Stray-Current Losses in Stranded Windings of Transformers

Previous solutions of the stray loss problem in transformer windings have been made on the assumption that the winding turns contain only one conductor. In a stranded winding this solution represents only the eddy-current loss component of the total stray losses. A second loss component is caused by circulating currents flowing back and forth between the strands. This circulating-current loss depends upon the relative physical location of the strands throughout the winding. Considering various types of stranding, this paper gives equations and charts for the circulatingcurrent loss in a number of different coil constructions as well as for the eddy-current loss.