Re-commissioning of the facilities

After a 10-year stoppage, the Cleuson-Dixence facilities have been re-commissioned this month at the end of four and a half years of works and six months of testing. The company Cleuson-Dixence Construction SA handed over the facility to Alpiq in line with the planned time schedule and budget. Together with the operation of the Bieudron power station, the rehabilitation of Grande Dixence will thus double its flexibility.

Following the failure of the Cleuson-Dixence penstock on December 12, 2000, EOS and Grande Dixence SA established the company Cleuson-Dixence Construction SA in 2003 in order to rehabilitate the installations linking the Grande-Dixence gravity dam to the Bieudron power station.

For Alpiq, an energy supplier that generates its own electricity, the re-commissioning of Cleuson-Dixence is a forward-looking project that is also one of the greatest commercial challenges of the coming years. The reinforcement of its production facilities will enable Alpiq to react very quickly to the demand for electricity during peak times. In addition, the Cleuson-Dixence facilities will make a vital contribution to the stability of the grid, particularly with regard to compensating for the fluctuations caused by the injection of wind energy into the European electricity grids.

Large-scale works carried out over four and a half years The repair works involved re-lining the entire existing penstock and bypassing the area of the accident. In 2006, the civil engineering works began with the excavation of the by-pass, and were then followed by substantial sheet-metal works, which lasted two and a half years. In total, 1,360 cylindrical steel sections - that is, 12,500 metric tons of steel - were manufactured in Linz, Austria, then transported by rail to Sion. These cylindrical steel sections were then transported by truck and cableway up to the various windows of the construction site, where they were inserted into the existing penstock. The entire rehabilitation process required the mobilization of 600 co-workers, 24 hours a day. The budget of 365 million Swiss francs was adhered to, as was the planned schedule.

1200 megawatts of additional peak-time energy in the grid With its 420-sq. km catchment area, its 35 glaciers, 80 water intakes and 400-million cu. metre reservoir capacity, the Grande Dixence facility is one of the flagships of Swiss hydroelectricty. It groups together the four hydroelectric power stations of Bieudron, Nendaz, Fionnay and Chandoline, which produce nearly one quarter of Valais’s hydroelectric energy, that is, nearly 4% of Switzerland’s consumption. In the words of Michael Wider, head of Alpiq’s Swiss Energy Division, “the re-commissioning of the Bieudron power station and its 1,200 megawatts doubles the flexibility of the Grande Dixence facility and thus increases the country’s supply security”. But the production of these super-peak kilowatt hours implies their transmission to the consumption centres via the very high-voltage grid. The latter should thus very soon be reinforced, particularly in Valais, where most of Switzerland’s hydroelectricity is generated. A key challenge is thus the construction of the Chamoson-Chippis transmission line which will link the 380-kilovolt grid in French-speaking Switzerland to the remainder of the Swiss grid.

The re-commissioning of the Cleuson-Dixence installations will be marked by an official event and an open day in spring 2010.