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CHAPTER-1

Company Profile

1.1 Vedanta

Vedanta is an LSE-listed diversified FTSE 100 metals and mining company, and India’slargest non-ferrous metals and mining company based on revenues. Its business is principallylocated 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 areprimarily engaged in copper, zinc, aluminium and iron businesses, and are also developing acommercial power generation business.

Founder of this recognition is Mr. Anil Agarwal, who is chairman of this group, a simpleperson without any special degree in management field but have a great experience in this fieldand 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 Indiaon 10 January 1966 as a Public Sector Undertaking.

In April 2002, Sterlite Opportunities and Ventures Limited (SOVL) made an open offerfor acquisition of shares of the company; consequent to the disinvestment of Government ofIndia'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 acquiredadditional shares to the extent of 18.92% of the paid up capital from GOI in exercise of "calloption" clause in the share holder's agreement between GOI and SOVL. With the aboveadditional acquisition, SOVL's stake in the company has gone up to 64.92%. Thus GOI's stake inthe 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 ZincSmelter Commissioned in 1968 Roast Leach Electrowining Technology with Conversion Process

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Gone through a series of debottlenecking 88,000 tonnes per annum of Zinc Captive PowerGeneration 29 MW DG Captive Power Plant commissioned in 2003 Certifications BEST4

Certified Integrated Systems ISO 9001:2000, ISO 14001:2004, OHSAS 18001:1999, SA8000:2001 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 1.1S. No MATERIAL QUANTITY

1 Zn 80,000MT

2 Acid 130,000MT

3 Cd 250MT

4 Zinc dust 360MT5 Work force 876 Nos.6 Managerial & Engineering Staff . 84 Nos.7 Supervisory & Technical Staff 58 Nos8 Labour 729 Nos.9 (a) Skilled 154Nos.

10 (b) Semi-Skilled 555Nos.

a. International Safety Award: 2006 by British Safety Council, UKb. ROSPA Gold Award for prevention of accidentsc. Operating Capacity (Per Year)

Raw Material Supplies:-

a. Zawar Minesb. Agucha Minesc. Rajpura Dariba Mines

Product Buyers:-

a. Tata

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b. Bhelc. Steel Companies

Process Collaborators:-

a. Krebs Penorrova, France Leaching, Purification, Electrolysisb. Lurgi, GMBH, and Germany Roaster and gas clearingc. Auto Kumpu Finland RTP, Wartsila Plantd. I.S.C., ALLOY, U.K. Zinc dust plant, Allen Power Plant

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CHAPTER-2

Zinc (Zn)

2.1 IntroductionZinc 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 SpecialHigh 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 metallicelement of hexagonal close-packed (hcp) crystal structure and a density of 7.13 grams per cubiccentimeter. It has only moderate hardness and can be made ductile and easily worked attemperatures slightly above the ambient. In solid form it is grayish white, owing to the formationof 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 twoof its outstanding characteristics: it is highly resistant to corrosion, and, in contact with iron, itprovides 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, isaccomplished at or near the mine by crushing, grinding, and flotation process. Onceconcentrated, the zinc ore is transferred to smelters for the production of zinc or zinc oxide. Theprimary product of most zinc companies is slab zinc, which is produced in 5 grades: special highgrade, high grade, intermediate, brass special and prime western. The primary smelters alsoproduce sulfuric acid as a byproduct.

With its low melting point of 420° C (788° F), unalloyed zinc has poor engineeringproperties, but in alloyed form the metal is used extensively. The addition of up to 45 percentzinc to copper forms the series of brass alloys, while, with additions of aluminum, zinc formscommercially significant pressure die-casting and gravity-casting alloys. Primary uses for zincinclude 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 highlydependent upon zinc’s resistance to corrosion and its light weight characteristics. The annualproduction volume has remained constant since the 1980s. India is a leading exporter of zincconcentrates as well as the world’s largest importer of refined zinc.

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2.2 Properties of Zinc (metallic) at 293K

TABLE 2.1:-Properties of ZincMaterial Quantity

1. Melting Point 693K

2. Specific Latent Heat of Fusion 10 J/ Kg3. Specific heat capacity 38510 J/ Kg4. Linear expansivity 31/k

5. Thermal conductivity 111 W/m/k

6. Electric Sensitivity 5.9ohm-meter7. 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-containingfeed material such as zinc-containing concentrates or zinc oxides. This is the process ofconverting zinc concentrates (ores that contain zinc) into pure zinc.

The most common zinc concentrate processed is zinc sulfide, which is obtained byconcentrating 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 zincproduced 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

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pyrometallurgical process (overall more energy-efficient, higher recovery rates, easier toautomate hence higher productivity, etc.).

In the most common hydrometallurgical process for zinc manufacturing, the ore isleached with sulfuric acid to extract the Zinc. These processes can operate at atmosphericpressure or as pressure leach circuits. Zinc is recovered from solution by electrowinning, aprocess similar to electrolytic refining. The process most commonly used for low-grade depositsis heap leaching. Imperial smelting is also used for zinc ores.

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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 sequentialprocess 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, resultingin so-called calcine;Step 3: Leaching transforms the zinc contained in the calcine into a solution such as zincsulphate, 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 meansof electrolysis leaving a zinc metal deposit (zinc cathodes);Step 6: Melting and casting: melting of the zinc cathodes typically using electrical inductionfurnaces and casting the molten zinc into ingots.

Additional steps can be added to the process transforming the pure zinc (typically99.995% pure zinc known as Special High Grade (’SHG’)) into various types of alloys or othermarketable products.

3.2 Raw Material Handling Section(RMH)

Smelters use a mix of zinc-containing concentrates or secondary zinc material such aszinc oxides as feed to their roasting plant. Debari smelter is characterized by a relatively highinput of secondary materials. Smelters located inland receive their feed by road, rail or canaldepending on site-specific logistical factors and the type of feedstock (eg, secondary zinc oxidescome in smaller volumes and are typically transported by road). Concentrate deliveries typicallyhappen in large batches (eg, 5,000 to 10,000 tonnes).

Hindustan Zinc Smelter Debari is strategically located close to the Zawar mines thatserves as a global concentrate hub and provides for an extensive multi-modal logistical

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infrastructure. It is 14 kms away from Udaipur well connected by rail, road and air. Most zincsmelters use several sources of concentrates. These different materials are blended to obtain anoptimal mix of feedstock for the roasting process.

The zinc concentrate is delivered by trucks and is discharged into twounderground bins. Several belt conveyors transport the concentrate from the undergroundbins to the concentrate storage hall. A Pay loader feeds the materials into two hoppers. Bymeans of discharging and transport belt conveyors including an over-belt magnetic separator, avibro 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 feedmaterial before the vibro screen. For moistening of the concentrate several spraying nozzles areforeseen in the concentrate storage hall, as well as on the conveying belt before theconcentrate feed bin.

Blended feed from the concentrate feed bin is discharged onto a discharge beltconveyor, which in turn discharges onto a rotary table feeder. The roaster is fed then bytwo slinger belts.

3.3 ROASTING PLANT

In Roasting Plant, oxidation of zinc sulfide concentrates at high temperatures into animpure 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 roastingtemperatures around 10% of the zinc reacts with the iron impurities of the zinc sulfideconcentrates to form zinc ferrite. A byproduct of roasting is sulfur dioxide, which is furtherprocessed into sulfuric acid. Zinc oxide obtained is then sent in leaching plant for furtherprocessing.

Firstly, zinc sulphide after ore concentration process is sent to furnace .There at 920-950degree temperature zinc sulphide combustion takes place producing calcine. Further oxidation ofSO2 maintains the temperature range, and then SO3 is sent to acid plant for production ofsulphuric acid. HZL, Dariba has 2 roaster units R4 and R5. Zinc Sulphide Concentrate isintroduced directly into the roaster and roasted in a turbulent layer, largely consisting of roastedmaterial especially Zinc Oxide (ZnO). This layer has been heated to ignition temperature by theepreheating device. The desired reaction is maintained by an exothermic reaction of SulfideConcentrate and air in the turbulent layer.

The surplus reaction heat is taken out of the roaster bed by cooling elements installed inthe turbulent layer in the form of evaporator heating surfaces connected to the Waste Heat

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Boiler. The waste heat is further utilized to generate electricity of about 9.6MW which is used inthe 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 atthe sulphuric acid plant resulting in marketable sulphuric acid.

For the treatment of Sulphur Dioxide (SO2) in the roasting off-gas, by passing throughthe Gas Drying Tower, the Sulphur Dioxide (SO2), cooled and saturated with water vapor, comesin direct contact with concentrated acid. Sulfuric Acid (H2SO4) of this concentration is veryhygroscopic (absorbs waters) and the gas is practically free from water vapor after leaving theDrying Tower.

After the Drying Tower, the Sulphur Dioxide (SO2) has to be converted into SulfurTrioxide (SO3) to allow the production of Sulphuric Acid (H2SO4) according to the followingreactions:

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 ispassed through scrubbing tower, which has sedimentation tank and SO2 stripper & wet gasprecipitator. In presence of V2O5, oleum is formed which further gives H2SO4.

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3.4 LEACHING PLANT

The calcine is first leached in a neutral or slightly acidic solution (of sulphuric acid) inorder to leach the zinc out of the zinc oxide. The remaining calcine is then leached in strongsulfuric acid to leach the rest of the zinc out of the zinc oxide and zinc ferrite. The result of thisprocess 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 anintermediate step, in the form of jarosite. Jarosite is a waste therefore it is sent to Effluenttreatment plant. There is still cadmium, copper, arsenic, antimony, cobalt, germanium andnickel 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 building2. Jarosite precipitation building3. Purification building4. 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. Afterpurification, concentrations of these impurities are limited to less than 0.02 milligram per literPurification is usually conducted in large agitated tanks called Pachukas. The process takes placeat temperatures ranging from 40 to 85 °C (104 to 185 °F). The zinc sulfate solution must be verypure for electrolysis to be at all efficient. Impurities can change the decomposition voltageenough 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 bedswhere the zinc sulphate goes with the solution as it is soluble. This ZnSO4 solution has pH of 5which is then sent to electrolysis process. Zinc calcine, leach solutions and cell house acid aremixed in 11 agitated tanks which are controlled to varied pH, from 2 to 5, by additions of cellhouse acid or calcine. Continuous pH monitoring is facilitated by submerged pH cells incontrolled tanks.

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After leaching, the acid leach slurry is distributed to four 24-m thickeners where the leachresidues are separated from the clear zinc sulphate solution. The residues are filtered and washedbefore 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 purificationcircuit. Solution flow rate from this circuit is approximately 450 m/h. An increase in acidconcentration from 3 to 4% resulted in a 5% increase in recovery. The higher the concentrationof 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 aspecialized form of electrolysis. The process works by passing an electric current through thesolution 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-coatedcathodes are removed and rinsed, and the zinc is mechanically stripped from the aluminumplates.

A portion of the electrical energy is converted into heat, which increases the temperatureof the electrolyte. A portion of the electrolyte is continuously circulated through the coolingtowers both to cool and concentrate the electrolyte through evaporation of water. The cooled andconcentrated electrolyte is then recycled to the cells. This process accounts for approximatelyone-third of all the energy usage when smelting zinc.

Zinc contained in the purified Zinc Sulphate (ZnSO4) is recovered as metal in theElectrolysis Plant. Zinc Electro-Winning is a method of depositing Zinc Metal (Zn) on thesurface of Aluminum Sheet (Al) in cell by passing electric current through the cell. The thicknessof Zinc Plating depends on the time spent in the electrolysis cell, the amount of current, and thechemical composition of the cell.

The electrolysis cells are arranged in one electrical circuit of two rows of cells each. Thecircuit 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 ineach cell is in parallel.Principle electrolysis reaction:

ZnSO4 + electricity →Zn++ + SO4-- & Zn++ + 2e- →Zn

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3.6 MELTING AND CASTING

Cathode melting will be carried out in two identical electric induction furnaces. Thefurnaces 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 ratethat molten metal is removed (pumped) from the furnace.

Each furnace is equipped with a still well equipped with one or more molten metalpumps. The pump delivers molten zinc to a launder system feeding the casting machine. Eachfurnace feeds a single casting line. In addition, provision is made to pump molten zinc from oneof the furnaces to the zinc dust production plant.

In addition to cathode bundles, the furnace chutes are designed to receive metallic zincfrom the dross separation plant and metallic zinc “skims” from the casting machines. Thismaterial is fed to any chute (normally one dedicated chute) from forklift transported to hoppersthat have been raised to the charging floor by the freight elevator (lift). The required amount ofnh4cl to enhance the melting of this material is manually added to each hopper prior to dumpingin the charge chute.

When cathode zinc is melted, a layer of dross comprised mainly of zinc oxide entrainedmolten zinc droplets is produced. This dross must be removed from the furnace once in every 24hours 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 spreadinga 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 forklifttote bin. During the drossing process, the furnace is operated under conditions of increasedventilation to contain the fumes and dust that are generated by the agitation and dross removalprocesses. The totes of furnace dross are transported by lift truck to the dross cooling area, toawait treatment in the dross separation plan

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Chapter 4

Project WorkTransformer

A transformer is an electrical device that transfers electrical energy between two ormore circuits through electromagnetic induction. Commonly, transformers are used to increaseor decrease the voltages of alternating current in electric power applications.

A varying current in the transformer's primary winding creates a varying magnetic flux inthe transformer core and a varying magnetic field impinging on the transformer's secondarywinding. This varying magnetic field at the secondary winding induces a varying electromotiveforce (EMF) or voltage in the secondary winding. Making use of Faraday's Law in conjunctionwith high magnetic permeability core properties, transformers can thus be designed to efficientlychange AC voltages from one voltage level to another within power networks.

Since the invention of the first constant potential transformer in 1885, transformers havebecome essential for the AC transmission , distribution, and utilization of electrical energy. Awide range of transformer designs is encountered in electronic and electric power applications.

4.1Basic principles

Ideal transformer

By law of Conservation of Energy, apparent , real and reactive power are each conservedin the input & output

For simplification or approximation purposes, it is very common to analyze thetransformer as an ideal transformer model as presented in the two images. An ideal transformeris a theoretical, linear transformer that is lossless and perfectly coupled; that is, there areno energy losses and flux is completely confined within the magnetic core. Perfect couplingimplies infinitely high core magnetic permeability and winding inductances and zeronet magnetomotive force.

Fig 4.1:-Ideal transformer connected with source VP on primary and loadimpedance ZL on secondary,

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A varying current in the transformer's primary winding creates a varying magnetic flux inthe core and a varying magnetic field impinging on the secondary winding. This varyingmagnetic field at the secondary induces a varying electromotive force (EMF) or voltage in thesecondary winding. The primary and secondary windings are wrapped around a core of infinitelyhigh magnetic permeability so that all of the magnetic flux passes through both the primary andsecondary windings. With a voltage source connected to the primary winding andload impedance connected to the secondary winding, the transformer currents flow in theindicated directions.

Fig 4.2:-Ideal transformer and induction law

According to Faraday's law of induction, since the same magnetic flux passes throughboth the primary and secondary windings in an ideal transformer, a voltage is induced in eachwinding, according to eq. (1) in the secondary winding case, according to eq. (2) in the primarywinding case.This is in accordance withLenz's law, which states that induction of EMF alwaysopposes development of any such change in magnetic field.

The transformer winding voltage ratio is thus shown to be directly proportional to thewinding turns ratio according to eq. (3).

According to the law of Conservation of Energy, any load impedance connected to theideal transformer' secondary winding results in conservation of apparent, real and reactive powerconsistent with eq. (4).

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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 terminalmarkings to define the relative polarity of transformer windings. Positively increasinginstantaneous current entering the primary winding's dot end induces positive polarity voltage atthe secondary winding's dot end.

Real transformer

Deviations from ideal

The ideal transformer model neglects the following basic linear aspects in realtransformers.

Core losses, collectively called magnetizing current losses, consist of

Hysteresis losses due to nonlinear application of the voltage applied in the transformercore, and

Eddy current losses due to joule heating in the core that are proportional to the square ofthe transformer's applied voltage.

Whereas windings in the ideal model have no resistances and infinite inductances, thewindings 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.

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Fig 4.4:- Leakage flux of a transformer

Leakage flux

The ideal transformer model assumes that all flux generated by the primary winding linksall the turns of every winding, including itself. In practice, some flux traverses paths that take itoutside the windings.]Such flux is termed leakage flux, and results in leakageinductance in series with the mutually coupled transformer windings. Leakage flux results inenergy being alternately stored in and discharged from the magnetic fields with each cycle of thepower supply. It is not directly a power loss, but results in inferior voltage regulation, causing thesecondary voltage not to be directly proportional to the primary voltage, particularly under heavyload.Transformers are therefore normally designed to have very low leakage inductance.

In some applications increased leakage is desired, and long magnetic paths, air gaps, ormagnetic bypass shunts may deliberately be introduced in a transformer design to limit the short-circuit current it will supply]Leaky transformers may be used to supply loads thatexhibit negative resistance, such as electric arcs, mercury vapor lamps, and neon signs or forsafely handling loads that become periodically short-circuited such as electric arc welders.

Air gaps are also used to keep a transformer from saturating, especially audio-frequencytransformers in circuits that have a DC component flowing in the windings.

Knowledge of leakage inductance is also useful when transformers are operated inparallel. It can be shown that if the percent impedance and associated winding leakage reactance-to-resistance (X/R) ratio of two transformers were hypothetically exactly the same, thetransformers would share power in proportion to their respective volt-ampere ratings (e.g.500 kVA unit in parallel with 1,000 kVA unit, the larger unit would carry twice the current).However, the impedance tolerances of commercial transformers are significant. Also, the Zimpedance and X/R ratio of different capacity transformers tends to vary, corresponding1,000 kVA and 500 kVA units' values being, to illustrate, respectively, Z ≈ 5.75%, X/R ≈ 3.75and Z ≈ 5%, X/R ≈ 4.75.

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Equivalent circuit

Referring to the diagram, a practical transformer's physical behavior may be representedby an equivalent circuit model, which can incorporate an ideal transformer.

Winding joule losses and leakage reactances are represented by the following series loopimpedances of the model:

Primary winding: RP, XP

Secondary winding: RS, XS.

In normal course of circuit equivalence transformation, RS and XS are in practice usuallyreferred 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 areproportional to the square of the core flux for operation at a given frequency. The finitepermeability 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-lineardue to saturation effects. However, all impedances of the equivalent circuit shown are bydefinition linear and such non-linearity effects are not typically reflected in transformerequivalent 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 basedon linearity assumptions, retains a number of approximations.]Analysis may be simplified byassuming that magnetizing branch impedance is relatively high and relocating the branch to the

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left of the primary impedances. This introduces error but allows combination of primary andreferred secondary resistances and reactances by simple summation as two series impedances.

Transformer equivalent circuit impedance and transformer ratio parameters can bederived from the following tests: open-circuit test,[m] short-circuit test, winding resistance test,and transformer ratio test.

4.2 Basic transformer parameters and construction

Fig 4.6:-Power transformer over-excitation condition caused by decreased frequency; flux(green), iron core's magnetic characteristics (red) and magnetizing current (blue).

Effect of frequency

Transformer universal EMF equation

If the flux in the core is purely sinusoidal, the relationship for either winding betweenits rms voltage Erms of the winding, and the supply frequency f, number of turns N, core cross-sectional area a in m2 and peak magnetic flux density Bpeak in Wb/m2 or T (tesla) is given by theuniversal EMF equation:

If the flux does not contain even harmonics the following equation can be used for half-cycle average voltage Eavg of any waveshape:

By Faraday's Law of induction shown in eq. (1) and (2), transformer EMFs varyaccording to the derivative of flux with respect to time. The ideal transformer's core behaveslinearly with time for any non-zero frequency. Flux in a real transformer's core behaves non-

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finite linear range resulting in magnetic saturation associated with increasingly large magnetizingcurrent, which eventually leads to transformer overheating.

The EMF of a transformer at a given flux density increases with frequency. By operatingathigher frequencies, transformers can be physically more compact because a given core is ableto transfer more power without reaching saturation and fewer turns are needed to ac achieve thesame impedance. However, properties such as linearly in relation to magnetization current as theinstantaneous flux increases beyond a core loss and conductor skin effect also increase withfrequency. Aircraft and military equipment employ 400 Hz power supplies which reduce coreand winding weight.Conversely, frequencies used for some railway electrification systems weremuch lower (e.g. 16.7 Hz and 25 Hz) than normal utility frequencies (50–60 Hz) for historicalreasons concerned mainly with the limitations of early electric traction motors. As such, thetransformers used to step-down the high over-head line voltages (e.g. 15 kV) were much heavierfor 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 intendedwill lead to reduced magnetizing current. At a lower frequency, the magnetizing current willincrease. Operation of a transformer at other than its design frequency may require assessment ofvoltages, losses, and cooling to establish if safe operation is practical. For example, transformersmay need to be equipped with 'volts per hertz' over-excitation relays to protect the transformerfrom 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 converterequipment and traction transformers have to accommodate different input frequencies andvoltage (ranging from as high as 50 Hz down to 16.7 Hz and rated up to 25 kV) while beingsuitable for multiple AC asynchronous motor and DC converters and motors with varyingharmonics mitigation filtering requirements.

Large power transformers are vulnerable to insulation failure due to transient voltageswith high-frequency components, such as caused in switching or by lightning.

Energy losses

Real transformer energy losses are dominated by winding resistance joule and corelosses. Transformers' efficiency tends to improve with increasing transformer capacity. Theefficiency 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 ofno-load loss, full-load loss, half-load loss, and so on. Hysteresis and eddy current losses areconstant at all load levels and dominate overwhelmingly without load, while variablewinding joule losses dominating increasingly as load increases. The no-load loss can besignificant, 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

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steel, or even amorphous steel for the core and thicker wire, increasing initial cost. The choice ofconstruction represents a trade-off between initial cost and operating cost.

Transformer losses arise from:

Winding joule lossesCurrent 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 toincrease.

Core lossesHysteresis losses

Each time the magnetic field is reversed, a small amount of energy is lost dueto hysteresis within the core.

where, f is the frequency, η is the hysteresis coefficient and βmax is the maximum fluxdensity, the empirical exponent of which varies from about 1.4 to 1.8 but is often given as 1.6 foriron.

Eddy current lossesFerromagnetic 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 thereforecirculate within the core in a plane normal to the flux, and are responsible for resistive heating ofthe core material. The eddy current loss is a complex function of the square of supply frequencyand inverse square of the material thickness.]Eddy current losses can be reduced by making thecore of a stack of plates electrically insulated from each other, rather than a solid block; alltransformers operating at low frequencies use laminated or similar cores.

Magnetostriction related transformer humMagnetic 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 asmagnetostriction, the frictional energy of which produces an audible noise knownas mainshum or transformerhum]Thetransformer hum is especially objectionable in transformerssupplied at power frequencies and in high-frequency flyback transformers associated with PALsystem CRTs.

Stray lossesLeakage 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 thatintercepts nearby conductive materials such as the transformer's support structure will give rise

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to eddy currents and be converted to heat. There are also radiative losses due to the oscillatingmagnetic field but these are usually small.

fig 4.7:-Core form = core type; shell form = shell type

Mechanical vibration and audible noise transmissionIn addition to magnetostriction, the alternating magnetic field causes fluctuating forces

between the primary and secondary windings. This energy incites vibration transmission ininterconnected metalwork, thus amplifying audible transformer hum.

Core form and shell form transformers

Closed-core transformers are constructed in 'core form' or 'shell form'. When windingssurround the core, the transformer is core form; when windings are surrounded by the core, thetransformer is shell form. Shell form design may be more prevalent than core form design fordistribution transformer applications due to the relative ease in stacking the core around windingcoils. Core form design tends to, as a general rule, be more economical, and therefore moreprevalent, than shell form design for high voltage power transformer applications at the lowerend of their voltage and power rating ranges (less than or equal to, nominally, 230 kV or75 MVA). At higher voltage and power ratings, shell form transformers tend to be moreprevalent.Shell form design tends to be preferred for extra-high voltage and higher MVAapplications because, though more labor-intensive to manufacture, shell form transformers arecharacterized as having inherently better kVA-to-weight ratio, better short-circuit strengthcharacteristics 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 highpermeability silicon steel.The steel has a permeability many times that of free space and the corethus serves to greatly reduce the magnetizing current and confine the flux to a path which closelycouples the windings. Early transformer developers soon realized that cores constructed from

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solid iron resulted in prohibitive eddy current losses, and their designs mitigated this effect withcores consisting of bundles of insulated iron wires. Later designs constructed the core by

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 lamination isinsulated from its neighbors by a thin non-conducting layer of insulation.The universaltransformer 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 encloselittle flux, and so reduce their magnitude. Thinner laminations reduce losses,]but are morelaborious and expensive to construct.[Thin laminations are generally used on high-frequencytransformers, with some of very thin steel laminations able to operate up to 10 kHz.

One common design of laminated core is made from interleaved stacks of E-shaped steelsheets capped with I-shaped pieces, leading to its name of 'E-I transformer'.[55] Such a designtends to exhibit more losses, but is very economical to manufacture. The cut-core or C-core type

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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 halvestogether with a steel strap. They have the advantage that the flux is always oriented parallel tothe metal grains, reducing reluctance.

Fig 4.10:-Laminating the core greatly reduces eddy- current losses

A steel core's remanence means that it retains a static magnetic field when power isremoved. When power is then reapplied, the residual field will cause a high inrush current untilthe effect of the remaining magnetism is reduced, usually after a few cycles of the applied ACwaveform. Overcurrent protection devices such as fuses must be selected to allow this harmlessinrush to pass. On transformers connected to long, overhead power transmission lines, inducedcurrents due to geomagnetic disturbances duringsolar storms can cause saturation of the core andoperation of transformer protection devices.

Distribution transformers can achieve low no-load losses by using cores made with low-loss high-permeability silicon steel or amorphous (non-crystalline) metal alloy. The higher initialcost of the core material is offset over the life of the transformer by its lower losses at light load.

Solid cores

Powdered iron cores are used in circuits such as switch-mode power supplies that operateabove mains frequencies and up to a few tens of kilohertz. These materials combine highmagnetic permeability with high bulk electrical resistivity. For frequencies extending beyondthe VHF band, cores made from non-conductive magnetic ceramic materials called ferrites arecommon. Some radio-frequency transformers also have movable cores (sometimes called 'slugs')which allow adjustment of the coupling coefficient (andbandwidth) of tuned radio-frequencycircuits.

Toroidal cores

Toroidal transformers are built around a ring-shaped core, which, depending on operatingfrequency, is made from a long strip of silicon steel or permalloy wound into a coil, powderediron, or ferrite. A strip construction ensures that the grain boundaries are optimally aligned,

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improving the transformer's efficiency by reducing the core's reluctance. The closed ring shapeeliminates air gaps inherent in the construction of an E-I core.The cross-section of the ring isusually square or rectangular, but more expensive cores with circular cross-sections are alsoavailable. The primary and secondary coils are often wound concentrically to cover the entiresurface of the core. This minimizes the length of wire needed and provides screening tominimize 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 asimilar 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 efficientin standby circuits), single-bolt mounting, and greater choice of shapes. The main disadvantagesare higher cost and limited power capacity (see Classification parameters below). Because of thelack of a residual gap in the magnetic path, toroidal transformers also tend to exhibit higherinrush current, compared to laminated E-I types.

Ferrite toroidal cores are used at higher frequencies, typically between a few tens ofkilohertz to hundreds of megahertz, to reduce losses, physical size, and weight of inductivecomponents. 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 coreaperture each time a single turn is added to the coil. As a consequence, toroidal transformersrated more than a few kVA are uncommon. Small distribution transformers may achieve some ofthe benefits of a toroidal core by splitting it and forcing it open, then inserting a bobbincontaining primary and secondary windings.

Air

A physical core is not an absolute requisite and a functioning transformer can beproduced 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 isinevitably high, resulting in very poor regulation, and so such designs are unsuitable for use in

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power distribution. They have however very highbandwidth, and are frequently employed inradio-frequency applications, for which a satisfactory coupling coefficient is maintained bycarefully overlapping the primary and secondary windings. They're also used for resonanttransformers such as Tesla coils where they can achieve reasonably low loss in spite of the highleakage 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 allcases the individual turns must be electrically insulated from each other to ensure that the currenttravels throughout every turn. For small power and signal transformers, in which currents are lowand the potential difference between adjacent turns is small, the coils are often woundfrom enamelled magnet wire, such as Formvar wire. Larger power transformers operating at highvoltages may be wound with copper rectangular strip conductors insulated by oil-impregnatedpaper and blocks of pressboard.[62]

White: insulator. Green spiral: Grain oriented silicon steel. Black: Primary winding madeofoxygen-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 capacitancebetween all ends of both windings. Since most cores are at least moderately conductive they alsoneed insulation. Bottom: Lowest capacitance for one end of the secondary winding needed forlow-power high-voltage transformers. Bottom left: Reduction of leakage inductance would leadto increase of capacitance.

High-frequency transformers operating in the tens to hundreds of kilohertz often havewindings made of braided Litz wire to minimize the skin-effect and proximity effectlosses.] Large power transformers use multiple-stranded conductors as well, since even at lowpower frequencies non-uniform distribution of current would otherwise exist in high currentwindings. Each stand is insulated, and the strands are arranged so that at certain points in thewinding, or throughout the whole winding, each portion occupies different relative positions in

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

Fig 4.13:-Cut view through transformer windings.

The windings of signal transformers minimize leakage inductance and stray capacitanceto improve high-frequency response. Coils are split into sections, and those sections interleavedbetween the sections of the other winding.

Power-frequency transformers may have taps at intermediate points on the winding,usually on the higher voltage winding side, for voltage adjustment. Taps may be manuallyreconnected, 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 suchas arc furnacetransformers, or for automatic voltage regulators for sensitive loads. Audio-frequency transformers, used for the distribution of audio to public address loudspeakers, havetaps to allow adjustment of impedance to each speaker. A center-tapped transformer is often usedin the output stage of an audio power amplifier in a push-pull circuit. Modulation transformersin AM transmitters are very similar.

Dry-type transformer winding insulation systems can be either of standard open-wound'dip-and-bake' construction or of higher quality designs that include vacuum pressureimpregnation (VPI), vacuum pressure encapsulation (VPE), and cast coilencapsulationprocesses.]In the VPI process, a combination of heat, vacuum and pressure is usedto thoroughly seal, bind, and eliminate entrained air voids in the winding polyester resininsulation coat layer, thus increasing resistance to corona. VPE windings are similar to VPI

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windings but provide more protection against environmental effects, such as from water, dirt orcorrosive 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 leveland 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 lifeexpectancy of insulation in all electric machines including all transformers is halved for aboutevery 7 °C to 10 °C increase in operating temperature, this life expectancy halving rule holdingmore narrowly when the increase is between about 7 °C to 8 °C in the case of transformerwinding cellulose insulation.

Small dry-type and liquid-immersed transformers are often self-cooled by naturalconvection and radiation heat dissipation. As power ratings increase, transformers are oftencooled by forced-air cooling, forced-oil cooling, water-cooling, or combinations of these. Largetransformers are filled with transformer oil that both cools and insulates thewindings.Transformer oil is a highly refined mineral oil that cools the windings and insulation bycirculating within the transformer tank. The mineral oil and paper insulation system has beenextensively studied and used for more than 100 years. It is estimated that 50% of powertransformers will survive 50 years of use, that the average age of failure of power transformers isabout 10 to 15 years, and that about 30% of power transformer failures are due to insulation andoverloading failures. Prolonged operation at elevated temperature degrades insulating propertiesof winding insulation and dielectric coolant, which not only shortens transformer life but canultimately lead to catastrophic transformer failure. With a great body of empirical study as aguide, transformer oil testing including dissolved gas analysis provides valuable maintenanceinformation. This underlines the need to monitor, model, forecast and manage oil and windingconductor insulation temperature conditions under varying, possibly difficult, power loadingconditions.

Building regulations in many jurisdictions require indoor liquid-filled transformers toeither use dielectric fluids that are less flammable than oil, or be installed in fire-resistantrooms. Air-cooled dry transformers can be more economical where they eliminate the cost of afire-resistant transformer room.

The tank of liquid filled transformers often has radiators through which the liquid coolantcirculates 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 ofgas accumulation due to internal arcing, is used to either alarm or de-energize thetransformer.] Oil-immersed transformer installations usually include fire protection measuressuch as walls, oil containment, and fire-suppression sprinkler systems.

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Polychlorinated biphenyls have properties that once favored their use as a dielectriccoolant, though concerns over their environmental persistence led to a widespread ban on theiruse.[75] Today, non-toxic, stable silicone-based oils, or fluorinated hydrocarbons may be usedwhere the expense of a fire-resistant liquid offsets additional building cost for a transformervault.PCBs for new equipment were banned in 1981 and in 2000 for use in existing equipment inUnited Kingdom Legislation enacted in Canada between 1977 and 1985 essentially bans PCBuse in transformers manufactured in or imported into the country after 1980, the maximumallowable 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 builtwith liquid nitrogen or helium cooled superconducting windings, which eliminates windinglosses without affecting core losses.

Insulation drying

Construction of oil-filled transformers requires that the insulation covering the windingsbe thoroughly dried of residual moisture before the oil is introduced. Drying is carried out at thefactory, and may also be required as a field service. Drying may be done by circulating hot airaround the core, or by vapor-phase drying (VPD) where an evaporated solvent transfers heat bycondensation on the coil and core.

For small transformers, resistance heating by injection of current into the windings isused. The heating can be controlled very well, and it is energy efficient. The method is calledlow-frequency heating (LFH) since the current used is at a much lower frequency than that of thepower 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 ofolder transformers.

Bushings

Larger transformers are provided with high-voltage insulated bushings made of polymersor porcelain. A large bushing can be a complex structure since it must provide careful control ofthe 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.

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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 andcurrent 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 interconnectedstar;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 inconstruction or electrical properties for certain installation requirements or circuit conditions.

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

Capacitor voltage transformer: Transformer in which capacitor divider is used toreduce high voltage before application to the primary winding.

Distribution transformer, power transformer: International standards make adistinction in terms of distribution transformers being used to distribute energy fromtransmission lines and networks for local consumption and power transformers beingused to transfer electric energy between the generator and distribution primary circuits.

Phase angle regulating transformer: A specialised transformer used to control the flowof real power on three-phase electricity transmission networks.

Scott-T transformer: Transformer used for phase transformation from three-phaseto 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.

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Instrument transformer: Potential or current transformer used to accurately and safelyrepresent voltage, current or phase position of high voltage or high power circuits.

Pulse transformer: Specialized small-signal transformer used to transmit digitalsignaling while providing electrical isolation, commonly used in Ethernet computernetworks 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 electricalenergy over long distances through wires. Wires have resistance which loses energy throughjoule heating at a rate corresponding to square of the current. By transforming power to a highervoltage transformers enable economical transmission of power and distribution. Consequently,transformers have shaped the electricity supply industry, permitting generation to be locatedremotely from points of demand.[92] All but a tiny fraction of the world's electrical power haspassed 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 transformeralso electrically isolates the end user from contact with the supply voltage.

Signal and audio transformers are used to couple stages of amplifiers and to matchdevices such as microphones and record players to the input of amplifiers. Audio transformersallowed 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 balancedvoltages to ground, such as between external cables and internal circuits.

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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, wasdiscovered independently by Michael Faraday in 1831 and Joseph Henry in 1832.Faraday wasthe first to publish the results of his experiments and thus receive credit for the discovery.Therelationship between EMF and magnetic flux is an equation now known as Faraday's law ofinduction:

where is the magnitude of the EMF in Volts and ΦB is the magnetic flux through the circuitin webers.

Faraday performed the first experiments on induction between coils of wire, includingwinding a pair of coils around an iron ring, thus creating the first toroidal closed-coretransformer.] However he only applied individual pulses of current to his transformer, and neverdiscovered the relation between the turns ratio and EMF in the windings.

Fig4.16:- Induction coil, 1900, Bremerhaven, Germany

Induction coils

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4.17:-Faraday's ring transformer

The first type of transformer to see wide use was the induction coil, invented byRev. Nicholas Callan of Maynooth College, Ireland in 1836. He was one of the first researchersto realize the more turns the secondary winding has in relation to the primary winding, the largerthe 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) ratherthan AC, induction coils relied upon vibrating electrical contacts that regularly interrupted thecurrent in the primary to create the flux changes necessary for induction. Between the 1830s andthe 1870s, efforts to build better induction coils, mostly by trial and error, slowly revealed thebasic principles of transformers.

First alternating current transformers

By the 1870s, efficient generators producing alternating current (AC) were available, andit was found AC could power an induction coil directly, without an interrupter.

In 1876, Russian engineer Pavel Yablochkov invented.[ a lighting system based on a setof induction coils where the primary windings were connected to a source of AC. The secondarywindings could be connected to several 'electric candles' (arc lamps) of his own design.The coilsYablochkov employed functioned essentially as transformers.

In 1878, the Ganz factory, Budapest, Hungary, began manufacturing equipment forelectric lighting and, by 1883, had installed over fifty systems in Austria-Hungary. Their ACsystems used arc and incandescent lamps, generators, and other equipment.

Lucien Gaulard and John Dixon Gibbs first exhibited a device with an open iron corecalled a 'secondary generator' in London in 1882, then sold the idea tothe Westinghousecompany in the United States. They also exhibited the invention in Turin, Italyin 1884, where it was adopted for an electric lighting system.However, the efficiency of theiropen-core bipolar apparatus remained very low.

Early series circuit transformer distribution

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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 lowvoltage load was a series circuit. Open-core transformers with a ratio near 1:1 were connectedwith their primaries in series to allow use of a high voltage for transmission while presenting alow voltage to the lamps. The inherent flaw in this method was that turning off a single lamp (orother electric device) affected the voltage supplied to all others on the same circuit. Manyadjustable transformer designs were introduced to compensate for this problematic characteristicof the series circuit, including those employing methods of adjusting the core or bypassing themagnetic flux around part of a coil.Efficient, practical transformer designs did not appear untilthe 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 whichthey have remained dominant ever since.

Fig4.18:-Shell form transformer.

Fig4.19:-Core form, front; shell form, back.

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Fig4.20:-Stanley's 1886 design for adjustable gap open-core induction coils

Closed-core transformers and parallel power distribution

In the autumn of 1884, Károly Zipernowsky, Ottó Bláthy and Miksa Déri (ZBD), threeengineers associated with the Ganz factory, had determined that open-core devices wereimpracticable, as they were incapable of reliably regulating voltage. In their joint 1885 patentapplications for novel transformers (later called ZBD transformers), they described two designswith closed magnetic circuits where copper windings were either a) wound around iron wire ringcore or b) surrounded by iron wire core.[The two designs were the first application of the twobasic transformer constructions in common use to this day, which can as a class all be termed aseither 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 theworld's first five high-efficiency AC transformers, the first of these units having been shipped onSeptember 16, 1884.]This first unit had been manufactured to the following specifications: 1,400W, 40 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 secondary windings traveledalmost entirely within the confines of the iron core, with no intentional path through air(see Toroidal cores 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 majorinterrelated innovations: one concerning the use of parallel connected, instead of seriesconnected, utilization loads, the other concerning the ability to have high turns ratio transformerssuch that the supply network voltage could be much higher (initially 1,400 to 2,000 V) than thevoltage of utilization loads (100 V initially preferred]When employed in parallel connectedelectric distribution systems, closed-core transformers finally made it technically andeconomically feasible to provide electric power for lighting in homes, businesses and publicspaces. Blaty had suggested the use of closed cores, Zipernowsky had suggested the useof 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 the EMF of anelectric current] although the term had already been in use by 1882.In 1886, the ZBD engineers

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designed, and the Ganz factory supplied electrical equipment for, the world's first powerstation that used AC generators to power a parallel connected common electrical network, thesteam-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 assignedto William Stanley the task of developing a device for commercial use in United States. Stanley'sfirst patented design was for induction coils with single cores of soft iron and adjustable gaps toregulate the EMF present in the secondary winding (see image).This design was first usedcommercially in the US in 1886 but Westinghouse was intent on improving the Stanley design tomake it (unlike the ZBD type) easy and cheap to produce.

s

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CHAPTER-5CONCLUSION

It was just like a dream come true for me to pursue training in Hindustan Zinc ltd. It wasreally 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 practicalexperience under the guidance of learned professionals.

Special thanks for my college and Hindustan Zinc Work .

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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