Operation of the Bois Plant Hydraulic Turbine in Bypass Operating Mode: Analysis of Fatigue Behaviour

During load tripping of the hydraulic turbine at the Bois power plant, the turbined flow is directly transferred and discharged into an external canal without releasing an alert flow. The operation of the turbine in bypass mode, which consists in maintaining flow through the penstock and the turbine nozzles, was therefore envisaged to reduce flow variations in the short-circuited section of the scheme, in which people may be found, particularly during the summer season (safety stake).To validate the feasibility of this type of operating mode and, specifically, to verify the structural integrity in operation of the components impacted by the jet (deflector, control rod, jack…), studies were jointly carried out by EDF and CETIM, and a test-calculation program was initiated. This program included preliminary calculations using a finite element model, a campaign of tests in operating conditions (with vibration measurements and dynamic extensometric measurements) and an analysis of the potential damage due to fatigue. In the end, the study made it possible to show that the damage due to fatigue resulting from the operation of the Bois turbine in bypass operating mode remained in an acceptable range.