Semi-empirical model of the losses in HTS tapes carrying AC currents in AC magnetic fields applied parallel to the tape face

Abstract

The AC losses are an important parameter of high-temperature superconductors (HTSs) to be used in electric power applications. To obtain an optimised design of such applications, models of the AC losses are needed. This article describes a semi-empirical model of the AC losses in HTS tapes as a function of temperature, magnetic field, transport current and frequency. The magnetic field (applied in parallel to the tape face) and the transport current are in phase with each other. The model considers flux-flow losses (based on the power law dependence) and hysteresis losses (based on the critical state model). Results obtained by the model are compared to experimental data obtained calorimetrically on a BSCCO/Ag tape in the temperature interval 41–94 K. Using the model, minima in losses per unit carried current and unit length are determined as a function of temperature and magnetic field. The currents at which these minima occur represent optimal operating currents of the conductor with respect to the losses. The model can be used to determine the losses in the inner part of the winding of e.g. a transformer coil. In the outer part of such a winding, large AC losses occur due to the magnetic field component perpendicular to the tape face.