The modelling of the transformer impedance frequency response
at no-load for a wide frequency range, particularly at low
frequencies, is not a simple task. At low frequencies, the
frequency-dependent non-linear effects present in the
ferromagnetic material are predominant in relation to the effects of
the other transformer components [6, 7]. In general, data on the
frequency response of open-circuit impedances used in the models
is originated from sweep frequency response carried out by
impedance analysers or by function generators. However, in these
devices, the instantaneous electrical power provided is low
(commonly