First variable-speed pumped storage set for 628-MW Nant de Drance

A partnership of a Swiss utility and a federal railway has awarded a 125 million euro (US$167 million) contract to Alstom to supply the 628-MW Nant de Drance hydroelectric project its first variable-speed pumped-storage power plant.

Swiss energy provider Alpiq, Forces Motrices Valaisannes, and Swiss federal railway SBB are building the 990 million franc (US$950 million) pumped-storage project at Finhaut in the Swiss Alps. (HNN 1/19/09)

Alstom said it is to supply four 157-MW vertical Francis reversible turbines, four 170-megavolt-ampere vertical asynchronous motor-generators, and other key equipment to the new plant. It also is to handle complete site delivery, installation, supervision, and commissioning.

Alstom said the new installation integrates two state-of-the-art technologies, a conventional pump-turbine and a variable-speed pump-turbine. The conventional unit pumps water into an upper reservoir during low energy demand and releases it to produce energy during peak times. The variable-speed unit regulates the level of the energy it consumes, contributing to better grid regulation.

The manufacturer said conventional pump-turbines only can operate on a fixed quantity of energy, while variable-speed units can regulate the level of energy they comsume. As a result the variable unit continues to function even at lower energy levels, assuring a steady refilling of the reservoir while contributing to stabilization of the network.

Alstom Hydro facilities in Grenoble, France, and Birr, Switzerland, are to be in charge of engineering and manufacturing the equipment for delivery in 2017.

Civil work began at Nant de Drance in 2008. The project is to include an underground powerhouse, a transformer cavern with common access tunnel of 5,500 meters starting at Le Chatelard, two parallel water conveyance systems with 250-meter headrace tunnel, 470-meter vertical shaft, 160-meter steel-lined pressure tunnel with manifold, and tailrace tunnel with manifold.

The project is to utilize the height difference of two existing reservoirs, Emosson and Vieux Emosson, in Finhaut between Martigny and Chamonix, to produce peaking power. Access to the completely underground plant is to be by a five-kilometer tunnel, minimizing environmental effects of the big power station.

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