1 - Alaska Energy Data Inventory

12-ft diameter power tunnel with a 6-ft diameter penstock, while the airchamber system consists of an ll-ft diameter power tunnel with a 6-ftdiameter penstock.Procedures for obtaining net heads and hydraulic capacity are the sameas those described for the recommended plan.E. Preliminary Stability Analysis Using Svee Equations - As in thedesign of a conventional surge tank, stability criteria will largely governthe horizontal cross-sectional area of the air chamber. The other factorin air chamber design which is important for stability is the total airvolume in the chamber. Once air volume dimensions for a stable air chamberare determined, the demand condition can be designed for by calculating themaximum downsurge and providing enough depth of water to contain thedownsurge with a reasonable safety factor. Maximum upsurge is alsocalculated. Maximum water hammer and thus penstock cost will decrease withan -increase in air chamber size. An economic study was conducted and itwas found to be uneconomical to increase air chamber size to reduce waterhammer. The results of the study are as follows:MAX. PRES. MAX. PRES.AIR CHAMBER GRAD. ELEV. GRAD. ELEV. PENSTOCKVOL~ME EXCAVATION AT TURBINE AT TANK STEEL TOTAL(ft ) COST ($) (FT) (FT) COST ($) COST ($)17,000 352,593 1,357 1 ,219 612,000 964,59323,000 477,037 1,317 1,178 600,000 1,077,03733,000 684,444 1,265 1, 127 525,000 1,209,44463,000 1,306,667 1,235 1,097 518,000 1,824,667As can be seen, on enlarging the air chamber, excavation costs increasefaster than penstock costs qecrease, and thus the smaller air chamber ismore economical based on this consideration alone.Selection of air chamber size to insure stab"ility involved an analysis offactors which influence stability, including:1. Turbine characteristics.2. Power conduit hydraulic losses.B4-7