Complete Description of BHEL TRAINING REPORT for final year student of mechanical . Total Vocational training Report is listed with the content and proper description of turbine blade as well as major component of the training place .

1. 1
VOCATIONAL TRAINING
REPORT
UNDER THE GUIDANCE OF
MR. VIKAS SINGH
(SENIOR PRODUCTION ENGINEER)
STM Assembly Section BHEL, Bhopal
MAULANA AZAD NATIONAL INSTITUTE OF
TECHNOLOGY, BHOPAL
SUBMITTED BY
Eshver Chandra
MANIT, Bhopal
Token no. : VT-115/2016

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CERTIFICATE
I am Eshver Chandra , student of 3rd year semester 6th of Bachelor of Technology,
department of Mechanical Engineering, Maulana Azad National Institute of
Technology Bhopal.
I here certify that this vocational training work carried out by me at Bharat Heavy
Electricals Limited, Bhopal and report submitted in partial fulfilment of the
requirements of the programme is an original work of mine under the guidance of
the experienced mentor Mr. Vikas singh (Senior Production Engineer) is not based
on or reproduced from any existing work of any other person or any earlier work
undertaken at any other time or for any other purpose, and has not been submitted
anywhere else at any time. And it is also based upon my individual observation and
work experience.
Eshver Chandra MR. VIKAS SINGH
MANIT BHOPAL (SR. PRODUCTION ENGINEER)
Token no.:VT-115/2016 STM Assembly Section, Block- 3
BHEL BHOPAL

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ACKNOWLEDGENT
I would like to express my gratitude for the people who were part of my project
report, directly or indirectly people who gave unending support right from the stage
the idea was conceived.
An engineer with only theoretical knowledge is not a complete engineer. Practical
knowledge is very important to develop and apply engineering skills. It gives me a
great pleasure to have an opportunity to acknowledge and to express gratitude those
who were associated with me during my training at BHEL, Bhopal.
I take this opportunity to express my sincere gratitude to the people who have been
helpful in the successful completion of my Industrial training and this project.
I would like to show my greatest appreciation to MR. VIKAS SINGH , Sr. Production
Engineer who granted me the permission of industrial training in the BHEL, Bhopal.
I would like to thanks to all those people who directly or indirectly helped and
guided us to complete my training and this project including the following
instructor, technical staff and supervisor of various section.
Thanking you,
Eshver Chandra
MANIT Bhopal

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INDEX
1. Certificate …………………………………………………………………………….2
2. Acknowledgement …………………………………………………………………..3
3. Index …………………………………………………………………………………...4
4. Bhel – An Overview …………………………………………………………….…5 – 7
5. Bhel Bhopal …............................................................................................................8 –9
6. Steam Turbine …………………………………………………………………10 – 12
7. Steam Turbine Components ………………………………………………...13 - 21
8. Turbine Governing System ………………………………………………….21 – 22
9. Principal of Operation and Design ……………………………………………….23
10. Impulse turbine – Blade Efficiency …………………………………………24 - 27
11. Reaction Turbine – Blade Efficiency ………………………………………..27 – 30
12. Operation and Maintenance …………………………………………………30 – 31
13. Speed Regulation ……………………………………………………………..31 – 32
14. Thermodynamics of Steam Turbine ………………………………………..32 – 33

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BHEL – AN OVERVIEW
Bharat Heavy Electrical Limited (BHEL) owned by the Government of India, is a
power plant equipment manufacturer and operates as engineering and
manufacturing company based in New Delhi, India. Established in 1964, BHEL is
India’s largest engineering and manufacturing company of its kind. The company
has been earning profit continuously since 1971-72 and paying dividends
uninterruptedly since 1976-77. It has been granted the prestigious Maharatna (big
gem) status in 2013 by Govt of India for its outstanding performance. The elite list of
Maharatna contains another 6 behemoth PSU companies of India.
BHEL was established in 1964 Heavy Electricals (India) Limited was merged with
BHEL in 1974. In 1982, it entered into power equipment, to reduce its dependence on
the power sector. It developed the capability to produce a variety of electrical,
electronic and mechanical equipments for all sectors, including transmission,
transportation, oil and gas and other allied industries. In 1991, it was converted into
a public limited company. By the end of 1996, the company had handed over 100
Electric Locomotives to Indian Railway and installed 250 Hydro-sets across India.
ITS OPERATION:-
BHEL is engaged in the design, engineering, manufacturing, construction, testing,
commissioning and servicing of a wide range of products, systems and services for
the core sectors of the economy, viz. power, transmission, industry, transportation,
renewable energy, oil & gas and defence.
It has a network of 17 manufacturing units, 2 repair units, 4 regional offices, 8 service
centres, 8 overseas offices, 15 regional centres, 7 joint ventures, and infrastructure
allowing it to execute more than 150 projects at sites across India and abroad. The
company has established the capability to deliver 20,000 MW p.a. of power
equipment to address the growing demand for power generation equipment.
BHEL has retained its market leadership position during 2015-16 with 74% market
share in the Power Sector. An improved focus on project execution enabled BHEL
record its highest ever commissioning/synchronization of 15059 MW of power
plants in domestic and international markets in 2015-16, marking a 59% increase
over 2014-15. With the all-time high commissioning of 15000 MW in a single year
FY2015-16, BHEL has exceeded 170 GW installed base of power generating
equipments.
It also has been exporting its power and industry segment products and services for
over 40 years. BHEL's global references are spread across over 76 countries across all
the six continents of the world. The cumulative overseas installed capacity of BHEL
manufactured power plants exceeds 9,000 MW across 21 countries

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including Malaysia, Oman, Iraq, UAE, Bhutan, Egypt and New Zealand. Their
physical exports range from turnkey projects to after sales services.
MANUFACTURINGUNIT IN INDIA
 Centralised Stamping Unit & Fabrication Plant (CSU & FP), Jagdishpur
 Insulator Plant (IP), Jagdishpur
 Electronics Division (EDN), Bangalore
 Industrial Systems Group (ISG), Bangalore
 Electro-Porcelains Division (EPD), Bangalore
 Heavy Electrical Plant (HEP), Bhopal
 Industrial Valves Plant (IVP), Goindwal
 Heavy Electrical Equipment Plant (HEEP), Ranipur (Haridwar)
 Central Foundry Forge Plant (CFFP), Ranipur (Haridwar)
 Heavy Power Equipment Plant (HPEP), Hyderabad
 Transformer Plant (TP), Jhansi
 Boiler Auxiliaries Plant (BAP), Ranipet
 Component Fabrication Plant (CFP), Rudrapur
 High Pressure Boiler Plant (HPBP), Tiruchirappalli
 Seamless Steel Tube Plant (SSTP), Tiruchirappalli
 Power Plant Piping Unit (PPPU), Thirumayam
 Heavy Plates & Vessels Plant (HPVP), Visakhapatnam
PRODUCTS OF BHEL
 Thermal power Plants
 Nuclear power Plants
 Gas based power Plants
 Hydro power Plants
 DG power Plants
 Boilers (steam generator)
 Boiler Auxiliaries
 Gas generator
 Hydro generator
 Steam turbine
 Gas turbine
 Hydro turbine

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 Transformer
 Switchgear
 Oil field equipment
 Boiler drum
 Piping System
 Soot Blowers
 Valves
 Seamless Steel Tubes
 Condenser s and Heat exchangers
 Pumps
 Desalination and Water treatment plants
 Automation and Control systems
 Power electronics
 Transmission system control
 Semiconductor devices
 Solar photo voltaic
 Software system solutions
 Bus ducts
 Insulators
 Control panels
 Capacitors
 Bushings
 Electrical machines
 DC, AC heavy duty Motors
 Compressors
 Control gears
 Traction motors
 Research and development products

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BHEL BHOPAL
Vision
A Global Engineering Enterprise providing Solutions for better tomorrow
Mission
Providing sustainable business solutions in the fields of Energy, Industry &
Infrastructure
Values
Governance, Respect, Excellence, Loyalty, Integrity, Commitment, Innovation,
Team Work
BHEL, Bhopal certified to ISO: 9001, ISO 14001 and OHSAS 18001, is moving
towards superiority by acquiring TQM as per EFQM/CII model of Business
Excellence. Heat Exchanger Division is accredited with ASME “U” Stamp. With the
slogan of “Kadam Kadam milana hai, grahak safal banana hai”, it is committed to
the customers. BHEL Bhopal has its own Laboratories for material testing and
instrument calibration which are accredited with ISO 17025 by NABL. The hydro
Laboratory and Centre for Electric Transportation are the only laboratories of it are
in this part of world.
Awards and Recognition
National e-Governance Award: Bharat Heavy Electricals Limited (BHEL), has been
conferred upon the prestigious National e-Governance Gold Award of Government
of India for 2012-13, in the category – “Innovative use of ICT by PSUs for Customer
Benefits”, for the project “Integrated system for Online Generation of Electrical
Specifications for Transformers” , developed by Informatics Centre (IFX)
department, BHEL, Bhopal.
CSI National Award (2013) : BHEL Bhopal has won the prestigious CSI National
Award for Excellence in IT 2013 in the category of Business Collaboration solutions:
Banking & Finance.
Award for Excellence in e-Governance initiatives in MP: IT department of BHEL,
Bhopal has been declared as Winner for Excellence Award in e-Governance
initiatives in Madhya Pradesh for 2012-13, in the category – “The best application
following best-practices of software development”, for the project “Online

9. 9
Recruitment system”, developed by Informatics Centre (IFX) department, BHEL,
Bhopal.
National e-Governance Gold Award 2014-15: Bharat Heavy Electricals Limited
(BHEL) Bhopal has been conferred with the prestigious National e-Governance Gold
award by Government of India during the 18th National Conference on e-
Governance held at Gandhinagar, Gujarat. The award was given for the ‘SAMPARK’
project, developed by Information Services and Technology department (ITS), BHEL
Bhopal.
PRODUCTS OF BHEL BHOPAL
Power Utilisation
AC Motors & Alternators
Transportation
Transportation Equipment
Power Generation
Hydro Turbines
Hydro Generators
Heat Exchangers
Excitation Control Equipment
Steam Turbines
Miscellaneous
Oil Rigs
Fabrication
Power Transmission
Transformer
Switchgear
On-Load Tap Changer
Large Current Rectifiers
Control & Relay Panels
Renovation & Maintenance
Thermal Power Stations

10. 10
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. Its modern manifestation
was invented by Sir Charles Parsons in 1884.
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 (1996) is by use of steam turbines. The steam turbine is a form of heat
engine that derives much of its improvement in thermodynamic efficiency from the
use of multiple stages in the expansion of the steam, which results in a closer
approach to the ideal reversible expansion process.
Steam turbines are used for the generation of electricity in thermal power plants,
such as plants using coal, fuel oil or nuclear fuel. They were once used to directly
drive mechanical devices such as ships' propellers (for example the Turbinia, the first
turbine-powered steam launch) but most such applications now use reduction gears
or an intermediate electrical step, where the turbine is used to generate electricity,
which then powers an electric motor connected to the mechanical load. Turbo
electric ship machinery was particularly popular in the period immediately before
and during World War II, primarily due to a lack of sufficient gear-cutting facilities
in US and UK shipyards.
STEAM TURBINE SYSTEM DIAGRAM

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There are 3 sections to a steam turbine viz. high pressure, intermediate pressure and
low pressure turbine. All three are mounted on the same shaft which rotates at about
3600 rpm in a generator to make electricity.
1. HP Turbine
2. IP Turbine
3. LP Turbine
HP Turbine
• Single flow
• Double shell casing
– Inner casing vertically split
– Outer casing barrel type & axially divided
– Single exhaust in L/H
• Mono block rotor
• Casing mounted valves
• Internal bypass cooling
• Transported as single unit
IP Turbine
• Double flow
• Double casing design with horizontal split
• Inlet from Lower half
• Single Exhaust from upper half
• Extraction connections from lower half
• Admission blade ring
LP Turbine
• Double flow
• Double shell casing
• Single admission from top half
• Outer Casing & condenser rigidly connected
• Push rod arrangement to minimize axial clearances
• Mono block rotor
• Inner / Outer casing fabricated

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HIGH PRESSURE TURBINE
INTERMEDIATE PRESSURE TURBINE
LOW PRESSURE TURBINE

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STEAM TURBINE COMPONENTS
 Steam turbine foundation or frame
 Rotor
 Governor Pedestal
 Turbine Casing
1. Upper Casing
2. Lower Casing
 Turbine Casing Flanges
 Steam Turbine Blades
1. Fixed Blades or Diaphragm
2. Moving Blades
 Valves
1. Main Stop Valve
2. Control Valve
 Turbine Governing System

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STEAM TURBINE FOUNDATION OR FRAME
 FRAME (BASE) - supports the stator, rotor and governor pedestal.
 SHELL – Consists cylinder, casing, nozzle, steam chest & bearing.
 ROTOR – consists of low, intermediate, high pressure stage blades and
possible stub shaft(s) for governor pedestal components, thrust bearing,
journal bearings, turning gear & main lube oil system.
 GOVERNOR PEDESTAL – consists of the EHC oil system, turbine speed
governor, and protective devices.
 STEAM TURBINE ROTOR – Multistage steam turbines are manufactured
with solid forged rotor construction. Rotors are precisely machined from solid
alloy steel forging. An integrally forged rotor provides increased reliability
particularly for high speed applications.
The complete rotor assembly is dynamically balanced at operating speed and
over speed tested in a vacuum bunker to ensure safety in operation. High
speed balancing can also reduce residual stresses and the effects of blade
seating.
 TURBINE CASING – The casing of turbine cylinders are of simple
construction to minimize any distortion due to temperature changes. They are
constructed in two halves (top and bottom) along a horizontal joint so that the

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cylinder is easily opened for inspection and maintenance. With the top
cylinder casing removed the rotor can also be easily withdrawn without
interfering with the alignment of the bearings.
Most turbines constructed today either have a double or partial double casing
on the high pressure (HP) or intermediate pressure (IP) cylinders. This
arrangement subjects the outer casing joint flanges, bolts and outer casing
glands to lower steam condition. This also makes it possible for reverse flow
within the cylinder and greatly reduces fabrication thickness as pressure
within the cylinder is distributed across two casings instead of one. This
reduced the wall thickness also enables the cylinder to respond more rapidly
to changes in steam temperature due to the thermal mass.
The high pressure end of the turbine is supported by the steam end bearing
housing which is flexibly mounted to allow for axial expansion caused by
temperature changes. The exhaust casing is centreline supported on pedestals
that maintain perfect unit alignment while permitting lateral expansion.
Covers on both the steam end and exhaust end bearing housings and seal
housings may be lifted independently of the main casing to provide ready
access to such items as the bearings, control components and seals.
TURBINE UPPER CASING

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TURBINE LOWER CASING
 TURBINE CASING FLANGES – One method of joining the top and bottom
halves of the cylinder casing is by using flanges with machined holes. Bolts or
studs are insertion into these machined holes to hold the top and bottom
halves together. To prevent leakage from the joint between the top flange and
the bottom flange the joint faces are accurately machined.

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Another method of joining top and bottom cylinder flanges is by clamps
bolted radially around the outer of cylinder. The outer faces of flanges are
made of wedge shaped so that the tighter the clamps are pulled the greater
the pressure on the joint faces.
 STEAM TURBINE BLADES - The energy conversion takes place through the
turbine blades. A turbine consists of alternate rows of blades. This blades
convert the chemical or thermal energy of working fluid into kinetic energy
and then from kinetic energy to mechanical energy as rotation of the shaft.
Figure: Turbine blades.
There are two types of blade, fixed and moving blade. Moving blade is also two
types.
One is impulse blade and another reaction blade.
Fixed blade:
A fixed blade assembly is very important for turbine blading. It is also known as
diaphragm. The shape of the blade is the key to the energy conversion process. Since
the fixed blades have a conversing nozzle shape, it is also called nozzles. When
steam is passed over the fixed blades, they increase the velocity of steam as an
operation of nozzles. Here blades are converted the thermal energy of steam into
kinetic energy by causing the steam to speed up and gain velocity.

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Moving blade:
Moving blade can be shaped in either of two ways: reaction shaped or impulse
shaped. The shape of the blade determines how the energy is actually converted.
Either type of moving blades or a combination of both can be attached to the shaft of
the rotor on dices, called wheels as shown in the figure. Along the outer rim of the
blades is a metal band, called shrouding which ties the blades together. The moving
blades convert the kinetic energy in the moving speed into the mechanical energy as
rotor rotation.

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Impulse turbines:
These turbines change the direction of flow of a high velocity fluid or gas jet. The
resulting impulse spins the turbine and leaves the fluid flow with diminished kinetic
energy. There is no pressure change of the fluid or gas in the turbine rotor blades as
in the case of a steam or gas turbine, all the pressure drop takes place in the
stationary blades.
Before reaching the turbine, the fluid's pressure head is changed to velocity head by
accelerating the fluid with a nozzle. Impulse turbines do not require a pressure
casement around the rotor since the fluid jet is created by the nozzle prior to
reaching the blading on the rotor. Newton's second law describes the transfer of
energy for impulse turbines.
Reaction turbines:
These turbines develop torque by reacting to the gas or fluid's pressure or mass. The
pressure of the gas or fluid changes as it passes through the turbine rotor blades. A
pressure casement is needed to contain the working fluid as it acts on the turbine
stages or the turbine must be fully immersed in the fluid flow. The casing contains
and directs the working fluid and, for water turbines, maintains the suction
imparted by the draft tube. Francis turbines and most steam turbines use this
concept. For compressible working fluids, multiple turbine stages are usually used
to harness the expanding gas efficiently. Newton's third law describes the transfer of
energy for reaction turbines.

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Blading stages:
Two successive fixed and moving blades are collectively known as blading stage.
The effects of pressure and velocity of working fluids depend upon the stage
conditions. In Ashuganj power station, the turbines which are used have 23 stages at
HP turbine and 21 stages at IP & LP turbine. Now the effects of pressure and velocity
on various blading stages are described in below:
Figure: Effects of stage on pressure and velocity.
For impulse blading velocity increases and pressure decreases across each row as the
steam passes through the fixed blading. Again when steam passes through the
impulse type moving blade, its velocity decreases, but its pressure remains constant
as shown in the figure.
For reaction blading velocity increases and the pressure decreases across each row as
the steam passes through the fixed blading. When steam passes through the reaction
type moving blade, its pressure and velocity both decreases as shown.
VALVES:
Steam from the boiler is routed to the turbine through a steam line that
contains the main stop valves and the control valves.
Main stop valves:
It is such a valve through which steam passes to the turbine blades. By controlling
this valve steam flow can be controlled. Each main stop valve consists of a valve
disk, a valve stem and a hydraulic actuator.

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The hydraulic actuator contains a piston and a compression spring. Since the valve
disk and stems are connected to the piston, movement of the piston causes
movement of the valve disc. During normal turbine operation, hydraulic oil is
directed into or out of the hydraulic actuator. Directing oil into the actuator opens
the valve and compresses the spring.
As long as the amount of oil in actuator is held constant, the valve will remain in the
same position. Bleeding oil from the actuator allows the spring to push on the piston,
closing the valve. Tripping the turbine causes hydraulic oil to be bled quickly from
beneath the piston, allowing the spring to quickly shut the valve. Steam pressure
also helps to close the valve by forcing the disc back toward the seat. When the valve
is closed as shown in figure (2), the flow of steam toward the HP turbine is shut off.
Control valves:
When the main stop valves are fully opened, the flow of steam into the HP turbine is
usually regulated by four or more control valves. The control valves regulate the
turbine speed or its power output. Steam from the main stop valve flows to the
control valves through a steam line. The steam is sent to different sections of the
turbines nozzle block through the four steam lines below the control valves. Each
control valve feeds only one section of the nozzle block.
The control valves are operated by hydraulic actuators. The control valves regulate
steam flow into the turbine by opening and closing in sequence. As each valve is
opened, more steam is admitted to the turbine. During normal operation, the control
valves are automatically positioned to compensate for changes in load. For example,
if load increases, the control valves are opened more which increase the flow of
steam into the turbine. If load decreases, the control valves are closed more which
decrease the flow of steam into the turbine. At full condition, all the control valves
are completely opened as shown in the figure.
TURBINE GOVERNING SYSTEM:
Mechanical governor:
The purpose of a mechanical governor is to maintain the speed of the turbine at a
desired value when the generator is disconnected from the power supply.
Main parts of mechanical governor:
Ø Flyweights
Ø Bracket
Ø Spring

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Mechanism:
When the turbine shaft rotates, the governor flyweights respond to the
centrifugal forces created by the rotations. As turbine speed increases, the centrifugal
force increases, causing the flyweights to move outward, overcoming the tension of
the spring.
Figure: Mechanical governors.
The force of the spring tends to pull the flyweights toward the center of the
governor. When turbine speed decreases, the centrifugal force also decreases,
allowing the spring to pull the flyweights inward.
Governing system at high speed:
When the speed of the turbine increases, the flyweights move outward, which causes
the pilot valve stem to move upward. The movement of the stem and disc unblocks
the port of the control oil line and allows oil to flow from the actuator, through the
pilot valve, to the drain. The resulting decrease in pressure beneath the piston allows
the actuator spring to expand, forcing the piston towards. This action decreases the
opening of the control valve. Less steam is admitted to the turbine and turbine speed
decreases.
Governing system at low speed:
When turbine speed decreases, the flyweights move inward and the connecting rod
moves downward. As the rod moves downward, the pilot valve also moves
downward. Then the pilot valve blocks the drain line and opens the lube oil supply
line. As a result, oil from the supply oil line flows through the pilot valve and then
into the control oil line to the actuator. Now the pressure of the lube oil causes the
piston to move upward. Thus the opening of the control valves increase and mare
steam is admitted to the turbine. Hence the turbine speed increases gradually until it
reaches at desire speed.

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PRINCIPLE OF OPERATION AND DESIGN
A simple turbine schematic of the Parsons type: rotating and fixed stators alternate
and steam pressure drops by a fraction of the total across each pair. The stators grow
larger as pressure drops.
An ideal steam turbine is considered to be an isentropic process, or constant entropy
process, in which the entropy of the steam entering the turbine is equal to the
entropy of the steam leaving the turbine. No steam turbine is truly isentropic,
however, with typical isentropic efficiencies ranging from 20–90% based on the
application of the turbine. The interior of a turbine comprises several sets of blades
orbuckets. One set of stationary blades is connected to the casing and one set of
rotating blades is connected to the shaft. The sets intermesh with certain minimum
clearances, with the size and configuration of sets varying to efficiently exploit the
expansion of steam at each stage.
Turbine efficiency
To maximize turbine efficiency the steam is expanded, doing work, in a number of
stages. These stages are characterized by how the energy is extracted from them and
are known as either impulse or reaction turbines. Most steam turbines use a mixture
of the reaction and impulse designs: each stage behaves as either one or the other,
but the overall turbine uses both. Typically, higher pressure sections are reaction
type and lower pressure stages are impulse type.
Impulse turbines

24. 24
A selection of impulse turbine blades
An impulse turbine has fixed nozzles that orient the steam flow into high speed jets.
These jets contain significant kinetic energy, which is converted into shaft rotation by
the bucket-like shaped rotor blades, as the steam jet changes direction. A pressure
drop occurs across only the stationary blades, with a net increase in steam velocity
across the stage. As the steam flows through the nozzle its pressure falls from inlet
pressure to the exit pressure (atmospheric pressure, or more usually, the condenser
vacuum). Due to this high ratio of expansion of steam, the steam leaves the nozzle
with a very high velocity. The steam leaving the moving blades has a large portion
of the maximum velocity of the steam when leaving the nozzle. The loss of energy
due to this higher exit velocity is commonly called the carry over velocity or leaving
loss.
The law of moment of momentum states that the sum of the moments of external
forces acting on a fluid which is temporarily occupying the control volume is equal
to the net time change of angular momentum flux through the control volume.
The swirling fluid enters the control volume at radius with tangential
velocity and leaves at radius with tangential velocity .
Velocity triangle

25. 25
A velocity triangle paves the way for a better understanding of the relationship
between the various velocities. In the adjacent figure we have:
and are the absolute velocities at the inlet and outlet respectively.
and are the flow velocities at the inlet and outlet respectively.
and are the swirl velocities at the inlet and outlet respectively.
and are the relative velocities at the inlet and outlet respectively.
and are the velocities of the blade at the inlet and outlet respectively.
is the guide vane angle and is the blade angle.
Then by the law of moment of momentum, the torque on the fluid is given by:
For an impulse steam turbine: . Therefore, the tangential force on the
blades is . The work done per unit time or power
developed: .
When ω is the angular velocity of the turbine, then the blade speed is .
The power developed is then
.
BLADE EFFICIENCY
Blade efficiency ( ) can be defined as the ratio of the work done on the blades to
kinetic energy supplied to the fluid, and is given by
Stage efficiency
Convergent-divergent nozzle

26. 26
Graph depicting efficiency of Impulse turbine
A stage of an impulse turbine consists of a nozzle set and a moving wheel. The stage
efficiency defines a relationship between enthalpy drop in the nozzle and work done
in the stage.
Where is the specific enthalpy drop of steam in the nozzle.
By the first law of thermodynamics
:
Assuming that is appreciably less than , we get ≈ Furthermore, stage
efficiency is the product of blade efficiency and nozzle efficiency,
or
Nozzle efficiency is given by =
where the enthalpy (in J/Kg) of steam at the entrance of the nozzle is and the
enthalpy of steam at the exit of the nozzle is .
The ratio of the cosines of the blade angles at the outlet and inlet can be taken and
denoted . The ratio of steam velocities relative to the rotor speed at the
outlet to the inlet of the blade is defined by the friction coefficient .
and depicts the loss in the relative velocity due to friction as the steam flows
around the blades ( for smooth blades).
The ratio of the blade speed to the absolute steam velocity at the inlet is termed the
blade speed ratio

27. 27
=
is maximum when or, . That
implies and therefore Now (for a
single stage impulse turbine)
Therefore, the maximum value of stage efficiency is obtained by putting the value
of in the expression of /
We get: .
For equiangular blades, , therefore , and we
get . If the friction due to the blade
surface is neglected then .
Conclusions on maximum efficiency
1. For a given steam velocity work done per kg of steam would be maximum
when or .
2. As increases, the work done on the blades reduces, but at the same time surface
area of the blade reduces, therefore there are less frictional losses.
Reaction turbines
In the reaction turbine, the rotor blades themselves are arranged to form
convergent nozzles. This type of turbine makes use of the reaction force produced as
the steam accelerates through the nozzles formed by the rotor. Steam is directed onto
the rotor by the fixed vanes of the stator. It leaves the stator as a jet that fills the
entire circumference of the rotor. The steam then changes direction and increases its
speed relative to the speed of the blades. A pressure drop occurs across both the
stator and the rotor, with steam accelerating through the stator and decelerating
through the rotor, with no net change in steam velocity across the stage but with a
decrease in both pressure and temperature, reflecting the work performed in the
driving of the rotor.

28. 28
Blade efficiency
Energy input to the blades in a stage:
is equal to the kinetic energy supplied to the fixed blades (f) + the kinetic
energy supplied to the moving blades (m).
Or, = enthalpy drop over the fixed blades, + enthalpy drop over the moving
blades, .
The effect of expansion of steam over the moving blades is to increase the relative
velocity at the exit. Therefore, the relative velocity at the exit is always greater
than the relative velocity at the inlet .
In terms of velocities, the enthalpy drop over the moving blades is given by:
(it contributes to a change in static pressure)
The enthalpy drop in the fixed blades, with the assumption that the velocity of steam
entering the fixed blades is equal to the velocity of steam leaving the previously
moving blades is given by:
Velocity diagram
= where V0 is the inlet velocity of steam in the nozzle
is very small and hence can be neglected
Therefore, =

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A very widely used design has half degree of reaction or 50% reaction and this is
known as Parson’s turbine. This consists of symmetrical rotor and stator blades. For
this turbine the velocity triangle is similar and we have:
,
,
Assuming Parson’s turbine and obtaining all the expressions we get
From the inlet velocity triangle we
have
Work done (for unit mass flow per
second):
Therefore, the blade efficiency is given by
Condition of maximum blade efficiency

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Comparing Efficiencies of Impulse and Reaction turbines
If , then
For maximum efficiency , we get
and this finally gives
Therefore, is found by putting the value of in the expression of
blade efficiency
Operation and maintenance
A modern steam turbine generator installation
Because of the high pressures used in the steam circuits and the materials used,
steam turbines and their casings have high thermal inertia. When warming up a
steam turbine for use, the main steam stop valves (after the boiler) have a bypass line
to allow superheated steam to slowly bypass the valve and proceed to heat up the
lines in the system along with the steam turbine. Also, a turning gear is engaged
when there is no steam to slowly rotate the turbine to ensure even heating to
prevent uneven expansion. After first rotating the turbine by the turning gear,
allowing time for the rotor to assume a straight plane (no bowing), then the turning
gear is disengaged and steam is admitted to the turbine, first to the astern blades

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then to the ahead blades slowly rotating the turbine at 10–15 RPM (0.17–0.25 Hz) to
slowly warm the turbine. The warm up procedure for large steam turbines may
exceed ten hours.
During normal operation, rotor imbalance can lead to vibration, which, because of
the high rotation velocities, could lead to a blade breaking away from the rotor and
through the casing. To reduce this risk, considerable efforts are spent to balance the
turbine. Also, turbines are run with high quality steam: either superheated (dry)
steam, or saturated steam with a high dryness fraction. This prevents the rapid
impingement and erosion of the blades which occurs when condensed water is
blasted onto the blades (moisture carry over). Also, liquid water entering the blades
may damage the thrust bearings for the turbine shaft. To prevent this, along with
controls and baffles in the boilers to ensure high quality steam, condensate drains
are installed in the steam piping leading to the turbine.
Maintenance requirements of modern steam turbines are simple and incur low costs
(typically around $0.005 per kWh); their operational life often exceeds 50 years.
Speed regulation
Diagram of a steam turbine generator system
The control of a turbine with a governor is essential, as turbines need to be run up
slowly to prevent damage and some applications (such as the generation of
alternating current electricity) require precise speed control. Uncontrolled
acceleration of the turbine rotor can lead to an overspeed trip, which causes the
nozzle valves that control the flow of steam to the turbine to close. If this fails then
the turbine may continue accelerating until it breaks apart, often catastrophically.

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Turbines are expensive to make, requiring precision manufacture and special quality
materials.
During normal operation in synchronization with the electricity network, power
plants are governed with a five percent droop speed control. This means the full
load speed is 100% and the no-load speed is 105%. This is required for the stable
operation of the network without hunting and drop-outs of power plants. Normally
the changes in speed are minor. Adjustments in power output are made by slowly
raising the droop curve by increasing the spring pressure on a centrifugal governor.
Generally this is a basic system requirement for all power plants because the older
and newer plants have to be compatible in response to the instantaneous changes in
frequency without depending on outside communication.
Thermodynamics of steam turbines
T-s diagram of a superheated Rankine cycle
The steam turbine operates on basic principles of thermodynamics using the part 3-4
of the Rankine cycle shown in the adjoining diagram. Superheated steam (or dry
saturated steam, depending on application) leaves the boiler at high temperature
and high pressure. At entry to the turbine, the steam gains kinetic energy by passing
through a nozzle (a fixed nozzle in an impulse type turbine or the fixed blades in a
reaction type turbine). When the steam leaves the nozzle it is moving at high velocity
towards the blades of the turbine rotor. A force is created on the blades due to the
pressure of the vapour on the blades causing them to move. A generator or other
such device can be placed on the shaft, and the energy that was in the steam can now
be stored and used. The steam leaves the turbine as a saturated vapour (or liquid-
vapour mix depending on application) at a lower temperature and pressure than it

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entered with and is sent to the condenser to be cooled. The first law enables us to
find an formula for the rate at which work is developed per unit mass. Assuming
there is no heat transfer to the surrounding environment and that the changes in
kinetic and potential energy are negligible compared to the change in
specific enthalpy we arrive at the following equation
Where
 Ẇ is the rate at which work is developed per unit time
 ṁ is the rate of mass flow through the turbine
Isentropic efficiency
To measure how well a turbine is performing we can look at its isentropic efficiency.
This compares the actual performance of the turbine with the performance that
would be achieved by an ideal, isentropic, turbine. When calculating this efficiency,
heat lost to the surroundings is assumed to be zero. The starting pressure and
temperature is the same for both the actual and the ideal turbines, but at turbine exit
the energy content ('specific enthalpy') for the actual turbine is greater than that for
the ideal turbine because of irreversibility in the actual turbine. The specific enthalpy
is evaluated at the same pressure for the actual and ideal turbines in order to give a
good comparison between the two.
The isentropic efficiency is found by dividing the actual work by the ideal work.
Where
 h3 is the specific enthalpy at state three
 h4 is the specific enthalpy at state 4 for the actual turbine
 h4s is the specific enthalpy at state 4s for the isentropic turbine

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Thank you