Dr. S. VIJAYA BHASKAR
Professor in Mechanical
EngineeringSreenidhi Inst. of Science & Tech.,
HYDRO ELECTRIC POWER PLANT:
Hydrological cycle / flow measurement
Drainage area characteristics
Storage and Pondage
Classification of dams and spill ways.
HYDRO PROJECTS AND PLANT: Classification –
Typical layouts – plant auxiliaries – plant
operation pumped storage plants.
The energy of water utilized for generation of
power using KE and PE of water by motion
and position respectively
• Hydro power is considered as one of the most
economic and non polluting sources of
• Power generated from water is termed as
• Hydro electricity means electricity generated
by hydropower or from the use of the
gravitational force of falling or flowing water.
Potential Energy is the stored energy in an object or
system because of its position or configuration.
Kinetic energy of an object is relative to other
moving and stationary objects in its immediate
• The study of water, including rain, snow,
water on earth’s surface, covering its
properties, distribution and utilization is
• The science which deals with rainfall and
run-off is also called hydrology.
• The evaporation of water from the surface
of river and oceans and its precipitation on
the earth is known as the hydrological cycle.
1) Precipitation: it is same as condensation i.e. converting
natural water vapour into water.
• Basically precipitation is of two types
a) liquid precipitation (rainfall).
b) solid precipitation (snow).
2) Run-off: it is the portion of precipitation which reaches the
streams again .
• Run off occurs only if the rate of precipitation exceeds the
rate of which water infiltrates into the soil.
• it takes place from the surface of oceans, rivers, lakes etc.
• The stored water is used for irrigation, water supply, energy
• It is a cyclic movement
of water from the sea
to the atmosphere of
evaporation and then
back to the earth
surface (sea, ocean) by
• The hydrological
Precipitation= run off
• The quantity of water flowing in a river would be
varying and may not be constant for a period of
• Therefore the flow measurement is very important.
• Using a channel of fixed cross section and
measuring the water velocity using current meters
at maximum points of the cross section at different
water levels at regular intervals the flow volume
may be measured.
• And by integrating the velocities over the cross
section total flow can be calculated.
• A curve can be plotted between gauge height and
• A hydrograph is a discharge vs. time curve of the water flow.
• It shows the variation of river flow with time.
• It may be plotted based on data, of weeks, months and even
• Discharge on y-axis and time on x-axis.
• Hydrograph gives
discharge available at
different time ( day, week,
month or year ).
• Maximum and minimum
runoff can also be studied.
• It gives mean run off.
• It helps in studying the
effects of storage on flow.
• The area under the hydrograph
gives total volume of water for
• In drainage area characteristics generally used to study the
hydro-graphs: flow duration curve, mass curve for estimation
of storage capacity of a reservoir.
• There are three types of streams based on nature of flow.
1) steady flow rivers.
2) flashy flow rivers.
3) Perennial flow.
STEADY FLOW RIVERS
• If the variation of discharge is less for a considerable time
such streams are termed as steady streams.
• In certain areas where soil surfaces are
impervious (solid), irregular distribution
• The streams in the geographical areas of monsoon lands
generally river flow levels are low in summer and high during
monsoon time. Such streams are called as perennial stream.
• Hydrologic data generally consist of a sequence of observations of
some phase of the hydrologic cycle made at a particular site.
• The data may be a record of the discharge of a stream at a
particular place, or it may be a record of the amount of rainfall
caught in a particular rain gauge.
Phases of Hydrologic Cycle
• Although for most hydrologic purposes a
long record is preferred to a short one, the
user should recognize that the longer the
record the greater the chance that there
has been a change in the physical
conditions of the basin.
Flow duration curve is a plot of discharge versus percentage of time
for which the discharge is available. It is obtained from hydrograph
The flow or discharge can be expressed as cubic meters per second,
per week or other unit of time.
This flow duration curve is also known as power duration curve.
Flow Duration Curve
• It is a plot of cumulative volume of water that can be stored
from a stream flow versus time in days, weeks or months.
• It shows a mass curve, Maximum intercept between line AB
and mass curve is known as reservoir capacity
• Slope of the mass curve at a point gives the rate of inflow at
• The collection of water in a reservoir upstream of the plant
and increasing the capacity of stream for a long period of
time a called storage.
• Storage plants work as base load stations.
• Base load plants are of high capacity and takes the load on
the base portion of the load curved.
• Peak load plants are designed for taking care of peak loads.
• For a short period of time the pondage increases the stream
capacity behind a dam near the plant.
• Pond permits to store water during off peak hours and this
could be used during peak hours of the same day.
• If there is a considerable distance between plant and the
reservoir, pond is needed at the plant to regulate the flow.
The following factors should be given careful consideration
while selecting a site for a hydro-electric power plant:
1. Water Available:
• The estimates of the average quantity of water available
should be prepared on the basis of actual measurements of
stream or river flow.
• The river flow data should be based on daily, weekly, monthly
and yearly flow ever a number of years.
• The plant capacity and the estimated output as well as the
need for storage will be governed by the average flow.
• The primary or dependable power which is available at all
times when energy is needed will depend upon the minimum
• The maximum of flood flow governs the size of the
headwords and dam to be built with adequate spillway.
• The output of a hydropower plant is not uniform due to wide
variations of rain fall. To have a uniform power output, a
water storage is needed so that excess flow at certain times
may be stored to make it available at the times of low flow.
• To select the site of the dam ; careful study should be made
of the geology and topography of the catchment area to see if
the natural foundations could be found and put to the best
3. Head of Water:
• The level of water in the reservoir for a proposed plant should
always be within limits throughout the year.
4. Distance from Load Center:
• Most of the time the electric power generated in a hydro-
electric power plant has to be used some considerable
distance from the site of plant.
• To be economical on transmission of electric power, the
routes and the distances should be carefully considered since
the cost of erection of transmission lines and their
maintenance will depend upon the route selected.
Before the Construction
of the Dam
After construction of
5. Access to Site :
• It is always a desirable factor to have a good access to the
site of the plant.
• This factor is very important if the electric power generated is
to be utilized at or near the plant site.
• The transport facilities must also be given due consideration.
6. Type of the Land of Site:
• The land to be selected should be cheap and rocky.
• The land should have largest catchment area to store water at
high head and will be economical in construction.
• The rock should be strong to withstand the stresses
transmitted from the dam structure as well as the thrust of
the water when the reservoir is full.
• The rock should remain stable in all conditions.
• Hydroelectric power plants use the potential energy of water
stored in a reservoir to operate turbines. The turbines are
connected to large generators, and can operate on varying
volumes of water to adapt to changing demand for electricity.
• Hydroelectric power plant capacity is related to the height and
capacity of a reservoir and require certain conditions in local
geography in addition to a water source.
• Hydro is a renewable energy source and more cost-effective than
many other renewable sources of energy such as photovoltaic.
• Hydropower currently provides about 25% of the world’s electricity
and is very flexible in scale. Commercial installations range from 1
MW up to the largest installation to date of 18,400 Megawatts
HYDRO-ELECTRIC POWER PLANT
The essential features of a water
power plant are as below:
1. Catchment area.
4. Inlet water way or spillways
6. Surge Tank
7. Prime Movers
8. Tail race or outlet water way
9. Power house.
1. Catchment Area:
• The catchment area of a hydro
plant is the whole area behind the
dam, draining into a stream or river
across which the dam has been
built at a suitable place.
ESSENTIAL FEATURES OF A WATER-POWER PLANT
F Flow Sheet of Hydro Electric Power Plant
Sluice Gate or Valve
1. Catchment Area:
• The catchment area of a hydro plant is the whole area behind the
dam, draining into a stream or river across which the dam has
been built at a suitable place.
ESSENTIAL FEATURES OF A WATER-POWER PLANT
• Whole of the water available from the catchment area is collected
in a reservoir behind the dam.
• The purpose of the storing of water in the reservoir is to get a
uniform power output throughout the year.
• A reservoir can be either natural or artificial.
• A natural reservoir is a lake in high mountains and an artificial
reservoir is made by constructing a dam across the river.
• A dam is built across a river for two functions: to impound the
river water for storage and to create the head of water.
• Dams may be classified according to their structural materials
such as: Timber, steel, earth, rock filled and masonry. Timber and
steel are used for dams of height 6 m to 12 m only. Earth dams
are built for larger heights, up to about 100 m.
4. Spill Ways:
• When the water enters the reservoir basin the level of
• To relieve of this excess water a structure is provided in
the body of dam or near the dam or on the periphery of
• The safeguarding structure is called spill ways.
• A headrace is a channel which leads water to a turbine and
a tailrace is a channel which conducts water from the
• The conduits may be open or close
• Open conduit ---- Canals and flumes
• Closed conduit --- Tunnels, pipelines
6. Surge Tanks:
• It is a small reservoir or tank in which the water level
rises or falls to reduce the pressure swings so that they
are not transmitted in full to a closed circuit.
7. Prime Movers:
• The prime mover converts the energy of water into
mechanical energy and further into electrical energy.
• They are classified into impulse and reaction turbines.
8. Draft Tubes:
• The draft tube serves two purposes.
• It allows the turbine to be set above tail water level,
without loss of head.
• It regains, by diffuser action, the majority of KE delivered
to it from the runner.
9. Power House:
• The power house is a building in which
• the turbines, alternators and the
• auxiliary plant are housed.
• 1) masonry dams
• 2) fill dams.
Masonry Dams FILL DAMS
i. Gravity dams
ii. Buttress dams
iii. Arch dams
i) EARTH FILL DAM
ii) ROCK FILL DAM
• Dam is a concrete or stone masonry barrier to raise water for
storage and also hydraulic head.
• The Dam must fulfil two fundamental functions.
◦ 1) it develops a reservoir which has a capacity to store water.
◦ 2) It builds up head and thus potential for the river i.e. water
Different types of dams:
1) Masonry dams
◦ 2) Fill dams.
◦ 3) Timer dams
Masonry dams are classified into three categories.
a) Gravity dams
b) Buttress dams
c) Arch dams
Fill dams are classified into two categories.
a) Earth Dams
b) Rock fill dams
1) solid gravity dam
• This dam is constructed using masonry concrete.
• It is bulky and massive than other types.
• Sound rock foundation is required.
• The height of the dam is limited by the strength of the
• The design is simple but it consume heavy materials.
• This type of dams are more economical at small river
• These dams provides safe and economical spillway
2) Arch dams:
• Arch dams are curved in plane.
• Structure is curved upstream.
• This type of dams are more economical and stronger than
• This type of dams are only suitable for narrow valleys with
steep slopes of solid rock to support the outward thrust of
• The water thrust is compression.
3) Buttress Dam:
• They are also known as hollow gravity dams inclined
upstream face so that the pressure of water create large
downward force which provides stability of sliding and
• The force is transmitted to a row of buttress.
• They are also safe against earthquakes.
• Hence countries like Japan and Italy are going for these dams.
• It requires 1/3 rd of material required for solid gravity dam.
• These dams are generally triangular in shape.
1) EARTH FILL DAMS:
• It is generally used for small capacity power plants.
• Cheaper than masonry dams.
• Can be built at any locations.
• Suitable for relatively pervious foundation.
• Gets stronger with age.
• Can be erected quickly.
◦ 1) requires more maintenance.
◦ 2) supplementary spill way is required.
◦ 3) fails suddenly with out any warning.
◦ 4) it is subjected to erosion and flood damage.
◦ 5) limited in height.
2) Rock Fill dam:
• These dams are eventually constructed in mountaneous
regions where rock is rather than earth is available.
• Rock fill dam consists of
◦ a) lose rock fill.
◦ b) an upstream dry rubble cushion of laid up stone bonding
into the dumped rock.
◦ c) an upstream impervious membrane on dry rubble
• The part of the dam which discharges the flood flow to the
down stream side is called as spillway.
• Spillways act as a safety valve for a dam.
• They are provided on dams to avoid damage to dams.
• They keep the reservoir level below the predetermined
• The down stream must always be provided a safe passage.
Types of spill ways
1) overflow spillways.
2) chute spillways.
3) shaft spillways.
4) side channel spillways.
5) siphon spillways.
• This is the simplest , low in cost and suitable for concrete dams.
• When dam reaches full reservoir level stream overflows from the
• There may be gate control at the top of the dam
• Counter weight is provided to lift the gate.
• This is widely used on gravity arch and buttress dams.
– This spillway is a channel made of reinforced concrete
– The water is discharged into steep sloped open channel
– This type of spillways are adopted to earth or rock fill
– This is simple in design and suitable for all foundations.
– In this spillways water drops through vertical shaft and
passes though a conduit horizontally and sends the
water down stream.
– When there is very limited space for spillways this type
– Main draw back is the hazard of clogging with debris.
– So we need to prevent debris from entering into
Side channel spillway:
– These are employed at narrow gorges or canyons.
– When scope for overflow on chute spillways is
very less this type is employed.
– The stream is discharged by siphonic action.
– When all the air is removed in siphon the space
gets filled with water, siphon action starts and
water starts flowing over the crest.
– This will continue until the reservoir level
becomes down below the inlet or mouth level.
• Way for juvenile
fish to bypass
• Decreases O2
levels in water
• Increase CO2
levels in water
• A simple surge tank is a vertical stand pipe connected to the
• Surge tanks are built high so that water can not overflow even with
a full load change on the turbine.
• The surge tank always placed on ground surface, above penstock
line, at the point where the latter drops rapidly to the power house.
• The height of the tank should be increased with the help of
• When a surge tank is
inclined to the horizontal its
effective water surface
increases and therefore ,
lesser height surge tank is
required of the same
diameter if it is inclined or
lesser diameter tank is
required for the same
• This type of surge tank is
more costlier than ordinary
type as construction is
difficult and is rarely used
unless the topographical
condition are in favour.
• This type of surge tank has
an expansion tank at the
top and expansion gallery
at the bottom, these
expansions limit the
• The upper expansion
chamber must be above
the maximum reservoir
level and the bottom
gallery must be below the
lowest steady running level
in the surge tank.
• Besides this the
intermediate shaft should
have a stable minimum
• The main function of this
surge tank is to create an
appreciable friction loss when
the water is flowing to or from
the tank thorough this
restricted orifice or throttle
• When the load on the turbine
is reduced the surplus water
passes through the throttle
and retarded head equal to
the loss due to throttle is built
up in the conduit.
• The size of the throttle
adopted is usually such as the
initial retarding head is equal
to the rise of water surface in
the tank when the full load is
rejected by the turbine.
• This type is rarely used.
Advantage is storage function of
the tank can be separated from
accelerating and retarding
Disadvantage is water hammer
pressure is transmitted directly
into the low pressure conduit.
• A differential surge tank
has a riser with a small
hole at its lower end
through which water
enters in it.
• The function of the surge
tank depends upon the
area of hole.
• This is known as tapered draft
tube and used in all reaction
turbines where conditions
permit. It is preferred for low
specific speed and large high
head units, vertical shaft Francis
• The maximum cone angle of
this draft tube is limited to 8° (a
= 4°) for the cause mentioned
• The hydraulic efficiency of such
type of draft tube is 90%.
• In any event, the draft tube
should be made as to secure a
gradual reduction of velocity
(uniform decease towards the
exit of draft tube) from the
runner to the mouth.
• A form that is theoretically
good is “Trumpet Shaped”.
• The elbow type draft tube is often preferred in most of the
power plants, where the setting of vertical draft tube does not
permit enough room without excessive cost of excavation.
• This offers an advantage in the cost of excavation ; specially
in the rock.
• If the tube is large in diameter ; it may be necessary to make
the horizontal portion of some other section than circular in
order that the vertical dimension may not be too great.
• A common form of section used is oval or rectangle.
Hydro electric plants are classified according
1)Based on available head
a) High head plants
b) Medium head plants
c) Low head plants
2) Based on nature of load
a) Base load plants
b) Peak load plants
3) Based on quantity of water available
a) Run-off river plants (with and without pond age).
b) Storage plants.
c) Pumped storage plants.
d) Mini and Micro hydel plants
• The water from the reservoir can be taken to a smaller
storage known as a forebay, by mans of tunnels.
• From the forebay, the water is then distributed to the
• The function of the forebay is to distribute the water to
penstocks leading to turbines.
• The inflow to the forebay is so regulated that the level in the
forebay remains nearly constant.
• The turbines will thus be fed with under a constant static
• Thus, the forebays help to regulate the demand for water
according to the load on the turbines.
• In the valve house, the butterfly valves or the sluice type
valves control the water flow in the penstocks and these
valves are electrically driven.
• Gate valves are also there in the power house to control the
water flow through the turbines. after flowing through tile
turbines . The water is discharged to the tail race.
• It is used If the head of water available is more than 50 m.,
then the water from the forebay is conveyed to the
turbines through pen-stocks.
• In these plants, the river water is usually tapped off to a
forebay on one bank of the river as in the case of a low
• From the forebay, the water is then led to the turbines
• A dam is built on the river and the water is diverted into a canal
which conveys the water into a forebay from where the water is
allowed to flow through turbines.
• After this, the water is again discharged into the river through a tail
race. At the mouth of the canal, head gates are fitted to control the
flow in the canal. Before the water enters the turbines from the
• It is made to flow through screens or trash-racks so that no
suspended matter goes into the turbines. If there is any excess
water due to increased flow in the river or due to decrease of load
on the plant, it will flow over the top of the dam or a waste weir can
be constructed along the forebay so that the excess water flows over
it into the river.
• For periodic cleaning and repair of the canal and the forebay, a drain
gate is provide on the side of the waste weir. The head gate is
closed and the drain gate is opened so that whole of the water is
drawn from the forebay and the canal for their cleaning and repair.
• Plants supplying base load which is generally
constant and runs without stop are known as
base load plants.
• These are of greater capacity.
• The run off river and storage type power
plants are used as base load plants.
• These plants supply power at the peak load
• When load is more than the average load.
• Run off river plants with pond age and
pumped storage plants are used as peak
• They store water during off peak time and
supply for peak hours.
• The load factor is low compared to base
• Pondage refers to the collection of water
behind the dam and increases the steam
capacity for short periods.
• This plant has a flexibility to meet the
• Hence the discharge is more than the
normal, may be 3 to 8 times more.
• Pondage increases the stream capacity for
short time periods.
• These plants can meet peak load demand
and also used as base load plants.
• These plants would have reservoirs of large
size to facilitate the storage of water and
thus it is independent of seasonal streams.
• The stream flows are considerably higher
than natural flow.
• There fore this plant can be used as base
load as well as peak load alternative.
• The majority of the hydro plants in world
are this type.
• Like peaking, pumped storage is a method of keeping water in
reserve for peak period power demands.
• Pumped storage is water pumped to a storage pool above the power
plant at a time when customer demand for energy is low, such as
during the middle of the night.
• The water is then allowed to flow back through the turbine-
generators at times when demand is high and a heavy load is place
on the system.
Pumped Storage Plants
• The reservoir acts much like a battery, storing power in the
form of water when demands are low and producing
maximum power during daily and seasonal peak periods.
• An advantage of pumped storage is that hydroelectric
generating units are able to start up quickly and make rapid
adjustments in output.
• They operate efficiently when used for one hour or several
• Because pumped storage reservoirs are relatively small,
construction costs are generally low compared with
conventional hydropower facilities.
Types of Micro-Hydroelectric
There are many
different types of Micro-
Here are 3 Micro-
Hydro systems from
Energy Systems and
How Micro-Hydro Systems Work
• Micro-Hydroelectric systems take water
from a stream and channel it into a pipeline
that creates a vertical drop in order for the
water to turn turbines that powers the system