Research On Magnetic Field And Eddy Current Losses And Its Impact Factors In End Region Of Turbogenerators

Large turbo-generator is a high technical equipment for electric power. Theturbogenerator is as the heart of power system. It becomes the development goalsof each domestic and foreign big power generation equipment manufacturingcompanie. Beside that, its key technology has been paid close attention byinternational academia and engineering. With the development of the generators,electromagnetic and thermal load increase. This could cause local overheating,which could lead to insulation deterioration, core slackness and vibration ofturbine-generator set. All of these could cause abnormal downtime, or threat topower system security. This brings a series of new challenges for the desigen andoperation of turbo-generators.The increased caparcity may result in the electrical and magnetic loadincrease, which could leads magnetic flux leakage to be crowd gathered in theend region of turbo-generators. On one hand, the magnetic flux leakage couldresults in eddy current generated in metal components in the end region of turbo-generators. On the other hand, the magnetic saturation could be more serious onthe flux screen and stator end cores. All of these are related on theelectromagnetic vibration and fever in the end region. It may cause end coreswarp and end teeth shed. In addtition, the magnetic field and eddy current lossesdistribution is random under different operating conditions and complex structurein end region. Hence, it is vital that conducting research on the magnetic fluxdistribution and eddy current and the relative actors in the end region of turbo-generators.In this dissertation,3D transient mathematic model of electromagnetic fieldis established based on electromagnetic theory. The research on the magneticfield and eddy current losses distribution in end region of turbogenerator isconducted for both thermal and nuclear power turbo-generator. In thisdissertation, multiple field-circuit coupled time stepping finite element method isproposed and adopted to solve the transient magnetic field in the end region ofturbogenerator. This method could avoids the the generator complex process oniterative calculation on the initial parameters during solving the magnetic field in the end region by the traditional method. This method could realize a strongcoupling for2D and3D fields by the connection of FEM and circuit. On the basisof the above research, stator leakage reactance is calculated by numerical andanalytical methods, respectively.3D nonlinear transient eddy current field in the end region of largeturbogenerator is established. Influence of copper, magnetic and composite alloyelectric screens on eddy current losses and axial flux on stator end cores and itsteeth is analyzed. Under no and rated load operation conditions, the difference ofclosed path for end leakage flux and spatial rotation law of leakage magnetic fluxin the end region of turbogenerator are revealed. Besides, influence of the copperscreen thickness on the magnetic field and eddy current loss is analyzed.The comprehensive comparison with electric and magnetic screens isresearched. The characteristics of axial magnetic flux leakage distribution on thestator end cores are comprised with different screens. Magnetic field amplituderotation is discussed with obstruction and evacuation screens in the end region ofturbo-generator. Based on the theoretical research, flux obstruction coefficienthas been proposed as a new concept. The flux obstruction coefficient of copperscreen is calculated with a unique structure form. The attenuation degree ofmagnetic flux leakage from the outer surface to the inner surface of copperscreen is comfired.Multi-layer perceptron neural network and support vector machine (SVM)models are established for the multiple factors that are copper screen thickness,copper screen conductivity and clamping plate relative permeability on the eddycurrent loss in the end region of turbogenerator. For these two different models,local training samples are set for learning. The prediction for eddy current lossesof end structures that are influenced by multiple factors, which are copper screenthickness, copper screen conductivity and clamping plate relative permeability isconducted with different cases. The generalization ability is discussed fordifferent data minings.The research on magnetic field and eddy current losses and its impactfactors in end region of turbogenerators could provide a reference for bothassessment of electromagnetic force and local temperature and optimizationdesign on the end structures of large power turbogenerators.