1 - Alaska Energy Data Inventory

1.04 HYDRAULIC TRANSIENTSA. Operating Requirements - The Snettisham project serves an isolatedload in Juneau. The Crater Lake unit may at times be handl ing the entireJuneau electrical demand. Such operation requires a plan which has thecapability for rapid load pickup, rapid load rejection, and inherentstability under load changes.B. Need for a Surge Tank - A surge tank is necessary to meet theoperating requirements discussed above. Maximum and minimum water hammere 1 evat ions at the turb i ne wi thout a surge tank are 1,700 ft and 480 ftrespectively, for a 3.5 s wicket gate closing and 5 s opening time.Maximum and minimum water hammer elevations with the selected surge tank\are 1263 ft and 597 ft, respectively (surge tank at sta 65+59). Inaddition, a surge tank would be required as a source of water to fulfillthe function of allowing rapid load pickup. Performance of the systemwithout a surge tank on both load rejection and load acceptance combinedwith the operating requirements discussed in the preceding paragraphindicate that a surge tank is necessary for the Crater Lake project.C. Net Turbine Heads Used for Design. This section describes how thenet heads used to specify the turbine were determined. Calculations of netheads are based on the following equations:KW = Q x Hn x E - 11.8; H = Q2 K.L -'kWCombining these equations yields: ! 0 3 - Hg 0 + 11.8 KW/E = 0 where:= Generator output (kW).o = Turbine discharge (ft 3 /s).Hn = Net Turbine head (ft).E = Plant efficiency.HL = Head loss (ft).K = Friction coefficient.Hg = Gross turbine head (ft) ..B1-25