What is a gas-insulated substation (GIS)?

A substation consists of many types of equipment such as transformers, circuit breakers, etc, to do the transmission and the distribution of the electric power. The components of the gas insulated substation are closely packed and due to this, the size of the substation has been reduced. The SF6 gas is used as an insulation medium in this substation. The major parts of this substation are contained in a sealed environment, this is achieved by using sulfur hexafluoride gas. So the major components of this substation are enclosed and because of this, the size of this substation is reduced. The high voltage carrying parts of this transformer is situated within a metal enclosure and it is held in a concentric configuration by cast epoxy spacer insulators. The sulfur hexafluoride gas is filled between the insulator and the conductor at a specified amount of pressure.

What are the advantages of a gas-insulated substation over a conventional substation?

  • The conventional substation would require a huge amount of space when compared to the gas insulated substation
  • In the conventional substation, each and every part is exposed to air and due to this, it will be polluted. While in case of the gas insulated substation the major parts are situated in a metal enclosure
  • The conventional substation parts are subjected to contamination, in the case of the gas insulated substation there won’t be any contamination due to the metal enclosure
  • Flashovers and breakdowns would occur frequently in the case of the conventional substation
  • Less maintenance is needed for gas insulated substations while the conventional substation would require huge maintenance
  • The installation of the gas insulated substation can be done quickly but it is not possible in the conventional type
  • The necessity of concrete work for the conventional substation is really high when compared to the gas insulated type.

What are the major components of a Gas insulated substation?

Why do we need a gas-insulated substation?

  • We can use this substation where sufficient space is not available
  • It can handle the climatic and seismic conditions at the site
  • It can be used in urban sites, like high rise building
  • It can be used in high altitudes
  • It can be used for underground powerhouse where space is the major constraint

What are the major properties of SF6 gas?

  • Nonpoisonous
  • Chemically stable
  • Noncorrosive
  • Good dielectric strength when compared to air
  • Arc quenching properties

What are the types of gas-insulated switchgear?

The need for uninterrupted electricity has been increased a lot, so due to this requirement for power supply, we must ensure the power supply protection. So in order to do this certain equipment such as generator and motor needs to be switched on and off many times, so the required means to do this process is called switchgear. Basically, most of the equipment which is used for the fault clearing process is a part of the switchgear.

Isolated phase GIS

In this type of switchgear, the bay phases are assembled individually. So in this system, every phase would have a circuit breaker, electrical isolator, and also a current transformer. The bay size of this GIS will be really big.

Integrated 3phase GIS

This is the exact opposite of the isolated type GIS in which all the three-phase of a circuit breaker, disconnectors, and current transformer are enclosed in a metal enclosure. The size of the integrated GIS is smaller than the isolated type.

Hybrid GIS

This is an integration of the isolated phase and also the three-phase common elements. The connection from the bus bar is done easily with the three-phase common bus bar system. There won’t be any phase to phase faults due to the isolated phase.

What are the safety features of the gas-insulated substation?

The live parts are supported by insulators, the insulator would act as a neighboring module so that gas won’t pass through it. The GIS consists of a gas monitoring system so that the density of the gas can be easily monitored. If pressure is reduced then the gas will automatically be tapped up.

What are the advantages of gas-insulated substations?

  • Due to their compact size, these substations can be used in cities
  • Good reliability
  • It only requires a small space
  • Fewer outages due to faults
  • Better safety
  • Provides protection against the pollution
  • There won’t be any fire risk due to the oil leakage 
  • It won’t generate any noise and no radio interference
  • Transmission and distribution can be easily done because they are located near the load center
  • It can be mounted in most places because of its compactness and the metal enclosure  
  • Very low maintenance is needed
  • It can be assembled easily and their commission can be done in the plant very easily

What are the major disadvantages of a gas-insulated substation?

  • When compared to conventional substations the initial cost of the gas insulated substation is really high
  • In case if there is an internal fault, then the damage will be huge
  • The internal fault diagnosis and rectifying would take a long time
  • The gas pressure should be checked in most of the compartment
  • The SF6 gas causes global warming

What are the applications of gas insulated substations?

  • It is installed in cities where space is a limiting factor  
  • It is mostly installed inside the building  
  • Hydroelectric station
  • Offshore power substation
  • Underground substation
  • High voltage applications
  • It can be installed in an industrial environment where the pollution is high


post-graduate in Electronics & communication.

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