Research On Vertical Vibration Isolation And Damping Performance Of Elastic Foundation Of Large Steam Turbine Generator Unit

Due to the continuous increase in the single unit capacity and the increasingly complex structure of nuclear power units,the dynamic characteristics of the generator units have also undergone major changes.The vertical natural vibration frequency is about 20 Hz,which has caused a series of problems,especially The normal operating frequency of the half-speed steam turbine unit of nuclear power plant is 25 Hz,which is close to the vertical natural vibration frequency of the conventional rigid frame foundation,which is easy to cause resonance.Compared with the conventional rigid frame foundation,the vertical natural frequency of the elastic foundation is about 5Hz,which can effectively avoid the normal working frequency of the start-up group and avoid resonance.At the same time,the elastic foundation has a good vertical vibration damping effect,which weakens the foundation platform and the lower part.The outstanding advantages of frame connection and avoiding uneven settlement of the foundation under dynamic load have been adopted by more and more power stations.However,the core technology products of elastic foundation vibration isolation are monopolized by foreign countries.The spring isolation of the turbine generator foundation Vibration technology is slowly developing in China,and it is still in the stage of absorption,introduction and development.In order to solve the stuck neck technology and realize the localization of spring vibration isolation bearings as soon as possible,this article is based on the foundation of the new type of vibration isolation and anti-seismic system project of nuclear power plant steam turbine generators.In the above,the research on the vertical vibration isolation and vibration reduction performance of the elastic foundation of the nuclear power plant steam turbine generator set was carried out.Based on the large-scale general-purpose finite element software ANSYS,considering different disturbance force input methods and different response analysis methods,the general law of the structural dynamic response of the spring-isolated basic structure under the forced vibration of the rotor is analyzed,and the spring-damping of the basic structure is further established The finite element model of the vibration isolation and vibration reduction structure analyzes the general law of the structural dynamic response of the spring-damped vibration isolation and vibration reduction structure under the forced vibration of the rotor.Finally,a comparative analysis of the response of the basic structure is carried out based on the dynamic foundation codes of various countries.The main research work and the conclusions obtained are as follows:1.Use ANSYS finite element software to establish a nuclear power steam turbine elastic foundation structure model,use an iterative method to determine the optimal stiffness of the spring vibration isolation element,and perform a modal analysis on the foundation model.The results show that the vertical first-order frequency(3.133Hz)of the elastic foundation is much smaller than the working frequency(25Hz)of the half-speed unit,which can effectively avoid resonance,effectively reduce the dynamic coupling between the steam turbine,the platform plate and the substructure,and respond to structural vibration.Has a good attenuation effect.2.The two methods of time history analysis and harmonious response analysis are used to compare and analyze the dynamic response of the elastic foundation under the dynamic vertical and three-direction excitation of the rotor.The results show that after the steam turbine is started,the platform plate quickly transitions from the free vibration working phase to the stable working phase.In the steady working phase,the vertical dynamic response of the platform plate and spring foundation is much smaller than that of the starting working phase.The attenuation rate of the spring axial force response reaches 75.9% and 72.9% respectively;the elastic foundation can eliminate the dynamic coupling between the machine,the roof and the lower structure,effectively isolate the upper dynamic load,and the vertical displacement,speed,and vertical force vibration isolation efficiency are average The values are 94.78%,95.00% and 97.84%,respectively,indicating that after the elastic vibration isolation foundation is adopted,the lower column structure can be designed according to static analysis.3.The dynamic response of the spring vibration isolation foundation and the spring-damping vibration isolation and vibration reduction foundation structure under the forced vibration of the rotor is studied.The results show that the three-way cylindrical viscous damper can achieve a certain vertical damping effect,and its damping effect is mainly concentrated in the start and stop stage of the steam turbine.In the stable working stage,the three-way cylindrical viscous damper can reduce the vibration no significant effect.In fact,the main function of the barrel damper is to attenuate the dynamic response during the start-up process to ensure that the platform board enters a stable working state more quickly.4.Comparative analysis of China’s "Power Machinery Foundation Design Code"(referred to as China Power Code),China "Turbine Generator Set Spring Vibration Isolation Fundamental Design Code"(referred to as China Vibration Isolation Code),and the United States"Large Turbine Generator Base Design Guide(referred to as the U.S.Design Guide),and the German“Power Equipment Basic Design Standard”(referred to as the German Design Standard)four procedures:rotor excitation disturbance force value,structure damping ratio value,structure dynamic response and vibration isolation efficiency The difference.The results show that the rotor vertical and lateral disturbance amplitude values of the four regulations are the same,but the magnitudes are different;the damping ratio is the largest in China’s dynamic code,followed by the Chinese vibration isolation regulations,and the American design guidelines are the same as the German design standards and the smallest;The dynamic response of the elastic foundation has the same changing trend,but the response amplitude is different.The magnitude of the vertical peak displacement in the steady-state phase is in the order of the American Design Guide,the Chinese Dynamic Code,the German Design Standard and the Chinese Vibration Isolation Regulation;the four regulations of vibration isolation efficiency The theoretical and numerical results of the calculations reached more than 90%.Among them,China’s dynamic code is slightly smaller,and the theoretical calculation results are larger than the numerical calculation results.