Guide on How to Develop a Small Hydropower Plant. Part 2
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Guide on How to Develop a Small Hydropower Plant ESHA 2004
Demand (Electric):
The instantaneous requirement for power on an electric system (kW or MW). Demand Charge that
portion of the charge for electric supply based upon the customer’s demand characteristics.
Direct Current (DC):
Electricity that flows continuously in one direction sd contrasted with alternating current.
Draft tube:
A tube full of water extending from below the turbine to below the minimum water tailrace level.
Energy:
Work, measured in Newton metres or Joules. The electrical energy term generally used is
kilowatt-hours (kWh) and represents power (kilowatts) operating for some period of time (hours)
1 kWh = 3.6x103 Joules.
Evapotranspiration:
The combined effect of evaporation and transpiration.
FDC:
Flow duration curve: a graph of discharges against v. the percentage of time (of the period of
record) during which particular magnitudes of discharge were equalled or exceeded.
Fish Ladder:
A structure consisting e.g. of a series of overflow weirs which are arranged in steps that rise about
30 cm in 3 50 4 m horizontally, and serve as a means for allowing migrant fish to travel upstream
past a dam or weir.
Flashboards:
One or more tier of boards supported by vertical pins embedded in sockets in the spillway crest.
Flow duration curve:
See FDC
Forebay:
A pond or basin of enlarged water. Surface and depth, usually at the end of a canal or leat, from
whence a penstock leads to a powerhouse.
Freeboard:
In a canal, the height of the bank above the water level.
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Gabions:
Large, usually rectangular, boxes of metal mesh filled with stones or broken rock.
Gate Valve:
A vertical gate type water control valve, requiring more space than an equivalent diameter butterfly
valve, which can be opened either mechanically or hydraulically.
Geotextiles:
Synthetic materials (e.g. polypropylene, nylon) woven into rolls or mats which are laid as
permanent but permeable foundation blankets under stone, rock or other revetment materials.
Governor:
A controlling device that adjust the flow of water through the turbine following the output signal of
a certain sensor (turbine speed, intake water level etc.).
Gravitational constant g:
Acceleration due to gravity, approximately 9.81 m/s2.
HDPE:
High-density polyethylene
Head, gross:
The difference in level between the water surfaces at intake and tailrace of a hydroelectric system
Head, net:
The head available for power generation at the turbine, incorporating all head losses in screens,
intakes, pipes, valves, draft tube and tailrace.
Headpond:
See “forebay”.
Hertz (Hz):
Cycles per second, as applied to ac generation.
Hydraulic gradient:
The hydraulic pressure profile along a pipe or conduit, which is flowing full.
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Infiltration:
The process whereby rainfall penetrates through the land surface to form soil moisture or
groundwater.
Installed capacity:
The total maximum capacity of the generating units in a hydropower plant.
Isovels:
Lines of equal velocity drawn on cross-sections of watercourses.
Leat:
An open channel that conveys water at a shallow gradient from a river intake to point where
sufficient head has been gained for a turbine to be installed. (Also sometimes called GOIT or
CONTOUR CANAL).
Load (Electrical):
The power capacity supplied by a particular plant on an electric system.
Load factor:
Is defined as the ratio annual energy output kWh/max power output x 8760 hours
Outage:
The period in which a generating unit, transmission line, or other facility, is out of service.
Output:
The amount of power (or energy, depending on definition) delivered by a piece of equipment,
station or system.
(In) Parallel:
The term used to signify that a generating unit is working in connection with the mains supply, and
hence operating synchronously at the same frequency.
Overspeed:
The speed of the runner when, under design conditions, all external loads are removed
P.E.:
Polyethylene
Peak Load:
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The electric load at the time of maximum demand.
Peaking Plant:
A power plant, which generates principally during the maximum demand periods of an electrical
supply network.
Penstock:
A pipe (usually of steel, concrete or cast iron and occasionally plastic) that conveys water under
pressure from the forebay to the turbine.
Percolation:
The movement of water downwards through the soil particles to the phreatic surface (surface of
saturation within the soil; also called the groundwater level).
Power:
The capacity to perform work. Measured in joules/sec or watts (1MW = 1 j/s). Electrical power is
measured in kW.
Power factor:
The ratio of the amount of power, measured in kilowatts (kW) to the apparent power measured in
kilovolt-amperes (kVA).
Rating curve:
The correlation between stage and discharge.
Reynolds Number:
A dimensionless parameter used in pipe friction calculations (interalia), and derived from pipe
diameter, liquid velocity and kinematic viscosity.
Rip-rap:
Stone, broken rock or concrete block revetment materials placed randomly in layers as protection
from erosion.
Runoff:
The rainfall, which actually does enter the stream as either surface or subsurface flow.
Run-of-river scheme:
Plants where water is used at a rate no greater than that with which it “runs” down the river.
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SOIL:
A parameter of permeability
Stage (of a river):
The elevation of water surface
Supercritical flow:
Rapid flow who is unaffected by conditions downstream
Synchronous speed:
The rotational speed of the generator such that the frequency of the alternating current is precisely
the same as that of the system being supplied.
Tailrace:
The discharge channel from a turbine before joining the main river channel.
Trashrack:
An structure made up of one or more panels, each generally fabricated of a series of evenly spaced
parallel metal bars.
Utilisation Factor:
The ratio found by dividing the number of hours per year (or other unit time) that a plant is
generating, by the number of hours in a year (or in the other unit time). (This is not the same as load
factor).
Weighted average rainfall:
The average rainfall over an entire catchment that allows for the variation in rainfall between the
wetter and drier areas.
Weir:
A low dam, which is designed to provide sufficient upstream depth for, a water intake while
allowing water to pass over its crest.
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