Improving the start-up of high head reversible pump-turbine units in the turbine mode

Pumped-storage plants using reversible pump-turbines are the most efficient way to store electrical energy at acceptable costs. However, to meet high and sudden variations in power demand, a large amount of power must be available to be released quickly at the required time. When peak power production is required, start-up in the turbine mode must be fast, efficient and reliable. A new hydraulic design, which provides an improvement of the S-shaped characteristic, removes the sources of speed instability during the start-up sequence of the turbine over a large operating head range and does not involve a special stabilizing technique, could be the solution.