A model for the current distribution and ac losses in superconducting multi-layer power cables

Abstract

A superconducting cable consisting of a several layers is described theoretically. Discretised equations are given that can be used to describe the current distribution in the cable as a function of cable current. Solutions are worked out for the case of an ideal Bean type II superconductor, taking into account layer current saturation at the critical current I c. The ac loss is shown to exhibit two different regimes. In a low current regime the current in each layer is below its respective I c value, resulting in magnetisation hysteresis loss in the presence of simultaneous currents and fields. In this regime all layer currents and the local magnetic fields are in phase with the externally applied current. As the critical current in a layer is reached it saturates with current and current redistribution occurs and an additional loss mechanism (saturation loss) appears that stems from the distortion of the local current and magnetic field values. Calculated ac loss values are compared to three cables from the literature, and good agreement is found.