Fabrication of 1kA class oxide superconducting transformer
for AC transport measurement cooled by cryocooler

Edmund S. Otabe, Takashi Yasuda, Teruo Matsushita
Iizuka, Kyushu Institute of Technology
Masataka Iwakuma
Fukuoka, Kyushu University
Takaaki Bohno
Ichihara, Fuji Electric Co. Ltd.

One of the common ways to obtain a high current (>100A) for
AC transport measurement of a superconductor is the use of a
current transformer with high transformer ratio. In this
study, an oxide superconducting transformer cooled by a
cryocooler was designed and fabricated. The operation
temperature of the transformer was designed to be 20-50 K,
depending on the condition of the cryocooler. The
temperature of a specimen was separately controlled in the
range of 50-100 K with another cryocooler. The primary peak
voltage and current were 40 V and 45 A, respectively. In
this case the peak current in the secondary winding was 1000
A. Bi-2223 Ag sheathed tape was used for the both
windings. The number of turns for the primary and the
secondary windings were 440 and 6, respectively. In
secondary winding, 6 parallel conductor was wound with the
transposition to uniform the current distribution in
parallel conductors.  A copper wire was also wound for the
primary winding for the test at the frequency higher than
100 Hz. An iron core was designed to attach to the coil to
obtain a better coupling between the primary and secondary
windings. The total size was about 200 mm in hight and 100
mm in diameter.