Variable speed pumping-up electrical power system

A variable speed pumping-up electrical power system comprising:

• a variable speed electrical machine;
• a frequency converter connected between said variable speed electrical machine and an a.c. power system;
• a pump/turbine driven by said variable speed electrical machine;
• a speed detector detecting the rotation speed of said pump/turbine;
• a power detector detecting effective power supplied to said variable speed electrical machine from said a.c. power system;
• a frequency converter controller controlling said frequency converter so as to eliminate any error between the value of effective power detected by said power detector and the value of effective power commanded by an externally-applied effective power command signal, a frequency detector detecting the frequency of said a.c. power system, a frequency controller comparing the frequency detected by said frequency detector with a frequency setting to generate a correction signal for correcting said effective power command signal, and means for correcting the value of the externally commanded effective power by said correction signal.