Gas Insulated Substation

Gas insulated substation (GIS) consist of components where active parts on high voltage potential are located in the middle of the aluminium alloy pipes and held in this location by epoxide resin insulators. The pipes are filled in with insulating gas and have earth potential. The GIS consists of typical HV components such as disconnectors, CBs, busbars, voltage and current transducers. GIS can save up to 90% of space compared with air insulated substation. It is particularly suitable for indoor and outdoor applications.

Technology Types

The technology type of GIS is defined by:

  • The insulation gas:

    • SF6
    • SF6 mixture with N2
    • SF6 free
  • The phase arrangement:

    • one phase per pipe
    • three phases per pipe
  • The voltage level

  • Application type:

    • indoor
    • outdoor

Components & enablers


Advantages & field of application

The GIS is applied in cases where the available space is very limited or the substations require complex connections. The single bays and busbars can be arranged very tightly because they are on earth potential. The GIS can be connected to overhead lines by bushings and to cables by special cable connectors.

The indoor GIS are mostly maintenance-free components that have higher reliability compared to air-insulated substations (AIS). Nevertheless, the total availability of GIS is comparable to AIS because of significantly longer (many weeks) repair times after a failure.

The GIS with non SF6 gas appeared recently on the market. The major advantage of non-SF6 gases is their very small or non-existing global warming potential. Therefore, two different applications need to be considered:

  • non-SF6 gas is used for insulation only (up to 420 kV)
  • non-SF6 gas is used for insulation and arc quenching (up to 170 kV)

Technology Readiness Level

TRL depends on the insulation gas used


HV: TRL 6 (insulation purpose and switchgear)

EHV: TRL 3 (switchgear)

EHV: TRL 6 (insulation purpose)



Research & Development

Current fields of research:

  1. The deployment of new insulation gas mixture as an alternative to SF6 to reduce the carbon footprint

  2. Alternative compact design configurations that limit required space, cost and construction time

  3. Fiber optics sensors and current measurement technologies that limit recalibration needs

Best practice performance

With SF6 gas

Rated voltage range: 52 kV to 1,200 kV

Rated current range: 2.5 kA to 8 kA

Standard definition: IEC 60517, IEC 62271

Expected lifetime: 50 years

Best practice application

Bergen, Norway


Norwegian seaports have set themselves the goal of reducing harmful emissions during ship lay times. One measure is to supply more and more ships with shoreside electricity from hydroelectric power. To provide the necessary grid infrastructure to handle higher voltages, the Norwegian energy provider BKK Nett is upgrading its transformer substation in Bergen from a 45 kV to a 132 kV operating level using "clean air" vacuum circuit-breaker and "clean air" instrument transformer, making it state of the art Gas Insulated Substation.

GIS features a rated voltage of 145 kV, a rated short-circuit breaking current of 40 kA, and a rated current of 3,150 A. The non-conventional low power instrument transformers (LPIT) used ensure an especially compact design.

The switchgear's size and weight are up to 20 percent less than in a system with conventional current and voltage transformers. The GIS will be climate neutral as the switching and insultation technology are based on clean air technology with no global warming potential.

Oerlikon, Switzerland


: Pilot high voltage, medium-voltage GIS installation using a new eco-efficient gas mixture as an alternative to SF6 which leads to low CO2 equivalent emissions.

170/24 kV, high voltage switchgear, rated voltage 170 kV, operating voltage 150 kV, rated short time withstand current 40 kA; medium voltage switchgear, rated voltage 24 kV, operating voltage 22 kV, rated short time withstand current 25 kA. Gas mixture SF6-free Fluoroketone-based on a chemical compound developed for switchgear applications.

The project is forecast to save 50% of CO2 emissions throughout the lifecycle of the equipment. These stems from 50% reduction in raw materials, manufacturing, thermal losses and 50% reduction in SF6 emissions based on a 30-year service life.

Etzel substation near Zurich, Switzerland


Pilot high voltage, 123 kV GIS installation using a new eco-efficient gas mixture as an alternative to SF6.

123 kV, high voltage switchgear, rated voltage 145 kV, operating voltage 123 kV, rated short-time withstand current 40 kA during 3 s; Gas mixture SF6-free Fluoronitrile / CO2 / O2-based on a chemical compound developed for switchgear applications in collaboration with 3M.

The project has been energised since 2018.



30 MW and 150 kV Gotland HVDC line featured the first fully redundant digital control and protection system and GIS for HVDC.

The voltage was increased to 150 kV using a thyristor module. The line includes a submarine section that is 93 km long.

The gas insulated switchgear for HVDC has allowed better use of available space because of its compact size and high reliability.


[1] CIGRÉ 2007: Final Report of the 2004 – 2007 International Enquiry on Reliability of High Voltage Equipment Part 5 – Gas Insulated Switchgear (GIS) [Link 1] [Link 2]

[2] Siemens. 8VN1 blue GIS up to 145 kV. [Link]

[3] ABB. Compact Gas-insulated Systems for High Voltage Direct Current Transmission: Basic Design. [Link]

[4] ABB. ewZ Oerlikon substation, Switzerland. [Link]

[5] Siemens. Siemens receives order for world's first SF6-free gas-insulated switchgear with "clean air" and vacuum switching technology for 145 kV. [Link]

[6] CIGRE, 2016, B3-106 , Application of a fluoronitrile gas in GIS and GIL as an environmental friendly alternative to SF6. [Link]

[7] CIGRE, 2018, B3-107, Application of a fluoronitrile gas in a 123 kV GIS pilot substation. [Link]

[8] Power Engineering International. HVDC Systems Gotland: the HVDC pioneer. [Link]