Power Transformer Modeling for Inrush Current Calculation

Abstract

In this thesis a general purpose transformer model for low and medium frequency transient studies is developed and verified. The inrush current phenomena during no-load energization of power transformer is analyzed with special attention. The main challenge is to develop a general model that is valid for a wide range of studies, while it relies on a limited number of commonly available input data. The development of such engineering model is the ultimate research goal.

The power transformer is an essential component in power systems and with exception of transmission lines, it has the greatest exposure to electrical transients of all devices. The models used to predict its transient behaviors are however not always adequate due to both lack of data/measurements and knowledge. Situations of special concern are inrush currents, switching and lightning impulse stresses, induced overvoltages and harmonics.

To predict the electromagnetic stresses on transformers, a calculation model must be established. The single-phase based equivalent representation used in most of the present simulation packages does not sufficiently account for the coupling between phases and the differences caused by various iron core structures. The representation of hysteresis, anomalous losses and remanence also needs improvements.

A valuable way to achieve a deeper understanding of the inrush current phenomena is through extensive laboratory measurements on distribution transformers and field measurements on power transformers. Experimental data are highly beneficial in the verification of the developed model.