High-Tc superconductors and AC loss in electrotecnical devices

To replace conventional normal conducting solutions in electrotechnical devices, high-Tc superconductors must offer distinct economical and technical benefits in terms of lower overall loss, volume and weight. Based on AC loss theory we design appropriate 50 Hz reference conductors for cables, transformers and other applications, calculate admissible limits for the conductor variables filament diameter, twist and matrix resistance and compare this to the present state of Bi-2223-tape conductors and AC loss measurements. Further the influence of perpendicular AC field components on losses is addressed. High current devices will require multistrand conductors, where nonuniform current distribution due to unbalanced magnetic coupling may result in partial saturation and enhanced losses. As an example we discuss the multilayer HTSC-cable and present a solution based on a ‘zero flux condition' for azimuthal and axial magnetic fields.