Abstract
In order to study the coupling fluid and thermal problems of the local winding in oil-immersed power transformers, the least-squares finite element method (LSFEM) and upwind finite element method (UFEM) are adopted, respectively, to calculate the fluid and thermal field in the oil duct. When solving the coupling problem by sequential iterations, the effect of temperature on the material property and the loss density of the windings should be taken into account. In order to improve the computation efficiency for the coupling fields, an algorithm, which adopts two techniques, the dimensionless LSFEM and the combination of Jacobi preconditioned conjugate gradient method (JPCGM) and the two-side equilibration method (TSEM), is proposed in this paper. To validate the efficiency of the proposed algorithm, a local winding model of a transformer is built and the fluid field is computed by the conventional LSFEM, dimensionless LSFEM, and the Fluent software. While the fluid and thermal computation results of the local winding model of a transformer obtained by the two LSFEMs are basically consistent with those of the Fluent software, the stiffness matrix, which is formed by the dimensionless scheme of LSFEM and preconditioned by the JPCGM and TSEM, has a smaller condition number and a faster convergence rate of the equations. Thus, it demonstrates a broader applicability.
Highlights
As the core equipment of power systems, power transformers are usually used for power transfer and voltage alternating, and its reliable operation is the premise to guarantee the quality of the power supply
The results show that the accuracy of least-squares finite element method (LSFEM) is higher than that of finite volume method (FVM), and the results of the fluid field calculated by the LSFEM have a high numerical stability; the LSFEM does not need an upwind scheme or grid refinement to avoid numerical oscillation
LSFEM and upwind finite element method (UFEM), while Fluent software is based on FVM, the different principle of finite element method (FEM) and FVM could result in some deviations
Summary
As the core equipment of power systems, power transformers are usually used for power transfer and voltage alternating, and its reliable operation is the premise to guarantee the quality of the power supply. Zhang et al, [27] constructed a 3-D computational fluid dynamic model for a transformer to generate the training data for response surface method (RSM) They employed two types of RSMs to evaluate their performance of designed cooling systems. The results show that the hybrid algorithm compensates for the problems of poor adaptability to irregular meshes and limited computational accuracy It can be seen from the above literature that the FVM is widely applied in fluid field analysis for its high calculation accuracy and good stability of numerical solution. To validate the proposed method, a local winding model of a transformer is built, and the results of the fluid-thermal fields of the model and the convergence rates are analyzed and compared
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