turbines

PROJECTCUMINTERNSHIP REPORTL&t-mhiTurbine generators pvt. Ltd.

SUBMITTED BY:-Anurag maheshwariDayalbagh educational instituteAgra

Preface

AcknowledgementFirst of all, I am highly grateful to my institute for giving me this wonderful opportunity to accomplish my training in this world-class company.Since the list is endless, yet I would like to thank some key people who certainly made my training successful.I would like to thank Ms. Poorvi Mehta for giving me the chance to fulfil my internship in this privileged company.I would like to thank Mr. Aloke Sarkar( General Manager-Production shop) for giving me valuable guidance throughout the training.I would like to thank Mr. Rajneesh Bajaj, Mr. Sanjay Narang, Mr. Devdutt, Mr. kaushik Das, Mr. Chetan Patil, Mr. Bharat Pawar, Mr. Sanjay Verma, Mr. Abhilash Dubey, Mr. Rajeev Vishwakarma, Mr. N.K. Dey for their valuable guidance during induction program.

CONTENT

L&T MHI TURBINE & GENERATOR

COMPANY PROFILE:

Larsen & Toubro Limited (L&T) is a technology, engineering, construction and manufacturing company. It is one of the largest and most respected companies in India's private sector. L&T was founded in Bombay (Mumbai) in1938by two Danish engineers, Henning Holck-Larsen and Soren Kristian Toubro. Both of them were strongly committed to developing India's engineering capabilities to meet the demands of industry.

More than seven decades of a strong, customer-focused approach and the continuous quest for world-class quality have enabled it to attain and sustain leadership in all its major lines of business. Considered to be the "bellwether of India's engineering sector", L&T was recognized as theCompany of the Yearin 2010.L&T has an international presence, with a global spread of offices. A thrust on international business has seen overseas earnings grow significantly. It continues to grow itsglobal footprint, with offices and manufacturing facilitiesin multiple countries.

L&T comprises engineering and construction projects, heavy engineering, Construction, electrical and electronics, information technology, machinery and industrial products and, L&T power. L&T has set up an organization focused on opportunities in coal-based, gas-based and nuclear power projects. L&T has formed two joint ventures with Mitsubishi Heavy Industries, Japan to manufacture super critical boilers and steam turbine generators. Larsen & Toubro Limited (L&T) and Mitsubishi Heavy Industries Limited (MHI) have inked a Joint Venture Agreement for setting up a manufacturing facility to supply Environment friendly super-critical Steam Turbine & Generator facility inHazira.This follows a Technology Licensing and Technical Assistance Agreement for manufacture of super-critical Turbine & Generator, signed between L&T MHI, and Mitsubishi Electric Corporation (Mitsubishi Electric).

The product, an integral component of energy efficient coal based power plants, is expected to meet the demand / supply gap for power plant equipment as envisaged in the countrys plan for a mega ramp up in power generation capacity using super-critical technology.

L&T POWER VISION 2015

L&T Power shall be Indias most preferred provider of equipment services and turnkey solution for fossil fuel-based power plants and a leading contributing to the nations power generation capacity.

L&T POWER MISSIONL&T Power shall provide products based on efficient and environment-friendly technology, consistently surpassing customer expectations of quality and on-time delivery.

L&T Power shall follow fair, transparent and ethical practices in its interactions with all stake holders and achieve performance excellence by innovation and continuous improvement in people, product and services.

L&T Power shall foster a culture of care, trust, challenge and empowerment among its employees.

LMTG MISSIONTo emerge as a Market leader in the field of Design, Manufacturingand Supply of Steam Turbines & Generators, through Continual Improvement, Employee Involvement, Safety and Respect for Environment.

Product at LMTG Supercritical Turbines:

Main steam pressure is 24.2 MPa and temperature is between 538 C to 600 C. While re-heater temperature is between 566C to 600C.

Company designs and manufactures tandem compounded steam turbine with following arrangement:

Unit size ranges from 500MW to 1000 MW capacity.

The combined HP/IP turbine is applied to 500MW, 600MW and 800MW while separate HP/IP is provided for 1000MW ratings.

500MW has one LP turbine while 600MW has one or two LP turbines depending on temperature.

800MW and 1000MW have two sets of LP turbines.

Introduction to Steam Turbine

Steam Turbine is a rotating machine which converts heat energy of steam to mechanical energy.

When a steam is allowed to expand through a narrow orifice, it assumes kinetic energy at the expense of its enthalpy. This kinetic energy of steam is changed to mechanical (rotational) energy through the impact or reaction of the steam against the blades.

The blades are designed in such a way, that the steam will glide on and off the blade without the tendency to strike it.

As the steam moves over the blades, its direction is continuously changing and centrifugal pressure exerted as a result is normal to the blade surface at all points. The total motive force acting on the blade is thus the resultant of all the centrifugal forces and the change in momentum. This causes the rotational motion of the blades.

Working PrincipleSteam Turbine is one of the principle equipment of a Thermal Power Plant along with boiler, condenser and heaters which work together on closed liquid vapour cycle. Steam Turbine is regarded as a prime mover which rotates the generator for producing electricity.

The driving force for rotation in turbine is generated by superheated steam supplied from Boiler. The potential energy of steam available in the form of pressure, temperature & heat is converted into kinetic energy in the row of fixed blades arranged circumferentially to form nozzles. The high velocity steam generated at the expense of pressure drop in nozzles passes through another row of blades mounted on shaft. While passing through this row, the steam reverses its path which gives rise to change in momentum. This change develops driving force according to second law of Newton which states that whenever there is change in momentum an impressed force is generated which is proportional directly to rate of change of momentum. Since these blades are mounted on shaft which is free to rotate, the developed force starts rotating the shaft.

Supercritical Turbine:

L&T MHI Turbine LMTG

Supercritical technology has evolved over the past 30 years. Advancements in metallurgy and design concepts have made supercritical technology units extremely reliable and highly efficient. Modern supercritical technology is largely available in Japan and Europe for Boilers & Turbines ranging up to 1000 MW.

The term "supercritical" refers to main steam operating conditions, being above the critical pressure of water (221.5 bar). The significance of the critical point is the difference in density between steam and water. Above the critical pressure there is no distinction between steam and water, i.e. above 221.5 bar, water is a fluid.If the steam pressure is greater than 275 bar, then conditions are Ultra Supercritical.

Supercritical steam cycle with one reheat:

a b: Condensate cycle up to Deaerator b c: Boiler feed pump discharge c d: Feed water heating d e: Main steam generation e f: Expansion in turbine f g: Reheat steam generation g h: Expansion in turbine

In supercritical cycle, equipment is designed to operate above the critical pressure of water. Supercritical boilers are once-through where in the feed water enters the economiser and flows through one path and main steam exits the circuit. Typically current supercritical units operate at 242 bar main steam pressure, 565C main steam temperature and 593C reheat steam temperature.

Advantages of Modern Supercritical Technology:

Higher Efficiency:

Supercritical steam conditions improve the turbine cycle heat rate significantly over subcritical steam conditions. The extent of improvement depends on the main steam and reheats steam temperature for the given supercritical pressure. A typical supercritical cycle will improve station heat rate by more than 5%. This results in fuel savings to the extent of 5%.

Emissions:

Improved heat rate results in 5% lesser fuel consumption and thus 5% reduction in CO2 emission per MWH energy output.

Operational Flexibility:

Supercritical technology units also offer flexibility of plant operation such as:

Shorter start-up times Faster load change flexibility and better temperature control Better efficiency even at part load due to variable pressure operation High reliability and availability of power plant

Thermal Cycle EfficiencyThe efficiency of a thermal power plant can be expressed as the product of efficiencies of its subsystem.

power plant = boiler x TG cycle x turbine x generatorTypical values of these efficiencies for a modern thermal power plant employing reheat and regenerative feed water heating are as follows:

boiler = 85 to 88% turbine = 60 to70% generator = 98 to 98.6% TG cycle = 44 to 48% (subcritical steam condition) = 48 to 53% (supercritical steam condition) powerplant= 37.5 to 43% Boiler , Turbine , Generator are fairly high and have almost peaked, only incremental improvements is taking place. TG Cycle is lower because it is governed by thermodynamic laws and depend on MS and RHS Temperature and Condenser Vacuum

MAIN COMPONENTS OF A STEAM TURBINE

Blades Turbine Casing Rotor Gland Seals Couplings Bearings Bearing Pedestals Stop & Control Valves Governing System Lubrication System Drain System Control & Instrumentation Turning Gear

Turbine Blades: Blades are the key component of turbine as conversion of energy to develop driving force takes place therein. The blades which form nozzles and are fixed are called stationary or guide blades. The blades mounted on rotor are called moving blades.

Turbine Casing: The guide blades of various stages are held in the stationary body called casing. It also acts as a cover for steam passage with connections for steam admission, exhaust and other flows.

Rotor: It holds the moving blades of various stages in the grooves machined in it.

Gland Seals: Since turbine casing and rotor are respectively stationary and rotating parts, there is bound to be clearance between the two at the ends. The steam tries to escape through these clearances causing working atmosphere non conducive in power station for working personnel. To minimize this leakage, gland seals are provided at the two ends of turbine.

Couplings: They connect the rotor s together and transmit the torque finally to generator for turning.

Bearings: For supporting the rotors at the two ends to enable them rotate freely bearings are provided. These bearings are journal bearings supplied with forced lubrication. Ball bearings are not suitable as they are not capable to take high loads. Bearing Pedestal: They support the bearings and house the lube oil piping and drain oil pipe work. They also enclose various instrumentation which monitors healthiness of turbine during operation.

Stop & Control Valves: Turbine does not run at full load at all the times. Its output is regulated by the electric grid it is connected. For producing power, matching to varying load demand, the supply of steam quantity is regulated by control valves. For taking care of emergency situations stop valves are also provided which cut off the supply of steam turbine under such situation. They have only two positions either fully open or fully closed.

Governing System: An elaborate governing system is provided for turbine to control the opening of control valves to supply amount of steam according to varying load demand. The system senses the load variation in the form of speed change, convert it to hydraulic signal, amplify it and operate the actuators/ servomotors coupled to control valves. Apart from load changes, the system also acts during emergency situations to safe guard the turbine. The system comprises of mix of electronic, electrical & hydraulic devices

Lubrication System: The TG journal bearings are provided with forced lubrication so as to form hydraulic film between journal & bearing surface to support the rotor. During the course of running the lube oil gets heated up due to friction and need to be cooled, filtered, purified and pumped back to bearings. A closed lubrication system consisting of a reservoir, pumps, filter cooler and purifier forms the essential part of turbine.

Drain System: During non-steady state operating conditions, the mismatch between turbine component metal temperatures and steam causes condensation which gets collected in piping & casings. This condensate is withdrawn by drain system otherwise it would flash back during load changes and deform casing rotor and blading.

Control & Instrumentation: During operation a host of parameters e.g. steam pressure, temperatures, lube oil pressure temperature, metal temperatures, expansions, rotor speed & eccentricity etc. are continuously monitored, supervised through various instruments and supervisory devices. On the basis of these control & instruments, safe, reliable and uninterrupted operation of turbine within defined design limits is ensured.

Turning Gear: A turning gear is provided to rotate the turbine rotor slowly prior to start-up and after the turbine is shutdown to allow unified warm-up and cooling, maintain eccentricity and to prevent the thermal distortion of the rotor. It can be electric motor driven unit and in others oil driven driving unit/hydraulic motor.

Super Critical Turbine Projects at L&T MHI Turbine Generator Pvt. Ltd., Hazira

Some of the completed and on-going projects at LMTG.

RAJPURA, Thermal Power Project, Punjab (2 660 MW) MAHAGENCO, Koradi, Maharashtra (3 660 MW) JAYPEE Super Thermal Power Project, M.P. (2 700 MW) APPDCL , Andhra Pradesh (2 x 800 MW ) RABIGH (2 x 120 MW )

Upcoming project:- RRVUNL, Rajasthan (2 x 660 MW )

Steam parameters

Main Steam Pressure 242 BarMain Steam Temp 565 0CReheat Temp 593 0C

Manufacturing and Assembly at Hazira:-

The complete turbine manufacturing is done in the following shops:

Fabrication Shop Machining Shop Assembly Shop Blade Shop Stator coil shop Ancillary shop HSBT Facility

Components manufactured in LMTG:-1. LP outer casing2. LP inner casing3. HP pedestal4. Generator Frame5. Main oil tank6. Blades7. Rotor ( only groove machining for holding blades)

Components of Assembly:-1. HIP2. LP1 & LP23. Valve assembly4. Generator5. Rotor6. Blades7. Pedestal

Steam flow in Turbine

DETAILS OF COMPONENTS OF STEAM TURBINETurbine CasingA turbine cylinder is essentially a pressure vessel with its weight supported at each and on the horizontal central line. It is designed to with stand hoop stresses in the transverse plane and to be very stiff in the longitudinal direction in order to maintain accurate clearance between the stationary and rotating parts of the turbine. Due to the need for internal access casings are split along horizontal centre line allowing the rotor to be inserted as a complete assembly flanges and bolting are required to withstand the pressure forces at the joint. Massive flanges set up thermal stresses and distortion which are minimized by suitable casing construction. Stress complexities are also set up by the steam entry, exist, regenerative extraction passages and gland housings at ends. HP & IP casings are of cast construction while LP is made by fabrication of carbon steel plates as it is not exposed to high pressure & temperature steam. Steam entry, exit, flanges & bolts and other features are as far as possible symmetrically arranged to have thermal symmetry and avoid distortion. Steam is admitted in casing and exhausted from it by pipes in radial orientation. At LP cylinder exhaust the connection to condenser however normally is rectangular. The steam in casings is therefore required to turn through a right angle to enter the axial flow blade and exhaust from it and at same time redistribute itself around circumference. The inlet and exhaust areas are therefore given sufficient space to allow an orderly flow without undue pressure loss or flow separation. Being under pressure, casing design integrity is checked after manufacture with hydraulic pressure testing to 150% of highest working pressure wherever possible constructionally.Forms of Casing:-A. Classification According to Direction of Flow a) Single Flow Casingb) Double Flow Casingc) Reversed Flow CasingB. Classification According to Number of Shells a) Single Shell Casing b) Double Shell Casing

Turbine RotorAmong the steam turbine assemblies, rotor is the most critical one. They are the vital element involved in conversion of kinetic energy of steam into mechanical energy of rotation. They run at high speed depending upon grid frequency (50Hz, 60Hz) and subjected to severe duty thermally also. They have four major portions: Axially flows path area - where group of stages are arranged, Gland seal area, bearing area, coupling ends. Rotors are classified in three broad categories:

A typical rotor consists of four areas: axially flows path area, gland seal area, bearing area & coupling ends. Based on flow path area, rotor is classified into-1. Disc type rotor There is no axial thrust on moving blades. This kind of rotor is used in Impulse turbines.2. Drum type rotor Axial thrust exists on the moving blades. This kind of rotor is used in Reaction turbines.Based on rotors critical speed, rotor can be classified into-

1. Flexible rotor Rotors having critical speed < Operating speed.2. Rigid rotor Rotors having critical speed > Operating speed.Critical speed is that speed of the rotor at which the natural frequency of the rotor matches with the rotational frequency at the operating speed. The critical speed of the rotor is a function of diameter of rotor and distance between the bearings. Critical speed should be at least 10% greater than operating speed.

If the bend shafts are coupled together, coupled ends will experience Bending moment resulting in excessive vibrations. So to minimize this bending moment, each shaft is arranged that coupled faces become parallel. To achieve this condition during initial erection, bearings are set at different heights so as to form a catenary shape. These bearing heights at different locations are determined by HSBT (High Speed Balancing Test).

Bearing and Bearing Pedestal

The Bearing performs the following functions: - It retains the rotor in correct radial position with respect to the cylinder. It provides low friction support and withstand dynamic load of rotating shaft. It takes away the heat generated due to friction.

Each turbine rotor has two journal bearings for both ends, and one shaft system has one thrust bearing. They are all of forced lubricated type, i.e., the load is carried by hydro dynamically generated film of lube oil. The bearing surface is made of Babbit metal which is an alloy having low coefficient of friction and an excellent conductor of heat.

For cooling & lubrication, oil is supplied at about 1 to 1.5 bar pressure through oil pump. Temperature of oil is maintained at 30-35C. All the bearings have thermocouples for detecting the metal and oil drain temperatures. The turbine is incorporated with grounding device to prevent the shaft voltage trouble.

Bearing Pedestal performs the following functions: - It supports the rotor via journal bearing & maintaining gland clearances & also inter-stage clearances. It houses the lubricating & jacking oil supply piping & bearing oil drain pipe work. Encloses various instrumentation connections. E.g. bearing temperature, speed measurement, differential expansion, electricity, vibration pick-up, etc. It covers the rotor coupling. Oil guard rings provided at the two ends of pedestals prevents the leakage of oil & vapors.

TURNING GEARA Turning Gear is engaged at start-up and shutdown to slowly rotate the turbine (10-15 RPM). It prevents the uneven expansion which may distort the turbine rotor and casings. Either it is an Electric motor driven or an oil driven/ hydraulic motor driven unit.

STEAM CHEST It is housing for emergency stop valves & governing valves. Steam is admitted to HP cylinder via the HP piping to these valves. Similarly, it is there between hot reheat pipes & IP cylinder. It is manufactured from alloy steel castings to withstand pressure stresses, thermal stresses & fatigue. IP chest (low pressure) is thinner but larger than HP chests.

STEAM STRAINER It is provided in order to avoid foreign solid particles being carried into turbine with incoming steam. It has 2-5 mm diameter holes. These are housed in chests provided in main/reheat pipes or in some cases, these are housed within the stop valve itself.

STOP VALVESIts purpose is to cut-off steam supply during shut down & emergency trip. It is either fully open or fully closed. These are normally provided with a pilot valve.

GOVERNOR VALVE It regulates steam flow to turbine according to load when machine is synchronized to the grid.

LOOP PIPESIt connects the steam chest to the turbine. The pipes enter the cylinder in upper half & lower preferably in radial direction.

CROSS OVER PIPESSteam from IP cylinder is taken to LP cylinder through large size cross over pipes.

FABRICATION SHOPThis shop is primarily for fabrication of outer casings of the LP turbine, HP Pedestal & Generator stator frame. Various types of welding processes like GMAW, GTAW, and SMAW & FCAW. The table below shows the general work system being carried out at the fabrication department.

INPUTSPROCESSESOUTPUTS

Raw materials like steel plates, steel sections, and pipes.

Semi-finished parts like castings, rough machined components, HIP outer casings

Finished parts like SSB Diaphragm blades, Rateau blades Cutting processes like CNC cutting, Manual cutting, Oxyfuel cutting & plasma cutting. Plate bending, Plate rolling & Pipe bending. Weld Edge preparations Fit up process Welding process Heat treatment Shot Blasting Painting LP inner & outer casings HP Pedestal Thermal Shield Main Oil Tank Top Seal Rings SSB, Bladed diaphragm, HP Nozzle ring HIP outer casing with welded steam inlet sleeves Generator stator frame

Some of the other facilities in the fabrication department are as follows: -1. CNC CuttingCNC gas cutting cuts C-steel plates up to 250 mm. CNC Plasma cutting cuts SS Plates up to 38 mm. The machine is pre-loaded with various profiles like circle, rectangle, etc. it can also be manually fed shape using USB port present in the main console. Gas cutting mainly involves pre-heating the material using oxy-acetylene mixture and then cutting using a high-pressure oxygen jet. 2. Bending / Rolling machineFully hydraulic machine with the main rotor running all the other motors and hydraulic components. Upper roll can be moved vertically up and down to adjust the thickness. Bottom two rolls can be moved horizontally.

3. Hydraulic Press Machine (200T)There is a main hydraulic motor present along with the oil sump to control all the operations. Various dies are present which can be easily fixed to the press as per the requirements. 2 cranes of 1 ton capacity are present on either side of the press in case load needs to be jot into position. 4. Shot Blasting BoothIt basically consists of impinging steel balls & grit onto the given job with a large force by using air pressure. It is a fully manually operated machine. 4 feeders are present which supply the balls to the machine. The balls after being used are collected using a feeder belt and reused.It is used to remove loose particles like dust from the surface of the job and also used to increase the roughness of the job which prevents its rusting. Painting needs to be done within 2 hours of the blasting operation. It is done using pipes fitted with nozzles and the direction can be easily controlled. Dust collector is present behind the machine to collect the dirt and scales.

5. Gas Fired Bogie Hearth Batch type FurnaceIt is basically a gas-fired furnace that uses PNG to light up the furnace. It is used for the purpose of stress relieving/ annealing. It is divided into 8 zones which can be individually controlled by the controller.

The cycle consists of heating the job at the rate of 80C and then further heating the job at the rate of 55C till it reaches a temperature of around 625C. Further it is held at this temperature for about 3.5 hrs. After this it is cooled at the same rates as it is heated. 4 thermostats are present in the furnace to continuously monitor the temperature. A chimney is provided at the rear to exhaust the combustion products. 2 blowers are present at the rear to pump in air for combustion.

Processing in Fabrication shop

Machine Shop

MACHINING WORKS AT LMTGThis shop is the back-bone of whole production. Some of the machine specifications comprising this shop are as follows:-

Machine Specifications: Gantry Plano Miller GPM /ST26

Make Schiess X axis (Columns)25m

Y axis (Vertical head)10.85m

Z axis (ram)0.3m

W axis (Cross rail)3m

Distance b/w columns8.5m

Max height of job5m

Max length24m

Power100KW

Torque9000Nm

HBM 101 /Gen 8Make Skoda, Czech Rotary table -150T

X axis (Column)19m

Y axis (Head stock)6m

Z axis (ram)1.3m

Power100KW

Max speed2500rpm

VPM/HBM 104/ST6Make- PAMA, Italy Rotary table 100TX axis (Column)15m

Y axis4.5m

Z axis (Ram)1.2m

W1000mm

Power91KW

Max speed2500rpm

VTL 101/ST5

Make HNK, KoreaMax Dia. Of Table6m

VC of table0-40rpm

Swing dia9.5m

Ht. of job4.5m

Power171KW

Spindle VC1000rpm

Wt. of job80MT

VTL 201/ ST9

Make HNK, KoreaDia3m

Spindle speed80rpm

X-200/ +2225mm

Y (ram)1800mm

W (cross rail)2m

Wt of job30T

Ht of job3m

Power60/75KW

Swing dia4m

PM 202/ ST 13

Make MHI, JapanX9m

Y4.9m

Z1m

W2.2m

Ht of job3.05m

Max speed4000rpm


Power45KW

PM 201/ Gen 6

Make MHI, JapanX5m

Y4.2m

Z1m

W2.2m

Max speed4000rpm

Ht of job3.05m


Power45KW

HBM 202/ UDM2X5m

Y2.1m

Z1.3m

W1.4m

Z+W1.4m

Speed400rpm

Power30KW

HBM 201/ UDM 1X4.6m

Y3.5m

Z0.9m

Max speed100

Power33KW

VTL 301/ Gen 7X1000/1700mm

Z1200mm

W1000mm

Speed120rpm

Table dia2.5m

Power33KW

Swing dia3m

Wt15T

Ht2m

FHB/HBM 203/UDM 5X6.4m

Y2.67m

Z1.1m

Speed210rpm

Power26KW

HBM 103/ST15Make- Pama , Italy Rotary table -100T

X15m

Y4.5m

Z1.2m

W1m

Speed210rpm

Power91kW

BLADE SHOPTurbine BladesBlades are the key component of a steam turbine as they convert the potential energy of steam available in the form of pressure, temperature & heat into rotational kinetic energy. Blades fitted in stationary casing are called guide blades/stationary blades and those fitted in the rotor are called moving blades. A group of guide & moving blade is called a stage of turbine. Blades have three main parts:

1. Aerofoil / Profile Section 2. Blade Root 3. Shroud

Aerofoil section:-It is the working part of blade where conversion of energy takes place to generate driving force. According to the shape of aerofoil, blades are classified into various forms as1. Cylindrical blades2. Twisted profile blades3. Twisted Profile Blade with Reducing Section: 4. 3-Dimensional Blades

BLADE ROOT

Blades are attached to casing or rotor in different ways depending upon the shear area required to resist against the steam bending and centrifugal force. The common types of arrangement used are as follows.1. Hook root2. T- root 3. Fir- tree root4. Finger /fork root5. Axial fir tree root

BLADE SHROUD

In order to minimize the steam leakage through the clearance between moving blade & casing and guide blade & rotor, a cover called shroud is provided at the tip of blades. The presence of shroud compels the steam to pass through the working part of blades thereby reducing the tip leakage losses and hence improve stage efficiency. It can be either riveted by tenon to main blade or it can be integrally machined with the blade. At present trend is towards integral shroud as it leads to robust design against vibration besides reducing tip leakages. Long blades of LP last stages in some designs are without shroud. Such blades without shroud and individually standing in axial fir tree roots are called free standing blades.

Turbine blades are subjected to high temperatures, centrifugal & bending stresses. So, the materials for turbine blades should meet the following requirements: - Adequate tensile strength for steady centrifugal & bending stresses Better creep strength for HP/IP blades exposed to high temperatures More ductility to accommodate stress peaks and concentration Higher impact strength since contact with foreign objects is sudden Higher fatigue strength to counter vibration excitation Ability to resist corrosion & scaling in fast flowing wet steam Better damping against vibratory stressesTo meet above requirements, the conventional 12% Cr steels with addition of Molybdenum and Vanadium are used to improve creep strength & proof strength. Addition of Niobium increases 0.2% rupture strength & creep properties for short term only.Since blades are subjected to wet steam in last stages of the LP turbine, the blades are alloyed with Titanium because of the following reasons:1. Ti has low density (60% of steels), so for same volume longer length of blades can be used for comparable stresses in root.2. Ti is corrosion and erosion resistant.3. Yield strength is 50% better than 12% Cr steels.4. Fatigue strength is much higher than 12% Cr steels.In the low-pressure end blades, the careful considerations are made for prevention of erosion & vibrations as well as better performance. Enough distance between the stationary blade and rotational blade is secured so that the moisture drips are formed into fine mist. Enough length of stellite strip is inserted into leading edge of last rotating row. There are narrow slits in the flow guide at the top of the last rotating blades, through which the drip or moisture from the last stationary blades are sucked to condenser. The leading edge of the blades is surface hardened. All the blades are carefully designed for vibratory strength. Especially for the long blades, the perfect tuning of the lowest natural frequencies is necessary.

There are several types of machine blade manufacturing. CNC 3- Axis Machine TAL BFW CNC 4-Axis Machine MAZAK NEXUS CNC 5-Axis Machine LEICHTI Machine Makino machine Twin Head Polishing Machines Sumitop wheel Buffing wheel Belt Type Polishing Machines Pencil Grinders

3-Axis Machines are having X, Y & Z axis, where straight profile blades without shroud can be easily machined with simple program. 4-axis machine has a C-axis through which root machining can be done. 5-Axis Machines are having X, Y, Z, Rotary table & Head tilting or Table tilting, where twisted profile blades with shroud and negative profiles are required. The program should be made with continuous 5 axis.

Blade Manufacturing Flowchart:Bar/ Blank cutting & Centre Drilling

Stationary bladesStationary bladesDispatchPreservationInspectionPin hole machiningMagnetic particle inspectionFinishing & PolishingTotal length maintaining (3 axis)Bend removal by hand pressure machineJig Groove and Weld Groove MachiningRoot Machining (4-axis)Blade Profile Roughing (5-axis)End cutting (3-axis)

TURBINE ASSEMBLY

HIP ASSEMBLY FLOWCHARTInterference check of inner components with respect to outer components

HIP Casing Hydro TestGland Bore settingHIP Outer Casing Levelling

Rotor TravelClearance AdjustmentTop halves installationRotor TravelInner components installation

LP ASSEMBLY FLOWCHARTOuter Casing Lower InstallationOuter Casing Upper InstallationRotor InstallationRotor TravelLP Bore Adjustment

Steam Deflector InstallationSteam Chamber InstallationInner casing L/H installation & centering

Gland Ring InstallationSpecial Stationary Blade Installation

Bottom Clearance AdjustmentInstalling upper components & measuring top clearance

GENERATORSGenerator is a machine which converts mechanical energy into electrical energy. An a.c generator is a magnetic field system and an armature assembly either of which may rotate relative to each other. The field system will always be the rotating member and is called the Rotor while the armature assembly, comprising armature winding and magnetic iron core, will be stationary and is called Stator.The basic principle of the electrical generator is based upon the Faradays Law of Electromagnetic Induction, which states, When the number of magnetic lines of force associated with a conductor changes, an induced voltage is setup in the conductor. The voltage induced is proportional to the rate of change of the magnetic lines associated with the conductor.

The general frequency equation is,f = (PxN) / 120 HzP= No. of poles of generatorN= Speed in RPMFor 50 Hz system,2-pole machine => 3000 rpm4-pole machine => 1500 rpm

The main parts of a generator are Stator, Rotor & Exciter, the details of which are given below:

STATOR Stator FrameThe stator frame and bearing brackets attached to both ends of the stator frame are constructed from rolled steel plate, and are welded into the required shapes. To ensure that the frame has required strength to be used as a pressure vessel, all parts of it are designed with a sufficient strength to enable it to withstand the higher of either twice the maximum operating gas pressure. Severe Hydrostatic Testing is used to ensure this strength.

Stator CoreIt consists of electrical steel sheets laminated within the frame. Cold-rolled silicon steel strips are used as the electrical steel sheet material. These are punched out in sector shape and coated on both sides with an insulating varnish which is baked on. This is done to prevent losses caused by eddy currents in the core laminations.

Flexible MountingThe magnetic force which develops between the rotor poles and the stator core induces a double-frequency vibration in the stator core.In two pole machines, since this vibration is of a high level, to prevent it from being transmitted to the frame and foundation, the stator core is supported from the frame by a flexible mounting. It is necessary for the flexible mounting to have not only radial mobility but also to have a circumferential rigidity large enough to support the weight of the core and to withstand the short-circuit torque. To satisfy these requirements, the flexible mounting is constructed with a number of leaf springs, with one end bolted to the bore ring and the other bolted to the outer frame.

Stator WindingThe stator coils are constructed as double-layer half coils and, after insertion in slots in Stator core, are end connected to form a complete winding.The conductors of each coil consist of a glass sheathed rectangular copper bars. A combination of hollow and solid strands consisting of four or six rows is used to achieve high cooling and low eddy current loss in the stator coil. Solid and hollow strands and a header are brazed at both ends of the stator coils where a water chamber is formed, and the coils are electrically connected by means of a series connector.The cooling water flows in and out of the stator coils through Teflon hoses with superior insulating capabilities. Dialastic Epoxy is used as the insulation for the stator coils. After several continuous windings of mica tape, surface protecting tape is wound on the coils. After this tape winding is completed, coils are placed in vacuum to remove moisture, solvents and bubbles, and they are pressure impregnated in low viscosity thermosetting resin. This results in the impregnating resin seeping into every part of the coil. After impregnation, the coils are pressed and heated to affect polymerizing curing, and thus an overall unified insulation is provided.

ROTORThe design and construction of rotor is difficult as its weight is considerably high and rotates at fairly high speed (3000 or 3600rpm). In order to accommodate the field windings to carry field current, a large number of deep slots are machined in the rotor. The length between the two bearings is limited to eight times the diameter of the rotor. The approximate weight of the rotor of 120MW is about 30-40tons. In order to achieve the efficient cooling of rotor it is necessary to allow ample passage in the rotor, through which cooling fluid can be circulated freely.The rotor shaft is a solid Ni-Mo-V or Ni-Cr-Mo-V steel forging. The rotor of a turbine generator rotates at high speed, making its mechanical structure of extreme importance. Special care is thus required with regard to materials, mechanical design and machining.

The rotor conductors for water-cooled generators use cold drawn silver bearing copper. Two U channels are combined to form one turn, and the rectangular space enclosed forms the path of the hydrogen gas for cooling the conductor. Radial ventilating ducts provided at the end part of the coil and the center of the straight section of the coil serve as coolant inlets and outlets.

Generator Assembly:

Rotor ForgingEnd PlatingTransport

Lathe

ROTORRotor AssemblyRotor WindingGroove & Pilot Hole MachiningPaintingHSBTSlot MachiningFinal Assembly

Final Lathe Machining

STATOR

Stator WindingCore Loop TestCore Assembly

Stator Frame FabricationHydro TestFrame Machining

GENERATOR TESTING:

Generator is tested for checking the Voltage, Amperage and Power factor as demanded by the customer.The Rotor is tested dynamically at the HSBT facility.The various tests for the Stator are:i. Open Circuit testii. Short Circuit testiii. Portier-Reaction testiv. Partial Discharge testv. Insulation Resistance testvi. High Voltage testvii. Leakage testviii. Rotor Run-out testix. Short Circuit Ratio Testx. Elcid Testxi. Bump Test

HIGH SPEED BALANCING FACILITY HSBT facility is used for balancing the rotor in accordance to its weight just to check that rotor geometrical axis and rotational axis are the same or not. If the geometrical axis and rotational axis are not same then rotor would rotate eccentrically disturbing other couplings and rotor and can cause accident if not balanced at right time. In this facility, rotor is rotated at about 3000 rpm in airproof (vacuum) environment to avoid air friction as this can cause massive accident. This facility is brought here with the help of GERMAN company.

Procedure for Balancing:-1. Initially, centering of rotor is done after inserting it into the vacuum chamber by means of dial gauges (4 dial gauges at 4 segments of rotor). 2. After this centering, rotor is rotated by about 30. If there is any misalignment then pedestal is rotated for proper centering of rotor.3. After this, rotor is rotated at about 600rpm for operating the jacking oil system. 4. Softwares for checking alignment are CAB920 for slow speeds and CABFLEX for high speeds.5. If any unbalancing is found in rotor then weight plugs can be added or removed to balance it. 28

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