Application of extremum co-energy principle for homogenizing current distribution in parallel-connected windings in transformers: Design optimization of winding turn allocation among winding layers

Parallel-connected windings are widely utilized for power transformers to reduce the copper loss. However, this reduction effect is often hindered by the proximity effect, which causes concentrated current distribution in parallel-connected windings. This paper addresses this issue by proposing a design optimization method of winding turn allocation among winding layers. This optimization method is based on the recently proposed insight on the proximity effect, referred to as the extremum co-energy principle. Experiment on a planar transformer with four primary winding layers was carried out to verify the proposed method. As a result, the proposed method successfully optimized the allocation of the winding turns to minimize the AC resistance.