Construction of the third and final section of the extra high voltage line linking the pumped storage power station in Nant de Drance to the power grid has started in Martigny in the Rhone valley.
Granted final approval by the Federal Inspectorate for Heavy Current Installations (ESTI) in January 2020, this underground project, launched by Alpiq and taken over by Swissgrid in 2013, entails drilling a tunnel with a diameter of roughly 2.5 metres at a depth of between 12 and 20 metres between different layers of the water table over a distance of 1.2 km. The particular geological conditions present at this exact location in the Rhone plain made this technological feat possible. La Bâtiaz – Le Verney will be the second underground line built by Swissgrid in Switzerland, but the first to be constructed at great depths over more than one kilometre.
Preparations for the two construction sites at Le Verney and La Bâtiaz have been underway since mid-May. In mid-June, work will begin on digging the Le Verney shaft. The mini tunnel boring machine will be installed on the main site at Le Verney in August and the drilling of the tunnel, which will take approximately eight months to complete, will begin in September 2020, in conjunction with the digging of the La Bâtiaz shaft.
It will take approximately two years of work before this underground cable link, which will connect the La Bâtiaz substation to the Chamoson – Romanel extra high voltage overhead line at Le Verney, can be put into service.
The Nant de Drance power plant is already connected to the grid
Swissgrid is responsible for connecting the Nant de Drance power plant to the transmission grid. The facility will be one of the most powerful pumped storage power stations in Europe and will produce around 2.5 billion kWh per year.
Two of the three sections of the Nante de Drance extra high voltage line have been in service since the end of November 2018. These are the 6.5 km of underground cable link connecting the power station to the Châtelard substation via the plant's access tunnel, and 12.5 km of overhead line connecting the Châtelard and La Bâtiaz substations. While construction continues on the third and final section, the station has been connected to the power grid by an interim solution: in 2019, voltage was increased to 380 kV on one of the two La Bâtiaz – Le Rosel overhead lines.