Swissgrid is testing an innovative and sustainable cable technology for the extra-high-voltage grid as part of a pilot project. What is behind these pressurized air cables – and what does Swissgrid want to find out by testing them?
Open to innovation – with responsibility
As the operator of the Swiss extra-high-voltage grid (220/380 kV), Swissgrid is in charge of ensuring safe and reliable power transmission. Swissgrid is therefore also responsible for selecting a reliable and efficient transmission technology. For the extra-high-voltage grid, it is essential to use technologies that have proven their worth following years of successful operating experience. Swissgrid is constantly testing new technologies – always with the aim of making the operation of the transmission grid safer and more reliable, while also taking environmental aspects into account.
One of these new technologies is pressurized air cables. These cables are regarded as a promising further development of gas-insulated lines – with one crucial difference: instead of containing climate-damaging SF6 gas, pressurized air cables use pressurized air as an insulating medium. This makes them more environmentally friendly. Pressurized air cables also offer theoretical advantages over conventional underground cables:
- Lower transmission losses, less reactive power
- Low electromagnetic fields
- A modular design to allow the targeted replacement of components
At the same time, pressurized air cables are still a very recent technology. There is no experience of using these cables in the extra-high-voltage grid, and their benefits have not yet been proven. Processes such as construction, maintenance and repairs also still need to be tested in practice.
Pilot project to gain operating experience
To change this, Swissgrid is launching a multi-year pilot project in Spreitenbach in association with the company Hivoduct LTD. Swissgrid has been holding discussions on pressurized air cables with Hivoduct LTD for years. Austrian Power Grid (APG), a transmission system operator from a neighbouring country, is also participating in this pilot project.
A test facility of approximately 80 metres in length comprising typical pressurized air cable elements is being installed on the site of Swissgrid’s Spreitenbach substation. Various methods are being used to lay the underground cables at the test facility, e.g. in microtunnels, tunnels or cable ducts. The aim is to gather important operating experience over a period of two to five years. The aspects to be analysed include the following:
- Long-term behaviour in real operating conditions and different weather conditions
- Transmission power and loadability with various intensities of current
- Temperature changes and pressurized air losses
- Reactive power compensation
- Electromagnetic fields
- Environmental impact
- Maintenance requirements and ease of repair
The pilot project for the use of pressurized air cables at the 220 kV voltage level in the Swiss extra-high-voltage grid is being monitored by an independent testing institute. An independent expert report will be produced on completion of the pilot project. The first results are expected to be published in mid-2028.
The tests will enable Swissgrid to collect empirical values over a period of several years on the safe and reliable operation of pressurized air cables in the Swiss extra-high-voltage grid before the technology can be put into practice in this grid in Switzerland. More precise cost estimates for pressurized air cables will also only be possible after the pilot project in Spreitenbach.
How the test facility works
The test facility in Spreitenbach is integrated into the extra-high-voltage grid at 220 kilovolts in real operation. It has a modular design and allows various operating modes – from a de-energised state to operation with a high current load. An integrated monitoring system continuously measures temperature, pressure and other operating parameters. In the event of a fault in the pressurized air cable system, the affected line can be quickly converted back to its original state and continue operating.
Conclusion
Swissgrid remains open to new technologies – but security of supply is the top priority. Although pressurized air cables have not been tried and tested in practice, the technology is promising. The practical tests in Spreitenbach will provide important findings for an objective evaluation of the technology. Long-term decisions about Switzerland’s energy future can only be made on the basis of sound data. Swissgrid is also in close contact with European grid operators and engages in technical dialogue with the authorities, research institutions and industry for this purpose. This allows Swissgrid to make an active contribution to the further development of innovative, reliable solutions in the energy system.
Three questions for...
What is so special about pressurized air cables?
In recent decades, there have only been gradual improvements to overhead lines or underground cables for the transmission of electrical energy, although the requirements have increased enormously. Pressurized air cables offer a new, sustainable alternative with improved properties for grid operators and local residents. Pressurized air cables are PFAS-free, reduce losses and electromagnetic fields, and can be laid very compactly underground. Pressurized air cables were invented in Switzerland, are produced locally and are more cost-effective than underground cables. They can make an important contribution to the efficient and environmentally friendly construction and operation of line projects within a reasonable period of time.
What do you expect from the pilot project in Spreitenbach?
The pilot project is a crucial practical test phase for us. The individual components have already been successfully type-tested with the standardised high safety margins – in principle, the technology is therefore ready for operation. In Spreitenbach, we will now demonstrate under real conditions and over extended periods of time that pressurized air cables work just as reliably in the overall system. It is particularly important to collect information on operational security, maintenance requirements and costs, and to establish a reference for other line projects. That is why we will also be comparing different types of installation. This experience will help us to prepare the technology for large-scale use in the extra-high-voltage grid and make use of its advantages for the energy transition.
What does the future hold for pressurized air cables?
As a very recent technology, pressurized air cables now need to prove their reliability in daily grid operations over an extended operating period. This includes managing repairs or pressure losses. Thanks to the pilot project in Spreitenbach, we are collecting the empirical values we need – in association with Swissgrid and other grid operators. At the same time, we are investing in portfolio expansion, cost optimisation and industrial production so that we will be able to rapidly scale the technology for all voltage levels. Our vision is that pressurized air cables will very quickly become the new standard for electrical power transmission. This is only possible if they are widely used and are economically competitive, as well as offering technical advantages.
Why underground cables should only be used selectively
Laying new underground cables in the Swiss transmission grid only remains possible to a very limited extent. This is the result of the Swissgrid cable study, which shows that the physical properties of traditional cable technologies make stable grid operation and the rectification of disturbances much more difficult. Underground extra-high-voltage lines reduce resonant frequencies, which increases the risk of oscillation amplification. An uncontrolled increase in the proportion of underground cables in the extra-high-voltage grid would have a negative impact on Switzerland’s security of supply. For future grid projects, the possibility of installing an underground cable should therefore be considered from an overall perspective.
You can find out more about the cable study in our blog post: «When physics sets limits for technology»
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