Analysis On Dynamic Characteristics Of Rotor-bearing System For Hydroelectric Set Under Hydraulic-Mechanical-Electrical Coupling System

With the rapid development of industrialization and urbanization,China’s energy demand continues to rise.Power system is becoming more and more complex with the continuous expansion of scale and the access of multiple energy sources.The safe and stable operation of power system is still the focus of current scholars’ research.As a renewable and clean energy,the proportion of hydropower energy in the whole energy system is expanding.The installed capacity of hydropower stations is also increasing,and the task of peak shaving and frequency modulation is becoming more and more heavy.Under the interaction of various factors,the problem of unit vibration is constantly highlighted.In this paper,the short-circuit fault of power system is simulated by establishing the hydraulic-mechanical-electrical coupling simulation model.The rotor-bearing system of hydroelectric set is studied.The influence of short-circuit fault in power system on the dynamic characteristics of rotor-bearing system and the influence of main parameters of excitation system on the dynamic characteristics of rotor-bearing system are analyzed under the condition of hydraulic-mechanical-electrical coupling.The main work and research results are as follows:1.Using modular modeling method and engineering calculation software MATLAB/SIMULINK,the models of each subsystem of the hydroelectric power system are established,and then the models of each component are built into a coupled simulation system.The model is used to simulate the short-circuit fault of power system.The motion differential equation of the structure system is constructed,and the electromagnetic parameters-excitation current and generator speed are updated in real time in the calculation time step.The coupling of the hydro-mechanical system and the rotor-bearing structure system is established by unbalanced magnetic pulling force.The influence of the clearing time and fault type of short-circuit fault on the vibration of the rotor-bearing structure system is analyzed.The results show that the stability of the power system has an important influence on the rotor-bearing system of the generating unit.The three-phase short circuit has the most significant effect on the stability of the rotor-bearing system of the generating unit.As long as the fault line is removed in time,the severe vibration of the generating unit can be effectively avoided.2.Short-circuit fault of power system will directly cause the change of voltage and power of power grid,and excitation system plays a vital role in the stability of power system.Based on the hydro-mechanical coupling simulation model and the differential equation of motion of the rotor-bearing structure system,the influence of the main parameters of the excitation system on the vibration of the rotor-bearing system is analyzed under the condition of short-circuit fault of the power system.The results show that the main excitation parameters have opposite effects on the stability of power system and on the vibration of rotor-bearing system.For example,the greater the excitation amplification factor,the faster the power system restores to stable state,but the longer the rotor vibration lasts;the smaller the excitation time constant is,the faster the power system restores to stable state,but the longer the duration of rotor vibration and the larger the amplitude of vibration will be.Therefore,many factors should be considered in the selection of parameters in actual production.