RAMAGUNDAM SUPER THERMAL
THIS IS TO CERTIFY THAT Mr. M.RAJ KIRAN, M.RAJ KUMAR,
E.BUCHANNA AND Mr. G.SAI SHARATH BEARING ROLL NO.
11E35A0305, 11E35A0301, 11E35A0303, 10E31A0312 OF MAHAVEER
INSTITUTE OF SCIENCE AND TECHNOLOGY AFFILIATED TO JNTU
HYDERABAD, MECHANICAL [B.TECH, 4TH YEAR] HAVE DONE A
PROJECT ON “MAINTAINENCE OF STEAM TURBINE” UNDER MY
GUIDENCE AND SUPERVISION AT RSTPS NTPC RAMAGUNDAM” FROM
16-01-2014 TO 15-02-2014 . PERFORMANCE OF THE PROJECT TRAINEE IS
I WISH THEM ALL THE BEST FOR THEIR FUTURE.
Mr. S.SATYANARAYAN A Mr. NAMDEV S UPPAR
The successful completion of my project is indeed practically incomplete without
mentioning of all those encouraging people who genuinely supported me throughout the
I would like to express my sincere gratitude to Shri NAMDEV S UPPAR(AGM-TM(
I/C)) who extended his support and accepted the proposal of carrying out the project
work on “STEAM TURBINE MAINTAINANCE”.
I’ am indebted to my project guide Shri S Satyanarayana (ASST MANAGER-TMD)
who spared his valuable time and energy to guide me patience fully and interactively
throughout the training.
I in deep sense of gratitude to record my thanks to Shri T.ASHOK who had forwarded
me to do my project work at NTPC-Ramagundam.
I express my profound gratitude to Sri SHANMUKH DEV (H.O.D-Mechanical
Department) and K.S.S.S.N REDDY(Principal) of MAHAVEER INSTITUTE OF
SCIENCE & TECHNOLOGY, Bandlaguda , Hyd Dist, for their support.
I extend my thanks to Shri E. Nandakishore (AGM-HR EDC), Shri P.M.G.V Srinivas
(DGM HR EDC), Smt. AshwiniRajkumar (ASST MANAGER HR EDC) and Shri C.
Keshavulu (SUB OFFICER HR EDC) also for their valuable advices and guidance to the
Finally, I thank one and all who have given their assistance directly or indirectly.
Power plants are the main source for large-scale production of electrical energy. Raw
materials used in thermal power plant are coal, water, oil and air. Thermal power plant
uses a dual phase cycle to enable the working fluid (water) to be used repeatedly. The
cycle used is “Modified Rankine cycle” which includes super heated steam, regenerating
feed water and reheated steam.
The main objective behind my project is to study about the thermal plant, how power is
generated, what are its sources, working of boilers, turbines, generators etc.
This work concentrates much about turbines, their maintenance and various equipments
installed to ensure the safe, reliable and efficient performance of the turbine. This deals
with the controls of a turbine to regulate the speed to required and tripping devices and
their working at emergencies.
NTPC-National Thermal Power Corporation, India’s largest power company was set up in the
year 1975 to accelerate power development in India. Today it has emerged as an Integrated
Power Major with a significant presence in the entire value chain of power generation business.
NTPC was ranked 317th in 2009, Forbes Global 2000 ranking of the World’s biggest
The total installed capacity of the company is 30,644MW (including JV’s) with 22 stations,
located across the country as of financial year 2009. The generation growth trend is shown
8. In addition under JV’s, 4 stations are there. By 2017, the power generation portfolio is expected
to have a diversified fuel mix with coal based capacity of around 53000MW, 10000MW through
gas, 9000MW through Hydro generation, about 2000MW from nuclear sources and around
1000MW from Renewable Energy Sources (RES). NTPC has adopted a multi-pronged growth
strategy which includes capacity addition through green field projects, expansion of existing
stations, joint ventures, subsidiaries and takeover of stations.
NTPC has been operating its plant at higher efficiency levels. Although the company has 18.79%
of the total national capacity it contributes 28.60% of total power generation due to its focus on
Power generation capacity based on fuel:
9. Regional spread of generating facilities:
Region Coal Gas Total(MW)
Fuel No.: of Plants Capacity(MW)
Coal 15 24,395
Gas/Liquid fuel 7 3,955
Total 22 28,350
Owned by JV’s:
Coal 3 814
Gas 1 1480
Total 26 30,644
Northern 7,035 2,312 9,437
Western 6,360 1,293 7,653
Southern 3,600 350 3,950
Eastern 7,400 - 7,400
JV’s 814 1,480 2,294
Total 25,209 5,435 30,644
ABOUT NTPC RAMAGUNDAM - RSTPS
10. NTPC Ramagundam, a part of National Thermal Power Corporation, is a 2600 MW Power
station situated at Ramagundam in the state of Andhra Pradesh, India. It is the current largest
power station in South India. It is the first ISO 14001 certified "Super Thermal Power Station" in
The TG Hall:
The TG Hall or the Turbo-Generator hall or the Turbine-Generator Hall is the hall or space
where the turbine-generator sets are present.
11. Turbo-Generator Hall, UNIT#7, NTPC Ltd., Ramagundam
NTPC Ltd., Ramagundam has two TG Halls one for STAGE - I and the other common for
STAGE-II and STAGE-III. These TG halls are equipped with heavy overhead cranes that assist
in transportation of material to, from and within the TG hall. These cranes find their use greatly
Unit-wise power generation:
The whole plant is divided into 3 stages, each stage being planned at one time.
STAGE 1 (3 * 200MW):
This stage consists of three units (Unit-1, Unit-2, Unit-3) each with a generation capacity of
200MW. The turbines for these three units were manufactured by The Ansaldo Energia Ltd. The
construction began in the late 1970s and these units have performed well over a long period
setting many records regarding maintenance and generation over the other two stages.
STAGE 2 (3 * 500MW):
This stage again consists of three units (Unit-4, Unit-5, Unit-6) each with a generation capacity
of 500MW. The turbines for these three units were manufactured by Bharat Heavy Electricals
Limited (BHEL). These Units have shown a relatively lower performance. Especially Unit-6 has
imposed many problems on the maintenance departments.
STAGE 3 (1 * 500MW):
12. This stage comprises only one unit (Unit - 7). This is a first of its kind in South India being a
computer operated unit. A wide disparity may be seen between the control rooms of the other
two stages and this computerized unit. To this day, many Power plant engineers train in this unit
to upgrade themselves to this new mode of operation. This unit also has the tallest chimney in
Outside view of STAGE-III (Unit#7)
Once in two years, these units are stopped and overhauled, one unit at a time. The overhauls are
usually taken up during the months June to September as the monsoons activate hydel power
generation which substitute the power generation lost due to the overhaul of the unit. The same
practice is followed all through the country. The overhauls usually take 15 to 20 days per unit
provided there is no major repair involved. Major repairs include turbine casing, turbine rotor
damage and other damages that require transporting the equipment to another location (usually
the manufacturer). The overhauls are the dissipaters of the annual PLF of any power plant.
As NTPC Ltd. is a Public Sector Undertaking (PSU), the generation is almost uniformly
distributed to 4-5 states all of them sharing about 20-25 percent of the Generation. The States
13. Andhra Pradesh
The switchyard is the place where the station last takes care of the power it produces. The
switchyard links the power generated to the southern Power grid. The major transmission points
Switchyard of NTPC Ltd., Ramagundam
The power station gets it water periodically released from the SRSP- Sriram Sagar project. This
water is stored in the balance reservoir. The water level in the balance reservoir is monitored
day-to-day, at POCHAMPADU DAM.
NTPC Ramagundam is a Thermal Power Station and hence uses coal. This coal is available at a
large scale from the Singareni Coal mining company nearby and is transported using the
MGR(Merry-go-round) system wherein, a train comes on one railroute, delivers coal and returns
on another route. The wagons arriving by this route are taken for coal collection wherein a
mechanism provided underneath the wagons opens on application of air pressure and drops the
coal it is carrying. A separate department (MGR Dept.) handles this process.
Coal also arrives by the Indian Railways. The wagons are routed via Ramagundam railway
station to the separate plant line and these coaches arrive at the wagon tippler. The wagons
arriving in this manner must be tilted at the wagon tippler to obtain the coal as they do not have
the drop mechanism underneath.
Other petroleum products required:
The station also requires various oils for the following purposes:
Turbine oil (SP-46)for turbine Lubrication
HFO, Heavy fuel oil for boiler start-up
Diesel for DG sets (Power backup)
Other oils for various hydraulic controls and circuits
These are periodically purchased as per requirement from the Indian oil corporation IOCL
The plant classifies its departments as O&M and Non-O&M.
Departments under O&M
15. The operation department has the maximum number of employees. It takes care of operation of
the various equipments and controls in the plant. The operation department takes care of the unit
control rooms(UCBs).A power plant operates 24 X 7 so, the operation department works in shifts
to take care of the units at all times.
This is the largest department under the Maintenance section. This department takes care of all
the electrical aspects of the plant. It takes care of the following sections.
Conveyor motors and other motors
All power transmissions
Civil Maintenance takes care of all the civil activities in the plant such as non-mechanical
constructions, maintenance of locations, scrap removal and ensuring a proper working condition
of minor equipments.
MGR (Merry-go-Round) Department:
This dept. takes care of the coal transport to the plant. The coal dig out at singareni mines is
transported to plant with separate wagons.
CHP (Coal Handling Plant):
This dept. takes care of all coal handling processes.
This dept. has the following sections
16. Primary and secondary air pumps
Boiler feed pumps
Boiler core parts
Turbine core parts
Turbine governing system
Control & Instrumentation:
This department deals with the maintenance of various control devices and instruments. It is
considered to be a part of the maintenance section. It has got the following sections.
1. Boiler C&I
2. ACS&DAS C&I
3. Turbine C&I
Departments under non-O&M:
Materials and contracts
17. The plant is headed by the General Manager (GM) to whom the AGM's report. The O&M group
being reported by the Additional General Manager (O&M) again to whom the AGMs of
concerned departments report.
The AGM's are again reported to by the Heads of various departments (DGM cadre) and so on
following the order below
ET (Executive trainee)
NTPC, Ramagundam has a very beautiful and a serene township. The TTS is the temporary
township constructed during the early stages of the plant .It is now resided by the secondary
employees of the organization (Contractors, Allied organization employees, service
organizations to the township like Dooradarshan...etc...)
The PTS is the permanent township where most of the employees reside with their families. It is
known for its serenity, cleanliness, Greenery and its parks.
The township has three schools. Kendriya Vidyalaya NTPC Ramagundam, Saint Claire High
school and the Sachdeva school of excellence (formerly Chinmaya Vidyalaya).
The township has a main shopping centre and four small shopping centers where the residents
may shop for groceries and other regular needs.
18. The township is well facilitated with banking( The State Bank of Hyderabad with an on-site
ATM), postal services,telephone and internet services(BSNL),Adequate water supply, 24*7
electricity right from the plant, Civil services and its own security.
Guest Houses and Restaurants:
There are two Guest houses. Jyothi bhavan for executives and Godavari Bhavan (Field Hostel)
for other employees, students and trainees. These are maintained by the Indian Coffee House
employees and are equipped with dining facilities thus forming as restaurants for the township
The township has beautiful parks namely the Ambedkar Park, the Chacha Nehru Park, the
Priyadarshini Park and other small parks and in it theaters are also there.
Overview about plant:
Installed capacity: 2600MW
Coal consumption: 13Million tons/year
Total area of plant: 10,000Acres
Total investment: Rs.10,000Crores
Ultimate Man-power: 1774
Reservoir capacity: 6Million metric cubic over 500acre
Daily production: 62.4Mu
Transmission system: 2430Km of 400KVlines
19. BASIC POWER PLANT OPERATING CYCLE
The thermal power plant uses a dual (vapour+liquid) phase cycle. It is a closed cycle to enable
the working fluid (water) to be used again and again. The cycle used is Rankine cycle modified
to include super heating of steam, regenerative feed water heating and reheating of steam.
1-2: Isentropic (reversible adiabatic) compression by pump work.
2-3: Constant pressure heat addition in boiler.
3-4: Isentropic expansion in turbine (HP).
4-5: Reheating, Constant pressure heat addition in boiler.
5-6: Isentropic expansion in turbine (IP & LP).
6-1: Constant pressure heat rejection in condenser.
Efficiency of the cycle can be increased by using reheat and regeneration techniques. Reheating
means using multiple turbines for expansion of steam and Regeneration constitutes drawing
steam at different stages and using feed water pumps.
Efficiency (ή) = net work done/heat input.
20. Block diagram of plant operating cycle:
On large turbines, it becomes economical to increase the cycle efficiency by implementing
reheat, which is a way of partially overcoming temperature limitations. By returning partially
expanded steam, to a reheat the average temperature at which heat is added is increased and by
expanding this reheated steam to the remaining stages of the turbine. The exhaust wetness is
considerably less than it would otherwise be conversely, if the maximum tolerable wetness is
allowed, the initial pressure of the steam can be appreciably increased.
Bleed steam extraction: for regenerative system, numbers of non-regulated extractions are
taken from HP, IP turbine.
Regenerative heating of the boiler feed water is widely used in modern power plants, the effect
being to increase the average temperature at which heat is added to the cycle, Thus improving
the cycle efficiency.
21. COAL TO STEAM:
Coal from the coal wagons is unloaded in the coal handling plant using wagon tippler. After
unloading, coal is transferred to crusher house using conveyor belts, where it is crushed down to
small size. The speed of conveyor belts is around 450-500 feet per minute. The conveyor belts
are driven with the help of roller bearing. This coal is transported up to the raw bunkers with the
help of belt conveyors. Coal is transported to bowl mills by coal feeders. The coal is pulverized
in the bowl mill, where it is ground to a powder form. This crushed coal is taken away to the
furnace through coal pipes with the help of hot and cold air mixture from primary air (PA) fan.
PA fan takes atmospheric air, a part of which is sent to air pre-heaters for heating while a part
goes directly to the mill for temperature control. Atmospheric air from FD fan is heated in the air
heaters and sent to the furnace for combustion.
Water from the boiler feed pump passes through economizer and reaches the boiler drum. Water
from the drum passes through down corners and goes to bottom ring header. From bottom ring
header is divided to all four sides of furnace. Due to heat and the density difference the water
rises up in the water wall tubes. It is partly converted to steam as it rises up in the furnace. This
steam and water mixture is again taken to the boiler drum where the steam is separated from
water. It follows the same path while the steam is sent to super heaters for superheating. The
super heaters are located inside the furnace and the steam is superheated to 540°C and finally it
goes to turbine. Flue gases from the furnace are extracted by induced draft fan which maintains
balance various super heaters in the pent house and finally pass through air pre heaters and goes
to Electro static precipitator(ESP), where the ash particles are extracted. ESP consists of metal
plates which are electrically charged. Ash particles are attracted on to these plates, so that they
do not pass through the chimney to pollute the atmosphere. Regular mechanical hammer blows
cause the accumulated ash to fall to the bottom of the precipitator where they are collected in a
hopper for disposal. This ash is mixed with water to form slurry and is pumped to ash pond.
STEAM TO MECHANICAL POWER:
From the boiler, a steam pipe conveys steam to the turbine through a stop valve, which can be
used to stop flow of steam in an emergency and through control valves that automatically
regulate the supply of steam to the turbine. Stop valve and control valves are located in a steam
chest governor, driven from the turbine shaft, operates the control valves to regulate the amount
steam used. This depends upon the speed of the turbine and the amount of electricity required
from the generator.
Steam from the control valves enters the high pressure cylinder of the turbine, where it passes
through a ring of stationary blades fixed to the cylinder wall, these acts as nozzles and direct the
steam into a second ring of moving blades mounted on a disc secured to the turbine shaft. This
second ring turns the shafts as a result of the force of the steam. The stationary and moving
blades together constitute a stage of the turbine and in practice many stages are necessary, so that
the cylinder contains a number of rings of stationary blades with rings of moving blades arranged
22. The steam passes through each stage in turn until it reaches the end of the HP cylinder and in its
passage some of its heat energy is changed into mechanical energy. The steam leaving the HP
cylinder CRH goes back to the boiler for reheating and returns by a further pipe HRH to the IP
cylinder. Here it passes through another series of stationary and moving blades. Finally, the
steam is taken to the LP cylinders, each of which it enters at the center flowing outwards in
opposite direction through the rows of turbine blades, an arrangement known as double flow to
the extremes of cylinder. As the steam gets up its heat energy to drive the turbine, its
temperature & pressure fall and it expands. Because of this expansion the blades are much larger
and longer towards the LP end of the turbine.
The turbine shaft usually rotates at 3000rpm. This speed is determined by the frequency of the
electrical system used and is the speed at which a 2-pole generator must be driven to generate
Alternating Current at a frequency of 50Hz in India. The speed is 3600rpm at a frequency of
60Hz for American systems.
When much possible has been extracted from the steam it is exhausted directly to the condenser.
This runs the length of the LP part of the turbine or may be beneath or on either side of it. The
condenser consists of a large vessel enclosing 20,000 tubes, each about 25mm in diameter. Cold
water from cooling tower is circulated through these tubes and as the steam from the turbine
passes round them it is rapidly condensed into water (condensate). Because water has much
smaller comparative volume than steam, a vacuum is created in the condenser. This allows the
steam to reduce down to pressure below that of the normal atmosphere and more energy can be
From the condenser, the condensate is pumped through Condensate Polishing Unit (CPU), Gland
Steam Condenser (GSC), Low Pressure Heaters (LPH) and drain cooler by the Condensate
Extraction Pump (CEP) after which it is passed through Deaerator for removing the dissolved
gases. Then its pressure is raised to the boiler pressure by the Boiler Feed Pump (BFP). It is
passed through further feed water heaters, High Pressure Heaters (HPH) to the Economizer and
then the boiler for reconversion into the steam.
23. STEAM TURBINES
Steam turbines are the devices which convert Heat energy of the steam into Mechanical energy.
The first device that may be classified as a reaction steam turbine was little more than a toy, the
classic Aeolipile, described in the1st century by Hero of Alexandria Roman Egypt. More than a
thousand years later, in 1543 Spanish naval officer Blasco De Garay used a primitive steam
machine to move a ship in the port of Barcelona. In1551, Taqi al-Din in ottoman Egypt described
a steam turbine with the practical application of rotating a spit. Steam turbines were also
described by Italian Giovanni Branca in 1629 and John Wilkins from England in 1648. The
devices described by al-Din and Wilkins are today known as steam jacks.
The modern steam turbine was invented in 1884 by the Englishman Sir Charles Parsons, whose
first model was connected to a dynamo that generated 7.5KW (10Hp) of electricity. The
invention of Parson’s steam turbine made cheap and plentiful electricity possible and
revolutionized marine transport and naval warfare. His patent was licensed and the turbine
scaled-up shortly after by an American, George Westinghouse. The parson’s turbine also turned
out to be easy to scale up. Parsons had the satisfaction of seeing his invention adopted for all
24. major world power stations and the size of generators had increased from his first 7.5KW to
Parsons First Turbine
Within parson’s life time, the generating capacity of a unit was enhanced about 10,000times.
And the total output from turbo-generators constructed by his firm C.A Parsons & Company and
their licensees, for land purposes alone had exceeded 30million Hp.
Turbines are broadly classified into two main types. They are
Impulse turbines and
An impulse turbine has fixed nozzles that orient the steam flow into high speed jets. These jets
contain significant kinetic energy, which the rotor blades shaped like buckets convert into shaft
25. rotation as the steam jet changes the direction. A pressure drop occurs across only at 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 exit pressure
(atmospheric pressure, or more often the condenser vacuum). Due to this high ratio of expansion
of steam in nozzle, it leaves with a very high velocity. Steam leaves the moving blades with
larger portion of maximum velocity. The loss energy due to this higher exit velocity is
commonly called the “carry over velocity” or “leaving loss”.
In the reaction turbine, the rotor blades are arranged to form convergent nozzles. This type of
turbine makes use of reaction force produced as steam accelerates through the nozzle formed by
the rotor. Steam is directed into the rotor by the fived vanes of the stator. It leaves stator as a jet
that fills the entire circumference of the rotor. The steam then changes the direction and increase
the speed relative to the speed of the blades. A pressure drop occurs across both the stator and
the rotor, with a steam accelerating through the stator and decelerating through the rotor, with no
jet change in the steam velocity across stage. But with a decrease in both temperature and
pressure, reflecting the work performed in the driving of the rotor.
Difference between Impulse and Reaction turbines
26. PORTIONS OF A STEAM TURBINE:
A typical steam turbine has 3 major portions, to extract maximum possible energy of steam and
convert it into mechanical energy. Though they are portions of a turbine but are referred as
turbine as the process of exposing vanes to steam and acquiring rotational energy is one after the
other but not simultaneously. The 3 major portions are
High Pressure turbine (HP)
Intermediate Pressure turbine (IP) and
Low Pressure turbine (LP).
HP turbine is of double cylinder construction. Outer casing is barrel type without any axial/radial
flanges. This kind of design prevents any mass accumulation and thermal stresses. Also perfect
rotational symmetry permits moderate wall thickness of nearly equal strength at all sections. The
inner casing is axially split and kinematic ally supported by outer casing. It carries the guide
blades. The space between casings is filled with the main steam. Because of low differential
pressure, flanges and connecting bolts are smaller in size. Barrel design facilitates flexibility of
operation in the form of short start-up times and higher rate load changes even at high steam
27. temperature conditions. For a typical 500MW, at HPT the temperature of steam would be around
540°C and pressure 170kg/sq.cm
IP turbine is of double flow construction. Attached to axially split out casing is an inner casing
axially split, kinematic ally supported and carrying the guide blades. The hot reheat steam enters
the inner casing through top and bottom center. Arrangement of inner casing confines high inlet
steam condition to admission breach of the casing. The joint of outer casing is subjected to lower
pressure and temperature at the exhaust. For a typical 500MW, at IPT the temperature of steam
would be around 540°C and pressure 170kg/sq.cm
Double flow LP turbine is of three-shell design. All shells are axially split and are of rigid
welded construction. The inner shell taking the first rows of guide blades is attached kinematic
ally in the middle shell. Independent of outer shell, middle shell is supported at four points on
longitudinal beams. Two rings carrying the last guide blade rows are also attached to the middle
shell. For a typical 500MW, at LPT the temperature of steam would be around 136°C and
STEAM SUPPLY AND EXHAUST CONDITIONS:
These include Condensing, Non-condensing, Re-heat, Extraction and Induction.
Condensing turbines are most commonly found in electrical power plant. These turbines
exhaust steam in a partially condensed state, typically of a quality near 90%, at a pressure well
below atmospheric to a condenser.
Non-Condensing are back pressure turbines are most widely used for process steam
applications. The exhaust pressure is controlled by regulating valve to suit the needs of the
process steam pressure. These are commonly found at refineries, distinct heating units, pulp and
paper plants and de-salination facilities where large amount of low pressure process steams are
Reheat turbines are also used almost exclusively in electrical power plants. In a re-heat
turbine, steam flow exits from high pressure section of the turbine and is returned to the boiler
where additional super heat is added. The steam then goes back into an intermediate pressure
section of the turbine and continues its expansion.
Extracting type turbines are common in all applications. In an extracting turbine, steam is
released from various stages of the turbine, and used for industrial process needs or sent to boiler
28. feed water heaters to improve cycle efficiency. Extraction flows may be controlled with a valve
or left uncontrolled.
Induction turbines introduce low pressure steam at an intermediate stage to produce additional
RSTPS STAGE-II TURBINE
RSTPS 500MW turbines are of condensing, tandem compound and reheat type. It consists of
three cylinders, horizontal disc and diaphragms and provided with nozzle governing. It is directly
coupled to generator. Turbine consists of 34 stages including HP turbine-14 stages, IP turbine-11
stages and LPturbine-9 double-flow stages.
MAIN COMPONENTS OF TURBINE:
HP & IP Cylinder: HP cylinder is of double shell construction and is made of
alloy steel. Outer shell is supported to the front pedestal (standard) at one end and exhaust
hood at the other end. Outer shell is common for HP and IP cylinders. The HP inner shell
is supported in the outer shell on four pads. The inner shell is keyed to outer shell on
upper and lower vertical center lines to locate it transversely. The horizontal joint
between cylinders is secured with the help of studs and nuts of alloy steel.
The HP turbine comprises of 14 stages including first stage, which is a Curtis wheel
stage. Each turbine stage consists of a diaphragm and set of moving blades connected to
a disc on the rotor.
LP Cylinder: The LP cylinder is of fabricated steel construction. The inner casing is
keyed to outer hood by four supporting pads for axial and transverse location. It is free to
expand for thermal differences.
The cross over pipe which carries steam from IP turbine to LP turbine is provided with an
expansion joint which absorbs the thermal expansion of the pipe without putting undue
stresses on turbine components. Exhaust hood spray will be done from condensate to
control the exhaust steam temperature through nozzles. Two expansion diaphragms are
29. provided on the top of LP turbine exhaust hood to rupture in case of condenser
HP, IP & LP Rotor: The turbine consists of HP and IP rotor combined and LP
rotor. Both are coupled rigidly. These rotors are supported on three journal bearings.
Bearing-I is of combined radial and thrust type. Others are journal bearings. Rotor bodies
are made of solid alloy steel forgings, which are machined. Rotor consists of shafts,
wheels, bearings, journals and coupling flanges.
Dove and tail grooves are machined on wheels to fix the moving blades.
Front Pedestal: Front pedestal is mounted at the front of HP cylinder and houses
turbine bearing-I, main oil pump on turbine shaft, centrifugal governor, operating
cylinder with its pilot valve, servo motor for control valve actuation, turbine oil trip
testing mechanism and hand lever for tripping of turbine.
Nozzles & Diaphragms: The steam is entered in to the turbine through nozzles
and flow is directed on to the buckets at the proper angle and velocity by the diaphragm
portion. Nozzles are made of solid chrome-iron alloy. In HP-IP cylinder, welded nozzles
Emergency Stop Valves: Two emergency stop valves are provided for 500MW
turbine. These valves are of full open or full close type. These valves are single disc type
operated by control oil pressure. Main steam enters through inlet passage. A strainer is
provided to prevent foreign material into the turbine and at outlet of valve, steam divides
into two passages and enter the top and bottom control valves steam pipes of turbine
Control Valves: There are six control valves through which steam is entering in to
the turbine. Three control valves mounted on the top of HP cylinder and three mounted at
the bottom. These control valves are of puppet type with venturi seat. The valve discs
have spherical seat to ensure tight seating. These valves are operated by double action
hydraulic oil servomotor. Sequential opening of control valves is effected by means of
cams and levers.
Combined Reheat & Intercept Valves: There are two parallel combined reheat
valves through which steam enters into IP turbine. It consists of an intercept valve and
reheat stop valve. Intercept valve of control type and stop valve is of full open/full close
type. A strainer is provided in valve to prevent foreign material entry in to the IP turbine.
These valve also operated by oil pressure.
30. Bearings & Couplings: HP – IP rotor and LP rotor are supported on three bearings.
Bearings No.1 is a combined radial and thrust type housed in Front Pedestal and other
bearings are journal type. HP – IP rotor is coupled to LP rotor by rigid coupling and LP is
coupled to Generator also by rigid coupling with gear wheel for turning gear
The thrust bearing absorbs axial thrust of turbine and generator; rotor consists of a
rotating thrust collar on the turbine shaft and two stationary Babbitt plates supported in
Barring gear or Turning gear: The steam turbine set is provided with an
automatic barring gear capable of continuously rotating the turbine shaft at 5.4rpm to
affect uniform cooling and warming up during shutdown and start up respectively. It is
meshed with AC motor and rotates Turbine rotor through gear train. It is provided in
between BP turbine and generator.
Emergency Blow down Valve: This valve is pneumatically closed and opened
by spring. Compressed air is used for closing the blow down valve and is admitted
through solenoid valve. Whenever turbine trips, control valves close fully. The control oil
system then energizes a solenoid air valve and release air from blow down valve and
makes it opened to condenser to carry.
Fixed points (turbine expansions):
Bearing housing between IP & LP
Rear bearing housing of LP turbine
Longitudinal beam of LP turbine
Front/rear housing of HPT can slide on base plates. Any lateral movements perpendicular to
machine axis are prevented by fitted keys. Bearing housings are connected to HP-IP casings by
guides, which ensure central position of casings while axially expanding and moving.
The LPT casing is located in center area of longitudinal beam by fitted keys cast in the
foundation cross beams. Axial movements are not restricted. The outer casing of LP turbine
expands from its fixed points towards generator. Bellows expansion couplings take the
differences in expansion between the outer casing and fixed bearing housing. Hence HPT rotor
& casing expands towards bearing-I while IPT rotor expands towards generator. The LPT rotor
expands towards generator. The magnitude of this expansion is reduced by the amount by which
the thrust bearing is moved in the opposite direction due to IPT casing expansion.
31. Turbine Oil Pump
In the 200 MW KWU turbines, single oil is used for lubrication of bearing, control oil for
governing and hydraulic turbine turning gear. During start-ups, auxiliary oil pumps (2Nos.)
supplies the control oil. Once the turbine speed crosses 90% of rated speed, the main oil pump
(MOP) takes over. It draws oil from main oil tank. The lubricating oil passes through oil cooler
(2 nos.) before can be supplied to the bearing. Under emergence, a DC oil pump can supply lub
oil. Before the turbine is turned or barred, the jacking Oil Pump (2 nos.) supplied high –pressure
oil to jack-up the TG shaft to prevent boundary lubrication in bearing. Refer to the below figures.
32. The oil systems and related sub-loop controls (SLCs) can be started or stopped automatically be
means of SGC oil sub-group of automatic control system. The various logics and SLCs under
SGC oil age given in the ATRS section.
MAIN OIL PUMP:
The main oil pump is situated in the front bearing pedestal and supplied the entire turbine with
lubricating oil and control oil, which is connected to the governing rack.
Turbine oil system consists of two no’s of injectors, Main oil pump, Oil coolers, duplex filter for
thrust bearing, Two no’s of AOPS, One EOP, Three no’s of JOPS and temperature control valve.
The Main Oil Pump Directly coupled with turbine shaft in bearing pedestal at bearing-I. After
2850 RPM of turbine speed the pump starts discharging oil pressure and running AOP
Automatically gets tripped at 540 RPM of turbine speed running JOP will get tripped.
33. Injector 1 and 2 takes oil from Main Oil Tank and provide suction of MOP. The MOP
Discharges Oil at 9.5kg/cm2 through Oil Coolers, temperature control valves and form the
lubricating oil header and uniformly flow through all turbine bearing with the help of throttle
valve. Here for the thrust bearing oil is only filtered with help of duplex of filter.
The oil temperature is maintained by temperature control valve, which is located after outlet of
oil cooler in MOT Room. The temperature of oil always maintained at 45 degrees.
TURBINE TURNING GEAR:
The turbine is equipped with a hydraulic turning gear assembly comprising two rows of moving
blades mounted on the coupling between IP and LP rotors. The oil under pressure supplied by
the AOP strikes against the hydraulic turbine blades and rotates the shaft at 110 rpm (220 rpm
under full vacuum condition). In addition, provisions for manual barring in the event of failure of
hydraulic turning gear have also been made. A gear, machined of the turning gear wheel,
engages with a Ratchets & Pawl arrangement operated by a lever and bar attachment.
TURBINE GLAND SEALING:
Turbine shaft glands are sealed with auxiliary steam supplied by an electro hydraulically
controlled seal steam pressure control valve. A pressure of 0.01 Kg/cm2 (g) is maintained in the
seals. Above a load of 80 MW the turbine becomes self sealing. The leak off steam from
HPT/IPT glands is used for sealing LPT glands. The steam pressure in the header is then
maintained constant by means of a leak-off control valve, which is also controlled by the same
electro hydraulic controller, controlling seal steam pressure control valve. The last stage leak-off
34. of all shaft seals is sent to the gland steam cooler for regenerative feed heating. Refer the below
TURBINE STEAM SEAL SYSTEM
TURBINE GOVERNING SYSTEM:
In order to maintain the synchronous speed under changing load/grid or steam conditions, the
KWU turbine supplied by BHEL at NTPC Ramagundam is equipped with electro-hydraulic
governor; fully backed-up by a hydraulic governor. The measuring and processing of electrical
signal offer the advantages such as flexibility, dynamic stability and simple representation of
35. complicated functional systems. The integration of electrical and hydraulic system is an excellent
combination with following advantages:
Exact load-frequency droop with high sensitivity.
Avoid over speeding of turbine during load throw offs.
Adjustment of droop in fine steps, even during on-load operation.
ELEMENTS OF GOVERNING SYSTEM:
The main elements of the governing system and the brief description of their functions are as
Remote trip solenoids (RTS).
Main trip valves (Turbine trip gear).
Starting and Load limit device.
Speeder Gear (Hydraulic Governor).
Aux. follow-up piston valves.
Follow-up piston valves.
Electro-Hydraulic Converter (EHC).
Sequence trimming device.
Solenoids for load shedding relay.
Extraction valve relay.
Oil shutoff valve.
Hydraulic protective devices.
Turbine Governor System type – 1:
Governors of the turbines basically control the steam flow to the turbine. The governor usually
takes the form of spring-loaded weights mounted on a shaft assembly that is driven by a worm &
wheel from end of the H.P. shaft. The weights, which are held by springs, tend to move outwards
due to centrifugal force and this movement is dependent upon the speed of the turbine shaft. The
movement of the weights is arranged to operate on oil relay valve and this valve through an oil
pressure relay system, opens or closes valves that admit steam to the turbine. When an increase
of load is required, more steam is admitted to the turbine by opening the steam valves.
Turbine Governor System type – 2:
The governor (A) is driven from the turbine shaft. An arm pivoted at (B) has attached to it, the
governor weights and a moveable sleeve (C). Sleeve (C) is connected to a floating lever (D) to
36. which is attached the spindle (E) of the pilot relay valve and the spindle (F) of the main steam
If the turbine shaft speed increases, the governor weight will move outwards causing sleeve C to
lift; this also tilts floating lever (D). These movements uncover the port (G) of the pilot valve
thereby allowing oil pressure to act on the top of the power piston (H). At the same time port (I)
in the pilot valve, allows oil to drain from the bottom (J) of the power piston. Due to this
operation, the steam valve will move towards the closed position, thus admitting less steam to
the machine. During installation and also afterwards, the governor springs are adjusted
periodically, so as to keep the range at which the governor operates between limits.
Loading on the machine is done/carried out by operating the hand wheel (K) thus opening the
steam valve. The hand wheel (K) is normally on remote operation from the control panel by
means of a reversible motor known as the “speeder motor”. Such governors do not use the
elector-hydraulic governors, which control the operation by electrical interfacing units i.e. the
electro-hydraulic converter. For detailed working of Governor, the drawing as shown below
should be referred.
SIMPLE TURBINE GOVERNOR SYSTEM TYPE – 2
The percentage of control valve opening on each turbine depends upon the electrical output from
that individual T.G, and in turn the entire system at the same speed (frequency). The system
frequency decreases, as more electrical load is required. To regain the previous frequency/speed,
37. the amount of fuel fed to the steam generator is increased adequately. Since with more customer
load on the system, the frequency tends to decrease then the governors on all the system turbine
need to operate (to open) the control valves to admit more steam to Turbine and allow the system
to supply the extra load.
Emergency governors (often referred as the Over speed Governor):
The emergency governor is the final line of defense to protect the turbine from dangerous over
speeds. This device, when actuated rapidly closes all valves associated with steam supply to the
turbine. Emergency governors are normally set to operate instantaneously if turbine speed
reaches 110% of rated (3300 rpm on a two pole turbine generator) or higher speeds. The
emergency governor shuts off the steam supply in the event of rotor speed increasing by more
than 10% above its normal speed. A sliding bolt or an eccentric ring is attached to the shaft.
These are held in position by means of a retaining spring.
38. The bolt or the ring flies out of the normal position. In doing so, it operates a trip and releases the
relay oil pressure, which is holding the emergency, valve open. The emergency valve then shuts
off the steam supply.
The emergency governor is tested at periods by deliberately over-speeding the machine when the
load has been taken off. Each of the twin bolts or rings is operated in turn. The one not being
tested is made inoperative by a selector lever.
To maximize turbine efficiency the steam is expanded, generating work, in a no of stages. These
stages are characterized by how the energy is extracted from them and are known as either
impulse or reaction turbine. The most steam turbines use a mixture of reaction and impulses
designs: each stage behaves as either one other, but the overall turbine use both. Typically,
higher pressure sections are impulse type and lower pressure stages are reaction type.
MAIN TRIP VALVES:
The main trip valves (two in number) are the main trip gear of the protective circuit. All turbine
tripping take place through these valves. The control oil from remote trip solenoids are supplied
39. Under normal conditions, this oil flows into two different circuits, called as the Trip oil and
Auxiliary trip oil. The trip oil is supplied to the stop valves (of HP turbine and IP turbine),
auxiliary trip oil flows in a closed loop formed by main trip valves and turbine hydraulic
The construction of main trip valves is such that when auxiliary trip oil pressure is adequate, it
holds the valve spools in open condition against the spring force. Whenever control oil pressure
drops or any of the hydraulic protective devices are actuated, the main trip valves are tripped.
Under tripped condition, trip oil pressure is drained rapidly through the main valves, closing
turbine stop and control valves.
Each of the HP and IP stop valves servomotors receives trip oil through their associated test
valves. The test valves have got port openings for trip oil as well as start-up oil. The test valves
40. facilitate supply of trip oil pressure beneath the servomotor disc. For the purpose of resetting stop
valves after a tripping, start up oil pressure is supplied to the associated test valves, which moves
their spool downwards against the spring force. In their bottom most position the trip oil pressure
starts building up the above the stop valve servomotor piston while the trip oil beneath the disc
gets connected to drain. When start-up oil pressure is reduced the test valve moves up draining
trip oil above the servomotor piston and building the trip oil pressure below the disc, thus
opening the stop valve. A hand wheel is also provided for manual operation of test valves.
41. Starting and load limit device:
The starting and load limit device is used for resetting the turbine after tripping, for opening the
stop valves and releasing the control valves for opening. The starting device consists of a pilot
valve that can be operated either manually by means of hand wheel or by means of a motor from
remote. It has got port connections with the control oil; start up oil and auxiliary start up circuits.
The starting device can mechanically act upon the hydraulic governor bellows by means of a
lever and link arrangement.
Before start-up, the pilot valve is brought to its bottom limit position by reducing the starting
device to 0% position. This causes the hydraulic governor bellows to be compressed, thus
blocking the build-up of secondary oil pressure. This is known as control valve close position.
With the pilot valve in the bottom limit position (starting 0%) control oil flows into the auxiliary
start-up circuit (to reset trip gear and protective devices) and into the start up oil circuit (to reset
turbine stop valves).
A build-up of oil pressure in these circuits can be observed, while bringing the starting device to
zero position. When the pilot valve i.e., the starting device position is raised, the start-up oil and
auxiliary start-up oil circuits are drained. This opens the stop valves: ESVs open at 42% and IVs
open at 56% positions of the starting device. Further raising of the starting device release
hydraulic governor bellows which is in equilibrium with hydraulic governor’s spring tension and
primary oil pressure (turbine speed) and raises the auxiliary secondary oil pressure; closing the
auxiliary follow-up drains of hydraulic governor.
43. VACUUM BREAKER:
The function of a Vacuum breaker is to cause an increase in condenser pressure by conducting
atmospheric air into the condenser together with the steam flowing from the LP bypass. When
the pressure in the condenser increases, the ventilation of the turbine balding is increased. This
causes the turbo set to slow down so that the running down time of the turbo set and the time
needed for passing through critical speeds are shortened.
The HP rotor is supported by two bearings, a Journal bearing at the front end of the turbine of the
combined journal and Thrust bearing adjacent to the coupling with the IP and LP rotor have a
journal bearing at the end of the shaft. The combined journal and bearing incorporates a journal
bearing and the thrust bearing which takes up a residual thrust from both the directions. The
bearing temperatures are measured in two opposite thrust pads.
The front and rear bearing pedestals of the HP turbine are placed on base plates. The pedestals of
the LP part are fixed in position. The front pedestal and the pedestal between the HP and the IP
parts are able to move in axial direction.
The brackets at the sides of the HP and IP parts are supported by pedestals at the level of the
machine axis. In the axial direction the HP and IP parts are firmly connected with the pedestal by
means of casing guides without restricting radial expansion. Since the casing guides do not yield
in response to axial displacement, the HP and LP casings as well as the associated bearing
pedestals move forward from the front LP bearing pedestal on thermal expansion.
Thrust bearing trip device:
The function of the thrust bearing trip is to monitor the shaft position in the bearing pedestal and,
if a fault occurs, to de pressurize the auxiliary trip medium and thus the trip oil in the shortest
possible time, thereby tripping the turbine.
The two rows of tripping cams, which are arranged on opposite sides of turbine shaft, have a
specific clearance, equivalent to the permissible shaft relative to pawl of the thrust-bearing trip.
If the axial displacement the shaft exceeds the permissible limit, the cams engage pawl, which
releases a piston to de pressurize the auxiliary trip oil and at the same time to actuate limit
46. Maintenance of Turbines
Maintenance of turbines includes the inspection of the working of turbines and ensuring that they
are working with the maximum efficiency.
This is done at two different times:
Over hauling and
Overhauling means regular inspection of the different components which includes turbines,
bearings valves etc., and their working.
Overhauling is done for every 20,000 to 25,000 working hours (2-3years).
This is done if there is a problem at present working condition i.e., more heat generation, less
turbine output etc.
Possible problems and their inspection methods:
Cracks in the blades (flank wear, crater wear).
Scales accumulation in the turbine blades.
Shaft and bearing failure.
Corrosion and erosion in the blades.
Inspection methods: Here we use non-destructive tests (NDT).
1. MPI (Magnetic Particle Inspection): In this blade is subjected to high magnetic
field followed by a fluorescent poured over the blade which highlights it.
2. NFT (Natural Frequency Test): In this the natural vibrating frequency of the blade
is being tested.
47. For bearings:
1. DTP (Dye-Penetration Test)
2. UST (Ultra-Sonic Test)
As accumulation of mass over the turbine blades causes loss of energy and decreases the
efficiency of the turbine and requires more energy for same work output.
To avoid this abrasive jet cleaning is used to remove the accumulated mass.
ABRASIVE JET CLEANING: the removal of dirt from a solid by a gas or liquid jet carrying
abrasives to ablate the surface.
In this process high speed abrasive jet is sprayed over the blades which removes the
accumulated mass over the turbine and improves the efficiency of the turbine. Abrasives used are
generally Aluminum Oxide (Al2O3) and Silicon Carbide (SiC).
Turbine oil system consists of two no’s injectors, main oil pump, oil coolers, duplex filter for
thrust bearing, two no’s of AOPS, one EOP, three no’s of JOPS and temperature control valve.
The main oil pump directly coupled with turbine shaft in bearing pedestal at bearing I. After
2850rpm of turbine speed the pump starts discharging oil pressure and running AOP
automatically gets tripped at 540rpm of turbine speed running JOP will get tripped.
Injector 1 and 2 oil from main oil tank and provide suction of MOP. The MOP discharges oil at
9.5Kg/cm^2 through oil coolers, temperature control valves and from the lubricating oil header
and uniformly flow through the entire turbine bearing with the help of throttle valve. Here for the
thrust bearing oil is only filtered with the help of duplex of filter. The all bearings return oil is
cooled to main oil tank.
The oil temperature is maintained by temperature control valve which is located after outlet of
oil cooler in MOT room. The temperature of oil is always maintained at 45ºC.
48. AUTOMATIC TURBINE TESTING (ATT)
Under the present crunch of power crisis, the economy dictates long internals between turbine
overhauls and frequent shutdowns. This warrants testing of equipments and protection devices at
regular intervals, during normal operation.
The steam stop valve and control valves along with all the protection devices on the turbine must
be always maintained in serviceable condition for the safety and reliability. The stop and control
valves can be tested manually from the location but this test does not cover all components
involved in a tripping. Also, manual testing always poses a risk of mal-operation on the operator,
which might result on loss of generation or damage to machine components.
These disadvantages are fully avoided with the Automatic Turbine Test.
A fully automatic sequence for testing all the safety devices has been incorporated which ensures
that the testing does not cause any unintentional shutdown and also provides full protection to
turbine during testing.
The Automatic Turbine Tester is distinguishable by following features:
Individual testing of each protective device and stop/control valve assembly.
Automatic functional protective substitute devices that protect turbine during ATT.
Only its pretest is carried out without any faults i.e. if the substitute circuit is healthy, the
main test begins.
Monitoring of all program steps for executions within a predefined time.
Interruption if the running time of any program steps is exceeded or if tripping is
Automatic re-setting of test program after a fault.
Full protection of turbine provided by special test safety devices.
49. Automatic turbine testing extends into trip oil piping network where total reduction of trip oil
pressure due to actuation of any protective device, is the criteria for the satisfactory functioning
During testing, general alarm or the cause of tripping is also initiated so that this part of alarm
annunciation system also gets tested. Also, during testing, two electrically formed values of
3300rpm take over protection of turbine against over speed.
The testing system or automatic turbine testing is sub-divided into two functional sub-groups.
STOP/CONTROL VALVES PROTECTIVE DEVICES
Automatic testing of protective devices:
ATT sub group for protective devices covers the following devices.
1. Remote trip solenoid-1,
2. Remote trip solenoid-2,
3. Over speed trip device,
4. Hydraulic low vacuum trip device and
5. Thrust bearing trip device.
During normal operation, protective devices act on the stop/control valves via the main trip
valves. Whenever any tripping condition (hydraulic/electrical) occurs, the protective device
concerned is actuated. It drains the control/auxiliary trip oil, closing the main trip valves. The
closure of main trip gear drains the trip oil, causing stop/control valves to close.
During testing, trip oil circuit is isolated and changed over to control oil by means of test
solenoid valves and the changeover valve. This control oil in trip circuit prevents any actual
tripping of the machine. However, all alarm/annunciation are activates as in case of actual
ATT for protective devices broadly incorporates the following sub program.
50. a) Preliminary test program
b) Hydraulic test circuit establishment
c) Main test program
d) Reset program.
52. TESTING OF PROTECTIVE DEVICES
The main trip valve and remote trip solenoid valves have already been discussed in previous
chapters; hence the remaining ones will be taken up here.
Over speed trip device: Trip consists of two eccentric bolts on the shaft with centre of
gravity displaced from the shaft axis. They are held in position against centrifugal force by
springs whose tensions can be adjusted corresponding to 110%-111% over speed. When over
speed occurs, the fly weights (bolts) fly out due to centrifugal force and strike against the pawl
and valves, draining auxiliary trip oil pressure and tripping turbine.
Hydraulic over speed trip device: two hydraulically operated over speed trips are
provided to protect the turbine against over speeding in the event of load coincident with failure
of speed governor.
53. When the preset over speed is reached, the eccentric fly bolt activates the piston and limit switch
via a pawl. This connects the auxiliary trip oil to drain, thereby depressurizing it. The loss of
auxiliary trip medium pressure causes the main trip valve to drop, which in turn causes the trip
oil pressure to collapse.
Lower Vacuum Trip Device:
With deterioration of vacuum, pressure builds-up over the diaphragm, the spool valve move
down, causing valve also to move towards lower position. The aux. trip oil pressure drains,
tripping main trip valve and turbine stop/control valves. During ATT, after hydraulic test circuit
is established, the HTT (Hydraulic Test Signal Transmitter) gets energized and connects the
space above diaphragm to atmospheric pressure through an office. The device operates, bringing
in the associated alarm. As soon as reset program starts, HTT is de-energized and vacuum trip
device is automatically reset, field adjustment facilities and checks have been provided when
turbine is stationary and there is no vacuum in the condenser.
Thrust Bearing Trip Device:
This device operates in case of excessive axial shift (>0.6mm) or excessive thrust pad wear. Two
rows of tripping cams on shaft engage with the pawl under high axial shift condition. Valve
spool moves up draining aux. trip oil and tripping the trip gear and turbine. During ATT,
associated ATT solenoid is energized and test piston valve. The piston rod actuates the pawl and
spool valve assembly, bringing in the associated alarms. During resetting, HTT is de-energized
and aux. start-up oil (control oil) reset the device back into normal position.
Automatic Testing of Stop/Control Valve:
The combined stop/control valves are final control elements of the turbine governing system.
They must be maintained in absolutely workable condition for safety and reliability of turbine.
All the four stop and control valve assemblies are tested individually.
54. TURBINE STRESS EVALUATOR (TSE)
SIGNIFICANCE OF TURBINE STRESS MONITORING:
It is important for the operator to know how quickly his turbine can be started up and changed in
load he can make without the fear of over-stressing the turbine components; thereby causing
excessive fatigue. Whenever steam inlet temperature changes within the turbine, the metal
temperature follows the steam temperature changes with a certain delay. This causes differential
thermal expansions within the turbine casing and shaft & corresponding stress in the metal.
Thermal over-stressing can reduce useful operation life of turbine and its components. Turbine
Stress Evaluator measures and calculates the relevant temperature valves and evaluates them in
an analog computing circuit and determines the allowable conditions of operation so that useful
life of the turbine shall not be unduly reduced. Thus it allows the operation of the turbine at the
highest possible rates of load/speed change while limiting the stresses within permissible values.
The results of TSE, which are the appropriate Operating instructions, are displayed by means of
an indicating instrument.
TASK OF TSE:
If the turbine is to be operated so that there is no undesirable material fatigue, these thermal
stresses must be kept within acceptable limits. The optimum balance between longevity on one
hand and material flexibility of operation on the other is achieved when the permissible range of
material stress can be utilized to the fullest extent.
The turbine stress evaluator provides the basis of continuously calculating permissible values for
desired changes in operating conditions at all times and under all operating states and by
displacing temperature margins, within which the speed/load can be changed during
loading/unloading of the machine. Signals from the TSE are also fed to the speed and reference
limiter of the turbine controller for use in set point and gradient (speed and load) control.
Shaft Temperature Simulation:
If the thermal stress in rotor is to be monitored, surface temperature on the inside of casing
surrounding the rotor is measured by a signal thermocouple at a point where the dynamic
behavior of temperature of the shaft corresponds to that of casing. It is taken as the surface
temperature of shaft itself. The corresponding mean shaft temperature, depending upon machine
load, steam temperature and time lapsed.
55. The mean internal (mid metal) shaft temperature can be calculated with an adequate degree of
accuracy by means of the following mathematical equation.
TM = Ts [1-(0.692e-t/T1+0.131e-t/T2+0.177e-t/TK)]
Where, TS: Surface Temperature T1: 2408.31
Tm: Mid metal Temperature T2: 457.O8
t: Time in minutes TK: 56.62
Various constants used in the above equation are derived from the shaft diameter and thermal
diffusivity of the rotor material. The solution of this equation is realized by means of three
integrators and one summing amplifier.
Normally 5 measuring points feed the TSE. First two measuring points are located in the body of
combined Stop/Control valves are called ADMISSION sensors. The next two are located in the
HPT cylinder adjacent to the first drum stage and are called HPT wall temperature sensors. The
last measuring point is in the flange of IPT cylinder inner casing, before the last drum stage to
represent the surface temperature of the shaft.
In the steam turbine, the kinetic energy of the steam is directly utilized to rotate the rotor.
Steam turbines can be directly coupled to high speed machines and generate power
ranging from a few MW to 1000MW.
Exhaust steam is free from oil; hence condensate can be reused as feed water.
Governing of steam turbines is easy.
A. Turbine. Encyclopedia Britannica online.
B. A new loo at Heron’s “STEAM ENGINE” (1992-06-25). Archive for History of Exact
D. Parson’s Sir Charles A. “THE STEAM TURBINES”.