BHARAT HEAVY ELECTRICALS LIMITED JHANSI

ROTATION REPORT AND PROJECT ON POWER TRANSFORMER

PROJECT MANAGER- MR. KRISHAN KUMAR (Sr.Design Engineer)

(TRE)

SUBMITTED TO- Dr. DHRUV BHARAGAV

D.G.M(H.R.D)

BHEL, JHANSI

2015

SUBMITTED BY-

SHIVAM DWIVEDI B.Tech ( EE) NIT AGARTALA

2015

BHARAT HEAVY ELECTRICALS LIMITED JHANSI

ROTATION REPORT

AND

PROJECT ON POWER TRANSFORMER

PROJECT MANAGER- MR. KRISHAN KUMAR (Sr.Engineer)

(TRE)

SUBMITTED TO- SUBMITTED BY- Dr. DHRUV BHARAGAV SHIVAM DWIVEDI

D.G.M(H.R.D) B.Tech ( EE )

BHEL, JHANSI NIT AGARTALA

Acknowledgement

I am extremely thankful & indebted to the numerous BHEL engineers,

who imparted me vital information about the functioning of their respective departments, thus helping me to attain an overall consideration about

the functioning of the organization. I am highly thankful to them for their support , guidance and amicable behavior.

I am highly indebted to my project guide Mr. KRISHAN KUMAR (Sr.Design Engineer) for finding some hours to guide me, from his busy schedule and helping me to grasp various concepts of power transformer . I also

convey my special thanks to all senior executives and members of BHEL, Jhansi.

Last but not the least, I would like to thank my parents & all my fellow

Trainees who have been a constant source of encouragement & inspiration during my training here. And a special thank to the H.O.D of my college he

helped me so much giving leave from my session so that I can concentrate on this project.

SHIVAM DWIVEDI

(13UEE063)

INTRODUCTION OF B.H.E.L

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

energy/infrastructure sector today. BHEL was established more than 40 years

ago when its first plant was set up in Bhopal 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 caters to core sectors of the Indian Economy viz., Power Generation &

transmission, Industry, Transportation, Telecommunication, Renewable Energy,

Defense, etc. The wide network of BHEL’s 17 manufacturing divisions, four

Power Sector regional centers, over 100 project sites, eight service centers and

18 regional offices, enables the company to promptly serve its customers and

provide them with suitable products, systems and services-efficiently and at

competitive prices. BHEL has already attained ISO 9000 certification for

quality management, ISO 27000 for Information Technology and ISO 14001

certification for environment management.

(3) VARIOUS BHEL UNITS

FIRST GENERATION UNITS

Bhopal : Heavy Electrical Plant.

Haridwar : Heavy Electrical Equipment Plant.

Hyderabad: Heavy Electrical Power Equipment Plant.

SECOND GENERATION UNITS

Tiruchy : High Pressure Boiler Plant.

Jhansi : Transformer and Locomotive Plant.

Haridwar : Central Foundry and Forge Plant.

Tiruchy : Seamless Steel Tube Plant.

UNITS THROUGH ACQUISTION & MERGER

Bangalore : Electronics Division

Electro Porcelain Division.

NEW MANUFACTURING UNITS

Ranipet : Boiler Auxiliaries Plant.

Jagdishpur: Insulator Plant.

Govindwal : Industrial Valve Plant.

Rudrapur : Component and Fabrication Plant.

Bangalore : Energy Systems Division

BHARAT HEAVY ELECTRICALS LIMITED JHANSI (UNIT)

A BRIEF INTRODUCTION

By the end of 5th five-year plan, it was envisaged by the planning commission

that the demand for power transformer would rise in the coming years.

Anticipating the country’s requirement BHEL decided to set up a new plant,

which would manufacture power and other types of transformers in addition to

the capacity available in BHEL Bhopal. The Bhopal plant was engaged in

manufacturing transformers of large ratings and Jhansi unit would concentrate

on power transformer upto 50 MVA, 132 KV class and other transformers like

Instrument Transformer s, Traction transformers for railway etc.

This unit of Jhansi was established around 14 km from the city on the N.H. No

26 on Jhansi Lalitpur road. It is called second-generation plant of BHEL set up

in 1974 at an estimated cost of Rs 16.22 crores inclusive of Rs 2.1 crores for

township. Its foundation was laid by late Mrs. Indira Gandhi the prime minister

on 9th Jan. 1974. The commercial production of the unit began in 1976-77 with

an output of Rs 53 lacs since then there has been no looking back for BHEL

Jhansi.

The plant of BHEL is equipped with most modern manufacturing processing

and testing facilities for the manufacture of power, special transformer and

instrument transformer, Diesel shunting locomotives and AC/DC locomotives.

The layout of the plant is well streamlined to enable smooth material flow from

the raw material stages to the finished goods. All the feeder bays have been laid

perpendicular to the main assembly bay and in each feeder bay raw material

smoothly gets converted to sub assemblies, which after inspection are sent to

main assembly bay.

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. This unit of BHEL is basically engaged in the production and

manufacturing of various types of transformers and capacities with the growing

competition in the transformer section, in 1985-86 it under took the re-powering

of DESL, but it took the complete year for the manufacturing to begin. In 1987-

88, BHEL has progressed a step further in under taking the production of AC

locomotives, and subsequently it manufacturing AC/DC locomotives also.

PRODUCT PROFILE OF BHEL JHANSI UNIT

1. Power transformer up to 400 KV class 250

MVA.

2. Special transformer up to 180 KV.

3. ESP transformer 95 KVp, 1400 mA.

4. Freight Loco transformer 3900 to 5400 KVA &

7475 . KVA for 3 phase.

5. ACEMU transformer up to 1000 KVA (1-

phase).

1385 KVA (3 phase).

.

6. Dry type transformer up to 6300 KVA 33 KV

class

7. Instrument transformer VT & CT up to 220 KV

class.

8. Diesel electric locomotives up to 2600 HP.

9. AC/DC locomotives 5000 HP.

10. Over Head Equipment cum Test Car

11. Well wagon 200 tone.

12.Rail cum road vehicle

13. Dynamic track stabilizer

PLANT LAYOUT

It has two product categories:-

(1) Transformer shop:-

There are ten bays in this shop i.e. from bay 0 to 9. Its comprises of

fabrication of transformer, winding section, core and punch section,

winding work for power transformers, manufacturing of dry –type

transformer and assembly of transformers

(2) Locomotive shop:-

This shop contain LOCO and LOCO production shop. LOCO

assembly is mainly done here. further there is LOCO test section in

this unit.

VARIOUS DEPARTMENTS/FUNCTIONS AT BHEL JHANSI

TRANSFORMER COMMERCIAL (TRC)

The objective of the department is interaction with the customers. It brings out

tenders and notices and also responds to them. It is this department that bags

contracts of building transformers. After delivery regarding faults, this

department does failures and maintenance. All such snags are reported to them

and they forward the information to the concerning department.

One of the major tasks of this department is to earn decent profits over all

negotiations. Transformer industry has become very competitive. The company

offering the lowest price gets the contract but this process may continue does

the work on very low profits. To avoid such a situation, a body by the name of

India Electrical and Electronics Manufactures Association (IEEMA) was set up.

This association helps to maintain a healthy competitive atmosphere in the

manufacturing of electrical appliances.

TRANSFORMER ENGINEERING (TRE)

The transformer manufactured in BHEL Jhansi range from 10 MVA to 250

MVA and up to 400 KV. The various transformers manufactured in this unit

are:-

POWER TRANSFORMER

a) Generator transformer

b) System transformer.

c) Auto transformer.

SPECIAL TRANSFORMER

a) Freight loco transformer.

b) ESP transformer.

c) Instrument transformer.

d) Dry type transformer.

.

FABRICATION

Fabrication is nothing but production. It comprises of three bays i.e. Bay 0,Bay1,

Bay2.

BAY-00 & 0:

It is a sub part of Fabrication. It is the preparation shop while the other two

bays form the assembly shop. This section has the following machines:

Planner machine – To reduce thickness

Shearing machine

CNC / ANC Flame Cutting machine – To cut Complicated shaft items

using Oxy-Acetylene flame

Bending machine

Rolling machine

Flattening machine

Drilling machine

Nibbling machine

Pantograph flame cutting machine

BAY-1

It is also a sub part of Fabrication. It is an assembly shop where different parts

of tank come from bay 0.Here welding processes are used for assembly, after

which a rough surface is obtained Grinder operating at 1200 rpm is used to

eliminate the roughness.

BAY-2

It is also a sub part of Fabrication It is an assembly shop dealing with making

different objects mentioned below.

1-Tank assembly 5-cross feed assembly

2-Tank cover assembly 6-core clamp assembly

3-End Frame assembly 7-pin and pad assembly

4-foot assembly

Before assembly, short blasting (firing of small materials i.e., acid pickling) is

done on different parts of jobs to clean the surface before painting.

NON DESTRUCTIVE TEST

1 Ultrasonic test to detect the welding fault on the CRO at the fault place

high amplitude waves are obtained.

2. Die Penetration test Red solution is put at the welding and then cleaned.

After some time white solution is mixed. Appearance of a red spot indicates a

fault at the welding.

3. Magnetic crack detection Magnetic field is created and then iron

powder is put at the welding. Sticking of the iron powder in the welding

indicated a fault.

4. X-Ray Test: It is same as human testing and the fault is seen in X-ray

film.

BAY-3

Here are basically three sections in the bay:

Machine section

Copper section

Tooling section

BAY 4

It is the winding section.

There are four types of coil fixed in a transformer, they are :

1. Low voltage coil (LV)

2. High voltage coil (HV)

3. Tertiary coil

4. Tap coil

The type of winding depends upon job requirement. Also, the width and

thickness of the conductors are designed particulars and are decided by design

department. Conductors used for winding is in the form of very long strips

wound on a spool, the conductor is covered by cellulose paper for insulation.

For winding first the mould of diameter equal to inner dia meter of required

coil is made .The specification of coil are given in drawing. The diameter of

mould is adjustable as its body is made up of wooden sections that interlock

with each other. This interlocking can be increased or decreased to adjust the

inner diameter of coil.

The moulds are of following types

1. Belly types

2. Link types

3. Cone type

BAY-5

It is core and punch section. The lamination used in power, dry, ESP

transformer etc for making core is cut in this section.

CRGO (cold rolled grain oriented) silicon steel is used for lamination, which

is imported in India from Japan, U.K. Germany. It is available in 0.27 and

0.28 mm thick sheets, 1mt wide and measured in Kg.The sheet s are coated

with very thin layer of insulating material called “carlites”.

For the purpose of cutting and punching the core three machines are installed

in shop

BAY-6

Single-phase traction transformer for AC locomotives is assembled in this

section. This Freight locomotive transformers are used where there is frequent

change in speed. In this bay core winding and all the assembly and testing of

traction transformer is done.

Three-phase transformers for ACEMU are also manufactured in this section.

The supply lines for this transformer are of 25 KV and power of the

transformer is 6500 KVA. The tap changer of rectifier transformer is also

assembled in this bay. Rectified transformer is used in big furnace like the

thermal power stations / plants (TPP).

BAY-7

1. This is the insulation shop. Various types of insulations are

2. AWWW - All Wood Water Washed press paper.

3. The paper is 0.2-0.5mm thick cellulose paper and is wound on the

conductors for insulation.

4. PRE COMPRESSED BOARD: This is widely used for general

insulation & separation of conductors in the forms of blocks.

5. PRESS BOARD: This is used for separation of coils e.g. L.V. from

H.V. It is up to 38 mm thick.

6. UDEL(Un Demnified Electrical Laminated) wood or Permawood

7. This is special type of plywood made for insulation purposes.

8. FIBRE GLASS: This is a resin material and is used in fire pron areas.

9. BAKELLITE

10. GASKET- It is used for protection against leakage.

11. SILICON RUBBER SHEET- It is used for dry type transformer.

BAY 8

It is the instrument transformer and ESP transformer manufacturing section.

INSTRUMENT TRANSFORMER

These are used for measurement. Actual measurement is done by measuring

instruments but these transformers serve the purpose of stepping down the

voltage to protect the measuring instrument. They are used in AC system for

measurement of current voltage and energy and can also be used for

measuring power factor, frequency and for indication of synchronism. They

find application in protection of power system and for the operation of over

voltage, over current, earth fault and various other types of relays.

ESP TRANSFORMER

The Electrostatic Precipitator transformer is used for environmental application.

It is used to filter in a suspended charge particle in the waste gases of an

industry. They are of particular use in thermal power stations and cement

industry.

The ESP is a single-phase transformer. It has a primary and secondary. The core

is laminated and is made up of CRGOS. It is a step up transformer. An AC

reactor is connected in series with primary coil. The output of the transformer

must be DC the is obtained by rectifying AC using a bridge rectifier (bridge

rectifier is a combination of several hundred diodes). A radio frequency choke

(RF choke) is connected in series with the DC output for the protection of the

secondary circuit and filter circuit. The output is chosen negative because the

particles are positively charged. The DC output from the secondary is given to a

set of plates arrange one after the others. Impurity particles being positively

charged stick to these plates, which can be jerked off. For this a network of

plates has to be setup all across the plant. This is very costly process in

comparison with the transformer cost. A relive vent is also provided to prevent

the transformer from bursting it higher pressure develops, inside it. It is the

weakest point in the transformer body. An oil temperature indicator and the

secondary supply spark detector are also provided.

One side of the transformer output is taken and other side has an ‘marshalling

box’ which is the control box of the transformer.

BAY-9

In this bay power transformer are assembled. After taking different input from

different bays 0-9 assembly is done Power transformer is used to step and step

down voltages at generating and sub-stations. There are various ratings –11KV,

22KV, manufactured, they are

1. Generator transformer.

2. System

3. Autotransformer.

A transformer in a process of assemblage is called a job. The design of the

transformer is done by the design deptt. & is unique of each job; depends on the

requirement of customer. The design department provides drawing to the

assembly shop, which assembles it accordingly.

The stepS involved in assembly are:

1. Core building

2. Core Lifting.

3. Unlacing.

4. Delacing and end-frame mounting.

5. High voltage terminal gear and low volt terminal gear mounting

6. Vapour phasing and oil soaking

7. Final servicing and tanking.

8. Case fitting.

STORE

There are three sections in store:

1. Control Receiving Section

2. Custody Section

3. Scrap Disposal Section

LOCOMOTIVE PRODUCTION (LMP)

There are following products are manufactured at Loco shops

Alternating Current Locomotive (ac Loco)

WAG-5H

AC./D.C. Loco

WCAM-2P

WCAM-3

W-broad gauge A-running in AC mode

C-running in DC mode G-hauling goods train

P-hauling passenger train M-hauling passenger

& goods train

Diesel Electric Locomotive Shunting (DESL)

350 HP

700 HP

Single Power Pack (SPP): One 700 HP m/c

is made as a single

Unit. It is a meter gauge locomotive

Twin Power Pack (TPP): 2 350HP m/cs are combined in 1 engine

& can be operated individually or in combination depending on

the load.

450 HP

1400 HP

1150 HP

1350 HP

2600 HP

1150 HP and 1350 HP DESL s are non-standard locomotives and are

modified versions of 1400 HP DESL based on requirement of customer.

Under mention are the new non-conventional products designed and

developed for Indian Railways based on their requirement.

OHE (Overhead electric) recording and testing cars

UTV(Utility vehicle )

RRV(Rail cum road vehicle)

DETV( Diesel electric tower car)

BPRV(Battery power road vehicle)

BCM(Blast cleaning machine)

200 T Well wagon for BHEL Haridwar

Metro Rake-Kolkata Metro Railways

LOCOMOTIVE MANUFACTURING (LMM)

This section deals with manufacturing of locomotives. The main parts of the

locomotive are

Under frame: The frame on which a locomotive is built

Super structure: The body of locomotive is called superstructure

or Shell and is made of sheet of Mild steel

DC motor

Alternator

Compressor

Flower

Static Rectifier-MSR

Static Converter-SC

Exchanger

Bogie-The wheel arrangement of a loco is called a bogie. A bogie

essentially contains

1-wheel axle arrangement

2-Suspension

3-Brake rigging

Traction transformer: It is fixed on under frame and gets supply from

an overhead line by equipment called pantograph. The type of

pantograph depends on supply. This transformer steps down voltage and

is fitted with a tap changer. Different taps are taken from it for operating

different equipment. One tap is taken and is rectified into DC using

MSR and is fed to the DC motor.

Railways has two types of power supplies – 25 KV , 1 Phase ,50hz AC

-1500 V DC

An AC/DC loco is able to work on both of these supplies. For e.g.

WCAM-3.

POWER

TRANSFORMER

INTRODUCTION

A transformer is a static electrical device that transfers energy by inductive

coupling between its winding circuits. A varying current in the primary

winding creates a varying magnetic flux in the transformer's core and thus a

varying magnetic flux through the secondary winding. This varying magnetic

flux induces a varying electromotive force (emf) or voltage in the secondary

winding.

Transformers range in size from thumbnail-sized used in microphones to units

weighing hundreds of tons interconnecting the power grid. A wide range of

transformer designs are used in electronic and electric power applications.

Transformers are essential for the transmission, distribution, and utilization of

electrical energy.

DESIGN OF POWER TRANSFORMER

1. CORES

Laminated steel core

Transformers for use at power or audio frequencies typically have cores made

of high permeability silicon steel. The steel has a permeability many times that of free space and the core thus serves to greatly reduce the magnetizing current

and confine the flux to a path which closely couples the windings. Early transformer developers soon realized that cores constructed from solid iron

resulted in prohibitive eddy current losses, and their designs mitigated this effect with cores consisting of bundles of insulated iron wires. Later designs

constructed the core by stacking layers of thin steel laminations, a principle that has remained in use. Each lamination is insulated from its neighbors by a thin

non-conducting layer of insulation.The universal transformer equation indicates a minimum cross-sectional area for the core to avoid saturation.

The effect of laminations is to confine eddy currents to highly elliptical paths that enclose little flux, and so reduce their magnitude. Thinner laminations reduce losses,but are more laborious and expensive to construct. Thin

laminations are generally used on high-frequency transformers, with some of very thin steel laminations able to operate up to 10 kHz.

Laminating the core greatly reduces eddy-current losses

One common design of laminated core is made from interleaved stacks of E-

shaped steel sheets capped with I-shaped pieces, leading to its name of 'E-I

transformer. Such a design tends to exhibit more losses, but is very economical to manufacture. The cut-core or C-core type is made by winding a steel strip around a rectangular form and then bonding the layers together. It is then cut in

two, forming two C shapes, and the core assembled by binding the two C halves together with a steel strap They have the advantage that the flux is always

oriented parallel to the metal grains, reducing reluctance.

A steel core's remanence means that it retains a static magnetic field when

power is removed. When power is then reapplied, the residual field will cause a high inrush current until the effect of the remaining magnetism is reduced,

usually after a few cycles of the applied AC waveform. Overcurrent protection

devices such as fuses must be selected to allow this harmless inrush to pass. On transformers connected to long, overhead power transmission lines, induced

currents due to geomagnetic disturbances during solar storms can cause saturation of the core and operation of transformer protection devices. [48]

Distribution transformers can achieve low no-load losses by using cores made with low-loss high-permeability silicon steel or amorphous (non-crystalline)

metal alloy. The higher initial cost of the core material is offset over the life of the transformer by its lower losses at light load.

Solid cores

Powdered iron cores are used in circuits such as switch-mode power supplies that operate above mains frequencies and up to a few tens of kilohertz. These materials combine high magnetic permeability with high bulk

electrical resistivity. For frequencies extending beyond the VHF band, cores made from non-conductive magnetic ceramic materials called ferrites are common.[46] Some radio-frequency transformers also have movable cores

(sometimes called 'slugs') which allow adjustment of the coupling coefficient (and bandwidth) of tuned radio-frequency circuits.

Toroidal cores

Toroidal transformers are built around a ring-shaped core, which, depending on

operating frequency, is made from a long strip of silicon steel orpermalloy wound into a coil, powdered iron, or ferrite. A strip

construction ensures that the grain boundaries are optimally aligned, improving the transformer's efficiency by reducing the core's reluctance. The closed ring

shape eliminates air gaps inherent in the construction of an E-I core. The cross-section of the ring is usually square or rectangular, but more expensive cores

with circular cross-sections are also available. The primary and secondary coils are often wound concentrically to cover the entire surface of the core. This

minimizes the length of wire needed, and also provides screening to minimize the core's magnetic field from generating electromagnetic interference.

Toroidal transformers are more efficient than the cheaper laminated E-I types for a similar power level. Other advantages compared to E-I types, include

smaller size (about half), lower weight (about half), less mechanical hum (making them superior in audio amplifiers), lower exterior magnetic field (about

one tenth), low off-load losses (making them more efficient in standby circuits), single-bolt mounting, and greater choice of shapes. The main disadvantages are

higher cost and limited power capacity (see Classification parameters below). Because of the lack of a residual gap in the magnetic path, toroidal transformers

also tend to exhibit higher inrush current, compared to laminated E-I types.

Ferrite toroidal cores are used at higher frequencies, typically between a few

tens of kilohertz to hundreds of megahertz, to reduce losses, physical size, and weight of inductive components. A drawback of toroidal transformer

construction is the higher labor cost of winding. This is because it is necessary to pass the entire length of a coil winding through the core aperture each time a single turn is added to the coil. As a consequence, toroidal transformers rated

more than a few kVA are uncommon. Small distribution transformers may achieve some of the benefits of a toroidal core by splitting it and forcing it open,

then inserting a bobbin containing primary and secondary windings.

Air core

A physical core is not an absolute requisite and a functioning transformer can be

produced simply by placing the windings near each other, an arrangement termed an 'air-core' transformer. The air which comprises the magnetic circuit is

essentially lossless, and so an air-core transformer eliminates loss due to hysteresis in the core material. The leakage inductance is inevitably high,

resulting in very poor regulation, and so such designs are unsuitable for use in power distribution. They have however very high bandwidth, and are frequently

employed in radio-frequency applications, for which a satisfactory coupling coefficient is maintained by carefully overlapping the primary and secondary

windings. They're also used for resonant transformers such as Tesla coils where they can achieve reasonably low loss in spite of the high leakage inductance.

Windings

Windings are usually arranged concentrically to minimize f lux leakage.

conducting material used for the windings depends upon the application, but in all cases the individual turns must be electrically insulated from each other to

ensure that the current travels throughout every turn. For small power and signal transformers, in which currents are low and the potential difference between

adjacent turns is small, the coils are often wound from enamelled magnet wire, such as Formvar wire. Larger power transformers operating at high voltages may be wound with copper rectangular strip conductors insulated by oil-

impregnated paper and blocks ofpressboard.

High-frequency transformers operating in the tens to hundreds of kilohertz often have windings made of braided Litz wire to minimize the skin-effect and

proximity effect losses. Large power transformers use multiple-stranded conductors as well, since even at low power frequencies non-uniform

distribution of current would otherwise exist in high-current windings. Each strand is individually insulated, and the strands are arranged so that at certain

points in the winding, or throughout the whole winding, each portion occupies different relative positions in the complete conductor. The transposition

equalizes the current flowing in each strand of the conductor, and reduces eddy current losses in the winding itself. The stranded conductor is also more flexible than a solid conductor of similar size, aiding manufacture.

The windings of signal transformers minimize leakage inductance and stray

capacitance to improve high-frequency response. Coils are split into sections, and those sections interleaved between the sections of the other winding.

Power-frequency transformers may have taps at intermediate points on the winding, usually on the higher voltage winding side, for voltage adjustment.

Taps may be manually reconnected, or a manual or automatic switch may be provided for changing taps. Automatic on-load tap changers are used in electric

power transmission or distribution, on equipment such as arc furnace transformers, or for automatic voltage regulators for sensitive loads.

Audio-frequency transformers, used for the distribution of audio to public address loudspeakers, have taps to allow adjustment of impedance to each

speaker. A center-tapped transformer is often used in the output stage of an audio power amplifier in a push-pull circuit. Modulation transformers in AM transmitters are very similar.

Dry-type transformer winding insulation systems can be either of standard open-wound 'dip-and-bake' construction or of higher quality designs that

include vacuum pressure impregnation (VPI), vacuum pressure encapsulation (VPE), and cast coil encapsulation processes. In the VPI process,

a combination of heat, vacuum and pressure is used to thoroughly seal, bind, and eliminate entrained air voids in the winding polyester resin insulation coat

layer, thus increasing resistance to corona. VPE windings are similar to VPI windings but provide more protection against environmental effects, such as

from water, dirt or corrosive ambients, by multiple dips including typically in terms of final epoxy coat.

COOLING-

To place the cooling problem in perspective, the accepted rule of thumb is that the life expectancy of insulation in all electric machines including all transformers is halved for about every 7°C to 10°C increase in operating

temperature, this life expectancy halving rule holding more narrowly when the increase is between about 7°C to 8°C in the case of transformer winding

cellulose insulation.

Small dry-type and liquid-immersed transformers are often self-cooled by

natural convection and radiation heat dissipation. As power ratings increase, transformers are often cooled by forced-air cooling, forced-oil cooling, water-

cooling, or combinations of these. Large transformers are filled with transformer oil that both cools and insulates the windings. Transformer oil

is a highly refined mineral oil that cools the windings and insulation by circulating within the transformer tank. The mineral oil and paper insulation

system has been extensively studied and used for more than 100 years. It is estimated that 50% of power transformers will survive 50 years of use, that the

average age of failure of power transformers is about 10 to 15 years, and that about 30% of power transformer failures are due to insulation and overloading failures. Prolonged operation at elevated temperature degrades insulating

properties of winding insulation and dielectric coolant, which not only shortens transformer life but can ultimately lead to catastrophic transformer failure. With

a great body of empirical study as a guide, transformer oil testing including dissolved gas analysis provides valuable maintenance

information. This can translate in a need to monitor, model, forecast and manage oil and winding conductor insulation temperature conditions under

varying, possibly difficult, power loading conditions.

Building regulations in many jurisdictions require indoor liquid-filled

transformers to either use dielectric fluids that are less flammable than oil, or be installed in fire-resistant rooms. Air-cooled dry transformers can be more

economical where they eliminate the cost of a fire-resistant transformer room.

The tank of liquid filled transformers often has radiators through which the

liquid coolant circulates by natural convection or fins. Some large transformers employ electric fans for forced-air cooling, pumps for forced-liquid cooling, or

have heat exchangers for water-cooling. An oil-immersed transformer may be equipped with a Buchholz relay, which, depending on severity of gas

accumulation due to internal arcing, is used to either alarm or de-energize the transformer. Oil-immersed transformer installations usually include fire

protection measures such as walls, oil containment, and fire-suppression sprinkler systems.

Polychlorinated biphenyls have properties that once favored their use as

a dielectric coolant, though concerns over their environmental persistence led to a widespread ban on their use. Today, non-toxic, stable silicone-based oils,

or fluorinated hydrocarbons may be used where the expense of a fire-resistant liquid offsets additional building cost for a transformer vault. PCBs for new

equipment was banned in 1981 and in 2000 for use in existing equipment in United Kingdom Legislation enacted in Canada between 1977 and 1985

essentially bans PCB use in transformers manufactured in or imported into the country after 1980, the maximum allowable level of PCB contamination in

existing mineral oil transformers being 50 ppm.

Some transformers, instead of being liquid-filled, have their windings enclosed

in sealed, pressurized tanks and cooled by nitrogen or sulfur hexafluoride gas.

Experimental power transformers in the 500-to-1,000 kVA range have been built with liquid nitrogen or helium cooled superconducting windings, which,

compared to usual transformer losses, eliminates winding losses without affecting core losses.

Insulation drying

Construction of oil-filled transformers requires that the insulation covering the windings be thoroughly dried of residual moisture before the oil is introduced.

Drying is carried out at the factory, and may also be required as a field service.

Drying may be done by circulating hot air around the core, or by vapor-phase drying (VPD) where an evaporated solvent transfers heat by condensation on

the coil and core.

For small transformers, resistance heating by injection of current into the

windings is used. The heating can be controlled very well, and it is energy efficient. The method is called low-frequency heating (LFH) since the current is

injected at a much lower frequency than the nominal of the power grid, which is normally 50 or 60 Hz. A lower frequency reduces the effect of the inductance in

the transformer, so the voltage needed to induce the current can be reduced. The LFH drying method is also used for service of older transformers.

TYPE OF TRANSFORMER

A wide variety of transformer designs are used for different applications, though they share several common features. Important common transformer types

include:

Autotransformer: Transformer in which part of the winding is common to both primary and secondary circuits.

Capacitor voltage transformer: Transformer in which capacitor divider is

used to reduce high voltage before application to the primary winding.

Distribution transformer, power transformer: International standards make a distinction in terms of distribution transformers being used to distribute

energy from transmission lines and networks for local consumption and power transformers being used to transfer electric energy between the

generator and distribution primary circuits.

Phase angle regulating transformer: A specialised transformer used to control the flow of real power on three-phase electricity transmission

networks.

Scott-T transformer: Transformer used for phase transformation from three-phase to two-phase and vice versa.

Polyphase transformer: Any transformer with more than one phase.

Grounding transformer: Transformer used for grounding three-phase circuits

to create a neutral in a three wire system, using a wye-delta transformer, or more commonly, a zigzag grounding winding.

Leakage transformer: Transformer that has loosely coupled windings.

Resonant transformer: Transformer that uses resonance to generate a high

secondary voltage.

Audio transformer: Transformer used in audio equipment.

Output transformer: Transformer used to match the output of a valve amplifier to its load.

Instrument transformer: Potential or current transformer used to accurately and safely represent voltage, current or phase position of high voltage or

high power circuits.

APPLICATION

Transformers are used to increase voltage before transmitting electrical energy

over long distances through wires. Wires have resistance which loses energy through joule heating at a rate corresponding to square of the current. By

transforming power to a higher voltage transformers enable economical transmission of power and distribution. Consequently, transformers have shaped

the electricity supply industry, permitting generation to be located remotely from points of demand. All but a tiny fraction of the world's electrical power has passed through a series of transformers by the time it reaches the consumer.

Transformers are also used extensively in electronic products to step-down the supply voltage to a level suitable for the low voltage circuits they contain. The

transformer also electrically isolates the end user from contact with the supply voltage.

Signal and audio transformers are used to couple stages of amplifiers and to match devices such as microphones and record players to the input of

amplifiers. Audio transformers allowedtelephone circuits to carry on a two-way conversation over a single pair of wires. A baluntransformer converts a signal

that is referenced to ground to a signal that has balanced voltages to ground, such as between external cables and internal circuits.

Testing of Power Transformer

The structure of the circuit equivalent of a practical transformer is

developed earlier.

The performance parameters of interest can be obtained by solving

that circuit for any load

conditions. The equivalent circuit parameters are available to the

designer of the transformers

from the various expressions that he uses for designing the

transformers. But for a user

these are not available most of the times. Also when a transformer is

rewound with different

primary and secondary windings the equivalent circuit also changes.

In order to get the

equivalent circuit parameters test methods are heavily depended upon.

From the analysis of

the equivalent circuit one can determine the electrical parameters. But

if the temperature

rise of the transformer is required, then test method is the most

dependable one. There are

several tests that can be done on the transformer; however a few

common ones are discussed

here.

Winding resistance test

This is nothing but the resistance measurement of the windings by applying a

small d.c voltage to the winding and measuring the current through the same. The

ratio gives the winding resistance, more commonly feasible with high voltage windings. For low voltage

windings a resistance-bridge method can be used. From the d.c resistance one can get the

a.c. resistance by applying skin effect corrections.

Polarity Test This is needed for identifying the primary and secondary phasor polarities. It is

a must for poly phase connections. Both a.c. and d.c methods can be used for detecting the polarities of the induced emfs. The dot method discussed earlier is

used to indicate the polarities. The transformer is connected to a low voltage a.c. source with the connectionsmade as shown in the fig. 18(a). A supply voltage

Vs is applied to the primary and thereadings of the voltmeters V1, V2 and V3 are noted. V1 : V2 gives the turns ratio. If V3 readsV1−V2 then assumed dot

locations are correct (for the connection shown). The beginning and end of the primary and secondary may then be marked by A1 −A2 and a1 −a2 respectively.If the voltage rises from A1 to A2 in the primary, at any instant it

does so from a1 to a2 inthe secondary. If more secondary terminals are present due to taps taken from the windingsthey can be labeled as a3, a4, a5, a6. It is the

voltage rising from smaller number towardslarger ones in each winding. The same thing holds good if more secondaries are present.Fig. 18(b) shows the d.c.

method of testing the polarity. When the switch S is closed if thesecondary voltage shows a positive reading, with a moving coil meter, the assumed

polarityis correct. If the meter kicks back the assumed polarity is wrong.

OPEN CIRCUIT TEST

As the name suggests, the secondary is kept open circuited and nominal value of the input voltage is applied to the primary winding and the input current and power are

measured. In Fig. 19(a) V,A,W are the voltmeter, ammeter and wattmeter respectively. Let these meters read V1, I0 and W0 respectively.Fig. 19(b) shows the equivalent circuit of

the transformer under this test. The no load current at rated voltage is less than 1 percent of nominal current and hence the loss and drop that take place in primary impedance r1 +jxl1 due to the no load current I0 is negligible. The active component Ic of the no load current I0

represents the core losses and reactive current Im is the current needed for the magnetization.

Thus the watt meter reading

The parameters measured already are in terms of the primary. Sometimes the primary voltage required may be in kilo-Volts and it may not be feasible to apply nominalvoltage to primary from the point of safety to personnel and

equipment. If the secondaryvoltage is low, one can perform the test with LV side energized keeping the HV side opencircuited. In this case the parameters

that are obtained are in terms of LV . These have tobe referred to HV side if we need the equivalent circuit referred to HV side.

Sometimes the nominal value of high voltage itself may not be known, or in doubt, especially in a rewound transformer. In such cases an open circuit

characteristics is first obtained, which is a graph showing the applied voltage as a function of the no load current. This is a non linear curve as shown in Fig. 20.

This graph is obtained by noting the current drawn by transformer at different applied voltage, keeping the secondary open circuited. The usual operating

point selected for operation lies at some standard voltage around the knee point of the characteristic. After this value is chosen as the nominal value the

parameters are calculated as mentioned above.

SHORT CIRCUIT TEST

The purpose of this test is to determine the series branch parameters of the equiv- alent circuit of Fig. 21(b). As the name suggests, in this test primary applied voltage, the

current and power input are measured keeping the secondary terminals short circuited. Let these values be Vsc, Isc and Wsc respectively. The supply voltage required to circulate rated

current through the transformer is usually very small and is of the order of a few percent of the nominal voltage. The excitation current which is only 1 percent or less even at rated voltage becomes negligibly small during this test and hence is neglected. The shunt branch

is thus assumed to be absent. Also I1 = I2 as I0 ≃ 0. Therefore Wsc is the sum of the copper losses in primary and secondary put together. The reactive power consumed is that

absorbed by the leakage reactance of the two windings.

If the approximate equivalent circuit is required then there is no need to separate r1and r2 or xl1 and x′l2. However if the exact equivalent circuit is needed then

either r1 or r′2 is determined from the resistance measurement and the other separated from the total.As for the separation of xl1 and x′l2 is concerned, they

are assumed to be equal. This is a fairly valid assumption for many types of transformer windings as the leakage flux paths are through air and are similar.

Load Test

Load Test helps to determine the total loss that takes place, when the transformer is loaded. Unlike the tests described previously, in the present case nominal voltage is applied

across the primary and rated current is drown from the secondary. Load test is used mainly 1. to determine the rated load of the machine and the temperature rise

2. to determine the voltage regulation and efficiency of the transformer. Rated load is determined by loading the transformer on a continuous basis and observ- ing the steady state temperature rise. The losses that are generated inside the transformer

on load appear as heat. This heats the transformer and the temperature of the transformer increases. The insulation of the transformer is the one to get affected by this rise in the

temperature. Both paper and oil which are used for insulation in the transformer start get- ting degenerated and get decomposed. If the flash point of the oil is reached the transformer

goes up in flames. Hence to have a reasonable life expectancy the loading of the transformer must be limited to that value which gives the maximum temperature rise tolerated by the insulation. This aspect of temperature rise cannot be guessed from the electrical equivalent

circuit. Further, the losses like dielectric losses and stray load losses are not modeled in the Electrical Machines I Prof. Krishna Vasudevan, Prof. G. Sridhara Rao, Prof. P. Sasidhara Rao

Indian Institute of Technology Madras equivalent circuit and the actual loss under load condition will be in error to that extent. Many external means of removal of heat from the transformer in the form of different cooling

methods give rise to different values for temperature rise of insulation. Hence these permit different levels of loading for the same transformer. Hence the only sure way of ascertaining

the rating is by conducting a load test. It is rather easy to load a transformer of small ratings. As the rating increases it becomes difficult to find a load that can absorb the requisite power and a source to feed the

necessary current. As the transformers come in varied transformation ratios, in many cases it becomes extremely difficult to get suitable load impedance.

Further, the temperature rise of the transformer is due to the losses that take place ‘inside’ the transformer. The efficiency of the transformer is above 99% even in modest sizes which means 1 percent of power handled by the transformer actually goes to heat up the

machine. The remaining 99% of the power has to be dissipated in a load impedance external to the machine. This is very wasteful in terms of energy also. ( If the load is of unity power

factor) Thus the actual loading of the transformer is seldom resorted to. Equivalent loss methods of loading and ‘Phantom’ loading are commonly used in the case of transformers. The load is applied and held constant till the temperature rise of transformer reaches a

steady value. If the final steady temperature rise is lower than the maximum permissible value, then load can be increased else it is decreased. That load current which gives the

maximum permissible temperature rise is declared as the nominal or rated load current and the volt amperes are computed using the same. In the equivalent loss method a short circuit test is done on the transformer. The

short circuit current is so chosen that the resulting loss taking place inside the transformer is equivalent to the sum of the iron losses, full load copper losses and assumed stray load

losses. By this method even though one can pump in equivalent loss inside the transformer, the actual distribution of this loss vastly differs from that taking place in reality. Therefore this test comes close to a load test but does not replace one.

In Phantom loading method two identical transformers are needed. The windings are connected back to back as shown in Fig. 22. Suitable voltage is injected into the loop formed by the two secondaries such that full load current passes through them. An equiv-

alent current then passes through the primary also. The voltage source V1 supplies the magnetizing current and core losses for the two transformers. The second source supplies

the load component of the current and losses due to the same. There is no power wasted in a load ( as a matter of fact there is no real load at all) and hence the name Phantom or virtual loading. The power absorbed by the second transformer which acts as a load is

pushed back in to the mains. The two sources put together meet the core and copper losses of the two transformers. The transformers work with full flux drawing full load currents and

hence are closest to the actual loading condition with a physical load.

Use of Power Transformer Generation of electrical power in low voltage level is very much cost effective. Hence

electrical power is generated in low voltage level. Theoretically, this low voltage level

power can be transmitted to the receiving end. But if the voltage level of a power is

increased, the current of the power is reduced which causes reduction in ohmic or I2R

losses in the system, reduction in cross sectional area of the conductor i.e. reduction in

capital cost of the system and it also improves the voltage regulation of the system.

Because of these, low level power must be stepped up for efficient electrical power transmission. This is done by step up transformer at the sending side of the power

system network. As this high voltage power may not be distributed to the consumers

directly, this must be stepped down to the desired level at the receiving end with the

help of step down transformer. These are the uses of electrical power transformer in the

electrical power system. Two winding transformers are generally used where ratio

between high voltage and low voltage is greater than 2. It is cost effective to use auto transformer where the ratio between high voltage and low voltage is less than 2. Again

three phase single unit transformer is more cost effective than a bank of three single phase transformer unit in a three phase system. But still it is preferable to use than the

later where power dealing is very large since such large size of three phase single unit

power transformer may not be easily transported from manufacturer's place to work site.

Transformer Basics – Efficiency

A transformer does not require any moving parts to transfer energy. This means that there

are no friction or windage losses associated with other electrical machines. However, transformers do suffer from other types of losses called “copper losses” and “iron losses”

but ge.

Copper losses, also known as I2R loss is the electrical power which is lost in heat as a result

of circulating the currents around the transformers copper windings, hence the name. Copper losses represents the greatest loss in the operation of a transformer. The actual watts of power

lost can be determined (in each winding) by squaring the amperes and multiplying by the

resistance in ohms of the winding (I2R).

Iron losses, also known as hysteresis is the lagging of the magnetic molecules within the core, in response to the alternating magnetic flux. This lagging (or out-of-phase) condition is due to

the fact that it requires power to reverse magnetic molecules; they do not reverse until the flux has attained sufficient force to reverse them.

Their reversal results in friction, and friction produces heat in the core which is a form of power loss. Hysteresis within the transformer can be reduced by making the core from special

steel alloys.

The intensity of power loss in a transformer determines its efficiency. The efficiency of a transformer is reflected in power (wattage) loss between the primary (input) and secondary

(output) windings. Then the resulting efficiency of a transformer is equal to the ratio of the power output of the secondary winding, PS to the power input of the primary winding, PP

and is therefore high.

An ideal transformer is 100% efficient because it delivers all the energy it receives. Real

transformers on the other hand are not 100% efficient and at full load, the efficiency of a transformer is between 94% to 96% which is quiet good. For a transformer operating with a

constant voltage and frequency with a very high capacity, the efficiency may be as high as 98%. The efficiency, ? of a transformer is given as:

Transformer Efficiency

where: Input, Output and Losses are all expressed in units of power.

Generally when dealing with transformers, the primary watts are called “volt-amps”, VA to differentiate them from the secondary watts. Then the efficiency equation above can be

modified to:

It is sometimes easier to remember the relationship between the transformers input, output and efficiency by using pictures. Here the three quantities of VA, W and ? have been

superimposed into a triangle giving power in watts at the top with volt-amps and efficiency at the bottom. This arrangement represents the actual position of each quantity in the efficiency

formulas.

Transformer Efficiency Triangle

and transposing the above triangle quantities gives us the following combinations of the same

equation:

Then, to find Watts (output) = VA x eff., or to find VA (input) = W/eff., or to find Efficiency, eff. =W/VA, etc.

Conclusion

Transformer design and manufacturing techniques have remained similar for

many years .over time, improvements have been made in materials, design programs and testing technique to allow for lighter and more efficient units to be produced. Proper procedure and handling for filed installation has proven to

be very critical in reducing moisture content and maximizing the life span of an installed unit.

Power in a Transformer

Where: FP is the primary phase angle and FS is the secondary phase angle.

Note that since power loss is proportional to the square of the current being transmitted, that

is:I2R, increasing the voltage, let’s say doubling ( ×2 ) the voltage would decrease the current by the same amount, ( ÷2 ) while delivering the same amount of power to the load and

therefore reducing losses by factor of 4. If the voltage was increased by a factor of 10, the

current would decrease by the same factor reducing overall losses by factor of 100

So if you increase the voltage the voltage out ,then the current decrease.

If you step up the voltage, so that voltage out is double the voltage input, you can see from basic algebra that the output current must be half what the output current is.

Transformer transform the power(p=voltage*current ) from one value to desired value what we require and does not regulate the voltage.

SHIVAM DWIVEDI 13UEE063