Research On Loss Characteristics Of Power Transformer Under Harmonic Excitation

In view of the increasing voltage and installation capacity of the transformer in the power system,actual operating condition is becoming more and more complicated.Traditional transformer loss measurement and calculation method are more and more difficult to adapt to the problem of complex excitation conditions.The research of transformer winding loss and stray-field loss characteristics under harmonic excitation has important engineering significance and application prospect for transformer design research and product optimization.In this paper,the excitation coil model in TEAM Problem21 is used as the object of study.By comparing loss measurement and calculation of coil winding of the sinusoidal excitation transformer,a more accurate excitation coil loss modeling method is obtained.Based on the P21°-EM1 and P21°-B models,the original measurement method is improved and the effectiveness of the improved method is proved by comparing with the traditional measurement method on the basis of the original measurement and simulation method.When the finite element analysis of transformer tank wall is carried out,the number of grids is large and the solution is slow.By comparing with the traditional finite element method,the finite element method with the boundary condition of the impedance is obtained,which is more suitable for solving the stray loss of magnetized steel under sinusoidal excitation.In this paper,the time domain analysis method is used to solve the problem that the coil winding loss and the stray-field loss of the structural parts are too long for the non-sinusoidal excitation condition.The frequency domain analysis method is used to simulate and compare the model.It is found that the frequency domain method has a good applicability in the linear problem(transformer winding loss problem and non-magnetic steel stray-field loss problem),and only a part of the nonlinear problem(the magnetic steel stray-field loss problem)is applicable.Through the comparison of the loss of the excitation coil,the non-magnetic steel and the magnetic steel under the harmonic excitation condition,it is found that the content and order of the superposition harmonic component are positively correlated with the model loss in the linear problem.However,the phase change of the harmonic component has no effect on the model loss.In the nonlinear problem,the content,order and phase of the superposition harmonic component are directly proportional to the model loss.