Investigation Of Large Turbo-Generator End Winding Dynamic Characteristics Based On FRF

Large turbo-generators bear double working frequency electromagnetic force during operation.If the natural frequency of stator end winding is close to its excitation frequency,resonance or excessive forced vibration response will cause serious consequences.Therefore,it is extremely important to grasp the dynamic characteristics of the end windings of large turbo-generators for its safe operation.In this thesis,the fine finite element model of the stator end winding is established firstly,which is consistent with the modal analysis.Then,the frequency response functions（FRFs）of single-layer winding and overall winding are obtained.After that,the modal parameters in the specified frequency range are identified based on the FRFs of the end winding.Further,the physical parameters obtained by the lumped mass method are modified by modal parameters,so as to establish a mathematical model to investigate the dynamic characteristics.of the end winding.The main research contents of this thesis are as follows.1.The modal parameters and FRFs of the structure are obtained according to the computational modal analysis method,and the modal test is carried out on the clamped-clamped beam structure for mutual verification.Then,taking the stator end winding of a600MW large turbo-generator as the research object,the fine finite element model is established for modal analysis.The results show that the natural frequencies of elliptic modes concentrate into 80～90Hz,and the maximum error between the natural frequency corresponding to the same vibration mode and the experimental measurement is only 1.84%,and the FRFs of single-layer winding and overall winding of the stator end can be further obtained.2.The least square complex frequency domain method（Poly-LSCF）is used to identify the modal parameters of the FRFs calculated by the finite element method.After the verification of the results of the clamped-clamped beam and simply supported plate,the modal parameters of the FRFs of single-layer winding and overall winding are further identified.For single-layer winding,12 modes are identified in 60～300Hz frequency range.Compared with the finite element results,the natural frequency error corresponding to the1st mode is the largest,which is 0.05%,and the damping ratio error of the 12th mode is the largest,which is 1%.For the overall winding structure,7 modes are identified in 75～115Hz frequency range.The mode shapes are mainly elliptic and three lobe.The errors of the natural frequency and damping ratio of the 1st mode are the largest,which are 0.27%and0.5%respectively.3.Aiming at the problem of large errors in the mass matrix and stiffness matrix obtained by the lumped mass method,the mass matrix and stiffness matrix are modified by the modal matrix.After the modified physical parameters are obtained,a mathematical model is established to investigate the dynamic characteristics of the structure.The method is verified on the clamped-clamped beam,and then the method is implemented on the single-layer winding and overall winding respectively.For the single-layer winding,the peak values of radial displacement response of each test point concentrate into 1×10^-7～7×10^-7m/N.For the overall winding structure,the peak values of radial displacement response of each test point are between 4×10^-9～2.5×10^-8m/N.Meanwhile,the vibration responses of the end winding are small in the frequency range of 90～100Hz.The above researches have theoretical guiding significance for grasping the dynamic characteristics of the end winding of a large turbo-generator and the subsequent structural optimization design.