Modeling and simulation of magnetizing inrush current of large power transformers

This paper presents a model for simulating magnetizing inrush current in large power transformer. The voltage and current distribution in the transformer winding under energisation conditions is formulated on the basis that the magnetic field can be considered as the composition of main flux in the iron core and leakage flux in the coil space. The calculation of the circuit parameters and the methods for solving the equations are also discussed. The simulation results for a single-phase, three-winding autotransformer and a three-phase, five-legged, three-winding transformer show the effect of energisation angle, the magnitude and the direction of the original residual magnetism on the inrush current. The difference of the B-H curves obtained from the measurements of the material of the iron core and the laminated iron core is also indicated. The proposed model is suitable to all kinds of structures of large power transformers