The Study Of Dynamic Characteristics Of Shaft System Of Francis Turbine Generator Units

Francis turbine generator units are large and complex equipments workingunder the combination action of intense electromagnetic field and strongcurrents power. The intense vibration phenomenon of the units hovers aroundthe hydropower stations like a mysterious ghost all over the world, whichseriously impacts on the safe operation of the hydropower stations.This thesis has structural dynamics, rotor dynamics and finite elementmethods as the theoretical basis, applies Pro/ENGINEER software and ANSYSsoftware to study the dynamic characteristics of the shaft system of Francisturbine generator units.Firstly, the solid geometric model and finite element analysis model of therotor, the shaft, the runner and the whole shaft system are built withPro/ENGINEER powerful modeling and assembly functions.Secondly, the natural frequencies and the mode shapes of the shaft systemand its components are respectively calculated with ANSYS software in freevibration state and in rotating state. The characteristics of the natural frequencies,the change law of the mode shapes and the distinction of the natural frequenciesbetween the free vibration state and the rotating state are respectively analyzed. Thirdly, the first two whirling speeds of the shaft system are calculated.And through comparing with the rated speed, the stability of the shaft systemoperation is analyzed.Fourthly, the frequencies of the main excitation sources upon the shaftsystem are calculated. The impact on the shaft system operation by the mainexcitation sources and the probability of the shaft system occurring resonancevibration are analyzed in rated condition.Finally, the free vibration stress of the runner and the blade are calculated.The internal relations between the blade cracks location and the free vibrationstress of the runner/blade are studied, and some significant conclusions aredrawn.The work of this thesis could not only offer some reference for analyzingthe reasons for the unit occurring resonance vibration and the blade occurringcracks but also lay a foundation of further study of the shaft system of Francisturbine generator units.