Generation of highly stable DC current by using a superconducting transformer

The purpose of this study is to generate a highly stable DC current by using a superconducting transformer. For the first trial stage, a 100 A class superconducting transformer was designed and fabricated for operation at the temperature of liquid nitrogen. The secondary coil of the transformer was wound with a superconducting Bi-2223 tape, and the turn ratio of the primary and secondary windings was about 11:1, which brought an output current of about 80 A by a small varying control current. The control system was constructed with a PC, an AD/DA conversion PCI board and a small current supply. The primary input current was controlled by a normal PID control program. The secondary output current was evaluated by measuring the voltage on a low resistivity shunt. As the result of this study, it was suggested that in the case of small impedance in secondary winding circuit, the DC output current with high stability can be obtained by applying an easy control algorithm to the program running on the controlling PC.