ACKNOWLEDGEMENT

The extensive training program at BHARAT HEAVY ELECTRICALS LIMITED

(BHEL), Bhopal was a great opportunity and an exceptional learning
experience for me. It is first hands on experience and an exposure of
practical world.

I got golden opportunity to work under the esteemed supervision of

Mr.Laljeet Oraon (Transformer manufacturing TRM). It was great
privilege for me to work under him. I am thankful to him for his extremely
patient gesture, to make training program fruitful for me and for rendering
every possible help to carry out this research project.

I offer my gratitude to the management and staff that have spent their
precious time, expressed keen interest and given continued encouragement
throughout the study and enabled the successful completion of my practical
at BHEL, Bhopal.

I am indebted to my parents, teachers and friends who helped and

encouraged me to work hard, move ahead and inspired me with words.
Their blessings made this work possible.

ASHUTOSH LAKRA
ENROLL NO: 1601025
VII SEM
ELECTRICAL ENGINEERING
BIT SINDRI , DHANBAD

2
Contents:

• Acknowledgement
• Company Overview
• Product Profile
• Bharat Heavy Electricals Limited (BHEL), Bhopal
• Various Divisions At BHEL Bhopal
• Transformer:
• Windings
• Material Used For Winding
• Magnetic Circuit
• Core:
• Short Circuit Resistance
• Tank
• Transformer Cooling
• Cooling System:
• Processing
• Accessories
• Oltc
• Transformer Fittings
• Transformer Testing:
• Major Landmarks / In house R&D Projects
• Erection At Site: Inspection
• Oil Filling
• High Voltage AC Motors/Generators
• Switchgear and Control Gears
• Traction Machines
• References
Company Overview:-
Bharat Heavy Electricals Limited (BHEL)

BHEL is the largest engineering and manufacturing enterprise in India in the

energy-related/infrastructure sector, today. BHEL was established more than 40
years ago, 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. The company has been earning profits continuously
since 1971-72 and paying dividends since 1976-77.

BHEL manufactures over 180 products under 30 major product groups and
caters to core sectors of the Indian Economy viz., Power Generation &
Transmission, Industry, Transportation, Renewable Energy, etc. The wide
network of BHEL's 14 manufacturing divisions, four Power Sector regional
centers, over 100 project sites, eight service centers, 18 regional offices and
one subsidiary enables the Company to promptly serve its customers and
provide them with suitable products, systems and services -- efficiently and at
competitive prices.

BHEL has acquired certifications to Quality Management Systems (ISO 9001),

Environmental Management Systems (ISO 14001) and Occupational Health &
Safety Management Systems (OHSAS 18001) and is also well on its journey
towards Total Quality Management.

• BHEL has installed equipment for over 90,000 MW of power generation --

for Utilities, Captive and Industrial users.
• Supplied over 2,25,000 MVA transformer capacity and other equipment
operating in Transmission & Distribution network up to 400 kV (AC & DC).
• Supplied over 25,000 Motors with Drive Control System to Power
projects, Petrochemicals, Refineries, Steel, Aluminum, Fertilizer, Cement
plants, etc.
• Supplied Traction electrics and AC/DC locos to power over 12,000 kms
Railway network.
 • Supplied over one million Valves to Power Plants and other Industries.

BHEL's operations are organized around three business sectors, namely

Power, Industry - including Transmission, Transportation and Renewable
Energy - and Overseas Business. This enables BHEL to have a strong
customer orientation, to be sensitive to his needs and respond quickly to the
changes in the market.

BHEL's vision is to become a world-class engineering enterprise, committed to

enhancing stakeholder value. The company is striving to give shape to its
aspirations and fulfill the expectations of the country to become a global player.

The greatest strength of BHEL is its highly skilled and committed 42,600
employees. Every employee is given an equal opportunity to develop himself
and grow in his career. Continuous training and retraining, career planning, a
positive work culture and participative style of management all these have
engendered development of a committed and motivated workforce setting new
benchmarks in terms of productivity, quality and responsiveness

Product Profile

With an export presence in more than 60 countries, BHEL is truly India’s

industrial ambassador to the world. This list is intended as a general guide and
does not represent all of BHEL's products and systems.

Thermal Power Plants

• Steam turbines and generators of up to 500MW capacity for utility and
combined-cycle applications; capability to manufacture steam turbines
with super critical steam cycle parameters and matching generator up to
1000 MW unit size.
Gas based Power turbines Plants
• Gas of up to 260MW (ISO) rating.
• Gas turbine based co-generation and combined-cycle systems for
industry and utility applications.

Hydro Power Plants

• Custom-built conventional hydro turbines of Kaplan, Francis and Pelton
types with matching generators, pump turbines with matching motor-
generators. Mini/micro hydro sets.
• Spherical, butterfly and rotary valves and auxiliaries for hydro station

G Power PlantsD
• HSD, LDO, FO, LSHS, natural-gas/biogas based diesel power plants, unit
rating up to 20MW and voltage up to 11kV, for emergency, peaking as
well as base load operations on turnkey basis.

Industrial Sets
• Industrial turbo-sets of ratings from 1.5 to 120MW.
• Gas turbines land matching generators ranging from 3 to 260MW (ISO)
rating.
• Industrial stream turbines and gas turbines for drive applications and co-
generation applications.

Boilers and Auxiliaries

• Steam generators for utilities, ranging from 30 to 500MW capacity, using
coal, lignite, oil, natural gas or a combination of these fuels: capability to
manufacture boilers with super critical parameters up to 1000 MW unit
size.
• Steam generators for industrial applications, ranging from 40 to 450t/hour
capacity using coal, natural gas, industrial gases, biomass, lignite, oil,
biogases or a combination of these fuels.
• Pulverized fuel fired boilers.
 • Stoker boilers.
• Pressure vessels.

Heat Exchangers and Pressure Vessels

• Air-cooled heat exchangers.
• Surface condensers.
• Steam jet air ejectors.
• LPG/propane storage bullets.
• Feed water heaters.

Power Station Control Equipment

• Microprocessor-based distributed digital control systems.
• Sub-station controls with SCADA.
• Static excitation equipment/automatic voltage regulator.
• Electro-hydraulic governor control.
• Turbine supervisory system and control.
• Controls for electrostatic precipitators.
• Controls for HP/LP bypass valves.

Switchgears
• Switchgear of the various types for indoor and outdoor applications and
voltage ratings up to 400 kV.
• Minimum oil circuit breakers (66K – 132kV).
• SF6 circuit breakers (132 kV – 400 kV).
• Vacuum circuit breakers (3.3 kV – 33 kV).
• Gas insulated switchgears (36 kV).

Transformers
• Power transformers for voltage up to 400 kV.
• HVDC transformers and reactors up to + 500 kV rating.
• Series and shunt reactors of up to 400 kV rating.
• Current transformers up to 400 kV.
 • Electro-magnetic voltage transformers up to 220 kV.
• Capacitor voltage transformers up to 400 kV.
• Special transformers: earthing; furnace; rectifier; electrostatic precipitator;
freight loco and AC EMU and traction transformers.

Insulators
• Disc/suspension insulators for AC/DC applications, ranging from 45 to
400 km electro-mechanical strength, for clean and pollute atmospheres.
• Pin insulators of up to 33 kV.
• Hollow porcelains of up to 400 kV.
• Solid core insulators of 25 kV rating (both porcelain and hybrid) for
railways.
• Disc insulators for 800 kV and HVDC transmission lines (BHEL is the first
Indian manufacturer to supply such insulators).

Capacitors
• AC Power capacitors for industrial and power systems of up to 250 kVAr rating
for application up to 400 kV, Coupling/CVT capacitors for voltages up to 400
kV.
• Low Tension Thyristor Switched Capacitors (LTTSC) for dynamic power factor
correction.

Energy Meters
• Single Phase, Poly Phase and Special-purpose electro-mechanical and
electrical meters.
Bharat Heavy Electricals Limited (BHEL), Bhopal

Heavy Electrical Plant, Bhopal is the mother plant of Bharat Heavy Electricals
Limited, the largest engineering and manufacturing enterprise in India in the
energy-related and infrastructure sector, today. With technical assistance from
Associated Electricals (India) Ltd., a UK based company; it came into existence
on 29th of August, 1956. Pt. Jawaharlal Nehru, first Prime minister of India
dedicated this plant to the nation on 6th of November, 1960.

BHEL, Bhopal certified to ISO: 9001, ISO 14001 and OHSAS 18001, is moving
towards excellence by adopting TQM as per EFQM / CII model of Business
Excellence. Heat Exchanger Division is accredited with ASME ‘U’ Stamp. BHEL
Bhopal has its own Laboratories for material testing and instrument calibration
which are accredited with ISO 17025 by NABL. The Hydro Laboratory, Ultra
High Voltage laboratory and Centre for Electric Transportation are the only
laboratory of it’s in this part of the world.

BHEL Bhopal's strength is its employees. The company continuously invests in

Human Resources and pays utmost attention to their needs. The plant's
Township, well known for its greenery is spread over an area of around 20 sq
kms. and provides all facilities to the residents like, parks, community halls,
library, shopping centers, banks, post offices etc. Besides, free health services
are extended to all the employees through Kasturba Hospital and chain of
dispensaries.
Various Divisions at BHEL Bhopal
BHEL Bhopal is divided into 12 blocks and produces a wide range of products
for different product groups.

Block 1
• PFM – Pre fabrication manufacturing
• HCM – Heated condenser manufacturing(Hydro, Water turbines)

Block 2
• EM – Electrical motors
• IMM – Industrial machines manufacturing division
• LEM – Large electrical motors
• TAM – Traction alternator & auxiliary machines
• TXM – Traction motors manufacturing division

Block 3
• TCB – Transformer Capacitor & Bushing
Block 4
• SCR – Switch gear Control gear & Rectifier
Block 5
• FYM – Foundry manufacturing division
Block 6
• STM – Steel turbine manufacturing
Block 7
• MOD & WEX – Modernization & work engineering
Block 8
• CIM – Coil insulation manufacturing
Block 9
• TXM – Traction motors
Block 10
• PRM – Pressure rectifier manufacturing
Block 11
• TGM – Tool and gauges manufacturing
Block 12
• NTB – 12 KV Transformer manufacturing
• UHV – Ultra high voltage
 TRANSFORMER

Definition: A transformer is a static piece of apparatus used for the transferring power
from one circuit to the other without change in frequency. It can raise or lower the
voltage with a corresponding decrease or increase in current.

Voltage transformation ratio:

• E1 = 4.44  f  N1  m
E2 = 4.44  f  N 2  m
•
E1 N1
=
•
E 2 N2

WINDINGS:

• Primary winding
• Secondary winding
• Linkage of the two by mutual inductance
Low Voltage Winding Design:
• Since voltage is less, hence turns will also be less.

• Phase current = MVA/( 3 *line voltage in KV) if winding is star connected

• Phase current = MVA/(3*line voltage in KV) if winding is delta connected
• This indicates low voltage winding shall be high.
• To carry high current the area of cross section of the conductors will be
large . This is accomplished by adopting more no. of parallel conductors
per turn.

High voltage winding:

• Large no. of turns
• Less current
• Disc coils are the best choice for the HV windings where a single disc can
have turns as high as 25 no.

Transformer winding is cylindrical and arranged concentrically. This design

offers substantial advantages like:

• Simplicity and elimination of weak insulation points by means of

symmetrical layout.
• Great mechanical resistance to short circuit stresses.
• Free oil flow through cooling channels.
• The rating and connection of the winding largely determine the choice of
the type of winding

The following four types of windings are generally used:

➢ Helical winding.
➢ Spiral winding.
➢ Continuous disc section winding.

Helical winding:
• To carry high current the area of cross section of the conductors should
be high. This is an accomplished by adopting more no. of conductors per
turn.
• Helical winding which is spring like, suits most for the LV windings.

This is generally used for low voltage windings and consists of a number of
parallel conductors simultaneously wound on an insulating cylinder of high
mechanical strength. Where current is very high, the conductors are transposed
to ensure equal current distribution in all strands, thereby reducing stray copper
losses to a minimum. To provide adequate cooling, axial and radial ducts are
provided by spacer blocks.

Spiral winding:
The spiral windings are generally used for voltages upto33 KV. These are
essentially same as helical windings, except that turns are not separated by
radial spacing blocks.

Continuous disc section winding:

This winding is used for voltages between 33 KV and 132 KV, the winding is
generally split into a number o separate coils, in order to limit the voltage per
coil.

These coils are made up of one or several flat conductors wound in spiral form.
These are stacked one above the other and connected in series by cross over s
made alternately on their inner and outer sides, so that the windings are
continuous without any joints between coils.

Such a winding is made in the simplest form proportioning the insulation at each
point to suit the power frequency and surge voltage stresses. For system
voltages above 66 KV, stress rings are usually incorporated to modify the
stresses at the ends of the winding.

To ensure adequate cooling, oil ducts are provided by vertical pressboards

spacing strips and horizontal radial spacing blocks between the sections.
Interleaved disc winding:
For EHV windings, interleaved disc winding is commonly used. By properly
interleaving the turns within a pair of discs, the series capacitance of winding
can be increased many times. This results in nearly uniform voltage distribution
under impulse conditions. Crossovers are made at the inside of the disc pair
and joints are made near the outside. More often partially interleaved disc coil is
used where only a part winding is interleaved and balance portion is continuous
disc construction.

MATERIAL USED FOR WINDING:

• P.I.C.C.- Paper Insulated Copper Conductor
• C.T.C.- Continuously Transposed Conductor
• Bunched P.I.C.C.
• Glued C.T.C.

MAGNETIC CIRCUIT:
• Magnetic circuit is formed by “CORE”
• CORE is a three or five lagged
• Coils which are of cylindrical shapes are assembled over the legs.

Other considerations:
• After designing the windings they are suitably placed over the core legs
keeping in mind the electrical stresses.
• Windings are designed for impulse withstand and short circuit forces also.
• This is followed by the cooling design.

CORE:
Any transformer consisting of core and windings core is the magnetic circuit
through which flux flows.

Materials used in core:

• The materials used for core making is low reluctance magnetic containing
silicon. This is called “CRGO” i.e. cold rolled grain oriented steel.
 • The grain orientation is technology which ensures that the flux flow
through the laminations with minimum resistance, resulting in low core
loss.

Type and construction of core:

There are following types of core available:-

• Two limb core

• Three limb core
• Five limb core
• Core with elliptical yoke section
• Core with flat yoke

Describing some terms in core construction:

Core diameter: diameter of the circle enclosing the steps of a core cross
section. All the steps are accommodated within this circle.

Frame size: the dimensions required to describe a core is called frame size. It
comprises description like core type, core diameter, leg centre and leg length.

Leg centre: this is the distance between the centerlines of main leg of a core.

Leg length: distance between top yoke level and bottom yoke level in a window
is called leg length.

Window: area enclosed by tops and bottom yoke and the main limbs. Yoke
bolts: bolts used in yokes to clamp the laminations together.
Top yoke level (TYL)/ bottom yoke level (BYL): edge of the top or bottom
yoke in the window.

Pin pad assembly: The arrangement to join clamps plates with end frames is
called pin pad assembly

SHORT CIRCUIT RESISTANCE:

Circular coil offers the greatest resistance to the radial component of
electromagnetic forces, since this is the shape which any coil will tend to
assume under short circuit stresses.

The longitudinal stresses are reduced by proper balancing of primary and

secondary ampere-turns, along the coil. In particular, the voltage adjustment
taps are distributed so as to keep imbalance of ampere-turns to a minimum.

Where large range of tappings are required, these are generally arranged in a
separate coil which is spread over the whole length of the coil stack, in order to
preserve magnetic balance between the windings as far as practicable, and to
minimise axial stresses under fault conditions.
TANK:
Tanks are fabricated from mild steel plates, electrically welded and are shot-
blasted, inside as well as outside to remove any scales before painting. The
inner surface is coated with suitable oil resistant paint whereas the outer
surface is painted with high quality anticorrosive paint system comprising of four
coats.

Tanks are designed and tested to withstand appropriate vaccum and pressure.
For special designs, the mechanical stresses are analysed by finite element
method. The welding are checked by ultrasonic/dye penetration method for any
defects.

The tank fabrication shop is fully equipped to make tanks of any shape and of
the larget sizes, including bell type construction. Thus construction allows
access to core and winding for maintenance purposes.

The flanges are designed so as to provide adequate gasket seating for

prevention of leakages. Suitable locking arrangements are provided inside the
tank so as to prevent movement of core and winding in transit.
Purpose of transformer tank:
Transformers tank is an enclosure which contains inside it the live parts such as
core and winding assembly, electrical connections and insulating oil.

Most basic classification:

• Conventional
• Bell type

Conventional tank: A tank in which the cover is flat and the tank to cover
junction is at the top of the tank.

Bell type tank: a tank in which the cover is not flat in shape and the tank and
cover junction is near the bottom of the tank.

Thus the tank has got two parts “TOP TANK & BOTTOM TANK”.

Tank Base:
Base can be with or without rollers. Rollers of four types and are of standard
design.skid base This base is suitable for placement on the plinth.

TRANSFORMER COOLING:

When the transformer is in service the windings get heated up. In oil filled
power transformer oil is the cooling medium for windings. Oil is in turn cooled by
means of radiators/integral coolers with water/air as cooling medium.

Types of cooling:
• ONAN cooling
• ONAF cooling
• OFAF cooling

ONAN cooling:

Oil flows is through natural convection. Air flow s also natural (not
forced).Cooling equipments used radiators.

ONAF Cooling:
The oil flow is through natural convection.Air flow is not natural but it is forced.
For cooling, equipments used are:radiators and fans,ONAF coolers.
OFAF Cooling:
Oil flow is forced by means of inline oil pumps. Air flow is forced by means of
fans/blowers. Cooling equipments used: Radiators,fans and pumps or integral
OFAF coolers.

COOLING SYSTEM:
Natural and Air blast cooling:
Detachable radiators are used to provide adequate cooling surface mounted
directly on the tank side or built up in one or two banks placed adjacent to the
transformer and connected to it by pipe work. The radiator element is made
from specially treated sheet steel plates. Two rolled and pressed plates are
welded together along the outer edges and along the troughs between flutes. A
number of such elements are welded into a mild steel header.

Water cooling:
The water cooling is usually of condenser type. Top oil pumped around a set of
tubes through which cooling water circulates. This type of cooling reduces the
space requirement considerably, and is recommended specially for generator
transformer where plenty of cooling water is available. To prevent any possible
leakage of water into the transformer oil, oil pressure is always maintained
higher than the circulating water pressure.

Forced oil cooling:

Hot oil from the top of the tank is pumped into a compact cooler with built-in
fans, and returned to the tank at the bottom. Alternatively a pump can be
introduced to force the oil circulation between the top and bottom main radiator
headers (where radiators are mounted in a separate bank).

PROCESSING:
The quality of a transformer, and consequently its performance and life
depends essentially on the factory processing, which is carried out at various
stages of manufacture.

All the coils are pre-shrunk before assembly. After the coils are assembled on
the core, the whole assembly is heated in an oven for extraction of moisture,
and also the coils are reduced to proper dimensions.
After final assembly, the core and coils are kept in their own tank, and the unit is
placed in a vacuum chamber for final drying. The chamber is heated up to
about 100°C and a vacuum of very high degree is maintained during dry –out.
Sometimes vacuum drying is done by drawing vacuum in its own tank and
keeping the whole transformer inside an oven.

Besides this conventional method of drying, most modern Vapour Phase Drying
method is used alternatively.

Much importance is attached to proper dry-out, as otherwise coils would

become loose in service and may get distorted under short circuit conditions.

The oil is treated separately in a filtering and degerating plant, and is kept
constantly under vacuum at a temperature of 80°C, so that moisture-free
degassed oil is always available. Ten thousand gallons of oil can be treated in
the plant at a time. Oil is tested for electrical strength, and moisture content
before the same is let into the transformer. The oil impregnation of winding
insulation is also done under high vacuum conditions. The dryness of insulation
is measured in terms of insulation resistance.

ACCESSORIES:
Oil conservator:
All power transformers are invariably provided with an expansion vessel called
Conservator. This is to take care of the changes in oil volume due to change in
ambient temperature, or as a consequence of changes in load on the
transformer. The oil level conservator thus rises or falls, resulting in
phenomenon called ‘Breathing’.

The conservator is fitted with an oil preservation system called ‘Air cell’, which is
a bag made of nitrile rubber and it floats on the oil surface inside the
conservator. The air cell inflates or deflates as the oil level in the conservator
falls or rises.

The above system prevents direct contact of transformer oil with atmospheric
air and retards oxidation and sludging, thereby greatly reducing the oil
deterioration/maintenance problems at site. Maintenance of the system is also
negligible, since once in operation it generally needs no attention other than
routine visual inspection.
Oil level gauge:
A magnetic oil level is fitted to indicate oil level in the conservator, float of which
is always beneath the air cell. This gauge is also provided with a switch which
gives alarm when the oil level falls below the minimum oil level or when air cell
is damaged and sinks.

Breather:
A breather is connected to the air cell and is used to dry the air that enters in
the air cell when the transformer breathes. The breather contains an absorbent
material like silica gel for absorbing the moisture present in the atmospheric air.
Air entering the breather is first drawn through an oil seal at the bottom, and
passes upwards through the silica gel crystals to the connecting pipe at the top
of the air cell.

During the upwards passage of air, any moisture present is absorbed by the dry
silica gel. The oil seal at the bottom ensures that the gel absorbs moisture only
when the transformer is breathing in.

Silica Gel Breathers:

Moisture is an enemy of transformer insulation system.
Whenever oil contracts transformer breaths in through breathers.
With air contains lot of moisture which is present in the air also go inside.
The silica gel present in the breathers absorb moisture and only dry air goes
inside.
After a certain level of absorption the color of silica gel crystals change from
blue to pink when these particles should be recharged or replaced.

Temperature indicators:
Each transformer is provided with dial type thermometers for oil and winding
temperature indication. The bulb is placed in an oil filled pocket screwed into
the transformer tank cover. The pocket or the bellow for winding temperature
indicator has a heating coil around it, temperature indicator pocket/bellow which
is fed by a CT provided on one of the transformer line terminals. As such any
changes in the load reflect in the heating of the winding temperature indicator
picket/bellow.

The expansion of the liquid in the bulb is transmitted through a capillary tube to
an indicating instrument. The dial type thermometer is also provided with
mercury switches for alarm and trip circuit operations in the event of excessive
temperature rise and also for operation of cooling fans and oil pump motors at
certain preset temperatures. A potentiometer device can also be provided for
remote temperature indication.

Pressure relief valve:

This is a spring loaded safety valve mounted on the tank cover for protection of
transformers in case of sudden over pressure. Valve diaphragm is sealed
against gasket by springs. Valve operation is effected when pressure inside the
tank exceeds opening pressure established by springs. The transformer
pressure is then rapidly reduced to normal value and spring returns the
diaphragm to closed position.

Bushings:
Oil filled porcelain bushings are used for taking out the terminals for voltage up
to a level of 33 KV. The bushing consists of a conductor within a porcelain
jacket. For 52 KV and above, condenser type bushings are used. The active
part of these bushings consists of an Oil impregnated paper (OIP) condenser
core manufactured from superior grade craft paper wound on aluminium tube.
This bushing is voltage graded by suitably interposed aluminium foils forming
condenser layers. Thus the electrical stresses are controlled throughout the
thickness and along the surface avoiding highly stress concentrations.

The condenser core is assembled with a mounting flange and porcelain

insulators at both outdoor and oil immersed end. The wound core is vacuum
dried and impregnated with high grade degassed and dehydrated transformer
oil. A prismatic or magnetic oil level gauge is provided to indicate the level of oil
in the bushings.

A self earthed test tap arrangement is provided on the flange which is used for
measurement of tan delta and capacitance of the bushings. Creepage distance
suitable for polluted atmosphere is also provided.

BHEL range of in-house manufacture of manufacture of bushings covers the

complete requirement up to 400 KV class and caters to requirement of both in-
house manufactured transformers as well as for other transformer
manufactures.

Depending on specific requirement of customer, Oil filled/Air/Compound filled

cable boxes are also manufactured.
Types of overhead bushings:
High voltage, low voltage and in some cases third winding “tertiary” or
“stabilising” leads are brought out through bushings.they are called HV
bushing,LV bushing and tertiary bushing.

These bushings can be mounted on the tank cover(or topmost horizontal plane
in the tank) or in some cases some bushings are mounted on vertical end walls.
Tap changers:
OLTC: On Load Tap Changer

It’s purpose is t add or subract turns from the main coil.It is housed inside the
transformer tank(except ctr oltc).these are the standard products and based on
the variant in use their dimensions are known is advance

The Tap Changers are used to vary the ratio of oil-immersed transformers
under load.

The M-type tap changers comprise a diverter switch and a tap selector in a
single column design. The V-type tap changer works as a selector switch
combining the features of a diverter switch and a tap selector.

Few important features of M-type tap changer are:

• High speed transition resistor type diverter switch with arc extinction at
the first current zero.
• Three pole design for neutral application at 350A, 500A and 600A ratings
for three phase Y-connected windings.
• Three pole fully insulated design at 350A, 500A and 600A ratings for
three phase Delta or Auto connected windings.
• Single phase designs at 350A, 500A, 600A, 800A, 1200A, 1500A and
1800A ratings for Auto connected or single phase transformers.
• Available with ±9, ±11, ±13, ±15, ±17 steps.
• Rapid tap change operation, low thermal stresses on the transition
resistors.
• Tap selector gear with steady torque during the tap changer operation.
• Long contact life.
• Diverters switch contacts easy to replace.

Few important features of V-type tap changers are:

• High speed transition resistor type diverter switch with arc extinction at the
first current zero.
• Three pole design for neutral application at 200A, 350A and 500A ratings
for three phase Y-connected windings.
• Three pole fully insulated design at 200A, 350A and 500A ratings for three
phase Delta or Auto connected windings.
• Single pole designs at 200A, 350A and 700A ratings for single phase
transformers.
 • Available up to ±13 steps.
• The technical data of tap changer type M and V have been verified by type
tests according to IEC recommendations publ. 214 (1976).
• BHEL range of in-house manufacture of tap changer covers the complete
requirement up to 400 KV class transformers and caters to requirement of
both, in-house manufactured transformers as well as for other transformer
manufacturers.

Control equipment:
The tap changer can be provided with local electrical, remote electrical
independent and remote electrical non-automatic/ automatic parallel operation.
Outdoor weather- proof kiosk for mounting of local electrical control equipment
and indoor control cubicle for the mounting of the remote control equipment can
also be supplied.

TRANSFORMER FITTINGS:
• Cooling equipments
• Terminal arrangements
• Conservator
• O.L.T.C
• Instruments
• Breathers etc.

Radiators:
Radiators used in transformer cooling are of standard profileThey are normally
described in the following fashion:

For eg: 10-5or9-34-3000

10:no of radiators.

5 or 9: no of flutes in a radiator element.

32:no of elements in a radiator.

3000:distance between valve centers.

Fans:
Cooling fans are normally classified on the basis of their size like 15,18, 24 or
36 inches.

Pumps:
Pumps are normally inline type. Its purpose is to pump oil through the
transformer to create forced flow of oil.

Mountings of radiators:
Radiators can be directly mounted on the tank wall,if the no. of radiators is not
large. Radiators can be mounted in a bank formation i.e. groups of radiators are
mounted on headers and are placed separately from tank.

Header:
Headers are pipes of square cross section. There shall be one top header and
one bottom header for a group of radiators. The header and radiator assembly
is supported over “A” frames (named so because of resemblance with alphabet
“A”)

Header Pipe Work:

The headers are in turn joined with the tank where suitable valves for connecting
pipe work are provided. These pipes require pipe supports with suitable
foundation.

Conservator Pipe Work:

It can be divided into parts:

• main conservator pipe work.

• auxiliary or oltc conservator pipe work

A conservator is a cyclinderical vessel which provides space for expansion of

oil inside the transformer or supplies oil to the transformer when transformer
oil cools and contracts in volume.

A conservator is always placed above the transformer.

When the conservator is used for the main transformer it is called main
conservator and when it is used for the oltc it is called auxiliary or oltc
conservator.
Termination:
Transformers are connected in the system by any of the these methods as
demanded by customers

• Overhead bushings
• Cable boxes
• Bus duct
• A combination of above

Cable Boxes:
In sites where customers has laid cables instead of overhead conductors the
termination(connections) is through cable boxes Cable boxes are enclosed and
are attached externally to the transformer tanks. They can be on the LV walls,
HV walls or on both LV and HV walls. Similarly instead of walls they can be
attached on the cover also

Bus duct:
Generator transformer primary is connected to the generator through bus
ducts. For bus duct connections bushings are brought out through cover or
through independent/common turrets. These bushings are enclosed
circumferentially by hoods which turn receive the bus duct flange.

Combination of Termination Methods:

Termination of different windings can be through different combinations.

For example

• Hv bushing,lv cable box

• Hv bushing,lv bus duct.etc

M.O.G WITH LOLA:

It stands for magnetic oil gauge with low level alarm.

This is used with conservator.

Its purpose is to indicate the oil level in the conservator vessel and to give alarm
when the oil level falls below the threshold limit.
Oil Surge Relay:
This is similar to MOG but is used in on load tap changer oil compartment.

PRV:
Pressure relief wall.

When transformer experiences excessive pressure due to extreme heating on

account of faulty operation or conditions then this valve saves the transformer
by releasing the excessive pressure and simultaneously disconnecting the
transformer from the lines.

This equipment is of spring loaded type.

OTI:
Oil temperature indicator;This consists of a bulb dipped in a oil cup on the cover
of the transformer tank cover. This bulb is connected to the meter placed in the
marshalling box meant for housing the equipment electrical controls by means
of a capillary.This indicates the temperature of the top part of the transformer
oil which is the hottest part.

AIR CELL:
When transformer breathes in air oxygen also gets in touch with the oil.Oxygen
oxides the insulating oil and contaminate it in terms of the electrical properties.

• Air cell is rubber bag compatible with the transformer oil and is fitted
inside the transformer conservator.When oil in transformer contracts, it
sucks air into the this bag and when oil expands it expels air.Thus Air
cells prevents atmospheric oxygen to come in contact with the oil.
TRANSFORMER TESTING:
Types of testings:

a)Routine tests

b)Type tests

Routine tests are conducted on each and every transformer of the lot/order.

Type tests are conducted on one transformer of a particular design and on

successful passing of this test the design of the transformer is said to be
validated.

Routine Tests :
1) Ratio test

2) Vector group verification

3) Winding resistance

4) Core loss

5) Load loss

6) Impedance measurement

7) Separate source voltage withstand test

8) Induced over voltage withstand test.

Type Tests:
1) Temperature rise test

2) Lightening impulse test

3) Vacuum and pressure test

Test Requirements:
In order to ensure the suitability of transformer for various possible
transients/overvoltage of system ,various national standards like is 2026(part-iii)
and international standard like IEC 60076-3 define the test levels and test
method requirement for different tests.

The major dielectric tests applicable for EHV class transformers are:

1)Lighting impulse withstand

2)Switching impulse withstand

3)Induced overvoltage with or without PD measurement.

4)Separate source voltage withstand test

Recently,IEC 60076-3 been revised to incorporate more stringent testing

requirement .The major changes wrt earlier edition of 1980 are:

PARAMETER EARLIER AS PER IEC-60076-3

REQUIREMENT
ACLD NA SPECIAL TEST FOR Um-72.5-
170KV.ROUTINE TEST FOR
Um>170kV
LI ROUTINE FOR ROUTINE FOR Um>72.5KV
Um>300kV
ASCD WITHOUT PD NA ROUTINE FOR Um<72.5KV
SI ROUTINE FOR ROUTINE TEST FOR
Um>300KV Um>170kV
ASCD WITH PD NA ROUTINE TEST
FOR72.5<Um<170KV.SPECIAL
TEST FOR Um>170Kv

INDUCED WITHOUT PD FOR NA

OVERVOLTAGE TEST Um<300KV WITH PD FOR
Um>300kV
CHOPPED WAVE LI NOT SPECIFIED 10%HIGHER THAN FULL
WAVE LEVEL
REPEAT DIELECTRIC 75% OF ORGINAL 80% OF ORIGINAL
TESTS

Salient features:
In order to meet the country’s demand of testing facility at par with international
standards, we have established an Ultra High Voltage (UHV) laboratory, which is
having certificate of Accreditation as per ISO/IEC 17025/1999 standards from
National Accreditation Board for Testing and Calibration Laboratories (N.A.B.L.),
Department of Science and Technology, India. Testing of transformers of rating
315 MVA 3-phase; 200 MVA1-phase in 400 KV class, Shunt reactors of rating 80
MVAR 3-phase in 400 KV class, ±500 KV DC 1-phase Converter transformer,
800 KV Bushing and CVT have been satisfactorily established.
This UHV lab is having internal clear dimensions of 67 M (L) × 35 M (W) ×35 M
(H) and is one of the largest screened laboratories in the world, attached to a
transformer manufacturing plant.

The major test equipments / facilities in our UHV lab are:

• 4 Million-volt, 400 KW Impulse Generator.

• 500 Kilo-volt, 15 KW Impulse Generator.
• 3.6 Million-volt, 400 pF Impulse voltage divider.
• 3 Million-volt Multiple Chopping gap.
• 1500 KVA, 1500 KV Cascade Connected testing transformer.
• 160 MVA, 66/650 KV 3- phase testing transformer.
• 3× 13.33 MVA, 11/90 KV, 1-phase transformers.
• 3×3.33 KVAR, 11KV, 1-phase reactors.
• 100 MVAR, 13-156 KV 3- phase Capacitor bank.
• 1.2 Million-volt, 30 mA DC voltage generator.
• 40 MVA, 0-11KV, 50 Hz, 3-phase MG set.
• 9 MVA, 0-11 KV, 30-180 Hz, 3-phase MG set.
• 7 MVA, 0-11 KV, 50 Hz, 3-phase MG set.
• 2 MVA, 0-11 KV, 30-180 Hz, 3-phase MG set.
• Partial Discharge detector and RIV meter.
• 2.5 M (dia) × 3.6 M (high) oil tank for Dielectric and Thermal Stability tests
on Bushings.
• 800 KV, 71.5 pF SF6 filled standard capacitor.
• Frequency Response Analyzer equipment.

400 kV Bushing under test

MAJOR LANDMARKS / INHOUSE R&D PROJECTS:
• Complete range of products are type tested as per IS/IEC.
• 2 nos. 200 MVA, single phase, 400 KV Generator transformers tested for
short circuit at KEMA-Netherlands for M/s NTPC, India in 2002.
• 186.2 MVA, 3- phase, 220 KV Generator transformer s tested for short
circuit at KEMA-Netherlands for M/s NTPC, India in 2000.
• 167 MVA, 1-phase, 400 KV Auto transformers tested for short circuit at
KEMA-Netherlands for M/s NTPC, India in 2002.
• 102 MVA, 1-phase, 400 KV Generator transformers tested for short circuit
at KEMA-Netherlands for M/s NTPC, India in1999.
• 100 MVA, 3-phase, 400 KV Tie transformers tested for short circuit at
KEMA-Netherlands for M/s NTPC, India in 2003.
• 70 MVA, 1- phase, 400 KV Generator transformers tested for short circuit
at KEMA-Netherlands for M/s NTPC, Bhutan in 2003.
• 50 MVA, 3-phase, 400 KV Station transformer tested for short circuit at
KEMA-Netherlands for M/s NTPC, India in 2000.
• Other transformers of rating 80 MVA, 63 MVA, 45 MVA, 40 MVA, and 25
MVA tested for short circuit at CPRI-Bangalore & Bhopal for M/s NTPC,
MSEB.
• 50 MVAR, 3-phase, 400 KV Controlled shunt reactor developed in-house
and installed at 400 KV Itarsi s/stn of M/s PGCIL, India in 2001.
• 2 MVA, 3-phase, 33 KV phase shifting transformer developed in-house
and installed at BHEL R&D complex at Hyderabad, India in 2002.
• 160 MVA, 3-phase, 66/650 KV OFAF cooled testing transformer
developed in-house and installed in BHEL-Bhopal UHV lab since 1987.
• On-load tap changer type tested at CESI-Italy and KEMA-Netherlands.
• 800 KV, 1250 Ampere bushing and 800 KV, 3000 pF CVT developed and
tested in-house.
• Export to more than 20 countries including Europe and Middle East.
• In-house development of computer software to analyse behaviour of
transformer under short circuit conditions, distribution of voltage under
Lightening/Switching impulse conditions etc.

ERECTION AT SITE: INSPECTION

Make visual inspection for any transit damage .Check nitrogen pressure. Check
various accessories for any type of type of transit damage .Make internal
inspection of the transformer to the extent possible for any visible discrepancy.
OIL FILLING:
Before filling the oil into transformer check the oil carefully for

a)Break down voltage

b)Moisture content

c)Tan delta and capacitance

If the oil is not having the properties as recommended by the standards,it must
be filtered with filters withbuilt in heaters and vacuum pumps for improving the
quality of oil.

For transformers dispa tched gas filled ,oil filling must always be done under
vacuum.

Precautions during Oil Filling:

Keep the oil free from contamination. All equipments used for oil filling should
be cleaned and flushed with oil before filling. Flexible steel hose or good and
known quality rubber hose alone should be used. Transformer must be
disconnected from the electricity from level in the the tank is lowered. Oil must
not be emptied near naked lights as the vapour released is inflammable.
High Voltage AC Motors/Generators

PRODUCT RANGE

1) Sq. Cage Induction Motors (SCIM)

UP TO 21000 KW, 4P

LOW VOLTAGE, 3.3 KV – 11 KV

50 & 60 HZ

2 POLE TO 24 POLE

2POLE MOTORS UPTO 4500 KW

2) Slip Ring Induction Motors (SRIM)

UP TO 10000 KW, 4 POLE

LOW VOLTAGE, 3.3 – 11 KV

50 & 60 HZ

4 POLE TO 12 POLE

3) SYNCHRONOUS MOTORS

UP TO 17500 KW, 4 POLE, CYL. ROTOR

3.3 – 11 KV

4 POLE TO 10 POLE CYL. ROTOR

UPTO 4500 KW (>8 POLE) SALIENT POLE ROTOR

BRUSHLESS EXCITER

4) ALTERNATORS

UP TO 25000 KVA, 4 POLE, CYL. ROTOR

UP TO 20000 KVA, 12 POLE, SALIENT POLE ROTOR

3.3 – 11 KV

BRUSHLESS EXCITER

5) FLAME PROOF MOTORS

UP TO 1200 KW, 4 POLE, TETV

6) PRESSURIZED MOTORS

UPTO 4500 KW, 4 POLE VFD SYN. MOTORS

UPTO 7500 KW, 4 POLE INDUCTION MOTORS

UP TO 4500 KW, 18 POLE SALIENT POLE SYN. MOTOR

UPTO 13 MW, 4 POLE CYL. ROTOR SYN. MOTOR

7) VFD MOTORS

UPTO 21000 KW, 4 POLE, CAGE INDUCTION MOTORS

UPTO 15000 KW, 4 POLE SYN. MOTORS

8) INDUCTION GENERATORS

UPTO 750 KW, 10 POLE

TECHNICAL SPECIFICATION FOR INDUCTION M/C

1) MECHANICAL OUTPUT IN KW

2) FREQUENCY IN HZ AND VARIATION

3) RATED VOLATGE AND PERMITTED VARIATION

4) SPEED AND ITS VARIATION

5) CLASS OF INSULATION

6) SITE AND OPERATING CONDITIONS

7) TYPE OF DUTY

8) AMBIENT TEMP./ WATER TEMP.

9) HAZARDOUS AREA CLASSIFICATION

10) DIRECTION OF ROTATION

11) TYPE (SCIM/SRIM)

12) LOAD DEATAILS : LOAD GD2/WR2 VALUE AND T/S CURVE

13) TYPE OF COUPLING(RIGID/FLEXIBLE/PULLEY/FLUID)

14) METHOD OF COOLING

15) TYPE OF PROTECTION

16) DETAILS OF SHAFT EXTENSION

17) METHOD OF STARTING

18) FAULT CAPACITY AND DURATION OF FAULT

19) ANY SPECIFIC REQUIREMENT

DESIGN CONSIDERATIONS

• LOAD DETAILS

• VARIATION IN SUPPLY VOLTAGE

• LOCKED ROTOR WITHSTAND TIME

• THERMAL WITHSTAND CHARACTERISTICS

• FREQUENCY OF STARTING

• VOLTAGE DIP DURING STARTING

CONSTRUCTIONAL FEATURES OF INDUCTION MOTORS

1) METHOD OF COOLING / ENCLOSURE / VENTILATION

2) STATOR

3) ROTOR

4) ENDSHIELD

5) BEARINGS

6) SLIPRING AND BRUSHES

7) TERMINAL BOXES

8) ACCESSORIES

CONSTRUCTIONAL FEATURES OF INDUCTION MOTORS

 Sample: Exploded view of stator components

Sample: Exploded view of rotor components

CONSTRUCTIONAL FEATURES OF INDUCTION MOTORS

Sample: Exploded view of different type of motor

Sample: Exploded view of different type of motor

Switchgear and Control Gears
Circuit Breaker

A circuit breaker is an automatically operated electrical switch designed to protect

an electrical circuit from damage caused by an overloaded or short circuit.gh
voltage circuit.

Circuit breakers are made in varying sizes, from small devices that protect an
individual household appliance up to large switchgear designed to protect high
voltage circuits feeding an entire city.

Difference between a switch and circuit breaker

Circuit Breaker: - A circuit breaker is an automatically-operated electrical switch

designed to protect an electrical circuit from damage caused by overload or short
circuit.

Air Blast circuit breaker

These types of breaker employ ‘air blast’ as the quenching medium. This rapidly
increases the dielectric strength of the medium between contacts and prevents
from reestablishing the arc.

Vacuum Circuit Breaker (VCB)

In This breaker, vacuum is being used as the arc quenching medium .Vacuum
offers highest insulating strength , it has far superior arc quenching properties
than any other medium.

when the contacts of the breaker are opened in vacuum, the interruption occurs
at first current zero with dielectric strength between the contacts building up at a
rate thousands of times that obtained with other circuit breakers.

Principle: When the contacts of the breaker are opened in vacuum (10-7 to 10-
5 torr), an arc is produced between the contacts by the ionization of metal vapors
of contacts. The arc is quickly extinguished because the metallic vapors,
electrons, and ions produced during arc condense quickly on the surface of the
circuit breaker contacts, resulting in quick recovery of dielectric strength. As soon
as the arc is produced in vacuum, it is quickly extinguished due to the fast rate of
recovery of dielectric strength in vacuum.
SF6 Circuit breaker

• Sulphur hexafluoride (sf6) gas is used as an arc quenching medium.

• SF6 is an electro-negative gas.
• It has strong tendency to absorb electrons.
• Free electrons in the arc are captured by the gas.
• Which build up enough insulation for high power and high voltage services.

ON LOAD TAP CHANGER (OLTC)

• ON LOAD TAP CHANGER (OLTC)

The type M on-load tap changers are used to vary the ratio of oil-immersed
transformers under load. In general, they are designed for network
transformers as well as industrial transformers application. The tap
changers comprise a diverter switch and a tap selector in a single column
design and represent the most resent state of technology. The tap
changers offer both transformer manufacture and user a great number of
essential advantages.

• ADVANTAGES
Versatile
Compact
Robustness-long life
Easy to install-cost saving
Reduced maintains
Traction Machines

BHEL’s capability and experience in the transportation field is very wide and
electrics are designed and manufactured for following applications:

• Diesel Electric Freight, passenger and shunting locos with DC & AC drive.
• 25KV AC and 1500 V DC freight and passenger electric locos.
• 25KV AC and 1500 V DC Electrical Multiple Units (EMU).
• Diesel Electrical Multiple Units (DEMU).
• Metro systems.
• Tram Cars
• Battery Powered Road Vehicles (BPRV)
• Electric Trolley Bus (ETB).
Railways Application:

• DIESEL ELECTRIC LOCOS

• ELECTRIC LOCOS
• DMEU/EMUS

Urban Transportation:

• ETB
• TRAMS
• MOTORS
• MONO RAILS
• SKY BUS

BHEL’s product range consists of large variety of Traction Machines:

• DC traction motors up to 750 kW.

• 3-Phase AC traction motors up to 1150 kW.
• AC traction alternators up to 3000 kW.
• DC traction generators up to 2000 kW.
• DC auxiliary machines up to 50 kW.
• DC blower motors up to 50 kW.
• DC and AC motor generators sets up to 25 kW.
• Motor Generator Sets up to 12 KW/ Motor Alternator Sets up to 20 KVA
RAILWAYS TRACTION

classification of
train

power application

diesel multiple unit locomotive

electric EMU electric

DEMU diesel

LOCOMOTIVES
Diesel locomotives:

Diesel-electric locomotives were introduced in the United States in 1924, and

have become the most widely used type of locomotive. The modern diesel-
electric locomotive is a self-contained, electrically propelled unit. Like the electric
locomotive, it has electric drive, in the form of traction motors driving the axles
and controlled with electronic controls. It also has many of the same auxiliary
systems for cooling, lighting, heating, and braking. It differs principally in that it
has its own generating station instead of being connected to a remote generating
station through overhead wires or a third rail. The generating station consists of
a large diesel engine coupled to an alternator or generator that provides the
power for the traction motors.

These motors drive the driving wheels by means of spur gears. The ratio of the
gearing regulates the hauling power and maximum speed of the locomotive. A
modern diesel-electric locomotive produces about 35% of the power of an electric
locomotive of similar weight. Diesel-mechanical locomotives have a direct
mechanical link consisting of a clutch and a series of gears and shafts between
the engine and the wheels, similar to the transmission in an automobile. Because
mechanical drives deliver less power to the wheels than electric and diesel-
electric systems, they are only used with the smallest locomotives. In diesel-
hydraulic locomotives the engine drives a torque converter, which uses fluids
under pressure to transmit and regulate power to the wheels. Hydraulic drives
are little used in the United States but are widely used in some countries, such
as Germany.

Electric locomotive:

An electric locomotive is a locomotive powered by electricity from an external

source. Sources include overhead lines, third rail, or an on-board electricity
storage device such as a battery, flywheel system, or fuel cell.

Electric locomotive receives current from overhead line through pentograph. This
high voltage is step down in case of single phase 25 KV supply and then fed
through control and stabilizing circuit to the motors. In case dc supply it is fed to
motor through control equipment.

Fundamentals of traction

Definition

Traction is defined as:

A physical process in which a tangential force is transmitted across an interface

between two bodies through dry friction or an intervening fluid film resulting in
motion, stoppage or the transmission of power.

The units of traction are those of force, or if expressed as a coefficient of traction

(as with coefficient of friction) a ratio.

Specifically, traction refers to the maximum frictional force that can be produced
between surfaces without slipping.

The traction produced by a vehicle if expressed as a force is synonymous with

tractive effort, or tractive force, and closely related to the term drawbar pull.
Types of Traction Systems:

1. Steam Locomotives
2. Internal Combustion Engines
3. Diesel Locomotives
4. Diesel Electric Locomotives
5. Battery operated Locomotives
6. Electric Traction Systems
Typical manufacturing operation sequence:
REFERENCES:

• Electrical Machinery by P.S. Bhimbra.

• BHEL Website – www.bhel.com .

• BHEL, Bhopal Website – www.bhelbhopal.com .

• Website – www.wikipedia.org .