UNIT 2:

Thermal and Hydro Power Plants:

Site Selection of Steam Power Plant:

The following consideration should be taken while site selection of steam power
plant.

1. Availability of raw materials

Huge quantity of coal and fuel are required to run a steam (thermal) power plant.
Therefore, it is important to locate the plant as near as possible to the coal fields
to reduce the transportation cost.

If it is not possible to locate the plant near the coal field, then it should be located
near the railway station or near to a port.

2. Ash disposal facilities

As a huge quantity of coal is burnt, this results in a huge quantity of ash too. The
ash handling problem is more serious as compared to handling of coal because it
comes out very hot and is very corrosive. If not disposed properly it will result in
environmental pollution and other hazards. Therefore there must be sufficient
space to dispose this large quantity of ash.

3. Nature of land
The land should have good bearing capacity about 1 MN/m2 as it has to withstand the
dead load of plant and force transmitted to the foundation due to working of
heavy machinery.
4. Cost of land
Large area is required to build a thermal power plant, therefore the land price
should be affordable (cheap). For eg: Large plant in the heart of city will be very
costly.

5. Availability of water
Water is the working fluid in a steam power plant, and a large quantity of water is
converted to steam in order to run the turbine. It is important to locate the plant
near the water source to fulfill its water demand through out the year.
6. Size of the plant
The capacity of the plant decides the size of the plant, large plant requires large
area and the smaller plant requires considerably smaller area. Therefore, the size
of the plant and its capacity play an important role in site selection of steam power
plant.

7. Availability of workforce
During construction of plant, enough labour is required. The labour should be
available at the proposed site at cheap rate.

8. Transportation facilities
Availability of proper transportation is another important consideration for the
site selection of steam power plant as a huge quantity of raw materials (coal &
fuel) through out the year and heavy machinery are to be brought to the site
during the installation.

9. Load centre
The plant must be near to the load centre to which it is supplying power in order
to decrease transmission loss and minimize transmission line cost.
10. Public problems
The plant should be away from the town or city in order to avoid nuisance from
smoke, ash, heat and noise from the plant.

11. Future extension

A choice for future extension of the plant should be made in order to meet the
power demand in future.
Introduction to Thermal Power Plant
Contents show

The Role of Thermal Power Plant in the Modern Power Generation

Scenario.

The development of thermal power plant in any country depends upon

the available resources in that country. The hydro-power plant totally
depends on the natural availability of the site and the hydrological cycle.
The new sites cannot be created manually for hydropower plants.

The development of nuclear power requires high investment and

technology. In many tinies, the hydro-power plant suffers if a drought
comes even once during a decade and the complete progress of the
nation stops. The calamity of rain drought on the power industry has been
experienced in many states in the country.
To overcome this difficulty, it is necessary to develop thermal power
plants in the country which are very suitable for baseload plants. The coal
resources in India account for about 5.7% of the proven reserves in the
world.

The geological reserves of coal in India are 193.8 billion tonnes. The
thermal power sector contributes nearly about 66% of installed capacity in
India.

The coal production in the country is increasing at the rate of 4.6% every
year and new plants are set up in many parts of the country to increase
the power production to meet the demand to increase the per capita
income of the country.

Due to increased power generation –

1. The country’s income can be increased.

2. The standard of living can be increased.
3. Reducing the unemployment
4. Development in all sectors.
5. Development in new technology.
6. The GDP of the country can be increased.
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Components of Thermal Power Plant

A thermal power plant generates electricity. In addition to generating
electricity, certain thermal power plants are designed to generate heat for
industrial purposes, such as district heating or water desalination.

The following are the components and operating principles of a

thermal power plant.

1. River or Canal
2. Heater
3. Boiler
4. Superheater
5. Economizer
 6. Alternator
7. Condenser
8. Cooling tower and ponds
9. Air pre-heater
10. Turbine
11. Feedwater pump
Here are the main components and functions of a thermal power plant
with a diagram.

#1 River or Canal
It is well known here that a large amount of water is required, and this
water is also used to generate electricity through the process of
electrolysis.

#2 Heater

Depending on the name according to which it is used, low-pressure

heaters or high-pressure heaters increase or decrease the pressure of
water.
#3 Boiler

There are two sections in the boiler: one for coal storage and handling,
which stores the coal and then uses it as needed. The ash handling and
storage plant is the other section, where the coal burning process’s
produced ash is sent for ash storage.

The pulverized coal and air mixture is added to the boiler, which is burned
in the combustion area. When the fuel is ignited, a sizable fireball forms in
the center of the boiler, radiating a significant amount of heat energy.

At high temperatures and pressures, the heat energy is used to turn the
water into steam. The boiler walls are covered with steel tubes where
steam is produced from water. After passing through the superheater,
economizer, and air preheater, the flue gases from the boiler are finally
exhausted into the atmosphere through the chimney.

#4 Superheater

This superheater tube is located at the very end of the boiler where the
water is the hottest. In the superheater, the saturated steam generated in
the boiler tubes is heated to a maximum temperature of 540 °C. The
superheated high-pressure steam is then fed into the steam turbine.

#5 Economizer

A boiler’s feedwater is heated by an economizer before being supplied to

the boiler. When the water pressure is raised, some heat is generated and
sent from the economizer to the boiler.

#6 Alternator

An alternator is connected to the steam turbine. Electricity is produced

when the turbine turns the alternator. A transformer is then used to
increase the electrical voltage that is generated before transmitting it to
the intended location.
#7 Condenser

The condenser is used to cool the working fluid or, more precisely, to
remove heat from the water. The condenser uses cold water circulation to
condense the exhaust steam. Here, the steam cools down and turns back
into water after losing both pressure and temperature.

Condensing is necessary because compressing a fluid in a gaseous state

requires a significant amount more energy than compressing a liquid. The
cycle becomes more effective as a result of condensing.

#8 Cooling Tower and Ponds

To condense the steam, a condenser needs an adequate quantity of

water. Most plants employ a cooled cooling system, which involves cooling
and reusing warm condenser water. A cooling tower is a 150m-tall
hyperbolic structure made of steel or concrete.

#9 Air Pre-Heater

Air from the atmosphere is drawn in by the main fan and heated in the air
pre-heater. In the boiler, pre-heated air is mixed with coal. Preheating the
air has the benefit of enhancing coal combustion.

#10 Turbine

The turbine’s primary purpose is to turn the blades when steam passes
through it, converting the heat energy into mechanical energy. Turbine
blades rotate as a result of high-pressure, superheated steam being fed
into the steam turbine.

The steam turbine, which serves as the prime mover, transforms the
energy in the steam into mechanical energy. As the steam travels through
the turbine, its pressure and temperature are reduced and its volume is
increased. The condenser exhausts the expanded low-pressure steam.
#11 Feedwater Pump

A feedwater pump once more supplies the condensed water to the boiler.
During the cycle, some water could be lost, but it is still adequately
supplied by an outside water source.

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The layout of the Modern Thermal Power Plant

The general layout of the thermal power plant is shown in the figure and it
consists of the following four circuits:

1. Coal and ash circuit

2. Ash and gas circuit
3. Feedwater and steam flow circuit
4. Cooling water circuit.
Working of Thermal Power Plant
Coal received in the coal storage yard of the power station is transferred
to the furnace by the coal handling unit. The heat generated due to the
burning of coal is used in converting water included in the boiler drum
into steam at suitable pressure and temperature.
The steam generated is passed through the superheater. Superheated
steam then flows through the turbine. The pressure decreases after some
work is done in the turbine. Steam after leaving the turbine pass through
the condenser which maintains the low pressure at the exhaust of the
turbine.

The pressure of the steam in the condenser depends on the flow rate and
temperature of the cooling water flow, and on the effectiveness of the air
removal equipment. Water circulating through the condenser may be
taken from various sources such as rivers, lakes, or the sea.

If insufficient water is not available, the hot water coming out of the
condenser can be cooled in cooling towers and circulated through the
condenser again. Bled steam from the turbine at extraction points is sent
to low-pressure and high-pressure water heaters.

The air taken from the environment is first passed through the air
preheater, where it is heated by exhaust gases. The hot air then passes
through the furnace. The exhaust gases flow through the dust collector
and then through the economizer, and air pre-heater, and finally, they are
exhausted into the atmosphere through the chimney.

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Factors for Selection of Site for Thermal Power

Plant
The following factors are to be considered for the selection of the site:
#1 Availability of Coal

The coal should be available in sufficient quantity nearer to the plant at a

low cost.

#2 Ash Disposal Facilities

There must be sufficient space to dispose of a large quantity of ash.

#3 Space Requirement

Sufficient land should be available for the construction of the plant at a

low cost with future expansion scope.

#4 Nature of land

The site for the plant should have good bearing capacity to withstand the
dead load of the plant.

#5 Availability of water

A large quantity of water should be available for drinking, condensing,

disposal of ash, and as feedwater at a low cost throughout the year nearer
to the site.

#6 Transportation facilities

The site should be connected by suitable transportation lines such as road

and rail to bring the machinery, coal, etc.

#7 Availability of labor

A cheap and large number of laborers should be available at the proposed

site as a large number of laborers are required during the construction of
the plant.
#8 Public problem

The site should be away from the towns to avoid the nuisance of smoke,
fly ash, etc.

#9 Nearness to the load centre

The site should be nearer to the load center to reduce transmission costs
and losses.

• The initial cost of the plant

• The nature and magnitude of the load to be handled.
• The necessity of future expansion of the plant.
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Materials Required for Thermal Power Plant

The following basic materials are essentially required by the thermal
power plant:

1. Feedwater
2. Coal
3. Cooling water.
4. Water for ash disposal.
5. SO2
6. Air
1. Feedwater

The feed water is the water circulated through a closed circuit of the
power plant which is further converted into steam in the boiler. For
example, a plant of 100 MW capacity may require nearly 500 tons of water
per hour to be circulated through the system
2. Coal

The coal is required for converting the feed water into the steam in the
boiler. A sufficient quantity of coal is required. So that the plant should
run without any stoppage due to the coal shortage. Nearly 1500 tons/day
coal is required for 100 MW capacity plant generating 5 kg/kWh of steam.

3. Cooling water

The cooling water is required for condensing the steam coming out from
the turbines. Nearly 25000 tons/hr quantity of water is required for a 100
MW plant.

4. Water for ash disposal

A large quantity of water is required for disposing of the ash. Nearly 5 kg

of water is required per kg of ash disposal.

5. SO2 (Low Sulfur contains coal)

We should always be required to have low sulfur content coal because on

burning such coal generates SO2 and it is highly poisonous to human and
animal health and as well as for the crops. Nearly 1.8 tons/hr amount of
SO2 is coming out by burning the coal containing sulfur up to 1 to 1.5% in
100 MW capacity plant. This SO2 should be properly removed from the
exhaust gases through improved technology.

6. Air

Air is required for the combustion of the fuel as well as required for
cooling the water in the cooling tower. Nearly 1200 tons of air per hour for
a 100 MW capacity plant, in addition to this nearly 25000 tons of air per
hour is to be required for circulating in the cooling tower.

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Types of Fuels Utilized in Thermal Power Plant

Following are the types of fuels utilized in thermal power plants:
 1. Natural gas
2. Coal
3. Oil
4. Geothermal energy
5. Nuclear fuel
6. Waste heat from industrial process
7. Biomass – These plants are fuelled by waste from sugarcane,
landfill methane and municipal waste, etc.
8. Solar heat
9. Blast furnace gas.
Advantages of Thermal Power Plants
The following are the advantages of thermal power plants:

1. The fuel cost of the thermal power plant is relatively low.

2. Thermal energy can be produced everywhere in the world.
3. The heat production system is simple compared to other
systems.
4. The overall system is cost-effective.
5. Easy mechanism.
6. The same heat could be reused.
7. Easier maintenance of the power station.
8. The use of water is prominent here, therefore any place with
ample water is a perfect location for installing a thermal
power plant.
9. These plants require comparatively small space to be
installed.
10. Its construction cost is cheaper due to the nearness of
urban areas.
11. These plants are completed within a few years.
12. They are generally located near the urban areas.
13. The scope of expansion is unlimited.
14. These are located in a place where the displacement of
people is minimum.
15. They can be located near the consumption centers.
16. The cost-benefit ratio is always better than the hydel
power plant.
Disadvantages of Thermal Power Plant
The following are the disadvantages of thermal power plants:

1. The raw materials used are exhaustible resources,

2. The ability of these plants depends on the quality of the coal.
3. High maintenance cost.
4. High production of CO2 in the atmosphere.
5. Exhaust gases harm the environment badly.
6. Low overall efficiency.
7. Thermal engines require a huge amount of lubricating oil that
is very expensive.
8. Nuclear thermal power plant demands an excessive amount
of water for cooling purpose.
9. Coal-type thermal power plant requires a larger duration
before it supplies the generated power to the grid.
10. This type of power station is ultimately responsible for
the rise in seawater levels.
11. Shorter life span.
12. It is very difficult to maintain the optimum supply for a
long period.
Turbines

What is a Steam Turbine?

A steam turbine is a mechanical device that transforms the
thermal power of steam into mechanical work in form of
rotational energy. This turbine is known as a steam turbine
because it uses steam as a working fluid.

In 1884, the first steam turbine was discovered by Sir Charles

A. Parsons. Steam turbines are most commonly used to generate
electricity in thermal power plants, as well as in various industrial
applications that need mechanical power.

In this turbine, the mechanical work generates with the help of the turbine
shaft. This shaft is coupled with the steam generator (as shown in the
below diagram). The steam generator converts the turbine shaft’s
mechanical power into electrical power.

The speed of the steam turbine is directly proportional to the output

power. Therefore, the steam turbines must work at the highest speed if
you want to achieve the highest output. The wheel turbines can’t rotate at
high speed like a steam turbine.
These turbines have many advantages over other types of turbines such as
steam turbines produce inexpensive electricity, and steam energy doesn’t
pollute the environment.

Due to these reasons, these turbines use reciprocating engines as prime

movers in large power plants. The steam turbines work on the basic
principle of thermodynamics. Therefore, when the steam expands, its
temperature drops.

Steam Turbine Working Principle

A steam turbine works on the basic principle of the Rankine cycle.
The basic principle of a steam turbine involves the expansion of high-
pressure steam through a series of stages, where it passes over sets of
stationary and rotating blades.

During the working of a steam turbine, first of all, water from an external
source (such as a river, sea or canal) is transferred into the boiler section
with the help of a pump. The boiler boils the water to a very high
temperature so that water can convert it into supersaturated steam.
In the boiler, the rate of steam generation varies according to the
combustion heat, flow rate, and the heat transfer surface area used. As the
steam is produced, it is directed from the boiler to the turbine area. As the
steam enters the turbine area, the pressure energy of the steam is
transformed into K.E. by passing it via a nozzle.

As the steam strikes the rotor blades, it creates dynamic pressure on the
shaft and rotor blades. Due to this reason, both the shaft and the blades
start rotating in an identical direction. Due to this process, the steam’s
thermal energy transforms into the rotational energy of the rotor blade,
and the rotor starts rotating.

A shaft is coupled with the turbine rotor. The shaft receives rotational
energy from the rotor and starts rotating.

A generator called a steam generator connects to the shaft via a coil. The
shaft rotates the generator coil in a magnetic field. As the coil rotates in a
magnetic field, electricity generates and flows inside the wires.

Due to the simple construction of steam turbines, the vibration is much

lower than with other engines with the same speed.

Types of Steam Turbines

There are multiple types of steam turbines designed according to their
different operations and their industrial importance. The types of steam
turbines are given below:

1) Based on the point of steam entry

i. Center admission turbine

ii. End admission turbine
2) Based on the application

i. Marine turbine
ii. Industrial turbine
iii. Utility turbine
3) Based on the pressure of the turbine

i. Low-pressure turbine
ii. Medium pressure turbine
iii. High-pressure turbine
4) Based on the exhaust condition of the turbine

i. Extraction cum condensing turbine

ii. Extraction turbine
iii. Backpressure turbine
iv. Straight condensing
5) Based on the steam flow

i. Radial flow turbine

ii. Axial flow turbine
6) Based on turbine blade design

i. Reaction Turbines
ii. Impulse Turbines
1) Based on the Exhaust Condition of the Turbine
In this category, the steam turbine has the following three types:

i) Condensing Steam Turbines

In these types of steam turbines, steam enters the turbine by a control
valve. The name of condensing turbine represents that the steam inside
the turbine can’t expand because this turbine is for condensing purposes.
Besides, the blade will get wet during the final phase.

The exhaust steam condenses in the condenser and the condenser

transforms this steam into water. This condensed water is again used in
the boiler to generate steam. These turbines are most common
in hydroelectric power plants.
ii) Back Pressure Steam Turbine
In this turbine, the steam in the turbine doesn’t expand completely. After
partial use of the steam thermal energy inside the turbine, all of the steam
is released at a specific temperature and pressure.

The steam parameters at the discharge are determined according to the

process requirements.
iii) Extraction Cum Condensing Turbine
The extraction cum condensing turbine has two inlet valves. The first
stage of the turbine is known as the “High Pressure (HP) stage,” and the
second stage is known as the “Low Pressure (LP) stage.”

As the HP phase completes, some steam is released. The remaining steam

enters the LP stage, where it is condensed further at low pressure.
2) Types According to Heat Drop Process
In this category, steam turbines have the following types:

i) Condensing turbine with generator

In this type of turbine, steam is sent to the condenser chamber at a
pressure below than the atmospheric pressure.

In this turbine, the steam is discharged from the intermediate stage and
used to heat the feed water. The exhaust steam’s latent heat during the
condensation process is dropped completely.

ii) Condensed turbines with various intermediate

extraction stages
In this steam turbine type, the steam is discharged from the intermediate
phase and used for industrial heating applications.
iii) Back Pressure Turbines
In the back pressure turbine, the exhaust steam utilizes for heating or
industrial applications. It is also possible to use a reduced vacuum turbine
where the exhaust stream can be utilized for heating and processing
applications. These turbines are also known as non-expanding turbines.

The turbine’s mechanical energy is utilized to operate mechanical or

electrical devices such as compressors, fans, pumps, etc. These steam
turbines have an easy configuration. They need very low or no cooling
water.

These turbines have a low price as compared to extraction steam turbines.

Back pressure steam turbine doesn’t reject heat during condensation;
therefore, it has high efficiency.
Back Pressure Turbine

iv) Topping Turbine

In the topping turbine, the exhaust steam is used in low-pressure and
medium-pressure condensing turbines. The topping turbine work under
higher initial steam temperature and pressure conditions. These turbines
are used primarily to expand the capacity of power plants.
3) Types according to the steam conditions at the turbine inlet
The steam turbine has the following types in this category:

i) Supercritical Pressure Turbines

These turbines use steam with a pressure greater than 225 atm.
ii) Ultra-high Pressure Turbine
It uses a temperature of 550° C or more and a steam pressure of 170 atm
or more.

iii) High-Pressure Turbine

It uses steam with pressures of more than 40 atm.

iv) Medium Pressure Turbine

These turbines consume up to 40 atm of steam pressure.

v) Low-Pressure Turbines
These types of steam turbines use steam with a pressure of 1.2 atm to 2
atm.
4) Types according to industrial use
According to the industrial applications, the steam turbine has the
following types.

i) Stationary turbines with constant speed

These turbines are mainly used to drive alternators.

ii) Stationary turbine with variable speed

These turbines are used to power pumps, air circulators, turbofans, and
more.

iii) Variable speed transient turbine

These turbines are typically used on railroad locomotives, ships, and
steamers.

5) Types According to Blade Design

According to the design of blades, steam turbines divide into two main
types.

i. Reaction Turbine
ii. Impulse Turbine
i) Reaction Turbine
In the reaction turbine, the steam flows through the blades. Then, it
expands on both the moving blades and fixed blades of the turbine.
Moving and fixed blades have a continuous pressure drop.

Reaction turbines are a little bit dissimilar from impulse turbines, which
consist of fixed nozzles and moving blades. As compared to impulse
turbines, reaction turbines have a lower pressure drop per stage. A
reaction turbine is generally more efficient.
An example of a reaction turbine is a Parson’s turbine. The reaction
turbine requires twice as many rows of blades as the impulse turbine for
the conversion of the same heat energy.

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ii) Impulse Turbine

It is one of the most famous types of steam turbines. In the case of an
impulse turbine, the steam exits the fixed nozzles at a very high speed and
hits the fixed vanes around the rotor.

The blade deflects the steam flow deflection without changing the
pressure. The shaft of the turbine rotates due to the changes in impulse.
In these turbines, steam which is injected at a very high speed from a fixed
nozzle hits the blades attached to the rotor. The blade changes the path of
the steam flow without varying the steam pressure.

The force generated by the change in torque causes the turbine shaft to
rotate.

Components of a Steam Turbine

The steam turbine has the following major parts:

1. Housing
2. Rotor blades
3. Rotor
4. Governor
5. Turning Gears
6. Sentinel Valve
7. Nozzle ring and reversing blade assembly
8. Labyrinth Seal

1) Housing
The housing bears all low-weight and high-weight operating loads. The
rotor, blades, governor, and many other internal components are installed
inside the turbine housing.
It designs in such a way that it minimizes the thermal load. It provides
safety to all the internal parts of the steam turbine.

2) Rotor
The rotor has multiple buckets that rotate with the rotor’s movement. It
has a shaft. One side of the shaft uses to connect the driven pump, and the
other end of the shaft uses for the speed controller and the quick speed
trip system.

It is a key part of a steam turbine that converts the thermal energy of the
steam into mechanical power.

3) Blades
These blades use to extract the energy of the high-velocity steam and
transfer it to the rotor. The design of these blades plays an important role
in turbine efficiency.

4) Governor
The governor system is a speed-dependent control system that installs in
a steam turbine. It is also known as a Controller. It uses to control the
speed of the turbine.

A governor valve installs to control the turbine speed by changing the flow
of steam by the turbine. It has a servo motor system, a counterweight with
a spring return, and a steam valve.

This turbine component records the speed of the turbine shaft via a direct
assembly or a magnetic pulse from the gear.
The variation in the outlet and inlet conditions of the steam turbine and
changes in the power required from the pump cause changes in the speed
of the turbine. This variation in speed causes the governor weights to be
rearranged, followed by the governor valves.

5) Labyrinth seal
The labyrinth seal is a method to reduce leaks from the high-pressure side
to the low-pressure side by permitting a small leak. The space between the
shaft and the labyrinth is kept as small as feasible.

6) Nozzle ring and reversing blade assembly

The nozzle ring is installed to the lower inner half of the steam end casing.
The nozzle installs inside the nozzle ring. It guides the steam from the
steam chamber to the 1st row of blades in the Curtis stage. The Curtis stage
contains two rows of blades.

The assembly of the reversing blade most commonly installs in between

the Curtis stage blade rows. This assembly attaches to the nozzle ring.
The main function of the reverse blade assembly is to reverse the
flow of steam as the steam leaves the Curtis stage blades in the 1st row and
directs the steam to the Curtis stage 2nd row blades.

7) Sentinel Valve
The sentinel valve works as a warning device. It installs on top of the
turbine outlet end casing, which shows that the pressure in the turbine
outlet end case is too high.

When the casing pressure becomes more than a certain level of operating
pressure, the sentinel valve leaks a small amount of steam into the
environment. During this leaking process, this valve produces an audible
noise. You can’t use this valve as a safety valve.
8) Turning Gears
These gears are usually used in large turbines. This gear slowly turns the
rotor during the heating and cooling process. This is to keep the rotor or
shaft at a near-uniform temperature around the perimeter to maintain
straightness and balance.

How to Calculate Steam Turbine Efficiency

A steam turbine has two different types:

1. Impulse reaction turbine

2. Reaction steam turbine
Both types of steam turbines work on different principles (as discussed
above). Therefore, these have different efficiency, but the below-given
formula can calculate the efficiencies of these turbines:

In the above-given equation, the input kinetic energy varies according to

the absolute velocity of the steam at the turbine inlet. While the work done
is dependent on many factors such as the steam’s relative velocity,
reduction in the amount of steam heat in the turbine, the angle of the
blade, and the guide vane’s angle at the turbine inlet.

In some cases, due to these factors, it is very hard to compute the work
done, and sometimes it is impossible to precisely calculate some specific
features such as steam pressure, temperature, and velocity.

The following are two various methods to calculate steam efficiency:

1. Blade efficiency (ɳb)

2. Stage efficiency (ɳs)
The steam velocity is used to calculate the blade efficiency (ɳb). In
contrast, the variation in the steam enthalpy uses to calculate the stage
efficiency (ɳs). The enthalpy describes the heat capacity of steam.
In both cases, the guide vane angle on the inlet side is indicated by α1, and
it performs a vital function in turbine efficiency. The cosine of this angle
performs a central function in determining the efficiency of the impulse
and reaction steam turbines.

The below-given diagram represents the blade efficiency for the impulse
and reaction turbines.

Figure: Blade efficiency of the reaction and impulse steam turbines

The above diagram is indicating clearly that an impulse turbine is less

efficient than a reaction steam turbine.

The highest efficiency of the impulse turbine can be attained by setting the
angle of the inlet blade at zero. This is because this angle minimizes
friction by decreasing the blade’s surface area.

You can also connect multiple turbines in series to maximize steam energy
before the steam is returned to the condenser. The stage efficiency
computation technique works best in this type of turbine assembly.
Steam Turbine Efficiency Formula
The steam turbine efficiencies can be calculated by the following formulas:

Isentropic Efficiency:- It is a ratio between the actual work and the

Isentropic work of the turbine.

CHP Electrical Efficiency:- It is a ratio between the net electricity

generated and the total fuel in the boiler. The following equation uses to
calculate it:

CHP electrical efficiency = Net electricity generated/Total fuel into

the boiler

Total CHP Efficiency:- It uses to measure the electricity and steam

produced by the total fuel inside the boiler. Total CHP efficiency can be
calculated by the following formula.

Total CHP efficiency = (Net steam to process + Net electricity

generated)/Total fuel into the boiler
P-V Diagram of Steam Turbine
A steam turbine works on the base of the Rankine cycle. A Rankine cycle
is an ideal thermodynamic cycle of a heat engine that transforms the heat
energy into mechanical work while undergoing a phase change.

The P-V diagram of the steam turbine is given below:

• Isentropic compression: In the above diagram, line 1-2

represents the isentropic compression stage. In this cycle, the
 liquid pumps from low pressure to high pressure. During this
process, the pump needs very low power for pumping liquid.
• Isobaric Heat Supply: Line 2-3 represents to isobaric heat
supply process. The high-pressure water goes into the boiler,
where it is heated via an external heat source at constant
pressure to convert it into dry saturated steam.
• Isentropic expansion: Line 3-4 represents the isentropic
expansion process. During this process, the dry saturated
steam is expanded by the turbine to produce electricity. In this
process, condensation occurs due to the reduction of pressure
and temperature of the steam vapors.
• Isobaric heat rejection: Line 4-1 represents to Isobaric
heat rejection process. During this process, the wet water
vapors enter the condenser, where they condense to a
saturated liquid at constant pressure.

Advantages and Disadvantages of Steam Turbine

The steam turbine has the following advantages and disadvantages:

Advantages of Steam Turbines

• They have a high thermal efficiency (i.e., 40%-60%)
• Steam turbines are designed for a wide range of power outputs,
from small-scale applications to large-scale power plants
generating hundreds or thousands of megawatts.
• They have long operational life and high reliability.
• They have the capability to use different fuel sources for steam
generation.
• They environmental friendly.
• Steam turbines have smooth and quiet operation.
• They can be connected with renewable energy sources to
produce cheap and environmentally friendly power.
• The electricity produced by a steam turbine has a relatively
low cost.
Disadvantages of Steam Turbines
• It has a high initial cost.
• These turbines have a complex design.
• They require regular maintenance.
• They have multiple stages and blade configurations.
 • The maintenance of these turbines is very hard.
• It has a longer start-up time as compared to a gas turbine and
is longer than a reciprocating engine.
• The steam turbine needs a large installation space.
• They are most efficient when working according to their
capacity. When operating at part load, the efficiency of the
turbine may reduce, making it less economical in situations
where variable power output is needed.

Applications of Steam Turbines

• Electricity Generation: Steam turbines are most commonly
used in thermal power plants for electricity production. In
thermal power plants, nuclear energy or fossil fuel (oil, natural
gas, or coal) is utilized to heat water and generate high-pressure
steam that is used to drive the turbine and, in turn, electricity
produces.
• Industrial Processes: They can be employed in different
industrial applications that need mechanical power, such as in
pulp and paper mills, chemical plants, and the oil and gas
industry.
• Waste-to-Energy Plants: In the waste-to-energy plant,
municipal solid waste is used to produce steam, which runs
steam turbines to generate electricity. This process assists to
lower the volume of waste going to landfills and produces
renewable energy at the same time.
• Cogeneration (Combined Heat and Power, CHP): In
cogeneration plants, they use to generate both useful heat and
electricity for different processes or district heating systems.
• Geothermal Power Plants: Steam turbines are used in
geothermal power plants, where steam is generated by utilizing
the Earth’s natural heat.
• Solar Thermal Power Plants: Solar thermal power plants
utilize a concentrated solar power (CSP) system to heat a liquid,
which is then utilized to generate steam. The output steam is
used to drive a turbine for electricity production.
• Biomass Power Plants: In the biomass power plant, these
turbines are used to produce electricity. In this power plant,
organic matters such as agricultural waste, wood, or dedicated
energy crops are combusted to produce steam.
• Marine Propulsion: Steam turbines are employed in marine
propulsion, mainly for large ships such as naval vessels and
ocean liners.
Steam Turbine VS Steam Engine
The main difference between the steam turbine and the steam engine is
given below:

Steam Turbine Steam Engine

Uses high-pressure steam to move a piston in a

Uses high-pressure steam to rotate a series of blades,
cylinder, converting thermal energy into reciprocating
converting thermal energy into rotational energy
motion

Steam engines generate extreme noise while

Steam turbines are usually quieter operating due to the reciprocating motion of the
piston and other parts.

It needs regular maintenance It is easier to maintain because of simple design

It has multiple stages and blade configurations It has fewer moving parts

It has ability to produce a large amount of power It usually generates less power

These turbines have more complex design due to

Steam engines have simpler design
multiple stages and blade configurations

They are used in large-scale power production plants They are ideal for smaller-scale applications

It works at high speeds, usually in the range of It works at lower speeds, usually in the range of tens
thousands of RPM to hundreds of RPM

Steam turbine has higher efficiency (up to 40-60%) Steam engine has lower efficiency (normally about
than steam engine because of the continuous 10% to 20%) due to energy losses in transforming
expansion of steam and fewer energy losses reciprocating motion to rotary motion

They are most commonly employed in large-scale They are employed in ships, locomotives, and
power generation applications. stationary engines for industrial applications
control and auxiliaries in thermal power plant
In a thermal power plant, control and auxiliary systems are crucial for the safe,
efficient, and reliable operation of the main power generation process. Here’s a
breakdown of their roles and functions:

### Control Systems:

Control systems in a thermal power plant are responsible for:

1. **Boiler Control:** Regulating the combustion process in the boiler to

maintain optimal temperature, pressure, and fuel-air ratio. This includes control
of fuel supply, air supply (combustion air), and boiler feedwater.

2. **Turbine Control:** Monitoring and controlling the steam flow through the
turbine to ensure it operates within safe limits and efficiently produces
electricity. This involves controlling steam inlet conditions, throttle pressure,
and governing speed.

3. **Generator Control:** Managing the output of the generator to match the

electrical demand and maintain grid stability. This includes voltage regulation,
frequency control, and synchronization with the grid.

4. **Plant Automation:** Integrating various subsystems (like boiler, turbine,

and generator controls) into a cohesive automated system for efficient operation
and response to varying load demands.

### Auxiliary Systems:

Auxiliary systems support the main power generation process by providing
necessary services and ensuring the plant operates smoothly. They include:

1. **Fuel Handling System:** Stores, transports, and supplies fuel (typically

coal, oil, or gas) to the boiler in a controlled manner.

2. **Water Treatment System:** Prepares feedwater to remove impurities that

can cause corrosion or scale buildup in the boiler and turbine. This ensures
efficient heat transfer and prevents equipment damage.

3. **Cooling Water System:** Circulates water to cool various equipment, such

as condensers and auxiliary systems, to maintain optimal operating
temperatures.

4. **Ash Handling System:** Collects and disposes of ash and other

combustion by-products from the boiler to maintain cleanliness and prevent
environmental contamination.
5. **Air and Gas Systems:** Provide combustion air to the boiler and manage
exhaust gases, including emission control systems to meet environmental
regulations.

6. **Electrical Systems:** Include transformers, switchgear, and protection

systems that distribute and protect electrical power within the plant.

### Importance:
Control and auxiliary systems ensure the thermal power plant operates safely,
efficiently, and reliably. They contribute to:

- **Operational Efficiency:** Optimizing fuel consumption, heat transfer

efficiency, and electricity generation.
- **Safety:** Monitoring and controlling critical parameters to prevent
equipment failures and unsafe conditions.
- **Reliability:** Ensuring continuous operation and quick response to load
changes or disturbances.
- **Environmental Compliance:** Managing emissions and waste disposal in
accordance with regulatory standards.

In summary, control and auxiliary systems are integral to the overall functioning
of a thermal power plant, supporting the primary goal of generating electricity
efficiently while meeting environmental and operational standards.
Site Selection for Hydroelectric Power Plant:
The Site Selection for Hydroelectric Power Plant includes several structures like
dam, conduits intakes, surge tank, power house and many others. It requires
several investigation and study to determine the most economical solution.

The following factors must be considered while on site selection for hydroelectric
power plant.

• Water availability
• Water storage
• Water head
• Accessibility of the site
• Distance from load centre
• Environment Aspects
Water Availability
The most important aspect for a hydel power plant is the water availability at the
site because all designs are based on it. Therefore the run-off data for the
proposed site should be available. It may not be possible to have run-off data but
data as rainfall over the catchment area is always available.

From the data available, estimate should be made about, average quantity of
water available, minimum and maximum quantity of water available throughout
the year can be determined. The details of availability of water is necessary:

• To setup peak load plants such as steam, diesel and gas turbine plant.
• To decide the capacity of hydel electric plant.
• To provide spillways (or) gate relief during flood period.
Water storage
There is a wide variation in rainfall over the year, so it is required to store water
for continuous generation of power. By using mass curve, the storage capacity
can be calculated. The expenditure on the project depends upon maximum
storage.

There are two types of storages.

• The storage is constructed to provide water for one year. In this case storage is full at
the begin of the year and becomes empty by the end of year. So there is no shortage of
water through out the year.
• The storage is constructed to provide water in sufficient quantity even during the
worst dry periods.
Water head
The available water head depends upon the topological conditions. To generate
required quantity of power, it is necessary to provide large quantity of water at a
sufficient head. An increase in head, for a given output reduces the quantity of
water to be supplied to the turbines. Hence water is supplied to the turbine at
high potential.
Accessibility of the site
The Site Selection for Hydroelectric Power Plant should be easily accessible in
order to use the electrical power generated. Because once the electricity is
produced it must be delivered where it is needed (homes, schools, office) etc., and
power must be transmitted over some distance to its users near the plant site.
The site should have transportation facilities of rail and road.
Distance from load centre
It is a supreme importance that the power plant must be setup near the load
centre. If distance between the load centre is less from power plant, then cost of
erection is reduced and maintenance of transmission line will be easier.
Environment Aspects
The land selected should be efficient and economical for the purpose of selection.
The projects should be designed on the basic of best available information to
enhance the local environment, and be in the best public interest.

The Site Selection for Hydroelectric Power Plant should fulfill the following
requirements.

• To assure safe, productive, healthy and culturally pleasing environment.

• To preserve important cultural, historic and natural aspects of site.
• To avoid health hazards and unintended consequences.
• The land selected for the site should be cheap and rocky.
Hydro Power Plant Layout
Contents show

In hydro power plant, the energy of water is used to move

the turbines which in turn run the electric generators. The energy of the
water used for power generation may be kinetic or potential. The kinetic
energy of water is its energy in movement and is a function of mass and
velocity, while the potential energy is a function of the difference in level
per head of water between two points.

In either case, continuous availability of water is a basic necessity, to

ensure this, water collected in natural lakes and reservoirs at high
altitudes may be used or water may be stored by constructing dams
across flowing streams.
Hydro-power is a conventional renewable source of energy that is clean,
free from pollution, and generally has a good environmental effect, but it
requires a large investment and involves the increased cost of power
transmission.

Hydro power plants are developed for the following purposes :

1. Generation of electricity at low cost.

2. To control the floods of the rivers.
3. Is to store the water for drinking and irrigation.
4. To develop the surrounding area.
Importance of Hydro-electric Power Plant
Water is the naturally available renewable source of energy. The power
generation from a hydroelectric power plant is clean and free from
pollution, generally, it has a good environmental impact.

The main aim of a hydro-electric power plant is to harness power from water flowing under pressure.
Nearly 30 to 35% of the total power generation of the world is met by a hydro-electric power plant.

Hydro-power plants are also developed for the following advantages:

1.
To control the floods of the rivers.
2.
Is to develop the irrigated lands.
3.
To have storage of drinking water.
4.
The running cost of these plants is very low compared to other
power plants.
5. Greater control over the turbines.
6. High reliability compared to other plants.
7. Absolutely no fuel charges.
8. The load can be varied quickly as per the changing demand.
9. These plants have no disposal problem
10. These plants have no environmental problems.
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Storage and Pondage:
During the rainy season, when the stream is in flood it carries a huge
quantity of water as compared to the stream in other times of the year i.e.
the quantity of water carried by it is very less. However, the demand for
power normally does not match such variation in the natural flow of the
stream.

Therefore, some arrangement in the form of storage and pondage of

water is required for the proper handling of the flow of water so as to
make it available in important quantity to meet the power demand at a
given time.

Storage

The storage may be defined as the impounding of a considerable amount

of excess runoff during seasons of surplus flow for use in dry seasons.
This is achieved by constructing a dam across the stream at a suitable site
and building a storage reservoir on the upstream side of the dam.

Pondage

The pondage may be defined as a regulating body of water in the form of

a relatively small pond or reservoir provided at the plant. The pondage is
used to regulate the variable water flow to meet power demand. It helps
in short term variations which occur due to:

•Sudden rise or drop in load on the turbine.

• Sudden changes in the inflow of water.
• Change of water demand by turbines and the natural flow of
water from time to time.
The turbines are required to meet the power demand higher than the
average load when the pondage supplies the excess quantity of water
required during that period.
Pondage increases the capacity of a river over a short time, such as a
week.

Storage, however, increases the capacity of a river over an extended

period of 6 months to as much as 2 years.
Factors to be considered for Selection of Site
for Hydro Power Plant:
Following factors should be considered while selecting the site for hydro-
power plant :

1. Availability of water: Large quantity of water should be

available throughout the year at the proposed site.
2. A requirement of head flow availability and storage capacity.
3. The character of the foundation, particularly for the dams.
4. The land should be cheap and rocky.
5. The topography of the surface at the proposed location.
6. Accessibility of the site i.e. the site should have transportation
facilities like road and rail.
7. Nearness to the load centre.
8. Availability of the materials for the construction.
9. Arrangement and type of dam, intakes, conduits, surge tank
and powerhouse.
10. Cost of project and period required for completion.
11. Impacts of water pollution.
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Hydropower Plant Layout

A simple layout of the hydropower plant as shown in fig. 2.3. It consists of
the catchment area, reservoir, dam, slice gate or valve, surge tank,
penstock, inlet valve, turbine, draft tube, powerhouse equipment, tailrace,
etc.
The collected water from the reservoir is supplied from the dam through
slice gate, penstock, inlet valve to the turbine. The turbine converts the
potential energy of the water into mechanical energy to run the generator.
The generator produces electric power. After doing the work water flows
into the tailrace through draft tube.

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Components for Hydro Power Plant Layout:

Following are the essential components of the hydro-power plant:

1. Catchment area
2. Reservoir
3. Dam
4. Spillways
5. Penstock
 6. Surge tanks
7. Prime movers
8. Draft tubes
9. Powerhouse and equipment.
#1 Catchment Area

The whole area behind the dam draining into a stream or river across
which the dam has been built at a suitable place is called the catchment
area.

#2 Reservoir

It is the area where the water is stored and utilized for power generation.
A reservoir may be natural or artificial.

A natural reservoir is a lake in high mountains. An artificial tank is built by

erecting a dam across the river.

#3 Dam

A dam is a barrier built across the river to store the water for power
generation. Dams are built of concrete or stone masonry, earth, or rockfill.
The dam stores the water on one side and on the other side, it is having a
powerhouse to generate the power.

#4 Spill Ways

It is a safety valve for a dam. It is provided to discharge the excess water

from the dam to safeguard the dam against floods.

#5 Penstock

It is a pipe connected between the surge tank and prime mover, usually,
these are of steel-reinforced concrete pipes.

#6 Surge Tank

There is a sudden increase in pressure in the penstock due to the sudden

decrease in the rate of water flow to the turbine when the gates admitting
water to the turbines are suddenly closed owing to the action of the
governor.

This happens when the load on the generator decreases. This sudden rise
of pressure in the penstock above normal due to reduced load on the
generator is known as the “water hammer”.

A surge tank is a small reservoir employed between the dam and the
powerhouse nearer to the powerhouse to reduce the pressure swings in
the penstock by allowing the excess water to enter into the surge tank
during low load periods and the stored water can be supplied to the
penstock during high load periods.
#7 Prime Mover

These are the turbines used to convert the kinetic energy of the water into
mechanical energy to produce electric energy.

#8 Draft Tube

It is a diverging discharge passage connected to the tailrace. It supports

the runner in utilizing the remaining kinetic energy of the water at the
discharge end of the runner.

#9 PowerHouse

A powerhouse consists of two main parts, a substructure to support the

hydraulic and electric equipment such as turbines,
generators, valves, pumps, governors, etc., and a superstructure to house
and protects these types of equipment.

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Types of Hydro Power Plan
Different types of hydro power plants can be classified as follows:

1. According to the availability of head

1. High head power plants
2. Medium head power plants
3. Low head power plants.
2. According to the nature of the load
1. Base load plants
2. Peak load plants.
3. According to the availability of water
1. Runoff river plant without pondage
2. Runoff river plant with pondage
3. Storage type plants
4. Pump storage plants
5. Mini and micro-hydel plants.
Based on the Availability of Water Head
According to the available water head, the power plants classifies into three types,
Low head plants
In this type of hydroelectric power plant, the available water head is less than 30m. In
this type of plant, by constructing a dam, the water is stored. And the power plant is
constructed at the base of the dam.
If the excess water is available in the dam, it will flow over the dam itself. In this type
of plant, Francis, propellor, or Kaplan type turbines are used in most of the cases.
Medium head plant
The hydroelectric power plant which has an available water head of 30m to 100m is
considered a medium head plant. In most cases, the Francis turbine is used in this
type of power plant.
High head plant
The hydroelectric plant having an available water head is more than 100m consider a
high head plant. In this type of plant, a bulk amount of water is available in the dam
from the rain or melting of snow.
These plants are constructed in hilly areas to achieve high water head. In most cases,
these plants are constructed on big rives in which the water is available throughout the
year.
The high head plant uses Francis turbine up to the head of 300m and Pelton turbine
uses if the available water head is more than 300m.
Based on the Nature of the Load
Two types of load can be connected with the power plant. The plant running
continuously throughout the day is said to be a base load plant. And the plant which
is used to meet the peak demand is known as peak load plants.
According to the type of load connected with the plant, the hydroelectric plants are
classified into two types;
Base load plant
These plants are used to take a load on the base portion of the load curve of the power
system network. The base load plants are large capacity plants as it is built to meet
the demand of the base load.
The load factor of these plants is very high. In most cases, these plants are runoff river
or storage type plants
Peak load plant
The hydroelectric power plant that was built only to meet the peak portion of the load
curve is known as the peak load hydropower plant.
The capacity of this plant is less than base load plants and these plants are turned ON
only while the peak demand of load and after this plant turned OFF. Therefore, these
plants are used to run for a short duration of time.
In most cases, these plants are runoff river plants with pondage or storage type of
hydel plant.
Based on the Quantity of Water Available
According to the quantity of water available to generate electric power, the
hydroelectric power plants are classified into five types;
Run-off river plants without pondage
This type of hydropower plant does not store water. It uses the water directly from the
river. The power output of these plants is not constant. Because there is no control
over the availability of water. Hence, the power output fluctuates and the utility of this
plant is very less compared to other plants.
Run-off river plants with pondage
In this type of plant, a pond is constructed behind the dam and near the plant. This
pond increases the utility of the power plant.
To meet fluctuating loads, the capacity of the pond decides based on the 24 hours
fluctuation in load demand. This plant can be used as a base load as well as a peak
load plant.
Storage type plant
This type of plant uses a reservoir to store water. In some areas where the water is
available in rainy seasons only. In this area, the storage type of plants is used to store
water in bulk amounts and use in dry seasons.
The storage type of plant can be used as base load and peak load plant. The capacity
of the plant decides by the water storage capacity of the reservoir.
Pumped storage peak load plant
This type of plant is used to meet the peak load demand. It has a reservoir to store the
water. When the load demand is high, it used the water of the reservoir. And when the
load demand is reduced, this plant is designed with a pump that is used to supply
water from tailrace to head race.
The pumped storage plants are used to run along with the steam (thermal) power plant
to improve the overall efficiency of a combined power plant. The pump of this plant is
energized from the secondary power plant like run-off river plant or nuclear plant.
In this plant, the required water is very less compared to other hydropower plants.
Mini and micro hydel plant
Mini and micro hydropower plants are used to meet the power crises. Mini power
plants work in the range of 5 to 20 m head and micro power plants work in the range
of fewer than 5 m available water head.
This plant is a small capacity plant. and the time required and cost to build this plant
are less compared to other hydroelectric plants. The mini-Hydropower Plant uses a
special type of turbine known as bulb type turbine.

#1 Base Load Plants

This types of power plant work independently and supply the power to the
whole load. This plant takes the load on the base portion of the load
curve. The load on the plant remains more or less uniform during the
operation period. It works for the whole time i.e. it supplies the power
when there is a requirement.

Baseload plants are generally large in capacity. The run-off-river and

storage-type plants are used as baseload plants. The load factor for such
plants is considerably high.
#2 Peak Load Plants

The peak load plants are designed for taking care of peak loads of the
demand curve. Run-off river plants with pondage and pumped storage
plants are generally used as peak load plants. These plants supply the
power to the load premises when there is a peak load period only. Rest of
the time the power is supplied by the main plant.

In these types of plants, the main power plant is always required and
hydro power plant works as a secondary plant and shares the load of two
to three hours. In case of runoff river hydro plants with poundage, a large
pound is essential and extensive seasonal storage is usually provided.

These power plants have large seasonal storage and relatively high heads
and are likely to be located on small watersheds. They store the water
during off-peak period and supply during peak periods on the top of the
load curve. The load factor of peak load plants is considerably low
compared with baseload plants.

#3 Runoff River Plants

A runoff river may be classified into two types:

1. Runoff river plant without pondage

2. Runoff river plant with pondage.
A runoff river plant without pondage is shown in the figure. This plant
does not store the water and uses the water as it comes. There is no
control over the flow of water so during high floods or low loads water is
wasted while during low run-off the plant capacity is considerably
reduced.
Due to non-uniformity of supply and lack of assistance from a firm
capacity the utility of these plants is much less than those of other types.
The head-on which these plants work varies considerably. During good
flow conditions, these plants may cater to the baseload of the system,
when flow reduces they may supply the peak demands.

Runoff river plant with pondage uses storage of water behind a dam at
the plant and increases the stream capacity for a short period, say a week.
Storage means a collection of water in upstream reservoirs and this
increases the capacity of the stream over an extended period of several
months.

The storage plants may work suitably as baseload and peak load plants.
This type of plant compared to without pondage, is more reliable.

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#4 Storage Type Plant (Reservoir Type)

A storage-type plant is one with a reservoir of sufficiently large size to

permit carry-over storage from the wet region to the dry region, and
therefore water supply is substantially constant and more than the
minimum natural flow of the water.
This plant can be used as a baseload plant as well as a peak load plant as
water is available with control when required. A simple storage plant is
shown in the figure.

It consists of a reservoir, a dam with penstock, and powerhouse

arrangements. The powerhouse is placed at the toe of the dam. The water
is allowed to store in a reservoir from the river or lakes in sufficient
quantity.

The water flows from the dam through the penstock when cresh gate is
opened to the powerhouse. In the powerhouse water with high pressure
enters the turbine to generate power. After doing the work water is
allowed to flow to the tailrace. A Pelton wheel is the common prime mover
used in such power plants.

#5 Pumped Storage Plants

The pumped storage plants are used at places where the quantity of water
available for power generation is low. Here the water passing through the
turbine is stored in a “tailrace pond”. During the low load periods, this
water is drawn back to the head reservoir applying the extra energy
available.
This water can be reused for generating power during peak load periods.
The pumping of water may be done seasonally or regularly depending on
the conditions of the site and the nature of the load on the plant.

The simple construction of the stored hydro-power plant is shown in the

figure. It consists of a headwater pond and dam, penstock connected
powerhouse with pumps and turbines, and trail race pond with the dam.
The water from the headwater pond is supplied to the powerhouse
through the penstock, where turbines are rotated for power generation.

From the turbine, the water is discharged into the tailrace pond. The water
stored in the tailrace pond is pumped back to the head reservoir with the
help of the pump during low-load periods. This water is again used for
power generation during peak load periods.

Such plants are usually interconnected with steam or diesel power plants
so that off-peak capacity of interconnecting stations is used in pumping
water and the same is used during peak load periods.

Advantages of Pumped Storage Power Plants

1. There is a substantial increase in peak load capacity.

2. Increased operating efficiency.
3. It can be used as both a base loads plant and a peak load
plant.
 4. Load the plant to remain uniform.
5. Improved load factor.
#6 Mini and Microhydel Plants

The hydro power plants working with 5 m to 20 m heads are known as

mini hydel plants and the hydel power plants working with heads less than
5 m heads are known as micro hydel plants. These plants can generate
power ranging from 100 KW to 5 MW within a period of one and a half
years.

These plants have a small reservoir with a dam and a small capacity
powerhouse using bulb turbines with a straight diverging tube that acts as
a draft tube. The water flows from a small reservoir through the small
penstock into the turbine in the powerhouse and generates the power.
After generating the power the water is discharged into the tailrace
through a draft tube.

Micro-hydel plants make use of standardized bulb sets with unit output
ranging from 100 to 1000 KW working under heads between 1.5 to 5 m.

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Advantages of Hydro Power Plant

The following are the advantages of a hydro-electric power plant:

1. Low operating cost compared to a thermal power plant.

2. The cost of generation is unaffected by the load factor.
3. No fuel charges.
4. The high useful life of about 100 – 125 years.
5. Low maintenance cost compared to the thermal power plant
6. Highly reliable.
7. It can be started quickly and synchronize the plant.
8. There is no problem with fuel and ash handling.
9. No nuisance of smoke exhaust gases and soots.
10. No health hazards due to air pollution.
11. It has no standby losses.
12. The machines used in hydel plants are robust and have
no problem with high temperatures and pressure.
 13. The efficiency of the hydel plant does not change with
age.
14. The number of operations required is considerably
small.
15. It can serve the purpose of flood control and stored
water can be used for drinking and irrigation work.
16. Less labour is required to operate the plant.
Disadvantages of Hydro Power Plant
Following are the disadvantages of a hydro-electric power plant:

1. High capital cost.

2. Power generation only dependent on the quantity of water
availability.
3. It takes a considerably long time for the construction
4. Site of the hydro-electric power station is always away from
the load centre, therefore transmission cost becomes high.
5. Sometimes isolated sites are difficult to access.

Different Types of Turbine used in Hydropower Plant

The turbines are used to convert the kinetic energy of water into mechanical energy.
According to the available water head and flow or volume of water, the hydropower
turbine is selected. The hydropower turbines are classified into two types;
• Impulse turbine
• Reaction turbine
Impulse Turbine:
As the name suggests, this turbine works on the principle of impulse. It uses the head
of water and converts the pressure of water into kinetic energy with the help of nozzles.
In some plants, one or more nozzles are constructed near the runner. This will increase
the velocity of the water. And this high-velocity water impinges on the turbine. The
turbine has a number of buckets fixed on the outer periphery of the wheel.
The bucket is used to change the direction of jet flow if required. The momentum of
water is used to convert kinetic energy into mechanical energy.
The pressure of water remains constant at atmospheric while passes through the
runner. An example of impulse turbine is Pelton turbine, cross-flow turbine;
Pelton Turbine
In a Pelton turbine, the blades are spoon-shaped and the water is allowed to strike via
a nozzle to the blade of a turbine. The blade of the Pelton turbine is also known as a
bucket. Sometimes, the Pelton turbine is also known as the Pelton wheel.
In some cases, instead of one nozzle, a set of nozzles are used to split into a number
of streams. These streams flow along the inner curve of the blade and pass in the
opposite direction. This creates an impulse on the blade of the turbine and generates
high torque by which the turbine starts rotating.
Generally, Pelton turbines are used in a hydroelectric power plant where the high head
and low flow should consider. The plants which have available water head more than
985 feet and have a reservoir of water uses the Pelton wheel.

Cross-flow Turbine
The shape of the cross-flow turbine is similar to the drum and water wheel. This turbine
is also known as the Ossberger turbine. The water strikes the rotor of the turbine. For
the first time, pressured water transfers impulse force inside the drum, and water
leaves the turbine rotor at ambient pressure.
After that, the cross-flow turbine changes the water pressure and converts it into
mechanical energy. This will be led to reduce the pressure of water and increase the
efficiency of the turbine and produce high torque that rotates the turbine and produce
mechanical energy.
Reaction Turbine
In a reaction turbine, first, the pressure energy of water is converted into kinetic energy
before supplied to the runner. So, entered water has partially pressure energy and
partially kinetic energy. After that, both energies are reduced simultaneously while
passing over the runner.
Hence, this turbine works on the principle of impulse reaction. The runner of this
turbine is under pressure (above atmospheric pressure). Therefore, the blade of this
turbine is filled with water in all conditions.
Examples of reaction turbines are Francis, Kaplan, and Propeller turbines.
Francis Turbine
Francis turbine is the most popular turbine compared to all other types of turbine used
in the hydroelectric power plant as it has high efficiency and wide range of water head.
This turbine is useful in the plant which has available water head between 130 to 2000
feet.
A Francis turbine can work on both orientations; vertical as well as horizontal. The
rapid water strikes the turbine and flows towards the center of the turbine. It leaves the
turbine axially parallel to the rotation axis once the water has flown through the turbine.
 •

Propeller Turbine
The propeller turbines are used in low-head plants. This type of turbine has a fixed or
adjustable propeller. The diameter of the propeller is large which results in slow
rotational speed.
A propeller turbine looks like a large propeller of ships and submarines. The turbine
has adjustable guide vanes. The water flow of the turbine is controlled by the vanes.
To transfer the energy of water, the vanes move the water into a runner.
The Kaplan turbine is also a type of propeller turbine. There are many other types of
turbine-like; bulb turbine, tube turbine, straflo turbine, etc. But out of these turbines,
the Kaplan turbine is widely used in hydroelectric power plants.
Kaplan Turbine
Kaplan turbine is a propeller-type turbine. It has adjustable blades. It was introduced
by Australian professor Viktor Kaplan in 1913. The Kaplan turbine is an evolution
version of the Francis turbine.
A Kaplan turbine can work with low-head power plants. This is not possible in the case
of the Francis turbine. The Kaplan turbine works efficiently with the water head ranges
between 33 to 230 feet and the output of the plant between 5 to 200 MW.
The runner diameter lies between 2 to 11 meters. The Kaplan turbines are widely used
in high-head and low-head hydroelectric plants.
 •

Advantages and Disadvantages of Hydropower Plant

Advantages:
The advantages of hydropower plants are listed below.
• It is an environmentally friendly power plant and a non-polluting clean source of
electrical energy.
• The operating cost of this plant is very less compared to other power plants like
steam and nuclear power plant.
• It takes a very short time to start and stop the plant.
• The life of this plant is very high. The approximate life of a hydropower plant is more
than 50 years.
• This plant can be operating as a base load plant as well as a peak load plant.
• Only water is required to operate this plant. So, we can say no fuel is used to run
this plant and this will reduce the operating cost of a plant.
• The water released from the plant can be used for irrigation and flood control
purposes.
• Compared to a steam power plant, less staff is required in a hydroelectric power
plant.
• The plant is not using any fossil fuels. So, there are no byproducts like ash.
• These plants are more reliable and it has high efficiency over a wide range of load
compared to other power plants.
Disadvantages:
The disadvantages of hydroelectric power plants are as listed below.
• The power developed from the hydroelectric plant depends on the quantity of water
and water head. To create a water head, a dam is needed, and to store water, a
reservoir is needed. So, the capital cost to build a dam and reservoir is very high.
• These plants are located in hilly areas. And in most cases, these areas are far from
the load center. So, we need to transmit power via the transmission line. Which
creates more transmission loss and increases the capital cost to connect the load
center and powerhouse via a transmission line.
• It takes more time required to build a dam and reservoir.
• In most places, the water is available in some seasons only. And this plant is
depending on the availability of water. This plant cannot operate in the dry season.
So, the hydroelectric plant depends on natural rainfall.
Governer action in hydroelectric power plants
In hydroelectric power plants, the governor plays a critical role in
controlling the operation of the turbines to maintain stability and
efficiency. Here’s an overview of governor action in hydroelectric
power plants:

### Function of Governor in Hydroelectric Power Plants:

1. **Speed Regulation:**
- The primary function of the governor is to regulate the speed of
the turbine-generator unit. It ensures that the turbine rotates at a
constant speed within allowable limits, which is crucial for
maintaining synchronous operation with the electrical grid.

2. **Load Frequency Control:**

- Governors in hydroelectric plants help maintain the system
frequency of the electrical grid by adjusting the turbine output in
response to changes in electrical load demand. This load-frequency
control is essential for grid stability and for ensuring that supply
matches demand in real-time.

3. **Flow Control:**
- Governors also control the flow of water through the turbine.
They adjust the turbine wicket gates or blades to regulate the
amount of water passing through, thereby controlling the power
output of the turbine-generator unit.
4. **Stabilization and Response:**
- Governors provide rapid response to sudden load changes or
disturbances in the grid. They adjust turbine output quickly to
stabilize the system frequency and maintain grid reliability.

5. **Efficiency Optimization:**
- By adjusting the turbine operation based on load demand and
water flow conditions, governors help optimize the efficiency of
power generation. They ensure that the turbine operates at its most
efficient point for given operating conditions.

### Types of Governors:

1. **Mechanical Governors:**
- Traditional hydroelectric plants often use mechanical governors,
which regulate turbine speed and output through mechanical
linkages and control mechanisms. These governors rely on hydraulic
or mechanical feedback to adjust turbine operation.

2. **Electronic Governors:**
- Modern hydroelectric plants may employ electronic governors,
which use electronic sensors and controllers to monitor turbine
speed and grid frequency. Electronic governors offer more precise
control and can be integrated into advanced control systems for
optimal plant operation.

### Importance of Governors:

- **Grid Stability:** Governors play a crucial role in maintaining
grid stability by adjusting turbine output to match changes in
electrical load demand and grid frequency.

- **Efficiency:** By optimizing turbine operation, governors

contribute to maximizing the efficiency of power generation from
hydroelectric plants, thereby enhancing overall plant performance.

- **Reliability:** Governors ensure that hydroelectric plants can

respond quickly and effectively to changes in grid conditions,
contributing to the reliable operation of the electrical grid.

In conclusion, governors in hydroelectric power plants are essential

for controlling turbine operation to maintain stability, optimize
efficiency, and ensure reliable performance in generating electricity
from water flow. They integrate with control systems to manage
turbine speed, output, and response to grid conditions, playing a
vital role in the overall operation of hydroelectric power plants.