Transport current ac losses and current-voltage curves ofmultifilamentary Bi-2223/Ag tape with artificial defects

Abstract

We experimentally studied the effects of a single artificial defectand a linear array of artificial defects on I-V curves, critical currentsand transport current ac losses of 55 filament untwisted Bi-2223/Ag tapes. Theartificial defect was a small hole drilled into the tape. The reduction in thecritical current measured on a 1 cm long section due to one hole of diameter0.9 mm was 33% and that due to a linear array of seven similar holes was62%. The slopes of the I-V curves, n, measured in this section were33, 16 and 5.8 in the original sample, in the sample with one defect and thesample with seven defects, respectively. Both Ic and the slope reductionwere smaller if the distance between the potential taps was increased. Thetransport current ac losses at 50 Hz and Irms = 10 A in the samplewith one defect measured in a 1 cm long section were practically the same asthose in the original sample (4.1×10-4 W m-1), butthey increased by 83% in the sample with a linear array of seven defects. Themeasured increase in losses per unit length was the smaller, the larger thedistance between the potential taps. A comparison between the measured andcalculated losses revealed that a formal application of the Norris equationsfor loss calculations in samples with local defects leads to an overestimationof the ac losses. A procedure for the calculation of transport current lossesin samples with local defects based on the Norris model is proposed andverified.