Sigre 2008K. Aguro, The Kansai Electric, Power Co. Inc.
M. Kato, Kyushu Electric, Power Co. Inc.
F. Kishita, Electric Power, Development Co., Ltd.An adjustable speed pumped storage system can control pump input power by varying pump rotating speed, and contributes to power system Automatic Frequency Control (AFC) operation with pumping operation, which can not be realized by conventional single speed unit, during light load hours such as night, holidays and so on. In Japan, 8 adjustable speed units, which are the largest number in the world, are operated at present, and furthermore 6units are under construction or planned. According to one year operation records of power utility companies the adjustable speed pumped storage systems are mainly used for pumping and are operated much longer time than single speed units (more than 7 times), while single speed units installed in the same power plant are mainly used for generating. This means the adjustable speed units are utilized to stabilize power system frequency. Utility companies consider advantages of the adjustable speed system as AFC operation and governor free operation in pumping mode, instantaneous active and reactive power control, reducing impact on power system at pump starting by gradually increasing its input power, and expanding turbine load range by speed optimization. Regarding the maintenance of the system, utility companies point out some additional maintenance items of AC-excitation system, generator-motor carbon brushes and its dust filters.
