A study on the inrush current phenomena in transformer substations

This paper investigates the inrush current phenomena in substations including parallel-connected transformers or transformer banks. It is based on analytical expressions for the transformers´ nonlinear, and generally not identical, magnetization curves (from curve fitting of experimental data) and the numerical solution of the differential equations. It is then possible to determine the waveforms of the interesting signals (i.e. currents, fluxes and voltages) of each transformer, the total substation current and the common bus voltage. This is followed by a study of the affecting parameters on the expected magnitudes of eventually strongly distorted waveforms of the individual transformers´ inrush currents. The effect of eventually existing power factor correcting shunt capacitors is also investigated. It is believed that the study provides helpful information regarding the protection of transformers and substations.