Cooling and Liquid Nitrogen Circulation of the 1000 m Class Superconducting DC Power Transmission System in Ishikari

A cooling and circulation test of a 1000 m class superconducting dc power transmission system constructed for the Ishikari project was performed. The heat leak of the system and the pressure drop over the distance that liquid nitrogen was circulated were measured to evaluate the performance of the system. Two types of cryogenic pipes were developed for the Ishikari project both comprising two inner pipes in a single outer pipe. Smooth pipes were used for both the inner and outer pipes. The heat leak was measured and found to be between 0.886 and 1.47 W/m per two inner pipes, which was dependent on the structures of the cryogenic pipes. The heat leak of the cable system, including the cryogenic pipe and the terminals, was found to be 1.69 kW. At a flow rate of 32 L/min the pressure drop was estimated to be 33 kPa over the 2000 m liquid nitrogen circulation. The data obtained in this study will be used for the design of longer superconducting power transmission systems in the future.