Grid project Beznau – Birr

Swissgrid is expanding the existing line between Beznau and Birr to 380 kV. A 1.3-kilometre section of the line at «Gäbihübel» near Bözberg/Riniken will be underground in future. The 220 kV line between Rüfenach and Habsburg will be dismantled.

Your contact for this grid project

Jan Schenk
Jan Schenk

Phone +41 58 580 21 11
info@swissgrid.ch

380 kV line
380 kV line
380 kV underground cabling
380 kV underground cabling
Dismantling
Dismantling
Existing line
Existing line
Substation
Substation

Overview

By increasing the voltage between Beznau (AG) and Mettlen (LU) from 220 to 380 kilovolts, Swissgrid is securing the energy distribution and security of supply in the metropolitan area of Zurich, Central Switzerland and the Swiss Central Plateau. The new construction of the approx. 6.5-kilometre Rüfenach – Habsburg section is the last part of the line between Beznau and Birr that has not yet been expanded.

Partial cabling at «Gäbihübel»

The project includes a first for Swissgrid: At Gäbihübel near Bözberg/Riniken, Swissgrid is laying a long section of an extra-high-voltage line underground for the first time. Transition structures will be built at both ends of the 1.3-kilometre section in order to connect the underground cable and overhead line. 5.2 kilometres of new overhead lines connect the underground cabled section to the route of the current line.

Easing the burden on the landscape and residential areas

After the cabling at Gäbihübel is commissioned, the entire overhead line between Rüfenach and Habsburg will be dismantled. As a result, the burden on the residential areas of Neu-Riniken and Hafen will be noticeably eased. Swissgrid considered the landscape as much as possible when positioning the two transition structures and the new section of overhead line.

A shop window for research and the public

At «Gäbihübel», the effects that cabling a long section of extra-high-voltage line has on the landscape and environment, the costs that result from this and the challenges presented in construction, operation and maintenance, will be visible for the first time. Swissgrid will provide scientific support for the project. In addition, from the beginning of 2019, a visitor centre at «Gäbihübel» is to show the public the opportunities and challenges presented by underground cabling transparently and objectively.

The costs for the entire project amount to around CHF 34 million.


Project

The project consists of the 1.3-km cable route, the northern and southern transition structures and 5.2 km of overhead line connections from pylon 20 in Rüfenach to pylon 30 in Krähtal and to the northern transition structure, as well as from the southern transition structure from pylon 32 in Villnachern to pylon 237 in Habsburg.

New construction of the extra-high-voltage line between Rüfenach (pylon 20) and Habsburg (pylon 237) with partial underground cabling at «Gäbihübel»
New construction of the extra-high-voltage line between Rüfenach (pylon 20) and Habsburg (pylon 237) with partial underground cabling at «Gäbihübel»
Visualisation of the partial cabling «Gäbihübel»
Visualisation of the partial cabling «Gäbihübel»

Carefully positioned transition structures

To connect the underground cabling with the overhead line connections, transition structures will be built to the north and to the south of «Gäbihübel». They each require an area the size of an ice hockey rink and are around 25 metres high.

Schematic representation of a transition structure
Schematic representation of a transition structure

Swissgrid optimised the locations of the two transition structures during the course of the project. The northern transition structure in the «Pfaffenfirst» region has been positioned so that it is concealed as much as possible by the surrounding forest. The forest clearance and reforestation work required for this has already been completed. The southern transition structure will be built in the «Untere Stockacher» region, directly below the SBB Bözberg route, in order to protect the scenery as much as possible and to combine the emissions from rail and transmission line infrastructures.

Transition structure north: excavation
1/5: Transition structure north: excavation
Transition structure north: transition of cable pipeline
2/5: Transition structure north: transition of cable pipeline
Transition structure south: reinforcement of the base plate
3/5: Transition structure south: reinforcement of the base plate
Transition structure south: concreting of the base plate
4/5: Transition structure south: concreting of the base plate
Transition structure south: building of the side walls
5/5: Transition structure south: building of the side walls

Laying the underground cable

For the excavation and construction works required to lay the high-voltage line under the ground, a 25-metre-wide route must be created along the length of the cable. The approx. 5-metre-wide cable trench will be excavated in the centre of this. To do this, around 30,000 m3 of excavated material will be added and removed in Bözberg and around 25,000 m3 in Villnachern. Then the two 1.5-metre-wide conduit blocks will be recessed into the ground. In a subsequent step, six cables will be installed in each conduit block. This is a logistically challenging task, as underground cables are significantly heavier than overhead lines as a result of their much thicker insulation. Finally, the two conduit blocks will be covered with around one metre of earth. The route will then be renaturalised, apart from a 4.5-metre-wide strip over the two conduit blocks.

Schematic representation of the cable trench during the construction phase
Schematic representation of the cable trench during the construction phase
Excavation of the cable pipeline
1/5: Excavation of the cable pipeline
Installation of the cable conduits
2/5: Installation of the cable conduits
Installation of the cable conduits
3/5: Installation of the cable conduits
Cementing of the cable conduits
4/5: Cementing of the cable conduits
Covering of the conduit blocks
5/5: Covering of the conduit blocks

Facts and figures relating to the partial cabling at «Gäbihübel»

Voltage level 380 and 220 kV
Number of cables 12
Cable weight 21 kg per metre
Total cable weight around 380 tons
Planner Axpo Power AG
Project management Gähler und Partner AG
General contracting ERNE Bauunternehmung AG
Cable supplier Brugg Cables

Construction of the overhead line connections

In parallel with the laying of the underground cable, the new sections of overhead line (5.2 kilometres in total), will be constructed. These connect the underground portion at «Gäbihübel» to the route of the existing overhead line. For this purpose, a total of ten new pylons will be constructed between pylon 20 at Rüfenach and the northern transition structure. Four new pylons will be constructed between the southern transition structure and pylon 237 at Habsburg. When planning the new overhead lines, Swissgrid attempted to find solutions that disturb the landscape as little as possible.

Dismantling previous overhead lines

The current 220 kV overhead line runs between Rüfenach and Habsburg, in part directly over the residential area (Neu-Riniken) or in its immediate vicinity (Hafen in the municipality of Bözberg). After the new line is commissioned, this overhead line is expected to be dismantled by 2021. This will noticeably relieve the burden on the residential areas.

Construction time of about three years

On 23 August, construction work at Gäbihübel officially began with the ground-breaking ceremony. The construction of transition structures, cable trenches and overhead line connections is expected to be completed by mid-2020, which is when the new line can be put into operation. The dismantling of the existing overhead line is to be completed by the end of 2021.

Project planning under optimum circumstances
Project planning under optimum circumstances

A project with an eventful pre-history

Initial plans to increase the voltage of the Beznau – Birr line to 380 kilovolts go back to the 1980s. In 1996 most of the overhead line sections were approved and built. In 2011, the Federal Supreme Court decided that a partial cabling project was to be developed at «Gäbihübel». In 2013, Swissgrid, now responsible for the transmission network, submitted a partial cabling project to the Swiss Federal Office of Energy (SFOE). In July 2016, it gave the green light.

Project advisory council

Up to the completion of the planning approval procedure in 2016, the project was supervised by a project advisory council. The following persons were members:

Municipality of Bözberg Heinz Dätwyler, Municipal Councillor
City of Brugg Daniel Moser, Chairman of the Municipality
Municipality of Riniken Daniel Obrist, Vice-Chairman of the Municipality
Municipality of Villnachern Christoph Kamber, Municipal Councillor
Birdlife Aargau Max Gasser
Pro Natura Aargau Dr. Johannes Jenny
WWF Aargau Tonja Zürcher
AKUT Andreas Brack
Landowner, Bözberg Markus Kreis

People & environment

Landscape

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.

Electromagnetic fields

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.

Soil

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

Forestry work

Permanent forest clearance (about 4,000 m²) will be carried out for the northern transitional structure, opposite the garage on Bözbergstrasse as well as for the pylon locations. Temporary forest clearance will occur at the location for the northern transitional structure and for the pylon construction sites in the forest (about 17,000 m²). The forestry work will be 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.


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