The upgrading of the existing 220kV line between Beznau in the canton of Aargau and Mettlen in the canton of Lucerne to 380kV is a key component of the “Strategic Grid 2025“, the national expansion plan for the transmission infrastructure of the Swiss transmission system operator (TSO) Swissgrid. The voltage increase ensures energy distribution and supply security in the Zurich metropolitan area, Central Switzerland, and the Swiss Central Plateau. The TSCNET shareholder has now put the first section between Beznau and Birr in Aargau into operation, one year earlier than planned.
This stretch was partly installed underground, namely across the so-called Gäbihübel near Bözberg/Riniken about halfway between Beznau and Birr. The cable laying at the Gäbihübel is the first time that part of an extra-high voltage line in Switzerland has been implemented using underground cables. Twelve cables with a weight of 30 tonnes each were installed in the conduit blocks in the summer of 2019. This was followed by the completion of the overhead line section. To connect overhead lines and underground cables, special structures were erected at both ends of the approximately 1.3-kilometre-long underground section. After a construction period of around two years, the Swissgrid control centre connected the new 380kV line to the transmission grid on 19 May 2020. The reasons for the early completion were Swissgrid’s successful project and implementation planning as well as the rather warm and dry weather.
Swissgrid is providing scientific support for the construction, commissioning, and further operation of the underground cable. Investigations are carried out, for example, on the thermal behaviour of the cable conductors depending on the current load, the temperature variation in the soil above the conduit block and in the surroundings, and the biodiversity in the soil. In May, work began on dismantling the old 220kV overhead line and restoration of the pylon sites to their original condition. The deconstruction work is expected to last until the end of 2020.