Grid Pradella – La Punt
«A valley that you will fall in love with» – that is how the Engadine tourism office describes the region surrounding the River Inn in the canton of Grisons. Anyone familiar with the alpine valley is sure to agree. Between the peaks you will find deep blue lakes, fragrant pine forests and romantic mountain villages with sweet-sounding names. And, right in the middle, between Pradella and La Punt, a Swissgrid extra-high-voltage line. How – ever, what sounds like an alien object in the Lower Engadine only impacts on the landscape when you take a closer look, as the line is well concealed, especially in the forested areas. If you take a second look, you will notice that the pylons between Zernez and La Punt only have conductors on one side. It looks unusual, but, as the line was built in the last century, it was enough to cover the demand for transport capacity at the time. This demand is greater today and will continue to be in the future. The expansion of the existing Pradella – La Punt line is part of Swissgrid’s Strategic Grid 2025. To ensure the security of supply in the canton of Grisons and the transportation of Engadine hydropower, Swissgrid is adding another «system» to the line. The pylons will then carry a 380-kilovolt line, each with three conductors, on both sides.
Many people ask why the line is not being installed underground if it is going to be renovated anyway. Swissgrid conducted a careful review of the underground option, which revealed that the landscape would only have benefited in some areas and the costs would have been disproportionately high. As an alternative measure for the expansion, a line with a lower voltage (110 kilovolts) was installed underground between Pradella and Bever and commissioned at the end of 2019. This marked the start of the dismantling of 1,100 pylons. This not only benefited the picturesque landscape, but also gave a number of municipalities access to broadband Internet, as a fibre-optic network was installed underground at the same time.
Below, Project Manager Robert Widmer provides some inside insights into the grid expansion project between Pradella and La Punt.
The construction permit has been issued. What happens next?
First, we start by procuring the necessary materials and services. The delivery periods for certain materials are quite long, so we are under a fair amount of time pressure. The steel required for the overhead lines, for example, which is delivered colour-coated for Swissgrid, has a delivery time of 12 months. So we had to establish the foundations for the procurement back in December 2019 because, if we want to be able to build in May 2021, all the necessary construction materials need to be on site by mid-April. Thorough and compliant procurement is crucial, as is the quality of the delivered materials.
The construction itself will then take place in two stages. As already mentioned, in May 2021, we will start with the construction and reinforcement of the pylons between Zernez and La Punt. The second stage will follow in May 2022, during which the pylons between the Pradella and Zernez section will be constructed and reinforced. The construction of the pylon foundations had already been approved previously and is already complete.
The overhead line is 50 kilometres long. What kind of scale are we looking at in relation to the materials that will be installed by specialist companies?
The amount of material to be procured is huge: we are talking about 5,005 tonnes of steel, 670 kilometres of conductors and underground cables, as well as over 3,200 insulators. We then need specialist installation companies to carry out the construction work, and will be working together with five different companies for both stages. This work will then proceed in parallel at various pylon locations.
How many specialists are involved in this kind of construction project?
Every installation company employs 20-25 staff on the construction site. This means that over 100 people will be on site for the entire project. As project manager, I will obviously also spend quite a bit of time on site together with Swissgrid’s local construction management. The management team will be on site every day. This is extremely important as it takes over all the coordination activities and answers the technical questions that constantly pop up during construction.
1,100 overhead line pylons to be removed
How much will this project cost?
The project will cost CHF 75 million. This includes the construction of the pylon foundations, the overhead lines and the alternative measures: Swissgrid is also financing the replacement of the 60-kilovolt overhead line between Pradella and Bever with a 110-kilovolt underground cable. This line has already been installed underground, allowing 1,100 overhead line pylons to be removed. This benefits the landscape enormously.
50 pylons will be replaced entirely rather than just being reinforced. How do you build pylons that are up to 70 metres high?
The outriggers are pre-assembled by two employees on the ground and then raised with the help of an assembly tower. Five overhead line fitters are generally at work, bolting the parts directly onto the pylon. The specialists are qualified climbers with all the necessary equipment and, of course, they are always secured, because at Swissgrid, safety is the top priority. Some pylons will also require the use of helicopters as they are located in very steep and almost inaccessible terrain. However, in general, we try to avoid the use of helicopters wherever possible.
Grid stability and security of supply are the priority
What challenges does Swissgrid still face in constructing the Pradella – La Punt line?
As we are building on existing pylons or even replacing pylons, we need to take the line out of operation. This needs to be coordinated with the European transmission system operators well in advance, as grid stability and security of supply are the priority. We already know that we will need to pause the construction work in both stages in August, because any decommissioning during this period would risk the grid stability. This is not really a problem as we have plenty of other work to finish, which does not directly involve the line.
The project will improve the security of supply. By how much and why?
The line between La Punt and Zernez currently only consists of a single line, as the transport demand was much lower when it was constructed in the 1960s than it is today. A second 380-kilovolt line will now be added. This will let us transport much more electricity and ensure the security of supply to the canton of Grisons as well as the transportation of Engadine hydropower.
When is the line currently scheduled to be commissioned?
The extra-high-voltage line is set to be commissioned at the end of October 2022.
Author
