Power transformer modeling based on wide band impedance and admittance measurements

This paper evaluates the transient behavior of a single-phase, two-winding, 127/12 V, 12 VA signal transformer according to two different high-frequency models. The first model is based on the direct measurement of the transformer´s impedance matrix, while the second model consists in a combination of the admittance matrix and voltage transfer measurements. Both are alternatives to obtain a model with more information on the transformer´s behavior at frequencies ranging from 10 Hz to 2 MHz. The admittance matrix resulting from the inversion of the measured impedance matrix (in the first model) and the modified admittance matrix (in the second model) are approximated by rational functions via the vector fitting technique, which leads to two equivalent RLC models that are stable and ready to be used in EMTP-like programs. The obtained models are first compared in the frequency domain with measurements carried out at the transformer terminals. Then, in order to validate the developed models in the time domain, comparisons between the theoretical and measured results of the transferred voltages from the primary to the secondary windings of the transformer are made. These comparisons consider distinct load conditions and the application of impulse waves with different time characteristics.