GIS vs AIS: Key Differences Explained

The electrical distribution, transmission, and generation systems all include substations. Since the flow of current is not always consistent, a device must be used to transition high voltage electricity into low voltage power appropriate for consumer distribution. This equipment is known as a substation.

Gas insulated substation and air-insulated switchgear are the two types of insulated substations. Let’s look more closely at the distinctions between them.

What is a GIS(Gas Insulated Switchgear)?

Gas Insulated Switchgear

Gas-insulated switchgear (GIS) is a type of electrical equipment that uses a gas, such as sulfur hexafluoride (SF6), to insulate and protect various components of a power system. It consists of metal-enclosed compartments that house circuit breakers, disconnectors, bus bars, transformers, earth switches, surge arresters, and other devices. GIS is mainly used for medium and high voltage applications, where space is limited, and reliability is essential.

A gas-insulated switchgear (GIS) is defined as a metal-enclosed switchgear that uses a gas, such as SF6, as the primary insulation between live parts and the earthed metal enclosure. The gas provides high dielectric strength, high thermal stability, and excellent arc quenching properties.

What is a AIS(Air Insulated Switchgear)?

Air Insulated Switchgear

Air-insulated switchgear(AIS) is a secondary power distribution device and medium voltage switchgear that helps redistribute the power of a primary power distributor powered by a high voltage distribution transformer.

AIS controls, protects and isolates electrical equipment in power transmission and distribution systems. The equipment is designed to be operated in the air at atmospheric pressure, which is why the name “air-insulated.”


Aside from the dielectric media used, AIS and GIS have a lot of notable distinctions. They are described in full further down.


Each type of switchgear’s longevity and maintenance depend on how it was built. While AIS insulates using air in a metal-clad structure, GIS uses the chemical gas sulfur hexafluoride. Since it is five times heavier than air, sulfur hexafluoride exhibits excellent extinction behavior.

Another notable distinction in terms of construction is that a steel AIS employs three-position power take circuits (on, off, and test). Electrical appliances are put permanently in GIS systems.

The AIS breaker may be dismantled for service and troubleshooting, unlike the hermetically mounted breakers, which are a “sealed-for-life” technology.

Gas Insulated Switchgear


Is the project’s schedule constrained? How much room do you physically have for switchgear? Installing GIS may go more quickly than installing its AIS metal-clad equivalent. This is mostly because GIS systems are substantially lighter and smaller, although gas is heavier than air.

GIS is easier to install if the technician doesn’t have to touch the gas themselves. A GIS installation reduces the typical installation time by about a third. Additionally, GIS systems are smaller than AIS. A GIS has a roughly 40% smaller physical footprint than an AIS.


In terms of its operations, GIS systems are much easier to manage on a routine basis because they have frontal access rather than rear access. They also have their own built-in testing equipment.

A flashover of electric current departs its intended path and travels through the air from one conductor to another or to the ground, which is known as an arc flash. Arc flashes can occur in electric systems, but they’re uncommon in GIS switchgear because all of the inside components are shielded, and only the cable compartment is accessible. No cables or links can come into contact with the live conductors because they are totally insulated.

GIS switchgear training is more expensive than AIS switchgear training.

Total Cost of Ownership

CEED Electrical Equipment Gas Insulated Switchgear GIS

Primary hardware, maintenance, operation, outage, and disposal costs should all be considered to evaluate the overall cost.

The following is a cost comparison of AIS switchgear and GIS gear:

  • Primary hardware is used since both substations are primary machinery. The cost of equipment such as support, conductors, land, installation, management, protection, and surveillance are usually high. This can result in a minor cost difference between the two systems.
  • Since the probability of failure of circuit breakers and disconnectors is lower in GIS, the maintenance cost of hv GIS is cheaper compared to AIS.
  • GIS training is much more expensive than AIS training.

The cost depends on various factors. To calculate the overall cost, After-use decommissioning and disposal costs should also be budgeted.

Environment Effect

CEED Electrical Equipment Gas Insulated Switchgear GIS

Though both AIS air insulated switchgear and GIS gear are essentially harmless, there are specific environmental effects to be mindful of since substations necessitate the use of power and gas, both of which should be protected at all costs. The following are the environmental implications of mv GIS and AIS:

  • Noise

When air-insulated circuit breakers and load break switches are triggered, they can generate a high amount of momentary noise. Other noise sources from switching equipment in a substation include corona discharges, arcing while switches are in operation, and so on.

Since the machinery in HV GIS installations is wholly enclosed, the noise levels are lower. The SF6 gas in the enclosures is a convenient and efficient sound absorber since new arc interruption technologies in SF6 gas demand lower energy levels, smaller, spring-operated devices with lower noise levels have been developed.

  • Gas leakage

Under certain conditions, the fluids utilized, such as SF6 gas and other lubricating oils, can escape into the environment. Since SF6 is classified as a greenhouse gas, manufacturers and consumers should take all necessary precautions to prevent construction and operational leakage.

To combat gas leakage, numerous countermeasures are generally taken. However, when comparing the two substations, the length of sealed surfaces within AIS and GIS differs. Within GIS, the whole length of SF6 seals is the longest. However, in AIS, oil-filled equipment may well be placed. However, because GIS equipment is usually installed indoors, it reduces environmental exposure while also increasing the life of the sealing systems.

In terms of gas leakage, HV GIS systems are safer compared to AIS.

In addition to the above, the our provides extensive instructions for installation, service, maintenance, repair, and correct disposal in order to reduce handling losses.

  • Weather conditions

All technologies must be designed to withstand the weather parameters such as temperatures, humidity, ice, rain or snow, wind, solar radiation, and so on at the installation site. In this scenario, there is no significant difference between systems.

On the other hand, MV GIS systems are typically installed indoors, so they don’t have to be concerned about the weather.

  • Pollution

Pollution has a proportional influence on switchgear based on the number of insulators and bushings in that switchgear. As a result, more compact medium voltage gas insulated switchgear systems offer some significant benefits. Naturally, indoor switchgear has more advantages than outdoor AIS.


Regardless of their difference, it is up to power plant proprietors to determine which substation to install in their power plants.

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If you’re looking for high-quality air and gas-insulated power stations, have a look at our switchgear service, which is the professional switchgear manufacturing company. Electrical switchgears here are built to the highest safety standards.


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