AC Loss of a Superconducting Multifilamentary Wire in an Elliptically Rotating Transverse Field

Abstract

It is expected that a superconducting wire is exposed to an elliptically rotating field, when it is used for AC 50Hz equipments such as superconducting armature- and exciting-windings of a cryoturbogenerator. This paper provides an expression for AC losses of a multifilamentary composite in an elliptically rotating transverse field H with the index of an ellipticity η(=H_n/H_m), where H_n and H_m are the shortest and the longest radii of the ellipse, respectively.
The coupling-current loss is simply given by a sum of two losses in the cases of reciprocative alternating fields with amplitudes H_n and H_m.
The hysteresis loss increases as η increases in the case of H_m>>H_dc, where H_dc is a superposed DC bias field. For the case of H_dc=0, on the other hand, the hysteresis loss first decreases rapidly as η increaes from zero, takes a minimum at η=0.5, and then increases gradually as η approaches 1.
The rapid decrease of the loss in the low η region is important for AC applications such as the armature winding, in which the field rotates with a small η. The present result cannot be expected from earlier works in which only the case of the circular rotation (η=1) was investigated.