In hydroelectric power station the kinetic energy developed due to gravity in a falling water from higher to lower head is utilized to rotate a turbine to produce electricity.

1. HYDRO POWER PLANT
Vinod Shrivastava
B.Tech MJPRU Bareilly
M. Tech NITTTR Chandigarh

2. INTRODUCTION
 In hydroelectric power station the kinetic energy developed due to
gravity in a falling water from higher to lower head is utilized to
rotate a turbine to produce electricity.
 The potential energy stored in the water at upper water level will
release as kinetic energy when it falls to the lower water level.
 This turbine rotates when the following water strikes the turbine
blades.
 To achieve a head difference of water hydroelectric electric power
station are generally constructed in hilly areas.

3. In the way of the river in hilly areas, an artificial
dam is constructed to create required water head.
From this dam water is allowed to fall toward
downstream in a controlled way to turbine blades.
As a result, the turbine rotates due to the water
force applied to its blades and hence the alternator
rotates since the turbine shaft is coupled with
alternator shaft.

4.  The main advantage of an electric power plant is that it does
not require any fuel. It only requires water head which is
naturally available after the construction of the required
dam.
 No fuel means no fuel cost, no combustion, no generation of
flue gases, and no pollution in the atmosphere.
 Due to the absence of fuel combustion, the hydroelectric
power plant itself is very neat and clean.
 In addition to that, it does not produce any pollution to the
atmosphere. Also from constructional point of view, it is
simpler than any thermal and nuclear power plant.

5.  The constructional cost of a hydroelectric power plant
maybe higher than that of other conventional thermal
power plants because of construction of a huge dam
across the flowing river.
 The engineering cost in addition to the constructional
cost is also high in a hydroelectric power plant.
 Another disadvantage of this plant is that it cannot be
constructed anywhere according to the load centres.
 So, long transmission lines are required to transmit the
generated power to the load centres.
Thus the transmission cost may be high enough.

8. Components of Hydro Power Plant
 There are only six primary components required to construct a
hydroelectric power plant. These are dam, pressure tunnel, surge
tank, valve house, penstock, and powerhouse.
 The dam is an artificial concrete barrier constructed across the way
of the river. The catchment area behind the dam creates a huge water
reservoir.
 The pressure tunnel takes water from the dam to the valve house.In
the valve house, there are two types of valves available.
 The first one is main sluicing valve and the second one is an
automatic isolating valve.

9.  The sluicing valves control the water flowing to the downstream and
automatic isolating valves stop the water flow when the electrical
load is suddenly thrown off from the plant.
 Automatic isolating valve is a protecting valve does not play any
direct role control the flow of water to the turbine. It only operates
during emergency to protect the system from burst out.
 The penstock is a steel pipeline of suitable diameter connected
between the valve house and powerhouse. The water flows down
from upper valve house to lower powerhouse through this penstock
only.
 In the powerhouse there are water turbines and alternators with
associated step up transformers and switchgear systems to generate
and then facilitate transmission of electricity.

10. CLASSIFICATION OF HYDRO
POWER PLANT

11. Classification According to the Extent of Water Flow
Regulation Available:
According to the extent of water flow
regulation available the hydroelectric power
plants may be classified into:
(1) Run-off river power plants without pondage.
(2) Run-off river power plants with pondage.
(3) Reservoir power plants.

12. 1. Run-off river power plants without
pondage.
 Some hydro power plants are so located that the water
is taken from the river directly, and no pondage or
storage is possible.
 Such plants are called the run-off river power plants
without pondage.
 Such plants can use water only as and when available;
these cannot be used at any time at will or fit any
desired portion of the load curve.
 In such plants there is no control on flow of water.

13. During high flow and low load periods, water is
wasted and during the lean flow periods the plant
capacity is very low.
As such these plants have a very little firm capac-
ity. At such places, the water is mainly used for
irrigation or navigation and power generation is
only incidental.
Such plants can be built at a considerably low cost
but the head available and the amount of power
generated are usually very low.

14. 2. Run-Off River Power Plants with
Pondage:
The usefulness of run-off river power plants is
increased by pondage.
Pondage refers to storage at the plant which
makes it possible to cope, hour to hour, with
fluctuations of load throughout a week or some
longer period depending on the size of pondage.
With enough pondage, the firm capacity of the
power plant is increased.

15. 3. Reservoir Power Plants:
 When water is stored in a big reservoir behind a dam, it is possible
to control the flow of water and use it most effectively.
 Storage increases the firm capacity of the plant and it can be used
efficiently throughout the year.
 Such a plant can be used as a base load or as a peak load plant as per
requirement.
 It can also be used on any portion of the load curve in a grid system.
 Most of the hydroelectric power plants everywhere in the world are
of this type.

16. B. Classification According to
Availability of Water Head:
According to availability of water head the
hydroelectric power plants may be classified
into:
(a) Low Head
(b) Medium Head and
(c) High Head Power Plants.

17. (a) Low Head
 A typical low head installation on a river consists
essentially of a dam across the stream to back up the
river and create a fall, the water flowing through the
turbines and remerging the river below the dam.
 A dam or barrage constructed across the river creates
the necessary head. The power plant is located near the
dam and therefore, no surge tank is required.
 In low head power plants Francis, propeller or Kaplan
turbines are employed.

19. (b) Medium Head Hydroelectric
Power Plants:
 In these power plants, the river water is usually tapped off to a forebay on
one bank of the river as in case of a low head plant.
 From the forebay the water is led to the turbines through penstocks.
 The forebay provided at the beginning of penstock serves as a water
reservoir for such power plants.
 In these plants, water is usually carried in open channel from main
reservoir to the forebay and then to the turbines through the penstock.
 The forebay itself serves as the surge tank in this case. In these plants
horizontal shaft Francis, propeller or Kaplan turbines are used.

21. (c) High Head Hydroelectric Power
Plants
 If high head is available, a site may be chosen, where a stream descending
a steep lateral valley can be dammed and a reservoir for storage of water is
formed.
 A pressure tunnel is constructed between reservoirs to valve house at the
start of penstock to carry water from reservoir to valve house.
 Surge tank (a tank open from the top) is built just before the valve house so
that the severity of water hammer effect on penstock can be reduced in case
of sudden closing of fixed gates of the water turbine.
 Surge tank also serves as a ready reservoir from which the turbine can draw
water temporarily when there is sudden increase in demand.

22.  The valve house consists of main sluice valves and
automatic isolating valves, which operate on bursting of
penstock and cut off further supply of water to
penstock.
 Penstocks are pipes and carry the water from the valve
house to the turbines.
 For heads above 500 m Pelton wheels are used while
for lower heads Francis turbines are employed.
 The generators used are of high speed and small
diameter. Penstocks are of large length and
comparatively smaller cross section.

24. C. Classification According to Type
of Load Supplied
According to the load supplied hydroelectric
power stations may be classified into:
(a) Base Load,
(b) Peak Load, and
(c) Pumped Storage Plants for the Peak Load.

25. (a) Base Load Plants:
 The plants, which can take up load on the base portion
of the load curve of the power system, are called the
base load power plants.
 Such plants are usually of large capacity. Since such
plants are kept running practically on block load (i.e.,
the load that is practically constant), load factor of such
plants is therefore high.
 Run-off river plants without pondage and reservoir
plants are used as base load plants.

26. (b) Peak Load Plants
 Plants used to supply the peak load of the system
corresponding to the load at the top portion of the load
curve are called the peak load plants.
 Runoff river plants with pondage can be employed as
peak load plants.
 If the pondage is enough, a large portion of the load can
be supplied by such a plant if and when required.
 Reservoir plants can of course be used as peak load
plants also.

27. (c) Pumped Storage Power Plants

28.  A pumped storage plant is a special type of plant meant to supply peak
loads.
 During peak load period, water is drawn from the head water pond through
the penstock and generates power for supplying the peak load During the
off peak pens the same water pumped back from the tail water pond to the
head water pond so that this water may be used to generate energy during
the next peak load period.
 Thus the same water is used again and again and extra water is needed only
to take care of evaporation and seepage.
 Generally the pumping of water from the tail water pond to the head water
pond is done at night when loads are low.
 The plant generates energy for supplying peak loads during day time.
 The off peak pumping maintains the firm capacity of die pumped storage
plant. The reservoir capacity should be such that the plant can supply peak
load for 4 to 11 hours.