Air-Insulated Substation vs. Gas-Insulated Substation: Which One is Right for Your Project?

Selecting an appropriate substation for a project is very difficult. You have to consider a lot of different things, such as space requirements, weather, budget, and time for installation. If you’re constructing in a remote region or even in a busy city, a lack of proper planning can affect costs, project timelines, and reliability. In this blog, we will compare the differences between AIS and GIS so you can make the right decision.

1) What is an Air Insulated Substation (AIS)?

An Air Insulated Substation (AIS) is a type of electrical substation with all of its high-voltage parts placed outdoors while its Air Acts as a Substation Insulator. Meaning its surroundings have to be air. Air is the enclosing substance which serves the purpose of insulation between conductors and grounded structures. This type of substation has been used for decades and seems to be a popular choice even today due to its cost-effectiveness and simplicity.

How does an Air-Insulated substation Works

AIS receives electrical energy at high voltages from power generation or transmission sources. It transforms that energy into lower voltage levels suitable for local distribution. The equipment is mounted on steel or concrete frames in open air. Because air serves as an electrical insulator between components, a larger space is needed to avoid short circuits between the parts. This is the reason why AIS is often implemented in areas where land is easily available and not an issue.

Key Components of AIS

These are the basic components of a substation comprises of:

i) Circuit Breakers: These protect the system by interrupting the flow of power in case of faults or overload conditions free of human involvement.

ii) Disconnect Switches: They allow for maintenance by providing access to service parts without bringing the entire system down. Thus, ensuring repair safety and operation under safe conditions.

iii) Busbars: As large strips of metal capable of carrying thick electrical currents in the substation, busbars connect the incoming and outgoing power lines with other equipment.

iv) Transformers: These devices step down or step up voltage levels as per the power system requirement. The transformers serve as the primary constituents in voltage conversion for AIS.

v) Insulators: These are made of porcelain or composite materials. Insulators support the live conductors and separate them from the grounded parts to avert short circuits and flashovers.

All components are spaced out over a wide area in the open air. In the absence of closed housing, reliable operation and safety are ensured through proper component spacing.

Typical Application Scenarios of AIS

• Semi-urban and Rural Power Distribution: Where land is cheap and spacious, AIS are most preferred.

• Power Plants and Industrial Zones: Industrial plants and large generation stations utilize AIS for easier maintenance. Power load and flow management are also adequately streamlined.

• Stable Moderate Climate Open Air Installations: Polished and moderately polluted regions pose no problem to AIS. Weather-affected external environments are no problem for the equipment.

• Substations Near Dams and Renewable Energy Projects: AIS technology is used in solar power plants and hydroelectric dams because it is economical and facilitates easy expansions.

Pros of AIS

+ Lower Installation and Operating Costs: Because no housing or gas systems have to be specially built, the air-insulated system substation is less expensive and easier to operate.

+ Easier Inspection and Maintenance: Because all equipment can be viewed easily, regular inspections and fault detection become quicker and more convenient.

+ Simple Design and Layout: The design can be easily understood and utilized by engineers and maintenance workers.

With proper care, Air-Insulated Substations (AIS) can continue to function effectively for over thirty years without major concerns.

Cons of AIS

However, while the benefits provide considerable value, AIS also comes with some downsides.

- Large Space Requirement: Because the construction needs operable safe spacing between parts, AIS requires considerable land area. This makes it inappropriate for urban areas that have spatial premium.

- Exposure to Weather and Pollution: Since the equipment is outdoors, it is directly exposed to rain and dust, snow, and even birds. Any of these can hinder productivity or, worse cause faults.

- Less Insulation Strength Relative to Gases: Compared to special gas types such as SF₆, the air has a lower insulating capability. This increases the chances of flashovers or electrical arcs, particularly in high-voltage systems.

- Cleaning and Maintenance Done Manually: A combination of dust, rust, and other environmental factors may damage components. Regular cleaning and servicing is imperative, as they help prevent faults or failures within the system.

2) What is a Gas Insulated Substation (GIS)?

A Gas Insulated Substation (GIS) is a type of electrical substation where the main components are enclosed in a metallic compartment containing an insulating gas under pressure. GIS is more compact than traditional substations since it uses sulfur hexafluoride (SF₆) as the substation gas. It is most suitable to place in areas where space is limited or in areas with extreme weather.

How does a Gas-Insulated substation Work

A GIS substation contains high-voltage components such as bus bars and power transformers sealed within metallic housing compartments filled with SF₆ gas. This gas has high dielectric strength, allowing it to prevent current from arcing between conductors. The closed design keeps the equipment safe from rain, dust, or other pollutants.

Electricity is brought to the substation, where it is routed through various gas-insulated components like circuit breakers, busbars, and disconnecting switches. These devices control the flow and step the voltage up or down as required.

• SF₆ Gas Purpose

Sulfur hexafluoride, or SF₆, is colourless, odourless, and cannot be set on fire. It is used in GIS because of its excellent insulating properties and its ability to extinguish an electric arc.

• SF₆ Advantages:

• Withstand and maintain much higher voltages where electricity cannot escape containment.

• Improves the safety of the system by suppressing arcs (sparks) during switching.

• Reduces material space constraints and allows for configuration components to be placed more closely together.

• SF₆ Disadvantages:

• Acts as a greenhouse gas and poses an environmental concern when released into the atmosphere.

• Prohibitive regulations for dealing, storing, and disposing of materials create the potential for accidental environmental leaks.

• Gas-insulated substation (GIS) systems require proper sealing to contain gas over prolonged periods.

• Despite these considerations, SF₆ is still the best choice for many high-voltage systems.

Key Components of GIS

i) Gas Insulated Circuit Breakers: These units serve the purpose of interrupting the current flow during faults by means of electrical contacts sealed in containers. They can filled with SF₆ and withstand very high voltages effortlessly.

ii) Gas-Insulated Busbars: These parts facilitate electricity conduction between different devices located within the substation. Their compact form enables increased power flow through a reduced spatial volume.

iii) Sealed Power Transformers (external or internal): Transformers can either rest externally GIS or may be partly covered. Such transformers alter the voltage levels safely, without direct contact with air.

iv) Monitoring and Gas Control Units: These assist in monitoring the appropriate gas pressure and quality of the gas. In particular, they help in early leak detection and ensure the safe operation of the system.

Gas-insulated bus bars allow for the compact containment of all parts of the system keeping it orderly and clean, while requiring the units to be stored in metal casings filled with insulating gas to keep them protected.

Typical Application Scenarios of GIS

Gas Insulated Substations (GIS) are most suitable for the following regions:

• Urban and Metropolitan Areas: GIS is an excellent answer to problems and needs in big cities (metropolitan areas) where land is scarce and expensive. Its compact design permits construction to be done in basements, rooftops, or small plots of land.

• Coastal and Industrial Areas with Severe Weather Wind: GIS is a good fit for areas with salt, dust, or high humidity. The sealed design protects components from corrosion and dirt.

• Subway and Roof-Mounted Systems: GIS can be installed in tunnels and underground stations or on the tops of buildings. It is flexible and does not require large open spaces.

• Airports, Rail, and Data Centers: Sensitive infrastructure projects trust GIS because of its dependability, safety, and capability to operate in constricted or closed spaces.

Pros of GIS

The following is a list of the main advantages of having a Gas Insulated Distribution station.

+ Compact Design Saves Space: Compared to AIS, GIS needs much less space. It can be installed in busy urban areas without much hassle.

+ Reliable operation in harsh environments: Dust, moisture, and pollution are kept out by the sealed system. GIS operates well in deserts, snowy regions, and coastal areas.

+ Minimal Maintenance Needed: Enclosed GIS systems avoid the need for regular cleaning or weather-related repairs since all parts are covered. This helps reduce long-term operational costs.

+ Reduced Electrocution/Fire hazard: Sealed and grounded enclosures prevent the possibility of electric shock or fire, greatly improving safety for nearby staff who work with GIS.

Cons of GIS

While GIS has its advantages, it also has some disadvantages:

- More Expensive: Compared to AIS, GIS systems cost more to construct because of the gas containers, sealing systems, and the need for special handling.

- Delays due to Specialized Maintenance and Tools: The need for specialized tools and trained workers can delay repairs, increasing the amount of time needed for routine maintenance, which can reduce overall efficiency.

- SF₆ Gas Environmental Impact: Although safe to use, SF₆ gas poses a dangerous impact on the environment if leaked. Careful tethering rules must be put in place to limit the damage.

- Hard to Add Components: Incorporating new components into existing GIS is more difficult compared to AIS expansions. Unplanned sealed designs make future additions more cumbersome.

3) AIS vs. GIS: Key Difference

The choice between an Air Insulated Substation (AIS) and a Gas Insulated Substation (GIS) depends on a number of factors. Each has its pros and cons and performs better in different situations. Below are the fundamental differences between the two types of substations.

a) Space Requirement

AIS: An AIS requires a lot of open area as all its components are spread out and installed outdoors. You need a wide area to build it.

GIS: As GIS is compact, it can be installed in tight places like basements, on rooftops or even underground. All parts are sealed in small metal enclosures.

b) Installation Time

AIS:  As a result of the wide layout and extensive outdoor work required, AIS takes a longer time to install. Ongoing site work in bad weather can also lead to delays.

GIS:  Due to the many pre-assembled parts, GIS is quicker to install. The set schedule for installation is maintained because it is less affected by weather.

c) Maintenance Needs

AIS:  Because AIS is open to the environment, dust, moisture, and pollution can significantly affect performance. Cleaning and checking are required regularly.

GIS:  Because of the seal GIS has, it needs very little maintenance, which lowers long-term upkeep costs.

d) Initial Cost

AIS:  The AIS is less costly to build. The components are less expensive, and no special enclosures or gas systems are required.

GIS:  GIS requires a greater initial investment. The cost is higher because of the gas system, sealed containers, and protective equipment.

e) Safety and Reliability

AIS:  Safety does exist with AIS, but it can be affected by weather, animals, or even dust. Equipment meant for outdoor use is prone to failure under harsh conditions.

GIS: GIS is superior when it comes to reliability. Its sealed construction prevents the entry of everything—weather, dust, and small animals. It is also safer for use which minimizes the chances of failure.

f) Environmental Impact

AIS: AIS poses no environmental risks as it employs air for insulation. However, the amount of land it uses could disrupt natural habitats, which is a concern.

GIS: GIS design contains SF₆ gas which is considered a powerful greenhouse gas. If allowed to escape, it could be detrimental to the ecosystem. Proper methods of handling are necessary.

g) Expandability

AIS: With AIS, components can be further added, and expansion is more convenient with a little additional space there.

GIS:  Flatness and compactness of GIS equipment make expansion difficult. The sealed design coupled with the compact layout means additional work will be needed unless the changes are designed from the beginning.

h) Suitability Based on Location

AIS:  Deals best with rural regions, industrial centers or any other site with a lot of lands. It’s appropriate when space is abundant.

GIS:  GIS works best with metropolitan regions, coastal areas, or areas experiencing heavily severe weather. It functions well when there is little space or harsh conditions.

Feature	AIS (Air Insulated Substation)	GIS (Gas Insulated Substation)
Space Needed	Large open area	Compact; fits small spaces
Installation Time	Slower	Faster
Maintenance	Frequent cleaning and checks	Very low maintenance
Initial Cost	Lower	Higher
Reliability	Affected by weather and dirt	High; sealed and protected
Environmental Risk	No gas involved	SF₆ gas risk if leaked
Ease of Expansion	Easy to expand with space	Hard to expand without planning
Best for	Rural, open locations	Urban, coastal, or space-limited sites

4) How to Choose the Right Substation for Your Project?

Finding a suitable substation may look like a rather complex task, but it becomes very simple once you know what to pay attention to. Below are six fundamental factors you have to keep in mind while making the decision.

• Space capacity: Currently, a large area is still available for AIS since all of its parts are set up. It is perfect for open spaces such as industrial regions or rural areas. GIS is small and adapts to areas with little available space such as urban buildings or underground structures.

• Environmental aspects: Dust, dirt, and other pollutants will have an effect on workflow and other moving parts of the system. That is why if your site is prone to dust, pollution, or salty air, GIS is a much better option as it is completely sealed off and protected from outside factors.

• Financial considerations: Working on limited budgets would favour AIS due to its lower upfront costs. GIS will always incur higher initial costs but often ends up being cheaper in the long term due to fewer repairs.

• Time of installation: Larger systems take longer to install and set up which is the case with AIS. GIS is much faster to set up since many of its components come pre-assembled into smaller parts.

• Amount of upkeep needed: Less upkeep usually translates into lower effort and cost and this is exactly why GIS is a better choice. Unlike AIS, GIS is much quieter and requires less upkeep.

5) Conclusion

To summarize, both AIS and GIS have their strengths based on the specific requirements of your project. AIS is budget-friendly and performs well in open areas, but is high-maintenance and time-consuming to install. GIS is more expensive but performs reliably in compact and harsh settings. Always remember your budget, available space, weather conditions, and the project's long-term objectives when selecting a substation.

Delixi provides power transmission and distribution equipment that are customized to fit the requirements of your project. Delixi Electric is the optimal partner for urban and rural applications because, with innovative products, exceptional performance, and expertise, we ensure efficiency and safety. Rely on them for comprehensive, trustworthy electrical solutions, knowing that power problems are handled with utmost expertise.

6) FAQ

1. Which is better, AIS or GIS?

The decision is made depending on space availability, budget, and other environmental factors. For cost-effective solutions in open areas, go with AIS. If you require reliability, and compactness, and can work in extreme or cramped spaces, GIS works best.

2. How much is GIS compared to AIS?

Due to the geometry, compact design, gas-insulated technology, and sealed components, GIS is more expensive upfront. AIS is cheaper at the start, but an increase in maintenance and costs is expected over time.

3. Why are GIS substations better suited for urban applications?

In GIS, compactness, sealing, and reduced footprint make it suitable for crowded urban regions. It offers better service in polluted environments and because of lower maintenance requirements, ensures reliable service.

4. Is AIS suitable for severe weather conditions?

Heavy snow, strong winds, or rain can negatively impact the effectiveness of the AIS system. The outdoor components can be damaged, therefore, making GIS a better alternative for harsher conditions.

5. Which substation is faster to install?

Due to its compact size, GIS is faster to install because of its pre-assembled parts. The spread-out configuration of AIS makes it more time-consuming to set up.