Recent activities for applications to HTS transformers in Japan

Domestic and international cooperative projects for applications of high-T_c superconducting (HTS) transformers have started in parallel over the world, taking into account the advantageous performances and merits. The applicability of high-T_c superconductors to ac uses in the region of liquid nitrogen temperature is considered in relation to the practical critical surface for temperature and magnetic field. Recent activities for the applications of HTS transformers in Japan are briefly summarized. The first topics are the developments of a 800 kV A laboratory-test device cooled by subcooled liquid nitrogen and the research and development of a high-voltage-type device to be tested in a power grid and the second topic is a conceptual design study of 20 MV A class practical devices in underground distribution substations. These activities in Japan are compared with other progressing plans in the world. Finally, it is pointed out that the projects to develop the prototypes of HTS transformers are relevant to economic strategy for prior investment in future worldwide HTS industries.