Gas-insulated substations (GIS)


The majority of our substations are air-insulated. However, we also operate gas-insulated substations (GIS) at some of our sites. This is an alternative design to air-insulated substations which is only installed and operated in special cases.

The colourless and odourless gas, SF6 (sulphur hexafluoride), is the insulation medium predominantly used in GIS. It is not toxic, flammable or ozone-depleting, and is also harmless to humans and animals. It is because of these characteristics that SF6 is not classified in the legislation as a hazardous substance.

However, because SF6 has a high global warming potential, for a few years now, it is only authorised for use in areas where controlled recovery is possible. This is to prevent its uncontrolled release into the atmosphere. Its use, for example, in window panes, car tyres or in the soles of shoes has been prohibited for several years. On the other hand, in industrial and medical applications, controlled use in encapsulated gas-tight systems is still permitted – not only in GIS but also in the operating facilities of air-insulated substations such as circuit breakers. Like all grid operators, Amprion has voluntarily undertaken to minimise SF6 emissions as far as possible during commissioning and operation, as well as during recovery of the gas. Our substations are equipped with various technical safety devices which indicate and report possible sources of error at an early stage. At the same time, our trained and certified staff use special devices when handling SF6 to prevent the gas from escaping into the environment.


Due to the high global warming potential of SF6, we are exploring the options of using alternative insulating gases or alternative gases to SF6. Amprion prioritises pilot runs of operating facilities containing alternative gases if they are technically feasible, have passed the necessary type tests and have demonstrated their operational capability. During these tests, the technical characteristics, environmental compatibility and potential application areas of the facilities are examined very closely. According to the current state of technology, alternative gases do not offer an equivalent substitute to SF6. Particularly in installed facilities, SF6 cannot simply be replaced by an alternative gas. To this end, manufacturers are re-developing or further developing operating facilities for alternative gases. As a result, the use of operating facilities with alternative gases is carried out in close consultation with leading manufacturers in order to ensure operating safety, and compliance with strict technical requirements. In outdoor technology, Amprion uses synthetic air as a climate neutral, alternative gas. A pilot project with 245 kV voltage transformers was already put into service with synthetic air in 2018. Current solutions are also being developed and will be used to insulate parts of 380 kV GIS substations with synthetic air in the next few years. In addition to synthetic air, another alternative gas is currently available for GIS in a gas mixture with fluorinated insulation gas.