Instandsetzung der Druckrohrleitung des Kraftwerks Cleuson-Dixence, Schweiz - Eine Herausforderung an den Stahlbau

Rehabilitation of the penstock of the power plant Cleuson-Dixence, Swiss — Challenges for the steel constructor.

The power plant Cleuson-Dixence in Swiss with its 1269 MW nominal capacity is one of the most impressive hydroelectric power plants all over Europe. Three world records are held of this plant: the highest output per Pelton-turbine with 423 MW, the highest pole-output of each AC generator and the highest head of 1883 m — resulting in a penstock of a designed internal pressure of 2070 m water column.
An accident on the existing penstock in the year 2000 has led to a stop of operations for almost a decade. The damage was apparently caused by a cold crack in a shop weld seam, which couldn't be detected properly during the originally performed NDT. Based on the results of detailed investigations it had been decided, that the entire penstock over its more than 4 km length had to be renewed completely. The concept of the rehabilitation was the construction of an additional penstock, inserted in the existing one. The nominal gap between the existing and the new penstock should be as small as possible and was defined with 130 mm. The gap shall be backfilled with concrete continuously after installation.
This concept was the basis for the award of the construction contract in the year 2006. The selection of the most proper fabrication- and installation procedures was a challenge in this project of superlatives.