Assessment of Structural Integrity and Potential Improvements of Micro Hydropower Turbine

Abstract

A comparative study of two different hydro power turbine designs, madeby Remote Hydrolight (RHL) was conducted. The shaft of the first designhas suffered from fatigue failures and a bushing was introduced to solvethe problem, giving the second design.In this thesis, flow calculations, finite element analysis (FEA), inspectionof micro structures and the weld were carried out, along with fatigue lifecalculations. This was done for both designs to compare the existingfatigue data with the findings. It was found that the introduction of thebushing is generally beneficial. The stresses at the weld toe previouslysubject to fatigue fracture were reduced by at least 52,5%.Two kinds of laboratory activities were carried out in this thesis. Firstly, ametallurgic analysis was performed and unveiled flaws on and in the weld.Micro cracks, cavities and general porosity suggested that the weldingprocedure also needs to be revised. Such cavities, especially if occurringat the weld toe of the outer rotor disk, may lead to fatigue failure, despitethe introduction of the bushing. In addition, a micro Vickers hardnesstest was conducted. The tests showed that a range of materials are usedfor making the turbine, with the shaft material having the highest tensilestrength.There exists too few fatigue data?s for establishing a fatigue stress limit forthe different components. Based on the data received, no reliable fatiguelife for the modified turbine with bushing can be calculated.