost effective choice for the majority of medium voltage applications where installation space is not at a premium. It also is easier to maintain and environmentally friendlier, which are also important factors for many organizations these days.

Gas insulated switchgear is preferred when space is limited, reliability is of the utmost concern, or you are planning a decades long installation. The high upfront cost can be offset by reduced maintenance and better performance in harsh conditions over time.

The most important factor? Don’t just consider the purchase price. Examine your space constraints, maintenance capabilities, environmental goals, and future operational needs. The right selection today will affect the performance of your electrical system for decades to come.

No matter if you choose AIS or GIS, always work with a company that has experienced electrical professionals who know all the nuances of switchgear installation and maintenance. The reliability of your entire electrical system depends on it.