Influence Of Liquid Film Parameters Of Guide Bearings On Dynamic Characteristics Of Rotor Of Vertical Hydroelectric Generating Set

With the development of a hydro turbine generating unit,the unit capacity and the size of the unit are increasing.Thus,the unit stiffness is relatively weakened,so that the problems of the stable operation in the hydro generating unit have become more and more serious.Large units generally use three guide bearings in vertical layout,and the crown and band of a high head Francis turbine runner are also generally equipped with a labyrinth seal.The parameter variation of liquid film in guide bearing involves changes in the nonlinear dynamic characteristics of the shaft system,thus changes the vibration characteristics of the shafting,and then exercises a great influence on the stability of the unit operation.In the shaft of vertical hydroelectric generating set,the guide bearings play a radial constraint role in the rotation of the unit and bear the external force in different directions.Guide bearings are journal bearings with lubricating film.In the running process,the film parameters,geometry parameters and the boundary are changing and the variation will cause liquid film pressure,film stiffness and damping changes,then lead to changes of vibration characteristics and stability in the hydraulic turbine shafting.The runner seal has certain influence on the dynamic characteristics of the shaft,and the existence of the seal will be considered when the system is analyzed in the paper.In this paper,the method of single parameter analysis will be adopted;the dynamic characteristics of the rotor system are calculated and analyzed with the method of finite element.Taking the shaft of the unit of Yu Zixi station as the research object,the influence of the guide bearing on the dynamic characteristics of the rotor system under different liquid membrane parameters,geometric parameters and boundary conditions will be analyzed.The main research contents and results are as follow:(1).Analysis the dynamic characteristics of the fluid film bearing and shaft system of hydro generator unit vibration characteristics with the number of the upper and lower guide bearing pad changes.The results show that: with the number of bearing pad changes,the load of pad bearing is more balanced,the eccentricity of bearing is reduced,and oil film stiffness and damping is increased.It also leads to the decrease of shafting vibration amplitude,and accelerates the rate of shafting tends to steady.(2).Bearing characteristics in different bearing clearance values of upper and lower guide bearing are calculated,and then analyzes the influence of bearing clearance value on the vibration characteristics and stability of the unit.The result indicates that: with the bearing clearance grows,eccentricity and oil film thickness increases,the bearing stiffness and damping coefficients reduces.And in the condition of same external excitations,shafting vibration amplitude increases,but the influence on the velocity of shafting tends to stable is slight.(3).Through the calculation for dynamic characteristic coefficient of the bearing under different oil film temperature,the influence of the temperature change of the bearing oil film on the vibration characteristics and stability of the shafting is analyzed.The results show that: with the oil film temperature increasing,the viscosity of the lubricating oil reduces and the eccentricity of the bearing increases.At the same time,the oil film stiffness increases and the vibration amplitude of the shaft reduces,then the velocity of shafting tends to stable changes slightly.(4).With the parameters of fluid film bearing changes,modal analysis is carried out in the unit rotating parts.The results show that: fluid film bearing parameters on the shafting has little effect on first-order and second-order critical rotating speed,but the third-order critical speed is greatly impacted.The higher the oil film temperature and the larger the bearing gap,the three-order critical speed value is gradually increased.With the bearing pad number increasing,the three-order critical speed reduces.Through deep research,this paper shows that the film parameters of the bearing have different influence on the shafting transverse vibration characteristics and stability.The corresponding variation rules can be obtained to provide important technical reference for reducing unit vibration and optimizing unit support structure in design process.