Digital modelling of modern single-phase distribution transformers

A new circuit-based mathematical model for single-phase distribution transformers made of modern grain-oriented steel is presented. The effects of mutual and leakage inductances, saturation, eddy current and hysteresis losses, and residual fluxes of the nonlinear steel core are included. Flux linkages of the primary and secondary windings are chosen as state variables. Eddy current and hysteresis losses are combined into a single core loss term accounted for by a voltage-dependent resistance load on the secondary. The authors discuss apparent and incremental inductance concepts, their relationship to one another, and their applicability to transformer modeling. Models based exclusively on one or the other of these inductances are presented and their shortcomings demonstrated through simulation. The model proposed makes a combined use of both apparent and incremental inductance to solve for currents from flux linkages, selecting between them based on whether or not the transformer is in saturation