Low-Order Wideband Isolation Transformer Modeling Based on Independent Branch Fitting

This article discusses the wideband modeling of an isolation transformer aiming at studying the transference of differential-mode voltage surges from the primary side to the secondary side. A modeling approach based on the independent fitting of the branch admittances associated with the equivalent pi-circuit of the transformer is proposed and validated. The resulting model is described either as a Norton-type equivalent circuit for time-domain simulations or as an equivalent circuit. The proposed modeling approach is used to calculate differential voltages transferred to the secondary side of the transformer for the application of impulse voltages at the primary side for different load conditions. The model performance is shown to be comparable to that of a pair of models based on the fitting of all elements of the admittance matrix of the transformer with a single set of poles, with the advantage of requiring a reduced number of circuit elements. It is shown that the tested transformer has a resonant behavior that amplifies differential-mode voltage surges with frequency content around 205 kHz. Also, the time-domain response of the transformer presents a damped oscillatory behavior in the no-load condition and a damped behavior if resistive loads are added at the secondary side.