Vocational training report from BHEL Bhopal on steam turbine

1. (12 JULY 2018 TO 25 JULY 2018)
In parTIaL fULfILLmenT Of The reqUIremenT fOr
bacheLOr Of engIneerIng (b.e)
Under The gUIdance Of
mr. ashIsh parIhar
(depUTY manager)
TransfOrmer manUfacTUrIng dIvIsIOn (Trm)
bheL,bhOpaL (m.p)
TechnOcraTs InsTITUTe Of TechnOLOgY & scIence,bhOpaL (m.p)
apprOved bY aIcTe & affILaTed TO rgpv
sUbmITTed bY
vIkash Yadav
e.n rOLL:- 0192me151203
TOken nO:- vT/2018/2597

2. cerTIfIcaTe
I am VIKASH YADAV , student of 4th year semester 7th of bachelor of
engineering , department of mechanical engineering , Technocrats
institute of technology & science, Bhopal (M.P)
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.
ASHISH PARIHAR (Deputy managr) 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.
VIKASH YAAV Mr. ASHISH PARIHAR
Token NO.-VT/2018/2597 (Deputy Manager)
TRM DEPARTMENT
Block-3 BHEL BHOPAL

3. 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. ASHISH PARIHAR, Dy.
Manager 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,
VIKASH YADAV
0192ME151203
TIT & SCIENCE
BHOPAL (M.P)

4. 4

5. 5
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

6. 6
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

7. 7
including Malaysia, Oman, Iraq, UAE, Bhutan, Egypt and New Zealand. Their
physical exports range from turnkey projects to after sales services.
MANUFACTURING UNIT 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

8. 8
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

9. 9
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

10. 10
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
Power Generation
Hydro Turbines
Hydro
Generators Heat
Exchangers
Excitation Control
Equipment
Steam
Turbines
Power Transmission
Transforme
r
Switchgear
On-Load Tap
Changer
Large Current
Rectifiers
Control & Relay Panels
Transportation
Transportation
Equipment
Miscellaneous
Oil Rigs
Fabrication
Renovation & Maintenance
Thermal Power
Stations

11. 11
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

12. 12
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
• Single flow
• Double shell casing
– Inner casing vertically split
HP Turbine
– 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

13. 13
HIGH PRESSURE TURBINE
INTERMEDIATE PRESSURE TURBINE
LOW PRESSURE TURBINE

14. 14
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

15. 15
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

16. 16
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

17. 17
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.

18. 18
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.

19. 19
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.

20. 20
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.

21. 21
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.

22. 22
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

23. 23
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.

24. 24
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

25. 25
y
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 velocit .
Velocity triangle

26. 26
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

27. 27
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

28. 28
=
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.

29. 29
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, =

30. 30
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

32. 32
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.

33. 33
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

34. 34
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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