dokumen.tips_hindustan-zinc-report (1).pdf

“Hindustan Zinc Limited”
An
Industrial Training Report
submitted
in partial fulfilment
for the award of the Degree of
Bachelor of Technology
in
Department of Electrical & Electronics Engineering
Supervisor: Submitted By:
Mr. Piyush Sharma Khushbu Shrimal
HOD EEE Roll No.12ECOEX301
Department of Electrical & Electronics Engineering
SS College of Engineering, Udaipur, Rajasthan
Rajasthan Technical University
SEPTEMBER, 2015-16

Candidate Declaration
I hereby declare that the work, which is being presented in the Industrial Training Report,
entitled “TRANSFORMER” in partial fulfillment for the award of Degree of “Bachelor of
Technology” in Dept. Of Electrical & Electronics Engineering and submitted to the Department
of Electrical & Electronics Engineering, SS College of Engineering, Udaipur, Rajasthan
Technical University is a record of my own investigations carried under the Guidance of Mr.
Piyush Sharma Department of Electrical & Electronics Engineering , SS College of Engineering,
Udaipur.
I have not submitted the matter presented in this report anywhere for the award of any other
Degree.
Supervisor: Submitted By:
Mr. Piyush Sharma Khushbu Shrimal
HOD EEE Roll No.12ECOEX301

ACKNOWLEDGEMENT
It’s a great pleasure to present this report of summer training in HINDUSTAN ZINC
LIMITED (DEBARI) in partial fulfillment of B-TECH Program under S.S. College of
Engineering, Rajasthan Technical University, Kota. At the outset, I would like to express my
immense gratitude to my training guide Mr. Nitesh for guiding me right from the inception till
the successful completion of the training.
I am falling short of words for expressing my feelings of gratitude towards him for
extending his valuable guidance about technology, equipments and support for literature,
critical reviews of project and the report and above all the moral support he had provided me
with all stages of this training.
I would also like to thank my friends and all my group members for their help and
cooperation throughout the training.
Khushbu Shrimal
12ECOEX301

PREFACE
Practical training is a way to implement theoretical knowledge to practical use to become
a successful engineer. It is necessary to have a sound practical knowledge because it is only way
by which one can acquire proficiency & skill to work successfully different industries.
It is proven fact that bookish knowledge is not sufficient because things are not as ideal in
practical field as they should be.
Hindustan Zinc Ltd. is one of the best examples to understand the production process &
productivity in particular of Zinc.
This report is an attempt made to study the overall production system & related action of
Zinc Smelter, Debari a unit of HZL. It is engaged in production of high grade zinc metal & other
by products viz. Cd, sulphuric acid etc. since 1968 by adopting Hydro Metallurgical technology.
Khushbu Shrimal

CONTENTS
Acknowledgement
Preface
1. Company Profile 6
1.1 Vedanta 6
1.2 Hindustan Zinc Limited 6
1.3 Zinc Smelter Debari 7
2. Zinc 9
2.1 Introduction 10
2.2 Properties of Zinc 10
2.3 Zinc Smelting 10
3. 3. Zinc Smelter Debari 12
3.1 General Process Overview 12
3.2 Raw Material Handling Section 12
3.3 Roasting Plant 13
3.4 Leaching Plant 15
3.5 Cell House 16
3.6 Melting & Casting 17
4. Project Work 18
4.1 Basic Principle 18
4.2 Basic Transformer parameters and Construction 23
4.3 Construction 26
4.4 Classification Parameters 33
4.5 Types 34
4.6 History 36
5. Conclusion 41
6. Reference 42

CHAPTER-1
Company Profile
1.1 Vedanta
Vedanta is an LSE-listed diversified FTSE 100 metals and mining company, and India’s
largest non-ferrous metals and mining company based on revenues. Its business is principally
located in India, one of the fastest growing large economies in the world.
In addition, they have additional assets and operations in Zambia and Australia. They are
primarily engaged in copper, zinc, aluminium and iron businesses, and are also developing a
commercial power generation business.
Founder of this recognition is Mr. Anil Agarwal, who is chairman of this group, a simple
person without any special degree in management field but have a great experience in this field
and a sharp sight of the future conditions and requirement.
1.2 Hindustan Zinc Limited
Hindustan Zinc Limited was incorporated from the erstwhile Metal Corporation of India
on 10 January 1966 as a Public Sector Undertaking.
In April 2002, Sterlite Opportunities and Ventures Limited (SOVL) made an open offer
for acquisition of shares of the company; consequent to the disinvestment of Government of
India's (GOI) stake of 26% including management control to SOVL and acquired additional 20%
of shares from public, pursuant to the SEBI Regulations 1997. In August 2003, SOVL acquired
additional shares to the extent of 18.92% of the paid up capital from GOI in exercise of "call
option" clause in the share holder's agreement between GOI and SOVL. With the above
additional acquisition, SOVL's stake in the company has gone up to 64.92%. Thus GOI's stake in
the company now stands at 29.54%.
Hindustan Zinc Ltd. operates smelters using
• Roast Leach Electro-Winning (RLE)
• Hydrometallurgical (Debari, Vizag and Chanderiya Smelters) and
1.3 Zinc Smelter, Debari-Udaipur
Location 14 km from Udaipur, Rajasthan, India. Hydrometallurgical Zinc
Smelter Commissioned in 1968 Roast Leach Electrowining Technology with Conversion Process

Gone through a series of debottlenecking 88,000 tonnes per annum of Zinc Captive Power
Generation 29 MW DG Captive Power Plant commissioned in 2003 Certifications BEST4
Certified Integrated Systems ISO 9001:2000, ISO 14001:2004, OHSAS 18001:1999, SA
8000:2001 Covered Area (Ha) 22.65 Total Plant Area (Ha) 126
Products Range
a. High Grade Zinc (HG) (25 kgs) & Jumbo (600 kgs)
b. Cadmium Pencils (150 gms)
c. Sulphuric Acid + 98% concentration
Awards & Recognitions
TABLE 1.1
S. No MATERIAL QUANTITY
1 Zn 80,000MT
2 Acid 130,000MT
3 Cd 250MT
4 Zinc dust 360MT
5 Work force 876 Nos.
6 Managerial & Engineering Staff . 84 Nos.
7 Supervisory & Technical Staff 58 Nos
8 Labour 729 Nos.
9 (a) Skilled 154Nos.
10 (b) Semi-Skilled 555Nos.
a. International Safety Award: 2006 by British Safety Council, UK
b. ROSPA Gold Award for prevention of accidents
c. Operating Capacity (Per Year)
Raw Material Supplies:-
a. Zawar Mines
b. Agucha Mines
c. Rajpura Dariba Mines
Product Buyers:-
a. Tata

b. Bhel
c. Steel Companies
Process Collaborators:-
a. Krebs Penorrova, France Leaching, Purification, Electrolysis
b. Lurgi, GMBH, and Germany Roaster and gas clearing
c. Auto Kumpu Finland RTP, Wartsila Plant
d. I.S.C., ALLOY, U.K. Zinc dust plant, Allen Power Plant

CHAPTER-2
Zinc (Zn)
2.1 Introduction
Zinc is a metallic chemical element with the symbol Zn and atomic number 30. In
nonscientific context it is sometimes called spelter. Commercially pure zinc is known as Special
High Grade, often abbreviated SHG, and is 99.995% pure.
Zinc is found in the earth’s crust primarily as zinc sulfide (ZnS). Zinc (Zn) is a metallic
element of hexagonal close-packed (hcp) crystal structure and a density of 7.13 grams per cubic
centimeter. It has only moderate hardness and can be made ductile and easily worked at
temperatures slightly above the ambient. In solid form it is grayish white, owing to the formation
of an oxide film on its surface, but when freshly cast or cut it has a bright, silvery appearance.
It’s most important use, as a protective coating for iron known as galvanizing, derives from two
of its outstanding characteristics: it is highly resistant to corrosion, and, in contact with iron, it
provides sacrificial protection by corroding in place of the iron.
Zinc ores typically may contain from 3 to 11 percent zinc, along with cadmium, copper,
lead, silver, and iron. Beneficiation, or the concentration of the zinc in the recovered ore, is
accomplished at or near the mine by crushing, grinding, and flotation process. Once
concentrated, the zinc ore is transferred to smelters for the production of zinc or zinc oxide. The
primary product of most zinc companies is slab zinc, which is produced in 5 grades: special high
grade, high grade, intermediate, brass special and prime western. The primary smelters also
produce sulfuric acid as a byproduct.
With its low melting point of 420° C (788° F), unalloyed zinc has poor engineering
properties, but in alloyed form the metal is used extensively. The addition of up to 45 percent
zinc to copper forms the series of brass alloys, while, with additions of aluminum, zinc forms
commercially significant pressure die-casting and gravity-casting alloys. Primary uses for zinc
include galvanizing of all forms of steel, as a constituent of brass, for electrical conductors,
vulcanization of rubber and in primers and paints. Most of these applications are highly
dependent upon zinc’s resistance to corrosion and its light weight characteristics. The annual
production volume has remained constant since the 1980s. India is a leading exporter of zinc
concentrates as well as the world’s largest importer of refined zinc.

2.2 Properties of Zinc (metallic) at 293K
TABLE 2.1:-Properties of Zinc
Material Quantity
1. Melting Point 693K
2. Specific Latent Heat of Fusion 10 J/ Kg
3. Specific heat capacity 38510 J/ Kg
4. Linear expansivity 31/k
5. Thermal conductivity 111 W/m/k
6. Electric Sensitivity 5.9ohm-meter
7. Temp. Coefficient of resistance 40/k
8. Tensile Strength 150Mpa
9. Elongation 50%
10. Young’ modulus 110Gpa
11. Passion’s Ratio 0.25
2.3 Zinc Smelting
Zinc smelting is the process of recovering and refining zinc metal out of zinc-containing
feed material such as zinc-containing concentrates or zinc oxides. This is the process of
converting zinc concentrates (ores that contain zinc) into pure zinc.
The most common zinc concentrate processed is zinc sulfide, which is obtained by
concentrating sphalerite using the froth flotation method. Secondary (recycled) zinc material,
such as zinc oxide, is also processed with the zinc sulfide. Approximately 30% of all zinc
produced is from recycled sources.
Globally, two main zinc-smelting processes are in use:
a. Pyrometallurgical process run at high temperatures to produce liquid zinc.
b. Hydrometallurgical or electrolytic process using aqueous solution in combination with
electrolysis to produce a solid zinc deposit.
The vast majority of zinc smelting plants in the western world use the electrolytic process,
also called the Roast-Leach-Electrowin (’RLE’) process, since it has various advantages over the

pyrometallurgical process (overall more energy-efficient, higher recovery rates, easier to
automate hence higher productivity, etc.).
In the most common hydrometallurgical process for zinc manufacturing, the ore is
leached with sulfuric acid to extract the Zinc. These processes can operate at atmospheric
pressure or as pressure leach circuits. Zinc is recovered from solution by electrowinning, a
process similar to electrolytic refining. The process most commonly used for low-grade deposits
is heap leaching. Imperial smelting is also used for zinc ores.

CHAPTER-3
Zinc Smelter Debari
Zinc Smelter Debari have following main plants
3.1 General Process Overview
The electrolytic zinc smelting process can be divided into a number of generic sequential
process steps, as presented in the general flow sheet set out below.
In Summary, the Process Sequence is:
Step 1: Receipt of feed materials (concentrates and secondary feed materials such as zinc oxides)
and storage;
Step 2: Roasting: an oxidation stage removing sulphur from the sulphide feed materials, resulting
in so-called calcine;
Step 3: Leaching transforms the zinc contained in the calcine into a solution such as zinc
sulphate, using diluted sulphuric acid;
Step 4: Purification: removing impurities that could affect the quality of the electrolysis process
(such as cadmium, copper, cobalt or nickel) from the leach solution;
Step 5: Electrolysis or electro-winning: zinc metal extraction from the purified solution by means
of electrolysis leaving a zinc metal deposit (zinc cathodes);
Step 6: Melting and casting: melting of the zinc cathodes typically using electrical induction
furnaces and casting the molten zinc into ingots.
Additional steps can be added to the process transforming the pure zinc (typically
99.995% pure zinc known as Special High Grade (’SHG’)) into various types of alloys or other
marketable products.
3.2 Raw Material Handling Section(RMH)
Smelters use a mix of zinc-containing concentrates or secondary zinc material such as
zinc oxides as feed to their roasting plant. Debari smelter is characterized by a relatively high
input of secondary materials. Smelters located inland receive their feed by road, rail or canal
depending on site-specific logistical factors and the type of feedstock (eg, secondary zinc oxides
come in smaller volumes and are typically transported by road). Concentrate deliveries typically
happen in large batches (eg, 5,000 to 10,000 tonnes).
Hindustan Zinc Smelter Debari is strategically located close to the Zawar mines that
serves as a global concentrate hub and provides for an extensive multi-modal logistical

infrastructure. It is 14 kms away from Udaipur well connected by rail, road and air. Most zinc
smelters use several sources of concentrates. These different materials are blended to obtain an
optimal mix of feedstock for the roasting process.
The zinc concentrate is delivered by trucks and is discharged into two
underground bins. Several belt conveyors transport the concentrate from the underground
bins to the concentrate storage hall. A Pay loader feeds the materials into two hoppers. By
means of discharging and transport belt conveyors including an over-belt magnetic separator, a
vibro screen and a hammer mill, the materials are transported to the concentrate feed bin.
Dross material from the cathode melting and casting process will be added to the feed
material before the vibro screen. For moistening of the concentrate several spraying nozzles are
foreseen in the concentrate storage hall, as well as on the conveying belt before the
concentrate feed bin.
Blended feed from the concentrate feed bin is discharged onto a discharge belt
conveyor, which in turn discharges onto a rotary table feeder. The roaster is fed then by
two slinger belts.
3.3 ROASTING PLANT
In Roasting Plant, oxidation of zinc sulfide concentrates at high temperatures into an
impure zinc oxide, called "Calcine". The chemical reactions taking place during the process are:
Approximately 90% of zinc in concentrates is oxidized to zinc oxide, but at the roasting
temperatures around 10% of the zinc reacts with the iron impurities of the zinc sulfide
concentrates to form zinc ferrite. A byproduct of roasting is sulfur dioxide, which is further
processed into sulfuric acid. Zinc oxide obtained is then sent in leaching plant for further
processing.
Firstly, zinc sulphide after ore concentration process is sent to furnace .There at 920-950
degree temperature zinc sulphide combustion takes place producing calcine. Further oxidation of
SO2 maintains the temperature range, and then SO3 is sent to acid plant for production of
sulphuric acid. HZL, Dariba has 2 roaster units R4 and R5. Zinc Sulphide Concentrate is
introduced directly into the roaster and roasted in a turbulent layer, largely consisting of roasted
material especially Zinc Oxide (ZnO). This layer has been heated to ignition temperature by thee
preheating device. The desired reaction is maintained by an exothermic reaction of Sulfide
Concentrate and air in the turbulent layer.
The surplus reaction heat is taken out of the roaster bed by cooling elements installed in
the turbulent layer in the form of evaporator heating surfaces connected to the Waste Heat

Boiler. The waste heat is further utilized to generate electricity of about 9.6MW which is used in
the plant.
Roaster part of plant also divided as follows:
1. Raw Material Handling (RMH)
2. Roaster
3. Waste Heat Recovery Boiler (WHRB)
4. Hot Gas Precipitator (HGP)
5. Gas Cleaning Plant (GCP)
6. Sulphuric Acid Plant (SAP)
7. Acid Loading Plant
ACID PLANT
The utilization of sulphur containing gases after zinc concentrate roasting is carried out at
the sulphuric acid plant resulting in marketable sulphuric acid.
For the treatment of Sulphur Dioxide (SO2) in the roasting off-gas, by passing through
the Gas Drying Tower, the Sulphur Dioxide (SO2), cooled and saturated with water vapor, comes
in direct contact with concentrated acid. Sulfuric Acid (H2SO4) of this concentration is very
hygroscopic (absorbs waters) and the gas is practically free from water vapor after leaving the
Drying Tower.
After the Drying Tower, the Sulphur Dioxide (SO2) has to be converted into Sulfur
Trioxide (SO3) to allow the production of Sulphuric Acid (H2SO4) according to the following
reactions:
SO2 + 1/2 O2 → SO3
SO3 + H20 → H2SO4
Gas coming out of hot gas precipitator has 7-8%of SO2 at 330 degree Celsius.SO2 gas is
passed through scrubbing tower, which has sedimentation tank and SO2 stripper & wet gas
precipitator. In presence of V2O5, oleum is formed which further gives H2SO4.

3.4 LEACHING PLANT
The calcine is first leached in a neutral or slightly acidic solution (of sulphuric acid) in
order to leach the zinc out of the zinc oxide. The remaining calcine is then leached in strong
sulfuric acid to leach the rest of the zinc out of the zinc oxide and zinc ferrite. The result of this
process is a solid and a liquid; the liquid contains the zinc and is often called leach product.
There is also iron in the leach product from the strong acid leach, which is removed in an
intermediate step, in the form of jarosite. Jarosite is a waste therefore it is sent to Effluent
treatment plant. There is still cadmium, copper, arsenic, antimony, cobalt, germanium and
nickel in the leach product. Therefore it needs to be purified.
The basic leaching chemical formula that drives this process is:
ZnO +H2SO4→ZnSO4 + H2O
MeO + H2SO4→MeSO4+ H2O
Me→ Metals other than Zinc present in concentration
Leaching Area is distributed in following buildings:
1. Weak acid leaching building
2. Jarosite precipitation building
3. Purification building
4. Gypsum removal building
PURIFICATION
It uses zinc dust, Potassium Antimony Tartarate (PAT) and steam to remove copper,
cadmium, cobalt, and nickel, which would interfere with the electrolysis process. After
purification, concentrations of these impurities are limited to less than 0.02 milligram per liter
Purification is usually conducted in large agitated tanks called Pachukas. The process takes place
at temperatures ranging from 40 to 85 °C (104 to 185 °F). The zinc sulfate solution must be very
pure for electrolysis to be at all efficient. Impurities can change the decomposition voltage
enough to where the electrolysis cell produces largely hydrogen gas rather than zinc metal.
That’s the reason zinc sulphide is passed through various thickeners and then hot filter beds
where the zinc sulphate goes with the solution as it is soluble. This ZnSO4 solution has pH of 5
which is then sent to electrolysis process. Zinc calcine, leach solutions and cell house acid are
mixed in 11 agitated tanks which are controlled to varied pH, from 2 to 5, by additions of cell
house acid or calcine. Continuous pH monitoring is facilitated by submerged pH cells in
controlled tanks.

After leaching, the acid leach slurry is distributed to four 24-m thickeners where the leach
residues are separated from the clear zinc sulphate solution. The residues are filtered and washed
before being pumped to the Lead Smelter for further processing to recover zinc and other metals.
These recovered metals are recycled as a fume to the zinc circuit through the Oxide Leach Plant.
Clear zinc sulphate solution flows continuously from the thickeners to the zinc dust purification
circuit. Solution flow rate from this circuit is approximately 450 m/h. An increase in acid
concentration from 3 to 4% resulted in a 5% increase in recovery. The higher the concentration
of the acid the better the dissolution of the zinc, so zinc is recovered mostly.
3.5 CELL HOUSE
Zinc is extracted from the purified zinc sulfate solution by electro winning, which is a
specialized form of electrolysis. The process works by passing an electric current through the
solution in a series of cells. This causes the zinc to deposit on the cathodes (aluminum sheets)
and oxygen to form at the anodes. Every 24 to 48 hours, each cell is shut down, the zinc-coated
cathodes are removed and rinsed, and the zinc is mechanically stripped from the aluminum
plates.
A portion of the electrical energy is converted into heat, which increases the temperature
of the electrolyte. A portion of the electrolyte is continuously circulated through the cooling
towers both to cool and concentrate the electrolyte through evaporation of water. The cooled and
concentrated electrolyte is then recycled to the cells. This process accounts for approximately
one-third of all the energy usage when smelting zinc.
Zinc contained in the purified Zinc Sulphate (ZnSO4) is recovered as metal in the
Electrolysis Plant. Zinc Electro-Winning is a method of depositing Zinc Metal (Zn) on the
surface of Aluminum Sheet (Al) in cell by passing electric current through the cell. The thickness
of Zinc Plating depends on the time spent in the electrolysis cell, the amount of current, and the
chemical composition of the cell.
The electrolysis cells are arranged in one electrical circuit of two rows of cells each. The
circuit is serviced by two transformer rectifiers that are connected in parallel by Aluminum (Al)
and Copper (Cu) bush bars. The cells are connected in series while the Anode/Cathode System in
each cell is in parallel.
Principle electrolysis reaction:
ZnSO4 + electricity →Zn++
+ SO4
--
& Zn++
+ 2e-
→Zn

3.6 MELTING AND CASTING
Cathode melting will be carried out in two identical electric induction furnaces. The
furnaces will have a guaranteed average melting rate of 22 tonnes per hour of zinc cathodes
(maximum ~ 24 tonnes per hour). The melting rate is infinitely variable between 0% and 100%
of the maximum melting rate and is controlled by the automatic control system to match the rate
that molten metal is removed (pumped) from the furnace.
Each furnace is equipped with a still well equipped with one or more molten metal
pumps. The pump delivers molten zinc to a launder system feeding the casting machine. Each
furnace feeds a single casting line. In addition, provision is made to pump molten zinc from one
of the furnaces to the zinc dust production plant.
In addition to cathode bundles, the furnace chutes are designed to receive metallic zinc
from the dross separation plant and metallic zinc “skims” from the casting machines. This
material is fed to any chute (normally one dedicated chute) from forklift transported to hoppers
that have been raised to the charging floor by the freight elevator (lift). The required amount of
nh4cl to enhance the melting of this material is manually added to each hopper prior to dumping
in the charge chute.
When cathode zinc is melted, a layer of dross comprised mainly of zinc oxide entrained
molten zinc droplets is produced. This dross must be removed from the furnace once in every 24
hours by manually skimming the dross from the surface of the bath in a process called drossing.
This process consists of opening one of the doors on the side of the furnace, manually spreading
a few kg of NH4Cl onto the dross layer, manually agitating the dross layer with a steel “rake”
and finally using the “rake” to drag the dross through the open door of the furnace into a forklift
tote bin. During the drossing process, the furnace is operated under conditions of increased
ventilation to contain the fumes and dust that are generated by the agitation and dross removal
processes. The totes of furnace dross are transported by lift truck to the dross cooling area, to
await treatment in the dross separation plan

Transformer
A transformer is an electrical device that transfers electrical energy between two or
more circuits through electromagnetic induction
or decrease the voltages of alternating current in electric power applications.
A varying current in the transformer's primary winding creates a varying
the transformer core and a varying magnetic field impinging on the transformer's secondary
winding. This varying magnetic field
force (EMF) or voltage in the secondary winding. Making use of
with high magnetic permeability
change AC voltages from one voltage level to another within power networks.
Since the invention of the first constant
become essential for the AC
wide range of transformer designs is encountered in electronic and electric power applications
4.1Basic principles
Ideal transformer
By law of Conservation of Energy
in the input & output
For simplification or approximation purposes, it is very common to analyze the
transformer as an ideal transformer model as presented in the two images. An ideal transformer
is a theoretical, linear transformer that is lossless and perfectly
no energy losses and flux is completely
implies infinitely high core
net magnetomotive force.
Fig 4.1:-Ideal transformer connected with source V
Project Work
is an electrical device that transfers electrical energy between two or
electromagnetic induction. Commonly, transformers are used to increase
A varying current in the transformer's primary winding creates a varying
magnetic field at the secondary winding induces a varying
(EMF) or voltage in the secondary winding. Making use of Faraday's Law
magnetic permeability core properties, transformers can thus be designed to efficiently
voltages from one voltage level to another within power networks.
Since the invention of the first constant potential transformer in 1885, transformers have
transmission , distribution, and utilization of electrical energy.
wide range of transformer designs is encountered in electronic and electric power applications
Conservation of Energy, apparent , real and reactive power are each conserved
transformer model as presented in the two images. An ideal transformer
transformer that is lossless and perfectly coupled
is completely confined within the magnetic core
implies infinitely high core magnetic permeability and winding inductances and zero
Ideal transformer connected with source VP on primary and
impedance ZL on secondary,
Chapter 4
is an electrical device that transfers electrical energy between two or
Commonly, transformers are used to increase
A varying current in the transformer's primary winding creates a varying magnetic flux in
ry winding induces a varying electromotive
Faraday's Law in conjunction
be designed to efficiently
voltages from one voltage level to another within power networks.
transformer in 1885, transformers have
, and utilization of electrical energy. A
wide range of transformer designs is encountered in electronic and electric power applications.
power are each conserved
transformer model as presented in the two images. An ideal transformer
coupled; that is, there are
magnetic core. Perfect coupling
and winding inductances and zero
on primary and load

A varying current in the transformer's primary winding creates a varying magnetic flux in
the core and a varying magnetic field impinging on the secondary winding. This varying
magnetic field at the secondary induces a varying electromotive force (EMF) or voltage in the
secondary winding. The primary and secondary windings are wrapped around a core of infinitely
high magnetic permeability so that all of the magnetic flux passes through both the primary and
secondary windings. With a voltage source connected to the primary winding and
load impedance connected to the secondary winding, the transformer currents flow in the
indicated directions.
Fig 4.2:-Ideal transformer and induction law
According to Faraday's law of induction, since the same magnetic flux passes through
both the primary and secondary windings in an ideal transformer, a voltage is induced in each
winding, according to eq. (1) in the secondary winding case, according to eq. (2) in the primary
winding case.This is in accordance withLenz's law, which states that induction of EMF always
opposes development of any such change in magnetic field.
The transformer winding voltage ratio is thus shown to be directly proportional to the
winding turns ratio according to eq. (3).
According to the law of Conservation of Energy, any load impedance connected to the
ideal transformer' secondary winding results in conservation of apparent, real and reactive power
consistent with eq. (4).

Fig 4.3:-Instrument transformer, with polarity dot and X1 markings on LV side terminal
Polarity
A dot convention is often used in transformer circuit diagrams, nameplates or terminal
markings to define the relative polarity of transformer windings. Positively increasing
instantaneous current entering the primary winding's dot end induces positive polarity voltage at
the secondary winding's dot end.
Real transformer
Deviations from ideal
The ideal transformer model neglects the following basic linear aspects in real
transformers.
Core losses, collectively called magnetizing current losses, consist of
• Hysteresis losses due to nonlinear application of the voltage applied in the transformer
core, and
• Eddy current losses due to joule heating in the core that are proportional to the square of
the transformer's applied voltage.
Whereas windings in the ideal model have no resistances and infinite inductances, the
windings in a real transformer have finite non-zero resistances and inductances associated with:
• Joule losses due to resistance in the primary and secondary windings
• Leakage flux that escapes from the core and passes through one winding only resulting in
primary and secondary reactive impedance.

Leakage flux
The ideal transformer
all the turns of every winding, including itself. In practice, some flux traverses paths that take it
outside the windings.]
Such flux is termed
inductance in series with the mutually coupled transformer windings.
energy being alternately stored in and discharged from the magnetic fields with each cycle of the
power supply. It is not directly a power loss, but results in inferior
secondary voltage not to be directly proportional to the primary voltage, particularly under heavy
load.Transformers are therefore normally designed to have very low leakage inductance
In some applications increased leakage is desired, and long magnetic paths, air gaps, or
magnetic bypass shunts may deliberately be introduced in a transformer design to limit the
circuit current it will supply
exhibit negative resistance, such as
safely handling loads that become periodically short
Air gaps are also used to keep a transformer from saturating, especially audio
transformers in circuits that have a DC component flowing in the windings.
Knowledge of leakage inductance is also useful when transformers are operated in
parallel. It can be shown that if the percent impedance
to-resistance (X/R) ratio of two transformers were hypothetically exactly the same, the
transformers would share power in proportion to their
500 kVA unit in parallel with 1,000
However, the impedance tolerances of commercial transformers are significant. Also, the Z
impedance and X/R ratio of different capacity transformers tends to vary, corresponding
1,000 kVA and 500 kVA units' values being, to illustrate, respectively,
and Z ≈ 5%, X/R ≈ 4.75.
Fig 4.4:- Leakage flux of a transformer
The ideal transformer model assumes that all flux generated by the primary winding links
Such flux is termed leakage flux, and results in
with the mutually coupled transformer windings. Leakage flux results in
power supply. It is not directly a power loss, but results in inferior voltage regulation
load.Transformers are therefore normally designed to have very low leakage inductance
tions increased leakage is desired, and long magnetic paths, air gaps, or
magnetic bypass shunts may deliberately be introduced in a transformer design to limit the
current it will supply]
Leaky transformers may be used to supply loads that
, such as electric arcs, mercury vapor lamps, and
that become periodically short-circuited such as electric arc welders
Air gaps are also used to keep a transformer from saturating, especially audio
s that have a DC component flowing in the windings.
parallel. It can be shown that if the percent impedance and associated winding leakage reactance
of two transformers were hypothetically exactly the same, the
transformers would share power in proportion to their respective volt
el with 1,000 kVA unit, the larger unit would carry twice the current).
kVA units' values being, to illustrate, respectively, Z
model assumes that all flux generated by the primary winding links
, and results in leakage
eakage flux results in
voltage regulation, causing the
load.Transformers are therefore normally designed to have very low leakage inductance.
tions increased leakage is desired, and long magnetic paths, air gaps, or
magnetic bypass shunts may deliberately be introduced in a transformer design to limit the short-
Leaky transformers may be used to supply loads that
, and neon signs or for
electric arc welders.
Air gaps are also used to keep a transformer from saturating, especially audio-frequency
s that have a DC component flowing in the windings.
and associated winding leakage reactance-
of two transformers were hypothetically exactly the same, the
respective volt-ampere ratings (e.g.
kVA unit, the larger unit would carry twice the current).
Z ≈ 5.75%, X/R ≈ 3.75

Equivalent circuit
Referring to the diagram, a practical transformer's physical behavior may be represented
by an equivalent circuit model, which can incorporate an ideal transformer.
Winding joule losses and leakage reactances are represented by the following series loop
impedances of the model:
• Primary winding: RP, XP
• Secondary winding: RS, XS.
In normal course of circuit equivalence transformation, RS and XS are in practice usually
referred to the primary side by multiplying these impedances by the turns ratio squared,
(NP/NS) 2
= a2
.
Fig 4.5:- Real transformer equivalent circuit
Core loss and reactance is represented by the following shunt leg impedances of the model:
• Core or iron losses: RC
• Magnetizing reactance: XM.
RC and XM are collectively termed the magnetizing branch of the model.
Core losses are caused mostly by hysteresis and eddy current effects in the core and are
proportional to the square of the core flux for operation at a given frequency. The finite
permeability core requires a magnetizing current IM to maintain mutual flux in the core.
Magnetizing current is in phase with the flux, the relationship between the two being non-linear
due to saturation effects. However, all impedances of the equivalent circuit shown are by
definition linear and such non-linearity effects are not typically reflected in transformer
equivalent circuits.With sinusoidal supply, core flux lags the induced EMF by 90°. With open-
circuited secondary winding, magnetizing branch current I0 equals transformer no-load current.
The resulting model, though sometimes termed 'exact' equivalent circuit based
on linearity assumptions, retains a number of approximations.]
Analysis may be simplified by
assuming that magnetizing branch impedance is relatively high and relocating the branch to the

left of the primary impedances. This introduces error but allows combination
referred secondary resistances and reac
Transformer equivalent circuit impedance and transformer ratio parameters can be
derived from the following tests:
and transformer ratio test.
4.2 Basic transformer parameters and construction
Fig 4.6:-Power transformer over
(green), iron core's magnetic
Effect of frequency
Transformer universal EMF equation
If the flux in the core is purely
its rms voltage Erms of the winding, and the supply frequency
sectional area a in m2
and peak magnetic flux density
universal EMF equation:
If the flux does not contain even
cycle average voltage Eavg of any waveshape:
By Faraday's Law of induction shown in eq. (1) and (2), transformer EMFs
according to the derivative of flux with respect to time.
linearly with time for any non
left of the primary impedances. This introduces error but allows combination
referred secondary resistances and reactances by simple summation as two series impedances.
derived from the following tests: open-circuit test,[m] short-circuit test, winding resistance test,
rmer parameters and construction
Power transformer over-excitation condition caused by decreased
(green), iron core's magnetic characteristics (red) and magnetizing current (blue).
universal EMF equation
If the flux in the core is purely sinusoidal, the relationship for either winding between
of the winding, and the supply frequency f, number of turns
and peak magnetic flux density Bpeak in Wb/m2
or T (tesla) is given by the
contain even harmonics the following equation can be used for
of any waveshape:
By Faraday's Law of induction shown in eq. (1) and (2), transformer EMFs
according to the derivative of flux with respect to time. The ideal transformer's core behaves
linearly with time for any non-zero frequency. Flux in a real transformer's core behaves non
left of the primary impedances. This introduces error but allows combination of primary and
tances by simple summation as two series impedances.
, winding resistance test,
excitation condition caused by decreased frequency; flux
characteristics (red) and magnetizing current (blue).
, the relationship for either winding between
, number of turns N, core cross-
or T (tesla) is given by the
the following equation can be used for half-
By Faraday's Law of induction shown in eq. (1) and (2), transformer EMFs vary
The ideal transformer's core behaves
Flux in a real transformer's core behaves non-

finite linear range resulting in magnetic saturation associated with increasingly large magnetizing
current, which eventually leads to transformer overheating.
The EMF of a transformer at a given flux density increases with frequency. By operating
athigher frequencies, transformers can be physically more compact because a given core is able
to transfer more power without reaching saturation and fewer turns are needed to ac achieve the
same impedance. However, properties such as linearly in relation to magnetization current as the
instantaneous flux increases beyond a core loss and conductor skin effect also increase with
frequency. Aircraft and military equipment employ 400 Hz power supplies which reduce core
and winding weight.Conversely, frequencies used for some railway electrification systems were
much lower (e.g. 16.7 Hz and 25 Hz) than normal utility frequencies (50–60 Hz) for historical
reasons concerned mainly with the limitations of early electric traction motors. As such, the
transformers used to step-down the high over-head line voltages (e.g. 15 kV) were much heavier
for the same power rating than those designed only for the higher frequencies.
Operation of a transformer at its designed voltage but at a higher frequency than intended
will lead to reduced magnetizing current. At a lower frequency, the magnetizing current will
increase. Operation of a transformer at other than its design frequency may require assessment of
voltages, losses, and cooling to establish if safe operation is practical. For example, transformers
may need to be equipped with 'volts per hertz' over-excitation relays to protect the transformer
from overvoltage at higher than rated frequency.
One example is in traction transformers used for electric multiple unit and high-
speed train service operating across regions with different electrical standards. The converter
equipment and traction transformers have to accommodate different input frequencies and
voltage (ranging from as high as 50 Hz down to 16.7 Hz and rated up to 25 kV) while being
suitable for multiple AC asynchronous motor and DC converters and motors with varying
harmonics mitigation filtering requirements.
Large power transformers are vulnerable to insulation failure due to transient voltages
with high-frequency components, such as caused in switching or by lightning.
Energy losses
Real transformer energy losses are dominated by winding resistance joule and core
losses. Transformers' efficiency tends to improve with increasing transformer capacity. The
efficiency of typical distribution transformers is between about 98 and 99 percent.
As transformer losses vary with load, it is often useful to express these losses in terms of
no-load loss, full-load loss, half-load loss, and so on. Hysteresis and eddy current losses are
constant at all load levels and dominate overwhelmingly without load, while variable
winding joule losses dominating increasingly as load increases. The no-load loss can be
significant, so that even an idle transformer constitutes a drain on the electrical supply.
Designing energy efficient transformers for lower loss requires a larger core, good-qualitysilicon

steel, or even amorphous steel for the core and thicker wire, increasing initial cost. The choice of
construction represents a trade-off between initial cost and operating cost.
Transformer losses arise from:
Winding joule losses
Current flowing through a winding's conductor causes joule heating. As frequency
increases, skin effect and proximity effect causes the winding's resistance and, hence, losses to
increase.
Core losses
Hysteresis losses
Each time the magnetic field is reversed, a small amount of energy is lost due
to hysteresis within the core.
where, f is the frequency, η is the hysteresis coefficient and βmax is the maximum flux
density, the empirical exponent of which varies from about 1.4 to 1.8 but is often given as 1.6 for
iron.
Eddy current losses
Ferromagnetic materials are also good conductors and a core made from such a material
also constitutes a single short-circuited turn throughout its entire length. Eddy currents therefore
circulate within the core in a plane normal to the flux, and are responsible for resistive heating of
the core material. The eddy current loss is a complex function of the square of supply frequency
and inverse square of the material thickness.]
Eddy current losses can be reduced by making the
core of a stack of plates electrically insulated from each other, rather than a solid block; all
transformers operating at low frequencies use laminated or similar cores.
Magnetostriction related transformer hum
Magnetic flux in a ferromagnetic material, such as the core, causes it to physically
expand and contract slightly with each cycle of the magnetic field, an effect known as
magnetostriction, the frictional energy of which produces an audible noise known
as mainshum or transformerhum]
Thetransformer hum is especially objectionable in transformers
supplied at power frequencies and in high-frequency flyback transformers associated with PAL
system CRTs.
Stray losses
Leakage inductance is by itself largely lossless, since energy supplied to its magnetic
fields is returned to the supply with the next half-cycle. However, any leakage flux that
intercepts nearby conductive materials such as the transformer's support structure will give rise

to eddy currents and be converted to heat. There are also radiative losses due to the oscillating
magnetic field but these are usually small.
fig 4.7:-Core form = core type; shell form = shell type
Mechanical vibration and audible noise transmission
In addition to magnetostriction, the alternating magnetic field causes fluctuating forces
between the primary and secondary windings. This energy incites vibration transmission in
interconnected metalwork, thus amplifying audible transformer hum.
Core form and shell form transformers
Closed-core transformers are constructed in 'core form' or 'shell form'. When windings
surround the core, the transformer is core form; when windings are surrounded by the core, the
transformer is shell form. Shell form design may be more prevalent than core form design for
distribution transformer applications due to the relative ease in stacking the core around winding
coils. Core form design tends to, as a general rule, be more economical, and therefore more
prevalent, than shell form design for high voltage power transformer applications at the lower
end of their voltage and power rating ranges (less than or equal to, nominally, 230 kV or
75 MVA). At higher voltage and power ratings, shell form transformers tend to be more
prevalent.Shell form design tends to be preferred for extra-high voltage and higher MVA
applications because, though more labor-intensive to manufacture, shell form transformers are
characterized as having inherently better kVA-to-weight ratio, better short-circuit strength
characteristics and higher immunity to transit damage.
4.3 Construction
Cores
Laminated steel cores
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
cores consisting of bundles of insulated iron wires.
Fig 4.8:-Laminated core transformer showing edge of laminations at top of photo
Fig 4.9:-Power transformer inrush current caused by residual flux at switching instant;
flux (green), iron core's magnetic characteristics (red) and magnetizing current (blue).
stacking layers of thin steel laminations, a principle that has remained in use. Each la
insulated from its neighbors by a thin non
transformer equation indicates a minimum cross
The effect of laminations is to confine eddy currents to hig
little flux, and so reduce their magnitude. Thinner laminations reduce losses,
laborious and expensive to construct.
transformers, with some of very thin s
One common design of laminated core is made from interleaved stacks of
sheets capped with I-shaped pieces, leading to its name of 'E
tends to exhibit more losses, but is very economical to
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
Laminated core transformer showing edge of laminations at top of photo
Power transformer inrush current caused by residual flux at switching instant;
stacking layers of thin steel laminations, a principle that has remained in use. Each la
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,
laborious and expensive to construct.[
Thin laminations are generally used on high
transformers, with some of very thin steel laminations able to operate up to 10
One common design of laminated core is made from interleaved stacks of
pieces, leading to its name of 'E-I transformer'.
tends to exhibit more losses, but is very economical to manufacture. The cut
eddy current losses, and their designs mitigated this effect with
Later designs constructed the core by
Laminated core transformer showing edge of laminations at top of photo
Power transformer inrush current caused by residual flux at switching instant;
stacking layers of thin steel laminations, a principle that has remained in use. Each lamination is
conducting layer of insulation.The universal
sectional area for the core to avoid saturation.
hly elliptical paths that enclose
little flux, and so reduce their magnitude. Thinner laminations reduce losses,]
but are more
Thin laminations are generally used on high-frequency
teel laminations able to operate up to 10 kHz.
One common design of laminated core is made from interleaved stacks of E-shaped steel
I transformer'.[55]
Such a design
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.
Fig 4.10:-Laminating the cor
A steel core's remanence
removed. When power is then reapplied, the residual field will cause a high
the effect of the remaining magnetism is reduced, usually after a few cycles of the applied AC
waveform. Overcurrent protection devices such as
inrush to pass. On transformers connected to long, overhead power transmission lines, induced
currents due to geomagnetic disturbances
operation of transformer protection devices.
Distribution transformers can achieve low no
loss high-permeability silicon steel or
cost of the core material is offs
Solid cores
Powdered iron cores are used in circuits such as switch
above mains frequencies and up to a few tens of kilohertz. These materials combine
magnetic permeability with high bulk electrical
the VHF band, cores made from non
common. Some radio-frequency transformers also have movable cores (sometimes called 'slugs')
which allow adjustment of the
circuits.
Toroidal cores
Toroidal transformers are built around a ring
frequency, is made from a long strip of
iron, or ferrite. A strip construction ensures that the
They have the advantage that the flux is always oriented parallel to
the metal grains, reducing reluctance.
Laminating the core greatly reduces eddy- current losses
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
Overcurrent protection devices such as fuses must be selected to allow this harmless
etic disturbances duringsolar storms can cause saturation of the core and
operation of transformer protection devices.
Distribution transformers can achieve low no-load losses by using cores made with low
permeability silicon steel or amorphous (non-crystalline) metal alloy
cost of the core material is offset over the life of the transformer by its lower losses at light load.
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
magnetic permeability with high bulk electrical resistivity. For frequencies extending beyond
, cores made from non-conductive magnetic ceramic materials called
frequency transformers also have movable cores (sometimes called 'slugs')
which allow adjustment of the coupling coefficient (andbandwidth) of tuned radio
Toroidal transformers are built around a ring-shaped core, which, depending on operating
long strip of silicon steel or permalloy wound into a coil, powdered
A strip construction ensures that the grain boundaries are optimally aligned,
They have the advantage that the flux is always oriented parallel to
current losses
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
ed to allow this harmless
can cause saturation of the core and
sses by using cores made with low-
crystalline) metal alloy. The higher initial
et over the life of the transformer by its lower losses at light load.
mode power supplies that operate
above mains frequencies and up to a few tens of kilohertz. These materials combine high
. For frequencies extending beyond
materials called ferrites are
frequency transformers also have movable cores (sometimes called 'slugs')
) of tuned radio-frequency
shaped core, which, depending on operating
wound into a coil, powdered
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 provides screening to
minimize the core's magnetic field from generating electromagnetic interference.
Fig 4.11:-Small toroidal core transformer
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
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 highbandwidth, 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
Fig 4.12:-Windings are usually arranged concentrically to minimize flux leakage.
The 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 of pressboard.[62]
White: insulator. Green spiral: Grain oriented silicon steel. Black: Primary winding made
ofoxygen-free copper. Red: Secondary winding. Top left: Toroidal transformer. Right: C-core,
but E-core would be similar. The black windings are made of film. Top: Equally low capacitance
between all ends of both windings. Since most cores are at least moderately conductive they also
need insulation. Bottom: Lowest capacitance for one end of the secondary winding needed for
low-power high-voltage transformers. Bottom left: Reduction of leakage inductance would lead
to increase of capacitance.
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 stand is 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.
Fig 4.13:
The windings of signal transformers minimize leakage inductance and stray capacitance
to improve high-frequency response. Coils are split into sections, and tho
between the sections of the other winding.
Power-frequency transformers may have
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 furnacetransformers, 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
in the output stage of an audio power
in AM transmitters are very similar.
Dry-type transformer winding insulation systems can be either of standard open
'dip-and-bake' construction or of higher quality designs
impregnation (VPI), vacuum pressure encapsulation
encapsulationprocesses.]
In the VPI process, a combination of heat, vacuum and press
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
ductor of similar size, aiding manufacture.
Fig 4.13:-Cut view through transformer windings.
frequency response. Coils are split into sections, and tho
between the sections of the other winding.
frequency transformers may have taps at intermediate points on the winding,
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
sed in electric power transmission or distribution, on equipment such
transformers, or for automatic voltage regulators for sensitive loads. Audio
, used for the distribution of audio to public address loudspeakers, have
taps to allow adjustment of impedance to each speaker. A center-tapped transformer
stage of an audio power amplifier in a push-pull circuit. Modulation transformers
transmitters are very similar.
type transformer winding insulation systems can be either of standard open
bake' construction or of higher quality designs that include
vacuum pressure encapsulation (VPE), and
In the VPI process, a combination of heat, vacuum and press
Cut view through transformer windings.
frequency response. Coils are split into sections, and those sections interleaved
at intermediate points on the winding,
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-
sed in electric power transmission or distribution, on equipment such
transformers, or for automatic voltage regulators for sensitive loads. Audio-
, used for the distribution of audio to public address loudspeakers, have
tapped transformer is often used
. Modulation transformers
type transformer winding insulation systems can be either of standard open-wound
that include vacuum pressure
(VPE), and cast coil
In the VPI process, a combination of heat, vacuum and pressure is used

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
The conservator (reservoir) at top provides liquid-to-atmosphere isolation as coolant level
and temperature changes. The walls and fins provide required heat dissipation balance.
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 underlines the 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.[75]
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 were 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 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 used is at a much lower frequency than that of the
power grid, which is normally 50 or 60 Hz. A lower frequency reduces the effect of inductance,
so the voltage required can be reduced.[81]
The LFH drying method is also used for service of
older transformers.
Bushings
Larger transformers are provided with high-voltage insulated bushings made of polymers
or porcelain. A large bushing can be a complex structure since it must provide careful control of
the electric field gradient without letting the transformer leak oil.
4.4 Classification parameters
Transformers can be classified in many ways, such as the following:
• Power capacity: From a fraction of a volt-ampere (VA) to over a thousand MVA.
• Duty of a transformer: Continuous, short-time, intermittent, periodic, varying.
• Frequency range: Power-frequency, audio-frequency, or radio-frequency.
• Voltage class: From a few volts to hundreds of kilovolts.

• Cooling type: Dry and liquid-immersed – self-cooled, forced air-cooled; liquid-immersed
– forced oil-cooled, water-cooled.
• Circuit application: Such as power supply, impedance matching, output voltage and
current stabilizer or circuit isolation.
• Utilization: Pulse, power, distribution, rectifier, arc furnace, amplifier output, etc..
• Basic magnetic form: Core form, shell form.
• Constant-potential transformer descriptor: Step-up, step-down, isolation.
• General winding configuration: By EIC vector group – various possible two-winding
combinations of the phase designations delta, wye or star, and zigzag or interconnected
star;other – autotransformer, Scott-T, zigzag grounding transformer winding.
• Rectifier phase-shift winding configuration: 2-winding, 6-pulse; 3-winding, 12-pulse; . . .
n-winding, [n-1]*6-pulse; polygon; etc..
4.5 Types
Various specific electrical application designs require a variety of transformer types.
Although they all share the basic characteristic transformer principles, they are customize in
construction or electrical properties for certain installation requirements or circuit conditions.
• 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.
• : 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.
• Pulse transformer: Specialized small-signal transformer used to transmit digital
signaling while providing electrical isolation, commonly used in Ethernet computer
networks as 10BASE-T, 100BASE-T and 1000BASE-T.
Fig4.13:An electricalsubstation in Melbourne, Australiashowing three of five 220 kV –
66 kV transformers, each with a capacity of 150 MVA
Transformers are used to increase (or step-up) 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.[92]
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 decrease (or 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
allowed telephone circuits to carry on a two-way conversation over a single pair of wires.
A balun transformer 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.

4.6 History
Discovery of induction
Fig4.15:-Faraday's experiment with induction between coils of wire
Electromagnetic induction, the principle of the operation of the transformer, was
discovered independently by Michael Faraday in 1831 and Joseph Henry in 1832.Faraday was
the first to publish the results of his experiments and thus receive credit for the discovery.The
relationship between EMF and magnetic flux is an equation now known as
induction:
where is the magnitude of the EMF in Volts and
in webers.
Faraday performed the first experiments on induction between coils of wire, including
winding a pair of coils around an iron ring, thus creating the first
transformer.]
However he only applied individual pulses of current to his transformer, and never
discovered the relation between the turns ratio and EMF in the windings.
Fig4.16:- Induction coil, 1900, Bremerhaven, Germany
Faraday's experiment with induction between coils of wire
independently by Michael Faraday in 1831 and Joseph Henry in 1832.Faraday was
relationship between EMF and magnetic flux is an equation now known as
is the magnitude of the EMF in Volts and ΦB is the magnetic flux through the circuit
winding a pair of coils around an iron ring, thus creating the first
discovered the relation between the turns ratio and EMF in the windings.
Induction coil, 1900, Bremerhaven, Germany
Induction coils
Faraday's experiment with induction between coils of wire
independently by Michael Faraday in 1831 and Joseph Henry in 1832.Faraday was
relationship between EMF and magnetic flux is an equation now known as Faraday's law of
is the magnetic flux through the circuit
winding a pair of coils around an iron ring, thus creating the first toroidal closed-core

The first type of transformer to see wide use was the
Rev. Nicholas Callan of Maynooth College
to realize the more turns the secondary winding has in relation to the primary winding, the larger
the induced secondary EMF will be. Induction coil
efforts to get higher voltages from batteries. Since batteries produce
than AC, induction coils relied upon
current in the primary to create the flux changes necessary for induction. Between the 1830s and
the 1870s, efforts to build better induction coils, mostly by trial and error, slowly revealed the
basic principles of transformers.
First alternating current transformers
By the 1870s, efficient
it was found AC could power an induction coil directly, without an
In 1876, Russian engineer
of induction coils where the primary windings were connected to a source of AC. The secondary
windings could be connected to several
Yablochkov employed functioned essentially as transformers.
In 1878, the Ganz factory
electric lighting and, by 1883, had installed over fifty systems in Austria
systems used arc and incandescent lamps, generators, and other equipment.
Lucien Gaulard and John Dixon Gibbs first exhibited a device with an open iron core
called a 'secondary generator' in London in 1882, then sold the idea to
the Westinghousecompany in the United States.
in 1884, where it was adopted for an electric lighting system.However, the efficiency of their
open-core bipolar apparatus re
Early series circuit transformer distribution
4.17:-Faraday's ring transformer
The first type of transformer to see wide use was the induction coil
Maynooth College, Ireland in 1836. He was one of the first researchers
the induced secondary EMF will be. Induction coils evolved from scientists' and inventors'
efforts to get higher voltages from batteries. Since batteries produce direct current (DC)
than AC, induction coils relied upon vibrating electrical contacts that regularly interrupted the
efforts to build better induction coils, mostly by trial and error, slowly revealed the
basic principles of transformers.
First alternating current transformers
By the 1870s, efficient generators producing alternating current (AC)
could power an induction coil directly, without an interrupter
In 1876, Russian engineer Pavel Yablochkov invented.[
a lighting system based on a set
windings could be connected to several 'electric candles' (arc lamps) of his own design.The coils
Yablochkov employed functioned essentially as transformers.
Ganz factory, Budapest, Hungary, began manufacturing equipment for
electric lighting and, by 1883, had installed over fifty systems in Austria
and John Dixon Gibbs first exhibited a device with an open iron core
company in the United States. They also exhibited the invention in Turin, Italy
core bipolar apparatus remained very low.
Early series circuit transformer distribution
induction coil, invented by
, Ireland in 1836. He was one of the first researchers
s evolved from scientists' and inventors'
direct current (DC) rather
that regularly interrupted the
efforts to build better induction coils, mostly by trial and error, slowly revealed the
alternating current (AC) were available, and
interrupter.
a lighting system based on a set
(arc lamps) of his own design.The coils
anufacturing equipment for
electric lighting and, by 1883, had installed over fifty systems in Austria-Hungary. Their AC
and John Dixon Gibbs first exhibited a device with an open iron core
They also exhibited the invention in Turin, Italy

Induction coils with open magnetic circuits are inefficient at transferring power to loads.
Until about 1880, the paradigm for AC power transmission from a high voltage supply to a low
voltage load was a series circuit. Open-core transformers with a ratio near 1:1 were connected
with their primaries in series to allow use of a high voltage for transmission while presenting a
low voltage to the lamps. The inherent flaw in this method was that turning off a single lamp (or
other electric device) affected the voltage supplied to all others on the same circuit. Many
adjustable transformer designs were introduced to compensate for this problematic characteristic
of the series circuit, including those employing methods of adjusting the core or bypassing the
magnetic flux around part of a coil.Efficient, practical transformer designs did not appear until
the 1880s, but within a decade, the transformer would be instrumental in the War of Currents,
and in seeing AC distribution systems triumph over their DC counterparts, a position in which
they have remained dominant ever since.
Fig4.18:-Shell form transformer.
Fig4.19:-Core form, front; shell form, back.

Fig4.20:-Stanley's 1886 design for adjustable gap open
Closed-core transformers and parallel power
In the autumn of 1884,
engineers associated with the Ganz factory, had determined that open
impracticable, as they were incapable of reliably regulating voltage.
applications for novel transformers (later called ZBD transformers), they described two designs
with closed magnetic circuits where copper windings were either a) wound around iron wire ring
core or b) surrounded by iron wire core
basic transformer constructions in common use to this day, which can as a class all be termed as
either core form or shell form (or alternatively, core type or shell type), as in a) or b),
respectively (see images).]
The Ganz factory had also in the autumn of 1884 made delivery of the
world's first five high-efficiency AC transformers, the first of these units having been shipped on
September 16, 1884.]
This first unit had been manufactured to the following specifications: 1,400
W, 40 Hz, 120:72 V, 11.6:19.4 A, ratio 1.67:1, one
In both designs, the magnetic flux linking the primary and seconda
almost entirely within the confines of the iron core, with no intentional path through air
(see Toroidal cores below). The new transformers we
core bipolar devices of Gaulard and Gibbs.
interrelated innovations: one concerning the use of parallel connected, instead of series
connected, utilization loads, the other
such that the supply network voltage could be much higher (initially 1,400 to 2,000 V) than the
voltage of utilization loads (100 V
electric distribution systems, closed
economically feasible to provide electric power for lighting in homes, businesses and public
spaces. Blaty had suggested the use of closed cores, Zipernowsky had suggested the
of parallel shunt connections, and Déri had performed the experiments;
Transformers today are designed on the principles discovered by the three engineers.
They also popularized the word 'transformer' to describe a device for altering
electric current]
although the term had already been in use by 1882.In 1886, the ZBD engineers
Stanley's 1886 design for adjustable gap open-core induction coils
core transformers and parallel power distribution
In the autumn of 1884, Károly Zipernowsky, Ottó Bláthy and Miksa Déri
engineers associated with the Ganz factory, had determined that open
impracticable, as they were incapable of reliably regulating voltage. In their joint 1885 patent
surrounded by iron wire core.[
The two designs were the first application of the two
efficiency AC transformers, the first of these units having been shipped on
Hz, 120:72 V, 11.6:19.4 A, ratio 1.67:1, one-phase, shell form.
In both designs, the magnetic flux linking the primary and seconda
below). The new transformers were 3.4 times more efficient than the open
core bipolar devices of Gaulard and Gibbs.]
The ZBD patents included two other major
connected, utilization loads, the other concerning the ability to have high turns ratio transformers
voltage of utilization loads (100 V initially preferred]
When employed in parallel connected
c distribution systems, closed-core transformers finally made it technically and
y had suggested the use of closed cores, Zipernowsky had suggested the
, and Déri had performed the experiments;
o popularized the word 'transformer' to describe a device for altering
core induction coils
Miksa Déri (ZBD), three
engineers associated with the Ganz factory, had determined that open-core devices were
n their joint 1885 patent
The two designs were the first application of the two
efficiency AC transformers, the first of these units having been shipped on
In both designs, the magnetic flux linking the primary and secondary windings traveled
re 3.4 times more efficient than the open-
The ZBD patents included two other major
concerning the ability to have high turns ratio transformers
When employed in parallel connected
core transformers finally made it technically and
y had suggested the use of closed cores, Zipernowsky had suggested the use
o popularized the word 'transformer' to describe a device for altering the EMF of an

designed, and the Ganz factory supplied electrical equipment for, the world's first power
station that used AC generators to power a parallel connected common electrical network, the
steam-powered Rome-Cerchi power plant.
Although George Westinghouse had bought Gaulard and Gibbs' patents in 1885,
the Edison Electric Light Company held an option on the US rights for the ZBD transformers,
requiring Westinghouse to pursue alternative designs on the same principles. He assigned
to William Stanley the task of developing a device for commercial use in United States. Stanley's
first patented design was for induction coils with single cores of soft iron and adjustable gaps to
regulate the EMF present in the secondary winding (see image).This design was first used
commercially in the US in 1886 but Westinghouse was intent on improving the Stanley design to
make it (unlike the ZBD type) easy and cheap to produce.
s

CHAPTER-5
CONCLUSION
It was just like a dream come true for me to pursue training in Hindustan Zinc ltd. It was
really a learning experience for me to have a feel of different Industrial aspects.
In this period I have Learnt those things, which I could not get from books i.e., the practical
experience under the guidance of learned professionals.
Special thanks for my college and Hindustan Zinc Work .

References
• “Plant Operating Manuals” Zinc Smelter Debari, Udaipur
• McCabe, Smith, Harriott “Unit Operations of Chemical Engineering” McGraw-Hill
International Editions.
• http://www.hzlindia.com/index.aspx Official Website of Hindustan Zinc Limited
• http://www.vedantaresources.com/default.aspx Offical Website of Vedanta Resources
HZL, Training Report

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