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Prepared by: Mohammad Shoeb Siddiqui
Senior Shift SupervisorSaba Power Company
Cell # +92 321 4598293
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What is Steam Turbine? A Steam Turbine is a device that extracts Thermal
Energy from pressurized Steam and uses it todo Mechanical Energy on a rotating output shaft.
Steam Turbine is device where Kinetic Energy(Heat) converted into Mechanical Energy (in shapeof rotation).
Turbine is an Engine that converts Energy of Fluidinto Mechanical energy & The steam turbine issteam driven rotary engine.
This Presentation is base on basic of Steam Turbine& 134 MW Toshiba Steam Turbine.
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In order to better understand turbine operation, Four BasicClassifications are discussed. Type of Steam Flow &
Division of Steam Flow, describes the flow of steam inrelation to the axis of the rotor. indicates whether thesteam flows in just one direction or if it flows in more thanone direction. Way of Energy Conversion & Type ofBlading, Reaction, Impulse and Impulse & ReactionCombine. identifies the blading as either impulse blading
or reaction blading. Type of Compounding & Cylinderarrangement refers to the use of blading which causes aseries of pressure drops, a series of velocity drops, or acombination of the two. (number of cylinders; whethersingle, tandem or cross-compound in design) ExhaustingCondition & Number of Stages is determined by whether
the turbine exhausts into its own condenser or whether itexhausts into another piping system.
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1. Type of Steam FlowTurbines may be classifiedaccording to the direction ofsteam flow in relation to theturbine wheel or drum
- Axial.
- Radial.
- Mixed
- Tangential Or Helical.
- Reentry
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Radial Flow:
A turbine may also be
constructed so that thesteam flow is in a radial
direction, either toward or
away from the axis. In
figure illustrates an
impulse, radial
flow, auxiliary turbine such
as may be used as a pump
drive.
The radial turbine is not nor
mally
the preferred choice for
electricity generation and is
usually only employed for
small output applicationsPrepared byMohammadShoeb SiddiquiSenior Shift Supervisor
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Axial Flow:
The great majority of
turbines, especially thoseof high power, are axial
flow. In such turbines the
steam flows in a direction
or directions parallel to the
axis of the wheel or rotor.
The axial flow type of turbi
ne is the most preferred for
electricity generation as
several cylinders can be
easily coupled together to
achieve a turbine with agreater output.
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Reverse Flow
In some modern turbine designs the
steam flows through part of the highpressure (HP) cylinder and then is
reversed to flow in the oppositedirection through the remainder of the
HP cylinder. The benefits of this
arrangement are:
outer casing joint flanges and boltsexperience much lower steam
conditions than with the one directiondesign
reduction or elimination of axial
(parallel to shaft) thrust created withinthe cylinder
lower steam pressure that the outer
casing shaft glands have toaccommodate
A simplified diagram of a reverse flow highpressure cylinder is shown in Figure Prepared by
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2. Way of Energy Conversion & Types of Blading
- Impulse turbines
- Reaction turbines
- Impulse & Reaction Combine
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By Types of Blading :
The heat energy contained within the steam that
passes through a turbine must be converted
into mechanical energy. How this is achieved
depends on the shape of the turbine blades. The
two basic blade designs are:
1. Impulse
2. Reaction
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Impulse:Impulse blades work on the principle
of high pressure steam striking orhitting against the moving blades.
The principle of a simple impulse
turbine is shown in Figure.
Impulse blades are usually
symmetrical and have an entrance
and exit angle of approximately 200.They are generally installed in the
higher pressure sections of the
turbine where the specific volume of
steam is low and requires much
smaller flow areas than that at lower
pressures. The impulse blades are
short and have a constant cross
section.
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Reaction:The principle of a pure reaction turbine
is that all the energy contained within the
steam is converted to mechanicalenergy by reaction of the jet of steam asit expands through the blades of the rotor.
A simple reaction turbine is shown inFigure. The rotor is forced to rotate as the
expanding steam exhausts the rotor arm
nozzles.
In a reaction turbine the steam expands when passing across the fixed blades
and incurs a pressure drop and anincrease in velocity. When passing
across the moving blades the steam
incurs both a pressure drop and adecrease in velocity
A section of reaction type blading isshown in Figure
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Impulse stage
Whole pressure drop innozzle (whole enthalpydrop is changed intokinetic energy in thenozzle)
Reaction stagePressure drop both instationary blades and inrotary blades (enthalpydrop changed intokinetic energy both in
stationary blades and inthe moving blades inrotor) Prepared by
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An impulse stage consists ofstationary blades forming
nozzles through which thesteam expands, increasingvelocity as a result ofdecreasing pressure. Thesteam then strikes the rotatingblades and performs work on
them, which in turn decreasesthe velocity (kinetic energy) ofthe steam. The stream thenpasses through another set ofstationary blades which turn itback to the original direction
and increases the velocityagain though nozzle action.
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In Reaction Turbine both themoving blades and the non-moving blades designed to actlike nozzles. As steam passesthrough the non-movingblades, no work is extracted.Pressure will decrease and
velocity will increase as steampasses through these non-moving blades. In the movingblades work is extracted. Eventhough the moving blades aredesigned to act likenozzles, velocity and pressure
will decrease due to workbeing extracted from thesteam.
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This utilizes the principle of
impulse and reaction. It isshown diagrammatically :
There are a number of rows ofmoving blades attached to therotor and an equal number offixed blades attached to the
casing. The fixed blades are setin a reversed manner comparedto the moving blades, and act asnozzles. Due to the row of fixedblades at the entrance, instead ofnozzles, steam is admitted for
the whole circumference andhence there is an all-round orcomplete admission. Prepared by
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Compounding of Impulse Turbine
This is done to reduce the rotational speed of the
impulse turbine to practical limits. (A rotor speedof 30,000 rpm is possible, which is pretty high forpractical uses.)
Compounding is achieved by using more than oneset of nozzles, blades, rotors, in a series, keyed toa common shaft; so that either the steam pressure
or the jet velocity is absorbed by the turbine instages.
Three main types of compounded impulse turbinesare:
a) Pressure compounded,
b) velocity compounded and
c) pressure and velocity compounded impulse turbines.
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When the velocity energy produced
by one set of fixed nozzles is unable
to be efficiently converted into
rotational motion by one set of
moving blades then it is common to
install a series of blades as shown in
Figure. This arrangement is known
as velocity compounding.
Velocity drop is arranged in many
small drops through many movingrows of blades instead of a single
row of moving blades.
It consists of a nozzle or a set of
nozzles and rows of moving blades
attached to the rotor or the wheel and
rows of fixed blades attached to thecasing.
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This is a combination of
pressure-velocity compounding.
Most modern turbines have acombination of pressure and
velocity compounding. This type
of arrangement provides a
smaller, shorter and cheaper
turbine; but has a slight
efficiency trade off.Turbines using this
arrangement are often referred
to as CURTIS turbines after the
inventor. Individual pressure
stages (each with two or more
velocity stages) are sometimescalled CURTIS stages.
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This setup of a nozzlefollowed by a set of movingblades, non
-moving
blades, and moving bladesmakes up a single Curtisstage. After steam exits thenozzle there are no further
pressure drops.However, across both setsof moving blades there is avelocity drop. This causesthe Curtis stage to beclassified as velocity
compounded blading.
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Turbines can be arranged either single cylinder or multi-stage in design.
The multi-stage can be either velocity, pressure or velocity
-pressure
compounded (discussed as earlier.
Single cylinder construction or Single Flow TurbineSingle cylinder turbines have only one cylinder casing(although may be is
multiple sections). Steam enters at the high pressure section of the turbine
and passes through the turbine to the low pressure end of the turbine then
exhausts to the condenser. Figure shows a single cylinder turbine with a
high, intermediate and low pressure section contained within the one
cylinder casing.
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Tandem construction or Compound Flow Turbine
Dictated by practical design and manufacturers considerations modern
turbines are manufactured in multiple sections also called cylinders.
Greater output and efficiency can be achieved by coupling a number ofindividual cylinders together in what is referred to as tandem (on one
axis).
Tandem compound
Large electric power generating turbines commonly have a highpressure casing, which receives superheated steam directly from the
boiler or steam generator. The high pressure turbine may then exhaustto an intermediate pressure turbine, or may pass back to a reheatsection in the boiler before passing to a reheat intermediate pressureturbine. The reheat turbine may then exhaust to one or more lowpressure casings, which are usually two exhaust flow turbines, with thelow pressure steam entering the middle of the turbine and flowing in
opposite directions toward two exhaust end before passing into thecondenser. When the turbine casings are arranged on a single shaft, theturbine is said to be tandem compounded.
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Tandem construction or Compound Flow Turbine
A tandem two cylinder turbine with a single flow high pressure (HP) cylinder and a
double flow low pressure (LP)cylinder is shown in Figure.
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Tandem Three Cylinder Turbine
It has a double flow LP cylinder with an IP cylinder arranged so that the
steam flow through it is in the opposite direction to the HP cylinder. This
design also greatly reduces the axial thrust on the rotor.
Tandem three cylinder turbine is shown in Figure as under:
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Tandem Cross-Compounding Turbine
In cross compound turbines, the high-
pressure, exhaust passes over to
intermediate or low pressure casings which
are mounted on separate shafts. The two
shafts may drive separate loads, or may be
geared together to a single load.
In some larger overseas installations that
operate at 60 hertz (frequency) the use of
cross-compounding is some times employed.
Cross-compounding is where the HP and IP
cylinders are mounted on one shaft drivingone alternator while the LP cylinders are
mounted on a separate shaft driving another
alternator. This is done so as the LP cylinder
with its large diameter blading can be
operated at a greatly reduced speed thus
reducing the centrifugal force.
Tandem cross-compounding turbine is
shown in Figure:Prepared byMohammad Shoeb SiddiquiSenior Shift Supervisor
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T d f li d bi i h fl
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Tandem four cylinder turbine with reverse flow
The final turbine arrangement that is becoming increasingly popular is
the “Tandem four cylinder turbine with reverse flow HP cylinder, double
flow IP and twin double flow LP cylinders”. This arrangement is shownin Figure:
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04. Number of Stages
- Single stage
- Multi-stage
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Prepared byMohammadShoeb SiddiquiSenior Shift Supervisor
In an impulse turbine,
the stage is a set of
moving blades behind
the nozzle. In a
reaction turbine, each
row of blades is calleda "stage." A single
Curtis stage may
consist of two or more
rows of moving blades.
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5. Exhaust Conditions
- Condensing
- Extraction
- Back-pressure
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By steam supply and exhaust conditions:
Condensing
Extraction, (Automatic or controlled )
Non-condensing (back pressure),
Mixed pressure (where there are two or more
steam sources at different pressures), Reheat (where steam is extracted at an
intermediate stage, reheated in the boiler, and re-admitted at a lower turbine stage).
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Condensing
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The condensing turbine processesresult in maximum power and electrical
generation efficiency from the steam
supply and boiler fuel. The power output
of condensing turbines is sensitive to
ambient conditions.
The cooling water condenses the steam
turbine exhaust steam in the condensercreating the condenser vacuum. As a
small amount of air leaks into the
system when it is below atmospheric
pressure, a relatively small compressor
(Vacuum pump) or Air Ejector System
removes non-condensable gases from
the condenser.
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Extraction
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In an extraction turbine, steam is withdrawn fromone or more stages, at one or more
pressures, for heating, plant process, or feed
water heater needs. They are often called"bleeder turbines.“The steam extraction pressure may or may notbe automatically regulated. Regulated extraction
permits more steam to flow through the turbine to
generate additional electricity during periods oflow thermal demand by the CHP system. In utility
type steam turbines, there may be several
extraction points, each at a different pressurecorresponding to a different temperature. The
facility’s specific needs for steam and power over
time determine the extent to which steam in anextraction turbine is extracted for use in the
process.
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Back-pressure
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Figure shows the non-
condensing turbine (also
referred to as a back-
pressure turbine) exhausts its
entire flow of steam to theindustrial process or facility
steam mains at conditions
close to the process heat
requirements.
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4. Rotational
Speed- Regular- Low-speed
- High-speed
5. Inlet steampressure
- High pressure(p>6,5MPa)
- Intermediatepressure(2,5MPa
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8 Application
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8. Application
- Power station- Industrial- Transport
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In actual practice, not all of the energy in the
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p , gysteam is converted to useful work. Lossescommon to all turbines are described
below:
Loss of working substance. Loss of steamalong the shaft through the shaft glands wherethe shaft penetrates the casing.
Work loss. Loss due to mechanical frictionbetween moving parts.
Throttling loss. Wherever there is a reductionin steam pressure without a corresponding
production of work, such as in a throttle valve.
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Leaving loss. The kinetic energy of the steam leavingthe last stage blading This leaving loss can be
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the last stage blading. This leaving loss can beminimized by lightly loading the last stage blading by
increasing the annular exhaust area of the turbine. Thisis often optimized through economic studies.
Windage loss. This is caused by fluid friction as theturbine wheel and blades rotate through thesurrounding steam.
Friction loss as the steam passes through nozzles andblading.
Diaphragm packing loss as the steam passes from onestage to another through the diaphragm packing.
Tip leakage loss in reaction turbines as steam passes
over the tips of the blades without doing any useful work.Prepared byMohammadShoeb SiddiquiSenior Shift Supervisor
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Rankine cycle with superheat
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Rankine cycle with superheatProcess 1-2: The working fluid is
pumped from low to high pressure.Process 2-3: The high pressure liquidenters a boiler where it is heated atconstant pressure by an external heatsource to become a dry saturated vapor.Process 3-3': The vapour is superheated.
Process 3-4 and 3'-4': The dry saturatedvapor expands through a turbine,generating power. This decreases thetemperature and pressure of the vapor,and some condensation may occur.Process 4-1: The wet vapor then enters a
condenser where it is condensed at aconstant pressure to become a saturatedliquid.
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Foundation IV (Intercept Valve)
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Rotor or Shaft
Cylinder or Casing
Blades
Diaphragm
Steam Chest
Coupling
Bearings
Labyrinth Seal
Front Pedestal
TSI
D
-EHC (Governor)
MSV (Main Steam Stop Valve)
CV(Control Valve)
IV (Intercept Valve)
CRV (Combined Reheat Valve)
Turbine Turning Gear
Turbine Bypass & Drains
Atmospheric ReliefDiaphragm (Rupture Disk)
Lube Oil System EHC Oil System
Gland Steam System
Condenser
Steam Jet Ejector
Vacuum BreakerPrepared byMohammadShoeb SiddiquiSenior Shift Supervisor
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F (B ) S t th t t t d
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Frame (Base): Supports the stator, rotor and
governor pedestal.
Shell: Consists cylinder, casing, nozzles, steamchest & bearing.
Rotor: Consists of low, intermediate, and high
pressure stage blades, and possible stub shaft (s)
for governor pedestal components, thrustbearing, journal bearings, turning gear & mainlube oil system.
Governor Pedestal: Consists of the EHC oilsystem, turbine speed governor, and protective
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An multistage steam turbines are
manufactured with solid forgedrotor construction. Rotors areprecisely machined from solid alloysteel forgings. An integrally forgedrotor provides increased reliabilityparticularly for high speedapplications.
The complete rotor assembly isdynamically balanced at operatingspeed and over speed tested in avacuum bunker to ensure safety inoperation. High speed balancingcan also reduce residual stresses
and the effects of blade seating.Prepared byMohammadShoeb SiddiquiSenior Shift Supervisor
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The casings 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
cylinder is easily opened for inspection andmaintenance. With the top cylinder casing
removed the rotor can also be easily
withdrawn with out interfering with the
alignment of the bearings.
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Most turbines constructed today either have a
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Prepared byMohammadShoeb SiddiquiSenior Shift Supervisor
Most turbines constructed today either have a
double or partial double casing on the high pressure(HP) and 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 reducesfabrication thickness as pressure within the cylinder
is distributed across two casings instead of one. This
reduced wall thickness also enables the cylinder to
respond more rapidly to changes in steam
temperature due to the reduced thermal mass.
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Th hi h d f th t bi i
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The high-pressure end of the turbine is
supported by the steam end bearing housing which is flexibly mounted to allow for axialexpansion caused by temperature changes.The exhaust casing is centerline supported onpedestals that maintain perfect unit alignment
while permitting lateral expansion. Covers onboth the steam end and exhaust end bearinghousings and seal housings may be liftedindependently of the main casing to provideready access to such items as the bearings,
control components and seals.Prepared byMohammadShoeb SiddiquiSenior Shift Supervisor
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Atmosphere Relief Diaphragm
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HP Turbine Casing IP Turbine Casing
LP Turbine Casing
HP Turbine Casing
CV
CV
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One method of joining the top
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One method of joining the top
and bottom halves of thecylinder casing is by usingflanges with machined holes.Bolts or studs are insertion intothese machined holes to holdthe top and bottom halvestogether.
To prevent leakage from the joint between the top flange andthe bottom flange the joint facesare accurately machined. Atypical bolted flange joint isshown in Figure.
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Another method of joining
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Another method of joining
the top and bottom cylinderflanges is by clamps boltedradially around the outer ofthe cylinder. The outer facesof the flanges are made
wedge-shaped so that the
tighter the clamps are pulledthe greater the pressure onthe joint faces. This methodof joining top and bottomcasings is shown in Figure.
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Blade design is extremely important in attaining
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Blade design is extremely important in attaining
high turbine reliability and efficiency. A largeselection of efficient blade profiles have beendeveloped and proven by extensive field serviceallowing for optimal blade selection for allconditions of service. Blades are milled fromstainless steel within strict specifications for properstrength, damping and corrosion resistantproperties.
Disk profiles are designed to minimize centrifugalstresses, thermal gradient and blade loading at thedisk rims.
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Rotary Blades
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09HP Turbine Blades
07 IP Turbine Blades
05 LP Turbine Blades
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Partitions between pressure stages in a
t bi ' i ll d di h Th
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turbine's casing are called diaphragms. Theyhold the vane-shaped nozzles and sealsbetween the stages. Usually labyrinth-typeseals are used. One-half of the diaphragm isfitted into the top of the casing, the other halfinto the bottom.
Nozzle rings and diaphragms are specifically
designed and fabricated to handle thepressure, temperature and volume of the
steam, the size of the turbine and the required
pressure drop across the stage. The nozzles
used in the first stage nozzle ring are cut from
stainless steel. Steam passages are then
precision milled into these nozzle blocks
before they are welded together to form the
nozzle ring. Prepared by
MohammadShoeb SiddiquiSenior Shift Supervisor
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The nozzles in the intermediatepressure stages are formed fromprofiled stainless steel nozzle sectionsand inner and outer bands These are
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and inner and outer bands. These arethen welded to a circular center sectionand to an outer ring then precisionmachined.
The low-pressure diaphragms in
condensing turbines are made bycasting the stainless nozzle sectionsdirectly into high
-strength cast iron. This
design includes a moisture catchingprovision around the circumference which collects released moisture andremoves it from the steam passage.Additional features such as windageshields and inter
-stage drains are used
as required by stage conditions tominimize erosion. All diaphragms are
horizontally split for easy removal andalignment adjustment.
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Steam Turbine Components And Relative Equipments
Various root fixing shapes have been
developed for turbine blading to suit
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Mohammad Shoeb SiddiquiSenior Shift Supervisor
p g
both construction requirements andconditions under which turbines
operate. The most popular types of
blade root fixing available are:
Grooves
Straddle
Rivet
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Steam Turbine Components And Relative Equipments
Straddle construction
Straddle construction is where the
blade root fits over the machining on
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Mohammad Shoeb SiddiquiSenior Shift Supervisor
g
the outer periphery of the rotor wheelor disc. An example of straddle fir
-tree
blade root construction is shown in
Figure A. while the disc peripheral
machining is shown in Figure B.
Once again with this type ofconstruction the blade roots are
installed through the closing blade
window slid around the circumference
of the disc into position, then the lastblade inserted is doweled in the closing
blade window location.
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Steam Turbine Components And Relative Equipments
Rivet construction
Rivet construction is where the blade root
either inserts into a groove or straddles the
disc and all blades are doweled into position.
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Mohammad Shoeb SiddiquiSenior Shift Supervisor
Peripheral blade fixing
On larger blading where the blade length is
relatively long a system of lacing wire or
shroud rings are installed to give the blading
additional support and reduce
vibration. The lacing wire is installed a small
distance from the outer ends of the blades while the shoud rings are fitted to tangs on
the outer edges of the blades and secured by
peening the tangs. A section of blading
showing the installation of the lacing wire is
shown in Figure A while a section of blading
showing shroud ring installation is shown inFigure B.
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Steam chest: The steamchest, located on the
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forward, upper half of theHP turbine casing, housesthe throttle valve assembly.This is the area of theturbine where main steamfirst enters the main engine.The throttle valve assemblyregulates the amount ofsteam entering the turbine.After passing through thethrottle valve, steam entersthe nozzle block.
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With multi-cylinder turbines it is necessary to have
some method of connecting individual cylinder rotors.
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It is also a requirement to connect the turbine to thealternator rotor. To achieve these connections we
use a device known as a coupling. These couplings
must be capable of transmitting heavy loads and in
some turbines are required to accommodate for axial
expansion and contraction.
The types of couplings generally employed in power
plants are:
Flexible coupling
Solid shaft couplingPrepared byMohammadShoeb SiddiquiSenior Shift Supervisor
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Flexible couplings
Where axial shaft movement is required a flexible
Steam Turbine Components And Relative Equipments
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coupling is employed and these are either:
1. Sliding claw (or tooth)
2. Flexible connection (between the two flanges)
With both of the above flexible couplings it is
necessary to have a separate thrust bearing for
each shaft to maintain the same relative position
between rotor and cylinder casing.
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Flexible connection coupling
Flexible connections such as the bibby coupling are constructed in twohalves. Each half is shrunk onto their
respective shaft and secured with keys
Steam Turbine Components And Relative Equipments
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respective shaft and secured with keysor driven pins. The halves aremachined with groves parallel ornearly parallel to that of the alignmentof the shaft. Flexible spring steel gridsare inserted into these machinedgroves and held in place with an outercover. This type of coupling is effective
in allowing axial expansion andcontraction along with the ability totolerate minor misalignment. A bibby coupling is shown in Figure.
The flexible couplings just mentionedare by no means the only flexiblecouplings available but they are thepreferred choice for high load
applications.Prepared byMohammadShoeb SiddiquiSenior Shift Supervisor
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Solid shaft coupling
When shaft movement is notrequired it is usual to install a
solid type coupling Two flanges
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solid type coupling. Two flangesare installed onto theirrespective shafts and then thetwo flanges are bolted togetherto form a solid joint as shown inFigure A.
Often teeth are machined on theouter rim of these couplings andused as a point for barring theturbine shaft. (more aboutbarring the turbine later). FigureB shows a solid shaft coupling
with a barring gear fitted Prepared byMohammadShoeb SiddiquiSenior Shift Supervisor
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Turbine Bearings
Journal Bearing:
The turbine rotors are
supported by two journalbearings Both the No 1
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supported by two journalbearings. Both the No.1and No.2 bearings areof a double
-tilting pad
type. The bearing metalis divided into six pads
which are self-aligned. Acenter adjustment of
these bearings caneasily be made withshimmed pads.
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A labyrinth seal is a typeof mechanical seal that
provides a tortuous path tohelp prevent leakage An
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provides a tortuous path tohelp prevent leakage. Anexample of such a seal issometimes found withinan axle's bearing to helpprevent the leakage of the oil
lubricating the bearing.A labyrinth seal may becomposed ofmany grooves that presstightly inside another axle, orinside a hole, so that the fluid
has to pass through a longand difficult path to escape. Prepared byMohammadShoeb SiddiquiSenior Shift Supervisor
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Labyrinth seals are utilized asend gland seals and also inter
-
stage seals. Stationary labyrinth
seals are standard for all
Steam Turbine Components And Relative Equipments
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seals are standard for allmultistage turbines and groovesare machined on the rotating partto improve the sealing effect. Theleakage steam from the outerglands is generally condensed by
the gland condenser. Someleakage steam from theintermediate section of the steamend gland seals can be
withdrawn and utilized by re-
injecting it into the low-pressure
stage or low-
pressure steamline. Prepared byMohammadShoeb SiddiquiSenior Shift Supervisor
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Toothed- wheel for speed sensors
The turbine rotating speed issensed by the magnetic pickups
FRONT STANDARD & TSISteam Turbine Components And Relative Equipments
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g psensed by the magnetic pickupsfaced to the toothed
- wheel (96
teeth) installed on the control rotor.The pulse signal is produced wheneach tooth passes the pickups. Thefrequency signals from two (2)
pickups are converted into digitalvalue proportional to the turbinespeed through F/D (Frequency toDigital) converters.
Other three (3) sensors are located
around toothed- wheel. These
sensors are used for trip detector. Prepared by
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The electromagnetic pickup use forspeed detector is fixed facing thetooth face of the speed detectinggear connected directly to the rotor
end of
the turbine. (Inside of
frontstandard) The turbine speed can be
FRONT STANDARD & TSISteam Turbine Components And Relative Equipments
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) pdetected as the sine wave frequencysignal in proportion to the turbinespeed. This frequency signal isconverted to an digital signal bymeans of the F/D converter tobecome a feedback signal to the
speed control circuit.Over speed detector also makefrequency signal in proportion to theturbine speed. They face to tooth
-
wheel on control rotor. Pickup isused eddy current type. Clearancebetween sensor face and tooth faceis different from electromagnetic
pickup type.Prepared byMohammadShoeb SiddiquiSenior Shift Supervisor
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Principles Of Governing
During operation of a Turbine Generator Unit
STEAM TURBINE SPEED CONTROL
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Prepared byMohammadShoeb SiddiquiSenior Shift Supervisor
During operation of a Turbine-Generator Unit
the Load carried by the Generator may vary
over time. In order to respond to changing
System Load demands the amount of steam
directed to the Turbine must be varied inproportion to each demand.
The function of a governor is to provide rapid
automatic response to load variations.
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STEAM TURBINE SPEED CONTROL
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System Features
Application:
D-EHC system can be applied to control, protection and monitoring of steamturbines for various type of power plants including conventional fossil-fired
power plants, combined cycle plants, co-generation plants, and atomic powerplants.
Steam Turbine Components And Relative Equipments
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Powerful and reliable controllers:
High-speed control with state-of-the-art microprocessor based control system
Distributed and hierarchical architecture consists of;System controller, Master controller, Programmable logic device,
Valve interface
Normal Operation:
During Normal Operation, the main stop valves, intermediate stop valves
and intercept valves are wide open. Operation of the T-G is under the control
of the Electro-Hydraulic Control (EHC) System. The EHC System iscomprised of three basic subsystems: the speed control unit, the load control
unit, and the flow control unit. The normal function of the EHC System is togenerate the position signals for the four main stop valves, four main control
valves, and intermediate stop valves and intercept valves. Prepared byMohammadShoeb SiddiquiSenior Shift Supervisor
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The main stop valve is locatedin the main steam piping
between the boiler and theoutlet piping to turbine controlvalve chest in turbine casing
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valve chest in turbine casing.The main stop valve has oneinlet and two identical outletpipe connections. Outlet pipesare welded directory.
The primary function of themain stop valves is to quicklyshut off the steam flow to theturbine under emergencyconditions such as failure of thecontrol valves to close on lossof load.
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Two combined reheatvalves are provided, onein each hot reheat line.Supplying reheat steam tothe turbine. As the nameimplies The combined
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implies. The combinedvalve is actually two valve.The intercept valve andthe reheat stop
valve, incorporated in onevalve casing. Althoughthey utilize a commonvalve casing, these valvesprovide entirely different
functions. Prepared byMohammadShoeb SiddiquiSenior Shift Supervisor
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The motor driven turning gear
is mounted on the turbine
bearing cap, adjacent to the
turbine-generator coupling soas to mesh with a bull gear
Turning Gear
Driven Motor
Turning Gear
Driven Chain
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(spacer disk gear type). Which
is bolted between the turbine-
generator coupling faces.
The primary function of the
turning gear is to rotate theturbine
-generator shaft slowly
and continuously during
shutdown periods when rotor
temperature changes occur.
Turning Gear
Turning Gear Oil Supply
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When the turbine is shutdown, cooling of its inner
elements is continues for many hours. If the rotor
is allowed to remain stationary during this coolingperiod, distortion begins almost immediately. This
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Prepared byMohammadShoeb SiddiquiSenior Shift Supervisor
p g y
distortion is caused by the flow of hot vapors to
the upper part of the turbine casing, resulting in
the upper half of the turbine being at a higher
temperature than the lower half. The parts do notreturn to their normal position until the turbine has
cooled to the point where both the upper and
lower halves are at approximately the same
temperature.
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Water induction can happen at any time;however the most common situations are
during transients such as start up, shut
down and load changes. In figure
illustrates the percentage of times variousevents contribute to water induction for aconventional steam cycle It is interesting
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conventional steam cycle. It is interesting
that only 18 percent of water induction
incidents occur when the unit is at load.
Turbine drains are necessary to avoidslugging nozzles and blades inside the
turbine with condensate on start-up; thiscan break these components from impact.
The blades were designed to handle
steam, not water.
Turbine casing drains remove thecondensate from the turbine casing during
warm-up, securing, maneuvering and other
low flow conditions. Prepared byMohammad Shoeb SiddiquiSenior Shift Supervisor
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The atmospheric relief diaphragm is a safety feature which protects the exhaust hood and condenseragainst excessive steam pressure in case thecondenser water for any reason is lost.
The device consists of hard rolled silver bearing
Steam Turbine Components And Relative Equipments
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The device consists of hard rolled silver bearingcopper sheet of sufficient area to pass full throttlesteam flow at a safe protective pressure. In normaloperation of the turbine with proper vacuum
conditions, the diaphragm is dished inward againstthe supporting grid by atmospheric pressure shouldthe vacuum conditions fail for any reason and theinternal exhaust hood pressure raise to approximately5 psig, it would force the diaphragm outward againstthe cutting knife. The diaphragm would be cut free asa disk relieving the exhaust pressure to atmosphere.
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Steam Turbine Components And Relative Equipments
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FunctionThe function of lubrication is to interpose a film of
lubricant such as grease or oil between the movingsurfaces in a bearing.
Steam Turbine Components And Relative Equipments
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g
Lubrication reduces friction, minimizes
wear, provides cooling and excludes water and
contaminants from bearing components. The
protection of rotating heavy machinery depends
greatly on the effective operation and supervision of
lubricating oil systems and bearings.
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Steam Turbine Components And Relative Equipments
Establishment of Oil Film
Oil lubricated bearings rely on the physical separation
of the two bearing surfaces by a thin film or wedge of
oil. In order to establish and maintain this oil film thefollowing conditions must be established.
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Prepared byMohammadShoeb SiddiquiSenior Shift Supervisor
1) There must be relative motion between the two beari
ng surfaces to build up sufficient pressure within the oil
to prevent the film breaking down.
2) There must be an uninterrupted supplyof oil available to the bearing.
3) The bearing surfaces must not be parallel and need
a narrow angle between them. This is to enable the oil
to be shaped into a thin wedge tapering off in the
direction of the motion
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Steam Turbine Components And Relative Equipments
Oil Film Dynamics
1). With the shaft at rest the journal lies in the
bottom of the bearing. The weight of the shaft
tends to squeeze the oil out of the bearing so
that metal to metal contact occurs
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Prepared byMohammadShoeb SiddiquiSenior Shift Supervisor
that metal to metal contact occurs.
2). As the shaft commences to rotate the first
action of the journal is to climb up the bearing
wall until it begins to slip and some metal to
metal contact occurs.
3) As the shaft continues to increase in speed
the oil is dragged around by virtue of viscosity
until it forms a thin oil wedge. it's
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Steam Turbine Components And Relative Equipments
The purpose of the
gland steam system
is to reduce steam
leakage to aminimum and toprevent air ingress.
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Prepared byMohammadShoeb SiddiquiSenior Shift Supervisor
p gOr
Function of the gland
sealing system falls
into two categories:• Seal the turbine
glands under all
operating conditions
• Extract leak-off steam
from the turbine
glands.
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Steam Turbine Components And Relative Equipments
Steam leakage leads to the requirement for
increased make up; this increases the load on
the feed and boiler water treatment chemicalsand to a deterioration of the working
environment surrounding the power plant
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Prepared byMohammadShoeb SiddiquiSenior Shift Supervisor
environment surrounding the power plant.
Air ingress leads to a loss of vacuum and hence
reduction in plant efficiency, and causesproblems of thermal stressing around the gland
as well as increases oxygen content of the
exhaust steam.
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Steam Turbine Components And Relative Equipments
Gland Steam CondenserThe gland steam condenser is cooled by the
condensate extracted from the main condenser and soacting as a feed heater. The gland steam often shares
its condenser with the air ejector reducing the cost of
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Prepared byMohammadShoeb SiddiquiSenior Shift Supervisor
j g
having two units.
A fan is fitted to induce a flow through the system
without incurring a negative pressure in the finalpocket as this would allow the ingress of air. This is
ensured by the fitting on valves to the exhaust line
from the glands so enabling the back pressure to be
set.
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A surface condenser is a
commonly used term for a water-
cooled shell and tube heat
exchanger installed on the
exhaust steam from a steam
turbine in thermal powerstations. These condensers are heat
exchangers which convert steam
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Prepared byMohammadShoeb SiddiquiSenior Shift Supervisor
from its gaseous to its liquid state at
a pressure below atmospheric
pressure. Where cooling water is in
short supply, an air-cooled
condenser is often used. An air-
cooled condenser is however
significantly more expensive and
cannot achieve as low a steam
turbine exhaust pressure as a water-
cooled surface condenser.
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The purpose of a Vacuum Breaker Valve is to quickly
allow air into the vacuum space of the condenser and
low pressure turbine exhaust hood. The vacuumbreaker valve is usually located on the steam turbine
or the condenser shell/transition.
A b k l i i ll bl b
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Prepared byMohammadShoeb SiddiquiSenior Shift Supervisor
A vacuum breaker valve is typically operable by a
controller responsive to losses of load on the steam
turbine.Once opened, the vacuum breaker valve will allow air
into the steam space to quickly reduce the existing
vacuum and hence reduce the acceleration of the
steam turbine upon loss of load by the generator.
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(1) Emergency trip pushbutton in control room
(2) Boiler Trip, Turbine trip
(3) Low condenser vacuum
(4) Low lube oil pressure
(5) LP turbine exhaust hood high temperature
(6) Thrust bearing wear
(7) Emergency trip at front standard
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( ) g y p
(8) Low hydraulic fluid pressure
(9) Loss of EHC
(10) Excessive turbine shaft vibration(11) Loss of two speed signals
- either Normal Speed Control or
Emergency Over speed Trip
(12) Over Speed Trip 1
(13) Over Speed Trip 2
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