Water-ring Characteristics and Control of Pump-turbine

Synchronous condenser pump(SCP) mode operation is one of the important operation modes for pumped-storage unit, and it is also a necessary working condition for pumping operation mode start-up. The key factors affecting the SCP operation stability are water-ring characteristics and its control methods. For a long time, there is a lack of systematic researches on the formation and development of water-ring, and water-ring control method purely depends on the on-site unit commissioning. Therefore, focusing on a medium specific speed pump- turbine model, unsteady flow analysis was made for different conditions by RNG k-ε turbulence flow model and volume of fluid (VOF) model. Water-ring thickness, power absorption and pressure pulsation in monitored points were obtained by considering runner rotating speed, pressure in spiral case, cooling flow rate of upper seal between runner and head cover, and guide vane opening. Meanwhile, the theoretical expression about the water-ring thickness was formulated. Once three of the four variables keep constant, the research indicates that water-ring thickness and power absorption increase with the guide vane opening decreasing, and air leakage increases with the guide vane opening increasing; water-ring thickness decreases with the unit speed increasing, and the pressure pulsation lowers with the unit speed increasing; water-ring thickness increases with the spiral case pressure increasing; water-ring thickness increases with cooling water flow rate increasing, and the pressure pulsation reaches maximum value at critical cooling water flow rate value. The research provides a theoretical foundation for the control of guide vane opening and cooling water flow of pumped storage unit under SCP mode running. © 2022 Chinese Society for Electrical Engineering. All rights reserved.