View inside powerhouse from ceiling crane level

Nant de Drance PSPP: Waterways Filled, First Turns of Pump Turbine Unit 1 Completed


Two major and long-awaited milestones attained

At the end of May 2020, the construction of the 900 MW pumped storage power plant Nant de Drance in the Swiss Alps entered the wet commissioning phase, the final stage in this enormous endeavor, often called “Project of the Century”. Two major and long-awaited milestones needed to be attained before being able to start testing and calibrating the pump turbines, including all auxiliary installations, under real-life conditions with waterflow reaching pressures of 40 bar and more.

Digital 3D model of the Nant de Drance power project

The first of these two milestone was the completion of the first-filling of the two parallel power waterways, each consisting of 2 km of pressure tunnels and a 440 m deep vertical shaft. Through them, more than one million m³ of water will be flowing each hour back and forth between the upper and the lower reservoirs via the reversible Francis pump turbines. The first-filling required a total of 125,000 m³ of water and was carried out in several stages between November 2019 and April 2020.

The second of the two milestones was reached on 28 May 2020. During the early morning hours, the sequence to start one turbine was manually executed and towards noon, all components were ready for the opening of the wicket gates, letting Unit Number 1 turn with water pressure for the first time! The rotational speed which was reached was intentionally limited to about 25 rpm. But to see the unit turn smoothly was reason enough to cheer. And because this first test went so well, close to nominal speed ─ approximately 400 rpm ─ was achieved a day later without any significant difficulty.

Connection of pressure tube to valve
Last control of installed generator

It is foreseen that Unit Number 1 will be synchronized with the grid within a few weeks. From then on, it will theoretically be possible to produce electrical energy.

Project of the Century

With its cost of approximately 2 billion Swiss Francs, the project will be an important part of Swiss and European energy strategies. Thanks to the 900 MW installed capacity, the power plant can produce large amounts of electricity or store energy within a very short time. The high level of flexibility will be one of the key strengths of this power plant in view of the fact that the amount of electricity produced from the new, renewable, volatile energy sources is steadily increasing.

Hydro Turbine Proof Test