Eddy-current resistance of multilayer coils

Most of the earlier studies of eddy-current resistance have been made by those interested primarily in the effect of compromise transpositions on the losses of rotating equipment. Their results have included formulas for the eddy-current resistance for perfect transpositions, but these have gotten into handbooks in difficult form or have been ignored entirely. Such formulas are presented here in more usable form, with more information on their limitations, and further formulas are derived for minimum losses for a number of different cases. Included is a set of curves showing eddy-current resistance as a function of the number of layers and conductor thickness. Formulas also are included that take into account the differing lengths of conductor in successive layers and that approximate the end losses in a spiral coil on account of radial flux.