Grid project Grynau – Siebnen

Swissgrid will replace the existing 220 kilovolt line between Grynau and Siebnen with a new 380 kilovolt overhead line. This will improve the security of supply in the Lake Zurich/Linth Plain region.

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
Dismantling
Dismantling
Existing line
Existing line
Substation
Substation

Overview

The existing 220 kV overhead line between Grynau and Siebnen is being replaced by a new 380 kV line. The voltage increase in the line between Grynau and Siebnen eliminates a 5-km congestion point in the Mettlen – Grynau line, which has already been upgraded to 380 kV. The grid project ensures the interna-tional and regional security of supply.


Project

The line of Swissgrid’s Grynau – Siebnen grid construction project has already been converted to 380 kV between the Siebnen substation and pylon no. 915 (near the A3 motorway in the municipality of Tuggen). There is still an approximately 5-km-long section that has not yet been converted to 380 kV. Swissgrid is installing the line in this section along a new route with 14 new pylons. The existing overhead line with 21 pylons will subsequently be dismantled.

Along the new planned line, the pylons will have one fewer crossbeam level. Besides this, individual py-lon locations on the Linth Plain have been moved. The pylons for the new 380 kV line are an average of 30 m higher than the ones in the existing 220 kV line.

Swissgrid will be submitting the planning approval dossier for the new 380 kV overhead line to the Swiss Federal Office of Energy (SFOE) during the course of 2020. The SFOE has decided that the line project will be publicly displayed once again.

Axpo is increasing the voltage of the existing 50 kV distribution grid line to 110 kV on a different route. For one thing, Axpo has planned the construction of the 110 kV line as an independent underground cable project and has withdrawn from the Swissgrid project for time reasons.

Route

A short section of the new 380 kV line leads along the Linth Canal in the municipality of Uznach. After crossing the canal, the line runs south-west towards the open Linth Plain and crosses a foothill of the Buchberg to reach the previously converted pylon no. 915 on the A13. The new 380 kV line passes around the village of Tuggen at a greater distance than the existing 220 kV line.

Schedule

2020 Start of the planning approval procedure
2022 Planning approval decision
2023 Public procurements
2024/2025 Construction/assembly
2025 Commissioning of the new line
2025 Dismantling the old line
Project planning, ideally without court proceedings

Underground cable study

Swissgrid has submitted the study for the underground installation of the line requested by the Federal Supreme Court to the SFOE. Regional development, the environment and economic viability are factors which are taken into consideration in addition to technical aspects..

  • Just like an above-ground overhead line, an underground cable has advantages and disad-vantages for nature. While an underground cable improves the natural scenery compared to an overhead line, the prominent transitional structures leave clear marks on the landscape.
  • From a soil protection perspective, laying an extra-high-voltage cable underground in the drained, peaty/marshy soils on the Linth Plain is quite challenging. There is the risk that the soil’s water balance and its fertility as a whole may be negatively affected.
  • The costs of an underground cable are around 3½ times those for the planned overhead line over the entire service life (life cycle cost).

Technical information on the Grynau – Siebnen line

Route length 5.2 km
Number of pylons 14
Height of the pylons 52 m – 83 m
Technical information
  • Lattice pylons
  • Reinforced concrete foundations
  • Plastic isolators
Conductors
  • 1,00 m2 Aldrey
  • Bundles of two
Costs 11.1 million Swiss francs

People & environment

Electromagnetic fields

Electromagnetic radiation will either meet or be well below the limit of 1 μT (microtesla) across the board. The burden on the population will be reduced by the greater distance of the line to the residential area.

Noises

Certain weather conditions, especially fog, rain, hoar frost or wet snow, can cause local electrical dis-charge in power lines. In electrical engineering, this physical phenomenon is referred to as corona dis-charge. It generates noises, which are perceived as rustling, crackling or buzzing. The noise pollution will be significantly reduced by the use of new technology and bundles of two.


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