Grid project Niederwil – Obfelden

Swissgrid is planning to replace the existing 220 kV line between Niederwil and Obfelden, which is around 17 kilometres long, with a 380 kV line. The new line will make a significant contribution to the security of supply in Central Switzerland, where the conurbations of Aargau, Zurich and Lucerne are located. The chosen planning corridor allows for a line routing that is much further from residential areas. Once the new line is in operation, it will be possible to dismantle the existing line, thereby significantly reducing the visual impact on these areas.

Your contact for this grid project

Sandra Bläuer
Sandra Bläuer

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

Planning corridor
Planning corridor
Dismantling
Dismantling
Existing line
Existing line
Substation
Substation

Overview

This project provides for the upgrade or replacement of the 17-kilometre 220 kV line between the substations at Niederwil (AG) and Obfelden (ZH) with a new 380 kV line. The line is part of the upgrade programme from Beznau to Mettlen. The Beznau – Mettlen line currently causes congestion in the Swiss and European transmission system. The replacement of the line will improve energy distribution in Central Switzerland, where the conurbations of Aargau, Zurich and Lucerne are located. The north-south connections need to be upgraded, even beyond the Swiss borders. New production patterns, such as the expansion of wind power in Northern Europe and the shutdown of nuclear power plants, require Switzerland to increase electricity exchange with Europe.

The Federal Council determines the planning corridor and technology

For each grid project, Swissgrid checks both cable and overhead line options. During the sectoral plan process, the Federal Council defines the planning corridor for the line and decides which technology will be used. This is based on the recommendation of a monitoring group deployed by the Swiss Federal Office of Energy (SFOE). Experts discuss and assess the corridor variants prepared by Swissgrid according to the criteria set out in the transmission line evaluation scheme (regional planning, technology, environment and economic efficiency).

For the Niederwil – Obfelden project, the Federal Council specified a combination of two overhead line sections with around 4.5 kilometres of underground cabling to cross the protected Reuss landscape. After weighing up the interests of all the parties involved, the Federal Council was unable to agree to the request received from multiple stakeholders to lay the entire line underground. In particular, the idea of laying cabling through woodland was rejected, as the Federal Council felt that the necessary clearing, major intervention in the ground and the associated environmental impact would be disproportionate. Further information on the decision regarding the corridor and the technology can be found in the Federal Council’s press release (German version).


Project

The Federal Council’s decision on the planning corridor and the technology forms the basis for the next project phase. Swissgrid started working on the construction project at the end of 2022. Detailed planning involves determining the exact line routing and locations, as well as specifying the dimensions of the pylons and the transition structures that will connect the overhead line section to the underground cable section. During the planning phase, Swissgrid attaches great importance to routing lines in a way that is as compatible with residential areas and as gentle on the landscape as possible. The corridor allows for a line routing that is far enough from residential areas to significantly reduce the visual impact thanks to the dismantling of the existing 220 kV line. In addition, Swissgrid is examining options for bundling its 380 kV line with Axpo's 110 kV line along two sections of the planning corridor. The construction project should meet the requirements of regional planning as well as landscape and environmental protection, and take into account the concerns of the local population as far as possible, whilst being both technically feasible and economically justifiable.

In recent months, Swissgrid has presented the current status of the line routing to the federal offices and cantons for preliminary review. Swissgrid will now examine the different views expressed and incorporate the relevant points into the construction project where possible.

General site plan Niederwil – Obfelden
General site plan Niederwil – Obfelden

Project Advisory Council

Swissgrid is responsible for drawing up the construction project on the basis of the planning corridor defined by the Federal Council. However, there is a certain degree of design latitude for every project. Swissgrid sets up a Project Advisory Council during the construction project phase to exchange information with stakeholders. This committee, initiated by Swissgrid, is made up of representatives of the cantons, municipalities, environmental associations and interest groups. The design latitude of a project can be applied to best effect when the members of the Project Advisory Council express their opinions candidly, point out options for action and introduce them constructively into the discussion. Swissgrid notifies the Project Advisory Council of the current status of the project and provides information about associated issues such as environmental measures, the route of the line and easements. In addition, Swissgrid accepts observations from the Project Advisory Council that enable the project to be optimised – for example to coordinate the line routing with the regional planning of the municipalities. The aim is to engage in dialogue with official bodies, municipalities and affected parties to find the best possible solution, taking into account the numerous demands placed on the project. The Project Advisory Council is a consultative forum which promotes mutual understanding and allows different concerns to be raised directly.

The following persons are members of the Project Advisory Council:

Canton of AargauAdrian Fahrni, Head of the Energy Department
Canton of ZurichSeverin Schwendener, Project Manager AWEL
Municipality of Affoltern am AlbisMarkus Gasser, City Councillor
Municipality of BesenbürenThomas Lang, Municipal Councillor
City of BremgartenStephan Troxler, City Councillor
Municipality of Fischbach-GöslikonWalter Stierli, Grand Councillor
Municipality of JonenDieter Brodbeck, Vice-Chairman
Municipality of NiederwilNorbert Ender, Mayor
Municipality of ObfeldenPeter Weiss, Municipal Councillor
Municipality of OttenbachPeter Weis, Municipal Councillor
Municipality of WohlenArsène Perroud, Mayor
Pro NaturaMatthias Betsche
REPLA Mutschellen-Reusstal-KelleramtAlain Maître
Verein Verträgliche Starkstromleitung ReusstalStephan Bärtschi
Zürcher Planungsgruppe KnonaueramtGabriela Noser Fanger

Project Advisory Council meeting held on 25 January 2024

The first meeting of the Project Advisory Council took place in Niederwil on Thursday, 25 January 2024. After a brief introduction and discussion of organisational points regarding the tasks of the Project Advisory Council, Matthias Schmid, Head of Project Lines / Substations at Swissgrid, explained the project development to date. Project Manager Luis Mata then informed the members about the current planning status of the Niederwil – Obfelden grid project. He explained the procedure for developing the approximate route and showed examples of the various transmission technologies. You can find the full presentation of the meeting in the download area below.

Schedule

Once the project planning has been completed, Swissgrid is expected to submit the planning approval application with all the necessary documents to the competent approval authority (Federal Inspectorate for Heavy Current Installations, ESTI), probably at the end of 2024. This application will then be made public, and the parties involved in or affected by the project can inspect the dossier. On obtaining the legally binding planning approval decision, the line can be built, which will take about three years. After the commissioning of the new 380 kV line, which is likely to take place at the end of 2031, the dismantling of the existing 220 kV line will begin. In the event of appeals and legal proceedings, commissioning may be delayed by several years.

Timetable for optimal project progress without court action
Timetable for optimal project progress without court action

People & environment

Landscape

Overhead line

Overhead lines are visible objects in the landscape and can have a negative impact on the landscape depending on their location. The interventions must be assessed by the federal government and the cantons in accordance with the protection objectives and the consideration of compliance with the federal tasks (ensuring the supply of energy).

Underground line

Underground cables are generally assessed more favourably in relation to the landscape than overhead lines. While the cable route is not visible on open terrain, it remains clearly visible in forested areas as a necessary zone without deep-rooted and high trees must be maintained.

Forests

Overhead line

Interventions in groves by route clearing and/or the suppression of growth. Higher pylons make it possible to cross above the forest. However, the effects on the landscape are greater. The land under overhead lines can be used for agricultural purposes.

Underground line

Interventions in groves are greater than the interventions required for an overhead line due to the need for route clearance. The cable route is clearly visible in the forest because, for underground cables, the area above the line has to be kept free of high trees and deep-rooted plants. The soil above the underground cable can be used for agricultural purposes.

Soil

Overhead line

Soil sealing takes place on a small scale around the pylon foundations. Temporary interventions, especially around the pylon locations, during the construction phase.

Underground line

Extensive impact during the construction phase. Around 20,000 m2 of soil is impacted to construct an underground line 1 kilometre long (construction, installation locations, construction tracks). Depending on the electricity load, the electrical losses heat the underground cable and the surrounding soil. Measuring installations are used to measure and monitor the soil temperature. Soil sealing takes place on a small scale around the coupling shafts.

Noise

Overhead line

The noise emissions are caused by electrical discharge on the conductors (corona noises), which occur on high-voltage overhead lines under certain weather conditions, such as fog, rain or snow.

Underground line

In the operating phase, the noise emissions originate from compensation systems. Compensation systems emit a humming noise similar to transformers.

Electromagnetic fields

Overhead line

The magnetic field depends on the current and the phase arrangement of the conductor. In an overhead line, the limit of 1 microtesla is complied with from a distance of about 60 – 80 metres from the line axis.

Underground line

In underground cables, the magnetic field depends on the current, the installation depth and the cable arrangement. The spatial expansion of the magnetic field 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 about 6 – 8 metres from the line axis of the underground cable. The magnetic field can amount to more than 100 µT directly above the line. A value of 100 μT must not be exceeded from a soil distance of 20 cm.

Electrical losses

Electric power transmission leads to electrical losses. A small portion of the power is transformed into heat. The voltage causes losses as well. With overhead power lines, these are known as «corona losses,» because the air serves as an insulator. In cables, it is the insulating material that conducts a small portion of the power, likewise resulting in losses. Since cables have a significantly larger cross section than overhead lines, they experience much lower conductor losses than the latter. However, the interplay of cable and grid generates reactive power, which has to be compensated for. These losses are much higher with cables than with overhead lines.


Downloads

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