This paper builds a novel coupled model which includes the electric circuit and the magnetic circuit of the three-phase five-legged transformer under direct current (DC) bias. In the magnetic circuit model, the eddy-currents, the iron core topology and the saturation characteristics of the core material are taken into account. The magnetomotive forces due to the eddy currents are given in the magnetic circuit equations. Combining the electrical circuit with the magnetic circuit, and considering

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... the nonlinear characteristic curve of iron core, the nonlinear equations can be obtained. A series of mathematics transformation is performed and the numerical nonlinear algebraic equations are solved. Then the experimental work of the three-phase five-legged transformer under DC bias has been done. Finally, the simulation results and the experiment results are compared. They are in good agreement. Meanwhile, DC bias problem on the three-phase five-legged transformers is analyzed. It demonstrates that the validity of the simulation model and the accuracy of analyzing DC bias phenomenon of the three-phase five-legged transformer.