In this paper a 30 m long one-phase coaxial YBCO cable with 1 kA transport current and 10 kV operating voltage was designed for the Super3C project to check the feasibility of YBCO tapes for low-loss cables. The final design incorporates cryogenic, mechanical and electromagnetic aspects. The electromagnetic losses during normal operation must be minimized. The cryogenic design must also take into account the generation of heat during short circuit conditions. Mechanical restrictions set the minimum gaps between the coated conductor tapes and the minimum lay angles in order to make the cabling feasible and to enable handling of the cable. The design of the electric insulation should be according to the international standard as far as applicable. The final design has to take into account all of the above restrictions.
Magneto-optical (MO) imaging, Hall probe measurements and the magnetic knife method were used for sample quality studies of multi-core Bi-2223/Ag tape with a columnar 60-filament structure made by the TIRT (tape in rectangular tube) process. While the magneto-optical imaging was made at 25 K and without transport current, Hall probe and magnetic knife measurements were performed for the sample carrying a direct current at 77 K.The MO image recorded at 25 K and external field 30 mT has shown non-uniform flux distribution in the three filament columns. 2D field profiles were analysed by the finite element method assuming ideal filament homogeneity. B z (x) was computed analytically with an assumption that current density flows straight through the cross-section of the filament columns. The best agreement of computed profiles with measured ones is achieved for equal currents flowing in all filament zones. According to the magnetic knife measurements, current density is lowest in the centre column, but in this method the magnetic self-field is hardly influencing the current distribution. A better understanding of such experimental differences is obtained with 3D modelling. Three different cases of meandering transport current were studied computationally in order to explain the measured results. Finally, we discuss the advantages and drawbacks of the methods used and present how they can together produce the most complex information.
During the last five years, the ac performance of high temperature superconductor (HTS) tapes has been under intense development due to the need of practical applications. In order to measure and understand the current density distributions inside these tapes, several methods have already been developed. However, no system has been able to give the time dependent, spatial distribution of the magnetic flux density at a selected distance above the HTS tape carrying any cyclic current signal. In this paper, such a system operating at a frequency range of 0–400 Hz is presented, and possible error sources are extensively investigated. Post-processing of the measured data is explained in detail and error analysis of several example measurements is given. Measurements with HTS and copper samples are compared in order to demonstrate the usefulness of the system.
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