Grid project: Underground cable in the Gotthard Road Tunnel

For the first time, an extra-high voltage line will be bundled with a national road tunnel. At the time of its planned commissioning, the approximately 18-kilometre-long Gotthard line will be the longest underground extra-high voltage line in Switzerland. The 220-kV overhead line over the Gotthard Pass was erected in the 1930s and requires a complete overhaul in the coming years. Carrying out this overhaul during construction of the second section of the Gotthard Road Tunnel gives Swissgrid the opportunity to create several synergies, including renewing the 220-kV line between Göschenen and Airolo, bundling the infrastructure inside the road tunnel, and further protecting the landscape in the surroundings of the tunnel.

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220 kV underground cabling

Dismantling

Existing line

Substation

Overview

The Swiss Federal Roads Office (FEDRO) is currently building the second tunnel.Gotthard Road Tunnel.
Swissgrid has submitted the building application for the underground cabling of the Airolo–Göschenen line in autumn 2022.
The 220-kV Swissgrid line between Göschenen and Airolo, which runs as an overhead line over the Gotthard Pass, will soon be reaching the end of its useful life and needs to be renovated.
The construction of second tunnel offers the opportunity to bundle the infrastructure and to lay new extra-high-voltage lines in the service duct that will run under the carriageway.
The sections of line between the Airolo substation and the south portal of the tunnel, and between the north portal and the cable end pylon in Göschenen, will also be laid underground.
This means that Swissgrid will be implementing the longest underground extra-high-voltage line in Switzerland. Combining this kind of line with a road tunnel is also a first in Europe.
Swissgrid has been tasked with checking the options for bundling infrastructure for each grid project. The Gotthard Tunnel meets the criteria for this kind of bundling with regard to deadlines and technical synergies.
The costs for the new line between Airolo and Göschenen total CHF 107 million.
The works will be carried out in parallel with the construction of the road tunnel and the cabling will be ready for use in 2029.

Cabling of the 220-kV line at the Gotthard (in German)

Project

Background

The Gotthard line Airolo - Mettlen was built in 1933 (150 kV), the voltage was increased to 220 kilovolts at the end of the 1950s. Part of the line has reached the end of its service life and needs to be renovated due to its age. For the first time, an extra-high voltage line will be bundled with a national road tunnel. At the time of its planned commissioning, the approximately 18-kilometre-long Gotthard line will be the longest underground extra-high voltage line in Switzerland.

Swissgrid's extra-high voltage line Mettlen - Airolo runs over the Gotthard and is important for transporting electricity in Switzerland from north to south. Another task that the 220-kilovolt line takes on is the removal of energy from the regional hydroelectric power plants, so the transmission network is an important element in achieving the goals of the federal government's Energy Strategy 2050.

Extra high voltage in the road tunnel – a trailblazing project

FEDRO is planning to build a new service duct under the carriageway of the new tunnel. Swissgrid plans to lay the extra-high-voltage line between Airolo and Göschenen in this service duct. The plan is a trailblazing project – combining an extra-high-voltage line with a road tunnel is a first in Europe. The laying of such a long cable is a technical challenge which will allow Swissgrid to gain valuable experience. Various federal authorities have investigated the technical feasibility and the various safety aspects of the plans. Swissgrid will comply with all safety regulations and emission limit values at the Gotthard.

Video "Cable route 220 kV-Airolo-Göschenen" (in German)

Use of various cabling technologies

Various technologies are used for cabling the line between Airolo and Göschenen. Between the Airolo substation and the Gotthard Road Tunnel's south portal, the line runs for more than 300 metres in a conduit block laid in the ground. In the interior of the tunnel, in the part of the service duct that lies under the hard shoulder, it will be attached to cable racks. From the north portal, the cables will be re-laid into a subterranean conduit block running 800 metres up to the cable end pylon in Göschenen and directly connected with the overhead line at the pylon that continues on towards Mettlen.

1/5: General site plan of the Gotthard line

Scheme Gotthard tunnel — 2/5: For the cabling of the extra-high-voltage line in the road tunnel, the cables under the hard shoulder of the carriageway are attached to cable racks.

3/5: The line runs in a separate service duct (known as “WELK”) for 17 km.

4/5: The line will be fed from the Airolo substation to the south portal of the Gotthard Tunnel for 300 metres in a conduit block laid underground.

5/5: From the north portal of the Gotthard Tunnel to the cable end pylon in Göschenen, the line will again run in a conduit block laid underground.

Easing the burden on the landscape at the Gotthard Pass

According to current schedules, the existing overhead line over the Gotthard Pass will be dismantled from 2029 onwards, following commissioning of the new cable through the Gotthard Road Tunnel. In all, more than 60 high-voltage pylons and 23 kilometres of overhead lines will be dismantled. This will noticeably ease the burden on the landscape surrounding the Gotthard Pass.

Dismantling of the 220-kV line Airolo – Göschenen

Bundling of line infrastructures

For each grid project, Swissgrid is obliged to check possible overhead line and cable variants and, in so doing, to evaluate a wide range of technological, environmental, economic and regional planning factors. For each grid project, it has also been tasked by the Swiss Federal Office of Energy (SFOE) with conducting feasibility studies to examine the potential for bundling infrastructure. The Gotthard Tunnel meets the criteria for this kind of bundling. The situation is ideal – but it cannot be replicated exactly in other grid projects.

Next steps

The works will be carried out in parallel with the construction of the road tunnel and the cabling is expected to be ready for use in 2029.

Technical details

As transmission technology offers various options, Swissgrid evaluated all of the technologies in depth. After careful analysis, Swissgrid opted for a highly cross-linked polyethylene (XLPE). This type of cable is now the standard for installing extra-high-voltage lines underground. It is also safe and offers the necessary flexibility.

Voltage of existing line	220 kV
Length of underground line between Airolo and Göschenen	18 kilometres
Length of overhead line to be dismantled	23 kilometres
Cable voltage	220 kV
Number of systems	1 x 220 kV
Number of cables in tunnel	3
Diameter of cable	approx. 150 mm
Investment by Swissgrid	CHF 107 million (total costs)

Links

FEDRO: A2 Second tube in Gotthard tunnel (in German)

Media release DETEC (in German): «DETEC to examine the bundling of power lines with roads and railways»

Blog: Pioneering Gotthard project as multifunctional infrastructure

Blog: Electricity flows over the Gotthard

Downloads

21 September 2022

Media release: Extra-high-voltage line through the Gotthard tunnel

PDF
21 September 2022

Flyer: Extra-high-voltage line through the Gotthard tunnel (in German)

PDF
21 September 2022

Mediakit Underground cable grid project in the Gotthard Road Tunnel (in German)

ZIP
2 June 2021

Media release: Old overhead line over the Gotthard Pass to be relocated to the new road tunnel

PDF
2 June 2021

Project flyer Gotthard (in German)

PDF

Grid technologies

The decision on whether to install a high-voltage line as an overhead line or as an underground cable is based on objective criteria. That's why Swissgrid checks the cable and overhead line options for every grid project.

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Emissions

It is hard to imagine our daily life without the numerous electronic gadgets and tools. However, we are much less aware that electric and magnetic fields are formed everywhere electricity is present: including in the generation, transmission and distribution of electric energy.

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Approval process

Swissgrid is responsible for the project planning for and implementation of the transmission lines.

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