Turbomachinery options for an underground pumped hydroelectric storage plant

Various turbomachinery options for underground pumped hydroelectric storage (UPHS) plants are reviewed. Current technology indicates that the maximum head for single-stage, reversible, Francis-type pump turbines is 625 m; for separate, single-stage, Francis-type turbines and multistage pumps, 672 m; for tandem units consisting of separate multijet impulse turbines and multistage pumps, 1440 m; and for multistage, reversible, ungated Francis-type pump turbines, 1290 m. Engineering design studies conducted for Argonne National Laboratory indicated that heads for the single-stage reversible units could be extended to 1000 m, developing 500-MW output per unit. The studies also indicated that two-stage, reversible, Francis-type pump turbines with adjustable wicket gates could be developed for power outputs up to 500 MW at operating heads as high as 1500 m. Results of these studies, including performance and design data, are presented. Using the cost of a single-stage, reversible, Francis-type pump turbine as 1, the approximate cost of other turbomachines is: 1.55 for a single-gated, two-stage, reversible pump turbine; 1.67 for a double-gated, two-stage, reversible pump turbine; 1.9 for an ungated, multistage, reversible pump turbine; and 3.3 for a tandem unit (Pelton and pump).