People & environment
Swissgrid will implement the most landscape-friendly line route possible when constructing the Gäbihübel partial underground cabling. Different versions and combinations of the cable route, locations of the transitional structures and the overhead line connections were reviewed. For example, the original position of the northern transitional structure was optimised so that it is concealed by the forest wherever possible. The overhead line connections are sympathetic to the landscape by blending in with the forest skyline.
An underground line causes electric and magnetic fields just like an overhead line. While electric fields are intercepted by the shielding in the cable, magnetic fields are generated externally. The spatial expansion of the magnetic fields is lower than for overhead lines, but the strength directly over the underground cable is much higher than under an overhead line. The limit of 1 microtesla is complied with from a distance of 6 – 8 metres to the line axis of the underground cable, while the corresponding distance for the overhead line is about 60 – 80 metres.
The «Gäbihübel» partial underground cabling project will allow important knowledge to be gained on the underground cabling of extra-high-voltage lines. Swissgrid is therefore developing a scientific programme in consultation with the competent authorities and departments. The aim is to check the assumptions that were made for the dimensioning of the underground line and involves recording the underground line's impact on the soil. A comparison of the measurements with the calculations allows conclusions to be drawn about the reliability of the assumptions made.
In particular, the following points will be analysed during operation:
- The temperature behaviour of the cable conductors under various operating conditions
- The temperature profile in the soil in the immediate vicinity and the wider area about 20 metres from the conduit block under various operating conditions
- The magnetic fields at different line loads
Permanent forest clearance (about 4,000 m²) was carried out for the northern transitional structure, opposite the garage on Bözbergstrasse as well as for the pylon locations. Temporary forest clearance was executed at the location for the northern transitional structure and for the pylon construction sites in the forest (about 17,000 m²). The forestry work was carried out in early 2018. The reforestation activities for the permanent forest clearance areas will take place in Linn, in the municipality of Bözberg, and in the areas in which pylons are removed. In Riniken, deforestation activities are necessary along the line route, since the overhead line is kept low. Small trees and shrubs will regrow in this area (maximum height of 12 m). In Villnachern, the conductors cross the riverside forest.