Loss and current distribution in foil windings of transformers

Detailed loss and current distributions in the foil-wound low-voltage winding of a 6 MVA power transformer using a finite-element analysis package are presented. The foil-winding eddy loss is estimated and its variation with clearance to yoke is examined. Plots of foil current and eddy-current density and loss-intensity distributions are shown and the magnitude and location of their maxima identified. These lead to the main finding that the foil-winding loss distribution is significantly nonuniform not only axially but also radially. This radial variation has been ignored in previous studies. This will have implications for the thermal performance which is outside the scope of the present study. Although the low-voltage foil winding is conventionally the inner winding, it is shown that making it an outside winding can result in a significant reduction in the maximum current density, loss intensity and the winding eddy loss as a percentage of the I²R loss. The radial short-circuit forces on the outside foil winding, being tensile, could also be an advantage. The variation of foil eddy loss with foil thickness is examined