The present paper deals with a new approach for the study of the steady-state and transient behavior of three-phase transformers. This approach based on magnetic equivalent circuit-diagrams, takes into account the nonlinear BH curve as well as zero- sequence flux. The nonlinear BH curve is represented by a Fourier series, based on a set of measurement data. For the numerical simulations, two methods have been developed, by considering the total magnetic flux respectively the currents as state variables. Numerical ...