Vedanta Hindustan zinc training
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About This Presentation
report
Slide Content
1
CHAPTER-1
Company Profile
1.1Vedanta
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 fastestgrowing 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.
1.2Hindustan 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 acquisitionof 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
1.3Zinc Smelter, Debari-Udaipur
Location14 km from Udaipur, Rajasthan, India.Hydrometallurgical Zinc
SmelterCommissioned in 1968 Roast Leach Electrowining Technology with Conversion Process
CHAPTER-1
Company Profile
1.1Vedanta
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 fastestgrowing 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.
1.2Hindustan 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 acquisitionof 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
1.3Zinc Smelter, Debari-Udaipur
Location14 km from Udaipur, Rajasthan, India.Hydrometallurgical Zinc
SmelterCommissioned in 1968 Roast Leach Electrowining Technology with Conversion Process
2
Gone through a series of debottlenecking 88,000 tonnes per annum of ZincCaptive Power
Generation29 MW DG CaptivePower Plant commissioned in 2003CertificationsBEST
4
Certified Integrated Systems ISO 9001:2000, ISO 14001:2004, OHSAS 18001:1999, SA
8000:2001Covered Area (Ha)22.65Total Plant Area (Ha)126
Products Range
a.High Grade Zinc (HG)(25 kgs) &Jumbo (600 kgs)
b.CadmiumPencils(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
Gone through a series of debottlenecking 88,000 tonnes per annum of ZincCaptive Power
Generation29 MW DG CaptivePower Plant commissioned in 2003CertificationsBEST
4
Certified Integrated Systems ISO 9001:2000, ISO 14001:2004, OHSAS 18001:1999, SA
8000:2001Covered Area (Ha)22.65Total Plant Area (Ha)126
Products Range
a.High Grade Zinc (HG)(25 kgs) &Jumbo (600 kgs)
b.CadmiumPencils(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
3
b.Bhel
c.Steel Companies
Process Collaborators:-
a.Krebs Penorrova, FranceLeaching, Purification, Electrolysis
b.Lurgi, GMBH, and GermanyRoaster and gas clearing
c.Auto KumpuFinlandRTP, Wartsila Plant
d.I.S.C., ALLOY,U.K.Zinc dust plant, Allen Power Plant
b.Bhel
c.Steel Companies
Process Collaborators:-
a.Krebs Penorrova, FranceLeaching, Purification, Electrolysis
b.Lurgi, GMBH, and GermanyRoaster and gas clearing
c.Auto KumpuFinlandRTP, Wartsila Plant
d.I.S.C., ALLOY,U.K.Zinc dust plant, Allen Power Plant
4
CHAPTER-2
Zinc (Zn)
2.1Introduction
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 abbreviatedSHG, 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 anda 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, butwhen 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 zinccompanies 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, butin 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 itslight 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.
CHAPTER-2
Zinc (Zn)
2.1Introduction
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 abbreviatedSHG, 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 anda 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, butwhen 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 zinccompanies 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, butin 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 itslight 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.
5
2.2Properties of Zinc(metallic) at 293K
TABLE2.1:-Properties of Zinc
Material Quantity
1.Melting Point693K
2.SpecificLatent Heat of Fusion 10 J/ Kg
3.Specific heat capacity 38510 J/ Kg
4.Linear expansivity 31/k
5.Thermal conductivity 111W/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
2.3Zinc Smelting
Zinc smelting is the process of recovering and refining zinc metal out of zinc-containing
feed material such aszinc-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 iszinc sulfide, which is obtained by
concentratingsphaleriteusing thefroth flotationmethod. 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
2.2Properties of Zinc(metallic) at 293K
TABLE2.1:-Properties of Zinc
Material Quantity
1.Melting Point693K
2.SpecificLatent Heat of Fusion 10 J/ Kg
3.Specific heat capacity 38510 J/ Kg
4.Linear expansivity 31/k
5.Thermal conductivity 111W/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
2.3Zinc Smelting
Zinc smelting is the process of recovering and refining zinc metal out of zinc-containing
feed material such aszinc-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 iszinc sulfide, which is obtained by
concentratingsphaleriteusing thefroth flotationmethod. 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
6
pyrometallurgical process (overall more energy-efficient, higher recovery rates, easier to
automate hence higherproductivity, 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 fromsolution 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.
pyrometallurgical process (overall more energy-efficient, higher recovery rates, easier to
automate hence higherproductivity, 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 fromsolution 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.
7
CHAPTER-3
Zinc Smelter Debari
Zinc Smelter Debarihave following main plants
3.1General 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
marketableproducts.
3.2Raw 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
CHAPTER-3
Zinc Smelter Debari
Zinc Smelter Debarihave following main plants
3.1General 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
marketableproducts.
3.2Raw 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
8
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.
Thezincconcentrateisdeliveredbytrucksandisdischargedintotwo
undergroundbins. Severalbeltconveyorstransporttheconcentratefromtheunderground
binstothe concentrate storagehall.A Pay loader feeds the materialsintotwohoppers. 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.
Drossmaterialfromthecathodemeltingandcastingprocesswillbeaddedtothefeed
material before the vibro screen. For moistening of the concentrate several spraying nozzles are
foreseenintheconcentratestoragehall,aswellasontheconveyingbeltbeforethe
concentrate feed bin.
Blendedfeedfromthe concentratefeedbinisdischargedontoadischargebelt
conveyor, whichinturndischargesontoarotarytablefeeder.Theroasterisfedthenby
twoslinger belts.
3.3ROASTING PLANT
In Roasting Plant, oxidation of zinc sulfide concentrates at high temperatures into an
impure zinc oxide, called "Calcine". Thechemical reactions taking place during the process are:
Approximately 90% of zinc in concentrates is oxidized to zinc oxide, but atthe roasting
temperatures around 10% of the zinc reacts with the iron impurities of the zinc sulfide
concentrates to formzinc ferrite. A byproduct of roasting issulfur dioxide, which is further
processed intosulfuric acid. Zinc oxideobtained 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
SO2maintains the temperature range, and then SO3is 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
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.
Thezincconcentrateisdeliveredbytrucksandisdischargedintotwo
undergroundbins. Severalbeltconveyorstransporttheconcentratefromtheunderground
binstothe concentrate storagehall.A Pay loader feeds the materialsintotwohoppers. 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.
Drossmaterialfromthecathodemeltingandcastingprocesswillbeaddedtothefeed
material before the vibro screen. For moistening of the concentrate several spraying nozzles are
foreseenintheconcentratestoragehall,aswellasontheconveyingbeltbeforethe
concentrate feed bin.
Blendedfeedfromthe concentratefeedbinisdischargedontoadischargebelt
conveyor, whichinturndischargesontoarotarytablefeeder.Theroasterisfedthenby
twoslinger belts.
3.3ROASTING PLANT
In Roasting Plant, oxidation of zinc sulfide concentrates at high temperatures into an
impure zinc oxide, called "Calcine". Thechemical reactions taking place during the process are:
Approximately 90% of zinc in concentrates is oxidized to zinc oxide, but atthe roasting
temperatures around 10% of the zinc reacts with the iron impurities of the zinc sulfide
concentrates to formzinc ferrite. A byproduct of roasting issulfur dioxide, which is further
processed intosulfuric acid. Zinc oxideobtained 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
SO2maintains the temperature range, and then SO3is 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
9
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 SO2at 330 degree Celsius.SO2gas is
passed through scrubbing tower, which has sedimentation tank and SO2stripper & wetgas
precipitator. In presence of V2O5, oleum is formed which further gives H2SO4.
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 SO2at 330 degree Celsius.SO2gas is
passed through scrubbing tower, which has sedimentation tank and SO2stripper & wetgas
precipitator. In presence of V2O5, oleum is formed which further gives H2SO4.
10
3.4LEACHING PLANT
The calcine is first leached in a neutral or slightly acidic solution (of sulphuricacid) 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 ofjarosite. Jarosite is a waste therefore it is sent to Effluent
treatment plant. There is stillcadmium,copper,arsenic,antimony,cobalt,germaniumand
nickelin 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 conductedin large agitated tanks called Pachukas. The process takes place
at temperatures ranging from 40 to 85 °C (104to 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. ThisZnSO4solution 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.
3.4LEACHING PLANT
The calcine is first leached in a neutral or slightly acidic solution (of sulphuricacid) 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 ofjarosite. Jarosite is a waste therefore it is sent to Effluent
treatment plant. There is stillcadmium,copper,arsenic,antimony,cobalt,germaniumand
nickelin 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 conductedin large agitated tanks called Pachukas. The process takes place
at temperatures ranging from 40 to 85 °C (104to 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. ThisZnSO4solution 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.
11
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 andwashed
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 thedissolution of the zinc, so zinc is recovered mostly.
3.5CELL HOUSE
Zinc is extracted from the purified zinc sulfate solution byelectro 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 (aluminumsheets)
and oxygen to form at the anodes. Every 24 to 48 hours, each cell isshut 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 cellby 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 circuitof 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
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 andwashed
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 thedissolution of the zinc, so zinc is recovered mostly.
3.5CELL HOUSE
Zinc is extracted from the purified zinc sulfate solution byelectro 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 (aluminumsheets)
and oxygen to form at the anodes. Every 24 to 48 hours, each cell isshut 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 cellby 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 circuitof 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
12
3.6MELTING 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~24tonnes 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 tothe zinc dust production plant.
In addition to cathodebundles, 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 treatmentin the dross separation plan
3.6MELTING 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~24tonnes 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 tothe zinc dust production plant.
In addition to cathodebundles, 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 treatmentin the dross separation plan
13
Chapter 4
Project Work
Transformer
Atransformeris an electrical devicethat transfers electrical energy between two or
more circuits throughelectromagnetic induction. Commonly, transformers are used to increase
or decreasethe voltages of alternating current in electric power applications.
A varying current in the transformer's primary winding creates a varyingmagnetic fluxin
the transformer core and a varying magnetic field impinging on the transformer's secondary
winding. This varyingmagnetic fieldat the secondary winding induces a varyingelectromotive
force(EMF) or voltage in the secondary winding. Making use ofFaraday's Lawin conjunction
with highmagnetic permeabilitycore properties, transformers can thus be designed to efficiently
changeACvoltages from one voltage level to another within power networks.
Since the invention of the first constantpotentialtransformer in 1885, transformers have
become essential for the ACtransmission,distribution, and utilization of electrical energy.A
wide range of transformer designs is encountered in electronic and electric power applications.
4.1Basic principles
Ideal transformer
By law ofConservation of Energy,apparent ,realandreactivepower are each conserved
in the input & output
For simplification or approximation purposes, it is very common to analyze the
transformer as an ideal transformer modelas presented in the two images. An ideal transformer
is a theoretical,lineartransformer that is lossless and perfectlycoupled; that is, there are
noenergy lossesandfluxis completely confined within themagnetic core. Perfect coupling
implies infinitely high coremagnetic permeabilityand winding inductances and zero
netmagnetomotive force.
Fig 4.1:-Ideal transformer connected with source VPon primary and load
impedance ZLon secondary,
Chapter 4
Project Work
Transformer
Atransformeris an electrical devicethat transfers electrical energy between two or
more circuits throughelectromagnetic induction. Commonly, transformers are used to increase
or decreasethe voltages of alternating current in electric power applications.
A varying current in the transformer's primary winding creates a varyingmagnetic fluxin
the transformer core and a varying magnetic field impinging on the transformer's secondary
winding. This varyingmagnetic fieldat the secondary winding induces a varyingelectromotive
force(EMF) or voltage in the secondary winding. Making use ofFaraday's Lawin conjunction
with highmagnetic permeabilitycore properties, transformers can thus be designed to efficiently
changeACvoltages from one voltage level to another within power networks.
Since the invention of the first constantpotentialtransformer in 1885, transformers have
become essential for the ACtransmission,distribution, and utilization of electrical energy.A
wide range of transformer designs is encountered in electronic and electric power applications.
4.1Basic principles
Ideal transformer
By law ofConservation of Energy,apparent ,realandreactivepower are each conserved
in the input & output
For simplification or approximation purposes, it is very common to analyze the
transformer as an ideal transformer modelas presented in the two images. An ideal transformer
is a theoretical,lineartransformer that is lossless and perfectlycoupled; that is, there are
noenergy lossesandfluxis completely confined within themagnetic core. Perfect coupling
implies infinitely high coremagnetic permeabilityand winding inductances and zero
netmagnetomotive force.
Fig 4.1:-Ideal transformer connected with source VPon primary and load
impedance ZLon secondary,
14
Avarying 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 varyingelectromotive force(EMF) or voltage in the
secondary winding. The primary and secondary windings are wrapped around a core of infinitely
high magnetic permeabilitysothat all of the magnetic flux passes through both the primary and
secondary windings. With avoltage sourceconnected to the primary winding and
loadimpedanceconnected 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 ofConservation 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).
Avarying 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 varyingelectromotive force(EMF) or voltage in the
secondary winding. The primary and secondary windings are wrapped around a core of infinitely
high magnetic permeabilitysothat all of the magnetic flux passes through both the primary and
secondary windings. With avoltage sourceconnected to the primary winding and
loadimpedanceconnected 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 ofConservation 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).
15
Fig 4.3:-Instrument transformer, with polarity dot and X1 markings on LV side terminal
Polarity
Adot conventionis 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
Hysteresislosses due to nonlinear application of the voltage applied in the transformer
core, and
Eddy currentlosses 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 lossesdue toresistance 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.
Fig 4.3:-Instrument transformer, with polarity dot and X1 markings on LV side terminal
Polarity
Adot conventionis 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
Hysteresislosses due to nonlinear application of the voltage applied in the transformer
core, and
Eddy currentlosses 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 lossesdue toresistance 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.
16
Fig 4.4:-Leakage flux of a transformer
Leakage flux
The idealtransformer 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
outside the windings.
]
Such flux is termedleakage flux, and results inleakage
inductanceinserieswith 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 inferiorvoltage 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.
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 theshort-
circuitcurrent it will supply
]
Leaky transformers may be used to supply loads that
exhibitnegative resistance, such aselectric arcs,mercury vapor lamps, andneon signsor for
safely handling loads that become periodically short-circuited such aselectric arc welders.
Air gaps are also used to keep a transformer from saturating, especially audio-frequency
transformers in circuits that have a DC component flowing in the windings.
Knowledge of leakage inductance is also useful when transformers are operated in
parallel. It can be shown that if the percent impedanceand associated winding leakage reactance-
to-resistance (X/R) ratio of two transformers were hypothetically exactly the same, the
transformers would share power in proportion to theirrespective volt-ampere ratings (e.g.
500kVAunit in parallel with 1,000kVA 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
1,000kVA and 500kVA units' values being, to illustrate, respectively,Z≈ 5.75%,X/R≈ 3.75
andZ≈ 5%,X/R≈ 4.75.
Fig 4.4:-Leakage flux of a transformer
Leakage flux
The idealtransformer 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
outside the windings.
]
Such flux is termedleakage flux, and results inleakage
inductanceinserieswith 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 inferiorvoltage 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.
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 theshort-
circuitcurrent it will supply
]
Leaky transformers may be used to supply loads that
exhibitnegative resistance, such aselectric arcs,mercury vapor lamps, andneon signsor for
safely handling loads that become periodically short-circuited such aselectric arc welders.
Air gaps are also used to keep a transformer from saturating, especially audio-frequency
transformers in circuits that have a DC component flowing in the windings.
Knowledge of leakage inductance is also useful when transformers are operated in
parallel. It can be shown that if the percent impedanceand associated winding leakage reactance-
to-resistance (X/R) ratio of two transformers were hypothetically exactly the same, the
transformers would share power in proportion to theirrespective volt-ampere ratings (e.g.
500kVAunit in parallel with 1,000kVA 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
1,000kVA and 500kVA units' values being, to illustrate, respectively,Z≈ 5.75%,X/R≈ 3.75
andZ≈ 5%,X/R≈ 4.75.
17
Equivalent circuit
Referring to the diagram, a practical transformer's physical behavior may be represented
by anequivalent circuitmodel, which can incorporate an ideal transformer.
Winding joule losses and leakage reactancesare 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,RSandXSare in practice usually
referred to the primary side by multiplying these impedances by the turns ratio squared,
(NP/NS)
2
=a
2
.
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.
RCandXMare collectively termed themagnetizingbranchof 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 currentIMtomaintain 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.Withsinusoidalsupply, core flux lags the induced EMF by90°. With open-
circuited secondary winding, magnetizing branch currentI0equals transformer no-load current.
The resulting model, though sometimes termed 'exact' equivalent circuit based
onlinearityassumptions, retains a number ofapproximations.
]
Analysis may be simplified by
assuming that magnetizing branch impedance is relatively high and relocating the branch to the
Equivalent circuit
Referring to the diagram, a practical transformer's physical behavior may be represented
by anequivalent circuitmodel, which can incorporate an ideal transformer.
Winding joule losses and leakage reactancesare 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,RSandXSare in practice usually
referred to the primary side by multiplying these impedances by the turns ratio squared,
(NP/NS)
2
=a
2
.
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.
RCandXMare collectively termed themagnetizingbranchof 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 currentIMtomaintain 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.Withsinusoidalsupply, core flux lags the induced EMF by90°. With open-
circuited secondary winding, magnetizing branch currentI0equals transformer no-load current.
The resulting model, though sometimes termed 'exact' equivalent circuit based
onlinearityassumptions, retains a number ofapproximations.
]
Analysis may be simplified by
assuming that magnetizing branch impedance is relatively high and relocating the branch to the
18
left of the primary impedances. This introduces error but allows combinationof primary and
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,
and transformer ratio test.
4.2Basic transformer parameters and construction
Fig 4.6:-Power transformer over-excitation condition caused by decreasedfrequency; flux
(green), iron core's magneticcharacteristics (red) andmagnetizing current (blue).
Effect of frequency
Transformer universal EMF equation
If the flux in the core is purelysinusoidal, the relationship for either winding between
itsrmsvoltageErmsof the winding, and the supply frequencyf, number of turnsN, core cross-
sectional areaain m
2
and peak magnetic flux densityBpeakin Wb/m
2
or T(tesla) is given by the
universal EMF equation:
If the flux does not contain evenharmonicsthe following equation can be used forhalf-
cycle average voltageEavgof any waveshape:
By Faraday's Law of induction shown in eq. (1) and (2), transformer EMFs vary
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 combinationof primary and
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,
and transformer ratio test.
4.2Basic transformer parameters and construction
Fig 4.6:-Power transformer over-excitation condition caused by decreasedfrequency; flux
(green), iron core's magneticcharacteristics (red) andmagnetizing current (blue).
Effect of frequency
Transformer universal EMF equation
If the flux in the core is purelysinusoidal, the relationship for either winding between
itsrmsvoltageErmsof the winding, and the supply frequencyf, number of turnsN, core cross-
sectional areaain m
2
and peak magnetic flux densityBpeakin Wb/m
2
or T(tesla) is given by the
universal EMF equation:
If the flux does not contain evenharmonicsthe following equation can be used forhalf-
cycle average voltageEavgof any waveshape:
By Faraday's Law of induction shown in eq. (1) and (2), transformer EMFs vary
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-
19
finite linear range resultinginmagnetic saturationassociatedwith 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 isable
to transfer more power without reaching saturation and fewer turns are needed to acachieve the
same impedance. However, properties such aslinearly in relation to magnetization current as the
instantaneous flux increases beyond acore loss and conductorskin effectalso increase with
frequency. Aircraft and military equipment employ 400Hz power supplies which reduce core
and winding weight.Conversely, frequencies used for somerailway electrification systemswere
much lower (e.g. 16.7Hz and 25Hz) than normal utility frequencies (50–60Hz) for historical
reasons concernedmainly with the limitations of earlyelectric traction motors. As such, the
transformers used to step-down the high over-head line voltages (e.g. 15kV) were much heavier
forthe 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-excitationrelaysto protect the transformer
from overvoltage at higher than rated frequency.
One example is in traction transformers used forelectric multiple unitandhigh-
speedtrain 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 50Hz down to 16.7Hz and rated up to 25kV) 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.Hysteresisandeddy currentlosses are
constant at all load levels and dominate overwhelmingly without load, while variable
windingjoule lossesdominating increasingly as load increases. The no-load loss can be
significant, so that even an idle transformer constitutes a drain on the electrical supply.
Designingenergy efficient transformersfor lower loss requires a larger core, good-qualitysilicon
finite linear range resultinginmagnetic saturationassociatedwith 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 isable
to transfer more power without reaching saturation and fewer turns are needed to acachieve the
same impedance. However, properties such aslinearly in relation to magnetization current as the
instantaneous flux increases beyond acore loss and conductorskin effectalso increase with
frequency. Aircraft and military equipment employ 400Hz power supplies which reduce core
and winding weight.Conversely, frequencies used for somerailway electrification systemswere
much lower (e.g. 16.7Hz and 25Hz) than normal utility frequencies (50–60Hz) for historical
reasons concernedmainly with the limitations of earlyelectric traction motors. As such, the
transformers used to step-down the high over-head line voltages (e.g. 15kV) were much heavier
forthe 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-excitationrelaysto protect the transformer
from overvoltage at higher than rated frequency.
One example is in traction transformers used forelectric multiple unitandhigh-
speedtrain 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 50Hz down to 16.7Hz and rated up to 25kV) 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.Hysteresisandeddy currentlosses are
constant at all load levels and dominate overwhelmingly without load, while variable
windingjoule lossesdominating increasingly as load increases. The no-load loss can be
significant, so that even an idle transformer constitutes a drain on the electrical supply.
Designingenergy efficient transformersfor lower loss requires a larger core, good-qualitysilicon
20
steel, or evenamorphous steelfor the core and thicker wire, increasing initial cost. The choice of
construction represents atrade-offbetween initial cost and operating cost.
Transformer losses arise from:
Winding joule losses
Current flowing through a winding's conductor causesjoule heating. As frequency
increases, skin effect andproximity effectcauses the winding's resistanceand, hence, losses to
increase.
Core losses
Hysteresis losses
Each time the magnetic field is reversed, a small amount of energy is lost due
tohysteresiswithin the core.
where,fis the frequency,ηis the hysteresis coefficient andβmaxis the maximum flux
density, the empirical exponent of which varies from about 1.4 to 1.8 butis often given as 1.6 for
iron.
Eddy current losses
Ferromagneticmaterials are also goodconductorsand a core made from such a material
also constitutes a single short-circuited turn throughout its entire length.Eddy currentstherefore
circulate within the core in aplane normal to the flux, and are responsible forresistive heatingof
the core material. The eddy current loss is a complex function of the square of supply frequency
and inversesquare 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
asmainshumortransformerhum
]
Thetransformer hum is especially objectionable in transformers
supplied atpower frequenciesand inhigh-frequencyflyback transformersassociated with PAL
systemCRTs.
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
steel, or evenamorphous steelfor the core and thicker wire, increasing initial cost. The choice of
construction represents atrade-offbetween initial cost and operating cost.
Transformer losses arise from:
Winding joule losses
Current flowing through a winding's conductor causesjoule heating. As frequency
increases, skin effect andproximity effectcauses the winding's resistanceand, hence, losses to
increase.
Core losses
Hysteresis losses
Each time the magnetic field is reversed, a small amount of energy is lost due
tohysteresiswithin the core.
where,fis the frequency,ηis the hysteresis coefficient andβmaxis the maximum flux
density, the empirical exponent of which varies from about 1.4 to 1.8 butis often given as 1.6 for
iron.
Eddy current losses
Ferromagneticmaterials are also goodconductorsand a core made from such a material
also constitutes a single short-circuited turn throughout its entire length.Eddy currentstherefore
circulate within the core in aplane normal to the flux, and are responsible forresistive heatingof
the core material. The eddy current loss is a complex function of the square of supply frequency
and inversesquare 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
asmainshumortransformerhum
]
Thetransformer hum is especially objectionable in transformers
supplied atpower frequenciesand inhigh-frequencyflyback transformersassociated with PAL
systemCRTs.
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
21
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 audiblenoise 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 audibletransformer 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, 230kV or
75MVA). 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.
4.3Construction
Cores
Laminated steel cores
Transformers for use at power or audiofrequencies typically have cores made of high
permeabilitysilicon steel.The steel has a permeability many times that offree spaceand 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
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 audiblenoise 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 audibletransformer 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, 230kV or
75MVA). 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.
4.3Construction
Cores
Laminated steel cores
Transformers for use at power or audiofrequencies typically have cores made of high
permeabilitysilicon steel.The steel has a permeability many times that offree spaceand 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
22
solid iron resulted inprohibitive eddy current losses, and their designs mitigated this effect with
cores 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 is
insulated from its neighbors by a thin non-conducting layer of insulation.The universal
transformer equation indicates a minimum cross-sectional area for the core to avoid saturation.
The effect of laminations is to confine eddy currents to highly elliptical paths that enclose
little flux, and so reduce their magnitude. Thinner laminations reduce losses,
]
but are more
laborious and expensive to construct.
[
Thin laminations are generally used on high-frequency
transformers, with some of very thin steel laminations able to operate up to 10kHz.
One common design of laminated core is made from interleaved stacks ofE-shapedsteel
sheets capped withI-shapedpieces, leading to its name of 'E-I transformer'.
[55]
Such a design
tends to exhibit more losses, but is veryeconomical to manufacture. The cut-core or C-core type
solid iron resulted inprohibitive eddy current losses, and their designs mitigated this effect with
cores 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 is
insulated from its neighbors by a thin non-conducting layer of insulation.The universal
transformer equation indicates a minimum cross-sectional area for the core to avoid saturation.
The effect of laminations is to confine eddy currents to highly elliptical paths that enclose
little flux, and so reduce their magnitude. Thinner laminations reduce losses,
]
but are more
laborious and expensive to construct.
[
Thin laminations are generally used on high-frequency
transformers, with some of very thin steel laminations able to operate up to 10kHz.
One common design of laminated core is made from interleaved stacks ofE-shapedsteel
sheets capped withI-shapedpieces, leading to its name of 'E-I transformer'.
[55]
Such a design
tends to exhibit more losses, but is veryeconomical to manufacture. The cut-core or C-core type
23
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 core greatly reduces eddy-current losses
A steel core'sremanencemeans that it retains a static magnetic field when power is
removed. When power is then reapplied, the residual field will cause a highinrush currentuntil
the effect of the remaining magnetism is reduced, usually after a few cycles of the applied AC
waveform.Overcurrent protection devices such asfusesmust be selected to allow this harmless
inrush to pass. On transformers connected to long, overhead power transmission lines, induced
currents due togeomagnetic disturbancesduringsolar stormscan cause saturation of the core and
operation of transformer protection devices.
Distribution transformers can achieve low no-load losses by using cores made with low-
loss high-permeability silicon steel oramorphous (non-crystalline) metal alloy. The higher initial
cost of thecore material is offset over the life of the transformer by its lower losses at light load.
Solid cores
Powdered iron cores are used in circuits such as switch-mode power supplies that operate
above mains frequencies and up to a few tens of kilohertz.These materials combine high
magnetic permeability with high bulk electricalresistivity. For frequencies extending beyond
theVHF band, cores made from non-conductive magneticceramicmaterials calledferritesare
common.Some radio-frequency transformers also have movable cores (sometimes called 'slugs')
which allow adjustment of thecoupling coefficient(andbandwidth) of tuned radio-frequency
circuits.
Toroidal cores
Toroidal transformers are built around a ring-shaped core, which, depending onoperating
frequency, is made from a long strip ofsilicon steelorpermalloywound into a coil, powdered
iron, orferrite.A strip construction ensures that thegrain boundariesare 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
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 core greatly reduces eddy-current losses
A steel core'sremanencemeans that it retains a static magnetic field when power is
removed. When power is then reapplied, the residual field will cause a highinrush currentuntil
the effect of the remaining magnetism is reduced, usually after a few cycles of the applied AC
waveform.Overcurrent protection devices such asfusesmust be selected to allow this harmless
inrush to pass. On transformers connected to long, overhead power transmission lines, induced
currents due togeomagnetic disturbancesduringsolar stormscan cause saturation of the core and
operation of transformer protection devices.
Distribution transformers can achieve low no-load losses by using cores made with low-
loss high-permeability silicon steel oramorphous (non-crystalline) metal alloy. The higher initial
cost of thecore material is offset over the life of the transformer by its lower losses at light load.
Solid cores
Powdered iron cores are used in circuits such as switch-mode power supplies that operate
above mains frequencies and up to a few tens of kilohertz.These materials combine high
magnetic permeability with high bulk electricalresistivity. For frequencies extending beyond
theVHF band, cores made from non-conductive magneticceramicmaterials calledferritesare
common.Some radio-frequency transformers also have movable cores (sometimes called 'slugs')
which allow adjustment of thecoupling coefficient(andbandwidth) of tuned radio-frequency
circuits.
Toroidal cores
Toroidal transformers are built around a ring-shaped core, which, depending onoperating
frequency, is made from a long strip ofsilicon steelorpermalloywound into a coil, powdered
iron, orferrite.A strip construction ensures that thegrain boundariesare optimally aligned,
24
improving the transformer's efficiency by reducing the core'sreluctance. The closed ring shape
eliminates air gaps inherent in the construction of an E-I core.The cross-sectionof 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 generatingelectromagnetic 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 powercapacity (seeClassification parametersbelow). 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 tohysteresis in the core material.The leakage inductance is
inevitably high, resulting in very poor regulation, and so such designs are unsuitable for use in
improving the transformer's efficiency by reducing the core'sreluctance. The closed ring shape
eliminates air gaps inherent in the construction of an E-I core.The cross-sectionof 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 generatingelectromagnetic 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 powercapacity (seeClassification parametersbelow). 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 tohysteresis in the core material.The leakage inductance is
inevitably high, resulting in very poor regulation, and so such designs are unsuitable for use in
25
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 forresonant
transformerssuch as Tesla coils where they can achieve reasonablylow loss in spite of the high
leakage inductance.
Windings
Fig 4.12:-Windings are usually arranged concentrically to minimize flux leakage.
Theconducting materialused 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 currentsare low
and the potential difference between adjacent turns is small, the coils are often wound
fromenamelled magnet wire, such asFormvarwire. Larger power transformers operating at high
voltages may be wound with copper rectangular strip conductors insulated by oil-impregnated
paper and blocks ofpressboard.
[62]
White: insulator. Green spiral:Grain orientedsilicon 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 ofleakage inductancewould lead
to increase of capacitance.
High-frequency transformers operating in the tensto hundreds of kilohertz often have
windings made of braidedLitz wireto 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 isinsulated, 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
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 forresonant
transformerssuch as Tesla coils where they can achieve reasonablylow loss in spite of the high
leakage inductance.
Windings
Fig 4.12:-Windings are usually arranged concentrically to minimize flux leakage.
Theconducting materialused 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 currentsare low
and the potential difference between adjacent turns is small, the coils are often wound
fromenamelled magnet wire, such asFormvarwire. Larger power transformers operating at high
voltages may be wound with copper rectangular strip conductors insulated by oil-impregnated
paper and blocks ofpressboard.
[62]
White: insulator. Green spiral:Grain orientedsilicon 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 ofleakage inductancewould lead
to increase of capacitance.
High-frequency transformers operating in the tensto hundreds of kilohertz often have
windings made of braidedLitz wireto 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 isinsulated, 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
26
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
moreflexible 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 capacitance
to improve high-frequency response. Coils are split into sections, and those sections interleaved
between the sections of the other winding.
Power-frequency transformers may havetapsat intermediate points on the winding,
usually on the higher voltage winding side, for voltage adjustment. Taps may be manually
reconnected, or a manual or automatic switch may be provided for changing taps. Automatic on-
loadtap changersare used in electric power transmission or distribution, on equipment such
asarc furnacetransformers, or for automatic voltage regulators for sensitiveloads. Audio-
frequency transformers, used for the distribution of audio to public address loudspeakers, have
taps to allow adjustment of impedance to each speaker. Acenter-tapped transformeris often used
in the output stage of an audio poweramplifierin apush-pull circuit.Modulation transformers
inAMtransmitters 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 includevacuum pressure
impregnation(VPI),vacuum pressure encapsulation (VPE), andcast coil
encapsulationprocesses.
]
In the VPIprocess, 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
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
moreflexible 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 capacitance
to improve high-frequency response. Coils are split into sections, and those sections interleaved
between the sections of the other winding.
Power-frequency transformers may havetapsat intermediate points on the winding,
usually on the higher voltage winding side, for voltage adjustment. Taps may be manually
reconnected, or a manual or automatic switch may be provided for changing taps. Automatic on-
loadtap changersare used in electric power transmission or distribution, on equipment such
asarc furnacetransformers, or for automatic voltage regulators for sensitiveloads. Audio-
frequency transformers, used for the distribution of audio to public address loudspeakers, have
taps to allow adjustment of impedance to each speaker. Acenter-tapped transformeris often used
in the output stage of an audio poweramplifierin apush-pull circuit.Modulation transformers
inAMtransmitters 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 includevacuum pressure
impregnation(VPI),vacuum pressure encapsulation (VPE), andcast coil
encapsulationprocesses.
]
In the VPIprocess, 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
27
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 isolationas 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 allelectric machinesincluding all transformers is halved for about
every 7°C to 10°C increase inoperatingtemperature, 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 andradiationheat 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 filledwithtransformer oilthat both cools and insulates the
windings.Transformer oil is a highly refinedmineral oilthat cools the windings and insulation by
circulating within the transformer tank. The mineral oil andpaperinsulation 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 about30% 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 testingincludingdissolved gas analysisprovides 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 haveheat exchangersfor water-cooling.
[
An oil-
immersed transformer may be equipped with aBuchholz relay, which, depending on severity of
gas accumulation due to internal arcing, is used to either alarmor de-energize the
transformer.
]
Oil-immersed transformer installations usually include fire protection measures
such as walls, oil containment, and fire-suppression sprinkler systems.
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 isolationas 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 allelectric machinesincluding all transformers is halved for about
every 7°C to 10°C increase inoperatingtemperature, 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 andradiationheat 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 filledwithtransformer oilthat both cools and insulates the
windings.Transformer oil is a highly refinedmineral oilthat cools the windings and insulation by
circulating within the transformer tank. The mineral oil andpaperinsulation 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 about30% 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 testingincludingdissolved gas analysisprovides 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 haveheat exchangersfor water-cooling.
[
An oil-
immersed transformer may be equipped with aBuchholz relay, which, depending on severity of
gas accumulation due to internal arcing, is used to either alarmor de-energize the
transformer.
]
Oil-immersed transformer installations usually include fire protection measures
such as walls, oil containment, and fire-suppression sprinkler systems.
28
Polychlorinated biphenylshave properties that once favored their use as adielectric
coolant, though concerns over theirenvironmental persistenceled to a widespread ban on their
use.
[75]
Today, non-toxic, stablesilicone-based oils, orfluorinated hydrocarbonsmay 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 KingdomLegislation 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 bynitrogenorsulfur hexafluoridegas.
Experimental power transformers in the 500‐to‐1,000kVA range have been built
withliquid nitrogenorheliumcooledsuperconductingwindings, 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 60Hz. 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 insulatedbushingsmade of polymers
or porcelain. A large bushing can be a complex structure since it must provide careful control of
theelectric field gradientwithout letting the transformer leak oil.
4.4Classification 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, orradio-frequency.
Voltage class:From a few volts to hundreds of kilovolts.
Polychlorinated biphenylshave properties that once favored their use as adielectric
coolant, though concerns over theirenvironmental persistenceled to a widespread ban on their
use.
[75]
Today, non-toxic, stablesilicone-based oils, orfluorinated hydrocarbonsmay 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 KingdomLegislation 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 bynitrogenorsulfur hexafluoridegas.
Experimental power transformers in the 500‐to‐1,000kVA range have been built
withliquid nitrogenorheliumcooledsuperconductingwindings, 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 60Hz. 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 insulatedbushingsmade of polymers
or porcelain. A large bushing can be a complex structure since it must provide careful control of
theelectric field gradientwithout letting the transformer leak oil.
4.4Classification 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, orradio-frequency.
Voltage class:From a few volts to hundreds of kilovolts.
29
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
currentstabilizer 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: ByEIC vector group–various possible two-winding
combinations of the phase designations delta, wye or star, andzigzag 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..
4.5Types
Various specific electrical applicationdesigns require a variety oftransformer types.
Although they all share the basic characteristic transformer principles, they are customize in
construction or electricalproperties 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
totwo-phaseand 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,
azigzag 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:Transformerused to match the output of a valve amplifier to its
load.
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
currentstabilizer 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: ByEIC vector group–various possible two-winding
combinations of the phase designations delta, wye or star, andzigzag 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..
4.5Types
Various specific electrical applicationdesigns require a variety oftransformer types.
Although they all share the basic characteristic transformer principles, they are customize in
construction or electricalproperties 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
totwo-phaseand 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,
azigzag 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:Transformerused to match the output of a valve amplifier to its
load.
30
Instrument transformer:Potential orcurrent transformerused 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 inEthernetcomputer
networks as 10BASE-T, 100BASE-T and 1000BASE-T.
Fig4.13:AnelectricalsubstationinMelbourne,Australiashowing three of five 220kV–
66kV transformers, each with a capacity of 150MVA
Transformersare used to increase (or step-up) voltage before transmitting electrical
energy over long distances throughwires. Wires haveresistancewhich 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 theelectricity supply industry, permitting generation to be located
remotely from points ofdemand.
[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 inelectronic productsto 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 ofamplifiersand to match
devices such asmicrophonesandrecord playersto the input of amplifiers. Audio transformers
allowedtelephonecircuits to carry on atwo-way conversationover a single pair of wires.
Abaluntransformer converts a signal that is referenced to ground to a signal that hasbalanced
voltages to ground,such as between external cables and internal circuits.
Instrument transformer:Potential orcurrent transformerused 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 inEthernetcomputer
networks as 10BASE-T, 100BASE-T and 1000BASE-T.
Fig4.13:AnelectricalsubstationinMelbourne,Australiashowing three of five 220kV–
66kV transformers, each with a capacity of 150MVA
Transformersare used to increase (or step-up) voltage before transmitting electrical
energy over long distances throughwires. Wires haveresistancewhich 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 theelectricity supply industry, permitting generation to be located
remotely from points ofdemand.
[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 inelectronic productsto 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 ofamplifiersand to match
devices such asmicrophonesandrecord playersto the input of amplifiers. Audio transformers
allowedtelephonecircuits to carry on atwo-way conversationover a single pair of wires.
Abaluntransformer converts a signal that is referenced to ground to a signal that hasbalanced
voltages to ground,such as between external cables and internal circuits.
31
4.6History
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 asFaraday's law of
induction:
whereis the magnitude of the EMF in Volts and ΦBis the magnetic flux through the circuit
inwebers.
Faraday performed the first experiments on induction between coils of wire, including
winding a pair of coils around an iron ring, thus creating the firsttoroidalclosed-core
transformer.
]
However he only applied individual pulses of current to his transformer, and never
discovered the relation between the turns ratio and EMF in the windings.
Fig4.16:-Induction coil, 1900, Bremerhaven, Germany
Induction coils
4.6History
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 asFaraday's law of
induction:
whereis the magnitude of the EMF in Volts and ΦBis the magnetic flux through the circuit
inwebers.
Faraday performed the first experiments on induction between coils of wire, including
winding a pair of coils around an iron ring, thus creating the firsttoroidalclosed-core
transformer.
]
However he only applied individual pulses of current to his transformer, and never
discovered the relation between the turns ratio and EMF in the windings.
Fig4.16:-Induction coil, 1900, Bremerhaven, Germany
Induction coils
32
4.17:-Faraday's ring transformer
The first type of transformer to seewide use was theinduction coil, invented by
Rev.Nicholas CallanofMaynooth 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 producedirect current (DC)rather
than AC, induction coils relied upon vibratingelectrical contactsthat regularly interrupted the
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, efficientgeneratorsproducingalternating current (AC)were available, and
it was foundAC could power an induction coil directly, without aninterrupter.
In 1876, Russian engineerPavelYablochkovinvented.
[
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.
In 1878, theGanz factory, Budapest, Hungary, began manufacturing 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.
Lucien Gaulardand 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
theWestinghousecompany 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
open-core bipolar apparatus remained very low.
Early series circuit transformer distribution
4.17:-Faraday's ring transformer
The first type of transformer to seewide use was theinduction coil, invented by
Rev.Nicholas CallanofMaynooth 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 producedirect current (DC)rather
than AC, induction coils relied upon vibratingelectrical contactsthat regularly interrupted the
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, efficientgeneratorsproducingalternating current (AC)were available, and
it was foundAC could power an induction coil directly, without aninterrupter.
In 1876, Russian engineerPavelYablochkovinvented.
[
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.
In 1878, theGanz factory, Budapest, Hungary, began manufacturing 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.
Lucien Gaulardand 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
theWestinghousecompany 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
open-core bipolar apparatus remained very low.
Early series circuit transformer distribution
33
Induction coils with open magnetic circuits are inefficient at transferring power toloads.
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 theWar 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.
Induction coils with open magnetic circuits are inefficient at transferring power toloads.
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 theWar 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.
34
Fig4.20:-Stanley's 1886 design for adjustable gap open-core induction coils
Closed-core transformersand parallel power distribution
In the autumn of 1884,Károly Zipernowsky,OttóBláthyandMiksa Déri(ZBD), three
engineers associated with the Ganz factory, had determined that open-core devices were
impracticable, 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
core or b)surroundedby 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),
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, 40Hz, 120:72 V, 11.6:19.4 A, ratio 1.67:1, one-phase, shell form.
In both designs, the magnetic flux linking theprimary and secondary windings traveled
almost entirely within the confines of the iron core, with no intentional path through air
(seeToroidal coresbelow). The new transformers were 3.4 times more efficient than the open-
core bipolar devices of Gaulard and Gibbs.
]
The ZBD patents included two other major
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 Vinitially preferred
]
When employed in parallel connected
electric distribution systems, closed-core transformers finally made it technically and
economically feasible to provide electric power for lighting in homes, businesses and public
spaces.Blaty had suggested the use of closed cores, Zipernowsky had suggested the use
ofparallel 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 alteringthe EMF of an
electric current
]
although the term had already been in use by 1882.In 1886, the ZBD engineers
Fig4.20:-Stanley's 1886 design for adjustable gap open-core induction coils
Closed-core transformersand parallel power distribution
In the autumn of 1884,Károly Zipernowsky,OttóBláthyandMiksa Déri(ZBD), three
engineers associated with the Ganz factory, had determined that open-core devices were
impracticable, 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
core or b)surroundedby 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),
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, 40Hz, 120:72 V, 11.6:19.4 A, ratio 1.67:1, one-phase, shell form.
In both designs, the magnetic flux linking theprimary and secondary windings traveled
almost entirely within the confines of the iron core, with no intentional path through air
(seeToroidal coresbelow). The new transformers were 3.4 times more efficient than the open-
core bipolar devices of Gaulard and Gibbs.
]
The ZBD patents included two other major
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 Vinitially preferred
]
When employed in parallel connected
electric distribution systems, closed-core transformers finally made it technically and
economically feasible to provide electric power for lighting in homes, businesses and public
spaces.Blaty had suggested the use of closed cores, Zipernowsky had suggested the use
ofparallel 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 alteringthe EMF of an
electric current
]
although the term had already been in use by 1882.In 1886, the ZBD engineers
35
designed, and the Ganz factory supplied electrical equipment for, the world's firstpower
stationthat used AC generators to power a parallel connected common electrical network, the
steam-powered Rome-Cerchipower plant.
AlthoughGeorge Westinghousehad bought Gaulard and Gibbs' patents in 1885,
theEdison Electric Light Companyheld an option on the US rights for the ZBD transformers,
requiring Westinghouse to pursue alternative designs on the same principles. He assigned
toWilliam Stanleythe 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 designwas first used
commercially in the US in 1886but Westinghouse was intent on improving the Stanley design to
make it (unlike the ZBD type) easy and cheap to produce.
s
designed, and the Ganz factory supplied electrical equipment for, the world's firstpower
stationthat used AC generators to power a parallel connected common electrical network, the
steam-powered Rome-Cerchipower plant.
AlthoughGeorge Westinghousehad bought Gaulard and Gibbs' patents in 1885,
theEdison Electric Light Companyheld an option on the US rights for the ZBD transformers,
requiring Westinghouse to pursue alternative designs on the same principles. He assigned
toWilliam Stanleythe 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 designwas first used
commercially in the US in 1886but Westinghouse was intent on improving the Stanley design to
make it (unlike the ZBD type) easy and cheap to produce.
s
36
CHAPTER-5
CONCLUSION
It was just like a dream come true for me to pursuetraining in Hindustan Zincltd. 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 ZincWork .
CHAPTER-5
CONCLUSION
It was just like a dream come true for me to pursuetraining in Hindustan Zincltd. 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 ZincWork .
37
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.aspxOfficial Website of Hindustan Zinc Limited
http://www.vedantaresources.com/default.aspxOffical Website of Vedanta Resources
HZL,Training Report
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.aspxOfficial Website of Hindustan Zinc Limited
http://www.vedantaresources.com/default.aspxOffical Website of Vedanta Resources
HZL,Training Report
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