Abstract: A variable-speed pumped-storage power generating system includes a variable-speed generator/motor, a frequency converter connected to an electric power system, and a pump/turbine driven by the generator/motor.

Abstract: Disclosed in a variable speed pumping-up electrical power system comprising a variable speed generator/motor, a frequency converter connected between the generator/motor and an a.c. power system, a controller controlling an effective power input to the generator/motor by controlling the frequency converter on the basis of the difference between an actual effective power input from the a.c. power system and an externally-applied effective power command, and a correction circuit correcting the effective power command on the basis of the difference between the frequency of the a.c. power system and a frequency setting.

Abstract: In a water level depressing operation of a multistage hydraulic machine, first, the guide vane in the maximum-pressure stage is totally closed. Then, the respective guide vanes in the remaining stages are left opened more or less, and compressed air is supplied, whereby the water level is depressed below the runner in the runner chamber in the minimum-pressure stage. Thereafter, the respective guide vanes in the stages other than the maximum-pressure stage are also totally closed. Then, when the water level in each of the runner chambers is raised as a result of, for example, leakage of water from the associated guide vane, compressed air is individually replenished to each of the runner chambers.