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FROM EOS TO GRANDE DIXENCE AND CLEUSON-DIXENCE

1922-1947: The Valais and the first Dixence dam

First Dixence, construction of the dam

In 1922, EOS began producing energy. To do this, the company became established in the Valais canton, which has 56% of Switzerland’s glaciers and the largest stored water resources in Europe. It bought some small power stations, and in 1927, it acquired the licences for the upper Dixence basin. In 1929, work began on the first Dixence dam, in the Val des Dix. This work lasted six years and required 1200 men.

After the end of the Second World War, with companies expanding rapidly, energy demand was continually increasing. In 1946, the Valais had 16 hydroelectricity projects, including the EOS dam at Cleuson, where construction work began in 1947.

1950: The birth of Grande Dixence S.A.

However, a project on a hitherto unknown scale was being planned: the collection of the water which flowed from the Vispa (Zermatt) to the Dranse (Bagnes) in a “super-Dixence” dam. The plans included a 100-kilometre network of tunnels and the enlargement of the first Dixence reservoir. The construction of the tallest gravity dam in the world was about to begin.

Grande Dixence S.A. was founded in 1950 to finalise the design, implement the project and operate the new complex.

1951-1965: The tallest dam in the world

Grande Dixence, first filling of the dam

Contrary to expectations, the Mauvoisin company obtained the licence to use water from the Dranse, and so additional water resources had to be found. EOS looked for new partners to finance and operate its new facility and found them in the German-speaking part of Switzerland, in Bernische Kraftwerke AG, Nordostschweizerische Kraftwerke and the Basel City Canton. EOS was the main shareholder, with 60% of the share capital.

In less than ten years, a workforce of 3000 men had built and commissioned Grande Dixence, the tallest gravity dam in the world. The first Dixence dam was submerged beneath the waters of the new reservoir.

1958: The Chamoson substation

Substation at Chamoson

A 220 kV substation was built at Chamoson in 1958 to transport the electricity produced by the Fionnay and Nendaz power stations.

1993-1998: The challenge of Cleuson-Dixence

Bieudron, Pelton turbine and injectors

From the 1980s onwards, the focus was no longer simply on the quantity of electricity produced, but also on issues such as available capacity, quality and safety. In 1993, Grande Dixence S.A. and EOS began implementing the Cleuson-Dixence project in order to improve the quality of the electricity produced, and this work was completed in 1998.

This was the last major project of the twentieth century, and it mobilised tremendous resources with the aim of optimising the existing installations. New tunnels and the Bieudron power station were built, so that better use could be made of the energy potential of the water stored behind the Grande Dixence dam, by reducing the time taken by the water to drive the turbines. The capacity of the facility thus rose from 800 to 2000 MW and it can now respond to daily and seasonal peaks in demand.

2000: The accident

On 12 December 2000, the penstock which brought water from the Grande Dixence dam to the Bieudron power station ruptured at a point between Péroua and Condémines. Water gushed from it, pouring down the mountainside and turning into torrents of mud and rock. Three people died. Since then, the Bieudron power station has been taken out of service, leading to a 1200 MW reduction in capacity.

2002: The creation of HYDRO Exploitation SA

In June 2002, Grande Dixence S.A., FMV SA and EOS Holding created HYDRO Exploitation SA. These three companies handed over the operation of their hydroelectric installations to this new company.

2005: Repair work

Initial reconstruction work at Cleuson-Dixence began in 2005. The entire section will be repaired by providing a new lining for the existing penstock, which means introducing a new steel pipe inside the original conduit. The actual area where the accident occurred will be bypassed by taking the penstock underground. The station is due to be recommissioned early in 2010.
 
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Grande Dixence SA
Rue des Creusets 41
1950 Sion
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