A three phase core-type transformer iron core model with included magnetic cross saturation

Three phase transformers used in the electric power applications are composed either of three single phase transformers or they are three limb core type. The majority of three phase core-type transformer dynamic models neglect magnetic nonlinearity and saturation. This paper presents two magnetically nonlinear iron core models of three phase three-limb transformer. Iron core model I is determined by described simultaneous excitation of three windings, where two currents are always constant, or by special single-phase excitaion.Iron core model II is determined by simultaneous three phase excitation with different currents. The comparison between measured and calculated currents confirms that results agree much better when the proposed iron core model II with included cross saturation is used in the dynamic transformer model instead of the iron core model I. Even more, the values of measured and calculated currents using iron core model II are almost the same.