Hydroelectric power (often called hydropower)
is considered a renewable energy source. A
renewable energy source is one that is not
depleted (used up) in the production of energy.
Through hydropower, the energy in falling water
is converted into electricity without “using up”
the water. Hydroelectric power (hydropower)
systems convert the kinetic energy in flowing
water into electric energy.
1. Source of power.
2.Interconnected with steam power plants, base
load is supplied by the hydro power plants while the
peak load is supplied by steam power plant, when
stream flow is less than maximum flow demand.
3.When stream flow is more than the maximum
flow demand, base load is supplied by the steam
power plants while the peak load is supplied by
hydro power plant.
1. No fuel charges.
2. Any hydro electric plant is highly reliable
3. Maintenance and operation charges are very low.
4. Running cost of plant is low.
5. It has no standby losses.
6. The plant efficiency doesn’t change with age.
7. It take a few minutes to run and synchronize the plant.
8. Less supervising staff is required.
9. No fuel transportation problem.
10. No ashproblem.
11. In addition to power generation these plants are also used for flood
control and irrigation purposes.
12. The have long life (100-125yrs, 20-45yrs of thermalplant)
• The initial cost is very high.
• It takes considerable time for the erection of such
• Such plants are usually located in hilly areas far
away from the load centre and as such they
require long transmission lines to deliver power,
hence the cost of transmission linear and losses in
them will be more.
• Power generation by the hydro-electric plants
depend upon quantity of water hence rain.
Selection of Site
• Availability of water
• Water storage
• Water head
• Accessibility of the site
• Distance from the load centre
• Type of the land of site
6. Surge tanks
7. Prime movers
8. Draft Tubes
9. Powerhouse and Equipment
Essential Features & Elements of
Hydro electric Power Plant
1. Catchment area: The
whole area behind the
dam draining into the
2. Reservoir: Used to
A. Natural (lake)
B. Artificial (dam, called
Dam: barrier to raise water for storage or diversion to
create a hydraulic head.
Types of dams:
A. Fill Dams : Earth dams, Rock Fill Dams
B. Masonary Dams: Solid gravity dams, Butteress dams,Arch dams.
C. Timber Dams
Selection of type of Dam
1. Nature of foundation
Sound rock formation in foundation: any type of dam
Poor rock and earth foundation: earth dam
2. Nature of valley
Narrow valley : arch dam
Rocky bed: Solid gravity dam
Wide valley weak foundation: Buttress dam
Any width of valley, good foundation : Steel Dam
Types of Dams
• Fill Dams
1. Earth fill dams: earth fill
dam, also called Earth Dam, or
Embankment Dam, dam built
up by compacting successive
layers of earth, using the most
impervious materials to form a
core and placing more
permeable substances on the
upstream and downstream
sides.Afacing of crushed
stone prevents erosion by wind
or rain, and an
ample spillway, usually of
• Arockfill dam is a type
dam which comprises
Used in mountainous
locations where rock is
• Solid Gravity Dam: Massiveand
bulky and depends upon its
weight on stability.
• It requires strong rock foundation
• Bhakra Dam is the highest
Concrete Gravity dam in Asia and
Second Highest in the world.
• Bhakra Dam is across river Sutlej
in Himachal Pradesh
• It is 740 ft. high above the deepest
foundation as straight concrete dam
being more than three times the
height of Qutab Minar.
• Length at top 518.16 m (1700 feet);
Width at base 190.5 m (625 feet),
and at the top is 9.14 m (30 feet)
• Is a gravity dam reinforced by structural
• A buttress dam or hollow dam is a dam
with a solid, water-tight upstream side that
is supported at intervals on the
downstream side by a series of buttresses
or supports. The dam wall may be straight
• Most buttress dams are made of
reinforced concrete and are heavy,
pushing the dam into the ground. Water
pushes against the dam, but the
buttresses are inflexible and prevent the
dam from falling over
• Buttress - a support that transmits a force
from a roof or wall to another supporting
• It has a relatively thin structure. Because
of this, these dams often use half as much
concrete as gravity dams can be used for
• An arch dam is a solid dam made
of concrete that is curved upstream in
plan. The arch dam is designed sothat
the force of the water against it,
known as hydrostatic pressure,
presses against the arch, compressing
and strengthening the structure as it
pushes into its foundation or
• An arch dam is most suitable for
narrow gorges or canyons with steep
walls of stable rock to support the
structure and stresses .Since they are
thinner than any other dam type,they
require much less construction
material, making them economical
and practical in remote areas.
• Timber Dams
• When wood in plentiful and more durable
material are not accessible timber is used for
low dams 12m.
• Aspillway is an integral part of a Dam.
• Aspillway is usually used to remove water from a
reservoir to prevent overflow and to release pressure on
a dam from increasing quantities of water. It is
normally composed of three major
• The approach facility admits flow to the spillway.
• The discharging conduit evacuates the flow from the
approach facility to an outlet structure.
• The outlet structure (tailwater channel) dissipates the
excessive energy of the flow from the discharging
conduits and conveys tranquil flow to the downstream.
• Overflow spillways are also
• This type of spillways
allows the passage of the
flood wave over its crest
(which is S-shaped).
• Can be classified under
controlled or uncontrolled.
• Widely used on Gravity
dams,Arch dams, and
• Chute spillways are common and
basic in design as they transferexcess
water from behind the dam down a
smooth decline into the river below.
• The spillway’s slope and its sides
are lined with concrete.
• In case of having sufficient stiff
foundation conditions at the spillway
location, a chute spillway may be
used instead of overflow spillwaydue
to economic consideration.
Side Channel Spillway
• It is employed when valley is too narrow in
case of solid gravity dams and when non rigid
dams are adopted.
• The side channel spillway is different from
chute spillway in the sense that after crossing
over the spillway crest. Water flows parallel to
the crest length in former, whereas the flow is
normal to the crest in the later.
• There may be natural depressions or saddle on the peripheryof
the reservoir basin away from the dam. The depressions may
be used as spillway.
• The bottom of the depression should be at full reservoir level.
• Crest is fixed at Full Reservoir Level. When
the water level in the reservoir rises over F.R.L
water starts spilling over the crest.
• Aheadrace is a channel which leads water to a turbine anda
tailrace is a channel which conducts water from the wheels.
• Open Conduit: Canals and Flumes
• Close conduits: Tunnels, pipelines and penstock
• Closed conduit for supplying water under
pressure to a turbine.
• Thinkness of penstock is given by:
• T = pd/2fn
p = pressure due to water
d = diameter of the penstock
f = Permissible circumferential stress
n = Joint efficiency
• A surge tank is small reservoir or tank in which water
level rises of falls to reduce the pressure swings so that
they are not transmitted in full to closed circuit.
1. They reduce the distance between the free water
surface and turbine thereby reducing water hammer
effect ( the change in in pressure rapidly above or
below normal pressure caused by sudden changes in
the rate of water flow through the pipe according to
the demand of the primemover) on the penstock.
2. To serve as supply tank to the turbine in case of
increased load conditions, and storage tank in case of
low load conditions.
• Impulse Turbines: Pressure energy of water is
converted to kinetic energy when passing
through nozzle and forms velocity of high
• Reaction Turbines: Water pressure combined
with the velocity works on the runner, power is
developed from the combined action of
pressure and velocity of water, that completely
fill the runner and water passage.
• It allows the turbine to be set above tail water
level, without loss of head, to facilitate inspection
• It regains, by diffuser action, the major portion of
the kinetic energy delivered to it from the runner.
1. Conical Type: used on low powered units for all
specific speeds and frequently od large head
units. Side angle 4 to 6 deg.
2. Elbow Type: Mostly used, vertical portion is a
conical section which gradually flattens in the
elbow section and then discharges horizontally.
High Head Power Plant
Head: 100m to 2000m
Water is stored in the lake
over the mountain during
high rainy season or when
Water should be available
throughout the year.
Pelton Wheel turbine is
Medium Head Plants
• Head : 30 to 100m
• Uses FrancisTurbine
• Forebay provided at the beginning of penstock at asreservoir.
• Water is carried in open canals from main reservoir to forebay thento
powerhouse through penstock.
Low Head Power Plants
• They consist of dam across the river.
• Asideway stream diverges from the river at the dam, powerhouseis
constructed over the stream, which further joins theriver.
• Vertical shaft Francis or Kaplan turbine
According to Nature of Load
Base Load Plants: they cater to the base load of
the system, they need to supply constant power
when connected to the grid.
Peak Load Plants: some of the plants supply
average load but also some peak load. Other
peak load plants are required to work only during
peak load hours.
According to the quantity of water
1. Run of river plants without pondage:
• No pondage.
• No control on flow of water.
2. Run of river plants with pondage
May work as base load or peak load plants.
Storage for a week
3. Storage Type Plant
The storage is large.
Used as base load and peak load plants
Controlled flow .
4. Pumped Storage plants
• These plants are employed
where quantity of water
required is inadequate.
• Water passing through the
turbine is stored in the tail
race pond. During low load
periods the water is pumped
back to the reservoir, which
can be used during peak
• Usually interconnected with
steam or diesel power
Mini & Microhydel plants
• Mini – 5m to 20 m head
• Micro – below 5 m head
These plants are scattered in our country and estimated
potential is 20,000MW.
Each plant generate about
100 to 1000kW per unit.
According to the head and
quantity of water
• Impulse Turbine: Requires high head and
small flow of water.
• Reaction Turbine: Requires low head and
high rate of flow of water.
According to the name of originator
• Pelton Turbine: It is an impulse type of
turbine used for high head and low discharge.
• Francis Turbine: It is reaction type of turbine,
used for medium high to medium low heads
and medium small to medium large quantities
• Kaplan Turbine: It is reaction type of turbine,
used for low head and large quantities of flow.
According to action of water
on the moving
• Impulse: Pelton
• Reaction: Kaplan, Francis, Propeller.
According to direction of flow of water in
• Tangential flow turbine (PeltonTurbine)
• Radial flow turbine ( not used)
• Axial flow turbine (KaplanTurbine)
• Mixed (radial and axial ) flow turbine (Francisturbine)
According to the position of turbine
• Shaft may be horizontal or vertical
• Pelton has horizontal axis
According to specific speed
• The specific speed is defined as the speed of a
geometrically similar turbine that would
develop one brake power horsepower under
the head of one meter.
Impulse Turbine-Pelton Turbine
• Tangential flow impulse
• Rotor has equally spaced
hemispherical buckets, Water
is transferred from high head
source through penstock pipes.
• All the available potential
energy is converted to kinetic
energy before the jet strikes the
• The pressure all over the wheel
is constant and equal to
atmospheric pressure, energy
transfer occurs due to purely
• The runner utilizes both potential and kinetic
• As the water flows through the stationary part of
the turbine, whole of its pressure energy is not
transferred to kinetic energy. When the water
flows through the moving parts, there is a change
both in the pressure and in the direction and
velocity of flow of water.
• The water which acts on the runner blades is
under pressure above the atmospheric.
• It is an inward mixed flow reaction turbine i.e. water under pressure
, enters the runner form the guide vanes towards the centre in the
radial direction and discharges out of the runner axially.
• It runs under medium heads and requires medium quantity of water.
• Water is brought down to the turbine and directed to a number of
stationary guide vanes.
• The head acting on the turbine is partly transformed into kinetic
energy and rest remains as pressure head.
• The runner is always full of water. The movement of runner is
affected by the change of both the potential and the kinetic energies
• The water is then discharged to the tail race, through draft tube.
Propeller & Kaplan Turbines
• Propeller turbine is a reaction turbine used for heads between
4m to 80 m and specific speed of 300 to 1000.
• Axial Flow Type
• It consists of axial flow runner
• With 4-6 or max 10 blades of air foil shape
In Propeller Runner blades are fixed and non adjustable as in
In Kaplan Turbine which is a modification of propeller turbine
the runner blades are adjustable and can be rotated aboutpivots
fixed to the base.
• It is a modified axial flow
turbine, the turbo generator
set using the bulb/tubular
turbine has the outer casing
of the shape of a bulb.
• The turbine generator set is
called bulb set and turbine
used is called bulb turbine.
The bulb unit is a water
tight assembly of turbine
and generator with
horizontal axis, submerged
in a stream of water.
Governing of Hydraulic Turbines
• Governing means the speed regulation. Under
normal conditions the turbine should run at
constant speed irrespective of changes in the
• This is achieved by means of a governor called
oil pressure governor.
Governing of Impulse turbines
• The quantity of water rejected from turbine nozzle and from
striking the buckets may be regulated in following ways:
• Spear regulation: To and fro motion of spear inside the
nozzle alters the cross sectional area of the stream.
• Deflector regulation: the deflector is generally a plate
connected to the oil pressure governor by means of levers.
When it is required to deflect the jet, the plate can be
brought in between the nozzles and buckets, thereby
diverting the water away from the runner and directing into
It is used when supply of water is constant but load fluctuates.
• Combined spear and deflector regulation: the speed is
regulated by spear and pressure is regulated by deflector
Governing of Reaction Turbines
• The guide blades of reaction turbine are pivoted and
connected by levers and links to the regulating ring.
• To the regulating ring are attached two long regulating
rods connected to the regulating lever.
• The regulating ring is keyed to the regulating shaft
which is turned by servomotor piston of oil pressure
• The penstock which feeds the turbine inlet is has relief
valve know as pressure regulator.
• When guide vanes have to be suddenly closed the
relief valve opens and diverts the water to tailrace.
• It may be defined as the science which deals with the depletion
and replenishment of water resources.
3. Run off tables and curves
• Hydrograph: It is defined as graph showing
discharge(run off) of flowing water with
respect to time for a specified time.
• It indicates the power available from the
stream at different times of day, week or year.
• Unit Hydrograph: It is a hydrograph which
represents unit run off resulted from an intense
rainfall of unit duration and specified areal
Flow Duration Curve
• Is a plot of discharge against the percentage of
time the flow was equaled or exceeded.
• It is the curve plotted between the flow
available during a period verses fraction of
• The area under the flow of the duration curve
gives the total quantity of run-off during that
• Aflow duration curve allows the evaluationof
low levels of flow.
• It is highly useful in the planning and design of
• It also finds use in the design of drainage
system and in flood control studies.
• Mass curve is the graph of cumulative values of water quantity
(run off) against time.Amass curve is integral curve of the
hydrograph which expresses the area under the hydrograph
from one time to another.