Approximate Decoupling Study Of Nonlinear Sealing Force Vibration Of Hydro-generator

Vibration has always been an unstable factor in the operation of hydroelectric generating units.Along with the increase of unit capacity and geometric size,more serious vibration hazards are caused.Hydraulic,electrical and mechanical factors are the three major factors leading to the vibration of the unit.In the shafting structure,the additional external forces on the turbine runner include sealing force,random hydraulic excitation,draft tube pressure pulsation and runner blade unbalanced f orce,etc.,and the additional external forces on the generator rotor include mechanical unbalanced force and unbalanced magnetic pull,etc.Seal exciting force is one of the additional external forces that affect the vibration of hydraulic turbine.In this paper,the muszynska nonlinear sealing force is taken as an additional external force into the turbine part of the shafting transient vibration differential equation,and the shafting nonlinear sealing force model is obtained.The approximate decoupling method of the differential equation of turbine vibration affected by the nonlinear sealing force is studied,which lays a foundation for the further study of turbine vibration based on the theory of vibration mechanics.Using Runge-Kutta method to simulate the amplitude and centroid trajectories of the rotor and runner before and after the approximate decoupling under rated and different conditions.The simulation results show that the approximate decoupling method proposed in this paper is effective.The main work of this paper is as follows:(1)This paper introduces the main hydraulic,mechanical and electrical factors that cause the vibration of the shaft system of the hydro generator set.The principle of sealing force formation and linear and nonlinear sealing force models are introduced in detail.(2)The Muszynska nonlinear sealing force model is used to describe the sealing force of the turbine during operation.The nonlinear sealing force model is combined with the transient model of the unit shafting,and the vibration differential equation of the turbine under the influence of the nonlinear sealing force is obtained,and then the vibration model of the unit shafting under the action of the sealing force is obtained.The approximate decoupling method of nonlinear seal force model of shafting is studied,which lays a foundation for further study of unit vibration based on vibration mechanics theory.(3)Under the rated condition,the nonlinear seal force model of the shafting before and after the approximate decoupling is simulated,and the amplitude change trajectory of the rotor and runner is obtained.It can be seen from the figure that the amplitude curve and centroid trajectory curve after the approximate decoupling fit well with the curve without decoupling.(4)Under the rated working condition,the relationship diagram of amplitude error caused by approximate decoupling with the change of sealing parameters is calculated through the simulation of control variables.It can be seen from the diagra m that when the sealing parameters change,the amplitude error changes in a small range.(5)Under different working conditions,the nonlinear seal force model of shafting under the action of external force with different amplitude and different rotation frequency is simulated,and the amplitude trajectory and centroid trajectory of rotor and runner before and after approximate decoupling are obtained.The results show that the approximate decoupling method is effective.