“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 inductionor decrease the voltages of alternating current in electric power applications.

A varying current in the transformer's primary winding creates a varyingthe transformer core and a varying magnetic field impinging on the transformer's secondary winding. This varying magnetic fieldforce (EMF) or voltage in the secondary winding. Making use ofwith high magnetic permeabilitychange AC voltages from one voltage level to another within power networks.

Since the invention of the first constantbecome 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 Energyin 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 corenet 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

or decrease the voltages of alternating current in electric power applications.

A varying current in the transformer's primary winding creates a varyingthe transformer core and a varying magnetic field impinging on the transformer's secondary

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

For simplification or approximation purposes, it is very common to analyze the transformer model as presented in the two images. An ideal transformer transformer that is lossless and perfectly coupled

is completely confined within the magnetic coreimplies 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

or decrease the voltages of alternating current in electric power applications.

A varying current in the transformer's primary winding creates a varying magnetic flux in the transformer core and a varying magnetic field impinging on the transformer's secondary

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

For simplification or approximation purposes, it is very common to analyze the 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 termedinductance 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 inferiorsecondary 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 thecircuit current it will supplyexhibit negative resistance, such assafely handling loads that become periodically short

Air gaps are also used to keep a transformer from saturating, especially audiotransformers 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 impedanceto-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 1,000However, 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 all the turns of every winding, including itself. In practice, some flux traverses paths that take it

Such flux is termed leakage flux, and results inwith the mutually coupled transformer windings. Leakage flux results in

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 voltage regulationsecondary 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

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 audios 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 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). 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

kVA units' values being, to illustrate, respectively, Z

model assumes that all flux generated by the primary winding links all the turns of every winding, including itself. In practice, some flux traverses paths that take it

, and results in leakage eakage flux results in

energy being alternately stored in and discharged from the magnetic fields with each cycle of the voltage regulation, causing the

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.

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.

Knowledge of leakage inductance is also useful when transformers are operated in 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). 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

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 purelyits rms voltage Erms of the winding, and the supply frequencysectional area a in m2 and peak magnetic flux densityuniversal EMF equation:

If the flux does not contain evencycle 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.

Transformer equivalent circuit impedance and transformer ratio parameters can be 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 forof 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.

Transformer equivalent circuit impedance and transformer ratio parameters can be , 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 prohibitivecores 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 lainsulated from its neighbors by a thin nontransformer equation indicates a minimum cross

The effect of laminations is to confine eddy currents to higlittle 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 ofsheets capped with I-shaped pieces, leading to its name of 'Etends 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;

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 lainsulated 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 hightransformers, with some of very thin steel laminations able to operate up to 10

One common design of laminated core is made from interleaved stacks ofpieces, 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; 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 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 remanenceremoved. When power is then reapplied, the residual field will cause a highthe effect of the remaining magnetism is reduced, usually after a few cycles of the applied AC waveform. Overcurrent protection devices such asinrush to pass. On transformers connected to long, overhead power transmission lines, induced currents due to geomagnetic disturbancesoperation of transformer protection devices.

Distribution transformers can achieve low noloss high-permeability silicon steel orcost of the core material is offs

Solid cores

Powdered iron cores are used in circuits such as switchabove mains frequencies and up to a few tens of kilohertz. These materials combine magnetic permeability with high bulk electricalthe VHF band, cores made from noncommon. Some radio-frequency transformers also have movable cores (sometimes called 'slugs') which allow adjustment of thecircuits.

Toroidal cores

Toroidal transformers are built around a ringfrequency, is made from a long strip ofiron, or ferrite. A strip construction ensures that the

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

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 highthe effect of the remaining magnetism is reduced, usually after a few cycles of the applied AC

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

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 lowpermeability 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 calledfrequency 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,

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

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 the effect of the remaining magnetism is reduced, usually after a few cycles of the applied AC

ed to allow this harmless inrush to pass. On transformers connected to long, overhead power transmission lines, induced

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 thobetween the sections of the other winding.

Power-frequency transformers may haveusually 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 onload tap changers are used in electric power transmission or distribution, on equipment such as arc furnacetransformers, or for automatic voltage regulators for sensitive loads. Audiofrequency transformers, used for the distribution of audio to public address loudspeakers, have taps to allow adjustment of impedance to each speaker. Ain the output stage of an audio powerin 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 encapsulationencapsulationprocesses.]In the VPI process, a combination of heat, vacuum and pressto 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

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

ductor of similar size, aiding manufacture.

Fig 4.13:-Cut view through transformer windings.

The windings of signal transformers minimize leakage inductance and stray capacitance 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 onsed 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 transformerstage 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 openbake' construction or of higher quality designs that include

vacuum pressure encapsulation (VPE), andIn 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

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

Cut view through transformer windings.

The windings of signal transformers minimize leakage inductance and stray capacitance 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 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

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 asinduction:

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 firsttransformer.] 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

Electromagnetic induction, the principle of the operation of the transformer, was 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

is the magnitude of the EMF in Volts and ΦB is the magnetic flux through the circuit

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

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.

Induction coil, 1900, Bremerhaven, Germany

Induction coils

Faraday's experiment with induction between coils of wire

Electromagnetic induction, the principle of the operation of the transformer, was 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 Faraday's law of

is the magnetic flux through the circuit

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 toroidal closed-core

However he only applied individual pulses of current to his transformer, and never

The first type of transformer to see wide use was theRev. Nicholas Callan of Maynooth Collegeto realize the more turns the secondary winding has in relation to the primary winding, the larger the induced secondary EMF will be. Induction coilefforts to get higher voltages from batteries. Since batteries producethan 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, efficientit was found AC could power an induction coil directly, without an

In 1876, Russian engineerof induction coils where the primary windings were connected to a source of AC. The secondary windings could be connected to severalYablochkov employed functioned essentially as transformers.

In 1878, the Ganz factoryelectric lighting and, by 1883, had installed over fifty systems in Austriasystems 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 coilMaynooth College, Ireland in 1836. He was one of the first researchers

to realize the more turns the secondary winding has in relation to the primary winding, the larger 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 current in the primary to create the flux changes necessary for induction. Between the 1830s and

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 of induction coils where the primary windings were connected to a source of AC. The secondary 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 Austriasystems used arc and incandescent lamps, generators, and other equipment.

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

company in the United States. They also exhibited the invention in Turin, Italy in 1884, where it was adopted for an electric lighting system.However, the efficiency of their

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

to realize the more turns the secondary winding has in relation to the primary winding, the larger s evolved from scientists' and inventors'

direct current (DC) rather that regularly interrupted the

current in the primary to create the flux changes necessary for induction. Between the 1830s and 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 of induction coils where the primary windings were connected to a source of AC. The secondary

(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 systems used arc and incandescent lamps, generators, and other equipment.

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

They also exhibited the invention in Turin, Italy in 1884, where it was adopted for an electric lighting system.However, the efficiency of their

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 openimpracticable, 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 corebasic 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 secondaalmost entirely within the confines of the iron core, with no intentional path through air (see Toroidal cores below). The new transformers wecore 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, closedeconomically feasible to provide electric power for lighting in homes, businesses and public spaces. Blaty had suggested the use of closed cores, Zipernowsky had suggested theof 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 alteringelectric 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 Dériengineers associated with the Ganz factory, had determined that openimpracticable, as they were incapable of reliably regulating voltage. In their joint 1885 patent 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

surrounded by iron wire core.[The two designs were the first application of the two 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),

The Ganz factory had also in the autumn of 1884 made delivery of the efficiency AC transformers, the first of these units having been shipped on

This first unit had been manufactured to the following specifications: 1,400 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 secondaalmost entirely within the confines of the iron core, with no intentional path through air

below). The new transformers were 3.4 times more efficient than the opencore bipolar devices of Gaulard and Gibbs.]The ZBD patents included two other major interrelated innovations: one concerning the use of parallel connected, instead of series connected, utilization loads, the other concerning the ability to have high turns ratio transformers 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 initially preferred]When employed in parallel connected

c distribution systems, closed-core transformers finally made it technically and economically feasible to provide electric power for lighting in homes, businesses and public

y had suggested the use of closed cores, Zipernowsky had suggested the, and Déri had performed the experiments;

Transformers today are designed on the principles discovered by the three engineers. o popularized the word 'transformer' to describe a device for altering

although the term had already been in use by 1882.In 1886, the ZBD engineers

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 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

The two designs were the first application of the two 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),

The Ganz factory had also in the autumn of 1884 made delivery of the efficiency AC transformers, the first of these units having been shipped on

This first unit had been manufactured to the following specifications: 1,400

In both designs, the magnetic flux linking the primary and secondary windings traveled almost entirely within the confines of the iron core, with no intentional path through air

re 3.4 times more efficient than the open-The ZBD patents included two other major

interrelated innovations: one concerning the use of parallel connected, instead of series concerning the ability to have high turns ratio transformers

such that the supply network voltage could be much higher (initially 1,400 to 2,000 V) than the When employed in parallel connected

core transformers finally made it technically and economically feasible to provide electric power for lighting in homes, businesses and public

y had suggested the use of closed cores, Zipernowsky had suggested the use

Transformers today are designed on the principles discovered by the three engineers. o popularized the word 'transformer' to describe a device for altering the EMF of an

although the term had already been in use by 1882.In 1886, the ZBD engineers

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