Bieudron Hydro Project

The Bieudron Hydro Project is a hydroelectric power plant located in the Swiss Alps in the Canton of Valais in Switzerland. Production began in 1998, with two world records set upon its completion: the world's most powerful Pelton turbine as well as the highest head used to produce hydro-electric energy. A penstock rupture in 2000 forced the closure of the power plant pending redesign, which is scheduled for completion in 2009.

Specifications

This facility houses three Pelton turbines, with each turbine rated at 423 MW (~567,000 HP); note that the turbine acceptance testing process reported a maximum turbine output power of 449 MW each (~602,000 HP) 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 (6130 feet) and a flow rate of 25 cumecs (cubic meters per second), with an efficiency in excess of 92% (~92.37%). The turbine assembly is a five-jet configuration; the stream of each jet is 193 mm (7.6 inches) in diameter with an exit velocity of 192 meters/second (630 ft/s). The kinetic energy of each of the 5 streams (i.e. 1 from each jet) is approximately 92.16 MW (Q = 5 cumecs, v = 192 m/s, H = 1869 m). The assembly rated pressure is 203.2 bars (2944 psi).

The combined flow rate for the three turbines is 75 cumecs. The facility peak power production is ~1269 MW. The turbines and associated valves were design 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 (under more than 1000 meters of head). 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 150 cumecs (>5280 cfs). The ensuing rapid release of a very large quantity of high pressure water destroyed approximately 100 hectares (1 km²) of pastures, orchards, forest, as well as washing away several chalets and barns around Nendaz and Fey. Three people disappeared in the tragedy.

The Bieudron facility has been inoperative since the accident; however it is scheduled to come back online in 2009. Much investigation went into the accident resulting in the almost complete redesign of the penstock. Legal action is still in process and there is no clear definitive publicly available information on the root cause of the rupture.

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 (it expands due to water loading during operation then contracts when the load is removed, leaving a gap). The damaged section of the penstock was rerouted around the previous location to where new (undamaged) more stable rock is available. Construction on the redesigned penstock is currently underway (as of June 2007). Redesign considerations include operational control of maximium agreed design limits under all conditions of assembly, design and service conditions (including water hammer pressure spikes).

References

* Helmut Keck, Gerald Vullioud, and Pascal Joye. "Commissioning and Operation Experience with the World's Largest Pelton Turbines Bieudron".

External links

* [http://www.cleuson-dixence.ch/en/rehabilitation/rehabilitation/le_projet/description_du_projet.htm Project rehabilitation]
* [http://www.msm.cam.ac.uk/phase-trans/2005/LINK/134.pdf 2005 report]