Grid technologies

Overhead line or cable?

The decision on whether to install a high-voltage line as an overhead line or as an underground cable is based on a wide range of criteria. That's why Swissgrid checks the cable and overhead line options for every grid project.

At the extra-high-voltage level (220 kV and 380 kV), electricity is currently predominantly transported using overhead lines. The air acts as a perfect insulator here, and the heat created by the electricity flow can be transferred well to the surroundings. In the winter, the low temperatures allow much more electricity to be transported than in the summer.

For voltages of up to 150 kV, underground cables are used where possible. Underground cables have been extensively tried and tested in this lower voltage range. By contrast, too few reliable empirical values are available at the extra-high-voltage level for distances of more than one

Freileitung
1/5: An overhead line consists of the totality of all phase and earth conductors on a supporting structure and is installed above ground. Overhead lines are used almost exclusively worldwide for energy transmission at high voltage levels, such as 220 and 380 kilovolts. The air surrounding the conductor serves as insulation.
Rohrblock
2/5: Concrete tube blocks are laid in open-air at approx. 1 to 2 meters deep. The width of the wiring trench is approx. 5 meters. A minimum width of approx. 25 meters is required for the construction.
Tunnelbau
3/5: To install underground cables without trenches, tunnels of approx. 3 to 4 meters in diameter are constructed in the form of galleries or microtunnelling. The cables are placed on specific cable holders.
Gesteuerte Bohrung
4/5: A drill head to control the digging direction under the obstacles of the surface. To prevent them from collapsing, a stabilizing liquid is squirted behind the drill head and the empty tubes for the cables are laid. This type of construction is suitable for short distances, for example, passages under rivers or roads.
5/5: Transfer between overhead lines and underground cables: Additional factors have to be taken into account when different technologies are used along a line. Among other things, line routing becomes more challenging, because connecting the underground cable with the overhead line requires the construction of cable transfer stations the size of an ice hockey rink. Ensuring that the cable transfer stations and cable trench route are positioned to avoid existing (traffic) infrastructure poses major challenges for the project planners and engineers.

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  • Research & development

    Swissgrid cooperates with universities to develop the new technologies and methods required to enable the efficient and secure transmission of energy.

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