Research On Calculation Method Of3D EDDY Current Field Structural Parts Losses In Large Power Transformer

It is of great significance to accurately calculate stray losses of structural parts of a large power transformer thus to avoid the local overheating for improving the reliability of transformer operation and ensuring the safety operation of power system. The local losses concentration is the direct reason of local overheating and operational failure caused by the inappropriate distribution of the magnetic leakage fields and stray losses.In the computation of three dimensional magnetic leakage field and its related structural part losses of large power transformer with a complex structure, when the complicated electromagnetic properties (anisotropy, nonlinearity, and so on) and discontinuity of laminated core material have to be considered, the computational scale will be too large to carry out the whole computation, or the calculated error become unacceptable if the conventional method is used, mainly because the contrast between the huge size of the computation region and very small skin depth. To treat with the problem, this thesis researches several methods of improving the calculation accuracy and reducing the calculation scale for these computations.In order to consider the higher-order harmonics of the field quantities (flux density B, eddy current density J), a time domain analysis method combining analytical and numerical solutions for laminated core homogenization is proposed in the thesis to calculate3D magnetic leakage field and its structural parts stray losses including nonlinear and anisotropic laminated core. On the premise of guarantee engineering precision, this method can reduce the scale of calculation and make it feasible to calculate this kind of problems.Although the calculation carried out in complex frequency domain is widely applied in3D eddy current field analysis due to its simplicity and time saving, it is not suitable for solving nonlinear problems. For preserving the advantages and improving calculation accuracy, the calculation method of traditional complex frequency domain is improved, and the discretized finite element equations of3D eddy current field are deduced considering the electromagnetic characteristics of different materials such as anisotropy, isotropy and nonlinearity in complex frequency domain. The nonlinear complex algebraic equations are solved by complex Newton-Raphson method, and the calculation results meeting engineering precision are obtained.Domain Decomposition Method (DDM) is another method reducing calculation scale of complicated problem. Overlapping Domain Decomposition Method (ODDM) is applied to the nonlinear FE analysis of3D eddy current field in complex frequency domain in the thesis. The solved region is divided into different sub-regions which are overlapped and influenced on each other. Different sub-regions can be meshed independently and solved with different discretization mode and method. The calculation scale is reduced and the computational complexity is decreased effectively.In order to verify the validity of the proposed methods and the self-compiled computer programs, the computation examples of small models and the models of real transformer products are adopted. A supplementary model of TEAM Problem P21C-M1is made, and the magnetic field distribution and losses of this model are measured. A simulation calculation is executed for this model with the proposed time domain analysis method for laminated core homogenization. In addition, the calculated results are compared with measured results of two large power transformers. The comparison of the computed and measured results confirmed the validity and efficiency of the methods proposed in this thesis.