Total primary inductance was actually determined by measuring
the secondary inductance and then multiply it with the turn ratio squared.
Imposed secondary voltage was then multiplied with the turn ratio, thereby
yielding the primary voltage. Optional L(U(f)) dependency may be determined
by regarding the fact that the mmf is proportional to the magnetizing current
and thereby inversely reactance dependent at a certain fixed voltage. The
voltage dependency at for instance "25Hz inductance" is therefore half
that for 50Hz.