3-D coupled electromagnetic-fluid-thermal analysis of 220kV three-phase three-limb transformer under DC bias

This paper take a typical 220kV three-phase three-limb oil-immersed transformer as an example, 3D coupled electromagnetic-fluid-thermal model was built. Using field-circuit coupled finite element method(FEM) to calculated the magnetic flux distribution of core and the current of windings under DC bias. Take the electric power losses of core and windings as heat source, the temperature distribution inside the transformer and the velocity of transformer oil are analyzed by finite volume method (FVM) in fluid-thermal field. In order to improve the accuracy of calculation results, the influence of temperature on the electrical resistivity of windings and the coefficient of viscosity of transformer oil are taken into account in the paper. By iterative computations, the power losses of windings are updated in accordance to the thermal field calculation result until the maximum difference of temperature between two adjacent steps is less than 0.1K.