A model based on a transformer topology for a frequency range of
10 Hz–100 kHz is described in [7, 9]. To consider the
frequency-dependent non-linear effects in the transformer,
correction functions are applied to the values for the resistances
and inductances of the model within this frequency range. These
correction functions are applied in the model in the frequency
domain. Thus, the use of the model, which considers the
frequency-dependent non-linear effects, is restricted to the analysis
of faults (frequency response analysis – FRA) and cannot be used
in studies in the time domain. In [10, 11], the least-squares (LS)
method is used to model the frequency response of the impedance
at the transformer input applied to the analysis of faults (FRA). In
the equivalent circuit of the model, only RLC cells are used to
represent the resonances of the frequency responses. Thus, the
frequency-dependent nonlinear effects in the core, which occur
mainly at low frequencies, are contemplated superficially by the
model.