Worked Example 12.1
The average monthly flows of a stream in a dry year are as follows:
Month J F M A M J J A S O N D
Q(m^3 s^1 ) 117 150 203 117 80 118 82 79 58 45 57 152
It is intended to design a hydroelectric power plant across the stream,
using the following data: net head at the plant site20 m; efficiency of the
turbine90%.
- Plot the flow and power duration curves and calculate the firm and
secondary power available from this source if the maximum usable
flow is limited to 150 m^3 s^1. - If it is intended to develop the power at a firm rate of 15 MW, either
by providing a storage or by providing a standby diesel plant with no
storage, determine the minimum capacity of the reservoir and of the
diesel unit.
Solution
Flow in descending order Frequency (months) Frequency equalled/
(m^3 s^1 ) exceeded (%)
203 01 8.3
152 02 16.7
150 03 25.0
118 04 33.3
117 05
117 06 50.0
82 07 58.3
80 08 66.7
79 09 75.0
58 10 83.3
57 11 91.7
45 12 100.0
- The flow duration curve (flow versus frequency equalled or
exceeded) is plotted in Fig. 12.23. The same plot can be used as a
power duration curve by multiplying the ordinates by a factor of
0.176 ( gH/10^6 ) to obtain the power in MW with 90% and
H20 m. The firm power available (equal to the area of the power
duration curve under the 45 m^3 s^1 line) is 7.95 MW. The secondary
power (equal to the area under the power duration curve between
the 150 and 45 m^3 s^1 lines) is 10 MW.