The Swissgrid substation at Fionnay GD in the Valais, which is located in a mountain cave, has been renovated. This is where the energy generated by the Fionnay / Grande Dixence power plant is fed into the electricity transmission system.

Caves and caverns have been used as shelters and storage areas since the dawn of time. These underground spaces, first natural and then, as technology progressed, drilled by man, proliferated in the Alps. In 1964, a 220-kV overhead switchgear was installed in a cave in Fionnay, in the Val de Bagnes in the Valais. The cave consists of three interconnected cavities adjacent to a further cavity where the Fionnay / Grande Dixence hydroelectric power plant can be found.

Having reached the end of its service life, the Swissgrid switchgear was renovated by the company during an outage of the power plant to enable work to be carried out on the production infrastructure by Grande Dixence SA. The cave in Fionnay houses equipment including two extra-high-voltage feeder lines for transporting the electricity generated by the Fionnay / Grande Dixence power plant to the Swissgrid substation in Chamoson, as well as three feeders connecting the power plant’s production machines. The new gas-insulated switchgear is supplemented by a newly constructed building for the control technology facilities. The three cavities that make up the cave each have an opening at an altitude of almost 1,500 metres near the village of Fionnay.

The Fionnay / Grande Dixence power plant was partially re-commissioned in January 2023 after more than five years of work. It is now once again able to generate hydroelectricity, which is transported by Swissgrid via its new switchgear at Fionnay GD. All these systems require constant monitoring. But how can people get to them in winter, when the road is closed due to heavy snowfall and risk of avalanche? Thanks to tunnels, which are usually kept closed, vehicles can access the village of Fionnay. From there, employees of the Fionnay / Grande Dixence power plant and Swissgrid use a tunnel to reach the equipment.

When the Fionnay / Grande Dixence power plant was built in the early 1960s, Swissgrid did not exist, and the companies responsible for generating electricity also owned the extra-high-voltage lines and installations that allowed them to transport the energy to their distribution centres. Swissgrid has been the owner of the extra-high-voltage lines and installations throughout Switzerland since 2013. It manages, maintains and develops the Swiss EHV grid as a whole. One of its tasks is to connect all the country’s major production units to the electricity transmission system. This is mission accomplished in the Val de Bagnes in the Valais, thanks to the renovation of the Swissgrid substation at Fionnay GD.