Inrush current of a three-phase power transformer

Abstract

Uncontrolled switching of transformers on the network is accompanied by a large asymmetry of currents in the iron core. As a result of such asymmetrical currents, large harmonic distortions of voltage and magnetizing current occur. Problems caused by inrush currents can cause failures in the transformer itself and can cause incorrect operation of protective relays, fuses and other types of protection in the power system. Finally, all of the above contributes to a significant reduction in the quality of the supplied electricity. This paper describes a mathematical model of a three-phase three-pole transformer. The hysteresis loop is also modeled using a simple analytical expression. With the help of this model, a simulation was made on a digital computer, taking into account the effect of saturation, residual magnetic flux and the selection of the moment of switching. For the purpose of experimental verification of the results, a laboratory model of a system for controlled switching of transformers was made. It was shown that the inrush current when using a controlled switching system is several times smaller than the inrush current that occurs during uncontrolled switching.

Goran Petrović

Full Professor | Department of Electrical Measurements

Prof. dr. sc. Goran Petrović is a full professor at the Faculty of Electrical Engineering, Mechanical Engineering and Architecture in Split. His research interests include measurement of electrical and process quantities, analysis of geoelectrical and geothermal features of the soil, instrumentation for smart grids, measurement and application of synchrophasors. He is the author of numerous papers published in top-tier scientific journals and contributed to valuable international and national scientific projects.