Research On Dynamic Characteristics Of Rotor And Its Support System Of 600MW Steam Turbo-generator Unit

The shaft system of a large turbo-generator set has the characteristics of multiple rotors,long span,and large mass.Its good dynamic characteristics are the precondition of safe and stable operation.There has many analysis methods of dynamic characteristics for turbo-generator set shaft and its support system.The laboratory simulation needs a physical scale model of the object,which make the method not only well-targeted,but also long-periodic,high cost and not universal;the transfer matrix method using lumped parameters is difficult to reflect the actual devices in the distribution of mass and moment of inertia;the field test method is expensive and risky,and is less chance of implementation.By using three dimensional finite element model to analyze the dynamic characteristics of rotor and foundation system,the defects of above methods can be overcome.Therefore,it is necessary to explore the 3D geometric modeling method for rotor and its support system of steam turbine generator set,and the conclusions of the finite element dynamic analysis would be used to guide field test,operation of the unit,and design and optimization of structure.The 3D models of rotors,shafts and support systems of a domestic 600 MW steam turbine generator with actual sizes were built in this dissertation.Dynamic characteristics were analyzed by using the methods of finite element,modeling and the test scheme has been designed to set the modal testing of the support system.Firstly,A simplified method of turbine blades was proposed with the 3D models,which are suitable for finite element methods.The models are mainly based on those simplified turbine blades according to the principles of dynamics.The dynamic characteristics of rotors and shaft system of the unit were analyzed by using the FEA software,Algor.Results show that the value of each modal frequency of the shaft system are following the arrangements in ascending order of the modal frequency value of each single rotor and the corresponding distribution of each modal shape.Meanwhile,the requirements about which both values of natural frequencies the rotors and the shaft system should be far from the operating frequency value are satisfied.Secondly,dynamic characteristics of support system of the unit were analyzed by using the FEA methods.Results show that the distribution of modal frequency in support system is intensive.A higher number of modal frequencies were also observed within its operating speed range.It should be considered that the modal frequencies decrease when considering the quality and stiffness of the shaft,resulting the effect that flexibility of foundation structures on the modal frequencies of the shaft can be neglected.Under the regular working conditions of steam turbine,the location of the maximum vibration of the foundation structure is most likely to appear in the second layer and the shear wall which between two condensers.The dynamic characteristics of the foundation structure meets the requirements of design.In the start-up process of the unit,the vibration in the positions of 2,3,4,5# bearing seats is higher than which in 1,7,8# positions and the trends of frequencies are more consistent.Finally,simplified modal testing program of support system has been designed according to the conditions of laboratory equipments and field,and the modal test has been conducted.The results show that the unit does not resonate with the foundation operating platform when it is working properly,the main vibration mode of the operating platform is tilting or torsion vibration.In addition,in order to evoke the low order modes of the structure effectively,larger excitation source and vibration sensors with higher level of sensitivity are needed,during the modal field test of Turbo support system.