Long-term operating characteristics of Japan’s first in-grid HTS power cable

• Published in: Physica. C, Superconductivity Superconductivity, 2015-11, Vol.518, p.126-129
• Main Authors: Nakano, Tetsutaro, Maruyama, Osamu, Honjo, Shoichi, Watanabe, Michihiko, Masuda, Takato, Hirose, Masayuki, Shimoda, Masahiro, Nakamura, Naoko, Yaguchi, Hiroharu, Machida, Akito
• Format: Article
• Language: English
• Subjects: Cooling system; High-temperature superconducting cable; In-grid operation
• ISSN: 0921-4534; 1873-2143
• DOI: 10.1016/j.physc.2015.04.010

•The in-grid operation had continued for more than one year without serious troubles.•The LN2 temperature and pressure were controlled stably within the preset range.•No degradation of Ic occurred against the designed value after in-grid operation.•The degradation rate of cooling power differed among the refrigerators. Tokyo Electric Power Company, Sumitomo Electric Industries, Ltd and Mayekawa Mfg. Co., Ltd have jointly conducted the first in-grid demonstration test of a high-temperature superconducting (HTS) cable in Japan, from FY2007 to FY2013. The objective of this project is to evaluate the reliability, stability and other characteristics of the system. The cable structure used in this project is the type of three-in-one cable. As a coolant, sub-cooled liquid nitrogen flows through the gap between the corrugated cryostat and the three cable cores. This structure can realize compactness and reduce heat invasion compared with three single-core HTS cables housed in separate cryostats. The cooling system consists of six refrigerators, two circulation pumps and a reservoir tank. Each refrigerator has a cooling power of 1.0kW at 77K, 0.8kW at 67K. The number of operating refrigerators is controlled so that the coolant temperature at the cable inlet is kept to preset value. The HTS cable was connected to the live electricity grid from October 29, 2012 to December 25, 2013. In-grid operation continued for more than one year without any accidental interruption of operation or other operating issues. During this time, we studied the operating performance of the HTS cable in dependence on the sub-cooled LN2 temperature.