Overhead line and 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 kilometer.