Analyse des contraintes relevées sur une pale du groupe A 3 N de la Rance

Abstract

A study of the behavior of the main mechanical parts of a machine under actual operational conditions can contribute valuable information towards the manufacturer's and designer's development studies. A bulb unit at the Rance power plant, which had been in service under a wide range of different conditions provided an interesting subject of investigation into the behavior of its main mechanical components in industrial service. A major investigation was successfully carried out by close collaboration between Electricite de France and Neyrpic, a Division of Alsthom, one of the manufacturers of these units. This development research enabled more economical low-head plant operation to be achieved. The author describes the results of strain gauge measurements on a runner blade, in which the results were transmitted through the sea water by raclio. The results provided a check on the design calculations and helped towards a better understanding of stresses arising under transient operating conditions. Characteristic operating conditions were covered with the sets operating as direct reverse pumps and turbines. The average stress measured in the blade mounting under peak operating conditions was 14 kg/sq.mm with the unit running as a turbine. The blade vibrated under the excitation of the fixed components and cavitation but at no time did this vibration assume dangerous proportions. No abnormal effects were observed when the machine cut out. This analysis will require completing with a study of the hydrodynamic pressure distribution, for which a special measurement programme has been carried out.