1 - Alaska Energy Data Inventory

I. Stability Routings.To de~onstrate the change in surge oscillations with varying surgetank diameters, stabil ity routings were performed using computer program1If'lISURGE Ilfor surge tank diameters of 4.5 ft, 6 ft (Thoma Diameter), and10 ft. The profiles of the surge tank water surface for the variousdiameters are shown on Plate B21 for the stability routing of conaition E.Condition E, as shown on Plate B18 is based on a small load increase from37,500 to 39,000 hp concurrent with expected losses, mi n imum power poo 1elevation (825 ft), and maximum tailwater (12.5 ft). As shown on Pl ateB21, the 4.5 ft diameter tank is unstable, and in a matter of severalminutes, surge oscillations have grown from approximately 14 ft to 42 ft.The 6.0 ft diameter tank, which is the theoretical minimum IIThoma ll diametershows surge osc ill at ions with no change in amplitude through the entirerecorded period of 400 s. These routings illustrate the justification fora 50 pct increase in Thoma Diameter. A 10 ft diameter was ultimatelychosen for the surge tank because 10 ft is believed to be the minimum sizevertical shaft that a contractor conveniently would build by conventionaldrilling and blasting. Condition E is based on expected hydraulic lossesin the power conduit and the expected turbine performance curve on PlateB18. The resultant profiles for the 10 ft diameter tank on Plate B21 showthat the situation is rapidly aampening and inherently stable. Thequiescent levels are the steady state surge tank water surfaces that wouldbe obtained once the surges have dampened to zero magnitude.J. Orifice Design.(l) General Ideal orifice action will provide an initialpressure level at the surge tank drift tunnel tee that will equal the surgetank water surface at the end of the quarter cycle. This is true for boththe load demand and load rejection cases. The discharges for the rejectionand demand conditions were 477.5 ft 3 /s and 500 ft 3 /s respectivelyresulting in an orifice of 4.4 ft diameter. Plate B18 shows the locationof conaitions A (reject) and D (demand) which determined the dischargesused in the orifice design. The surge tank wi 11 be offset from the maintunnel resulting in a horizontal orifice.B3-13