Insulation System in Turbo Generators (2)

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A Mini Project Work Submitted in partial fulfillment of the Requirements for the award of degree of BACHELOR OF TECHNOLOGY In Under The Guidence Of Dept. of Electrical and Electronic Engineering Mannan Institute of Science and Technology Aloor(V), Chevella(M), Ranga Reddy(Dist.). By ELECTRICAL & ELECTRONICS ENGINEERING Mr.J.P.Balaji (HOD) INSULATION SYSTEM IN TURBO GENERATORS S.ANURAG (08J51A0241) D.VAMSHI RAJ (08J51A0214) A.ARUN KUMAR (08J51A0201) S.SUMAN (08J51A0240)

Transcript of Insulation System in Turbo Generators (2)

Page 1: Insulation System in Turbo Generators (2)

A Mini Project Work

Submitted in partial fulfillment of the

Requirements for the award of degree of

BACHELOR OF TECHNOLOGY

In

Under The Guidence Of

Dept. of Electrical and Electronic Engineering

Mannan Institute of Science and Technology

Aloor(V), Chevella(M), Ranga Reddy(Dist.).

By

ELECTRICAL & ELECTRONICS ENGINEERING

Mr.J.P.Balaji (HOD)

INSULATION SYSTEM IN TURBO GENERATORS

S.ANURAG (08J51A0241)D.VAMSHI RAJ (08J51A0214)

A.ARUN KUMAR (08J51A0201)S.SUMAN (08J51A0240)

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ACKNOWLEDGEMENT

We take this opportunity to record our gratitude to all those who helped us in successful completion of the project.

for having permitted us to carry out this project.

We immensely be grateful to Sri. B. PRASADA RAO garu, CEO (chief

us permission for undergoing study project training in their company.

for allotting us this project.

impossible.

2011

We wish to express our deep sense of gratitude to our Internal Guide

executive officer) of BHARAT HEAVY ELECTRICALS LIMITED for giving

and useful suggestions, which helped us in completing the project work in time.

We take immense pleasure in thanking Mr. BABU RAO garu , Principal of our college and Mr. J.P. BALAJI garu, Head of the department

MR.M.N.V. SURYA PRASAD and MR.S.JITHENDER REDDY for her able guidance

We wish to thank MR. S.K.SAHOO garu, HRD-MANAGER, BHEL

Finally, we wish to express our profound thanks to all the employees, in charges and workmen without whose support, completion of this project would have been

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ABSTRACT

BHEL is the largest engineering and manufacturing enterprise in India in the energy related infrastructure sector today which manufactures turbo generators (2-pole and 4-pole) ranging up to 150 MHz. The manufacturing process of turbo generator is mainly divided into stator section and rotor section where stator frame, stator core, stator windings, end covers are received from the stator building section and rotor with rotor windings and rotor retaining rings is received from rotor section and assembled at the assembly section. Each and every process is carried out in a sequential process. Turbo generators are designed with the Closed circuit air cooling with water or air coolers mounted in the pit. The layout of the manufacturing plant is such that it is well streamlined to enable smooth material flow from the raw material stages to finished goods. The raw material that are produced for manufacture are used only after thorough material testing in the testing lab and with strict quality checks at various stages of productions. Latest technologies like vacuum press impregnated micalastic high voltage insulation, polyester fleece tape impregnation for outer corona protection are implemented to produce high quality insulation for turbines, outstanding performance and long lasting lifetime.

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INDEX

BHARAT HEAVY ELECTRICALS LIMITED.

Introduction

History of Turbo Generators

Principle of operation

Synchronous generators classification based on the medium used for generation

Components of Turbo Generator

Stator

Rotor

Stator

Stator frame

Stator core

The purpose of stator core

Preparation of laminations

Compounding operation

Blanking & notching operation

The different operation in manufacturing of laminations

Deburring operation

STATOR

INTRODUCTION

ABOUT THE COMPANY:

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1. General

2. Preheating

3. Impregnation

4. Post curing

5. Electrical testing

Rotor

Rotor shaft

Rotor winding

Construction

Conductor material

Insulation

Rotor slot wedges

Rotor Retaining rings

BHEL insulation system for Turbo Generators

BITUMEN system & life extension

Various insulation system & practices

VPI system

Introduction to VPI system

Features and benefits

VPI of resin poor insulated jobs

Process of VPI

VACCUM PRESSURE IMPREGNATION

INSULATION SYSTEM

ROTOR

CONCLUTION & FUTURE SCOPE

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BHARATH HEAVY ELECTRICALS LIMITED

ABOUT THE COMPANY

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ABOUT THE COMPANY: BHARAT HEAVY ELECTRICALS LIMITED

Bharat Heavy Electrical Limited (BHEL) is today the largest engineering Enterprise of India with an excellent track record of performance.

Its first plant was set up at Bhopal in 1956 under technical collaboration with M/s. AEI, UK followed by three more major plants at Haridwar, Hyderabad and Tiruchirapalli with Russian and Czechoslovak assistance.

These plants have been at the core of BHEL’s efforts to grow and Diversify and become India’s leading engineering company.

The company now has 14 manufacturing divisions, 8 service centers and 4 power sector regional centers, besides project sites spread all over India and abroad and also regional operations divisions in various state capitals in India for providing quick service to customers.BHEL manufactures over 180 products and meets the needs of core sectors like power, industry, transmission, transportation (including railways), defense, telecommunications, oil business, etc.

Products of BHEL make have established an enviable reputation for high quality and reliability. BHEL has installed equipment for over 62,000 MW of power generation for Utilities, Captive and Industrial users.

Supplied 2,00,000 MVA transformer capacity and sustained equipment operating in Transmission & Distribution network up to 400kV – AC & DC, Supplied over 25,000 Motors with Drive Control System Power projects.

Petrochemicals, Refineries, Steel, Aluminum, Fertilizer, Cement plants etc., supplied Traction electric and AC/DC Locos to power over 12,000 Km Railway network. Supplied over one million Valves to Power Plants and other Industries.

This is due to the emphasis placed all along on designing, engineering and manufacturing to international standards by acquiring and assimilating some of the best technologies in the world from leading companies in USA, Europe and Japan, together with technologies from its-own R & D centers.

BHEL has acquired ISO 9000 certification for its operations and has also adopted the concepts of Total Quality Management (TQM).

BHEL presently has manufactured Turbo-Generators of ratings up to 560 MW and is in the process of going up to 660 MW.

It has also the capability to take up the manufacture of ratings unto 1000 MW suitable for thermal power generation; gas based and combined cycle power generation as-well-as for 13 diverse industrial applications like Paper, Sugar, Cement, Petrochemical, Fertilizers, Rayon Industries, etc.

The Turbo generator is a product of high-class workmanship and quality. Adherence to stringent quality-checks at each stage has helped BHEL to secure prestigious global orders in the recent past from Malaysia, Malta, Cyprus, Oman, Iraq, Bangladesh, Sri Lanka and Saudi Arabia. The successful completion of the various export projects in a record time is a testimony of BHEL’s performance.

Bharat Heavy Electrical Limited (BHEL) is, today, a name to reckon with in the industrial world. It is the largest engineering and manufacturing enterprises of its kind in India and is one of the leading international companies in the power field.

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BHEL offers over 180 products and provides systems and services to meet the needs of core sections like: power, transmission, industry, transportation, oil & gas, non-conventional energy sources and telecommunication.

A wide-spread network of 14 manufacturing divisions, 8 service centers and 4 regional offices besides a large number of project sites spread all over India and abroad, enables BHEL to be close to its customers and cater to their specialized needs with total solutions-efficiently and economically.

An ISO 9000 certification has given the company international recognition for its commitment towards quality.

With an export presence in more than 50 countries BHEL is truly India’s industrial ambassador to the world.

BHEL Hyderabad unit’s manufacture includes the following.

Gas turbines

Steam turbines

Compressors

Turbo generators

Heat Exchangers

Pumps

Pulverizers

Switch Gears

Oil rigs

BHEL Hyderabad is the only one in Asia that has the latest type of insulation system called the Vacuum Pressure Impregnation System.

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A turbo generator is a turbine directly connected to electrical generator for the generation of electric power. An electrical generator is a machine which converts mechanical energy to electrical energy.

Generators are based on the theory of electromagnetic induction, which was discovered by Michael Faraday in 1831, a British Scientist. Faraday discovered that if an electric conductor, like a copper wire, is moved through a magnetic field, electrical current will flow(be induced) in the conductor. So the mechanical energy of the moving wire is converted into the electric energy of the current that flows in the wire.

Turbo generator or A.C. generators or alternators operates on the fundamentalPrinciples of FARADAYS LAWS OF ELECTROMAGNETIC INDUCTION. In them the standard construction consists of armature winding mounted on stationary element called stator and field windings on rotating element called rotor. The stator consists of a cast-iron frame, which supports the armature core, having slots on its inner periphery for housing the armature conductors. The rotor is like a flywheel having alternating north and south poles fixed to its outer rim. The magnetic poles are excited with the help of an exciter mounted on the shaft of alternator itself. Because the field magnets are rotating the current is supplied through two slip rings. As magnetic poles are alternately N and S, they induce an e.m.f and hence current in armature conductors. The frequency of e.m.f depends upon the no.of N and S poles moving past a conductor in 1 second and whose direction is given by Fleming ’s right hand rule.

MEDIUM USED FOR GENERATION:

Turbo generators in Thermal, nuclear, Gas station• High speed – 3000 rpm• Min poles – 2 poles• Horizontal construction• Cylindrical rotor

Hydro generators in hydel plants

TURBO GENERATOR

HISTORY OF TURBO GENERATORS:

PRINCIPLE OF OPERATION:

INTRODUCTION:

SYNCHRONOUS GENERATORS CLASSIFICATION BASED ON THE

• vertical construction• salient rotor

• more poles – 6 or more• low speed – 1000 to 500 rpm

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Stator Frame

Stator Core

Stator Windings

End Covers

Rotor Shaft

Rotor Windings

Rotor Retaining Rings

The following auxiliaries are required for operation:

Bearings

Cooling System

Oil Supply System

Excitation System

COMPONENTS OF TURBO GENERATOR:

STATOR

ROTOR

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STATOR

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T TOR

The stator frame is of welded steel single piece construction. It supports the laminated core and winding. It has radial and axial ribs having adequate strength and rigidity to minimize core vibrations and suitably designed to ensure efficient cooling. Guide bars are welded or bolted inside the stator frame over which the core is assembled. Footings are provided to support the stator foundation.

Fig: stator frame

ATOR CORE:-The stator core is stacked from the insulated electrical sheet steel lamination andmounted in supporting rings over the insulated dovetail guide bars. In order to minimize e

current losses core is made of thin laminations. Each lamination layer is made of individua

sections. The ventilation ducts are imposed so as to distribute the gas accurately over the c

and in particularly to give adequate support to the teeth.The main features of core are –1. To provide mechanical support.2. To carry efficiently electric, magnetic flux.3. To ensure the perfect link between the core and rotor.

AS

STATOR FRAME:

TS

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To support the stator winding To carry the electromagnetic flux generated by rotor winding.

So selection of material for building up of core plays a vital role. The losses in the core are of two types.Hysterysis Loss: Due to the residual magnetism in the core material.Hysterysis loss is given by Wh α βmax 1.6Eddy Current Loss: Due to the e.m.f induced in the core of the stator. Eddy current loss is given by We α βmax2 f2 t2 In order to reduce the hysterysis loss, silicon alloyed steel, which has low hysterysis constant is used for manufacture of core. The composition of silicon steel is Steel - 95.8% Silicon – 4.0% Impurities - 0.2%From the formula it is seen that eddy current loss depends on the thickness of the laminations. Hence to reduce the eddy current loss core is made up of thin laminations which are insulated from each other. The thickness of the laminations is about 0.5mm. The silicon steel sheets are of COLD ROLLED NON-GRAIN ORIENTED (CRANGO) type as it provides the distribution of flux throughout the laminated sheet.

For high rating machines each laminations is build of 6 sectors (stampings), each of 60 cut according to the specifications. Press tools are used in the manufacture of laminations. Press tools are mainly of two types.

Compounding tools. Blanking and slot notching tools.

LAMINATIONS ARE MANUFACTURED IN TWO DIFFERENT WAYS

In this method the stamping with all the core bolt holes, guiding slots and winding slots is manufactured in single operation known as Compounding operation and the press tool used is known as Compounding tool. Compounding tools are used for the machines rated above 40 MW.

In case of smaller machines the stampings are manufactured in two operations. In the first operation the core blot holes and guiding slots are only made. This operation is known as Blanking and the tools used are known as Blanking tools. In the second operation the winding slots are punched using another tool known as Notching tool and the operation is called Notching.

THE PURPOSE OF STATOR CORE

PREPARATION OF LAMINATIONS:

COMPOUNDING OPERATION:

BLANKING AND NOTCHING OPERATIONS:

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LAMINATIOS:

In this operation the burrs in the sheet due to punching are deburred. There are chances of short circuit within the laminations if the burrs are not removed. The permissible is about 5 micrometer. For deburring punched sheets are passed under rollers to remove the sharp burs of edges.

Then depending on the temperature withstand ability of the machine the laminations are coated by varnish which acts as insulation. The lamination sheets are passed through conveyor, which has an arrangement to sprinkle the varnish is obtained. The sheets are dried by a series of heaters at a temperature of around 260-350 C. Two coatings of varnish are provided in the above manner till 12-18mm thickness of coat is obtained.The prepared laminations are subjected to following tests:

Xylol test - To measure the chemical resistance. Mandrel test - When wound around mandrel there should not be any

cracks. Hardness test - Minimum 7H pencil hardness. IR value test - For 20 layers of laminations insulation.

The stator laminations are assembled as separate cage without stator frame. The entire core length is made in the form of packets separated by radial ducts to provide ventilating passages for the uniform cooling of the core. The thickness of each lamination is 0.5mm and the thickness of lamination separating the packets is about 1mm. The lamination separating each packet has strips of nonmagnetic material that are welded to provide radial ducts. The segments are staggered from layer to layer so that a core of high mechanical strength and uniform permeability to magnetic flux is obtained. Stacking mandrels and bolts are inserted into the windings slot bores during stacking provide smooth slot walls.

THE DIFFERENT OPERATIONS IN MANUFACTURE OF

Deburring operation:

Varnishing:

ASSEMBLY OF CORE:

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Fig: assembly of coreTo obtain the maximum compression and eliminate under setting during operation, the laminations are hydraulically compressed and heated during the stacking procedure when certain heights of stacks are reached. The complete stack is kept under pressure and located in frame by means of clamping bolts and pressure plates. The clamping bolts running through the core are made of nonmagnetic steel and are insulated from the core and pressure plates to prevent them from short circuiting the laminations and allowing the flow of eddy currents. The pressure is transmitted from the clamping plates to the core by clamping fingers. The clamping fingers extend up to the ends of the teeth thus, ensuring a firm compression in the area teeth.

Fig: assembled coreThe core building or assembling method depends on the insulation system used.1. For resin rich insulation system the laminations are stacked in the frame itself.2. For resin poor insulation system (VPI) cage core of open core design is employed.

Stator winding is the one which induces emf and supplies the load. Stator winding is placed in the slots of stator core. Due to the advantages of generation and utilization of 3 phase power we use three phase windings for generation. So number of slots must be a multiple of 3 (or 6 if two parallel circuits are required).

STATOR WINDINGS:

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Generally two layer lap winding, chorded to about 5/6 pitch which practically eliminates 5th

and 7th harmonics from the flux wage or open circuit induced emf wave is used. The stator coil is made up of number of strips instead of single solid piece to reduce the skin effect.

Copper material is used to make the coils. This is because

i. Copper has high electrical conductivity with excellent mechanical properties.

ii. Immunity from oxidation and corrosion. iii. It is highly malleable and ductile metal.

There are two types of coils manufactured in BHEL, Hyderabad.

Diamond pulled multiturn coil (full coiled): Roebel bar (half coiled).

Generally diamond pulled multiturn coils are used for low capacity machine. In this coils are pulled in a particular shape similar as diamond that’s why they are called so.

In large capacity machines we use ROEBEL bars. These coils were constructed after considering the skin effect losses. In the straight slot portion, the conductors or strips are transposed by 360 degrees. The transposition is done to ensure that all the strips occupy equal length under similar conditions of the flux. High purity (99%) copper conductors/strips are used to make the coils. This results in high strength properties at higher temperatures so that deformations due to the thermal stresses are eliminated. The high voltage insulation is provided according to the resin poor mica base of thermosetting epoxy system. Several half overlapped continuous layers of resin poor mica tape are applied over the bars. The thickness of the tape depends on the machine voltage.

Fig: stator windings

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3.6.1 Slot Discharges:

Slot discharges occur if there are gaps within the slot between the surface of the insulation and that of the core. This may cause ionization of he air in the gap, due to breakdown of the air at the instances of voltage distribution between the copper conductor and the iron.

Within the slots, the outer surface of the conductor insulation is at earth potential, in the overhanging it will approach more nearly to the potential of the enclosed copper. Surface discharge will take place if the potential gradient at the transition from slot to overhang is excessive, and it is usually necessary to introduce voltage grading by means of a semi-conducting (graphite) surface layer, extending a short distance outward from the slot ends. 3.6.2 MANUFACTURE OF STATOR COILS:

Various operations carried out during manufacture of stator coil are

1. Set the straightening and cutting machine using guide pilot. 2. Cut the conductor strips as per the requirement. 3. Set the press for “Roebel Transposition”. 4. Assemble strips with respect to template and transpose. 5.Assemble both halves of coil sides to from 1.One Roebel half bar 2. Insert insulation of halves between quarter bars matching the straight part zone as per drawing.

Fig: stator coils

6.Cure half coil on hydraulic press. This process is known as Baking.

(a) Remove insulation at the ends of the strips.

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(b) Test for inter-strip and inter-halves shorts. 7.Set the universal former as per standards. Check the setting of universal former for (a)Length of straight part also mark diagonals/former walls inside for cross check. (b)Check for marking made by template. 8.(a) Place the bar on former. (b) Form the overhang bends as per standards. © Remove clamps and inserts overhand insulation to both roebel halves with an

application of araldite mixture. (d) The bar is allowed to cure by giving supply to heating clamps. 9.Remove heating clamps and take out the bar halves from former. (b)Round off sharp edges of straight part and dress up overhang halves insulation of both

halves with out damage to copper strip insulation and to copper stacks.

3.6.3 PROCESS OF TAPING:

1.Tape the bar with Resin poor fine mica paper tape on straight part of bar taking copper foil outside the tape.

2.Tape with one layer of conductive polyester fleece tape.

a)Provide main insulation

b)OCP protection tape

3.Tape the straight part of bar with conductive polyester fleece tape with starting and ending shall be on straight part of bar.

4.Tape with mica splitting tape with accelerator taking Ocp layer into and leaving.

5.Tape the straight part of bar with polyester Conductive fleece tape.

6.Provide End Corona protection taping.

7.Provide overhang with protective tape (Polyester glass tape)

8.Test for inter-strip shorts.

Fig: mica taping machine.

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3.7 STATOR END COVERS:

The stator end covers are attached to end flanges of stator frame and also rest on the foundation plate. The end covers are made up of non-magnetic material (Aluminium castings) to reduce stray load and eddy current losses.

3.7.1 PHASE CONNECTORS:

The phase connectors consist of flat copper sections, which results in low specific current loading. The phase connectors are wrapped with resin rich mica tape. After curing the connectors are attached to the pressure plate with clamps and bolts.

3.7.2 RESISTANCE TEMPERATURE DETECTORS :

The temperature measurements on the generator are made with RTDs. They are placed at various sections of the core and winding. When making measurements with RTDs the resistance element is exposed to the temperature to be measured.

The RTD works on the principle of the change in electrical resistance of a conductor due to temperature. R= Ro (1+ α T) ;Where Ro = reference resistance at room temperature; R= temperature coefficient of resistance ; T = temperature difference in C.

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ROTOR

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Rotor is the rotating part of alternator. It is used to support field winding placed in slots on the rotor.

FOR 2-POLE GENERATOR:

Solid rotors are manufactured from forged alloy steel with suitable alloying elements to achieve very high mechanical and superior magnetic properties. This type of rotor can withstand even upto speed of 3000 rpm. Rectangular or trapezoidal rotor slots are accurately machined to close tolerances on slot milling machine.For indirectly cooled generator rotors, ventilation slots are machined in the teeth.

FOR 4-POLE GENERATOR:

For directly cooled rotors, sub slots are provided for cooling Generator rotors of 1500 RPM are of round laminated construction. In this case rotor is made up of two parts (1) core, (2) lamination. The outer diameter of core and the inner diameter of laminations are equal. So for inserting the core inside the laminations the laminations are first red heated at medium temperature for 15 hours in BELL FURNACE. After that the core is shrunk fitted inside the laminations. Thus punched and varnished laminations of high tensile steel are mounted over machined shaft and are firmly clamped by end clamping plates.

Fig: rotor body.

ROTOR:

ROTOR SHAFT :

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Rotor shaft is a single piece solid forming manufactured from a vacuum casting. It is forged from a vacuum cast steel ingot. Slots for insertion or the field winding are milled into rotor body. The longitudinal slots are distributed over the circumference such that two solid poles are obtained.

To ensure that only a high quality product is obtained, strength tests, material analysis and ultrasonic tests are performed during the manufacture of rotor. The high mechanical stresses resulting from the centrifugal forces and short circuit torque’s call for a high quality heat treated steel. After completion, the rotor is balanced in various planes at different speeds and then subjected to an over speed test at 120% of the rated speed for two minutes.

Fig. rotor shaft.

Approximately 60% of rotor body circumference has longitudinal slots which hold the field winding. Slot pitch is selected so that the two solid poles are displaced by 180 degrees. The rotor wedges act as damper winding within the range of winding slots. The rotor teeth at the ends of

rotor body are provided with axial and radial holes enabling the cooling air to be discharged into the air gap after intensive cooling of end windings.

and series connected such that two coil groups form one pole. Each coil consists of several series connected turns, each of which consists of two half turns connected by brazing in the end section. Thickness of each strip can be made upto 10.5 mm but here in BHEL we make only upto 5.3 mm. The rotor bearing is made of silver bearing copper ensuring an increased thermal stability. For ventilation purpose the slots are provided on the coil and on inter strip insulation layer both.

The individual turns of coils are insulated against each other by interlayer insulation. L-shaped strips of laminated epoxy glass fiber fabric with nomex filter are used for slot insulation.

ROTOR WINDINGS :The rotor windings consist of several coils inserted into the slots

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Fig: rotor winding.

The slot wedges are made of high electrical conductivity material and thus act as damper windings. At their ends the slot wedges are short circuited through the rotor body. The inter space between the overhang is called slot through.

The field winding consists of several series connected coils inserted into the longitudinal slots of rotor body. The coils are wound so that two poles are obtained. The solid conductors have a rectangular cross section and are provided with axial slots for radial discharge or cooling air. All conductors have identical copper and cooling duct cross section. The individual bars are bent to obtain half turns. After insertion into the rotor slots, these turns are brazed to obtain full turns. The series connected turns of one slot constitute one coil. The individual coils of rotor are connected in a way that north and south poles are obtained.

content of approximately 0.1%. As compared to electrolytic copper, silver alloyed copper features high strength properties at high temperatures so that coil deformations due to thermal stresses are eliminated.

The insulation between the individual turns is made of layer of glass fiber laminate.

The coils are insulated from the rotor body with L-shaped strips of glass fiber laminate with nomex interlines.

To obtain the required leakage paths between the coil and the rotor body thick top strips of glass fiber laminate are inserted below top wedges. The top strips are provided with axial slots of the same cross section and spacing as used on the rotor winding. Insulation b/w overhang is done by blocks made of HGL.

INSULATION

CONDUCTOR MATERIAL: The conductors are made of copper with a silver

CONSTRUCTION

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To protect the winding against the effects of centrifugal forces, the winding is secured in the slots with wedges. The slot wedges are made of copper alloy featuring high strength and good electrical conductivity. They are also used as damper winding bars. The slot wedges extend beyond the shrink seats of retaining rings. The wedge and retaining rings act on the damper winding in the event of abnormal operations. The rings act as short circuit rings in the damper windings.

The spaces between the individual coils in the end winding are filled with insulated members that prevent coil movement. Two insulation plates held by HGL high glass laminate plates separate the different cooling zones in the overhangs on either sides.

The centrifugal forces of the rotor end winding are contained by single piece rotor retaining rings. Retaining rings are made of non-magnetic high strength steel in order to reduce stray losses. Each retaining ring with its shrink fitted. Insert ring is shrunk on to the rotor body in an overhang position. The retaining ring is secured in the axial position by snap rings.

Fig: rotor retaining rings

The rotor retaining rings withstand the centrifugal forces due to end windings. One end of each ring is shrunk fitted on the rotor body while the other end overhangs the end windings without

contact on the rotor shaft. This ensures an unobstructed shaft deflection at the end winding.

END WINDING BRACING

ROTOR RETAINING RINGS

ROTOR FANS

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The cooling air in generator is circulated by two axial flow fans located on the rotor shaft one at each end. To augment the cooling of the rotor winding, the pressure established by the fan works in conjunction with the air expelled from the discharge parts along the rotor. The blades of the fan have threaded roots for being screwed into the rotor shaft. The blades are drop forged from an aluminium alloy. Threaded root fastenings permit angle to be changed. Each blade is secured at its root with a threaded pin.

Fig: rotor fan

BEARINGS

VENTILATION AND COOLING

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overhang portions. epoxy mica paper tape all over the oil periphery with varying number of layers on straight and requirement hence for unique in nature to each other. The main insulation consists of resin poor range Ac Induction and synchronous machines. Theses are designated to meet specific customer 3.Resin poor Micalastic Insulation System: Resin poor micalastic system is adopted for large

during coil manufacture and housing. tape on overhang with a final layer of polyester shrink tape. The system is highly productive backed epoxy micafolium on straight portion & resin rich polyester backed epoxy mica paper 2.Resin Rich micalastic Insulation System : The system provides use of Resin rich polyester

become absolute. spare motors to suit the customer requirements are required. In the coming years this system may 1.Resin flux Insulation System : This system is used on earlier designs & where duplicate or

Large & medium range motors are provided with following insulation system.

The replacements are required because of vibration / external damage etc.

winding components.tightening of fasteners/supports, modification of busbars, use of new wedges & other

Rehabilitation, if needed, requires restoration of varnish, removal of bitumen & cleaning, life of bar insulation.

Major inspection of the machine condition is by checking the healthiness of windings & would need to be attended to have life extension above their estimated life of 25 years.

Though outage due to insulation failures has been considerably low, yet these machinery met any of sets.to thermal expansion of the winding during normal or abnormal temperature eyeing is not

Mechanical damage most commonly associated with this system ie., tape separation, due negligible service failure has been reported on these sets.

The experience with Bitumen system has been generally satisfactory & practically

Micalastic system has been adopted for high rating machinery.rich Thermo setting type as a step towards increasing reliability and upgrading technology. BHEL had Bitumen insulation system for low & medium rating TGS and switched over to resin

BHEL INSULATION SYSTEM FOR TURBO GENERATORS:

BITUMEN SYSTEM & LIFE EXTENSION:

VARIOUS INSULATION SYSTEMS & PRACTICES:

INSULATION SYSTEMS

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RESIN POOR RESIN RICH

1.Epoxy resin content is about 8%.

2.This method follows Thermo Setting Process.

3.There is a need for addition of resin from outside.

4.Time required for this cycle is less.

5.Repairing is very difficult.

6.Over all cost is less compared to resin rich.

1.Epoxy resin content is about 40%.

2. This method also follows Thermo Setting Process.

3. Further addition of resin is not required from outside.

4.Its a very long process and time consuming.

5.Repairing is easy.

6.Over all cost is more.

The brief comparison of Resin poor over Resin rich is as follows:

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DR. MEYER brought the VPI system with the collaboration of WESTING HOUSE in the year 1956. Vacuum Pressure Impregnation has been used for many years as a basic process for thorough filling of all interstices in insulated components, especially high voltage stator coils and bars.

VPI is a process, which is a step above the conventional vacuum system. VPI includes pressure in addition to vacuum, thus assuring good penetration of the varnish in the coil.

The result is improved mechanical strength and electrical properties. With the improved penetration, a void free coil is achieved as well as giving greater mechanical strength.

With the superior varnish distribution, the temperature gradient is also reduced . In order to minimise the overall cost of the machine & to reduce the time cycle of the

insulation system vacuum pressure Impregnated System is used. The stator coils are taped with porous resin poor mica tapes before inserting in the slots of

cage stator, subsequently wounded stator is subjected to VPI process, in which first the stator is vacuum dried and then impregnated in resin bath under pressure of Nitrogen

gas.

Fig: VPI system

• State-of-the-art process for completely penetrating air pockets in winding insulation.

VACUUM PRESSURE IMPREGNATIONINTRODUCTION TO VPI SYSTEM:

Features and Benefits:

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• Increases voltage breakdown level. (Even under water!)

• Proven submergence duty system

• Improved heat transfer- windings are cooler, efficiency is improved.

• Improves resistance to moisture and chemicals.

• Increases mechanical resistance to winding surges.

Variant-01 Variant-02 Variant-03 Any other information

Preheating 60 5 C for 3hrs

60 5 C for 12hrs

60 3 C for 12hrs

Vacuum to be maintained

0.4mbar 0.2mbar/0.4mbar <0.2mbar

(both together shall not exceed 50hrs including rising time)

Vacuum heating time

3hrs

0.2mbar for 9hrs 0.4mbar for 17hrs

Stopping vacuum pumps for 10min shall check 17hrs vacuum drop. The vacuum drop shall not exceed by 0.06mbar for 10min

Increase in pressure

40min 80min 80min

Maximum pressure

3bar 4bar 4bar

Pressure holding

3hrs 3hrs 3hrs

Post curing At140 5 C for 14hrs

At140 5 C for 32hrs

At140 5 C for 32hrs

1.General:

Vacuum Pressure Impregnation of resin poor insulated jobs:

PROCESS:

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• The jobs that are entering tank for Vacuum Pressurised Impregnation shall not have any oil based coatings. Any such, rust preventive/ corrosion preventive viz., red oxide etc., shall be eliminated into the tank. • Resin in the storage tank shall be stored at 10 to 12 C and measured for its viscosity, viscosity rise. • Proper functioning of the impregnation plant and curing oven are to be checked by production and cleared for taking up of job for impregnation

2.Preheating:

• The job is to be loaded in the curing oven and heated. The temperature is to be monitored by the RTD elements placed on the job and the readings are logged by production. The time of entry into the oven, time of taking out and the temperature maintained are to be noted. Depending on convenience of production the jobs can be preheated in impregnation tank by placing them in tubs. • The impregnation tubs used for impregnation of jobs are to be heated in the impregnated tank itself, when the jobs are preheated in the curing oven.

3. Impregnation:

• Job insertion into preheated tub and insertion into tank

By the time, the preheating of job is completed, it is to be planned in such a way that the heating of tub and tank heating matches with the job. This is applicable when the job is heated in the curing oven separately. The preheated job is to be transferred into the tub by crane handling the job safely and carefully with out damage to the green hot insulation.

• Insertion of tub with job into the impregnation tank

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Fig: VPI Resin tub

The warm tub with job is inserted into impregnation tank by sliding on railing, in case of horizontal tank. The thermometer elements are to be placed at different places on the job. The connection for inlet resin is to be made for collection of resin into tub. After ensuring all these the lid of the impregnation tank is closed. In case of vertical tank the job along with tub is slinged and inserted carefully into impregnation tank without damage to insulation.

• Drying the job in vacuum

The job is to be dried under vacuum. Drain out the condensed moisture/ water at the exhausts of vacuum pumps for efficient and fast vacuum creation. Also check for oil replacement at pumps in case of delay in achieving desired vacuum.

• Heating the resin in the storage tank The completion of operations of drying and the heating of the resin in the storage tank are to be synchronized. The heating of resin in the tank and pipeline is to be maintained as at preheating temperature.

• Admission of resin into impregnation tank

The resin is allowed into the impregnation tank tub if required from various storage tanks one after the other up to a level of 100mm above the job generally, after which the resin admission is stopped. After 10mins of resin settling the tank is to be pressurized by nitrogen. While admitting resin from storage tanks pressurize to minimum so that nitrogen will not affect resin to spill over in tank.

• Pressurizing/gelling

The pressure cycle is to be maintained.

• Withdrawal of resin from impregnation tank to storage tank

The resin that is pressurized as per pressure cycle by which the opening of relevant valves will allow the resin to come back to the storage tank. The job also shall be allowed for dripping of residue of resin for about 10min. After dripping, withdrawal of resin in various storage tanks is to be carried out.

• Taking out the tub with job from impregnation tank

The lid is then opened after taking precautions of wearing mask and gloves for the operating personnel as a protection from fumes. The job is withdrawn from impregnation tank by sliding on railing for horizontal and slinging on to crane for vertical impregnation tanks.

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4. Post curing: The job is post heated. The time for raising from job temperature to this temperature as per relevant annexure. The time at which the heating is started, achieved and maintained is to be logged.

5.Electrical testing:

All jobs that are impregnated till above process, are to be tested for electrical tests. After ensuring that all the temperature/vacuum conditions stipulated for drying, impregnation and curing operations have been properly followed, the job is to be released for this operation.

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CONCLUSION :

The Vocational training at BHEL Hyderabad helped us in improving our practical knowledge and awareness regarding Turbo Generator to a large extent.Here we came to know about the technology and material used in manufacturing of turbo generators. Besides this, we also visualized the parts involved or equipments used in the power generation.Here we learnt about how the electrical equipments are being manufactured and how they tackle the various problems under different circumstances. At least we could say that the training at BHEL Hyderabad is great experience for us and it really helped us in making or developing our knowledge about turbo generator and other equipment used in power generation.

FUTURE SCOPE

AND

CONCLUSION

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FUTURE SCOPE:

The technology research and investigations division of BHEL is currently investigating the technical and logistical merit of performing offline quadratic-rate partial discharge tests on the stator winding insulation of its hydro & turbo generators. A series of laboratory based insulation research studies on stator bars have been conducted to gain a better understanding of the various partial discharge phenomena involved. Results thus far obtained from these tests have provided valuable insight into the discharge activity of operation.

REFERENCES:

www.indiamart.com

www.eriks.co.uk

www.seimens.com

www.bhel.com

A text book of electrical technology by B.L.THERAJA.

A text book of electrical machines by P.S.BIMBRA.