Handbook of Civil Engineering Calculations

standard designs that will match any site needs in regard to head, capacity, and excavation
restrictions.
The Francis turbine, Fig. 15, is a good example of such designs. A horizontal-shaft
Francis turbine may be a better choice for some small projects because of lower civil-en-
gineering costs and compatibility with standard generators.
Efficiency of small turbines is a big factor in station design. The problem of full-load
versus part-load efficiency, Fig. 17, must be considered. If several turbines can fit the site
needs, then good part-load efficiency is possible by load sharing.
Fitting new machinery to an existing site requires ingenuity. If enough of the old pow-
erhouse is left, the same setup for number and type of turbines might be used. In other in-
stallations the powerhouse may be absent, badly deteriorated, or totally unsuitable. Then
river-flow studies should be made to determine which of the new semistandard machines
will best fit the conditions.
Personnel costs are extremely important in small hydro projects. Probably very few
small hydro projects centered on redevelopment of old sites can carry the burden of work-
ers in constant attendance. Hence, personnel costs should be given close attention.
Tube and bulb turbines, with horizontal or nearly horizontal shafts, are one way to
solve the problem of fitting turbines into a site without heavy excavation or civil engi-
neering works. Several standard and semistandard models are available.
In low head work, the turbine is usually low-speed, far below the speed of small gen-
erators. A speed-increasing gear box is therefore required. A simple helical-gear unit is
satisfactory for vertical-shaft and horizontal-shaft turbines. Where a vertical turbine
drives a horizontal generator, a right-angle box makes the turn in the power flow.
Governing and control equipment is not a serious problem for small hydro plants.
Related Calculations. Most small hydro projects are justified on the basis of
continuing inflation which will make the savings they produce more valuable as time
passes. Although this practice is questioned by some people, the recent history of infla-
tion seems to justify the approach.
As fossil-fuel prices increase, small hydro installations will become more feasible.
However, the considerations mentioned in this procedure should be given full weight be-
fore proceeding with the final design of any plant. The data in this procedure were drawn
from an ASME meeting on the subject with information from papers, panels, and discus-
sion summarized by William O'Keefe, Senior Editor, Power magazine, in an article in
that publication.

Relative discharge

FIGURE 17. Steep Francis-turbine

efficiency falloff frequently make mul-

tiple units advisable.

High-specific-speed

Francis turbine

Tubular turbine with

fixed guide vanes

Turbine

efficiency,%