A Three-Phase Core-Type Transformer Iron Core Model With Included Magnetic Cross Saturation

The behavior of a power transformer (PT) depends considerably on the properties of the magnetically nonlinear iron core. This paper deals with the modeling of a three-phase, three-limb power transformer laminated iron core. The proposed iron core model is given by the corresponding partial derivatives of measured flux linkage characteristics. The magnetically nonlinear characteristics of flux linkages are determined by the controlled simultaneous magnetic excitation of all three limbs. This enables determination of magnetic cross couplings between different limbs, due to the saturation. The obtained iron core model integrated in the circuit model of PT is compared to the classical saturated iron core model without cross couplings, by analyzing the transient behavior of an unsymmetrically excited transformer. The numerical results obtained by the proposed iron core model agree with the measured results much better than those obtained by the existing nonlinear iron core model known from literature.