power output gQH332 kW, assuming a Francis-type turbine
(low head, small discharge and efficiency of around 92%).
- The reservoir capacity0.54.52 106 2.26 106 m^3. The reduced
demand line with this storage is the line OB on Fig. 12.25(a), giving a
drop of 2.5 106 m^3 in 14 4-week periods. Therefore, the drop in
power
0.92 1000 9.812.5 106 40/14 4 7 24 60 60 103
26.6 kW.
Hence 26.6 kW must be supplied by an auxiliary plant.
- For constant-output, low-head, small discharges, a Francis-type
machine is appropriate. The power output is rather small and
uniform, and hence one machine will normally do. However, a
minimum of two units may be provided in case of breakdowns/main-
tenance. The following options exist:
(a) designing and operating two units sharing the power output
equally (too small a power output per machine and hence inef-
ficient);
(b) designing one unit only and the second, of similar size, as a
standby unit (uneconomical);
(c) in view of the above, it is desirable to design and operate one
unit only and to provide a diesel unit as a standby.
The specific speed,
NsNP1/2/H5/4.
Adopting0.7 (Table 12.1) and runner diameter D4.43 (Q/N)1/3
we can obtain the operating speed (from equation (12.3)) as
N810 rev min^1. Choosing the nearest synchronous speed of
750 rev min^1 (page 482),
D4.43(0.92/750)1/3475 mm
and the specific speed
Ns 750 332 1/2/405/4136.
538 HYDROELECTRIC POWER DEVELOPMENT
