Prediction of resistive and hysteretic losses in a multi-layerhigh-Tc superconducting cable

Abstract

In this work, a model of a multi-layerhigh-Tc superconducting (HTS) cable that computes the current distribution across layers as wellas the AC loss is presented. The case of a four-layer cable is analysed, but the methoddeveloped can be applied to a cable with an arbitrary number of layers. The cable ismodelled by an equivalent circuit consisting of the following elements: nonlinear resistances,linear self- and mutual inductances, as well as nonlinear, hysteretic inductances. The firstelement takes into account the typical current–voltage relation for superconductors, thesecond introduces coupling among the layers and depends on the geometrical parameters ofthe cable, while the third describes the hysteretic behaviour of superconductors.In the analysis presented, the geometrical dimensions of the cable are fixed, except for thepitch length and the winding orientation of the layers. These free parameters are varied inorder to partition the current across the layers such that the AC loss in the superconductoris minimized.The model presented allows us to evaluate rapidly the current distribution across thedifferent layers and to compute the corresponding AC loss. The rapidity of the computationallows us to calculate the losses for many different configurations within a reasonable time.The model has first been used for finding the pitch lengths giving an optimal currentdistribution across the layers and for computing the corresponding AC loss. Second, themodel has been refined, taking into account the effects of the magnetic self-field which,especially at high currents, can sensibly reduce the transport capacity of the cable, inparticular in the outer layers.