Electromagnetic Design And Analysis Of 6.6MVA HTS Traction Transformer

With the rapid development of the world economy,people’s living standards are improved day by day,and there are more travel requirements than in the past.High-speed trains are the most convenient,fast and environmentally friendly way of travelling.Therefore,all countries in the world are vigorously developing high-speed railways,and the speed of trains is also used as a criterion to evaluate the strength of country’s railways.The higher speed of the train,the higher requirement of the on-board equipment.Therefore,while the train is high-speed,it also puts forward the requirement of lightweight on-board transformer.The application of high temperature superconducting materials provides an idea for lightweight transformer.Generally speaking,researches of HTS traction transformer technology in many countries is not very mature.At present,it remains at the stage of prototype.Relying on the transformer project of the research group,this thesis is committed to developing a 6.6MVA traction transformer for the high-speed train and finally getting on the train for tests.Based on the design process of conventional transformers and the electromagnetic characteristics of superconducting materials,this thesis presents a preliminary structure parameters,which covers the selection of tapes used in superconducting windings,the determination of winding modes,the calculation of equivalent resistance,the engineering algorithm of short-circuit impedance and the thermal budget in the direction of transformer efficiency.After completing the preliminary structural design,a small capacity transformer of 320VA is wound up,and the critical current and AC loss test platform is built to test the transformer.The measured critical current values obtained from tests were put into the subsequent simulation model as an important parameter.The experimental and simulation results of AC loss are compared and mutually verified.Considering the anisotropy of superconducting materials,the calculation method of the critical current is given.For the winding of high temperature superconducting transformer,the idea of calculating AC loss by using Norris model of single-band transmission loss combined with the characteristics of superconducting coils is proposed.Then,based on COMSOL finite element software,the electromagnetic field distribution and AC loss of HTS transformer are modeled and calculated,which includes the homogenization of two-dimensional axisymmetric model of superconducting winding,the equivalent treatment of Roebel cable at low voltage side,and the simplified consideration of transformer core.The influence of ferromagnetic materials and winding arrangement parameters on AC loss is given.In order to meet the requirement of transformer efficiency,flux diverters are added at the end of transformer windings,and the influence of the structure of flux diverters on AC losses is analyzed in depth.Finally,based on the structure of L049₄3,the AC loss of L049₄3 is calculated by adding the optimum flux diverter structure,which meets the design requirements.