The water in the river is
diverted by the weir through an opening in the river side (the intake)
into an open channel. A settling basin is used to remove sand particles
from the water. The channel follows the contour of the hillside so as to
preserve the elevation of the diverted water. The water then enters a tank
known as the forebay and passes into a closed pipe known as the penstock.
This is connected at a lower elevation to a waterwheel, known as a turbine.
The turning shaft of the wheel can be used to rotate a mechanical device
(such as a grinding mill, oil expeller, wood lathe and so on), or to operate
an electricity generator.
Penstock
The penstock is the pipe
which conveys water under pressure from the forebay tank to the turbine.
The major components of the penstock are shown in figure 8. The penstock
often constitutes a major expense in the total micro hydro budget, as much
as 40% is not uncommon in high head installations, and it is therefore
worthwhile optimising the design. The trade-off is between head loss and
capital cost. Head loss due to friction in the pipe decrease dramatically
with increasing pipe diameter. Conversely, pipe costs increase steeply
with diameter. Therefore a compromise between cost and performance is required.
The design philosophy is
first to identify available pipe options, then to select a target head
loss, 5% of the gross head being a good starting point. The details of
the pipes with losses close to this target are then tabulated and compared
for cost effectiveness. A smaller penstock may save on capital costs, but
the extra head loss may account for lost revenue from generated electricity
each year.
Penstock Jointing
Pipes are generally supplied in standard
lengths and have to be joined together on site. There are several ways
of doing this and the following factors should be considered when choosing
the best joint system for a particular scheme:
- suitability for chosen pipe material
- skill level of personnel installing the pipe
- wether any degree of joint flexibility is required
- relatively costs
- ease of installation
Methods of pipe jointing fall roughly into
four categories:
- flanged
- spigot and socket
- mechanical
- welded
The following are some pictures and video of the penstock pipe installation method in some countries :
Video :
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