Through use of smart grids, countries around the world are aiming to realize construction of 21st-century electric systems that provide people with abundant, affordable, clean, efficient and reliable electric power regardless of time or location. In addition to adding advanced functions to the nation's electricity grid and thus enhancing reliability, efficiency and security, a smart grid also contributes to the strategic climate-change goal of reducing carbon emissions. This paper describes the trend toward smart grids in Japan for smooth integration of increased use of renewable energy sources and conventional bulk power systems. Several ongoing Japanese field tests relating to smart grids are also briefly introduced.
Multi-laminated HTS tape conductors wound into double-pancake coils have recently been used for large SMES. If the HTS tapes are simply laminated to form a conductor, the current distribution in the laminated tape conductor of the coil is not homogeneous because of the differences among the tape inductances. Transposition of these tapes at the innermost or outermost layer of the coil is effective for homogeneous current distribution. However, this method requires the same number of singlepancake coils as that of the HTS tape conductor, and hence the number of HTS tape conductors is restricted. In this paper, we propose a new method to control the current distribution in the laminated conductor using tape transposition at the innermost layer of a double-pancake coil and also adjusting the gap between the laminated tapes. We apply this method to a double-pancake coil for SMES, analyze the current distributions for multi-laminated (three to ten times) HTS tape conductors, and show the homogeneous current distribution of the laminated tape conductors for an arbitrary HTS tape number.