Introduction to Hydropower

Chapter One
Chapter One
Introduction
By Yimam A.(MSc.)
December 16, 2020
By Yimam A.(MSc.) Chapter One December 16, 2020 1 / 42

Chapter One
Outline
1 Sources of Energy
2 History of hydroelectric power plant
3 Essential elements of hydroelectric power plant
4 Working principle of hydroelectric power plant
5 Hydropower basics
6 Advantages and disadvantages of hydroelectric power plant

Chapter One
Learning Objectives
At the end of this chapter the students should be able to:
Understand the history of hydroelectric power plant in the world and in Ethiopia
Understand the essential elements of hydroelectric power plant with their function and
sketch the diagram that shows a hydro power plant layout.
Understand working principle of hydroelectric power plant
Understand basic formula used to calculate power obtained from hydro power plant
Understand factors determining potential of hydro power
Understand the advantages and disadvantages of hydroelectric power plant

Chapter One
Sources of Energy
Sources of Energy
Energy sources are mainly categorized in to two big classes
1 Renewable sources: The sources of energy which are being produced continuously in
nature and are inexhaustible are called renewable sources of energy (non-conventional
energy). They are available in plenty and by far most the cleanest sources of energy
available on this planet. e.g. solar, wind, tidal, hydropower
2 Nonrenewable sources: A nonrenewable resource is a natural resource that cannot
be re-made or re-grown at a scale comparable to its consumption. They are called
non-renewable because they cannot be re-generated within a short span of time. Non-
renewable sources exist in the form of fossil fuels, natural gas, oil and coal.

Chapter One
Sources of Energy
Cont....
Hydropower Engineering refers to the technology involved in converting the pressure
energy and kinetic energy of water in to more easily used electrical energy.
Hydropower is a power that is derived from the energy of moving or stored water, that
can be harnessed for useful purposes.
Hydropower is a renewable, non-polluting and environment friendly source of energy.
Oldest energy technique known to mankind for conversion of mechanical energy into
electrical energy.

Chapter One
History of hydroelectric power plant
First hydro power is used by the Greeks to spin water wheels for crushing wheat into
ﬂour before more than 2000 years ago.
For many centuries, hydropower had been used to produce mechanical power to perform
a range of activities, including grain milling, textile processing and other light industrial
operations.
First hydroelectric station was started in America in 1882 when U.S establishes a ﬁrst
hydro power station which generate 12.5 kW of power and thereafter development took
place very rapidly.
In the late 1940’s, big dams for hydropower had been built.

Chapter One
Cont....
Today it reaches up to 22,500 MW(Three Georges dam) of china is the world largest
hydroelectric power plant.
In 19th century, electrical generator was developed.
In 1878 the world’s ﬁrst hydroelectric power scheme was developed at Crag side in
north Umberland.
Appleton, Wisconsin became the ﬁrst operational hydroelectric generating station in
the United States,
In 1882,Hoover Dam (U.S) initial 1,345 MW power station was the world’s largest
hydroelectric power station in 1936.

Chapter One
The historical and present hydroelectric power in Ethiopia
Name of Hydropower Scheme Year of Commissioning(G.C) Installed Capacity(MW)
Aba Samuel(Akaki River) 1932 6
Awash II(Awash River) 1966 32
Awash III(Awash River) 1971 32
Koka (Awash River) 1960 42.3
Fincha(Fincha River) 1973 100
Gilgel Gibe I(Omo River) 2004 184
Gilgel Gibe II(Omo River) 2004 420
Gilgel Gibe III(Omo River) 2016 1870
Melka Wakena(Wabe Shebele River) 1989 153
Tis Abay I(Nile River) 1953 11.5
Tis Abay II(Nile River) 2001 75
Tana Beles(Belesa River) 2010 460

Chapter One
Essential elements of hydroelectric power plant
Figure: Layout of hydroelectric power plant

Chapter One
Catchment area and reservoir
The catchment area is the area bounded by water sheds, which drains into a stream or
river across which the dam has been built at a suitable place. Or
The area behind the dam, which collects rain water, drains into a stream or river, is
called catchment area.
Water collected from catchment area is stored in a reservoir, behind the dam.
The purpose of the reservoir is to store the water during excess ﬂow periods(rainy
season) and supply it during lean ﬂow periods(dry season).
Water surface in the storage reservoir is known as head water level or simply head race.

Chapter One
Cont....
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.
The capacity of reservoir depends on the difference between run offs during high and
lean flows.
Water held in upstream reservoir is called storage whereas water behind the dam at
the plant is called pondage.

Chapter One
Dam
A dam is a barrier which confines or raise water for storage or diversion to create a
hydraulic head. The purpose of the dam is to store the water and to regulate the out
going flow of water.
The dam helps to store all the incoming water. It also helps to increase the head of the
water. In order to generate a required quantity of power it is necessary that a sufficient
head is available.
The dam is the most expensive and important part of a hydro project.
It should be built at a location where the height of the river is sufficient to get the
maximum possible potential energy from water.
Gate: A gate is used to regulate or control the flow of water from the dam.

Chapter One
Spillway
Excess accumulation of water endangers the stability of dam construction. Also in
order to avoid the over flow of water out of the dam especially during rainy seasons
spillways are provided.
This prevents the rise of water level in the dam. It acts as a safety valve.
It discharges the overflow of water to the downstream side when the reservoir is full, a
condition mainly arising during flood periods.
These are generally constructed of concrete and provided with water discharge opening
shut off by metal control gates.

Chapter One
Surge tank
A surge tank is a small reservoir or tank which is open at the top.
The water level in the surge tank rises or falls to control the pressure variation. During
more pressure water hammering occurs in the penstock, which damages it if surge tank
is not provided.
A reduction in load on the generator causes the governor to close the turbine gates and
thus create an increased pressure in the penstock.
This may result in water hammer phenomenon and may need pipe of extraordinary
strength to withstand it otherwise the penstock may burst.
Pressure Tunnel: It is a passage that carries water from the reservoir to the surge
tank.

Chapter One
Cont....
To serve as a supply tank to the turbine when the water
in the pipe is accelerated during increased load conditions
and as a storage tank when the water is decelerating during
reduced load conditions.
To reduce the distance between the free water surface in the
dam and the turbine, thereby reducing the water hammer
eﬀect on penstock and also protect the upstream tunnel
from high pressure rise.
Figure: simple surge tank

Chapter One
Cont....
Water hammer effect :
Water hammer effect is the sudden rise in pressure in the closed conduit or penstock due
to the sudden decrease in flow of water to the turbine.
The rate of flow of water striking the runner is reduced by governor in order to maintain
the constant speed of the runner when the load on the generator decreases.

Chapter One
Penstock
Penstock is a closed pipe of steel or concrete for supplying water under pressure to the
turbine.
It helps to increase the kinetic energy of the water coming from the dam.
Penstock is made up of a very strong material which can sustain the high pressure of
water like steel,asbestos,cement,cast steel.
Inlet valve:
Water from the penstock ﬂows to the turbine through the inlet valve.
The valve may be partially closed or open thereby regulating the pressure of water
ﬂowing to the turbine.

Chapter One
Hydraulic Turbine(Prime Mover)
The hydraulic turbine converts the energy of water into mechanical energy. The me-
chanical energy(rotation) available on the turbine shaft is coupled to the shaft of an
electric generator and electricity is produced. The water after performing the work on
turbine blades is discharged through the draft tube.
The prime movers which are in common use are Pelton wheel, Francis turbine and
Kaplan turbine.
Tail water level or Tail race
Tail water level is the water level after the discharge from the turbine.
The discharged water is sent to the river, thus the level of the river is the tail water
level.

Chapter One
Draft tube
The draft tube is a conduit which connects the runner exit to the tail race where the
water is being finally discharged from the turbine.
It serves the following purpose’s :
1 It allows the turbine to be set above tail water level without loss of head, to carryout
inspection and maintenance.
2 It regains by diffuser action , the major portion of the kinetic energy delivered to it from
the runner.
3 It increases the output power.
4 It increases the efficiency of hydro power plant.

Chapter One
Electric generator, Step-up transformer and Pylon
As the water rushes through the turbine, it spins the turbine shaft, which is coupled
to the electric generator.
The generator has a rotating electromagnet called a rotor and a stationary part called
a stator. The rotor creates a magnetic ﬁeld that produces an electric charge in the
stator. The charge is transmitted as electricity.
The step-up transformer increases the voltage and the current coming from the stator.
The electricity is distributed through power lines also called as pylon.

Chapter One
Working principle of hydroelectric power plant
Initially the water of the river is in catchment area.
From catchment area the water ﬂows to the dam.
At the dam the water gets accumulated, thus the potential energy of the water increases
due to the height of the dam .
When the gates of the dam are opened then the water moves with high kinetic energy
into the penstock.
Through the penstock water goes to the turbine house.
Since the penstock makes water to ﬂow from high altitude to low altitude, thus the
kinetic energy of the water is again raised.

Chapter One
Cont....
In the turbine house the pressure of the water is controlled by the controlling valves as
per the requirements.
The controlled pressurized water is fed to the turbine.
Due to the pressure of the water the light weight turbine rotates.
Due to the high speed rotation of the turbine the shaft connected between the turbine
and the generator rotates .
Due to the rotation of generator the ac current is produced.
This current is supplied to the powerhouse .
From powerhouse it is supplied for diﬀerent purposes through transmission lines.

Chapter One
Cont....
Figure: working principle of hydro power plant

Chapter One
Hydropower basics
Cont....
Hydropower is a power that is derived from the energy of moving or stored water, that
can be harnessed for useful purposes.
Theoretical power from the hydro power is given by:
p(w) = ρgHQ
Where
ρ = density of water = 1000kg/m3
g = gravitational constant = 9.81m/s2
H= design head(net head) (m)
Q = water ﬂow(discharge) m3/s

Chapter One
Hydropower basics
Cont....
The amount of energy available in a stored water is the product of the weight times
the height that the water falls.
E = W = mgh, m = ρv
E = ρvgh[joules]
Where
m = mass of water
v = volume of water(m3)
h = height of water fall (m).
g = acceleration due to gravity = 9.81m/s2

Chapter One
Hydropower basics
Cont....
⇒ Then the output power
P = dE/dt = d(ρvgh/dt)
= ρgh(dv/dt)
Pth = ρgHQ(watts)
Where: Q = dv/dt water ﬂow rate (m3/s)
⇒ The power at the out put of the turbine is:
P = ρgHQηt
Where:
g = gravitational constant = 9.81m/s2
H = head (m)
Q = water ﬂow (m3/s)By Yimam A.(MSc.) Chapter One December 16, 2020 27 / 42

Chapter One
Hydropower basics
Cont....
⇔ Therefore the power at the out put of the generator is:
Pactual = ρgHQηtηg
Where:
ηg = generator eﬃciency

Chapter One
Hydropower basics
Factors determining potential of hydropower
From the basic formula
P(W) = ρgHdη
P(kW) = gHdη
The factors which aﬀects the potential of hydropower are the following:
Head and head losses
Flow rate
System losses
Component ineﬃciencies

Chapter One
Hydropower basics
Hydraulic head
Head is one of the factors which have great influence on the system capacity.
In any real system water losses its some energy because of frictional drag and turbulence
as it flows in channels and through pipes and the effective head will be less than actual
head.
These flow losses vary from system to system: in some cases the effective head can be
less than 75 % of actual head, in others it can be greater than 95 % . For example two
systems with flow rate of 100m3/s and plant efficiency of 83%.
First system Second system
Effective head 10 m 110 m
Available power(gHQη) 8,142.3 kW 8,9565.3 kW

Chapter One
Hydropower basics
Cont....
Gross Head(Hg) of A hydropower facility is the difference between headwater eleva-
tion and tail water elevation. With the use of survey instrument, gross head can be
determined systematically and accurately.
Maximum Head (Hmax) - above which the excess water spilled after impounding during
or after a heavy rainy season with possible flood.
Minimum Head (Hmin)- below which the reservoir should ideally be not allowed to be
drawn down , and water contents in a given reservoir is said to have been lowered down
so a dead storage state.
Design Head (Hd) - which is used the actual in water capacity calculation for a given
HEPP, which can also be referred to as the effective head , which in turn equal to the
growth head minus hydraulic losses before entrance to the turbine and outlet losses.

Chapter One
Hydropower basics
Cont....
Design head (eﬀective head):
Hd = Hg − hf − h
Where
h is the height of the nozzle above the tailrace (if the turbine is Pelton turbine)
hf the frictional head loss in penstock
Hg the gross head

Chapter One
Hydropower basics
Cont....
Figure: Hydraulic head

Chapter One
Hydropower basics
Flow rate
Flow rate is another very important factor which can influence system capacity.
For example:Two systems with effective head of 100 meters and plant efficiency of 83%.
First system Second system
Flow rate 0.0024m3/s 6000m3/s
Available power(gHQη) 1.95 kW 4,885,380 kW
System Losses :
• When electricity is transported along a transmission system, the losses occur.
• As a result, what comes out of the system at the consumer is less than what is input
into the system at the generation site.

Chapter One
Hydropower basics
Component Inefficiencies
Inefficiencies is due to component losses. These include losses in:
Penstock
Turbine
Generator
Transmission line
Step up & step down transformer
The generator efficiency gives the ratio between mechanical energy of the turbine shaft
and electrical energy delivered from the generator.

Chapter One
Hydropower basics
Figure: Component Ineﬃciencies

Chapter One
Advantages and disadvantages of hydroelectric power plant
Advantages of hydroelectric power plant
It is totally renewable and non polluting (no fuel charges)
The plant is highly reliable and its maintenance and operation charges are very low.
Running cost of the plant is low.
In addition to power generation, hydro-electric power plants are also useful for ﬂood
control, irrigation purposes, ﬁshery and recreation.
Have a longer life(100 to 125 years) as they operate at atmospheric temperature against
20-45 years of a thermal plant.
Water stored in the hydro-electric power plants can also be used for domestic water
supply.

Chapter One
Cont....
The hydroelectric power plant does not require a highly skilled workers.
The man power requirement is also low(less supervising staﬀ is required)
No ash problem and atmosphere is not polluted since no smoke is produced in the
plant.
The number of operations required is considerably small compared with thermal power
plants.

Chapter One
Disadvantages of hydroelectric power plant
The initial cost of the plant is very high.
It takes much longer time in design and execution. The gestation period of hydroelectric
power plants may extend from 10 to 15 years
Since they are located far away from the load center, cost of transmission lines and
transmission losses will be more.
Power generation is dependent on the nature ,so during drought season the power
production may be reduced or even stopped due to insuﬃcient water in the reservoir.
Water in the reservoir is lost by evaporation. Large storage based hydroelectric plants
have environmental impact and rehabilitation issues.

Chapter One
Social and Environmental Impacts
Social Impacts:
Population displacement
Loss of social networks and changing way of living
Dams can facilitate development of diseases
Diversion of mountain streams
Blockage of fish passage both upstream and downstream
Storing water in reservoir may reduce the final flow as a result of evaporation

Chapter One
Cont....
Environmental impacts:
Reduction in the ﬂow of soil and nutrients
Pollution is stored in the reservoir
Possible dam failure
Loss of cultural heritage
local increase in water vapor and some temperature eﬀect
Vegetation rotting under water produces methane-implies emissions

Chapter One
Thank You!

Introduction to Hydropower

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Introduction to Hydropower