Robert E. Schwall

Quenches in a high-temperature superconducting tape and pancake coil

Abstract Stability and normal-zone propagation experiments have been performed on singlelength and double-pancake coils made of Bi-2223/Ag high-temperature superconducting tape. Experiments were conducted with liquid nitrogen and gaseous helium cooling in temperatures from 5 to 77 K. No distinctive normal-zone propagation was observed in the single-length conductor tests. Non-uniform critical currents were, however, observed over the length of the conductor. To dramatize the effect on the stability of a magnet wound with this kind of non-uniform conductor, a pancake coil was wound with conductors composed of a two-tape bundle on the inner turns and a single-tape on the outer turns. Quenches of the coil were observed when currents higher than the critical current of the single-tape section were applied and held for more than a few minutes. The coil quenched without a distinctive ‘normal’ front propagation or a large temperature gradient.

Coil and HTS Development for Fault Current Limiters

Fault current limiters are being developed to limit peak currents in transmission and distribution systems. The authors company* has developed a large, robust, high temperature superconducting (HTS) coil for this application. The development included the design of a composite superconductor and a coil configuration specifically for high transient currents and the resulting high transient forces. The results of the testing of the coil including critical current, transient impedance and ac loss data will be described.

AC Loss Measurements on Multifilamentary BSCCO 2223 High-Temperature Superconductors

A calorimetric method for measuring AC loss in long lengths of high temperature superconductor (HTS) at 77 K has been developed. Complementary systems with resolution down to 1 mW/cc have been installed at Oak Ridge National Laboratory (ORNL) and American Superconductor Corporation (ASC) and give consistent results, confirming the reliability of the technique. AC excitation fields up to 0.25 T and at 5 to 60 Hz are supplied by a multifilament BSCCO solenoid which has been in operation for over a year; this is the world’s first HTS magnet system that performs a useful technical function in a cost-competitive manner. Results are presented on 85 filament BSCCO composite conductors showing dependence suggesting hysteretic losses.