3-D Coupled Electromagnetic-Fluid-Thermal Analysis of Oil-Immersed Triangular Wound Core Transformer

This paper presents a 3-D coupled electromagnetic-fluid-thermal analysis method for temperature rise prediction in oil-immersed triangular wound core transformer. The temperatures rising inside the transformer are mainly determined by the heat sources and the heat convection effect of the transformer oil. The heat sources which include the electric power losses of transformer core, high-voltage windings, and low-voltage windings can be investigated by electromagnetic analysis using the finite element method in no-load and rated load running situations, respectively. Then, the calculation results of electric power losses are brought into the fluid-thermal field analysis as the heat sources. The temperature distribution inside the transformer and the velocity of transformer oil are analyzed by the finite volume method in the fluid-thermal field. To improve the accuracy of calculation results, the influence of temperature on the electric power losses and the parameters of transformer oil are considered in this paper. Using iterative computations, the power losses of windings are updated in accordance with the thermal field calculation result until the maximum difference of temperature between two adjacent steps is less than 0.01 K. At the end of this paper, the simulation results of coupled analysis used in the 10 kV oil-immersed triangular wound core transformer are compared with analytical formula results proposed by the International Electrotechnical Commission standard, and the good agreement of hot-spot temperature indicates the validity of coupled analysis.