In the field of applying superconducting technology to electric power, superconducting magnetic energy storage (SMES) features highly efficient electric power storage as well as high-speed energy storage and output in comparison with conventional energy storage equipment. With superior qualities of this kind, SMES is expected to bring about a wide range of benefits, such as a stabilization of the power system, maintenance of power quality, and power load leveling. However, extensive R & D for SMES is required to achieve further cost reductions because many issues are yet to be resolved with respect to cost-performance and practicality. Given this situation, a 5-year national government project was started in 1999, focused on the development of cost reductions for small-scale SMES associated with power system control to meet market needs and soon become feasible. This paper outlines the ongoing R & D under the national governmental project, the need for cost reductions, and the study results of marginal costs, which can accommodate SMES costperformance.
Optimal SMES system concepts were developed for power system stabilization (available capacity of 54MJ, available output power of 100MW) and load fluctuation compensation or frequency regulation (available capacity of 1, 800MJ, available output power of 100MW) applications. The system details designs mainly composed of the superconducting coil, which aimed to achieve a cost decrease for each usage, based on four different schemes. The details of the designs and cost-reduction efforts were reviewed. Furthermore, to verify the validity of the development concept and the performance based on the detailed design result of the superconductor, five kinds of short superconductors (about 10m) selected respectively from among four kinds of superconductors were made for trial purposes. The performance of these prototypes was analyzed, including the measurement of current-carrying characteristics, stability and AC loss. Especially, the AC loss characteristic was measured with two devices: “superconductor coupling loss measurement device” of Kagoshima University; and “actual AC loss measurement device”, equipment was that built to enable the measurement and assessment of AC loss under conditions closely approximating the actual magnetic fields.