Lucknow Public School

PHYSICS (042)
AISSCE PRATICAL
(SESSION : 2025-26)

CERTIFICATE
This is to clarify that Piyush Saxena of Class XII bearing Roll No.
__________ has completed his project on topic “Transformer” in
accordance with specification prescribed by CBSE Board, New
Delhi.

Teacher Signature Principal Signature

__________ __________
 Lucknow Public School

ACKNOWLEDGEMENT
I am grateful to all those who have guided me by all means in
preparation of this project.

I am highly thankful to my respected physics teacher, Mr.Awadhesh

Kumar Srivastava for his invaluable guidance, help and constant
encouragement in the completion of this project.

I wish to acknowledge my thanks to my principal, Mr. Pramod Kumar

Singh, who contributed in the preparation of this project indirectly
by his valuable moral support.

Last but not least I am also thankful to all those whose names are
not mentioned above but helped encouraged and inspired me knowing
or unknowing in doing this work.
 Index

S. No. Topic Page No.

1. Introduction 1
2. Basic Principal & Working of a Transformer 2
3. Construction & Components of a Transformer 5
4. Types of Transformers 7
5. Applications of in Real Life 11
6. Advantages and Disadvantages of Transformers 14
7. Conclusion 17
8. References 18
 Introduction
Electricity has become an inseparable part of modern life. From lighting our
homes to powering complex industries, it plays a vital role in every aspect of
human activity. However, the generation of electricity and its utilization
often take place at different locations, making its transmission over long
distances essential. This is where a device called the transformer becomes
extremely important.

A transformer is an electrical device that is used to increase or decrease

the voltage of an alternating current (AC) without changing the frequency. It
plays a crucial role in ensuring efficient transmission and distribution of
electricity across long distances with minimal loss. In the absence of
transformers, power losses during transmission would be extremely high,
making electricity supply inefficient and expensive.

Objective of This Project:The main objective of this project is to

understand the working principle, construction, and types of
transformers, supported by mathematical explanations and real-
life applications. Through this project, we aim to explore how such
a simple yet powerful device forms the backbone of our modern
electrical systems.
 Basic Principle and Working of a
Transformer

A transformer works on the principle of electromagnetic induction,

specifically mutual induction between two coils. When alternating current
(AC) flows through one coil (called the primary coil), it creates a changing
magnetic field around it. This changing magnetic field induces a voltage in
another nearby coil (called the secondary coil) without any physical
connection between them.

Faraday’s Law of Electromagnetic Induction:

The working of a transformer is governed by Faraday’s Second Law, which
states:

"The induced electromotive force (emf) in a coil is directly

proportional to the rate of change of magnetic flux through the coil."
𝑑Φ
emf = −𝑁
𝑑𝑡
Where:

• 𝑁 = number of turns in the coil

• Φ = magnetic flux
𝑑Φ
• = rate of change of magnetic flux
𝑑𝑡

Basic Structure of a Transformer:

A simple transformer has two coils of wire — the primary coil and the
secondary coil — wound on a soft iron core. The iron core is laminated to
reduce energy losses due to eddy currents.

• Primary Coil: Connected to the input AC voltage source.

• Secondary Coil: Connected to the output where voltage is either
increased or decreased.
The alternating current in the primary coil generates an alternating magnetic
flux in the iron core. This flux passes through the secondary coil and induces
an electromotive force (emf) in it, depending on the number of turns in each
coil.

Step-Up and Step-Down Transformers:

The transformer can either increase or decrease the voltage depending on
the number of turns in the primary and secondary coils:

• Step-Up Transformer:

o Secondary coil has more turns than the primary coil.

o Output voltage is greater than input voltage.
o Used in power stations to increase voltage for transmission.
• Step-Down Transformer:

o Secondary coil has fewer turns than the primary coil.

o Output voltage is less than input voltage.
o Used near homes to reduce voltage for safe domestic use.

Transformer Equation:
The relationship between the input and output voltage is given by:
𝑉𝑠 𝑁𝑠
=
𝑉𝑝 𝑁𝑝

Where:

• 𝑉𝑠 & 𝑉𝑝 are voltage in secondary and primary coil respectively

• 𝑁𝑠 & 𝑁𝑝 are number of turns in secondary & primary coil respectively

Important Notes:
• Transformers work only with alternating current (AC) and not direct
current (DC), because mutual induction requires a changing magnetic
field.
 • The frequency of the voltage remains the same after transformation.
• The power (in ideal transformers) remains constant:

𝑉𝑝 𝐼𝑝 = 𝑉𝑠 𝐼𝑠

This means that if voltage increases, current decreases, and vice versa.
 Construction and Components of a
Transformer

The construction of a transformer may seem simple, but each component

plays a crucial role in ensuring its efficiency, safety, and durability. A well-
designed transformer not only works efficiently but also minimizes energy
losses.

Main Components of a Transformer:

1. Core-
• The core provides a path for the magnetic flux generated in the
transformer.
• Made of soft iron or silicon steel laminations to improve magnetic
properties and reduce eddy current losses.
• The core is laminated (i.e., made of thin sheets insulated from each
other) to minimize energy losses due to eddy currents.

There are two common core types:

• Core Type: Windings surround the laminated core limbs.

• Shell Type: Core surrounds the windings. Offers better protection and
is used for high-voltage applications.

2. Windings (Primary and Secondary Coils)-

• Made of copper or aluminum wire.
• The primary winding is connected to the input AC source.
• The secondary winding is connected to the load.
• Both windings are electrically insulated from each other and wound on
the core.

The number of turns in each winding determines whether the transformer is

step-up or step-down.
3. Insulating Material-
• Electrical insulation is placed between the windings and the core to
prevent short circuits and ensure safety.
• Materials used: paper, pressboard, insulating oil, varnish, etc.
• High-voltage transformers use oil-impregnated insulation for better
heat dissipation and dielectric strength.

4. Transformer Oil (in Oil-Cooled Transformers)-

• Acts as a coolant and an insulator.
• Absorbs the heat generated by the core and windings and transfers it
to the cooling system.
• Usually made from mineral oil with high dielectric strength.

5. Tank and Conservator (for large transformers)-

• The transformer is housed in a steel tank filled with insulating oil.
• The conservator is an expansion tank mounted above the main tank to
accommodate oil expansion during heating.
• Breather systems are used to prevent moisture from entering the oil.

6. Bushings-
• These are insulated devices that allow safe connection of the
transformer windings to external electrical circuits.
• Prevent leakage of current from the windings to the transformer body.

7. Cooling System-
• As transformers generate heat, a cooling system is essential.

• Methods include:

o Natural air cooling (AN)

o Oil natural air natural (ONAN)
o Oil forced air forced (OFAF)
• Large transformers may have radiators, fans, or pumps for forced
cooling.
 Types of Transformers

Transformers come in many types, each designed for specific purposes. The
type of transformer used depends on its application, voltage levels, current
requirements, and design.

Understanding the classification of transformers helps us recognize their

role in different parts of the electrical system — from small devices like
mobile chargers to large-scale power transmission.

Classification of Transformers
A. Based on Function
1. Step-Up Transformer
• Increases the voltage from the primary to the secondary coil.
• Used in power stations for transmission of electricity over long
distances.
• Reduces power loss by increasing voltage and decreasing current.
2. Step-Down Transformer
• Decreases the voltage from the primary to the secondary coil.
• Used near homes and industries to supply safe voltage levels.
• Commonly seen in adapters and household power supplies.

B. Based on Construction
1. Core Type Transformer
• Windings are placed around two limbs of the core.
• Simple design, used in low to medium voltage applications.
2. Shell Type Transformer
• Core surrounds the windings.
• Better mechanical strength and compact size.
• Preferred for high-voltage applications.
C. Based on Usage
1. Power Transformer
• Used in transmission networks at high voltage levels (typically above 33
kV).
• Operates at near full load continuously.
• Large in size and used in generating stations and transmission
substations.
2. Distribution Transformer
• Used to distribute electricity to homes and industries at lower voltage
levels (usually below 11 kV).
• Operates at partial load.
• Mounted on poles or placed in small enclosures.
3. Instrument Transformer
• Used in measurement and protection systems.

• Types:

o Current Transformer (CT): Measures high current by stepping it

down to a safe level.
o Potential Transformer (PT): Measures high voltage by stepping
it down.
4. Isolation Transformer
• Has equal number of turns in primary and secondary coils.
• Does not step voltage up or down.
• Used for electrical isolation and safety, often in hospitals or
laboratories.
5. Auto-Transformer
• A single winding acts as both primary and secondary.
• Less copper and cheaper.
• Used in voltage regulation, starters for motors, etc.
 Advantages and Disadvantages of
Transformers

Transformers play a vital role in modern electrical systems. Their ability to

change voltage levels with high efficiency makes them crucial in power
distribution and many electronic devices. However, like any device, they come
with both strengths and limitations.

Advantages of Transformers
1. Efficient Transmission of Power
• Transformers enable power to be transmitted at high voltage and low
current, significantly reducing energy losses (I²R losses) over long
distances.
• This makes large-scale electrical power distribution possible and
economical.
2. Voltage Regulation
• Transformers can step-up or step-down voltage to suit the needs of
various devices and applications.
• This allows the same electrical source to power everything from
industrial machines to household appliances.
3. High Efficiency
• Modern transformers can reach efficiencies of 95% to 99%.
• This means very little electrical energy is wasted, even under
continuous operation.
4. Simple Design and Reliable Operation
• Transformers have no moving parts, reducing wear and mechanical
failure.
• They require low maintenance and can operate continuously for years.
5. Versatile Applications
• Used in power plants, homes, industries, hospitals, communication
systems, and renewable energy systems.
• Also used in measurement systems (CTs and PTs) and medical
equipment (isolation transformers).
6. Safety in Electrical Systems
• Transformers allow for electrical isolation, preventing direct contact
with high voltage circuits.
• They help protect sensitive devices from voltage spikes and surges.

Disadvantages of Transformers
1. Not Suitable for DC Supply
• Transformers work only with alternating current (AC).
• They cannot operate with direct current (DC) unless special converter
circuits are used.
2. Size and Weight
• Power transformers, especially those used in substations, are large and
heavy.
• Installation and transportation require special equipment and high
costs.
3. Energy Losses
• Although efficient, transformers still experience:

o Copper losses (I²R)

o Iron losses (eddy currents and hysteresis)
o Leakage flux and dielectric losses
4. Noise and Vibration
• Transformers can produce a low-frequency humming sound due to
magnetostriction and core vibrations.
• This may be undesirable in quiet environments like offices or homes.
5. Initial Cost
• High-quality transformers, especially for high-voltage or sensitive
applications, can be expensive to manufacture and install.

Comparison Table
Advantages Disadvantages
High efficiency (up to 99%) Works only with AC supply
Simple, durable, and reliable Can be large and heavy (power types)
Voltage can be stepped up/down Energy losses (though small)
Safe electrical isolation Noise due to vibrations
Widely applicable in many fields Expensive installation and maintenance
 Conclusion

In this project, we explored the fundamental concept, working principles,

mathematical relationships, and real-life applications of transformers, a
critical component in modern electrical systems. Starting from the basic idea
of mutual induction, we studied how transformers transfer electrical energy
from one circuit to another without any physical contact and how they make it
possible to change voltage levels efficiently.

Transformers are indispensable in power generation, transmission, and

distribution. They play a key role in reducing energy loss by stepping up
voltages for long-distance transmission and stepping them down for safe
domestic or industrial use. Their usage extends far beyond the power grid —
from mobile phone chargers to medical equipment, industries, and renewable
energy systems.

We also examined the mathematical principles behind transformer operation,

including equations for voltage, current, power, and efficiency. Furthermore,
the project highlighted various types of losses in transformers and the
methods used to minimize them, ensuring reliable and efficient performance.

Finally, we evaluated both the advantages and limitations of transformers.

While they are highly efficient and widely used, transformers also face
challenges such as size, noise, and incompatibility with DC systems. However,
these limitations are often outweighed by their immense utility and impact.

Final Thought
As a Class 12 Physics student, this project has deepened my understanding of
electromagnetic induction, practical electrical engineering, and the crucial
role that transformers play in ensuring that electricity reaches our homes,
schools, hospitals, and industries safely and efficiently.
 References

Books and Textbooks

1. NCERT Physics Textbook – Class 12 Part 2
2. Concepts of Physics – H.C. Verma (Volume 2)
3. Principles of Physics – Resnick, Halliday & Walker

Web Resources
4. www.ncert.nic.in
5. www.learncbse.in – Class 12 Physics Notes
6. www.electrical4u.com – Transformer Working and Types
7. www.byjus.com – Transformer Explanation with Diagrams
8. www.toppr.com – Transformer and Its Applications
9. www.tutorialspoint.com – Electrical Engineering Basics