Internship report

Submitted by: Rabia Basree Ilyas

Intern Id: 026/2025

Department: Power Transformer

Date: 20 July 2025

University: Lahore College For Women

University
 Table of contents:

1. Preface

2. Introduction to Transformers

 Definition and Importance

 Purpose and Basic Operation

 Working Principle

3. Components of Transformer

 Core (Materials and Properties)

Power Transformer

 Windings (Primary and Secondary)

o Types:
• Multi-layer
• Helical
• Helical/Spiral
• Disc
• Foil
• Cylindrical
• Cross-over
• Disc & Continuous Disc

 Insulation

 Transformer Oil

 Converter Tank

 Breather

 Cooling System

 Tank
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 Tap Changer

4. Diagram of Transformer
5. Flow Chart Diagram of Manufacturing

6. Transformer Tests

 Routine Tests

 Type Test

 Special Tests

7. Losses in Transformer

 Core Losses (Hysteresis, Eddy Current)

 Copper Losses

 Other Losses (Stray, Dielectric)

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 Managing Losses

8. Conclusion

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 Preface:
This report provides a comprehensive overview of power transformers, which are
indispensable devices in modern electrical power systems. Transformers play a
crucial role in the efficient transmission and distribution of electrical energy by
stepping up or stepping down voltage levels without any moving parts. The report
begins by introducing the basic principles and operation of transformers, emphasizing
their reliance on electromagnetic induction and alternating current for energy transfer.

A detailed explanation of the key components of transformers—including the core,

windings, insulation, cooling systems, and tap changers—is provided to highlight
how each part contributes to the overall performance and reliability of the device.
Various core materials and winding types are discussed to demonstrate the
importance of material selection and design in minimizing energy losses and
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enhancing efficiency.

The report also covers the different types of tests conducted on transformers to ensure
their safety, durability, and compliance with design specifications. These tests,
including routine, type, and special tests, verify aspects such as insulation integrity,
mechanical strength, and noise levels under operating conditions.

Losses in transformers, primarily core (iron) losses and copper losses, are examined
in detail. Understanding these losses is essential for optimizing transformer design
and operation to reduce energy waste and heat generation. Additional minor losses
and the methods used to manage and minimize all losses are also addressed.

Overall, this report aims to provide a thorough understanding of power transformers,

their components, working principles, testing procedures, and efficiency
considerations. It serves as a valuable resource for students, engineers, and
professionals involved in the design, operation, and maintenance of electrical power
systems.

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Introduction of Pel:
Pak Elektron Limited, commonly known as PEL, is a prominent Pakistani company
that holds the distinction of being a pioneer in the manufacturing of electrical goods
in the country. Established in 1956 through a technical collaboration with M/s AEG
of Germany, PEL has a long history of contributing to Pakistan's engineering sector.

In 1978, the company was acquired by the Saigol Group of Companies, which further
diversified its operations. Initially focused solely on power equipment like
transformers and switchgear, PEL ventured into the home appliance market in 1981.

Power Transformer
Today, PEL operates with two main divisions:

 Power Division: This division is responsible for the manufacturing and

distribution of essential electrical capital goods, including power transformers,
distribution transformers, switchgear, and energy meters. They also undertake
construction of grid stations and electrification works, playing a significant
role in Pakistan's power infrastructure.

 Appliances Division: This segment focuses on manufacturing, assembling,

and distributing a wide range of home appliances. Their product portfolio
includes refrigerators, air conditioners, deep freezers, washing machines,
microwave ovens, water dispensers, and LED TVs, among others.

PEL has a strong commitment to quality and innovation, having formed alliances
with various international giants over the years, such as General Electric, Fujitsu, and
Hitachi, to bring advanced technologies to Pakistan. With its extensive product range
and historical presence, PEL is a well-recognized brand in Pakistani households and a
key player in the nation's electrical and electronics industry.

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 Power Transformer
PEL's Power Transformer Department is a crucial
part of its Power Division, responsible for the design,
manufacturing, and supply of high-quality power
transformers for various applications in Pakistan and
internationally. Here's an overview:

Establishment and Expertise:

 PEL established its power transformer

division in 2005, building upon its extensive
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experience in manufacturing distribution

transformers since 1956.

Product Range and Capacity:

 The department specializes in producing

power transformers with ratings typically
ranging from 10/13 MVA, 20/26 MVA, and
31.5/40 MVA, for voltages up to 132 KV.
There are indications they can manufacture up
to 100 MVA and 132 KV.

 They manufacture transformers in both

ONAN (Oil Natural Air Natural) and ONAF
(Oil Natural Air Forced) cooling
configurations.

Key Operations and Quality Assurance:

 Design: The design department is central,

handling client specifications, cost estimation,
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and dimensional sketches. They utilize
 software like Pro-E and AutoCAD for electrical and mechanical design of
core, windings, and tank.

 Materials: PEL emphasizes high-quality materials, including:

o 99.99% pure electrolytic copper for windings (using multiple

conductors and CTC).

o Cold Rolled Grain Oriented (CRGO) steel sheets for magnetic cores,
with robust clamping and cutting techniques to minimize no-load
losses.

o High-quality accessories from international suppliers like OLTC from

MR (Germany), High Voltage Bushings from PASSONI & VILLA
(Italy), Buchholz Relays from EMB (Germany), insulation material

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from WEIDMANN (Switzerland), silicon steel from THYSSEN
(Germany), and cooling fans from SCHORMANN (Germany).

 Manufacturing Process: This involves slitting and cutting core sheets with
high-precision CNC machines, stacking them for optimized losses and
strength, assembly of core and windings, mounting tap-changers and
bushings, vacuum drying to remove moisture, and oil filling under vacuum.
Tank fabrication involves high-grade CR steel and rigorous leakage testing.

 Testing: Finished products undergo rigorous testing at PEL's test field,

including all routine tests as per IEC 60076-1. They also have facilities for
type tests like Impulse Test and Temperature Rise Test. This ensures product
longevity and adherence to international standards.

 Customization: PEL manufactures transformers for private customers based

on their specific requirements and specifications.

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 Introduction to Transformers

Transformers are static electrical devices used to transfer electrical energy between
two or more circuits through electromagnetic induction. They play a crucial role in
electrical power systems by stepping up or stepping down voltage levels, allowing
efficient transmission and distribution of electrical energy. Transformers are widely
used in power plants, substations, and industrial applications.

Purpose and Basic Operation of a Transformer

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The main purpose of a transformer is to increase (step up) or decrease (step down) the
voltage level while maintaining the same frequency. This is essential in minimizing
power loss during transmission over long distances. A transformer operates based on
the principle of electromagnetic induction, which involves the transfer of energy from
one winding (primary) to another (secondary) through a shared magnetic field in a
magnetic core.

Working Principle of a Transformer

The working principle of a transformer is based on Faraday’s Law of

Electromagnetic Induction. When AC flows through the primary winding, it
generates a changing magnetic field that induces voltage in the secondary winding.
The voltage induced depends on the number of turns in each coil. This relationship is
given by: V₁ / V₂ = N₁ / N₂. Transformers operate only with AC, as DC cannot produce
a changing magnetic field

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Components of Transformer:
The components of transformer are as following:

1. Core:
Core is made of soft iron. It provides low resistive path. Links primary and secondary
coil.

Core material and types:

Transformer core acts as” Bridge” between energies. It is responsible for conducting

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the magnetic field between primary and secondary coil.

Material:’

Choosing right material is critical for transformer core.. the material determines
magnetic permeability, energy loses and overall performance of core.

The material that are used are:

1. Silicon steel:

Properties:

 High magnetic permeability

 Minimize energy losses.
 High saturation flux density.
2. Amorphous alloys:

Properties:

 Low core losses

 Saturation flux density
 Enhanced efficiency 8
3. Ferrite:
 Properties:

 Reduce eddy current losses.

 Saturation flux density
 Low loss
4. Powered iron:

Properties:

 Adjustable permeability
5. Nano Crystalline Alloys:

Properties:

 Low core losses

 High saturation flux.
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 Good thermal stability.

2. Windings:
There are mainly two types of windings:
1. Primary winding:
Connected to input.
2. Secondary winding:
Connected to output.

The other types of windings are:

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Figure: Types of winding
 Multi-Layer Helical Windings

 Helical Windings or Spiral Windings

 Disc Windings

 Foil Windings

 Cylindrical Windings

 Cross- Over Windings

 Disc & Continuous Disc Winding

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 Aluminum Windings

1. Multi-Layer Helical Windings Used for high voltage transformers (≥110

kV). Comprise numerous series-connected cylindrical layers. External layers
are shorter than inside ones for consistent capacitance, improving surge
behavior.
2. Helical Windings or Spiral Windings For low voltage and high capacity
transformers (160-1000 kVA, 0.23-15 kV) with high current and few turns.
Conductor strips ≥75−100mm2, max 16 parallel. Types: single, double, disc-
helical.
3. Disc Windings Designed by connecting insulated conductor discs in series,
separated by spacers. Distinct from helical as they have numerous turns per
disc (helical has single twist). Used in ≥25 kV transformers, mechanically
robust.
4. Foil Windings Made from thin aluminum or copper sheets with thin
insulation, forming multilayer spiral windings. Can use single or multiple
parallel sheets. Applicable in high capacity transformers with currents from
12-600 A.
5. Cylindrical Windings Used for low voltage (up to 6.6 kV) and current
ratings (10-600 A), often in multi-layer forms. Circular conductors wound on
vertical strips create oil ducts for cooling. Applicable up to 33 kV, 800 kVA,
80 A; max bare conductor diameter 4 mm. 10
6. Cross-Over Windings Used in small transformers, separated into coils to
reduce inter-layer voltage (≤800−1000 V). Coils divided axially by 0.5-1 mm,
 with 6 mm spacing for insulation. Coil axial length ≈50 mm, width 25-50 mm.
Stronger than cylindrical windings.
7. Disc & Continuous Disc Winding Used in high capacity transformers,
featuring multiple discs or flat coils in series/parallel. Formed from spirally
wound rectangular strips (conductor area 4-50 mm2, current 12-600 A).
Minimum oil duct width 6 mm for 35 kV. Provides maximum mechanical
axial strength.
3. Insulation:
Prevents short circuit between windings and turns.
4. Transformer oil:
(Coolant) To maintain temperature of transformer.
5. Converter tank:
Small tank place above the tank to maintain the temperature because it
expands and contracts with temperature.
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6. Breather:
It Contains silica gel. it prevents addition of moisture in coil.
7. Cooling system:
It includes radiator fans. Use to keep transformer within safe temperature.it
can be tubes of oil.
8. Tank:
The outer coverage of transformer.
9. Tap changer:
It allows changing number of turns in transformer.

Diagram of transformer:

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 Figure: complete labelled diagram of transformer

Flow chart diagram of making of transformer:

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Start

Core Making Windings Carpentry

Core cutting Creating coil of conductive material Structure making

Core stacking LV windings and HV windings Fitment

Core coil assembly 12

VPD

Vacuum
 Transformer tests:
There are three type of transformer tests:

 Routine tests
 Special tests
 Type tests

1. ROUTINE TESTS

These are done on every unit before dispatch from the factory.

Test Name Purpose

Measurement of winding resistance Check for correct winding and detect any short circuits.
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Ratio and polarity test Confirms correct turns ratio and polarity.

No-load loss and current Measures core losses and magnetizing current.

Short-circuit (load) loss and impedance

Measures copper losses and leakage reactance.
voltage

Ensures insulation integrity between windings and

Insulation resistance test
earth.

Dielectric test (Applied voltage test) Verifies insulation withstand capability.

Induced over-voltage withstand test Checks inter-turn insulation.

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2. TYPE TESTS
Done on one unit of a design type to prove the transformer meets design
specifications.

Test Name Purpose

Measures how much the transformer heats under full

Temperature rise test
load.

Lightning impulse test Simulates effects of lightning strikes.

Switching impulse test (for high voltage

Simulates switching surges.
class)

Short-circuit test (mechanical strength) Verifies ability to withstand mechanical stresses.

Sound level measurement Ensures noise emissions are within limits.

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3. SPECIAL TESTS (DONE UPON REQUEST)

Conducted based on customer requirements or special standards.

Test Name Purpose

Partial discharge test Detects internal insulation defects.

Measurement of zero-sequence impedance For system studies involving unbalanced loads.

Harmonic analysis of no-load current Assesses core saturation and harmonics.

Determination of capacitance Used in diagnostic testing.

Frequency response analysis (FRA) Checks mechanical integrity of windings.

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Losses in Transformer
 Transformers are essential devices in electrical power systems, but like all electrical
equipment, they experience energy losses during operation. These losses reduce the
overall efficiency of the transformer and result in heat generation, which must be
managed to maintain performance and longevity. Understanding these losses is
critical for designing efficient transformers and optimizing their operation.

Types of Losses in Transformer

The losses in a transformer are generally categorized into two main types: core losses
(also called iron losses) and copper losses.

1. Core Losses (Iron Losses)

Core losses occur in the magnetic core of the transformer and are mainly due to two
phenomena:
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 Hysteresis Loss: When the alternating magnetic field reverses direction in the
core, the magnetic domains inside the core material lag behind the changing
magnetic field. This lag causes energy dissipation in the form of heat. The
hysteresis loss depends on the material properties of the core, the frequency of
the alternating current, and the maximum flux density.

 Eddy Current Loss: The alternating magnetic flux induces circulating currents
(eddy currents) inside the conductive core. These currents flow in loops within
the core, generating heat and wasting power. To reduce eddy current losses,
transformer cores are laminated into thin insulated sheets, which restrict the
flow of eddy currents.

Core losses occur regardless of the load on the transformer and are therefore also
called no-load losses. They depend primarily on the voltage and frequency.

2. Copper Losses

Copper losses are caused by the resistance of the transformer windings when current
flows through them. According to Joule’s law, power loss due to resistance is
proportional to the square of the current and the winding resistance:
15 Where I is the current through the winding and R is its resistance. These losses vary
with load current and are also called load losses.
Copper losses generate heat in the windings, which must be dissipated to prevent
damage and maintain transformer efficiency.

Other Losses

 Stray Losses: Caused by leakage flux inducing currents in non-metallic parts

or structural components near the transformer, such as clamps or tank walls.

 Dielectric Losses: Occur in the insulating materials due to their non-ideal

dielectric properties.

Although these additional losses are generally small compared to core and copper
losses, they contribute to the overall efficiency.

Managing Transformer Losses

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Reducing losses improves transformer efficiency and reduces operating costs. Some
common methods include:

 Using high-grade silicon steel or amorphous alloy cores to minimize

hysteresis and eddy current losses.

 Laminating the core to restrict eddy currents.

 Designing windings with larger cross-sectional areas and using conductors of

high conductivity (copper or aluminum) to reduce resistance.

 Proper cooling systems to dissipate heat from losses and maintain temperature
within safe limits

Conclusion:
Transformers are vital components in electrical power systems, enabling efficient
voltage conversion through electromagnetic induction. Their design involves careful
selection of core materials, winding types, and insulation to optimize performance
and minimize losses. Despite inherent losses such as core and copper losses, proper
material choice, construction techniques, and cooling methods help reduce energy
waste and improve efficiency. Rigorous testing ensures reliability and safety under 16
various operating conditions. Overall, transformers play a crucial role in minimizing
power loss during transmission and maintaining stable, efficient power distribution.
 Power Transformer

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