1 - Alaska Energy Data Inventory

Maximum net head was calculated using the maximum pool elevation of1,019 ft, tailwater of 11.0 ft, expected losses, rated generator power of31.05 MW, and 86 pct plant efficiency. The maximum net head was found tobe 990.5 ft.Design net head was chosen as the expected normal operating head of theturbine, which, based on expected power generation and reservoir storage,is 945.5 ft. Peak efficiency is desired at this head.Critical or minimum net head was calculated using the minimum poolelevation of 820 ft, maximum tailwater of 12.5 ft, expected losses, 27 MWpower, and 86 pct plant efficiency. The critical net head was found to be788.0 ft.Rated net head has been established as the lowest net head at which thefull gate output of the turbine can produce the generator blocked output of34,.50 MW corresponding to a turbine output of 47,000 hp. Rated net heaahas been set at 945.5 ft.Maximum discharge (hydraulic capacity) is 518 ft3/s . This is basedon the Long Lake turbine model with a prototype turbine throat diameter of51.5 inches, 100 pct wicket gate opening, and generator blocked output of34.50 MW. This occurs at a net turbine head of 912 ft.The U.S. Bureau of Reclamation recommends that maximum and minimum netheads not depart from design head by more than 125 pct or less than 65 pctrespectively for Francis turbines. Our departures are 105 pct and 83 pctfor maximum and minimum net heads, and are thus well within theserecommended limits.D. Turbine Sizing.The major design parameters used in turbine sizing were to achievemaximum efficiency at normal operating heads, and to match the turbine withthe generator which is specified at 31.05 MW.Bl-26