Calculation And Verification Ofstray Loss Of Transformer Basedon Surface Impedance Method

High voltage power transmission has become the main force of power lines in China.Large capacity power transformer is the key electromagnetic equipment.Because of its complex internal structure,the uneven distribution of magnetic leakage in the structure of tank,core,shielding,etc.is more and more serious.The stray loss caused by the leakage flux leads to a series of serious problems,which not only makes the loss and temperature rise of transformer increase sharply,but also easily causes the danger of local overheating,which ultimately affects the safe operation of transformer.Therefore,the study of leakage flux distribution and loss calculation can provide specific analysis methods and data support for the structural optimization of power transformer.In the calculation process of stray loss of transformer,the structure such as tank has the characteristics of multi-scale and small penetration depth,which makes it impossible to meet the requirements of both calculation accuracy and efficiency during the solution process.Therefore,this paper focuses on the above problems.Firstly,the distribution of eddy current in the conductor is investigated,and the characteristics of transformer materials are analyzed.the applicability of related materials is analyzed based on the surface impedance theory to determine the research object.Secondly,in order to solve the problem that one-dimensional surface impedance boundary can not calculate the magnetic density of the corner area,so it is modified.The boundary condition of surface impedance considering the corner area is given and compared with the finite element calculation results,which is proved to be correct.Then,based on the theory of surface impedance,the application of the theory in the modeling of transformer structure(such as large-scale sheet material)is carried out.The complete expression of the three-dimensional eddy current problem of the global surface impedance under the A,φ-A a method is given.The surface impedance boundary condition is incorporated into the discrete equation of the finite element and its calculation characteristics are analyzed.In addition,to solve the problem that the global surface impedance modeling can not obtain the internal electromagnetic data,and then can not accurately calculate the stray loss,a local surface impedance modeling method is proposed,in which different boundary conditions are applied to different regions of the structure.Finally,the international team reference model P21-B is taken as the research object to build the transformer stray loss test system.Through the corresponding experimental research and simulation analysis,the correctness of the local surface impedance modeling method is verified.The local surface impedance method overcomes the difficulty of generating a large number of sectioning elements by the traditional finite element method,considers the influence of conductor corner area on impedance boundary conditions,and realizes the accurate calculation of stray loss.On the premise of guaranteeing the calculation accuracy,it can save the calculation resources and improve the calculation efficiency,which has high engineering practical value.