Chapter 5 - Publications, US Army Corps of Engineers

EM 111O-2-17O1
31 Dec 1985
(usually 115 percent of nameplate). At the present time, only a
single rated capacity value is specified, and this value includes
overload characteristics (see Section 6-lb). Chapter 6 gives
additional information on plant size selection.
(1) Maximum and minimum turbine discharge and the turbine~s
usable head range establish limits on the amount of energy that can be
developed at a site. In making energy computations, it is necessary
to check to insure that the net head and usable discharge values for
each time interval fall within the allowable range for the type of
turbines being considered, so these values must be identified.
Sections 2-6 and 5-5 provide general information on turbine characteristics
and turbine selection. Following is some specific data on
discharge and head ranges for the various types of turbines.
(2) In planning studies, plant size is often specified initially
in terms of hydraulic capacity. The hydraulic capacity would also be
the plant~s maximum discharge, and in most cases can be assumed to be
the same as the plant’s rated discharge (see Section 6-lb(8)). The
maximum (or rated) discharge of individual units would be defined by
the number and size of the units (see Section 6-6f).
(3) Cavitation problems and the possibility of rough operation
preclude generation below a minimum discharge (see Section 5-5d), and
the minimum discharge for a single unit establishes the plant?s
minimum allowable power discharge. Table 5-1 lists factors for
computing minimum discharges for different types of turbines given a
units rated discharge. These values can be used for initial power
studies, but once a unit design has been selected, the specific
minimum discharge characteristics of that unit should be used.
(4) Likewise, a turbine is only capable of operating
satisfactorily over a limited head range (Section 5-5b)~ and this
should be reflected in energy studies. For preliminary studies, the
maximum head ranges listed in Table 5-1 should be used. These ranges
are only approximate. Once a unit design has been selected, the
specific head range characteristics of that unit should be used
instead.
Je Wlcfs Curve. When hand routing techniques and certain
computer programs are used to evaluate the energy output of a storage
project, kW/cfs versus elevation and kW/cfs versus head curves are
sometimes used to simplify the analysis. These curves account for the
variation of powerplant efficiency with head, and the kW/cfs versus
elevation curves account for head loss and tailwater elevation as
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