Abstract: During the pumping operation of pump-turbine units in the Fujiang pumped storage power plant, the motor power varies greatly because of a short vane opening period, causing severe fluctuations in the grid frequency. To stabilize the operation, this paper formulates a scheme of staged linear vane opening for this plant. We examine the stability of unit operation under different vane openings based on the experimental data of a high-lift model runner, and develop a method to find the maximum vane opening for efficient and economical pumping operation through analysis on the relationships of vane opening and working head versus pump flow, shaft power and efficiency.. Comparative analysis on the pressure pulsations in pumping and generating modes reveal that the pressure pulsations in generating mode are much stronger than those in pumping modes, and that the scheme of staged linear vane opening also improves pumping operation. An analysis of the pumping operation in zero flow condition shows that during pump startup, either slow vane opening operation or a smaller target vane opening helps eliminate large pressure pulsations at zero flow. Calculations of the hydraulic transients show that at each stage of the pump startup in the staged linear opening scheme, fluctuations in water pressure and shaft power are weak and decay more quickly, the units run more stably, and the risk of pressure pulsations stronger than those in generating modes is very low. The conclusions above are also useful for other high-lift pump storage stations with similar unit flow, torque and pressure pulsations of the runners.

Key words: pumped storage unit, pumping mode, staged linear vane opening, efficiency, pressure pulsation