214 



HYDRAULIC EQUIPMENT 



Let us assume that a selection of a wheel is to be made for an 

 installation, and that performance curves are desired, showing the 

 expected efficiency for various loads and speeds. Curves A, B, and 

 C, in Fig. 108 may each represent a possible curve, dependent 

 upon the revolutions selected for the turbine in question, the rev- 

 olutions being directly proportional to the specific speeds, and 

 they will illustrate the manner in which the efficiencies at partial 

 gate openings will fall off in any one case, depending upon the 

 actual revolutions per minute selected for the design of the wheel. 



5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100105110115120125130135 

 Horse Power in Per cent of Normal Full Load at Normal Head 



FIG. 109. 10,000 Horse-power Turbine-curves Showing Efficiency and Power 

 for Constant Speed and a Normal Head of 32 Feet for^Various Heads 

 as Shown. 



They will also give an idea as to the margin between the normal 

 full load and the power at which the points of maximum efficiency 

 will occur. In the selection of a speed for any installation, there- 

 fore, aside from the cost of the generators, the question of the 

 wheel efficiencies at partial gate openings has a considerable 

 bearing. Where a unit is likely to operate under a very wide 

 range in power, it would be advisable to select a wheel repre- 

 sented by curve A, giving a high efficiency for a considerable 

 range in power. 



Actual Speed. For speeds used in a number of hydro-electric 

 developments and corresponding heads and capacities, see table 

 on page 316. 



Characteristic Curves. For studying the action of a turbine 

 under different conditions of operation, the characteristic curves, 

 as shown in Figs. 110, 111, and 112, are extensively used, and 

 from these curves it can at a glance be seen at what speed the 



