Variable speed pumping-up generator

Claim 1

An adjustable speed pumping-up generator including an induction generator motor having, a stator with a primary winding connected to a power system; a rotor with a secondary winding connected to a pump turbine having guide vanes and means for adjusting said guide vanes; an AC exciting unit for adjustable frequency excitation of said secondary winding; and said rotor having a rotary shaft which is driven, in a generation mode, by said pump turbine which, in a pumping up mode, drives said pump turbine in the pumping up mode, said adjustable speed pumping-up generator comprising: a first speed control means receiving an external power command signal to be engaged in the generation mode for adjusting speed of said pump turbine to an optimum value in accordance with said external power command signal by adjusting said guide vane means of said pump turbine; a back-up speed control means operating when the speed of said pump turbine is determined to be out of a predetermined operable range while said first speed control means is operating for returning the speed of said pump turbine to said predetermined operable range by controlling said AC exciting unit; wherein said first speed control means and said back-up speed control means are set so that a decreasing speed limit setting that causes said operating of said back-up speed control means is set to be less than a minimum setting of said first speed control means by an amount larger than a single amplitude of sustained speed oscillations achievable under control of said first speed control means.