What is gas Insulated Switchgear?

Many facilities are using gas insulated switchgear today than ever before. In a study by Fortune Business Insights, the gas insulated switchgear market was found to be the fastest growing. Several reasons can explain that. In this article, you will read about what gas insulated switchgear means, its use and reasons for its rapid uptake.

Gas-insulated switchgear (GIS)
Gas-insulated switchgear (GIS)
Source: https://www.hitachienergy.com/

Introduction to Switchgear

Switchgear means the combined electrical apparatus that comprises the necessary equipment for making, carrying, and breaking electrical circuits in a power system. This includes switching and protective devices such as circuit breakers, fuses, contactors, relays, voltage and current transformers, etc.

The main types of switchgear are low-voltage (less than 1000 V AC), medium-voltage (1000-36 kV AC), and high-voltage (above 36 kV AC).

Electrical switchgear is also classified based on the type of insulation used. Common insulation mediums include air, oil, and gas. Our main focus is on gas insulated switchgear, also called GIS switchgear. Let’s see what it means.

What is Gas Insulated Switchgear?

Gas insulated switchgear, GIS, is used to mean a type of electrical switchgear in which the majority of components are enclosed in gas-filled chambers.

The main gas used in GIS is sulfur hexafluoride, also shortened to SF6. The gas offers superior electrical insulation as well as arc quenching properties when compared to air.

As a result, switchgear sizes greatly reduce when using gas insulation. Weight too. This makes GIS switchgear suitable for confined, indoor spaces where high voltages are to be carried.

Gas Insulated Switchgear Design

The design of GIS includes using a dielectric gas (typically sulfur hexafluoride (SF6) to insulate the various switchgear components in grounded, metal enclosures. The gas is usually at the moderate pressure of 400-600 kPa. This helps prevent it from leaking or condensing in low temperatures.

SF6 is a colorless, inert gas that’s roughly 5 times the density of air and offers about 2-3 times as much insulation. When it comes to handling arc flashes, the gas is also much superior and around 100 times better than air.

The gas insulated switchgear design ensures your apparatus can take advantage of these properties and more. The various parts also come already assembled and gas filled at the factory. This makes installing GIS easier.

Ultra High-Voltage-Gas insulated Switch Gear
Source: https://electrical-engineering-portal.com/ultra-high-voltage-uhv-ac-gis

Gas Insulated Switchgear Working Principle

The gas insulated switchgear working principle is based on the use of a dielectric gas, such as SF6, to insulate electrical equipment. As an insulating material, SF6 has several advantages over other types of insulation, including excellent thermal and dielectric properties.

GIS operates using a combination of vacuum and gas to keep the live parts isolated. This allows the switchgear to be highly compact and efficient, while also providing excellent reliability and low maintenance requirements.

During arc flash quenching process, the SF6 will usually decompose. However, the products of decomposition always reconstitute back to SF6, thereby allowing for the gas to work for a long time.

Advantages of Gas Insulated Switchgear

Gas insulated switchgear started seeing serious development in the late 1960s. In the recent past, the equipment has become increasingly popular – and for pretty good reasons. Some of the key advantages of gas insulated switchgear include:

Increased Reliability

GIS switchgear is less susceptible to environmental conditions such as moisture, dust, and salt air. This results in higher reliability and uptime. It also means the switchgear is well-suited for use in locations where environmental conditions are harsh, such as coastal areas or desert environments.

Reduced Maintenance

Since gas insulated switchgear components are sealed inside a gas filled enclosure, they do not come into contact with the surrounding environment. This results in less maintenance requirements, as there is no need to test or inspect the apparatus on a regular basis.

More Compact

Another of the advantages of gas insulated switchgear lies in its compact size. By eliminating the need for air insulation, GIS can be many times smaller than air-insulated switchgear. This makes it a good option for areas where space is limited, such as indoor or urban settings.

Decreased Arcing

Because the components are enclosed in the modules, arc causing occurrences such as vermin entry or accumulation of conductive dust prevented. This results in a decrease of arc flashes, and an overall increase in safety. In addition, SF6 is itself an excellent arc-quenching medium.

Easy Install

The gas insulated switchgear installation procedure is one of the easiest, seeing that the equipment comes pre-assembled. This not only means equipment that’s easier to install, but also switchgear that can be installed in a shorter time frame.

Disadvantages of Gas Insulated Switchgear

While GIS switchgear has many advantages, it is also important to understand its limitations. This can help when deciding between this and other types of switchgear insulation types such as air, oil, and others. The drawbacks include the following:

  • High Cost: One of the biggest gas insulated switchgear disadvantages is its high cost. The initial investment is typically much higher than other types of switchgear. However, the minimal maintenance requirement can offset that in the long run.
  • Longer Outages: in the event that gas insulated switchgear suffers an internal fault, repair works can take longer due to its sealed condition.

Applications of Gas Insulated Switchgear

Gas insulated switchgear is commonly used in high-voltage applications such as transmission and distribution, as well as in medium-voltage applications like substations. A gas insulated substation provides many benefits including reduced footprint and excellent reliability.

GIS switchgear is also becoming increasingly popular for use in industrial and commercial properties. In indoor and confined spaces, gas insulated switchgear requires less space than conventional air-insulated switchgear. This makes it ideal for use in indoor or confined spaces.

Due to its compact design and improved safety features, gas insulated switchgear is also used in underground switchgear. This is particularly useful for applications where land space may be limited or where there are concerns about environmental factors, such as weather or soil conditions.

Gas Insulated Switchgear Maintenance

GIS switchgear can fail when one of these problems occurs: SF6 gas leak, if the microwater in the gas exceeds the specified level, or when individual switchgear components fail.

In order to ensure the safe and reliable gas insulated switchgear operation, it is important to regularly test and maintain the equipment. Users are required to keep a maintenance checklist for the following reasons.

  • To prevent component failure
  • To optimize the switchgear performance

To help identify (and fix) problems at their early stages

  • To help minimize outage time
  • To extend switchgear lifespan

GIS switchgear maintenance includes regular inspections of the switchgear, testing, and other activities that aim to ensure the entire apparatus is in good condition.

Gas insulated switchgear manufacturers will usually advise on the testing and other maintained needs, their frequency, and more. That said, a typical maintenance checklist will involve the following.

  • Visual inspections– these include annual visual inspections as well as condition and maintenance inspections every 5 to 10 years, depending on manufacturer recommendations.
  • Tests– gas insulated switchgear testing involves using various tools to perform various tests including voltage withstand test, contact resistance, relay operation, and test to confirm other parameters.
  • Lubricating Parts– GIS switchgear components normally come lubricated for life. However, a need to oil them can arise, but usually after many years.
  • Component Replacement– this may include breaker replacement, SF6 gas removal or recharge, and more.

Gas Insulated switchgear Vs. Air Insulated Switchgear

Are you torn between GIS and AIS switchgear? While both types of switchgear may appear to use similar mediums, there are several key differences between them. The main difference between gas insulated switchgear and air insulated switchgear is in the insulation medium.

Gas insulated switchgear uses a gas, typically SF6, to insulate the electrical equipment, while air insulated switchgear uses air.

As a result, gas insulated switchgear is more compact and efficient than air insulated switchgear. Other notable differences between gas insulated switchgear and air insulated switchgear include the following:

Switch Gear Technology powerline Magazine
Switch Gear Technology powerline Magazine
Source: https://powerline.net.in/2018/06/29/switchgear-technology/

GIS vs. AIS Switchgear: Construction

GIS uses gas-filled, earthed modules to house the components. The gas insulated switchgear parts are also a fixed design and sealed for life. In contrast, AIS switchgear breakers are normally accessible and withdrawable.

GIS vs. AIS Switchgear: Cost

Due to its construction and use of SF6 gas, GIS switchgear tends to be more expensive upfront than air insulated switchgear. In comparison to AIS switchgear, the higher cost can vary between 10 and 40 percent more.

GIS vs. AIS Switchgear: Installation

GIS switchgear often comes pre-assembled, making it ideal for remote locations or buildings without space to install AIS. It also weighs less and is easier to transport. Therefore, unlike AIS switchgear, gas insulated switchgear takes less time to set up.

GIS vs. AIS Switchgear: Maintenance

SF6 switchgear almost requires no maintenance, and can be safely serviced in longer intervals. In contrast, AIS needs regular maintenance and must be serviced more frequently to ensure optimal performance and longevity, since it is always exposed to the elements.

Overall, gas insulated switchgear offers many advantages, which make it a preferred choice for many designers, engineers, and end users. Air insulated switchgear has its place, too, especially since it’s less costly than GIS switchgear, among other benefits. The type to use, therefore, mostly depends on the prevailing factors.


Gas insulated switchgear signifies a major evolution in the field of electrical power distribution. Characterized by a compact and modular design, it allows for a more efficient utilization of space, among other benefits such as high reliability and minimal maintenance. Many power companies are now turning to GIS as a key component of their smart grid infrastructure, which is helping to drive further innovations in this area.

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