A premiere for Swissgrid

Swissgrid is extending the existing power line between Beznau and Birr to 380 kV. Part of the line will run underground on a 1.3-kilometre section of the "Gäbihübel" near Bözberg/Riniken. This is a first for Swissgrid - in which Axpo is also involved. It plans the underground cabling for the national grid company.

The voltage increase in the line between Beznau (AG) and Mettlen (LU) from 220 kV to 380 kV is part of Swissgrid's "Strategic Grid 2025". It will help to increase security of supply in the Zurich conurbation and central Switzerland. There is still a 6.5-kilometre-long section between Beznau and Birr, which is now being upgraded and is scheduled to go into operation in the course of 2020.

This video from Swissgrid shows exactly where the pipeline runs through:

On a 1.3-kilometre section of the "Gäbihübel" near Bözberg/Riniken, Swissgrid is laying an extra-high voltage cable of a 380 kV line underground for the first time - a technically challenging project. This video explains exactly how this is done and what has to be taken into account for such a project (German version): 

Axpo is also involved in the pioneering "Gäbihübel" project. It is responsible for planning the project. This business is one of Axpo's milestones in the strategically important third market business.

What are the challenges of this project? Thomas Jödicke, the project manager responsible for the Networks Division at Axpo, mentions the following points:

• The general conditions: Due to the long planning process - the first plan submissions date back to 1988, when Axpo still owned the line - and due to objections from the local population, the general conditions changed, which led to many project changes. The planning had to be adjusted accordingly.
• The technical challenges: The 12 cables laid on the section weigh over 300 tonnes in total. In addition, the cables are quite stiff with an outer diameter of 13.5 cm and a cross-section of the aluminium conductor of 2500 m². Pulling in these cables in the cramped conditions of the transition structures and through the cable protection pipes was correspondingly challenging. In addition, as with any large construction site, there were surprises. For example, the subsoil in the area of the SBB railway line, which had to be crossed under, was much rockier than assumed, so that the drill head had to be replaced once during the drilling of two parallel 38 m long concrete pipes, each with a diameter of 2 m.

Construction work on the "Gäbihübel" started as early as August 2018, and it is expected that the construction of transition structures, cable trenches and overhead line connections will be completed by mid-2020 and the new line will be ready for operation. The current 220 kV overhead line will then be dismantled.

All pictures and videos in this article: @Swissgrid