Turbines are used in power plants to generate electricity. Steam turbines extract thermal energy from pressurized steam which causes the turbine's rotor blades to spin, generating rotational mechanical energy. This rotational energy is then used to power an electrical generator, converting the energy into electricity. There are two main types of steam turbines - impulse turbines which keep steam pressure constant and reaction turbines where steam pressure decreases as it passes through. Modern steam turbines power over 80% of the world's electricity generation through this process of converting fuel energy to thermal energy, then to kinetic energy, and finally to electrical energy.

1. Uses of Turbines in Power Plant
-by Souptik Chatterjee

2. Turbine
A turbine is a rotary mechanical
device that extracts energy from a
fluid flow and converts it into
useful work. A turbine is a
turbomachine with at least one
moving part called a rotor
assembly, which is a shaft or drum
with blades attached. Moving fluid
acts on the blades so that they
move and impart rotational energy
to the rotor.

3. Working Principle
The working principle is very much simple.
• When the fluid strikes the blades of the
turbine, the blades are displaced, which produces
rotational energy.
• When the turbine shaft is directly coupled to
an electric gene- -rator mechanical energy is
converted into electrical energy. • This electrical
power is known as hydroelectric power.

4. Basic Types of Turbines
• Water Turbine
• Steam Turbine
• Gas Turbine
• Wind Turbine
Although the same principles apply to all
turbines, their specific designs differ sufficiently
to merit separate descriptions.

5. Steam Turbine
A steam turbine is a device that extracts thermal energy from
pressurized steam and uses it to do mechanical work on a
rotating output shaft.
• This turbine was invented by Sir Charles Parsons in 1884
• Steam turbines are used for the generation of electricity in
thermal power plants, such as plants using coal fuel oil or
nuclear fuel.
• Steam turbines are made in a variety of sizes ranging from
small to large . used as mechanical drives for pumps,
compressors and other shaft driven equipment, used to generate
electricity (upto1.5 GW) .

6. Applications
• Fuel used are biomasses, coal etc.
• Modern steam turbines has automatic control
system.
• steam heated processes in plants and factories.
• steam driven turbines in electric power plants.
• Because the turbine generates rotary motion, it
is particularly suited to be used to drive an
electrical generator about 90% of all electricity
generation in the United States

7. Steam Turbine Working Principle
High pressure steam is fed to the turbine and passes along the
machine axis through multiple rows of alternately fixed and
moving blades. From the steam inlet port of the turbine towards
the exhaust point, the blades and the turbine cavity are
progressively larger to allow for the expansion of the steam.
The stationary blades act as nozzles in which the steam expands
and emerges at an increased speed but lower pressure. (Bernoulli's
conservation of energy principle - Kinetic energy increases as
pressure energy falls). As the steam impacts on the moving blades
it imparts some of its kinetic energy to the moving blades.

8. There are two basic steam
turbine types, impulse
turbines and reaction
turbines, whose blades are
designed control the speed,
direction and pressure of the
steam as is passes through
the turbine
TYPES OF STEAM TURBINES

9. IMPULSE TURBINES
The steam jets are directed at the
turbine's bucket shaped rotor blades
where the pressure exerted by the jets
causes the rotor to rotate and the
velocity of the steam to reduce as it
imparts its kinetic energy to the blades.
The blades in turn change change the
direction of flow of the steam however its
pressure remains constant as it passes
through the rotor blades since the cross
section of the chamber between the
blades is constant. Impulse turbines are
therefore also known as constant pressure
turbines.
The next series of fixed blades reverses the
direction of the steam before it passes to
the second row of moving blades.

10. REACTION TURBINES
The rotor blades of the reaction turbine are
shaped more like aerofoils, arranged such that
the cross section of the chambers formed
between the fixed blades diminishes from the
inlet side towards the exhaust side of the blades.
The chambers between the rotor blades
essentially form nozzles so that as the steam
progresses through the chambers its velocity
increases while at the same time its pressure
decreases, just as in the nozzles formed by the
fixed blades. Thus the pressure decreases in both
the fixed and moving blades. As the steam
emerges in a jet from between the rotor blades,
it creates a reactive force on the blades which in
turn creates the turning moment on the turbine
rotor, just as in Hero's steam engine. (Newton's
Third Law - For every action there is an equal
and opposite reaction)

11. Practical Machines
Steam turbines come in many configurations.
Large machines are usually built with multiple
stages to maximise the energy transfer from the
steam.
To reduce axial forces on the turbine rotor bearings
the steam may be fed into the turbine at the mid
point along the shaft so that it flows in opposite
directions towards each end of the shaft thus
balancing the axial load.
The output steam is fed through a cooling tower
through which cooling water is passed to condense
the steam back to water.

12. Conventional Energy Generation
The first practical electricity generating system using a
steam turbine was designed and made by Charles
Parsons in 1885 and used for lighting an exhibition in
Newcastle. Since then, apart from getting bigger, turbine
design has hardly changed and Parson's original design
would not look out of place today. Despite the
introduction of many alternative technologies in the
intervening 120 years, over 80 percent of the world's
electricity is still generated by steam turbines driving
rotary generators.

13. ENERGY CONVERTION PROCESS
Electrical energy generation
using steam turbines involves
three energy conversions,
extracting thermal energy
from the fuel and using it to
raise steam, converting the
thermal energy of the steam
into kinetic energy in the
turbine and using a rotary
generator to convert the
turbine's mechanical energy
into electrical energy.

14. Electromechanical Energy Transfer
The steam turbine drives a generator, to convert the
mechanical energy into electrical energy. Typically this
will be a rotating field synchronous machine. These
machines are described more fully in the section on
Generators.
The energy conversion efficiency of these high capacity
generators can be as high as 98% or 99% for a very large
machine.
Note: This means that a 1000MW generator must
dissipate 20 MW of waste heat and such generators
require special cooling techniques.

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