1 - Alaska Energy Data Inventory

C = Coefficient of hydraulic losses.H = Pressure head at the surge tank (ft).g = Acceleration due to gravity (32.2 ft/s2).The Thoma Formula will calculate a surge tank area which providesborder 1 i ne stab i 1 ity i. e., the amp 1 itude of the water surf ace movement inthe tank ne ither increases nor decreases with time. The Thoma F ormu 1 aassumes a small load change along with constant turbine efficiency.Standard practice is to first calculate the diameter which corresponds tothe Thoma area and then -j ncrease the "THOMA DIAMETER II by factors rangi ngbetween 25 and 50 pct.The Thoma Formula is a dependable tool but it does not reflect avariety of conditions which can influence surge tank areas necessary toobtain stabil ity. One important factor is the amount of rotative inertiaprovided by other sources of power generation in the system. As discussedin the literature, other power installations which are interconnected witha project having a surge tank, tend to increase the stability (safetyfactor) of the surge tank. This type of safety factor cannot be countedupon for the Crater Lake Project, which would indicate the design should beconservative. The Thoma Formula resulted in a minimum diameter of 6.07 ftand a diameter of 9.1 ft with the 50 pct increase. A diameter of 10.0 ftwas finally selected beCause it was felt that the 10 ft diameter verticalshaft would be the minimum size that a contractor would conveniently build.F. Load Rejection Surge & Tank Top Elevation:(1) General - Conditions A, B, and C are shown on Plate B18.These points are located on a vertical line which represents the blockedoutput of the system. This blocked output is equal to the rated output ofthe generator (31,050 kW) divided by the power factor of 0.9 resulting in agenerator output of 34,500 kW. The equivalent turbine output under theseconditions is equal to 47,190 hp. Surge elevations for the variousconditions were calculated with minimum hydraulic losses, minimum tai1waterEL, (11.0 ft) and blocked output. The oscillation of the surge tank watersurface elevation for the various conaitions are shown on Plate B19.B3-1O