What is Gas Insulated Switchgear and How does it Work?

When it comes to electrical load centres, it becomes reasonably necessary to build a substation as it has various economic and profitable benefits. But one significant obstruction in establishing a substation is the ample space required for its setup. Generally, the load centres are situated at congested places where sufficient land for building conventional electrical substations is hardly available. And a very convenient solution to this problem is using GIS or gas-insulated switchgear technology because all essential components of GIS, the metal-enclosed switchgear, can easily be assembled in minimal space.

Now before you start thinking of multiple questions about this switchgear technology, let's dive deep into the details and understand what precisely a GIS does and how!

What is a Gas Insulated Switchgear?

Generally, switchgear combines switches, fuses, and circuit breakers in an electric power system. The primary function of switchgear, connected directly to the power supplies, is to isolate, protect, and control various electrical devices connected to the system. In electric substations, these are placed on either side of the voltages of the power transformers.

Gas insulated switchgear is a compact metal encapsulated device that incorporates different high-voltage elements such as disconnectors and circuit breakers, and SF6 gas is used as insulation between live parts of the equipment and the earthed metal enclosure. These devices have a broad functional range extending from 12 KV systems to 800 KV systems. Moreover, one can operate these devices very securely in restricted areas. For instance, the extension of city buildings, remote industrial and hydropower plants, offshore platforms, and roofs can have these devices installed.

What are the advantages and disadvantages of GIS?

Advantages

It offers high flexibility and reliability as compared to other solutions.
It reduces the space requirement of outdoor or indoor substations significantly.
One can use it in all types of bus bars, including single, double, double bus bar, double-circuit breaker, and ring type bus bar.
It provides security against ecological processes.
It gives a generous and accessible choice for site installation.
It needs less maintenance and involves low operating costs.

Disadvantages

It is a little expensive when compared with conventional switchgear or air-insulated ones.
In case of an internal fault, extended phase outages and severe damages occur.
SF6 gas acquisition and supply to the site is complicated and involves uncertainty.
When an internal fault occurs, it takes more time to repair the damaged part at the substation
It requires a sufficient gas stock.

How does a GIS work?

Gas-insulated switchgear plays a vital role, acting as a critical switch to work and shield substations. It comprises isolators that open or close and cut off current circuits, the disconnectors that electrically isolate circuits and open voltage and other components.

Apart from isolators and circuit breakers, another crucial component found in GIS are the grounding devices and lightning strikers that prevent electrical shock and dielectric breakdowns, respectively, enhancing the overall safety of the entire substation.

While the SF6 gas works like an insulation material, vacuum is mainly used for the interruption. However, different SF6 gas pressures are required for insulation and interruption in GIS. This gas pressure is usually kept under 2.5 bar for insulating, whereas it ranges from 5 – 7 bar for interrupting.

The gas-insulated switchgear has broad applicability, including power transmission, railways, congested town buildings, valleys and mountain regions, underground substations, Substation automation, industrial complexes, and many more.