In order to supply large amounts of electric power to meet increasing demand, a high-Tc superconducting cable compact enough to be applied to ducts without construction of new underground tunnels is desired. There are, however, many key technologies which are necessary to develop long high-Tc cables capable of large capacity in compact size. For the purpose of studying these technologies, two systems were developed and tested. At the first step, a 7m long, 3-phase 1kA superconducting cable system was developed to study issues concerning large current loading. The measurements of AC losses and inductance show that total AC loss of this cable was 3.5W/m/cct at 1kA loading, that hysteretic loss was dominant, and that the magnetic shields were effective enough to reduce the eddy current losses in thermally insulated pipe. As the next step, a 30m long, 66kV-1kA high-Tc superconducting cable system prototype was developed to study issues for long-length cables. In this system, an AC current of 40kV-1kA was successfully applied in sub-cooled liquid nitrogen (72K, 1.2kg/cm2abs) regardless of mechanical history, such as handling in the factory, transportation, laying and the axial force due to contraction during cool down.
