Analysis of Dynamic Characteristics of Francis Hydro-Turbine Main Shaft System

How, Weng Fong (2022) Analysis of Dynamic Characteristics of Francis Hydro-Turbine Main Shaft System. Final Year Project (Bachelor), Tunku Abdul Rahman University College.

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Abstract

Excessive rotor vibration in hydropower turbine eventually lead to damages including impact damage, fatigue damage and loosening of bolts. Recent studies show that the excessive vibration on the hydro turbine shaft still remains unsolved. Angular velocity and forced vibration in hydro turbine excites the natural frequency of hydro turbine shaft causes resonance in turbine shaft which eventually lead to components wear hence require frequent maintenance. This project aimed to develop a finite element model for the Francis Hydro Turbine Main Shaft and analyse the vibrational characteristics of the shaft model through modal analysis, determine effective optimization in number of guide bearing and guide bearing location that can increase the natural frequency of the shaft system and ultimately minimizing the vibration response in a Francis Hydro Turbine Main Shaft System. A Francis Turbine main shaft system is modelled in ANSYS software to determine the modal properties of the shaft model. The study is done under ANSYS Modal Analysis and ANSYS Harmonic Analysis simulation. The shaft model is verified with an established finite element model from peers and system optimization is carried out to determine the effective guide bearing location of the shaft model. After determining the optimal location for guide bearing through direct optimization, the parameters are loaded into the model to further analyse the results obtained. The results show that by simply varying the location of the existing guide bearing will not improve the natural frequency of the shaft system and the shaft system may fail at the edge where the turbine runner or generator rotor is mounted. Any additional bearing on the shaft system has improved the natural frequency of the system. However, the frequency where the maximum amplitude of steady state response occur will also increase when only one guide bearing is added. The optimal solution is by adding one bearing at the location 3042.8mm off set from the generator rotor mounting because it has 112.2% improvement in natural frequency and 65% reduction in frequency response maximum amplitude for the shaft system. The vibration results obtained can be used as a reference for the hydro turbine system design.