In (19), kAC is the AC resistance coefficient according to
[27], which is a constant when switching frequency is set. km
stands for the coil numbers in the transformer, for singlephase
transformer, the value is 2 and for three-phase, it is 6.
According to TABLE III, the mean length per turn of the
winding l0 and the window area WA can both be expressed by
the dimensional variables a, b, d and h. As a result, the
whole winding loss can be simplified as below: