Ohkawachi pumped-storage scheme in Japan

The 1280 mw Ohkawachi pumped-storage project, now under construction in Japan, will be the largest pure pumped-storage scheme in the country. Two of the four units will incorporate a newly developed adjustable speed system, which has been designed to achieve better control and stability of the power system frequency in the pumping mode and improved efficiency in the generating mode. This article describes the main civil structures of the project and outlines the design principles of the adjustable speed system.