APPLICATION OF SINTER-FORGED BI-2223 BARS TO 1500-A AC POWER UTILITY SERVICE AS HIGH-FREQUENCY CURRENT LEADS IN A 77-4 K TEMPERATURE-GRADIENT

Two assemblies of Pb-BSCCO 2223 superconductor bars were produced for use in ac connections between utility system lines at room temperature and a fault-current limiter operating at 4 K. Each assembly consistin g of four parallel bars arranged within a IDD mm-diameter boundary, de livered 1500 A (peak), 50-60 Hz ac through the 77-4 K range of the tem perature gradient while dissipating < 0.3 W. The sinter-forged bars di splayed dc critical current densities of 950-1300 A cm(-2) at 77 K and > 5000 A cm(-2) at 4 K; magnetic field sensitivity was relatively sma ll. Although thermal conductivity tests showed values much higher than those found in the literature for polycrystalline Pb-BSCCO 2223 made by other processes, this undesirable result was counterbalanced by the relatively high values of critical current, which enabled the use of bars with smaller cross-sectional areas. Typical 50-Hz ac power losses at 77 K in each bar (with a cross-sectional area of 0.54 cm(2)) were 1 mW cm(-1) of length at 310 A and 1.75 mW cm(-1) at 375 A. Losses wer e much smaller at 4 K. Bars were 25 cm long, including ends that carri ed silver contacts sinter forged to the ceramic, with a 21 cm silver-f ree length in the thermal gradient between the fixed-temperature termi nals. Thermal efficiency of the assemblies was assessed by helium boil off tests.