Then, to reduce Im it is necessary to reduce the voltage Vm
on the magnetizing branch. It depends on the value of the
burden connected at the output. The larger the burden, the
higher the voltage; but even with zero burden, some value
of Vm remains due to the voltage drop on Z2. The zero-flux
method requires an external source to compensate all
external and internal voltage drops. Fig. 2 shows the method
proposed in [4].