Major milestone for Nant de Drance as intake valves set to open

19 November 2019

A major milestone is to be achieved this month at the Nant de Drance pumped storage power plant in Switzerland as the plant’s two penstocks will be  filled with water for the first time.

After passing the final round of dry safety tests, the two 425-metre vertical penstocks that connect the upper Vieux Emosson and lower Emosson reservoirs will be opened in stages starting at the end of November. They will first be filled to the same level as the lower Emosson reservoir. During this initial phase, tests will be run to ensure the pipes and the main valves are watertight and working properly.

The penstocks will then both be filled up to the upper level – that of the Vieux Emosson lake. The water will be kept at that level for several weeks to ensure that the rock around the penstocks is stable.

The next step will be to conduct mechanical and electrical tests on the six pump turbines; the first tests with water will be carried out in early 2020 and will continue over several months to be sure that the turbines are working optimally. The six 150MW turbines will then gradually be brought into operation, and the power plant is expected to be fully up and running by the third quarter of 2021.


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