Double-stage regulated pump-turbines for Yang Yang, Korea

Large double-stage regulated Francis pump-turbines have been introduced for the first time in the world at the 1000 MW Yang Yang pumped-storage scheme in Korea, with a head of 817 m. The technology offers several advantages, such as a better efficiency as a result of the higher specific speed, and less stress on the turbine components since the total head is divided into the two stages. Moreover, the fast mode changes can be done by dewatering the units and starting the frequency converter.