This facility houses three Pelton turbines, with each turbine rated at 423 MW ; note that the turbine acceptance testing process reported a maximum turbine output power of 449 MW each due to better than expected efficiency and ideal test conditions. At the rated power of 423 MW each turbine operates at a head of ~1869 meters and a flow rate of 25 cubic meters per second, with an efficiency in excess of 92%. The turbine assembly is a five-jet configuration; the stream of each jet is 184.7 mm in diameter with an exit velocity of 191.5 meters/second is approximately 92.16 MW. The assembly rated pressure is 203.2 bars. The combined flow rate for the three turbines is 75 cubic meters per second. The facility peak power production is ~1269 MW. The turbines and associated valves were designed and developed by VA Tech of Switzerland.
Penstock rupture
On December 12, 2000, at approximately 20:10, the Cleuson-Dixence penstock, feeding the Pelton turbines at Bieudron, ruptured at ~1234 meters AMSL. The failure appears to have been due to several factors including the poor strength of rock surrounding the penstock at the rupture location. The rupture was approximately 9 m long by 60 cm wide. The flow rate through the rupture was likely well in excess of. The ensuing rapid release of a very large quantity of high pressure water destroyed approximately 100 hectares of pastures, orchards, forest, as well as washing away several chalets and barns around Nendaz and Fey. Three people were killed. The Bieudron facility was inoperative after the accident; however, it became partially operational in December 2009, and fully operational in January 2010. Much investigation went into the accident resulting in the almost complete redesign of the penstock. Legal action is still in process and the root cause of the rupture is unknown.
Redesign
However details regarding the redesign are available. The redesign calls for improvements in the pipe's lining as well as the addition of grouting around the penstock to reduce water flow between the penstock and the surrounding rock due to dynamic variation of the pipe diameter during operation. The damaged section of the penstock was rerouted around the previous location to where new more stable rock is available. Construction on the redesigned penstock was completed in 2009. Redesign considerations include operational control of maximum agreed design limits under all conditions of assembly, design and service conditions.
