A comprehensive study on the design and fabrication of Two Pole Turbo Generators at the facility of Bharat Heavy Electrical Ltd., Hyderabad.

1. Study of
Turbo Generators
Guided By Prepared by
Mr P.Srinivasa Rao Padmanav Mishra
Sr. Engineer, 114EE0153
E.M. Technology, Srinibash Sahoo
BHEL,Hyd 714EE3079

2. PREFACE
In-plant Training is a very important aspect of engineering which gives an
engineering undergraduate the much-required exposure to the industrial
environment. Understanding how a big institution functions complement the
theoretical concepts learned in college and helps a student to understand the
concepts completely.
We would like to stress that this training at Bharat Heavy Electricals Limited,
Hyderabad has been a very encouraging and informative undertaking. This
enlightening experience under a helping guidance enabled us to gain much-
needed insight into the productionand manufacturing process ofturbo generators.

3. ACKNOWLEDGEMENT
Forthe successfulcompletion of this project, we are indebted to countless people
without whom the success of this project would not have been possible.
First of all, we would like to convey our sincere thanks to Mr. Vikram Jeet
Mahanta who facilitated this training. We would also like to thank our guide Mr.
P.Srinivasa Rao (Sr. Engineer, E.M. Technology, BHEL, Hyd), for providing us
with an opportunity to undergo training under his able guidance.
And last, but not the least, we would like to express our sincere thanks and
gratitude to all the officials and employees at BHEL, Hyderabad for their
excellent guidance and constant support throughout the training period.

4. CONTENTS
Chapter No. Topic Page No.
1. Details of Project
1.1 Site Location
1.2 Site Details
2. Details of Study
2.1 Information
2.2 Stator
2.3 Rotor
2.4 Excitation System
2.5 Cooling System
2.6 Insulation System
2.7 Testing of Generator
3. Conclusion

5. CHAPTER 1
DETAILS OF PROJECT
1.1 Site Location
The study for the project has been done at the manufacturing plant
of BHARAT HEAVY ELECTRICALS LIMITED, HYDERABAD.
The area of focus was 02 ELECTRICAL MACHINERY where the
manufacturing of two pole turbo generator takes place from paper to
product. The department has been segregated into various shops which
work together in an intelligent symbiosis. The shops have been arranged
according to the stages of production. Over the period of one month, the
work produced in the shops were observed and duly noted. The following
is the block diagram of shops.

6. 1.2 Site Details
BHEL is an integrated powerplant equipment manufacturer and one
of the largest engineering and manufacturing companies in India in terms
of turnover. It was established in 1964, ushering in the indigenous Heavy
Electrical Equipment industry in India - a dream that has been more than
realized with a well-recognized track record of performance. BHEL has
been engaged in the design, engineering, manufacture, construction,
testing, commissioning and servicing of a wide range of products and
services for the core sectors of the economy, viz. Power, Transmission,
Industry, Transportation (Railway), Renewable Energy, Oil & Gas and
Defence.
As a member of the prestigious 'BHEL family', BHEL-Hyderabad
has earned a reputation as one of its most important manufacturing units,
contributing its lion's share in BHEL Corporation's overall business
operations. The Hyderabad unit was set up in 1963 and started its
operations with manufacture of Turbo-generator sets and auxiliaries for 60
and 110 MW thermal utility sets. Over the years it has increased its
capacity range and diversified its operations to many other areas. Today, a
wide range of products are manufactured in this unit, catering to the needs
of variety of industries like Fertilisers & Chemicals, Petrochemicals
& Refineries, Paper, sugar, steel etc. BHEL-Hyderabad unit has
collaborations with world renowned MNCs like M/S General Electric,
USA, M/S Siemens, Germany, M/S Nuovo Pignone etc.
BHEL-Hyderabad is now a global enterprise providing solution for
a better future. Development of newer technologies, products, improved
processes, better services and management practices have made BHEL a
pioneer in engineering.

7. CHAPTER 2
DETAILS OF STUDY
2.1 Information
2.1.1 Turbo Generators
A turbo generator is a machine which combines the turbine with
the electric generator for the production of electric power. Large steam-
powered turbo-generators meet the major percentage of the electricity
demand with gas powered turbo-generators acting as auxiliary power
units.
2.1.2 Principle of Operation
Turbo Generator converts mechanical energy into electrical
energy. It works onthe principle of “Faraday’s Laws ofElectro-Magnetic
Induction”. Faraday’s law states that emf is induced in a conductor when
magnetic flux linkage through it changes. The emf can be generated by
relative motion between coil and flux and has the magnitude
Emf= N
𝑑∅
𝑑𝑡
In turbo generators, Rotor is supplied with DC current which produces
the magnetic field. The 3 phase stator winding is laid in the stator core.
When generator rotor coupled with turbine rotates, it causes the magnetic
field in the stator core to vary which in turn produces the necessary emf.
3 phase stator winding produces synchronous magnetic field at speeds of
120𝑓
2𝑃
where f is the frequency of the current produced and P is the
number of poles.
2.1.3 Sizing of Generator Module
Equation for sizing of generator module
P=K*As*Bδ*D2*L*ns

8. Here,
P= MW Output
As= Electric Loading (Amp.Cond/cm)
Bδ= magnetic Loading (gauss)
D= Stator Bore Diameter (cm)
L= Stator Core Length (cm)
ns= Rated Speed
D2
L= Volume of Rotor or Size of the Machine
2.1.4 Generator specification and components
Specifications
1. Speed – 3000 RPM
2. Number of Poles – 2
3. Horizontal Construction
4. Cylindrical Rotor
Components
1. Stator
2. Rotor
3. Excitation System

9. 2.2 Stator
The Stator consists of the following parts:
1. Stator Frame
2. Stator Core
3. Stator Winding
4. Stator End Cover
5. Bushings
6. Generator Terminal Box
Fig S.1
2.2.1 Stator Frame
The Stator frame is the rigid fabricated cylindrical frame which
withstands the weight of lamination core, winding, and the forces and
torque during operation. It is the horizontally split type and welded
construction which is firmly fixed to the foundation plates with bolts
through the feet.
2.2.2 Stator Core
The Stator core is made up of insulated steel lamination sheets
stacked uponeach other. It has a low loss index and suspended in the stator
frame with the help of insulated rectangular guide bars. The stator core is
axially compressed by the help of clamping fingers, pressure plates, and
non-magnetic clamping bolts. The main features of stator core include

10. carrying the magnetic flux efficiently and adding to the mechanical
support.
Fig S.2
The selection of material for building up of the core is very important as if
affects the losses considerably. The two types of losses that occur are the
Hysteresis Loss and the Eddy Current loss.
Hysteresis Loss: Hysteresis Loss occurs due to the residual magnetic flux
in the core material and is given by:
Wh α Kh*βmax
1.6
Eddy Current Loss: When emf is induced in the core, eddy currents are
produced and cause losses given by the relation:
We α βmax
2
*t2

11. To minimize the Hysteresis losses, silicon alloyed steel sheets are used in
building up of the core. The sheets have the following composition
Steel -95.5%
Silicon -4%
Impurities -0.2%
The sheets are 4% Silicon Alloyed COLD ROLLED NON-GRAIN
ORIENTED SHEETS (CRNGO). To reduce the Eddy Current Losses, the
core is build-up of 0.5mm thickness laminations, which are insulated from
each other. The sheets are insulated by CLASS-B type of varnish.
Lamination Preparation
The coreis built up ofsectors of60degrees, 6 in total. Theinsulation
used between the laminations is ALKYD PHENOLIC VARNISH dried at
suitable temperatures. The thickness of varnish varies between 8 to 10
microns and is sprinkled uponthe sheets when it passes through a conveyor
belt and dried at temperatures of300-400o C. The prepared laminations are
passed for various tests suchas Xylol test, Mandrel test, and Viscosity test
among many.
Assembly of Core
The statorlaminations 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 passage for the cooling of the core. The
segments are staggered from layer to layer so that a coreofhigh mechanical
strength and uniform permeability of magnetic flux is obtained. The
laminations are then hydraulically compressed and heated while stacking
up to obtain maximum compression. The complete stack is held by means
of clamping bolts and pressure plates.

12. Fig S.3
2.2.3 Stator Winding
The stator winding of a two pole turbo generator is a fractional pitch
three phase two layer lap winding type with 60o phase spread fractional
winding which reduces the higher order harmonics and the pitch is so
selected that 5th and 7th harmonics are greater reduced. Theslot bottombars
and top bars are displaced from each other by one winding pitch and
connected at their end to form coil groups.
Conductor Construction
The conductorbar consists of a large number of separately insulated
strands which are transposed to reduce the skin effect losses and equalize
the induced EMF in all strands, which minimize the circulating currents.
The insulated copper strips are first straightened and are subjected to
insulator stripping at points and cutting. After aligning the top and bottom
dye, the conductors are pressed and checked as per technological
requirement. The first and second bundle are assembled together to form a
single bundle and an insulation sheet is kept between the two bars and
joined together to form a single bar.

13. The bars are subjected to horizontal and vertical pressure of
150Kgs/cm2 at a temp of 150oC for a duration of 2-3 hours. Passing gauges
and lamp test is conducted for inter-strip and inter half shorts. Bending
operation is done on bending table. First and the second bend is carried out
to achieve the overhang, third bend formation the coil is laid on universal
former.
Insulation
Insulation is basically done to prevent any kind of short circuit
between the bar and the stator core when the bar is assembled in the stator
of the generator. Every individual bar consisting of uneven surface and
width space are filled with nomax and Mica fleece on both sides with
further tapping done by PTFE tape (Poly Tetra Fluoro Ethylene) and
subjected to further processing. The final tapping is carried out on the bar
by two ways, Manual Tapping, and Machine Tapping. Resin rich and resin
poorinsulating materials are characterized by the contact of Epoxy Resin.
In Resin rich system the content of Epoxy Resin is 40%, and in Resin poor
system the content of the resin is 8%.
Connection of Bars
Brazing facilitates the electrical connection between the top and
bottom bars. One top bars strand each is brazed to one strand of the
associated bottombar so that beginning ofeach strand is connected without
having any electrical contact with the remaining strands. This connection
offers the advantage that circulating current losses in the stator bars is kept
small.
2.2.4 Stator End Cover
The ends of the stator frame are closed by the pressure exerting end
shields. The end covers are made up ofnon-magnetic material (Aluminium
Castings) to reduce stray load and eddy current losses. The end shields
feature a high stiffness and accommodates generator bearings; they are
horizontally split to allow for assembly.
2.2.5 Bushings
The beginning and the ends of three phase windings are brought out
from the stator frame through the bushings, which provide high voltage
insulation. The bushings are bolted to the stator frame at exciter side by

14. their mounting flanges. The generator main leads are connected to the
terminal connectors outside the stator frame.
Constructor of Terminal Bushings
The bushing conductor consists of high conductivity copper buses.
The connection flanges are silver-plated to minimize the contact
resistances ofthe bolted connections. The supporting insulator of glass silk
cloth is impregnated with epoxy resin. The copperbuses areattached to the
insulator at one end and canbe expanded freely. This facilitates the thermal
expansion between the terminal bushing and the phase connectors. For
prevention of eddy current losses and inadmissible overheating, the
mounting flange is made of glass silk cloth as well.
Cooling of Terminal Bushings
The heat from the terminal bushings is extracted by cold air. Cold
air from the discharge end of the fan is pressed into the insulator. The hot
air is sucked into the intake of the fan via the passage between the two
copper buses.
2.3 Rotor
Rotor consists of the following parts
1. Rotor body/shaft
2. Damper bar
3. Rotor End Wedge
4. Rotor Winding
5. Retaining Ring
6. Shrink Seat
7. Transverse Slots
8. Rotor Wedge
Fig R.1

15. 2.3.1 Rotor Shaft
The rotor shaft is a single piece solid forging manufactured from a vacuum
casting. Slots for insertion of field winding are milled into the rotor body.
The longitudinal slots are distributed over the circumference to obtain
solids poles. Strength test, material analysis, and ultrasonic tests are
performed during manufacture of the rotor. After completion, the rotor is
placed in various planes at different speeds and then subjected to an over
speed test at 120% of rated speed.
Fig R.2
2.3.2 Rotor Windings
The rotor of turbo generator accommodates field winding which has
several series connected coils inserted into longitudinal slots of the rotor
body in such a way that two poles are obtained.
The solid conductors are provided with axial slots for the radial discharge
of cooling gas. The individual conductors are bent to obtain half after
insertion into rotorslots. Theseturns are combined from full turns the turns
of one slot constitute the individual coils of the rotor winding are series
connected in such a way that one north and one south magnetic pole is
obtained. *Ref Fig R.3

16. Fig R.3
2.3.3 Field connection
The field current is supplied to the rotor windings through radial terminal
bolts and two semi-circular conductors located in the hollow bores of the
excitor and rotor shafts. The field connection provides electrical
connection between the rotorwinding and exciter. The connectionfrom the
radial bolts goes to the coil which in turn being series connected to other
coils provide a two pole rotor.
2.3.4 Bearing
The generator rotoris supported intwo sleeve bearings. To eliminate
shaft current between the exciter from foundation plate and oil piping,
bearing is insulated. The temperature of each bearing is maintained with
two RTD’s (Resistance Temperature Detector) embedded in the lower
bearing sleeve so that the ensuing point is located directly below the
Babbitt. The oil supply ofbearings is obtained from the turbine oil system.
2.3.5 Rotor Conductor
The conductors are made with a silver content of approximately 0.1%
as compared to electrolytic copper. After quality checking the ventilation
holes are punched and conductors are bent more than 90o so as to sustain
spring back effect.

17. The conductors are heated and pressed at the bending so that the cross
section of the conductors shall be equal throughout. The process is called
ANNEALING. *Ref Fig R.4
Fig R.4
2.3.6 Dovetail Punching & Window Dimension
A small portion near the bend is removed so as to prevent any damage
to the insulation trough while lying in the slots. The process is called relief
filling. Then dovetail punching is made which provides good brazing
process when the two conductors are joined. Window dimensions are
checked for the conductors. The dimension of the window decreases from
the top to bottom conductors.
2.3.7 Rotor Slot Wedges
To protect the winding against the effect of centrifugal force the
winding has to be firmly secured in the slot with wedges. The wedges are
made from an alloy having high strength and good electrical conductivity
and also function as damper winding bars. The slot wedges extend below
the shrink seats of the retaining rings. The ring acts as a short circuit in
damper windings.
2.3.8 Rotor Retaining Rings
The Rotor retaining rings balance the centrifugal force due to the end
windings. One end of each ring is shrunk on the rotor bodywhile the other
end of the ring overhangs the end winding without contacting on the shaft

18. which ensures unobstructed shaft direction of the end winding. The shrunk
on the hub at the free end of the retaining ring serves to reinforce it and
secures the end winding in the axial direction. To reduce stray losses and
to provide strength, the rings are made up of non-magnetic cold worked
materials. These act as short circuit rings to the induced current to the
damper system.
2.3.9 Terminal Lug
The terminal lug is a copper conductor of rectangular cross section.
One end of the terminal lug is braced to the rotor winding while the other
end is screwed to the radial bolt.
2.3.10 Radial Bolt
The field current lead located in the shaft bore is connected to the
terminal lug at the end winding through a radial bolt. The radial bolt is
made from steel and screwed into the field current lead in the shaft bore.
2.3.11 Field Current Lead
The leads are run in the axial directions from the radial bolt to the end
of the rotor. They consist of two semi-circular conductors insulated from
each other by an intermediate plate and from the shaft by a tube.
2.3.12 Rotor Fan
The cooling air in the generator is circulated by axial fans located on
the rotor shaft. In cooling of the rotor winding the pressure established by
the fan works in conjunction with the air discharged from the rotor. The
moving blades of the fan have threaded roots that permit the blade angle to
be adjusted. The blades are drop forged from an aluminum alloy and
screwed into the rotor shaft which is secured by a threaded pin at its end.

19. 2.4 Excitation system
The different type of A.C exciters used in A.C generators are:
1. High-Frequency Excitation
2. Brushless Excitation
3. Static Excitation
The type of excitation used for field windings in the A.C generators is
of Static Excitation type. The system is highly reliable with least
maintenance and is ideally suitable for turbo generators. This system
consists ofrectifier transformer, thyristor converts, field breaker and AVR.
This system provides fast response and has less maintenance.
Exciters are those components, which are used for providing high voltage
to the generator during the start-up conditions. The main parts included in
the exciter assembly are:
1. Rectifier Wheels
2. Three phase main exciter
3. Three phase pilot Exciter
4. Automatic Voltage Regulator
*Ref Fig E.1
Fig E.1

20. 2.4.1 Rectifier Wheels
The main components of the rectifier wheels are the Silicon Diodes,
which are arranged in the rectifier wheels in a three-phase bridge circuit.
The internal arrangement of the diode is such that the contact pressure is
increased by centrifugal force during rotation.
There are some additional components contained in the rectified wheels.
Once diode each is mounted in each light metal heat sunk and then
connected in parallel. For the suppression of momentary voltage peaks
arising from commutation, RC blocks are provided in each bridge in
parallel with one set of diodes. The rings from positive shrunk onto the
shaft. This makes the circuit connections minimum and ensures
accessibility of all the elements.
2.4.2 Three phase Pilot Exciter
The three-phase pilot exciter is a six-pole revolving field unit; the
frame accommodates the laminated corewith the three-phase winding. The
rotor consists of a hub with poles mounted on it. Each pole consists of
separate permanent magnets, which are housed, in non-metallic enclosures.
The magnets are placed between the hub and external pole shoe with bolts.
The rotor hub is shrunk on to the free shaft end. The three phase A.C
generated by the pilot exciter is rectified and controlled by the Automatic
Voltage Regulator to provide variable D.C for excitation of the main
exciter. *Ref Fig E.2

21. 2.4.3 Three Phase Main Exciter
Three phase main exciter is a six-pole armature unit, the poles are
arranged in the frame with the field and damper winding. The field winding
is arranged on laminated magnetic poles. At the pole shoe, bars are
provided which are connected to form a damper winding. The three phase
winding is inserted in the slots of the laminated rotor. The winding
conductors are transposed within the core length and end turns if the rotor
windings are secured with steel bands. The connections are made on the
side facing the rectifier wheels. After full impregnation and curing, the
completed rotor is shrunk onto the shaft.
2.4.4 Automatic Voltage Regulator
The general Automatic Voltage Regulator is fast working solid
thyristor controlled equipment. It has two channels. One is an auto channel
and the other is manual. The auto channel is used forthe voltage regulation
and the manual channel is used for current regulation. Each channel has its
own control for reliable operation.
The main features of AVR are:
1. It has an automatic circuit to control outputs of the auto channel
and manual channel and reduces disturbances at the generator
terminals during transfer from autoregulation to manual regulation.
2. It has stator current limitations for optimum utilization of lagging
and leading reactive capabilities of a turbo generator.
3. Automatic transfer from automatic regulation to manual regulation
takes place in case of PT fuse failure or some internal faults in the
auto channel.
4. The generator voltage in both channels that is in the auto channel
and the manual channel can be controlled automatically.
Flowchart of Brushless Excitation

22. 2.5 Cooling System
Cooling is one of the basic requirements of a generator. The effective
working of generator considerably depends on the cooling system. It is
inter-related with the type of insulation used. The generator losses are
usually dissipated as heat, and the heat raises up the temperature of the
generator. That shall affect the insulation greatly unless it is cooled. So the
cooling system is employed and the class of insulation depends on the
cooling system installed. The various methods of cooling are:
1. Air Cooling-60MW
2. Hydrogen Cooling-100MW
3. Water Cooling-500MW
4. H2 and Water Cooling-1000MW
2.5.1 Air Cooled Turbo Generator
In Air Cooled Turbo Generator, the stator winding is indirectly air
cooled whereas the rotorwinding and statorcoreis directly air-cooled. This
type ofcooling is applicable for30-60 MW generators. In this type of turbo
generator, there are vertically side mounted coolers in a separate housing.
2.5.2 Hydrogen Cooled Turbo Generator
The increased generator rating had the problem of insufficient cooling
through air cooling system. The augmentation by improper circulation of
air and increased circulation speed is corrected by the use of Hydrogen as
the cooling medium. Lower density, non-supporter of combustion makes
it as an ideal substituent for Air cooling systems.
2.5.3 H2 and Water Cooled Turbo Generator
For additional cooling in large rating machines, a Primary Water
cooling systemwith demineralized water flowing through the hollow stator
conductors is used.
The two-pole turbo generator uses direct cooling for the rotor winding and
indirect cooling for the stator winding. The losses in the remaining
generator components, suchas iron losses, winding losses, and stray losses
are dissipated through the air. The heat losses arising in the generator
interior are dissipated through the air. Direct cooling of rotor essentially
eliminates hot spots and differential temperatures between adjacent

23. components, which could result in mechanical stress, particularly to the
copper conductors, insulation, and rotor body. Indirect air cooling is used
for statorwinding. Fans arranged on the rotordraw the cooling air for axial
flow ventilation. Lateral openings in the stator housing discharge the hot
air. The three primary flow paths of air are described below
*Ref Fig C.1, C.2
Fig C.1
Fig C.2

24. Flow Path 1
The air directed into the rotor cools the rotor windings; part of cooling
air flows pastthe individual coils forcooling the rotorvia bores in the rotor
teeth at the end of the rotor body. The other portion of cooling airflow is
directed from the rotor end winding space into the slot bottom ducts from
where it is discharged into the air gap via a large number of radial
ventilating slots in the coils and bores in the rotor wedges. Along these
paths, the heat of rotor winding is directly transferred into the cooling air.
Flow Path 2
The air is directed over the stator end windings into the cold air ducts
and the compartments in the stator frame between generator housing and
rotor core. The air then flows through the air gap in the slot into the stator
core where it absorbs heat from stator core and stator winding.
Flow Path 3
This path is directed via the rotorretaining ring. The air flows pastthe
clamping fingers through the ventilating slot in the stator core and into the
hot air compartments of the stator frame. This air flow mainly cools the
rotor retaining rings, the ends of the rotor body and the ends of the stator
core.
Flows 2&3 mix in the air gap with 1 leaving the rotor. The cooling air
flows outward radially through the ventilating lots in the coreand winding.
The hot air is discharged into the air cooler.

25. 2.6 Insulation System
Insulation is one of the most important requirements in an electrical
system. It provides resistance from high voltage malfunctions and
withstands mechanical strain. The insulating material is selected based on
its electrical, mechanical, thermal, and chemical properties. Insulates are
extremely diverse in origin and properties. In electrical machines, insulates
should have the following properties:
1. High dielectric strength sustained at elevated temperatures.
2. High receptivity or specific resistance.
3. Low dielectric hysteresis.
4. Good thermal conductivity.
5. High degrees of thermal stability.
6. Low dissipation factor.
7. Resistance to oils, liquids, gas, flames, acids and alkalis.
8. Should be resistant to thermal and chemical deterioration.
Besides the following properties, the further effects considered for
insulating materials are:
1. Fall in resistance with an increase in temperature.
2. The sensitivity of insulation in the presence of moisture.
3. Decrease in resistance with an increase in applied voltage.
2.6.1 Epoxy Resins
Epoxy resins are polyethers derived from epichlorohydrin and
bisphenol monomers through condensation polymerization process. In
epoxy resins, cross-linking is produced by cure reactions. The liquid
polymer having a reactive functional group like oil etc. is the prepolymer.
The prepolymer of epoxy resin is allowed to react with curing agents to
produce three-dimensional cross-linked structures. Epoxy resins exhibit
outstanding toughness, chemical inertness, and excellent mechanical and
thermal shock resistance. They also possess good adhesion property.
Epoxy resins can be used up to 300o F and with special additions can be
used up to 500o F. Epoxy resins act as an effective coating material.

26. 2.6.2 Insulating Material for Laminations
The core stacks are subjected to high pressure during assembling and
to avoid metal-to-metal contact, laminations must be well insulated.
Homogeneity in thin layer toughness and high receptivity is required for
good lamination insulation. Varnish is used as insulating material for
laminations.
Varnish is the mosteffective type ofinsulation in terms ofavailability.
It makes the laminations nest proof and is not affected by temperature
produced in the electrical machine. Varnish is applied to both sides of
lamination to a thickness of about 0.006mm. On plates of 0.35mm
thickness, varnish gives a stacking factor of 0.95. The process used in
BHEL is thermos settling process of insulation, which is of two types:
 Resin Rich System of Insulation.
 Resin Poor System of Insulation.
2.6.3 Resin Rich System
The Resin Rich system of insulation is used for all machines. It
contains 40% ofEpoxyResin, so it gives good thermal stability. Resin Rich
insulation consists of the following materials in percentage composition:
1. Mica Paper Tape: 40-50%
2. Glass Paper Tape: 20%
3. Epoxy Resin: 40%
The bars are insulated (or) taped with resin rich tape and are placed in
the pre-assembled stator core including stator frame. In resin rich system,
Mica gives a good dielectric strength, Glass fiber tape provides mechanical
strength and Epoxy resins canwithstand high temperatures. But this system
has the disadvantages of being time-consuming and costly therefore has
been replaced by VPI system.
2.6.4 Vacuum Pressure Impregnation
Vacuum Pressure Impregnation is the process by which the fully
wound stator is completely submerged in Resin. Through a combination of
dry and wet vacuum and pressure cycles, the resin is assimilated
throughout the insulation system. Post operation the Stator becomes a
monolithic and homogenous structure. The VPI system used in BHEL
consists of various cycles which begin with pre-heating the stator up to

27. 60oC. The VPI chamber @ 60oC initiates the vacuum cycle (0.2mbar) with
a holding time of 9hours. Before resin flooding, vacuum drop test is
performed for 10mins at a pressureof 0.006bar. Resin along with hardener
@60C is then flooded at a composition ratio of 1:1. Post settling of the
resin, N2 gas enters the chamber and is maintained at a pressureof 4kg/cm2
for 80mins. The statoris rotated at 4-10 RPMfor 2hours. In the post-curing
process, the system is heated to 140oC and kept for 24 hours. After which
it is cooled down to 80oC and the ends of the stator is coated with anti-
fungal paint to protect the components from moisture.
2.7 Testing of Turbo-Generator
The fulfillment of requirements is necessary to estimate the
performance of generator. Various tests are performed to ensure that the
generator meets the required parameters. The following first two tests are
conducted onthe stator and rotor before assembling and the third and final
routine tests are conducted after assembling the Turbo Generators.
 Tests conducted on Rotor.
 Tests conducted on Stator.
 Routine Tests on Turbo Generators.
2.7.1 Measurement of D.C Resistance of Rotor Winding
The D.C resistance value of rotor winding is measured by using a
micro-ohmmeter. Theresistance and temperature are measured using RTD.
The resistance at the temperature T is obtained byusing specified formulae.
A deviation of ±10% from the design values is acceptable.
2.7.2 Measurement of Impedance
The impedance test of the rotor is done by plotting a graph between
voltage v/s current. Current obtained by increasing voltages in steps of50V
(up to 200V) is plotted in a graph. This test is done to ensure that the
impedance increases with increase in voltage.
2.7.3 Inter-Turn Insulation Test
The insulation between the windings of the rotor is tested by applying
a high-frequency current of about 500HZ. It is ensured that the insulation
withstands this test.

28. 2.7.4 Ring Flux Test on Stator Core
Ring flux test is carried out on the stator corebefore winding is put in
the slot. The rated flux density is generated in the stator core by passing
current in it. The rise in temperature and generation of heat is monitored
byRTD’s. If any hotspot is found in the core, it is detected and rectification
is carried out using phosphoric acid as an electrolyte.
2.7.5 Measurement of D.C Resistance of Stator Winding
The D.C resistance of stator winding is measured in the same way as
for RotorWinding. The micro-ohmmeter is connected to 230V AC supply.
The measuring leads of micro-ohmmeter are connected across R phase of
stator terminals. The resistance is calculated using formulae and the value
of resistance obtained from RTD’s. The acceptable variation in maximum
and minimum value of stator DC resistance is ±5%.
2.7.6 Test of Resistance Temperature Detector (RTD)
The RTD leads are shorted and one lead of megger is connected to it.
The megger is run for 60seconds and the value of insulation resistance is
obtained. The value of insulation resistance should not be less than 1M.
The RTDterminals are then removed and connected to the multimeter. The
resistance value is then noted down. For three wire RTD, the continuity
between shorted terminals is checked.
2.7.7 MechanicalRun and Measurementof vibrations at Rated Speed
The machine is rolled and run at rated speed. The vibrations are
measured on both bearing housings in horizontal, vertical and axial
directions. The temperature of the stator is monitored by monitoring the
RTDs embedded in core, tooth, and winding. The vibrations should be less
than microns and noise level in between 75-90dB.
2.7.8 Open Circuit Test
The machine is prepared for a run at rated speed with constant
monitoring of motor input voltage and current. The excitation is gradually
increased in steps of 20, 40, 60, 80, 90, 100, 105, 110 and 120% of the
rated voltage of machine. The open circuit characteristics are plotted from
open circuit results by selecting X-axis as field current and Y-axis as %
rated voltage. From the open circuit test, the iron losses are obtained.

29. 2.7.9 Short Circuit Test
The machine is run at rated speed with shorted terminals. The drive
motor input voltage and current are noted when the machine is excited
gradually in steps, at 20%, 40%, 60%, 80%, 100% rated current of the
machine. The excitation is then reduced and cut off. The speed is reduced
and the temperature is checked from the machine RTDs. From the short
circuit test, we get copper losses. The short circuit characteristics are
plotted from SSC results by selecting field current as X-axis and % rated
current as Y-axis.
2.7.10 Measurement of Rotor Impedance (Rotor inside Stator)
A variable 50Hz A.C voltage of single-phase is applied across the
input leads and readings of voltage and current are noted down by
increasing voltage in steps of 50V. Rotor Impedance is measured at a
standstill and at the rated speed of the machine. The impedance of rotor is
plotted as applied voltage v/s Impedance.
2.7.11 H.V Test on Stator and Rotor Windings (Machine at rest)
The high voltage is applied to winding by gradually increasing it to
required value and maintain it for one minute before decreasing it
gradually. The transformer is then switched off and winding is discharged
to by shorting it to earth. The test is conducted on all the phases and rotor
winding separately. When high voltage test is done on one phase winding,
all other phase windings, rotor winding, instrumentation cable and stator
body is earthed. The test is done to check the insulation of winding and
hence known as insulation test.
High Voltage Test levels
Stator Winding: (2Ut + 1) KV *Ut is the rated voltage of machine.
Rotor Winding: (10 * Up) V *Up is the excitation voltage.

30. 2.7.12 Balancing Test
Balancing of the rotor is done to decrease vibration due to
centrifugal force and to increase quality, and performance. Balancing test
gives data required for balancing operation of the rotor. It is carried out in
two steps:
1. Static balancing 2. Dynamic balancing
Static balancing:
In static balancing, the rotor is put on two plain rails. Rails replace
the shaft at the bearing ends. The rails should be perfectly horizontal as
possible. The rotor should be in a position to swing on these rails without
friction. Then the eccentric force is balanced. This static balancing is only
useful to bring the center of gravity very near to the axis of the shaft but
for exact balancing dynamic balancing is needed.
Dynamic balancing:
It helps in finding forces and torques on the shaft when the machine
runs. This balances the deviation of the center of gravity from the axis of
rotation. Rotation is essential for dynamic balancing. Turbo generators are
generally dynamically balanced under rotorhot conditions. The weights on
either side of the axis of the rotor are determined. The centrifugal force on
the bearings is measured and if weights on either side of the axis of the
rotor are not same then the weights are added accordingly.

31. CONCLUSION
This training has proved to be quite fruitful. It gave us a chance to
encounter various machines and components such as turbo generators,
pumps, turbines, switch gear which are manufactured at BHEL,
Hyderabad. The architecture, the way the various units are linked, and the
controlengineering of the systems corroborates to the fact that engineering
is not just the structural description but also about planning and
management.