TN-Board-Class-11-Basic-Electrical-Engineering-Textbook.pdf

A publication under Free Textbook Programme of Government of Tamil Nadu
Department of School Education
Basic Electrical
Engineering
THEORY & PRACTICAL
Untouchability is Inhuman and a Crime
GOVERNMENT OF TAMIL NADU
HIGHER SECONDARY FIRST YEAR
VOCATIONAL EDUCATION
EMA_English_FM_Rev.indd 1 11/9/2020 3:49:16 PM

Government of Tamil Nadu
First Edition - 2018
Revised Edition - 2019
Published under New Syllabus
Tamil Nadu Textbook and
Educational Services Corporation
in
State Council of Educational Research
and Training
© SCERT 2018
Printing & Publishing
Content Creation
The wise
possess all
NOT FOR SALE
ii

iii
W
e are living in a modern world where all the systems are interconnected and in-
terdependent with electrical sciences. By the year 2050, the demand of electri-
cal energy is double or even become triple due to the advancement in modern
technology. Now-a-days, affordable knowledge is essential in the field of electrical sciences for
better understanding of electrical appliances.
This book has been written primarily as a text book for the students and is designed to
serve the introductory part of the subject, electrical engineering in school education under
vocational stream. The basic concepts of electrical sciences are explained with neat diagrams
for better understanding to the learners.
This Electrical Machines and Appliances (EMA) book has been written with the inspira-
tion and interaction of scholars in electrical fields in India and abroad. The resource materials
and ideas for making this book is obtained from experts in the field of electrical engineering
in around the country to meet the curriculum to international standards. The design of this
book is based on bloom’s taxonomy which is a learning tool for all students. The theory and
problems available in this text book obviously motivates the students for better understand-
ing. The contents of this book are mainly confined to the content of syllabus fulfilling the
objectives.
I along with team members originally undertook the task of writing the text book for
the vocational group students as basic subject in the field of electrical engineering due to the
knowledge which have experienced in three decades. My experience in teaching taught me
Preface

two things about students; need for better understanding of concepts and relating the con-
cepts to the real life cycle. This intention forced me in making this book as effective one as a
learning material for the vocational group students. As a result, the students will definitely
follow along with the subject teacher in demonstrating an example in handling classes. I
hope this book will definitely satisfy the primary needs of the student’s community to pur-
sue secondary level courses.
Myself with our subject experts’ team have provided this text book a more knowledge-
able and readable one fulfilling the needs of students. Consequently, the teacher will feel
more comfortable using the book because it reflects the electrical engineering concepts in
a pedagogy way.
I would like to extend my sincere appreciation to the faculty from various academic
institutions for the improvement of this text book writing.
Finally, it is an immense pleasure to express the gratitude and sincere thanks to all of
them who has given this opportunity to take part in writing the book for vocational stream
students.
iv

How to Use the Textbook
Illustrate the complete overview of chapter
Chapter Outline
Model questions to face various competitive exams
Competitive
Exam Questions
Explanation of scientific terms
Glossary
Assess students to pause, think and check their understanding
Evaluation
List of professions related to the subject
Career corner
List of digital resources
Web links
List of related books for further details of the topic
References
Directions are provided to students to conduct activities
in order to explore, enrich the concept.
Activity
Visual representation of the lesson to enrich learning .
Infographics
To motivate the students to further explore the content
digitally and take them in to virtual world
Amazing facts, Rhetorical questions to lead students
to biological inquiry
Learning objectives are brief statements that describe what
students will be expected to learn by the end of school year,
course, unit, lesson or class period.
Learning Objectives:
v

Career Guidance
VOCATIONAL STREAM
After completion of Higher Secondary course (+2), Vocational stream
students undergo the following courses as detailed below:
LATERAL ENTRY FOR DIPLOMA IN ENGINEERING: (FOR +2
STUDENTS)
The Vocational stream students, on completion of Higher Secondary, are
eligible to continue their educational career to Polytechnic colleges by lateral
entry.
(i.e.) They can directly join in the SECOND YEAR of the concerned
Diploma course.
After that, they can register their names in the “Board of Apprenticeship
training, No. 4th Cross street, CIT Campus, Taramani, Chennai – 13” for
employment opportunities.
LATERAL ENTRY FOR BE / B.TECH : (FOR DIPLOMA HOLDERS)
On completion of Diploma courses of any trade, the students can directly
join in the SECOND YEAR of the Engineering course (BE / B.TECH) in Anna
University and Affiliated colleges, by lateral entry.
Then, they can register their names in the “Board of Apprenticeship
training, No. 4th Cross street, CIT Campus, Taramani, Chennai – 13” for
employment opportunities.
NATIONAL CAREER SERVICE
The students who need for employment opportunities and career
guidance, including counselling both in Government, Private and Public
sector can see the website for further details.
vi

vii
Contents
E-book Assessment DIGI links
Lets use the QR code in the text books ! How ?
• Download the QR code scanner from the Google PlayStore/ Apple App Store into your smartphone
• Open the QR code scanner application
• Once the scanner button in the application is clicked, camera opens and then bring it closer to the QR code in the text book.
• Once the camera detects the QR code, a url appears in the screen.Click the url and goto the content page.
vii
Serial
No.
Unit
No.
Chapter Title
Page
No.
Month
1. 1 Introduction to Electrical Engineering 1-12 June
2. 2 Electrical Fundamental Terms 13-37 July
3. 3 Electro Magnetism 38-53 July
4. 4 Batteries 54-70 August
5. 5 AC Circuits 71-89 August
6. 6 Transformer 90-104 September
7. 7 DC Generator and DC Motor 105-121 October
8. 8 Alternators and AC Motors 122-139 October
9 Engineering Materials 140-152 November
10 Electronics 153-168 December
Model Question Paper 169-171
Basic Electrical Engineering Practical 172-239
Case Studies 240-242
Basic Electrical Engineering

Basic Electrical
Engineering
THEORY
viii

Introduction to Electrical Engineering
1
1.1 Introduction about Electricity, Methods of Power Generation
1.2 Introduction of LT/HT Line
1.3 Electrical Safety and Precautions
1.4 Electric Shock
1.5 Preventive measures of Electrical Shock
1.6 First Aid
Introduction To Electrical Engineering
If you want to shine like a sun, first
burn like a sun.
—Dr. A.P.J. Abdul Kalam
T
he objective of this lesson is to know about Electricity, the methods of power generation.
Beyond this, about the safety precautionary measures of electricity and also what are the
first aids to be given to a person who is affected by electric shock.
Introduction to Electrical Engineering
EMA_English_Chp01.indd 1 12/17/2019 4:42:42 PM

2
Basic Electrical Engineering — Theory
This subject is introduced in the
higher secondary level. In this subject,
students are taught how to maintain and
repair electrical appliances and electrical
machines and how to connect electrical
circuits and repairing minor or major
faults in the circuits and motor, rewinding
of electrical machines both theoretically
and practically. So, by learning this
subject, students are able to learn on their
own by practicing such learning.
We know that the Earth consists
of five big natural element such as water,
land, air, fire and sky. The sixth important
energy developed by human is called
“Electricity”. In this modern world, in
our day today life, electricity plays a vital
role. Simply to say, a man can live without
food but cannot live without electricity.
Thus in our life, the electrical goods play
an important role. Hence the students
must know about this source and how it
is applied.
All matters whether solid, liquid
or gaseous consist of minute particles
known as atom. According to modern
research, electric current means electrons
movement only. So we need to know about
atom.
1.1.1 Atom
It has a hard-central core known as
nucleus. It contains two types of particles;
INTRODUCTION ABOUT
ELECTRICITY, METHODS
OF POWER GENERATION
one is known as proton and carries positive
charge. The other is neutron, which is
electrically neutral. i.e. it carries no charge.
Around the nucleus, in an elliptical orbit,
the electrons are revolving. Electrons
carry the negative charge. The number
of electrons and number of protons in an
atom are equal. So the atom is electrically
neutral. The number of protons in the
nucleus of atom gives the atomic number.
The total number of neutron and proton
are known as atomic weight, because
negligible weight of the electron is not
taken to calculate atomic weight.
1.1.2
Methods Of Electricity
Production
Electricityisproducedbyextraction
of electrons from an atom. The energies
which are used to produce electricity are:
a) Friction
b) Light
c) Pressure
d) Heat
e) Chemical Action
f) Magnetism
a) Electricity due to Friction
Due to the friction of two materials,
electrons come out from one material
to join with the other material. The
material which loses the electron gets
(+)ve charge and the material which
attracted the electron gets (–)ve charge.
This type of electricity is called Static
Electricity.
Example :- Materials like glass, rubber,
wax, silk, reyon, nylon etc.

3 Introduction to Electrical Engineering
b) Electricity due to Light
When the light falls on the photo
sensitive materials, the electrons from
the surface produce the flow of current.
The material which emits electrons
due to the light fallen on the surface is
called “photo sensitive material”.
Example :- Sodium, Potassium,
Lithium and Caesium.
BENJAMIN FRANKLIN
Born: January 17, 1706
Died: April 17, 1790
F
ranklin started exploring the
phenomenon of electricity in
1746.
He was the first to label as
positive and negative respectively and
also the first to discover the principle
of conservation of charge. In 1748, he
constructed a multiple plate capacitor,
that he called as “electrical battery”.
He made important contribu
tions to science, especially in the
understanding of electricity, and is
remembered for the wit, wisdom, and
elegance of his writing
c) Electricity due to Pressure
Electrons in the outermost orbit of an
atom is extracted due to the pressure
applied to an atom and thus electricity
is produced. This is called “Piezo
Electricity”. In a telephone, diaphragm
is pressured by the sound waves.
Because of this, electric waves are
produced depending upon the pressure
of sound waves.
d) Electricity due to Heat
If the ends of two dissimilar metal rods
are joined together to form a junction
and is heated, voltage is developed at
the other ends and this effect is known
as thermo electric effect.
In the above four methods, sufficient
electricity is not produced and the
energy of electricity is also less. The
other two following methods are used
to produce sufficient electricity with
high energy.
A solar power plant in Kamuthi, Tamil
Nadu has just became the world’s largest
plant. With a capacity to produce 648 MW
of electricity, this plant comprises of
2.5 million individual solar modules and
covers an area of 10 sq km.

4
e) Electricity due to Chemical Action
By using chemical action method,
electrons are extracted from an atom
and electricity is produced. The voltage
developed in storage battery is due to
this chemical action only.
f) Electricity due to Magnetism
In this method, electrons are extracted
from an atom due to magnetism. In
generators, conductors are moving
within the magnetic field to generate
electricity.
1.1.3
Power Generating Plants
Today, approximately seven electric
power generating stations are available in
our country.
TYPES OF POWER GENERATING
PLANTS
a) Hydroelectric Power Plant
b) Thermal Power Plant
c) Atomic Power Plant
d) Gas Power Plant
e) Diesel Power Plant
f) Solar Power Plant
g) Wind Power Plant
a) Hydroelectric Power Plant
From the water reservoir, the water
is taken through the joint tubes to
the water turbine. For the rotation of
turbine, the kinetic energy of water is
converted into mechanical energy and
is converted into electrical energy by
using generator.
This type of plant is placed in Tamil
Nadu at Mettur, Kunda, Pykara,
Suruliyaru and Kadamparai.
b) Thermal Power Plant
Chemical energy is converted into
heat energy by burning coal or lignite
in boiler plant. Water in the boiler is
converted into steam by heat energy.
This steam is flowing through the
steam turbine which is connected to the
generator and this energy is converted
into mechanical energy by the rotation
of turbine. The mechanical energy is
again converted into electrical energy
by the use of generator.
This type of plant is placed in Tamil
Nadu at Ennore (Chennai), Neyveli,
Tuticorin and Mettur.
Thermal power plants play a major
role for the requirement of electricity
in Tamil Nadu.
c) Atomic Power Plant
By the diffusion of an atom of Uranium
or Thorium, more heat is produced.
The atomic power plant is working
based on this principle. The heat energy
produced is used to rotate the steam
turbine and this energy is converted
into mechanical energy. The generator
converts the mechanical energy into
electrical energy.
This plant is placed in Kalpakkam near
Chennai,Koodangulam in Tirunelveli
District and Tharapur in Rajasthan.
Leakage of radiation by this plant may
cause pollution and affect the health of
the people.
d) Gas Power Plant
Theprocessofgeneratingelectricalenergy
with the help of gas turbine (which acts
as a prime motor) is known as Gas power

plant. It is available in Ramanathapuram
and Nagapattinam districts.
e) Diesel Power Plant
This type of plant is used in places
where continuous supply of electricity
is needed i.e. in big factories. Electricity
is produced by the generator which is
connected to a big diesel engine.
Depending upon the requirements,
different capacities of small or large
diesel generators are used in hotels,
hospitals, jewellery shops, cinema
theatres, shipyards, etc.
f) Solar Power Plant
Forthepurposeofminimumproduction
of electricity, this type of plant is placed
on the roof of the buildings. In this
plant, electricity is produced by using
sun-rays. This is used in houses, hotels,
hospitals, traffic signal lights, etc.
g) Wind Power Plant
The Wind mill is rotated by heavy speed
of wind. Electricity is produced by the
generator which is operated by wind-
mill. This plant is placed at Kayathar
in Thirunelveli and Aralvaimozhi in
kanniyakumari District.
Fig 1.1 Types of Power Plants
Hydro Power Plant (Mettur) Thermal Power Plant (Neyveli)
Atomic Power Plant (Kalpakkam) Gas Power Plant (Chennai)
Diesel Power Plant (Chennai) Solar and Wind Plant (Kamuthi)

6
Fig 1.3 HT Lines
ELECTRICAL SAFETY
AND PRECAUTIONS
1.3
A man who works in the electrical
appliances must handle the work carefully
without any damage to the equipment
and workers. They must know all the
operations of electrical equipment clearly.
Electrical accident may occur only due to
carelessness. Due to this, workers will get
injured and cause damages. To avoid this,
electrical workers must follow the rules
and regulations while working.
1.3.1
Steps to be followed while
handling Electrical Equipments
1. Before the use of equipment, one must
know about the complete operation of
the equipment. Electrical connections
are made properly according to the
connection diagram.
2. Only the skilled person is allowed to
operate, testing and repairing machines.
3. Apersonwhoworksintheelectricpostand
tower post must wear safety belt and gloves.
4. After earthing, the overhead lines can be
discharged by discharge rod.
5. Check the condition of all hand tools.
6. While changing the fuse wire, keep the
main switch ‘OFF’. Use proper rating of
fuse wire for replacement.
INTRODUCTION OF LT/
HT LINE
Generated power from power station is
transmitted and is distributed through
transformers, overhead lines and cables to
the end users.
1.2.1 LT Lines
In India, low
Tension (LT) supply is
440 volts for three-phase
connections and 230
volts for single-phase
connection. Consumer of
electricity like individual houses, shops,
small offices and smaller manufacturing
units get their electricity on LT connection.
Fig 1.2 LT Line
1.2.2 HT Line voltage
High tension (HT) supply is
applicable for bulk power purchase which
needs 11 Kv or above. Major industries are
operating at High Tension supply only.

7. Under faulty conditions, the appliances
in houses must be checked and ensure
that the equipment is disconnected from
the supply.
Example:- Fan, Grinder, Mixie etc.
8. If fire occurs in the electrical circuit, the
main switch is turned OFF immediately.
For extinguishing electric fire, use of
carbon-di-oxide extinguisher or dry
powder extinguisher is advised.
(Water should not be used to extinguish
electric fire because it conducts electricity
and will cause severe accident.)
9. If any person gets electric shock by
touching the electric wire, the supply
should be disconnected immediately. The
person must be removed from the wire
using dry stick, drywooden plank or dry
cloth.
10. Sweating hand should not be used to
switch ON or work on the electric supply.
If the person has sweating on the hand
continuously, he must wear gloves.
ELECTRIC SHOCK
1.4
Human body has a electrical
conducting property. Without sweating
the resistance of human body is
approximately 80000Ω (ohm) and during
sweating, resistance of the human body is
approximately 1000Ω (ohm). If we touch
any current carrying conductor, the current
is conducted through our body to earth and
we get electric shock more over nervous
structure, heart, lungs, and brain can also
be affected. If the current is heavy, even
death may occur. Therefore, we must know,
even though current is essential, if it is used
wrongly, it will cause heavy loss i.e death and
economical loss.
To prevent such electrical shocks,
we must know about the preventive
measures and protective measures for
safety precautions.
PREVENTIVE MEASURES
TO AVOID ELECTRIC
SHOCK
1.5
Some of the methods employed to
avoid electric shock are listed below:
• The operation of electrical equipment
must be clearly known.
• Damaged wire should not be used for
wiring or electrical connection.
• The electrical instruments used for
connection (i.e switch, plug, pushing
etc). It should not have any scratch or
break.
• Thehandtoolsshouldbeproperlyinsulated.
• Proper earthing should be provided.
• For any reason, do not operate by
overcoming the safety rules.
FIRST AID
1.6
When a man gets affected by
an electrical shock in an unavoidable
condition, he must be given first aid before
taking to the hospital.
When a person is affected by current
shock, the circuit should be disconnected
first. If the main switch is nearer, put off the
switch. Using any wooden stick, we could
disconnect the person from the circuit.
Then immediately take him to hospital.
If the affected person loses
consciousness, but breathes normally, then

8
loosen his clothes and apply cold water on
his face and keep him in open air.
If the person does not breathe, then
immediately arrange artificial method of
respiration for breathing.
There are two methods of artificial
breathing.
1.6.1 Holger Nelson Method
Fig 1.4 Holger Nelson Method
In this method, the victim should
be kept in the bed facing the ground. The
helper sitting at his head should massage
his back using both hands. This is done
within two seconds.
1.6.2 Mouth to Mouth Method
In this method, the helper pushes
air by keeping his mouth on the victim’s
A tall thun-
derstorm cloud
can hold over
100 million volts
of potential. The
voltage potential in a lightning bolt is
proportional to its length, and varies
depending on the diameter of the bolt,
air density and impurities of the air.
mouth. By closing his nose, the air is filled
in lungs
Fig 1.5 Mouth to Mouth Method
Activities
Students are asked to do the con-
cept of static electricity by seeing
the picture shown.
When was electricity first used in
homes?
Edison’s light bulb was one of the first ap-
plications of electricity to modern life. He
initially worked with J. P. Morgan and a few
privileged customers in New York City in the
1880s to light their homes, pairing his new
incandescent bulbs with small generators.

1. Produce electricity by any two materials applying friction method.
2. How the supply leakage electric shock can be eradicated?
Hydroelectric Power Plant - நீர் மின் நிலையம்
Thermal Power Plant - அன மின் நிலையம்
Gas Power Plant - வாயு மின் நிலையம்
Diesel Power Plant - டீசல் மின் நிலையம்
Solar Power Plant - சூரிய ஒளி மின் நிலையம்
Wind Power Plant - காற்றாலை மின் நிலையம்
L.T – Low Tension Line - குறைவழுத்த மின்சாரம்
H.T – High Tension Line - உயவழுத்த மின்சாரம்

10
1. The smallest particle of an ele-
ment is known as
a) Atom
b) Molecule
c) Nucleus
d) Electron
2. The Atom is composed of
a) Electrons only
b) Protons only
c) Neutrons only
d)
Electron, Proton and
Neutron
3. HT Line means
a) 230V
b) 440V
c) Above 11 Kv
d) Below 11 Kv
4. LT Lines means
a) 230 volts or 440 volts
b) 440 Kv
c) Above 11 Kv
d) Below 11 Kv
5. In case of Electric fire, use
a) Dry sand
b) Wet sand
c) Carbon powder
d) Water
6. The number of electrons in an atom
are
a) Equal to the neutrons
b) Equal to protons
c)
Equal to the atomic structure
d) None of these
7. The supply voltage used for single
phase domestic purpose is
a) 110–120V
b) 120–130V
c) 220–230V
d) 400–440V
8. Switch should always be connected
with
a) Neutral wire
b) Earth wire
c) Phase wire
d) None of these
9. Without the sweating of human
body, the resistance is approxi-
mately.
a) 80 kΩ
b) 40 kΩ
c) 10 kΩ
d) None of these
Choose the Correct Answer:

Answer the Questions not Exceeding one page
1. Explain the method of preventing an electric shock.
2. Explain the different types of first aid given to electric shock.
Answer the Questions in Briefly
1. Define Atom.
2. What is electricity?
3. What are the methods used for production of electricity?
4. Define L.T Line.
5. Define H.T Line.
6. What are the precautions taken to avoid electric shock?
7. What are the different methods of artificial respiration?
3

12
Reference Book
1. ‘A text book of Electrical Technology’ Volume I and Volume III by B.L. Theraja and
A.K. Theraja, S. Chand Company Ltd
Answer the Questions not Exceeding two page
1. Explain the various methods adopted for power generation.
2. Writedownthestepstobefollowedwhilehandlingelectricalequipment.

13 Electrical Fundamental Terms
13
Electrical Fundamental Terms
“Black colour is sentimentally bad, but black
board makes the student’s life bright”
—Dr. A.P.J. Abdul Kalam

14
F
undamental terms are mostly important for doing Electrical circuits. This chapter deals
about the properties, types of conductors and insulators. Basically each one should know
about current, voltage, resistance, laws, emf and potential difference. The objective of this
lesson is also to know about the types of electrical circuits.
Calculation of power consumption is easily explained in this chapter. It is used to
calculate the power consumed (unit) in home, factory, etc. and the cost of expenses is
also calculated. This is very much useful to the younger generation to learn how to min-
imize the usage of electricity. It is helpful to reduce the unwanted usage of electricity and
the expense is reduced. Thereby it induces individual saving habit.
2.1 Introduction
2.2 Conductors – Properties – Types
2.3 Insulators – Properties – Types
2.4 Electrical Terms (Factors)
i) Current iii) Resistance – Laws
ii) Voltage iv) Electro Motive Force (EMF)
v) Potential Difference (PD)
2.5 OHM’s Law – Explanation
2.6 Types of Electrical Circuits
i) Series Circuit
iii) Series-Parallel Circuit
ii) Parallel Circuit iv) Kirchhoff’s Law
v) Work, Power and Energy
2.7 Capacitor – Types – Uses

INTRODUCTION
2.1
In this modern world, electricity
plays a major role in human life. This is
because, electrical appliances play an im-
portant role in our day to day life. Accord-
ing to theory, the current flow is nothing
but flow of electrons. The force required
to move electrons from higher level to
lower level is called voltage.
Hence conductors are required to
conduct the current from one place to an-
other place. They are classified in to three
types, namely solid conductors, liquid
conductors and gaseous conductors. The
material which does not conduct current
is called an insulator. Another one is a
semi-conductor, which has the property
in between the conductor and insulator.
Semi-conductors are used in making elec-
tronic devices.
First, let us study the types and
properties of conductors.
CONDUCTORS
2.2
The wire which carries or conducts
the current from the supply to the load is
called conductors. The example of loads
are fan, bulb, mixie, motors etc. Based on
the state the conductors, they are classi-
fied into three types:
i) Solid Conductors
ii) Liquid Conductors
iii) Gas Conductors
i) Solid Conductors
These conductors are converted into
thin wire, thin rod or strap for the pur-
pose of conduction.
Some of the examples of solid good
conductors are Silver, Copper, Brass,
Aluminium, Tungsten, etc.
ii) Liquid Conductors
The conductors in the form of liq-
uids are called liquid conductors.
Liquid conductors are mostly used in
batteries.
Example: Mercury, Sulphuric Acid,
Nitrate etc.
Mercury is used in high power
vapour lamp and automatic circuit
breakers.
iii)Gas Conductors
The conductors in the form of gas are
called gas conductors. These are used
in gas discharge lamps at high tem-
perature which are used in big shops,
malls, etc.
2.2.1 Properties of Conductors
So far we have studied about the
types of conductors. Let’s see the proper-
ties of good conductors.
• They conduct the current easily,
because they have low resistance
• Have high tensile stress
• They are more flexible
• They are not affected by corrosion
due to air, rain, heat, etc
• They are not affected by heat pro-
duced in conductor, when current
flow takes place

16
• Easy to solder
• Cost of the conductor is low and is
easily available to buy
INSULATORS
2.3
Insulator is a non-conducting ma-
terial, i.e. it resists electricity. It has high
resistance value normally in mega ohms.
Insulators should be good in condi-
tion, then only they prevent electric shock
due to current leakage. Generally, insulators
are classified into three types. Some exam-
ples of the three types of insulators are:
i) Hard Insulators: Bakelite, porcelain,
wooden plank, glass, mica, etc.
ii) Soft Insulators: Rubber, poly-vinyl
chloride, varnish coated papers, etc.
iii)Liquid Insulators: Mineral oil,
shellac, varnish, etc.
Properties of Insulators
The following are the important
properties of insulating materials. They are:
• High resistance and specific
resistance
• High dielectric strength
• Good mechanical strength
• It withstands high temperature
• May not get change in the shape due
to high temperature
• It does not absorb water
• It can be made to any shape
• It does not catch fire easily
ELECTRICAL TERMS
2.4
Here we study the electrical funda-
mental terms used in electrical engineering.
2.4.1 Current
Flow of electron in a conductor is
called as current. It is represented by the
letter ‘I’ and the unit is called ampere(A).
Current can be measured by ammeter.
1 Ampere: “One coulomb charge cross-
ing over the area of cross section of the con-
ductor in one second is called 1 ampere.
1 Coulomb: A collection of 2π × 1018
electrons has a charge of one coulomb.
Example:-Forwatertoflowthrough
a pipe from one end to the required place,
some pressure is required. In the same way,
electric pressure is required to move the
electron from one end to another end. This
flow of electron is called current and the
pressure required to move the electron is
called electric pressure or voltage.
2.4.2 Voltage
The electric pressure which is used to
move electrons from one end to another end
Fig 2.1 Hard Insulator

is called voltage. It is represented by the letter
‘V’ and the unit is volt. It is measured by volt-
meter. The other parameters termed as volts
are EMF, Potential and Potential Difference.
i) Electro Motive Force (EMF)
It is the force which causes the flow
of electrons in any closed circuit. It is
represented by volt.
ii) Potential and Potential Difference
The work done in bringing unit positive
charge from infinity to that point against
the application of electric field is called
potential. It is also represented as volt.
The difference of potential between
any two points in a electrical circuit
is called potential difference and is
expressed as volts only.
The following table represents the
difference between electromotive force
(EMF) and Potential Difference (PD).
Electro Motive
Force
(EMF)
Potential
Difference
(PD)
i)
EMF refers to
source of
electricity only.
PD exists between
any two points in a
circuit.
ii)
It is measured
when the circuit
is open.
It is measured on a
closed circuit.
iii)
It does not
depend upon the
resistance of the
circuit.
It depends upon
the resistance of the
circuit and is directly
proportional to it.
iv)
It is greater than
the potential
difference in the
same circuit.
It is less than the
electromotive force.
2.4.3 Electric Power
Power is rate of doing work.
The power is obtained by the following
expressions.
P = V × I. The unit is watt
P = Power
V = Applied Voltage
I = Current
2.4.4 Resistance
Resistance may be defined as the
property of a substance to oppose the
flow of current flowing through it. It is
represented by the letter R and the unit
is ohm(Ω). It is measured by ohm meter.
Mega ohms value is measured by using
megger
2.4.5 Laws of Resistance
The resistance of a conductor in a
circuit depends upon the following:
• It depends upon the material used
and its properties
• Resistance value of a conductor is
directly proportional to the length of
the conductor
• It is inversely proportional to the area
of cross section of a conductor
• It also depends upon the temperature
of the conductor when the current is
flowing through it
OHM’S LAW
2.5
In an electrical circuit the current,
voltage, and resistance are related to one
another. The relationship was derived by
the scientist Georg Simon Ohm. So it is
called Ohm’s Law.

18
Ohm’s law states that, “At a constant tem-
perature in any closed circuit, the current is
directly proportional to the voltage applied
and inversely proportional to the resistance
of the circuit.˝
i.e I α V and I α 1/R from this
V = I R and R = V
I
Where, V = Voltage in volts. I =

current in ampere and R = Resistance in
ohm
Georg Simon Ohm
Born: 1789
Died: 1854
G
eorgSimonOhm(1789–1854)
was a German physicist and
mathematician. As a school
teacher, Ohm began his research with
the new electrochemical cell, invented
by Italian scientist Alessandro Volta.
Ohm found that there is a direct
proportionality between the potential
difference applied across a conductor
and the resultant electric current. This
relationship is known as Ohm’s law.
V= I × R
R=V
I
I
=V
V
I
R
R
Problems
1) Supply voltage of the circuit is 240V.
The resistance value is 60Ω. Calculate
the current flowing through this circuit.
Voltage (V) = 240V
Resistance (R) = 60Ω
Current (I) = ?
According to ohm’s law, I = V
R
Current I =
240
60
= 4A
2) An electrical circuit has 1000W power
and the value of voltage is 240V. Find
the value of current flowing through it.
Power (P) = 1000W
Voltage(V) = 240V
Current(I) = ?
Power, P = V × I
1000 = 240 × I
I =
1000
240
= 4.16 A
3) Voltage of the circuit is 230V and
current 10A is flowing through it. Find
the value of Resistance.
Voltage (V) = 230V
Current (I) = 10 A
Resistance (R) =?
R

i.e 10 =
230
R
R =
230
10
= 23Ω
4) An electrical circuit is having 40Ω
resistance value. When 6A current
is following through this circuit, find
the voltage?
Resistance (R)= 40Ω
Current (I) = 6A
Voltage (V) = ?
R
i.e 6 = V
40
Voltage (V) = 6 × 40 = 240V.
TYPES OF CIRCUITS
2.6
The circuit is defined as the cur-
rent flowing from the supply points
through the load to complete the path. In
this chapter, we will study about the types
of the electrical circuits. There are three
types of electrical circuit namely;
i) Closed circuit,
ii) Open circuit and
iii) Short circuit.
These are explained below
i) Closed Circuit
When loads are connected in series
between two terminals of electric supply,
in such a way that the current passing
through the load is to activate the circuit.
It is called as closed circuit.
Fuse Switch
Globe
Fig 2.2 Closed Circuit
Example:- In our home, each room
has different wiring circuit i.e lighting cir-
cuit, power circuit, etc.
For example, if we switch ON the light
circuit, the light will glow, it is called a
closed circuit.
ii) Open Circuit
In this circuit, if there is no way to
the flow of current due to disconnection
of wire or the switch is in OFF condition,
then the circuit is called open circuit.
Fig 2.3 Open Circuit
Fuse Switch
Globe
Ex: In lighting circuit, if the switch is
in OFF condition or the wire is broken in
any place the lamp will not glow and it is
called an open circuit.
iii)Short Circuit
In this circuit, the two terminals
of the supply is connected directly with-
out a load and the current flow is infinite

20
because of very low resistance. It causes
heavy damage to the load.
Fuse Switch
Globe
Fig 2.4 Short Circuit
Here we will study about the classifi-
cation of the Electrical circuits. They are,
i) Series circuit
ii) Parallel circuit
iii) Series-parallel circuit
iv) Mesh (or) Network circuit
2.6.1 Series Circuit
Fig 2.5 Series Circuit
When three resistors are connect-
ed in series with each other as shown in
Figure 2.5, so that the same current passes
through all of them is called series circuit.
Here the resistors R1
, R2
and R3
are
connected in series. The current flowing
in all three resistors is same as that of sup-
ply current. But across each resistor, it has
a potential drop depending on their resis-
tance value.
According to Ohm’s law
V1
= I.R1
, V2
= I.R2
, V3
= I.R3
The sum of the three potential
drops in equal to the supply voltage
I = I1
= I2
= I3
V = V1
+ V2
+ V3
V = IR1
+ IR2
+ IR3
V = I(R1
+ R2
+ R3
)
V
I
= R1
+ R2
+ R3
Where R = R1
+ R2
+ R3
V
I
= R.
 Important rules for series circuit
1. In series circuit, the current flows
through only one path.
2. If one more resistance is to be
added, the total value of resis-
tance is increased. Total resistance
is equal to the sum of all the resis-
tance connected to this circuit.
i.e R = R1
+ R2
+ R3
+……..
3. The current flows in all resistor is
same
i.e, I = I1
= I2
= I3
4. The sum of the potential drop
across each resistor is equal to the
supply voltage i.e V = V1
+ V2
+ V3
5. If there is a fault in any place of
the circuit, the total circuit will be
inactive.
Example:- In many of the plac-
es like temple functions, malls, theatres
and marriage halls, serial sets are used
to make different decorative items using

serial bulbs. In serial circuit, the path of
the current flow is only one. So if any fault
(brake in wire connection) occurs in any
one place of the circuit, the total circuit
(serial set) is inactive.
2.6.2 Parallel Circuit
When resistors are connected
across one another so that the same volt-
age (supply voltage ) is applied between
the end point of each resistor, then they
are said to be in parallel connection.
In this circuit, the voltage across
each resistor is same as supply voltage but
the current in each resistor is different. In
this circuit, the sum of the current I1
, I2
and I3
is equal to supply current I, i.e I =
I1
+ I2
+ I3
According to ohm’s law
I
V
R
=
l l l
V
R
V
R
V
R
1 2 3
1 2 3
= = =
, ,
But I = I1
+ I2
+ I3
I = + +
V
R
V
R
V
R
1 2 3
1 1 1
1 2 3
R R R
+ +






I
V
=
1
R
+
1
R
+
1
R
1 2 3
I
V R
=
1
1 1 1 1
1 2 3
R R R R
= + +
=
+ +
R R R R R R
R R R
2 3 1 3 1 2
1 2 3
R =
R R R
R R +R R +R R
1 2 3
2 3 1 3 1 2
Important rules of a parallel circuit
i) In parallel circuit, the current flows
through two or more parallel paths at
a junction.
ii) Current varies in different resistances
i.e The sum of the current is equal to
supply current.
I = I1
+ I2
+ I3
+…
iii) The voltage is same in all resistors as
supply voltage.
V = V1
= V2
= V3
=…
Fig 2.6 Parallel Circuit

22
iv) The total value of the resistance is
reducedbyaddingonemoreresistorin
the circuit. If resistances are connected
in parallel then the total resistance
R =
R R R
R R +R R +R R
1 2 3
2 3 1 3 1 2
v) If there is a fault in any one resis-
tor, the other two resistors will work
because the current will flow through
these resistors.
Example: In our home or factories,
different types of electrical appliances are
used, i.e, fan, bulb, television, motor, heat-
er, etc. Each one has a separate circuit. For
example if there is a fault in fan circuit, the
fan circuit alone is inactive. Other circuits
like bulb, television etc will work contin-
uously. So, in parallel circuits there are a
number of current paths available.
PROBLEMS – (Series Circuit)
1) 10Ω, 20Ω and 30Ω resistances are
connected in series. The circuit volt-
age is 240V. Calculate the i) Total
resistance ii) current of this circuit.
R1
= 10Ω, R2
= 20Ω, R3
= 30Ω
V = 240V
R = ?
I = ?
When the resistors are connected in
series
Then R = R1
+ R2
+ R3
=10 + 20 + 30 = 60Ω
Total Resistance R = 60Ω
I
A
=
= =
V
R
240
60
4
Current I = 4A.
2) Three resistances 5Ω, 15Ω and R3
are connected in series. Resistance
of this circuit is 60Ω. Find the value
of R3
.
R = 60Ω, R1
= 5Ω, R2
= 15Ω, R3
=?
When the resistance are connected in
series
Then R = R1
+ R2
+ R3
60 = 5 + 15 + R3
and
60 = 20 + R3
R3
= 60–20 = 40Ω.
PROBLEMS – (Parallel Circuits)
1) Two resistances 8Ω and 2Ω are

connected in parallel. Voltage of this
circuit is 240V. Find the value of
i) Total Resistance
ii) Current.
R1
= 8Ω, R2
= Ω
R =?
In parallel circuit
R
R R
R R
=
+
=
+
= =
1 2
1 2
8
8 2
16
10
1 6
× 2
Ω
.

I=
V
R
,I=
240
1.6
=150A
2) Threeresistors6Ω,3Ωand2Ωarecon-
nected in parallel. The current flow of
this circuit is 2A. Find out the value of
i) Total Resistance
ii) Voltage.
R1
= 6Ω, R2
= 3Ω, R3
= 2Ω, I = 2A
R = ? V= ?
When they are connected in parallel
Then
R=
R R R
R R +R R +R R
=
6 3 2
3 2 + 6 2 +(6 3)
1 2 3
2 3 1 3 1 2
× ×
× × ×
( ) ( )
R =
+ +
= =
36
6 12 18
36
36
1Ω
I
V
R
V
V V
=
= =
2
1
2
,
2.6.3 Series - Parallel Circuit
In series parallel circuit, one or
more resistors are connected in series with
more resistors connected in parallel. This
is the combination of series parallel circuit.
Fig 2.7 represent, five resistors con-
nected in series parallel circuit. Here R1
,
R2
are connected in series and R3
, R4
, and
R5
are connected in parallel. These paral-
lelly connected resistors are connected in
series with R1
and R2
.
Hence the total resistance of the
circuit is
R R +R
R R R
R R R R R R
1 2
3 4 5
4 5 3 5 3 4
+
2.6.4 Kirchhoff’s Laws
Scientist Kirchhoff derived two
more laws based on ohm’s law namely,
i) Kirchhoff’s Current Law (KCL)
ii) Kirchhoff’s Voltage Law (KVL)
Current law is based on the current
and voltage law is based on the voltage.
These laws are explained as follows.
Kirchhoff’s Laws are used in deter-
mining the equivalent resistance of a com-
plex network and the current flowing in
the various conductors.
i) Kirchhoff’s Current Law (KCL)
The sum of the current flowing to-
wards a point (i.e junction) is equal to the
sum of the current flowing away from the
point. In other words, the algebraic sum of
Fig 2.7 Series - Parallel Circuit

24
the currents at any junction of a network
is zero.
Fig 2.8(i) represents Kirchhoff’s
Current Law. In this, I1
, I2
and I3
represent
the current flowing towards the junction
point I4
and I5
represent the current flow-
ing away from the junction point.
I1
+ I2
+ I3
= I4
+ I5
I1
+ I2
+ I3
− I4
− I5
= 0
ii) Kirchhoff’s Voltage Law (KVL)
In any closed electric circuit, the al-
gebraic sum of the potential drop is equal
to the supply voltage.
Fig 2.8(ii) represents, loads R1
, R2
,
and R3
connected in series. Potential drop
across R1
is IR1,
potential drop across R2
is
IR2
and potential drop across R3
is IR3
.
Gustav Robert Kirchhoff
Born: 1824
Died: 1887
G
ustav Robert Kirchhoff (1824-
1887) was a German physicist
who contributed to the
fundamental understanding of electrical
circuits. Kirchhoff formulated his circuit
laws, which are now ubiquitous in
electrical engineering.
V IR
V IR
IR
V V V V
IR IR IR IR
1 1
2 2
3
1 2 3
1 2 3
=
=
=
= + +
= + +
V3
Problems:
Example: 1
Calculate the current in a 2Ω resis-
tor using Kirchoff’s law in the following
circuit.
Fig 2.8(i) Kirchhoff’s Current Law
Fig 2.8(ii) Kirchoff’s Voltage Law

In the closed Loop ABEFA.
3I 2 I I 35
3I 2I 2I 35
5I 2I 35
1 1 2
1 1 2
1 2
+ + =
+ + =
+ =
( )
(1)
In the closed loop BCDEB
4I 2 I I 4
4I 2I 2I 4
2I 6I 4
1 3 15I
2 1 2
2 1 2
1 2
1
+ + =
+ + =
+ =
( )×
( )
,
0
0
0
+
+ =
+ =
( )− ( ) =
=
6I 1 5
2I 6I 4
3 2 13I 65
I
2
1 2
1
1
0
0
65
13
,
=
= 5A.
Substituting the value of I1
in equa-
tion 2, we get
2I 6I 4
2 5 6I 4
1 6I 4
6I 4 1 3
6I 3
I A
1 2
2
2
2
2
2
+ =
× + =
+ =
= − =
=
=
0
0
0 0
0 0 0
0
30
6
5
Then current in 2Ω resistor is I1
+ I2
= 5 + 5 = 10A
Example: 2
Find the current in the 3Ω resistor
in the circuit as shown.
In the closed Loop ABEFA
I 3 I I 1 V
I 3I 3I 1
4I 3I 1
1 1 2
1 1 2
1 2
+ + =
+ + =
+ =
( ) 0
0
0

(1)
In the closed Loop BCDEB
2I 3 I I 2 V
2I 3I 3I 2
3I 5I 2
2 1 2
2 1 2
1 2
+ + =
+ + =
+ =
( ) 0
0
0

(2)
3 4
I2
11I 5
2 0
50
11
4 545A 4 55A
. .
4 12I 2 I 8
1 2
0 0
(2)
(1) x 3 12I 1
+9I2
=30 ------- (3)

(4)
Substituting the value of I2
is equal to
3I 5I 2
3I 5 4 55 2
3I 2 22 75
2 75
I
916A
1 2
1
1
1
+ =
+ × =
= −
= −
=
= −
−
0
0
0
0
2 75
3
.
.
.
.
.
I
I 916A
1 = −0.
The value of current I1
is negative,
So the current flow in the curcuit, is in op-
posite direction.
The current in 3Ω resistor is I1
+ I2
= −0.92 + 4.55 = 10A
2.6.5 Work, Power and Energy
We are going to study about the
work,powerandenergytheirinter-relation
(2)
(3)
(2)

26
and calculation of power and energy in
electric circuit.
i) Work
Work is said to be done by Force
‘F’ when the point of its application moves
through a distance ‘S’.
Mathematically, Work = Force ×
distance = F × S =FS.
The unit of force is Newton (N). If
1 Newton force moves a body to a distance
of 1 metre, then the work done is 1Nm

(Newton - metre)
In an electric circuit, if 1 volt elec-
tric potential causes 1 coulomb of electric
charge to pass through it, then the work
done is equal to 1 joule.
1 joule = 1 volt × 1 coulomb
Coulomb = Ampere × time
i.e J V I t
= × ×
ii) Power
Power is the rate of doing work. Its
unit is watt (W).
Power =
Power VI watt
work done
time
=
Joule
time
=
V I t
t
× ×
=
P [V
V IR P I R
1 KW 1 watt
1 HP 746 watt
2
= =
=
=
, ]
000
iii)Energy
The amount of work done by an
equipment during a time period of ‘t’ sec-
onds. The unit of energy is joule.
Energy = power × time watt sec
The energy spent for the appliances
in 1 kwh is called as one unit i.e
1 unit = 1kWh
The power of iron box is 1000 watt.
when used for 1 hour, the energy
consumed is, 1000 watts × 1 hour =
1000Wh = 1kWh = 1unit.
Example: 1
The resistance of a lamp is 10Ω and
2A current is flowing through it. Calcu-
late the power of the lamp.
Solution:
Resistance (R) = 10Ω
Current (I) = 2A
Power = I2
.R
=22
× 10 =40W
Example: 2
In a factory, the following appli-
ances are used
a) 3hp motor works 5 hours per day.
b) 100W capacity of 40 lamps glow
8 hours per day.
c) 1500W capacity of heater works
6 hours per day.
Calculate the cost of energy con-
sumed in 30 days. (1unit cost is Rs. 6.00)
Solution:
a) 3hp motor works 5 hours per day
Energy
1119 kwh 1119 unit
Wh
=
= =
× ×
=
3 746 5
1000
11190
1000
0 0
. .

b) 100w capacity of 40 lamps glow
8 hours per day
Energy Wh
32kWh 32 units per day
=
= =
× ×
=
100 40 8
1000
32000
1000
c) 1500w heater works 6 hours per day
Energy
9kWh 9 units per day
Wh
=
= =
×
=
1500 6
1000
9000
1000
The total number of units consumed
in 30 days
= + +
( ) ×
= ×
=
1119 32 9 3
52 19 3
1565 7 units
.
.
.
0 0
0
Cost of electricity by for 30 days (1
unit=Rs.6)
= ×
=
=
1565 7 6
9394 2
Cost Rs 9394
.
.
.
CAPACITORS
2.7
Capacitor can be defined as, two
electrodes are separated by an insulating
di-electric medium. It is a device to store
electrical energy and to release it when re-
quired.
The charge in the capacitor is de-
noted by capacitance (Q) and the unit is
farad (F). The Di-electric medium can be
air, mica, wax coated paper or oil etc.
2.7.1 Working Principle
In Fig 2.9, a simple parallel plate

capacitor is connected with a battery.
Suppose plate ‘A’ is connected to the
+ve terminal and plate ‘B’ is connected to
–ve terminal of DC supply. On closing the
switch there will be momentary flow of
electrons from positive to negative. Some
electrons are withdrawn from the plate ‘A’,
leaving positively charged and transferred
to plate ‘B’ giving it a negative charge. This
flow of electrons gives charging current
which decreases and finally ceases when
the voltage across the capacitor plate has
Fig 2.9 Parallel Plate Capacitor
Symbols of Capacitor

28
become equal and opposite the applied
voltage. The charged capacitor is now full
of stored energy. This stored energy can
be used again when needed.
The factors on which the capacity
of capacitor depends are:
a. Directly proportional to the area of
the plate of the condenser.
b. Inversely proportional to the dis-
tance between the plate.
c. The nature of di-electric insulating
material.
2.7.2 Capacitance(C)
Capacitance of capacitor is defined
as the ratio between the charge given to
the condenser and supply voltage. It is de-
noted by the letter C.
Suppose a charge +ve ‘q’ units is giv-
en to condenser, the potential will then be
raised. The greater the charge given to the
condenser, the greater is the rise in its po-
tential.
we have q α v (or)
q
v
constant.
C =
q
v
farad
Hence, c is the capacity of the
condenser.
q is the charge given to the
condenser
v potential difference between the
plates.
The unit of capacity is ‘Farad’. A ca-
pacitor is said to posses a capacity of one far-
ad,whenitspotentialisraisedbyonevolt,and
when one coulomb of charge is given to it.
1 Farad =
1 coloumb
1 volt
2π × 1018
number of electrons is
mentioned as one coulomb.
2.7.3 Types Of Capacitor
Usually there are three types of ca-
pacitor. They are
1) Fixed capacitor
2) Variable capacitor and
3) Electrolytic capacitor
i) Fixed Capacitor
a) Mica Capacitor

Mica capacitor is widely used in ra-
tio circuit where fixed value con-
densers are required. These have
metal foil sheets forming the coat-
ing and separated by a flat mica
sheet as the dielectric medium
b) Paper Capacitor

Paper is rolled in the form of cyl-
inder and dipper in wax solution
in order to exhaust the air placed
in between two thin aluminium
plates. This type of capacitor is
used in de-coupling circuits.
c) Ceramic Capacitor
These are the modern capacitors. In
this, ceramic is used as di-electric
Figure 2.10 Capacitors

medium. The performance of this
capacitor may not be affected even
it get heated.
ii) Variable Capacitor

These capacitors are used in radio
receivers for tuning the receiver to a
particular transmitting station. In this
type, air is used as dielectric medium
between Aluminium plates.
iii)Electrolytic Capacitor

Another type of capacitors, which can
have a very large capacity of 10 to 100
μF in the electrolytic capacitor, is used
in Radio circuit and Electric circuit.
This is made by very thin Aluminium
sheets which are separated by a thin
layer of Aluminium Borate as Dielec-
tric medium.
2.7.4 Uses of Capacitors
1. Capacitors in Fluorescent Tube
(i) When connected parallel with the
supply, it improves power factor.
(ii) When connected in series with
one of the two tube connected in
parallel, it minimise the strobo-
scopic effect.
(iii)
It helps to avoid radio interfer-
ence when connected parallel
with the two contacts of tube
starter. Here, it eliminates the
sparkling due to the opening
of two contacts.
2. In motors
When connected in series with
starting winding of the single phase
motor, it splits one phase into two phases
and gives starting torque to the motor.
Example: Table fan, ceiling fan, and small
one phase motors.
3. In parallel with the supply lines
To improve the power factor be-
cause it takes leading current.
4. In eliminators
(An appliance which reduces 230 v Ac
to 3, 6, 9v Dc)
Capacitor is connected in parallel
with Dc side to filter remaining A.C.
5. In petrol cars
It is connected in parallel with the two
contacts of a distributor to avoid spark-
ing due to opening of these contacts.
These are the uses of capacitors in
various places.
Worked example:
Example:1 In an unbalanced bridge
circuit, calculate the current flowing through
all resistors by using Kirchoff’s Law.

30
In Closed Loop ABDA,
I1
+ 5I3
− 4I2
= 0
I1
− 4I2
+ 5I3
= 0 (1)
Closed Loop BCDB
2(I 1
− I3
) − 3(I2
+ I3
) −5I3
= 0
2I1
− 2I3
− 3I2
− 3I3
− 5I3
= 0
2I1
− 3I2
− 10I3
= 0 (2)
Closed Loop ABCA
I1
+ 2(I1
− I3
) + (I1
+ I2
) − 2=0
I1
+ 2I1
−2I3
+ I1
+ I2
=2
4I1
+ I2
− 2I3
= 2
1 4 5
2 3 10
4 1 2
0
0
2
1
2
3
−
− −
−




















=










I
I
I
∆ =










= +
( )+ − +
( )+ +
( )
= +
−
− −
−
1 4 5
2 3 10
4 1 2
0 0
1 6 1 4 4 4 5 2 12
16 144 +
+ =
7 23
0 0.
∆1
0 4 5
0 3 10
2 1 2
0 0 0 0 0
0 0
=










= +
( )+ +
( )+ +
( )
= + =
−
− −
−
6 1 4 2 5 6
8 3 110
∆2
1 2 4 4 5 4
2 2 4
=










= +
( )+ − +
( )+ +
( )
= + =
−
−
1 0 5
2 0 10
4 2 2
0 0 0 0 0
0 0 0
0
∆3
1 6 4 2 12
6 16 1
=










= − +
( )+ +
( )+ +
( )
= − + =
−
−
−
1 4 0
2 3 0
4 1 2
0 0 0
0
I
I
I
A
A
1
2
3
1 110
230
0 4782
2 40
230
0 174
3 10
230
0 0434A
.
.
.
Current through 1Ω resistor I1
=
0.4782A
Current through 2Ω resistor (I1
– I3
) =
0.4782 – 0.043 = 0.4352A
Current through 3Ω resistor = (I2
+ I3
)
= 0.174 + 0.043 = 0.217A
Current through 4Ω resistor I2
=
0.174A
Current through battery (I1
+ I2
) =
0.4782 + 0.174 = 0.6522A
Example.2
In a house, the following equip-
ment are used.
1) 1HP motor works 3 hours per day.
2) 40w, 10 lamps glow 5 hours per day.
3 900w capacity of heater works
2 hours per day.
Calculate the cost of energy con-
sumed in 60 days.
[For domestic purpose unit rate
is (1−100)-NIL,(101−200) Rs.3.50
(201−500) = Rs. 4.60, 500 units =
Rs. 6.60

1) 1HP motor works 3 hours per day.
Energy
2 238 kwh
2 238 unit per day
Wh
=
=
× ×
=
=
1 746 3
1000
2238
1000
.
.
2) 40w, 10 lamps glow 5 hours per day.
Energy
2 kwh
2 units per day
Wh
=
=
=
× ×
=
40 10 5
1000
2000
1000
3) 900w heater works 2 hours per day.
Energy
18 kwh
18 units per day
Wh
=
=
=
×
=
900 2
1000
1800
1000
.
.
4) Total number of units consumed in
60 days = 60 (2.238 + 2 + 1.8)
= + +
( )
= ×
=
6 2 238 2 18
6 6 38
362 28
0
0 0
. .
.
.
Total number of unit = 362
Unit
limit
Charge
per unit
Usage
unit
Cost
in Rs
1−100 NIL 100 NIL
101−200 3.50 3.50 × 100 350
201−500 4.60 4.60 × 162 745.20
Total 1095.20
Cost of electric charge for 60 days = Rs.
1095.20/-
Important note
Current - I – Ampere
Voltage – V – Volts
Resistance – R – Ω(ohms)
Emf – Volts
P.D – Volts
Power – P – watts
Ohms Law I = V/R
V = IR
R = V/I
Power P = I2
R
P = V × I
SeriescircuitIiscommontoallload,
V= V1
+V2
+V3
+…., R=R1
+R2
+R3
+……
Parallel circuit V is common to all
load.
I = I1
+ I2
+ I3
….
Resistance R
R R
R R R R R R
R
=
+ +
1 2 3
2 3 1 3 1 2
(if 3 loads)
Kirchoff’s
i) Current Law = I1
+ I2
+ I3
= I4
+ I5
(or)
I1
+ I2
+ I3
− I4
− I5
= 0
ii) Voltage Law V= IR1
+ IR2
+ IR3
ie V= V1
+ V2
+ V3
Power Calculation
Power consumed = KW × hour = Kwh
= 1unit.

32
Some Animals use electricity to survive in nature. Many of these animals are
found in the ocean where some use electricity to detect objects around them and
others use electricity to fend off predators or even hunt for food. One of the most
famous of the electric animals is the electric eel. The electric eel can produce
large amounts of electricity, even enough to kill a human or stun a large horse.
The eels typically swim into a school of fish, discharge a large amount of electric-
ity, and then dinner is served!
Current Tariff Calculation for Domestic Purpose
Units
Tariff Charges Units Cost
Fixed Subsidy From To Rs.
Upto 100 0 150 1 100 1.50
Upto 200 20 150 1 200 1.50
Upto 500 30 150 1 100 1.50
101 200 2.00
More than
500 50 150 1 100 1.50
101 200 3.50
201 500 4.60
501 onwards 6.60

1. Do the following by practice.
2. To make the simple wiring circuits
i)
One bulb is controlled by one switch in parallel connection. One bulb is
controlled by 2 switches.
ii)
In series connections, more than one lamp i.e series bulb connection is
controlled by single switch.
Conductors - மின் கடத்திகள்
Insulators - மின் கடத்தா ெபாட்கள்
EMF - மின்னியக் விைச
Resistor - மின் தைட
Capacitor - மின்ேதக்கி
Specific Resistance - இனத்தைட
Inductance - மின்ண்
Power - மின் திறன்
Energy - மின் ஆற்றல்

34
1. The material that does not con-
duct current is
a) conductor
b) insulator
c) semiconductor
d) none of these
2. Good conductor has a property of
a) low resistance
b) high resistance
c) medium of these two
d) none of these
3. Mineral oil is a
a) solid conductor
b) liquid conductor
c) soft Insulator
d) liquid Insulator
4. The value of current is measured
by
a) ammeter
b) voltmeter
c) wattmeter
d) energy meter
5. The unit of current is
a) voltage
b) watts
c) ohms
d) ampere
6. Thevalueofvoltageismeasuredby
a) voltmeter
b) ammeter
c) wattmeter
d) megger
7. The unit of volt is
a) watts
b) volt
c) ampere
d) ohms
8. The value of resistance is
measured by
a) voltmeter
b) wattmeter
c) ohm meter
d) none of these
9. The units of resistance is
a) ohms
b) watts
c) ampere
d) volt
10. EMF is measured in
a) volt
b) ohms
c) ampere
d) watts
11. Unit of power is
a) volt
b) ampere
c) watts
d) none of these
12. The power is measured by
a) wattmeter
b) ampere
c) voltmeter
d) none of these

13. According to ohm’s law I is
equal to
a) V2
/R
b) I2
R
c) V/I
d) V/R
14. The value of resistance in short
circuit is
a) low
b) very low
c) high
d) medium
15. Number of current path in a
series circuit is
a) two
b) three
c) one
d none of these
16. The unit of force is
a) newton
b) ampere
c) volts
d) joule
17. The value of 1HP is
a) 1000w
b) 750W
c) 900w
d) 746w
18. The unit of capacitance is
a) volt
b) ampere
c) farad
d) watts
19. Copper is a good
a) conductor
b) insulator
c) semi conductor
d) none of these
20. capacitor is denoted by the letter
a) q
b) v
c) i
d) c

36
Answer the Questions in Briefly:
1. What is called as a conductor?
2. What are the types of conductor?
3. What is called as an insulator?
4. What are the types of insulators?
5. Define current.
6. Define voltage.
7. Define Resistance.
8. What is called Electromotive force (EMF)?
9. What is called Potential Difference?
10. Explain the term ‘Electric power’.
11. Define ohm’s Law.
12.
Voltage of circuit is 240v and 12 A current is flowing through it.
Find the value of Resistance.
13. Explain ‘open circuit’.
14.
Two resistance 3Ω and 6Ω are connected in parallel Voltage of the
circuit in 240v. Find the value of total resistance.
15. What is called Work?
16. Explain the factors on which the capacity of condenser depends.
17. Define ‘capacitance’ of a capacitor.
3

1. What are the types of conductors Explain.
2. Explain the construction and working of series circuit.
3. Explain the construction and working of parallel circuit.
4. Explain the Kirchoff’s Laws.
5. Explain the construction and working principle of condenser.
6. What are the types of capacitors? Explain.
1. Explain the properties of a conductor.
2. Explain the properties of insulators.
3. Explain the difference between Electromotive force and Potential
Difference.
4. What are the important rules for series circuit?
5. What are the important rules for parallel circuit?
6. Three resistors 3Ω,6Ω and 18Ω are connected in parallel. The current
flow of the circuit is 3A. Find the value of i)Total Resistance ii)voltage.
7. Explain the laws of Resistors.
Reference Book
1. A text book of Electrical Technology’ Volume I by B.L. Theraja and A.K. Theraja, S.
Chand Company Ltd.

38
Electro Magnetism
T
o know the classification of properties of magnetic materials, terming it makes
it easy to read the concepts of magnet and also the types of electromagnetic
induction, Hysteresis and its laws are the scope and objective for learning.
Knowledge is truth of things to find
in every case of every kind.
— Thiruvalluvar
355
EMA_English_Chp03.indd 38 10-02-2019 12:28:17

39 Electro Magnetism
3.1 Magnetism – Introduction.
3.2 Properties of Magnets
i) Classification of Magnets
ii) Comparison of Electro Magnet and Permanent Magnet.
3.3 Magnetic Materials, Magnetic Terms and Properties
3.4 Electro Magnetism
3.5 Electro Magnetic Induction
3.6 Hysteresis Loop
3.7 Rules and Laws Related to Magnetism.
Magnetism is a force field that acts
on some materials. A physical device which
possesses this force is called as a magnet.
The force to attract iron is known
as Magnetism. The substance which pos-
sesses magnetism is called Magnet. The
materials attracted by a magnet are known
as Magnetic materials.
Magnetism plays an important role
in electricity. Without the aid of magnet, it
is impossible to operate devices like gen-
erator, electric motors, transformers, elec-
trical instruments, etc. Magnetism is also
used in the functioning of radio, televi-
sion, phones and ignition system of auto
mobiles. In this chapter salient features of
MAGNETISM -
INTRODUCTION
3.1
magnetism and function of magnetism in
the electrical equipment are explained.
• Magnets attract magnetic substances
such as iron, nickel, cobalt and its
alloy.
• If a magnet is freely suspended, its
pole will always tend to set themselves
in the direction of north and south.
• Like poles repels and unlike poles
attracts each other.
Fig 3.1 Like Poles
PROPERTIES OF MAGNETS
3.2

40
Cylindrical magnet are some types based
on shapes.
Fig 3.3 Permanent Magnets
ALNICO (Aluminium-Nickel-
Cobalt) is an alloy metal specifically
used as permanent magnet because it
can be lifted up to 50 times weight load
compared to its own weight. Permanent
magnets can be formed by touch method,
electric current method and induction
method.
b)
Temporary Magnet (or) Electro
Magnet
When an electric current is passed
through a coil of wire wrapped around a
soft iron core, a very strong magnetic field
is produced.
This is called as electro magnet.
If the current is cut off, the core will
be demagnetized, and hence known as
temporary magnet.
Fig 3.4 Electro magnet
• If a magnet is broken into number of
pieces, each piece becomes an inde-
pendent magnet which has North
and South.
• A magnet can impart its proper-
ties by induction to any magnetic
material.
Fig 3.2 UnLike Poles
• A magnet loses its properties when
it is heated, hammered or dropped
from height.
3.2.1
Classification of Magnets
1. Natural Magnet
The magnet found in nature is
known as lodestone. The natural mag-
net is one of the iron ore magnetite with
chemical composition Fe3
O4
2. Artificial Magnet
The magnets prepared by artificial
method are called artificial magnets. It
can be made in different shape, size and
strength only in certain metals. There are
two types of artificial magnet.
a) Permanent Magnet
In a permanent magnet, the mag-
netic materials can retain magnetic prop-
erty permanently for a long time. Bar mag-
net, Horse Shoe magnet, Ring Magnet,

3.2.2
Comparison of Electromagnet
Permanent Magnet.
ELECTRO
MAGNET
PERMANENT
MAGNET
1.
Polarity can be
changed easily.
Polarity cannot
be changed easily.
2.
Strength can be varied. strength cannot
be varied.
3. More cost. Less cost
4.
Suitable for motor
generator of large size.
Not suitable for
large size.
5.
Used in electric bells,
signals, escalators,
cranes.
Not used in any
of these.
6.
Cannot be used in
navigation
Mostly used in
navigation as
magnetic needle
7.
Cannot be used in
cycle and Motor cycle
dynamo.
Used in cycle
and Motor cycle
dynamo.
Magnetic materials are classified
based on permeability property by three
types.
a) Dia-Magnetic Materials
b) Para Magnetic Materials
c) Ferro Magnetic Materials
a) Dia – Magnetic Materials
•
The materials which are repelled
by a magnet are known as dia-
magnetic materials. Ex: zinc,
mercury, lead, sulphur, copper,
silver, Bismuth, wood, etc.
•
The permeability value of these
materials is less than one.
MAGNETIC MATRIALS
3.3
b) Para Magnetic Materials
•
The materials which are not
strongly attracted by a magnet
are known as paramagnetic mate-
rials. Ex: (aluminium, tin, plati-
num, magnesium etc.).
•
materials is just greater than one.
c) Ferro -Magnetic Materials
•
The materials which are strongly
attracted by a magnet are known
as ferromagnetic materials. Ex:
(iron, steel, nickel, cobalt, etc.)
•
materials is very high (var-
ies from several hundreds to
thousands).
•
Materials which are easily
magnetized with a high relative
permeability, low coercive force
(small hysteresis) are called soft
ferromagnetic materials.
•
Materials which are difficult to
magnetize, but retain magnetism
with great tenacity, with low rel-
ative permeability, high coercive
force are called hard ferromag-
netic materials.
3.3.1
Magnetic Terms and Properties
a) Magnetic Field:
Fig 3.5 Magnetic Field Lines

42
•
Themagneticfieldaroundamagnet
is represented by imaginary lines
called magnetic line of force.
•
The magnetic line of force
emerges from north pole to south
pole and it continues through the
body of magnet to form a closed
loop.
•
Two magnetic lines of force will
not intersect each other.
•
If magnetic lines of force are rows
together, the field is strong. If they
are spaced out the magnetic field
is weak.
b) Magnetic Flux
•
The amount of magnetic field
produced by a magnetic source is
called magnetic flux.
•
It is denoted by Greek Letter ϕ
and its unit is weber.
c) Magnetic Flux Density
•
The magnetic flux density is the
flux per unit area at right angles
to the flux.
Magnetic flux density, B = ϕ/A wb/m²
d) Permeability
• Permeabilityofamaterialmeans,the
conductivity for magnetic flux. The
greater the permeability of material,
the greater is its conductivity of
magnetic flux and vice-versa. Air or
Vacuum is the poorest conductor of
magnetic flux. The absolute (actual)
permeability µ0
(Greek Letter ‘mu’)
of air is 4π×10–7
Henry/metre.
The absolute (actual) permeability
of magnetic material(μ) is much
greater than μ0
.
The ratio between permea-
bility of material and permea-
bility of air (μ0
) is called relative
permeability(μr
)
μr
=μ/μ0

The relative permeability for air is
1 ( μr
=μ0
/μ0
)
The value of μᵣ for all non- magnetic
material is also 1.

The relative permeability of magnetic
materials is very high. For example,
soft iron (i.e pure iron) has a relative
permeability of 8000, whereas its val-
ue for perm alloy (22% Iron, +78%
nickel) is as high as 50,000.
e) Magneto Motive Force (MMF)
It is a magnetic pressure which tends
to set up magnetic flux in a Magnetic circuit.
The work done in moving a unit
magnetic pole once round the magnetic
circuitiscalledMMF.Itisequaltotheproduct
of current and number of turns of the coil.
MMF = Number of turns × current.
Its unit is Ampere-turns
f) Reluctance
The opposition that the magnetic
circuit offers to magnetic flux is called
reluctance. Magnetic materials (eg iron, steel)
have low reluctance, on the other hand non-
magnetic materials have a high reluctance.
Reluctance S = l/ μ0
μr
A
g) Magnetic Neutral Axis (MNA)
The imaginary line which is
perpendicular to the magnetic axis and

passes through the centre of the magnet is
called magnetic neutral axis. There is no
magnetic influence along this line.
Magnetic Axis (MA) is the imagi-
nary straight line joining North to South
pole. There is maximum magnetic influ-
ence along this line.
i) Magnetic Saturation
The limit beyond which the strength
of magnet cannot be increased is called
magnetic saturation.
ii) Residual Magnetism
It is the magnetism which remains in
a material when the effective magnetizing
force has been reduced to zero.
iii) Magnetic Retentivity
The property of retaining magnetism
by a magnetic material is called Magnetic
Retentivity.
iv) Hysteresis
The energy required to demagne-
tize the residual magnetism of material is
known as hysteresis.
v) Leakage Flux
Leakage flux is defined as the
magnetic flux which does not follow the
particularly intended path in a magnetic
circuit.
Taking the example, solenoid you
can explain the leakage flux and the fringing
both. When a current is passed through
solenoid, magnetic flux is produced by it.
vi) Coercivity
Coercivity is a measure of the
ability of a ferro magnetic materials to
withstand an external magnetic field with-
out becoming demagnetized.
When current is passed through a
coil of wire, a magnetic field is set up around
the coil. If soft iron bar is placed inside the
coil of wire carrying current, the iron bar
becomes magnetized. This process is known
as electro magnetism.
The iron remains as a magnet as
long as the current is flowing in the circuit.
It looses its magnetism when current is
switched off.
The polarity of an electromagnet
depends upon the direction of the current
flowing through it.
If the direction of current is altered,
the polarity of the magnetic field will also
be changed.
Fig 3.6 Magnetic Field Lines
3.4.1
Electro Magnetism in a Current
Carrying Conductor
A magnetic field is formed around a
conductor carrying current. The direction
ELECTRO MAGNETISM
3.4

44
of the magnetic field depends on the di-
rection of the current flow.
Fig 3.7 Right Hand Grip Rule
Right Hand Grip Rule
•
It is used to determine the direction
of the magnetic field in a current
carrying conductor.
•
If you wrap your fingers around
the wire with your thumb pointing
direction of current flow, your index
finger will point the direction of
magnetic field.
Right Handed Cork Screw Rule
•
Assume a right handed cork screw to
be along the wire to advance in the
direction of current.
•
The motion of handle gives the
direction of magnetic lines around
the conductor.
Force Between Parallel Conductors
When two current carrying
conductors are parallel to each other, a
mechanical force act on each conductor.
This force is due to magnetic field produced
in the two conductors. If the currents are in
the same direction, the forces are attractive.
If the currents are in the opposite direction,
the forces are repulsive.
i) Current in The Same Direction
Fig 3.8 Currents in Same Direction
• If two wires (A, B) carrying current in
same direction are brought together,
their magnetic fields will aid one
another and attracts.
• Since the flux lines around two
conductors are going in the same
direction, the flux lines join and the
field brings the wire together.
ii) Current in The Opposite Direction
Fig 3.9 Currents in Opposite Direction
•
If two wires (A, B) carrying current
in opposite directions are brought
together their magnetic field will
oppose one another.
•
Since the flux lines around two con-
ductors are going in the opposite
direction, the flux lines cannot cross
and the field moves the wires apart.
A B

3.4.2 Solenoid
A current carrying wire is made
to form a loop and a number of loops are
wound in the same direction to form a coil.
More magnetic fields will add to make the
flux lines through the coil stronger and
dense.
A helically wound coil that is made to
produce a strong magnetic field is called
a solenoid.
The flux lines in a solenoid act in
the same way as in a magnet. They leave
the north pole and go around to the south
pole.
The directions of the magnetic field
in a solenoid is known by the following
rules.
End Rule
Look at the end of the solenoid of
the electromagnet. If the current in the coil
is clock wise the end is Southpole . If the
current in the coil is counter-clockwise the
end is North pole.
Fig 3.10 End Rule
Helix Rule
Hold the right hand palm over the
solenoid in such a way the fingers point
in the direction of current in the solenoid
conductors. Then the thumb indicates the
direction of magnetic field (North) of the so-
lenoid.
Fig 3.11 Helix Rule
Uses of Solenoid
• Used for Circuit Breaking.
• Voltage Regulating Device.
• Automatic Motor Starter.
• Contactor, Elevator, Crane.
Toroid
A helix bent into a circular form is
known as Toroid ( i.e coiled coil)
Fig 3.12 Toroid
ELECTROMAGNETIC
INDUCTION
3.5
Electricity induced by the magnetic
field is known as Electro Magnetic
Induction.

46
S.NO PROPERTIES MAGNETIC CIRCUIT ELECTRIC CIRCUIT
1 Definition The closed path followed by magnetic
flux is called magnetic circuit.
Theclosedcircuitfollowedbyelectric
currentiscalledelectriccircuit.
2 Driving Force MMF is the pressure required to set
up the magnetic flux in magnetic
circuit (Ampere-Turn)
EMF is the pressure required to
set up the current in an Electric
circuit (Volt).
3 Response
FLUX (Ø) =
MMF
Reluctance
weber
( ) ( )=
EMF
Resistance
Ampere
CURRENT I ( )
4 Impendance RELUCTANCE(S)=l/(μ0
μr
A)
[AT/Weber]
RESISTANCE (R)=ρl/A(ohms)
5 Admittance
PERMEANCE =
1
Reluctance
wb AT
[ / ] CONDUCTANCE =
1
Resistance
( )
Siemens
6 Proportionality
Permeability
M H
RELUCTIVITY=
1
( / ) Conductivity
ohm meter
RESISTIVITY=
1
( – )
7 Density FLUX DENSITY B = μ H(wb/m2
) CURRENT
DENSITY J=I/A(Amp/ m2)
8 Field Intensity MAGNETICFIELD
INTENSITY(H)=NI/l(AT/m)
ELECTRIC FIELD
INTENSITY=E/l(volt/m)
3.4.3
Comparision Between Magnetic and Electric Circuits
Whenever a conductor or coil is
moved or rotated in a magnetic field and cut
the magnetic line of force (flux), an EMF will
be induced in that conductor or coil.
3.5.1
Faraday’s Law of
Electromagnetic Induction
FIRST LAW: Whenever a conductor cuts
magnetic flux, an EMF is induced in that
conductor.
SECOND LAW: The magnitude of the
induced EMF is directly proportional to
the rate of change of flux linked with the
conductor.
The two types of EMF induced are:
i) Dynamically induced EMF.
ii) Statically induced EMF.
3.5.2 Dynamically Induced EMF
Moving a coil/conductor in a
uniform magnetic field will induce an EMF
which is known as dynamically induced
EMF. Generators work on this principle.
Consider a conductor of length l
(meters) placed in a uniform magnetic field
of density B(wb/m²), moved with a velocity
V(m/s) perpendicular to the direction of the

magnetic field. Then the flux is cut by the
conductor and an EMF is induced.
The magnitude of EMF inducede is
e = BlV sinθ
3.5.3
Statically Induced Emf
By keeping a conductor or coil in
statically and varying the magnetic field
will induce an EMF in the conductor or
coil which is statically induced EMF.
Statically induced EMF can be
classified as self inductance and mutual
inductance.
(a) Self Induction
• Thisisthe EMF inducedinacoildueto
the change of its own flux linked with it.
• If current through the coil is changed,
then the flux linked with its own
turns will also change, which will
produce self induced EMF.
• The induced EMF is always opposite
in direction to the applied EMF.
Fig 3.13 Self Induction
(b) Mutual Induction
It is the ability of one coil to produce
an EMF by induction. When the current in the
secondcoilchanges,bothcoilsareplacednearer.
• When two coils are placed nearer and
current is passed through one of the
coil, magnetic flux will be produced
which is common to both coils.
•
When current through first coil is var-
ied, the magnetic flux will vary, which
will induce an emf in second coil.

The north pole of a magnet points roughly toward Earth's north pole and vice-versa.
That's because Earth itself contains magnetic materials and behaves like a gigantic
magnet.

If you cut a bar magnet in half, it's a bit like cutting an earthworm in half! You get
two brand new, smaller magnets, each with its own north and south pole. (This is,
of course, a joke. You don't get two worms if you cut a worm in half. But you do get
two magnets.)

If you run a magnet a few times over an unmagnetized piece of a magnetic material
(such as an iron nail), you can convert it into a magnet as well.

48
Fig3.14 Mutual Induction
LENZ’S LAW
A change in current produces an
emf, whose direction is in such a way
that it opposes the change in current.
Fleming’s Right Hand Rule
The direction of induced EMF in
generators and alternators (Dynamically
induced emf) is known by Fleming’s Right
hand rule.
Stretch the thumb, forefinger and
middle finger mutually at right angles [90°]
to each other.
If the thumb indicates the direction
of motion of the conductor, the forefinger
indicates direction of the magnetic flux, then
the middle finger indicates the direction of
the induced EMF.
Fig 3.15 Right Hand Rule
Take a piece of iron bar AB and
magnetise the same by placing it within the
field of solenoid. The field H produced by the
solenoid is called the magnetising field. The
field (H) can be increased (or) decreased by
increasing(or)decreasingthecurrentthrough
it. Let ‘H’ be increased slowly from zero to a
maximum value and the corresponding value
of flux density (B) be noted. If we plot the
relation between H and B, OA is obtained.
The material becomes magnetically saturated
at point A and has the maximum flux density
induced in it (H = OM).
Fig 3.16 Hysteresis Loop circuit
Now if ‘H’ is decreased slowly by
decreasing the current in the solenoid, the
flux density(B) will not decrease along AO
butwilldecreaselessrapidlyalongAR1.
When
H is made to be zero, at that time, B will not
be zero but will have the value OR1.
It means
that on removing the magnetising force, H
the iron bar is not completely demagnetized.
This value (B = OR1
) is the retentivity of the
material (Residual magnetism).
To demagnetise the bar, we have to
supply the force H in the opposite direction.
HYSTERESIS LOOP
3.6

Positive
Saturation
Coercive Force
(positive)
Coercive Force
(negative)
Residual Magnetism
(positive)
B
c
a
f
g
H
b
d
Residual Magnetism
(negative)
Negative
Saturation
Fig 3.17 Hysteresis Loop
When H is reversed by reversing the current
through the solenoid, then B is reduced to
zero at point C where H = OC. This value is
required to clear off the residual magnetism.
This is known as the coercive force and is a
measure of the coercivity of the material.
After reducing the magnetism to
zero, if the value of H is further increased
in the negative direction ( i.e reversed direc-
tion), the iron bar reaches a state of magnet-
ic saturation at point A1
, which is negative
saturation (H = OL). By taking H back from
its value corresponding to negative satura-
tion (OL) to its value for positive saturation
(OM), the closed loop which is obtained
when iron bar is taken through one com-
plete cycle of magnetism. This loop is called
Hysteresis Loop .
In this BH curve, it is seen that B
always lag behind H. The two never attain
zero value simultaneously .Hysteresis liter-
ally means to lag behind . The closed loop
OAR1
, CA1
R2
C1
A which is obtained when
iron bar is taken through one complete cy-
cle of reversal of magnetisation is known as
Hysteresis loop.
Hysteresis Loss
• It is the loss of power due to hysteresis
and expressed in watts or KW.
•
Hysteresis cannot be avoided but can be
minimised by selecting proper metal.
•
Lesser the hysteresis constant, better
the metal for A.C electromagnet.
•
So, usually silicon steel is used for A.C
circuitasit'shysteresisconstantis0.001.
RULES/LAWS RELATED TO MAGNETISM
3.7
Rule or Law Uses
Cork Screw Rule To find out the direction of line of force (magnetic field) around a
straight current carrying conductor.
Helix Rule To find out polarity of the poles of an electromagnet (solenoid)
End Rule To find out polarity of the poles of an electromagnet (solenoid)
Fleming’s Right Hand Rule To find out the direction of current in the conductor of a generator.
Fleming’s Left Hand Rule To find out the direction of rotation of the armature of D.C motor.
Lenz’s Law To find out the direction of the counter current produced in the
armature.
Ampere rule To find out the direction of line of force around the current
carrying conductor.

50
1. Apply the magnetic rule by using two magnets.
2. How can the induced current be known by mutual induction method.
3. Do the magnetism practice observed from the diagram.
Permanent Magnets - நிைலக் காந்தம்
Artificial Magnets - ெசயற்ைகக் காந்தம்
Electro Magnets - மின்காந்தம்
Mmf- Magneto-Motive-Force - மின் இயக் விைச
Magnetic Flux - காந்தப் லம்
Magnetic Saturation - காந்தப் ரிதம்
Residual Magnetism - தங்கிக் ெகாண்ட காந்த சக்தி
Hysteresis Loop - காந்தத் தயக்க வைளயம்

1. Magnetic field lines
a) intersect each other
b) cannot intersect.
c) are crowded near poles
d) All of the above.
2. In an electro magnet, when cur-
rent is switched off, the Iron bar
a) holds its magnetism
b) gains voltage
c) losses its magnetism
d) gains current
3. The direction of magnetic lines
of force is
a)
from south pole to north pole
b)
from north pole to south pole
c)
from one end of the magnet
to other
d) none of the above.
4. The permanent magnet is used in
a) Dynamo
b) Energy meters
c) Transformers
d) Loud Speaker
5. Magnetic properties in a mag-
net can be destroyed by
a) heating
b) hammering
c)
by inductive action of
another magnet
d) by all above methods.
6. A permeable substance is one
a) which is a good conductor
b) which is a strong magnet.
c) which is a bad conductor
d) throughwhichthemagneticline
of forces can pass very easily.
7. A material which is slightly repelled
by magnetic field is known as
a) Ferro magnetic material
b) Para magnetic material
c) Dia magnetic material
d) Conducting material.
8. Totalnumberofmagneticfieldlines
passing through an area is called
a) Magnetic flux density
b) EMF
c) Magnetic flux
d) Voltage.
9. The commonly used material for
shielding or screening magnet is
a) Copper
b) Aluminium
c) Soft Iron
d) Brass
10. The unit of magnetic flux density is
a) weber/m2
b) lumens
c) tesla

52
11. Indicate which of the following
material does not retain magne-
tism permanently.
a) Soft iron
b) Stainless steel
c) Hardened steel
d) None of the above.
12. The material having low reten-
tivity are suitable for making a
a) weak magnet
b) temporary magnet.
c) permanent magnet
13. The absolute permeability (μo
) of
air or vacuum is
a) 4π × 10-7
H/M
b) 4π × 10-3
Henry/Metre
c) 4π × 103
H/M
d) 4π × 107
H/M
14. Which of the following circuit
element stores energy in an
electromagnetic field?
a) Capacitor
b) Inductance
c) Resistance
d) Variable Resistance.
15. EMF induced by motion of conduc-
tor across magnetic field is called
a) emf
b) dynamic emf
c) static emf
d) rotational emf
16. The magnitude of the induced emf
in a conductor depends on the
a) flux density of the magnetic field.
b) amount of flux cut
c) amount of flux linkages
d) rate of change of flux linklages.
Answer the Questions in briefly
1. What is magnetism?
2. Why is ALNICO used for permanent magnet?
3. State any three uses of permanent magnets.
4. State Maxwell cork’s screw rule.
5. What is solenoid and Toroid?
6. What are the uses of solenoid?
7. Define End Rule.
8. Define Faraday’s laws of electromagnetic induction.
9. State Flemings right hand rule.
10. Define Lenz’s law.
11. What is hysteresis loss?
3

1. Compare electro magnet and permanent magnet.
2. Explain magnetic materials?
3. Define Flux, MMF and Reluctance.
4. Define Magnetic saturation, Retentivity and Residual magnetism.
5. Compare magnetic and electric circuit.
6. How to do you increase the magnitude of induced emf.
Reference Book
1. ‘A text book of Electrical Technology’ Volume B.L. Theraja and A.K. Theraja, S. Chand
Company Ltd.
1. Explain the types of electro magnetic induction with neat diagram.
2. Explain hysteresis loop with a neat diagram.

54
Batteries
T
he main objective of a battery is to know the classifications of the various
types of cells, also to know about the chemical
reactions during charging
and discharging, maintenance, and tips for care of battery.
— Swami Vivekananda

55 Batteries
Battery is a device that transforms
chemical energy into electrical energy.
Batteries consist of electro chemical cells
that are electrically connected.
Every battery has two terminals. The
positive one is called ‘Anode’ and negative one
is called ‘Cathode’ as shown in and Fig 4.1.
Battery is a storage device used for
the storage of chemical energy and for the
transformation of chemical energy into
electrical energy.
Battery consists of a group of two
or more electric cells connected together
electrically in series. Battery acts as a por-
table source of electrical energy.
Battery or cell is an electrochemical
device consisting of two electrodes made up
of different material and an electrolyte. The
chemical reactions between the electrodes
and the electrolyte produce voltage.
INTRODUCTION AND
DEFINITION
4.1
4.1 Introduction and Definition
4.2 Dry Cell
4.3 Voltaic Cell
4.4 Secondary Cell and its Classification
4.5 Lithium Ion Battery
4.6
Seven Features About Disparity Between Lead Acid Battery and Lithium
Ion Battery
4.7 UPS Battery
4.8 Maintenance of Batteries
4.9 Do’s and Don’ts of Storage Battery
4.10 Nine Tips for Proper Battery Care
Fig 4.1 Simple Battery Structure

56
CellsareClassifiedasDryandWetCells.
CELL
DRY CELL WET CELL
4.1.1 Dry Cell
Dry cell is one that has a paste (or)
gel electrolyte. It is semi sealed and can be
used in any position. Nowadays the term
‘Dry cell’ refers to a cell that can be oper-
ated in any position without leakage.
4.1.2 Wet Cell
Wet cells are cells that must be
operated in an upright position. These cells
have vents to allow the gases generated
during charging or discharging to escape.
The most common wet cell is the Lead-
Acid cell.
4.1.3 Primary Cells
Primary cells are those cells that are
not rechargeable. That is, the chemical re-
action that occurs during discharges is not
easily reversed. When the chemicals used
in the reactions are all converted, the cell is
fully discharged. It must then be replaced by
a new cell.
Example:-
Voltaic cell, Leclanche cell, Alkaline
cell, Mercury cell, Lithium cell.
The most common and the least
expensive type of a dry cell battery in the
Zinc-carbon type as shown in figure 4.2.
DRY CELL
4.2
Fig 4.2 Dry Cell.
The Zinc-carbon consists of a
zinc container which acts as the nega-
tive electrode. In the center, carbon rod
which is a positive electrode is present.
The electrolyte takes the form of a moist
paste, made up of a solution containing
ammonium chloride. As with all primary
cells, one of the electrode becomes de-
composed as part of chemical reaction.
As a result, cells left in equipment for
long periods of time can rupture, spill-
ing the electrolyte and causing damage
to the other parts.
Zinc-carbon cells are produced in
common standard sizes. These include
1.5v AA, C, D cells.
(AA-pen type cell, C-minimum size,
D-large/Economy size.)

57 Batteries
4.2.1 Uses of Primary Cell
Primary cells are used in electron-
ic products ranging from watches, smoke
alarms, cardiac pacemaker torches, hear-
ing aids, transister radios, etc.
4.2.2 Series Cell Connection
Cells are connected in series by con-
necting the positive terminal of one cell to
the negative terminal of the next cell. (See
the connection diagram in fig. 4.3)
Fig 4.3 Batteries Series Connection
Identical cells are connected in series
to obtain a higher voltage is available as a
single cell. With this connection of cells,
the output voltage is equal to the sum of the
voltages in the cells.However, the ampere
hour (A-h) rating remains equal to that of a
single cell.
4.2.3 Parallel Connection
Cells are connected in parallel
by connecting all the positive terminals
together and all the negative terminals
together as shown in the figure 4.4.
Identical cells are connected in par-
allel to obtain a higher output current or
ampere-hour rating. With this connection
of cells, the output ampere-hour rating is
equal to the sum of the ampere-hour rating
of all the cells. However, the output voltage
remains the same as that of a single cell.
When connecting groups of cells or
batteries in parallel, each group must be
in the same voltage level paralleling two
batteries of unequal voltage levels set up a
difference of potential energy between the
Fig 4.5 Voltaic Cell
Fig 4.4 Batteries Parallel Connection

58
two. As a result, the higher voltage battery
will discharge its current into the other
battery until both are at equal voltage value.
A voltaic cell is an electrochemical cell
that uses a chemical reaction to produce elec-
trical energy. In this cell, Anode is an electrode
where oxidation occurs. Cathode is an elec-
trode where reduction occurs.
In a voltaic cell, copper and zinc are the
two electrodes and sulphuric acid is an elec-
trolyte. When placed together, a chemical re-
action occurs between the electrodes and the
sulphuric acid.
This reaction produces a negative
charge on the zinc (surplus of electron) and a
positive charge on the copper (deficiency of
electrons). If an external circuit is connected
across the two electrodes, electrons will flow
from the negative zinc electrode to the positive
copper electrodes as shown in fig 4.5.
The electric current will flow as long as
the chemical action continues. In this type of
cell, the zinc electrode is eventually consumed
as a part of the chemical reaction.
The voltaic cell is also known as wet
cell, because in this, a liquid solution is used as
an electrolyte.
We learn that most of the primary cell
exceptrechargeableonesareusedonetimeonly.
Itdoesnotsupplycurrentcontinuously.Thesec-
ondary cells overcome this disadvantage.
VOLTAIC CELL
4.3
In a secondary cell, the charging
and discharging processes are taking place
according to Faraday’s law of electrolysis.
SECONDARY CELL
4.4
A cell that can be recharged by send-
ing electric current in the reverse direction
to that of a discharge mode is known as a
secondary cell. Secondary cells are Storage
batteries since, after it is charged, it stores
the energy until it is used or discharged.
4.4.1
Secondary Cell Classification
Secondary cells may be classified as
(i) Lead acid cell
(ii) Alkaline cell
Example: Nickel iron cell, Nickel cad-
mium cell
Secondary cell is a type of electrical
battery, which can be charged, discharged
into a load, and recharged many times,
as opposed to a disposable or primary
battery, which is supplied fully charged and
discharged after use. It is composed of one
or more electro chemical cells. The term
‘accumulator’ is used, as it accumulates
and stores energy through a reversible
electrochemical reaction. Rechargeable
batteries are produced in many different
shapes and sizes, ranging from button cells
to mega watt systems connected to stabilize
an electrical distribution network.
Several different combinations
of electrode materials and electrolytes
are used, including Lead-acid, Nickel-
cadmium, Nickel-metal hydride, and Lith-
ium ion.

59 Batteries
Initial cost of rechargeable batteries
will be more than the disposable batteries, but
have a much lower total cost of ownership.
Storagebatteryisacelloraconnected
group of cells which converts chemical
energy into electrical energy by reversible
chemical reaction and may be recharged by
passing a current through in the direction
opposite to that of its discharge.
4.4.2 Lead Acid Battery
The battery which uses sponge lead
and lead peroxide for the conversion of
the chemical energy into electrical energy
is called lead acid cell battery. This type of
battery is most commonly used in the pow-
er stations and substations, because it has
higher cell voltage and lower cost.
Construction
First of all, we shall see the various
parts of the lead acid cell battery with the help
of fig 4.6 . The container and the plates are the
main parts of the lead acid cell battery.
1. Container
The container stores chemical energy
which is converted into electrical energy
with the help of plates. The container is
made of glass, lead lined wood, ebonite, hard
Grid Plate
Positive Plate
Negative Plate
Negative Pore
Negative cell
connection
Negative
plate pack
Valve adapter and valve
Microporous separator
Positive plate pack
Positive cell
connection
Electronlyte-tight sealing ring
Fig 4.6 Lead Acid Battery

60
rubber of bituminous components, ceramic
materialsormouldedplasticandareseatedat
the top to avoid the discharge of electrolyte.
At the bottom of the container, there are four
ribs, on two of them rest on the positive plate
and the others support the negative plate.
The prism serves as the support
for the plates, and at the same time pro-
tects them from short-circuit. The mate-
rial which the battery containers are made
should be resistant to sulphuric acid.
2. Plate
The plates of the lead acid cell is of
diverse designs and they all consist some
form of a grid which is made up of lead
and the active material. The grid is essential
for conducting the electric current and for
distributing the current equally on the active
material. If the current is not uniformly
distributed, then the active material will
loosen and fall out.
Fig 4.7 Plate Arrangements of
Lead-Acid Battery
The grids are made up of an alloy of
lead and antimony. The grid for the positive
and negative plates are of the same design,
(as shown in fig. 4.7) but the grids from the
negative plates are made lighter because
they are not as essential for the uniform
conduction of the current.
The number of negative plates in
a cell is always more than one number of
positive plates in a cell, so that end plates at
both the sides of the group remain negative.
3. Active Material
The material in a cell which takes
active participation in a chemical reaction
during charging or discharging is called
the active material of the cell. The active
element of the lead acid cells are
(a) Lead Peroxide (PbO2
)
It forms the positive active material.
The PbO2
is dark chocolate brown in colour.
b) Sponge Lead (Pb)
It forms the negative active materi-
al. It is grey in colour.
(c) Dilute Sulphuric Acid (H2
SO4
)
It is used as an electrolyte. It
contains 31% of sulphuric acid.
4.Separators
The separators are thin sheets of
non-conducting material made up of chem-
ically treated leadwood, porous rubbers or
mats of glass fibre and are placed between the
positive and negative to insulate from each
other. Separators are grooved vertically on
one side and are smooth on the other side.
5. Battery Terminals
A battery has two terminals:–
Positive and Negative

61 Batteries
A) Working Principle
In a lead acid cell, sulphuric acid is used
as an electrolyte. In this H2
So4
, electrolyte is
pouredafterpouringwaterinit.Then,sulphuric
acid dissolves and the molecules of hydro-
gen and sulphate are formed. In this, hydrogen
ionsarepositiveandsulphateionsarenegative.
Two electrodes of battery are dipped
in an electrolyte and DC supply is given as
an input. Hydrogen positive ions go towards
negative plate of electrode. Sulphate negative
ions go towards positive plate of the elec-
trode. In this way lead acid battery functions.
The sign(+) indicates positive termi-
nal and sign(−) indicates negative terminal
Positive terminal-17.5mm dia
Negative terminal-16mm dia
b) Chemical Reactions During
Discharging
When the cell is discharging, current
flow in the external circuit is from positive
to negative. (See fig. 4.8) The flow of current
through the electrolyte (H2
SO4
) splits into
positive hydrogen ion (H2–
+
) and two nega-
tive sulphate ions (SO4
–2
).
Each sulphate ions move towards the
cathodeandonreachingthere,giveuptwoelec-
trons to become radical SO4
, attack the metallic
lead cathode and form lead sulphate, whitish
in colour according to the chemical equation.
At Anode, H2
combines with oxygen of
PbO2
and H2
SO4
attacks lead to form PbSO4
.
At Anode:
PbO H H SO PbSO H O
2 2 2 4 4 2
2
+ + → +
At cathode: Pb SO PbSO
+ →
4 4
Fig 4.8 Discharging Process
Physical Changes While Discharging
1. Both the positive and negative plates
are slowly converted into lead sul-
phate PbSO4
(white in colour)
2. Water is formed during discharge.
So the acid becomes more and more
dilute. Specific gravity of sulphuric
acid solution decreases.
3. Decrease in emf
c)
Chemical Reaction During
Charging
For recharging, the anode and
cathode are connected to the positive and the
negative terminal of the DC main supply.The
hydrogen ions are positively charged move
towards the cathode. (as in fig 4.9)
Sulphate ions move to the anode, and
the following chemical reaction occurs.
AtAnode:PbSO H Pb H SO
4 2 2 4
+ → +
At Cathode:
PbSO SO H O PbO H SO
4 4 2 2 2 4
2 2
+ + → +

62
Fig 4.9 Charging Process
Physical Changes While Charging
1. Anode and cathode return back to
their original colour (i.e positive plate
dark brown and negative plate grey).
2. Specific gravity of an electrolyte is
increased due to absorption of water.
3. Increase in emf values.
d)
Difference Between Primary And
Secondary Cells
Primary Cell Secondarycell
1. Primary cell cannot
be recharged.
Secondary cell can
be recharged.
2. Chemical energy
is converted into
electrical energy.
In this, Electrical
energy is converted
into chemical energy.
3. Internal resistance
is high.
Internal resistance
is low.
4. It is light in
weight.
It is heavy in weight.
5. It is less expensive. More expensive.
6. It is disposable. Not disposable
and needs regular
maintenance and
periodic recharging.
7. Short life. Long life.
8. Low efficiency. High efficiency.
9. Less maintenance. High maintenance.
LITHIUM - ION BATTERY
4.5
A Lithium-ion battery is a type of
rechargeable battery in which lithium ions
move from the negative electrode to the
positive electrode during discharge and
lithium ions move from positive electrode
to the negative electrode when charging.
The three primary functional com-
ponents of a lithium ion battery are the
positive electrode, negative electrode and
electrolyte. The negative electrode is made
from carbon. The positive electrode is a
metal oxide and electrolyte is a lithium
salt in an organic solvent.
Nominal Cell Voltage
Fig 4.10 Lithium Ion Battery
NMC: 3.6/3.85 Volt
Lithium ion battery is a primary cell
type battery. (see fig 4.10) It is available in
variety of sizes and configurations. Depend-
ing on the chemicals used with lithium, the
cell voltage is between 2.5 to 3.6volt.

63 Batteries
Advantages of Lithium Battery
The are many advantages of using
lithium-ion battery.
i) High Energy Density
The main advantage of lithium ion
battery is high energy density. In mobile
phones, it needs to operate for a long time
between charges while still charging more
power, there is always a need to batteries,
with a much higher energy density. It is a
distinct advantage.
ii) Self Discharge
One issue with batteries is that they
loose their charges overtime. The main
advantage is that the rate of self-discharge is
very low than that of the other batteries.
iii)No Requirement For Priming
In this, lithium ion battery does not
need to be primed, but the other batteries
require priming.
iv) Low Maintenance
Lithium ion battery does not require
any maintenance to ensure the performance.
Disadvantages
The disadvantages of lithium ion
battery are as follows:
i) Protection Required
Lithium ion cells require protection
from being overcharged and discharged too
much. In addition, they need to have the
current maintained within safe limits. Ac-
cordingly, lithium ion battery disadvantage
is that they require protection to ensure that
is it kept within the safe operating limits.
ii) Ageing
Another disadvantage of this battery
is ageing. The battery is dependent upon
the number of charge and discharge cycles
that the battery has undergone. Lithium ion
battery should be kept in a cool storage area,
that will increase the life of battery.
iii)Transportation
Lithium ion battery applications are
restricted on their transportation, especially
by air. These batteries require care and pro-
tection while on transportation.
iv) Cost
The cost of lithium ion battery is high
compared with other types of batteries.
SEVENFEATURESABOUT
THEDISPARITYBETWEEN
LEAD ACID AND
LITHIUMIONBATTERIES
4.6
1. Weight
Lithium ion batteries are one third
the weight of lead acid batteries
2. Efficiency
Lithium-ion batteries are of nearly
100% efficiency both charge and discharge,
allowing the same ampere hours both in and
out. But lead acid cell battery is 85% efficiency.
3. Discharge
Lithium-ion batteries are discharged
100%, but lead acid batteries discharge less
than 80%.
4. Life Cycle
Life cycle of the lithium-ion battery
is 400–1200 cycles, whereas lead acid bat-
tery life cycle is 400 to 500 cycles
5. Voltage
Lithium-ion batteries maintain their
voltage throughout the entire discharge
cycle. This allows greater and longer lasting
efficiency of electrical components. Lead

64
acid cell battery voltage drops consistently
throughout the discharge cycle.
6. Cost
Despite the higher upfront cost of
lithium ion batteries, the true cost of owner-
ship is less than lead acid battery when con-
sidering the life span and performance.
7. Environmental Impact
Lithium ion batteries are a much
cleaner technology and are safer for the
environment.
Applications
Lithium-ion batteries are one of the
most popular types of rechargeable bat-
teries for portable electronics with a high
energy density, tiny memory effect and
low self-discharge. Also used in electric
vehicle and aerospace application.
UPS BATTERY
4.7
Fig 4.11 UPS Battery
ON
OFF
Main 230V
Input
230V Input
UPS Output
UPS Battery
ON
OFF
ON
OFF
ON
OFF
ON
OFF
ON
OFF
Fig 4.12 Components of UPS System

65 Batteries
An uninterruptible power supply is
called UPS. It is a device that permits sup-
ply to keep on running for a short period of
time, when the primary power is off.
UPS contains a battery that “kicks
in” when the device senses a loss of power
from the primary source (as in fig. 4.11).
If you are using computer, when the
UPS notifies you of the power loss, you have
time to save and data you are working on
and exit, before the secondary power source
runs out. When all power runs out, any
data in computers Random Access Memory
(RAM) is erased when power surges occur,
a UPS intercepts the surge, so that it doesn’t
damage the computer.
MAINTENANCEOF
BATTERIES
4.8
How does UPS work?
In a continuous UPS, the computer is
always running short of battery power and
the battery is continuously being recharged.
The battery charger continuously produces
DC power, which the inverter continuous-
ly turns back into 120 volt AC power. If the
power fails, the battery provides power to
the inverter.
Components of UPS (Ref. fig. 4.12)
1. The Static Bypass
2. The Rectifier
3. The Battery
4. The Inverter
Types of UPS
Types
Range
Line interactive
-
0.5 to 3 KVA
Stand by Online Hybrid
-
0.5 to 5 KVA
Stand by Ferro Double
-
3.0 to 15 KVA
Conversion Online
-
5.0 to 5000KVA
1. Battery should be cleaned properly
2. Cable connection of the battery needs
to be clean and tightened, Many bat-
tery problems are caused by dirty and
loose connection.
3. The fluid level of the battery will
always be higher at a full charge.
4. Distilledwateraloneisthebestforfilling
because other types of water are loaded
with chemicals and minerals that are
harmfultothebattery.Don’toverfillthe
battery especially in warm weather.
5. Use silicon seals in the cable leads.
Coat the cable washer end with grease
or petroleum jelly (vaseline).
DO’SANDDON’TOF
STORAGEBATTERY
4.9
Do’s
1. Store batteries in a clean, ventilated
and dry area.
2. Store batteries in a fully charged state.
3. Ensurethecorrectpolarityconnection
when recharging.
4. Follow proper recharging schedules
to prevent overcharging.
5. Keep the battery away from spark,
heat and sources of fire.
6. Use proper size of cables along with
correct plugs.
7. Charge the batteries immediately
after it is discharged.

66
NINETIPSFORPROPER
BATTERYCARE
4.10
1. Size your battery correctly.
2. Periodically check the voltage of your
batteries.
3. Don’t try to charge alkaline batteries.
4. Prevent alkaline batteries from leaking.
5. Take care with parallel connections.
6. Give VRLA (Valve-Regulated Lead-
Acid) battering breathing space.
7. Don’t leave Lead-Acid batteries in a
discharged state.
8. Take off golden ornaments when
connecting a battery.
9. Protect from cold temperatures and
snowy climates.
8. Terminal bolts are to be tightened
withspringwashersandapplytorque.
The tightness is to be checked.
Don’ts
1. Do not add any acid or distilled water
in battery, during supply.
2. Do not tamper the vent plug.
3. Do not over tight or make loose the ter-
minal bolts which may cause terminal
breakageorfireduetoloosecontact.
4. Do not keep any metal object to rest
on battery. It may cause short circuit.
5. Do not keep the battery in direct
sunlight, dust or moist area.
6. Do not allow discharged battery for
more than 12 hours in idle condition.
Precautions
1. Always handle a battery and its parts
after wearing hand gloves, as the acid is
corrosive.
2. Always pour the acid into water and not
thewaterintotheacid.Heatisproduced
when the acid is mixed with water.
3. Since the electrolyte is highly corro-
sive, the storage of electrolyte is used
only glass or lead lined container If
the batteries are handled with the
above precautionary measures, the
life of the battery will be prolonged.
Follow the correct procedures and be
safe while handling the battery.
1. Test the supply voltage from lemon?
2. Test the voltage produced in carrot?
3. How to produce electricity from orange?

67 Batteries
Battery - மின்கலம்
Dry cell - உலர் மின்கலம்
Wet cel - பசை மின்கலம்
Separators - பிரிப்பான்
Charging - மின்னேற்றம்
Discharging - மின்னிறக்கம்
UPS-Battery-Un-
Interrupted Power Supply
- தடையில்லா
மின்சாரம் தரும்
சாதனம்
Battery System
Solar Irradiance Solar Water Heating
System
Solar panel
Solar
collector
To taps
Boiler
Tank
Cold water
feed
Pump
Controller
DC Loads
Battery
Battery
Charger
Applications of Solar Battery System
Solar Battery Systems
Solar panels absorbs sunlight as a
source of energy to generate electricity
(or) heat. A photo voltaic modules, an
inverter, a battery park for storage inter
connection wiring, and optionally a
solar tracking mechanism.
Solar Water Heating Systems
Itistheconversionofsunlightintoheatfor
waterheatingusingasolarthermalcollec-
tion.Avarietyoflongitudesareavailableof
varyingcosttoprovidesolutionindifferent
climatesand latitudes.Solarwaterheating
systemsarewidelyusedforresidentialand
industrialapplications.

68
1. Battery is a storage of _______
energy
a) Heat energy
b) Electrical energy
c) chemical energy
d) Solar energy
2. In battery, chemical energy is trans-
formed into ________ energy.
a) Electrical energy
b) Light energy
c) Sound energy
d) Heat energy.
3. Primary cells are ______
a) not rechargeable
b) chargeable
c) partly chargeable
d) none
4. In dry cell, carbon rod is ________
electrode
a) Positive electrode
b) Negative electrode
c) Phase
d) Neutral
5. In a voltaic cell, the electrolyte used is
_________
a) Hydrochloric acid
b) Nitric acid
c) Sulphuric acid
d) Dilute nitric acid
6. Voltaic cell is ____ type of cell
a) Dry
b) Wet
c) Solid
d) None
7. Charging and discharging process
in secondary cell is by which law?
a) Ohm’s law
b) Faraday’s laws of electrolysis
c) Lenz’s laws
d) current law
8. Lead acid battery is commonly used in
______
a) Railway station
b) Radio station
c) T.V.Station
d) Power station and substation
9. Separators in battery is a _______
material
a) conductive
b) non –conductive
c) partly conductive
d) heavy conductive
10. The voltage range of lithium-ion bat-
tery is ______
a) 2 to 2.5V
b) 2.5 to 3.6V
c) 3.6 to 5V
d) 5 to 6.6V
11. Advantage of using lithium ion
battery is ____
a) High energy density
b) low energy density
c) medium energy density
d) poor energy density
12. The battery used in electric vehicles
and Aerospace applications is_______
a) Lead acid cell battery
b) Lithium-Ion battery
c) UPS battery
d) charger battery

69 Batteries
1. What is meant by battery?
2. State the different types of battery?
3. Write about the primary cell?
4. State the uses of a primary cell?
5. What is called a secondary cell?
6. What is a Lead Acid cell battery?
7. What is a the use of separators?
8. What is a Lithium-ion battery?
9. Write short notes on a UPS Battery?
10. Write down the types and range of UPS?
11. What are the precautions to be followed in battery?
3
1. Write about a voltaic cell and its constructional details?
2. State the differences between primary and secondary cell?
3. State the advantages of lithium-ion battery?
4. Write seven features about the disparity between a lead Acid and a Lithium
ion battery?
5. State the Do’s and Don’ts of a storage battery?
6. What are the maintenances to be observed in batteries?

70
Reference Book
1. A text book of Electrical Technology’ Volume I and Volume III by B.L. Theraja and
A.K. Theraja, S. Chand Company Ltd.
1. With a neat sketch and explain dry cell.
2. Explain the construction of Lead Acid battery.
3. Explain the chemical reactions and physical changes during discharging
in Lead-Acid battery.
4. Explain the chemical reactions and physical changes during charging in
Lead-Acid battery.
5. Explain in detail about Lithium ion battery with diagram.
6. Draw and explain about an UPS battery with circuit diagram.

71 AC Circuits
71
AC Circuits
If What is truth? the question be,
It is to speak out evil – free.
— Thiruvalluvar
291
T
he learning objective of AC circuit is preferably to know RLC-circuits, its advantages
and disadvantages, and digital energy meter. According to the trend of applications, it is
necessary to know the various types of connections in AC circuits.

72
Basic Electrical Engineering Theory
AC CIRCUITS -
INTRODUCTION
5.1
An alternating voltage may be
generated in two methods:
(i) By rotating a coil at constant angular
velocity in a uniform magnetic field
(ii) By rotating a magnetic field constant
angular velocity within a stationary
coil
Ineithercasethegeneratedvoltagewill
be of sinusoidal waveform. The magnitude of
generated voltage depends upon:
(i) Number of turns of the coil
(ii) The strength of magnetic field
(iii) The speed of rotation
The first method is used for small
A.C generators and the second method is
used for large type of A.C generators.
In figure 5.1, an Alternating current
shows the change in the direction of
current and magnitude at regular intervals
of power system. Alternating current plays
a vital role in today’s energy generation.
1 cycle
Polarity
change
t
Voltage is
negative
+
0
-
Voltage is positive
Voltage
Fig 5.1 Voltage vs Time
AC WAVE FORM AND IT’S
CHARACTERISTICS
5.2
A wave form is a representation of
low alternating current (AC) that varies
with time. The most familiar AC waveform
is the sine wave, which derives its name
from the fact that the current (or) voltage
varies with the sine of the elapsed time.
5.1 AC Circuits - Introduction
5.2 AC wave form and it’s characteristics
5.3 Advantages and Disadvantages of AC supply
5.4 R-L-C Circuits
5.5 Three phase Star/Delta connections
5.6 Digital energy meter

73 AC Circuits
Fig 5.2 (b)
In fig 5.2 (a) A stationary magnetic
field and rotating coil
In fig 5.2 (b) A stationary coil and
magnetic field rotating
If a coil rotates in the magnetic
field or rotates inside the coil, there is an
alternating emf induced in the coil. The
generated alternating emf depends upon
the number of turns of coils, magnetic
field and the angle between the coil and
magnetic field.
Induced emf e = BlV sinθ
Where
B = flux density in weber/m²
l = length of the conductor in meter
V =
velocity of the conductor in meter/
second
Ø =
angle between magnetic field and
conductor
Fig 5.3 Rotating Coil in a Magnetic Field
In the figure above, a rectangular
coil having ‘N’ turns and rotating in
counter clock wise direction in a uniform
magnetic field with an angular velocity of
‘ω’ radians/sec is shown.
So, the generated A.C e.m.f. value is
also depends upon the value of the angle
between the magnetic field and the coil.
The sine wave may be drawn by
taking the Electro motive force in ‘Y’ axis
and time in ‘X’ axis.
In figure 5.4, a coil is rotating in a
magnetic field in anti-clock wise direction.
Let us assume that the coil is in the position
‘O’. Now the angle between the magnetic
field and coil is zero. Then, the e.m.f in the
coil is also zero (ie, sin Ø = 0)
Fig 5.2

74
Now the coil moves to the position
‘a’ and the angles between the magnetic field
and coil is Ѳ. Then, e.m.f. is equal to BlVsinθ.
Now the coil moves to the position ‘b’
and the angle between the magnetic field and
coilis90°.Thensin90=1.Theemfismaximum.
This emf is called as positive maximum.
Now the coil moves to the position
‘d’ and the angle between the magnetic field
and coil is zero. In this position emf is zero.
Nowthecoilmovestotheposition‘f’the
anglebetweenmagneticfieldandcoilis90o,sin
90 = 1 and the e.m.f is maximum in magnetic
side, so it is called as negative maximum.
Now the conductor moves to the
position ‘0’, the emf is zero.
Similarly, the conductor rotates
one revolution in the magnetic field. This
rotation produces the sine wave form.
a) Cycle
One complete set of positive and
negative values of alternating quantity is
known as cycle. One complete cycle is said
to spread over 360° or 2π radians.
b) Time Period
Time period is denoted by ‘T’. The
time taken for any wave to complete one
full cycle is called the time period.
c) Frequency
The frequency of a wave is defined as
the number of cycles that a wave completes
in one second. It is denoted by the letter ‘F’
and its unit is cycles/second or Hertz(Hz).
In India, the supply frequency is 50Hz.
Frequency is calculated by
F =
PN
120
Hz
Where
F = Frequency in Hertz
P = Number of poles
N = Revolution in r.p.m
d) Instantaneous Value
At any given time, it has some
instantaneous value. This value is different at
different points along the waveform. During
the positive and negative cycle, these values
are positive and negative respectively.
e) Peak Value
The peak value of the sine wave is
the maximum value of the wave during
positive half cycle or negative half cycle.
f) Peak Factor
The ratio of maximum value to the
r.m.s. value of an alternating quantity is
known is peak factor
Peak factor =
Max.Value
R.M.S. value
1.414
=
g) Average Value
The average value of the sine wave
is the ratio of total area under the half-
cycle curve to the distance of the curve
Average Value =
Area under the Curve
Base Length
Fig 5.4 Generation AC Waveform

75 AC Circuits
h) Effective Value or RMS Value
The value of an Alternating Current
(or) Voltage is equal to the square root of
the arithmatic mean of the squares of the
instantaneous values taken through one
complete cycle.
R.M.S. Value =
Im
or
Em
2 2
A.C ammeters and voltmeters are
calibrated to record r.m.s. values.
i) Form Factor
The ratio of r.m.s value to the
average value of an alternating quantity is
known as form factor
Form factor =
(R.M.S.Value)
(average value)
= 1.11
The form factor is useful in rectifier
service because it enables to find the
r.m.s.value from average value and vice versa.
j) Power Factor
Cosine value of angle between
voltage and current is called as power
factor. Power factor is also defined as the
ratio of true power to apparent power
Power factor = cos Ѳ (Ѳ is angle
between voltage and current)
Power factor =
VI cos
VI
=
True power
Apparent power
θ
The power factor can never be greater
than the value 1. If the powerfactor is 1, it
is called as unity power factor. The word
lagging or leading with the numerical value
of power factor should be noted to signify
whether the current lag or leads the voltage.
5.2.1 Phase
Phase of a particular value of an
alternating quantity is the fractional
part of the time period or cycle through
which the quantity has advanced from the
selected zero position of reference.
t = T
A
t = 0
Current ωt = t/4
π/2 3π/2 2π
π
Fig5.5 Phase
5.2.2 Phase Difference
Fig 5.6 Phase Difference
When two alternating quantities of
the same frequency have different zero points,
they are said to have a phase difference.

76
The angle between zero point is the
angle of phase difference Ѳ. It is generally
measured in degrees or radians. The
quantity which passes through its zero
point earlier is said to be leading while the
other is said to be lagging.
ADVANTAGES AND
DISADVANTAGES OF AC
SUPPLY
5.3
Advantages
1) It is easy to transmit alternating current
from one place to another place.
2) High voltage can be generated easily.
3) The cost of AC equipment is low.
4) It is possible to convert into DC.
5) Step down, step up voltage can be easily
done by transformer.
6) A.C Motors are cheap.
Disadvantages
1) A.C cannot be stored in Batteries.
2) ComparedtoDC,A.Ccircuitshouldhave
good insulation because of high output
voltage which causes electric shock.
3) The voltage drop is occurred due to high
starting current in AC.
4) The speed of the AC motor depends
upon the frequency.
5) In Inductive load, power factor will be low.
R-L-C SERIES CIRCUITS
5.4
In this circuit, the three (R,L,C)
components are all in series with the
Voltage source.
5.4.1.
AC circuits with pure resistance
A circuit having only resistance
and without inductance and capacitance
is called pure resistance circuit
Fig 5.7 AC through Resistance
Let
The value of resistance is R
The value of current is I
The value of Electro motive force is E
Then
Current I
Electromotive Force E
sis ce R
( )
Re tan
=
( )
( )
I
E
R
=
×
Power = Current EMF
In this circuit power factor is unity,
because the angle between current and
voltage is zero (cosØ = 1).

77 AC Circuits
5.4.2.
AC circuits with pure
Inductance
A circuit having only inductance
and without resistance and capacitance is
called pure Inductance circuit.
Fig 5.8 AC through Inductance
If A.C current flows through a coil,
Back emf is induced due to inductance of
the coil. This Back emf opposes supplied
voltage in a pure inductance coil. Back emf is
equal to supply voltage. In inductive circuit
only, the frequency is same for voltage and
current, but they are out of phase and current
is lagging by 90o to the voltage.Therefore
powerfactor (cos 90=0)is zero.
5.4.3. Inductive Reactance
Inductive reactance means the
opposition due to self inductance to the
A.C current through a coil. It’s unit is ohm
and it is denoted by the letter “XL”
XL = 2πfL
Where
XL-Inductive reactance in ohm
f-frequency in Hertz
L-Inductance in Henry
5.4.4.
AC Circuits with pure
capacitance
Two conducting plates separated by
insulating material is called as capacitor.
The insulating materials are be air, mica
and paper.
Fig 5.9 AC through Capacitance
In the first half cycle (up to 90o)
capacitor is charged and from 90o to 180o
the capacitor is discharged. Similarly in
the second half cycle, capacitor is charged
first and discharged next, in opposite
direction. So, in one cycle, capacitor is
charged and discharged two times, in
capacitor only. In A.C circuit, the current
is leading by the voltage at 90o

78
5.4.5 Capacitive Reactance
The resistance offered by a capacitor
is called as capacitive reactance. The unit
of capacitive reactance is ohm(Ω) and it is
denoted by letters Xc.
Xc
fc
=
1
2π
Where
Xc = capacitive reactance in ohm
C = capacitance in farad
F = frequency in Hertz
5.4.6 AC – RL SERIES CIRCUITS
Fig 5.10 AC through RL Series Circuit
Resistance and inductance are
connected in series as in fig. 5.10. In
resistance there is no phase difference
between Current and Voltage. But in
inductance, current leads 90º by voltage.
V = Voltage across the resistance (Volts)
V = Voltage acr
R
L o
oss the inductance (Volts)
R = Resistance (in ohms)
X = In
L d
ductive reactance
V = I R
V = I X
V = V + V
V =
R
L L
2 R L
2 2
V
V + V
V = (IR) + (I L)
V = I R + I XL
V = R +
2 2
2 2 2 2
2
R L
X
X
2 2
L
2
V
I
R XL
Z R XL Z
V
I
2 2
2 2
I
5.4.7 AC-RC CIRCUITS
In fig. 5.11 resistance and
capacitance are connected in series. In
resistance there is no phase difference
between current and voltage. But in
capacitance, voltage is 90º lagging by
current.
VR
= Voltage across the resistance (Volts)
VL
= Voltage across the inductance (Volts)
Fig 5.11 AC through RC Series Circuit

79 AC Circuits
R sis ce in ohms
X Inductive capi ce
V I R
V I
C
R
C
=
=
= ×
=
Re tan ( )
tan .
×
×
= +
= +
= +
= +
X
V V V
V V V
V I I X
V I R I X
C
R C
R C
R C
C
2 2 2
2 2
2 2
2 2 2 2
( ) ( )
V
V I R X
V
I
Z R X
C
C
= +
= = +
2 2
2 2
5.4.8 IMPEDANCE
Impedance is the total opposition
offered by the circuits elements [ie,
Resistance, Inductance and capacitance]
simply, Impedance is defined as the ratio
of the voltage to current
Im ( )
pedance Z
Voltage V
Current I
=
( )
( )
5.4.9 RLC Series Circuit
Fig 5.12 AC through RLC Series Circuit
In this RLC circuit resistance,
inductance and capacitance are connected
in series. In this the current is same. The
voltage is differed by circuit elements,
Total supply voltage is ‘V’
I = IR
= IL
= Ic
And
V = VR
+ VL
+ VC
VR
= Voltage across the resistance
VL
= Voltage across the inductance
VC
= Voltage across the capacitance
And also
VR
is in phase with current
VL
leads current by 90o
VC
lags current by 90o
(i) If inductive reactance is greater
than capacitive reactance (XL
XC
)
V IR IX IX
V I R I X
L C
L
2 2
2 2 2
( ) ( )
( X
V I R X X
V
I
R X X
C
L C
L C
)
( )
( )
2
2 2
2 2
V2
=V2
R
+(VL
- VC
)2
V= V2
R
+(VL
- VC
)2
Impedance Z R X X ohms
V
I
Z
L c
= +
( )
=






2
2
Power factor
R
Z
and power P VI watts
cos
cos
θ
θ
=
=
(ii) If capacitive reactance is greater
than Inductive reactance (XC
XL
)
Im ( )
cos
pedance Z R X X ohms
Power factor
R
Z
And power P
C L
= +
=
=
2 2
θ
V
VI watts
cosθ

80
THREE PHASE STAR/
DELTA CONNECTIONS
5.5
3 phase A.C generator is shown in Fig
5.13. Three identical windings A,B and C are
placed 1200 electrical degree apart. It rotates
in anti-clock wise direction. It generates 3
phase supply. Three phases are indicated in
Red (R), Yellow (Y) and Blue (B) colors.
5.5.1 Poly Phase System
If the armature of an alternator
generating AC apply is having only one
winding, it generates single phase supply.
Instead of one winding, if the alternator has
two or three windings, then two or three
phases are generated respectively. So a system
produces more than one phase is called poly-
phase system.
a′
120˚
120˚
b′
c′
c
a
b N
N
Fb
Fa
Sa
Fc
Sb
a4
a2
Sc
a3
a5
a8
a6
a
S
S
Fig 5.13 Poly Phase System Generation
5.5.2.
Reasons for the Use of Three-
Phase System
Three phase system is preferred
over single phase system for the following
reasons.
i. Three phase power has a constant
magnitude whereas single phase power
pulsates from zero to peak value at twice
the supply frequency.
ii. A three phase system can set up
a rotating magnetic field in stationary
windings. This cannot be done with a
single phase current.
iii. For the same rating, Three
phase machines (generators, motors,
transformers) are smaller, simpler in
construction and have better operation
than single phase machines.
iv. To transmit the same amount
of power to a fixed distance at a given
voltage. The three phase system requires
only three-fourth weight of copper that is
required by the single phase system.
v. The voltage regulation of a three
phase transmission line is better than that
of a single phase line.

Electricity travels at the speed of light - more than 186,000 miles per second!

Electricity always tries to find the easiest and shortest path to the ground.
 Electricity can be made from wind, water, the sun and even animal poop.
 A 600-megawatt natural gas plant can power 220,000 homes.
 The first power plant - owned by Thomas Edison - opened in New York City in 1882.

81 AC Circuits
5.5.3. Phase Sequence
It is the term which is used to
represent in what sequence the three
phase voltage or current attains maximum
value. If the phase sequence is said to be R,
Y, B then first red phase attains maximum
value with a phase difference of 120o each,
the yellow phase and blue phase attains
their peak value.
5.5.4.
Inter Connection of Three
Phases
In a three phase alternator, there
are three windings or phases. Each phase
has two terminals. If a separate load
is connected across each winding six
conductors are required to transmit power.
This will make the system complicated
and expensive. In practice, three windings
are interconnected to give two methods of
connection.
Star (Y) connection
Mesh (∆) connection.
5.5.5. Star Y Connection
In this method, similar ends of the
three phases are joined together to form a
common junction (N) supply is taken from
other three ends. The common junction
(N) is called the star point or netural
point. The voltage between any one line
and netural is called phase voltage. The
current flows through that phase is called
phase current. Voltage between any two
lines is called line voltage and current
through that line is called line current.
In this connection,
Phase current = Line current
Fig 5.14 Star Connection
Iph
= IL
Phase voltage
LineVoltage EL
= =
3 3
If the neutral wire is taken for
external connection, then the system
is called a three-phase four wire star
connected system. If the neutral wire is
not taken for external connection, then the
system is called a three phase three wire star
connected system.

82
Total power p = 3 × power in each phase
Power in each phase P = Vph
Iph
cosθ
P = 3× ×
V
I
L
L
3
cosθ
( )
where as I = I , V =
V
3
ph L ph
L
∴ =
P V I
L L
3 cosθ
5.5.6. Delta or Mesh Connection(∆)
Fig 5.15 Delta Connection
Inthismethodofinterconnection,the
dissimilar ends of the three phase windings
are joined together. The finishing end of one
phase is connected to the starting end of the
other phase so as to obtain Mesh or Delta
connection. The three line conductors are
taken from the three junctions of the Mesh
or Delta and they designated as R, Y and B.
This is called three phase three wire delta
connected system. Since no neutral exists in
a Delta connection, only three phase, three
wire system can be formed.
In this connection, the line voltage
is equal to the phase voltage.
Phase Volltage = Line voltage
Vph
= VL
Phase Current = Line current
Iph
=
IL
3
POWER
Total power P = 3 × power per phase
P = 3 Vph
Iph
cosθ
P V
I
V I I
I
i e Power V I
L
L
ph L ph
L
L L
= × × ×
= =
=
3
3
3
3
cos
,
. ., cos
θ
θ
Where cosθ is power factor.
5.5.7
Advantages of Star Connection
Over Delta Connected System
Astarconnectedalternatorwillrequire
less number of turns than a delta connected
alternator for the same line voltage.
A star connected alternator requires
less insulation over a Delta connected
alternator for the same line voltage.
In star connection, Three-phase,
Four-wire system permits to use two
voltage ie, Phase voltage as well as line
voltage.
In star connection single phase
loads can be connected between any one

83 AC Circuits
line and the neutral. Such a flexibility is
not available in Delta connections.
In star connection, the neutral
point can be earthed. Moreover, earthing
of neutral permits to use protective
devices to protect the system in case of
ground faults.
DIGITAL ENERGY
METER
5.6
Digital energy meters display the
energy used on an LCD or LED display, and
some can also transmit readings to remote
places. In addition to measuring energy
used, these meters can also record other
parameters of the load and supply, such
as instantaneous and maximum demands,
voltage, power factor and reactive power
etc. They can also support to record the
amount of energy used during on-peak
and off-peak hours.
The digital energy meter has
a power supply, metering circuit, a
processing and communication circuit
(microprocessor/microcontroller) and
other add on modules such as RTC
(Real Time Clock), LCD (Liquid Crystal
Display), communication ports, modules
and so on.
In the metering circuit, the voltage
and current inputs through current
transformer and potential transformer has
a voltage reference followed by an ADC
(Analog to Digital Convertor) section,
to convert the analog inputs into digital
forms. These inputs are then processed
using a digital signal processor, to calculate
various metering parameters.
The processing and communication
section has the responsibility of calculating
various desired quantites, from the
digital values generated by the metering
section. This has the responsibility of
communicating and interfacings with
other ‘add on modules’ connected as slaves
to it.
RTC (Real Time Clock) and other
add-onmodulesareattachedasslavestothe
processing and communication sections
Voltage
sensor
Current
sensor
Digital meter
COM - port
Signal
conditioner
PIC
Fig 5.16 Block Diagram of Digital Energy Meter

84
for various input/output functions. In
some meters, most of these modules RTC,
LCD controller, Temperature sensor,
memory, ADC (Analog Digital Converter)
may be implemented inside the processing
and communication circuit.
Fig 5.17 Digital Energy Meter
Advantages of Digital Energy Meters
i) High accuracy
ii) Robustness
iii) No moving parts
iv)
Easy to gauge readings through
digital display
v) Over current protection
vi)
Readings can be stored and print
out may be taken
vii) Smaller in size
viii) Consumes less power
ix) Long life
x) Easy to carry anywhere
xi) Remote control is possible
Points to Remember
‘
‘ Induced E.M.F e = Blv sinθ
‘
‘ Frequency f =
PN
Hz
120
‘
‘ Average value =
2Im
≠
or
Vm
2
≠
‘
‘ R.M.S. value =
I
or
V
m m
2 2
‘
‘ Formfactor=
RMS Value
Average Value
= 1.11
‘
‘ Peak factor =
Max. Value
RMS Value
=1.414
‘
‘ Power factor=
V cos
I θ
VI
‘
‘
In pure resistance circuit, power
factor is one (unity)
‘
‘
In pure inductive or capacitive
circuit, power factor is zero
‘
‘ Inductive reactance XL
= 2πfl
‘
‘ Capacitive reactance XC
= 1/2πfC
‘
‘ Impedance Z
I
=
V
In RLC series circuit powerfactor
cos θ =
R
Z
Both in RLC series and RLC parallel
circuit
‘
‘ Power P = VI cosθ watts
In Star Connection
Phase current = Line current
Iph
= IL
Phase voltage =
(Line Voltage)
3
V
V
ph
L
=
3
π
π

85 AC Circuits
In Delta Connection
Phase voltage = Line Voltage
Vph
= VL
Phase current =
Line current
3
I
I
ph
L
=
3
Both in star and Delta connection
in three phase system
Power p = 3V I cos
L L θ
Digital energy meters displayed the
energy consumption accurately.
1. Practice the following (dynamo) type of voltage generation.
connection
to bicycle
frame
connection to
bicycle frame
light
bicycle tyre
dynamo
to light
copper
coil
iron core
N S
rotating
ridged knob
magnet
AC Supply ᅳ மாறுதிசை மின்சாரம்
Frequency ᅳ அலைவு வேகம்
Average Value ᅳ சராசரி மதிப்பு
Peak Value ᅳ உச்சமதிப்பு
Time Period ᅳ கால அளவு
Instantaneous Value ᅳ கன மதிப்பு
Effective Value ᅳ பயன் மதிப்பு
Form Factor ᅳ வடிவுக்காரணி
Peak Factor ᅳ உச்சக்காரணி
Power Factor ᅳ திறன்காரணி
Voltage Sensor ᅳ மின்னழுத்த உணர்வி
Current Sensor ᅳ மின்னோட்ட உணர்வி

86
1. The unit of the flux density is
a) Ampere b) Volt
c) Weber d) Weber/m2
2. The unit of the frequency is
a) Henry b) Hertz
c) Cycles d) Ampere
3. The value of form factor is
a) 2/π b) π/2
c) 1.414 d) 1.11
4. The value of peak factor is
a) 2/π b) π/2
c) 1.414 d) 1.11
5. In the value of power factor,
which is incorrect
a) Unity b) 0.8 leading
c)
0.8 lagging d) 1.5
6. Power factor of pure resistive
circuit is
a) Unity b) Leading
c) lagging d) None of
the above
7. Power factor of pure Inductive
circuit, with respect to current is
a)
unity b) leading
c) lagging d)
none of
the above
8 Power factor of pure capacitive cir-
cuit, with respect to current is
a) unity b) leading
c) lagging d) none of the
above
9. The unity of Inductance is
a)
Henry b) Hertz
c) Farad d) Ohm
10. The unit of capacitance is
a) Henry b) Hertz
c) Farad d) Ohm
11. The unit of Impedance
a) Henry b) Hertz
c) Farad d) Ohm
12. The unit of Capacitive reactance
and Inductive reactance is
a) Henry b) Hertz
c) Farad d) Ohm
13. Inductive reactance XL
is equal to
a) 2πfc b) 1/2πfc
c) 2πfl d) 1/2πfl

87 AC Circuits
14. Capacitive reactance XC
is
equal to
a) 2πfc b) 1/2πfc
c) 2πfl d) 1/2πfl
15. Star connection is also known
a) Delta b) Y
c) Mesh d) None of
the above
16. Delta connection is also known as
a) Star b) Y
c) Mesh d) None of
the above
17. XL
denotes
a) Resistance
b) Inductive reactance
c) Capacitive reactance
d) Impedance
18. XC
denotes
a) Resistance
b) Inductive reactance
c) Capacitive reactance
d) Impedance
19. Four wire system can be
obtained from
a) Series connection
b) Parallel connection
c) Star connection
d) Delta connection
20. In three phase, phase difference is
a) 90o b) 180º
c) 120º d) 360º
21. In star connection, phase current
Iph is equal to
a) VL
b) IL
c) Vph d)
IL
3
22. In Delta connection, phase voltage
Vph is equal to
a) VL
b) IL
c) Vph d)
IL
3
23. Digital energy meters are used for
the following reason
a) High accuracy
b) Small size
c) Long life
d) All of the above

88
1 Define ‘cycle’ in alternating current.
2. Define frequency.
3. Define Amplitude or maximum value.
4. Define effective value or RMS value.
5. Write short notes on Average value.
6. Define form factor.
7. Define peak factor.
8. Write short notes on ‘phase’.
9. What is Inductance and it’s unit?
10. What is Capacitance and it’s unit?
11. What are the uses of capacitors?
12. What is Impedance and it’s unit?
13. What is Inductive reactance?
14. What is Capacitive reactance?
15. What is phase sequence?
16. What are the two connections of three phase system?
3

89 AC Circuits
1. Explain the power factor with vector diagram.
2. Briefly explain the AC circuit which is having only resistance.
3. Briefly explain the AC circuit which is having only Inductance.
4. Briefly explain the AC circuit which is having only capacitance.
5. Explain the reasons for the use of three phase system over single phase
system.
6. What are the advantages of star connection over Delta connected
system?
7. What are the advantages of digital energy meter?
1. Explain RLC series circuit with neat diagram.
2. Explain the star connection of three phase system with neat diagram.
3. Explain the Delta connection of three phase system with neat diagram.
4. Explain how alternating current and voltage is generated with neat
diagram.
Reference Book
1. ‘A text book of Electrical Technology’ Volume I, by B.L. Theraja and A.K. Theraja,
S. Chand Company Ltd.

90
6.1 Transformer - Introduction
6.2 Construction and Types of Transformer Core
6.3 Working Principle or Operation of a Transformer
6.4 EMF Equation
6.5 Types of Instrument Transformers
6.6 Losses in Transformers
6.7 Testing Methods of Transformer
6.8 Protective Devices of Transformer
Transformer
6
T
he main objective of learning this lesson is to know in detail about Transformer, its
construction, operation, losses, testing method, protective devices of transformer, which
are existing under new technique.
All lights are not lights for the wise;
Truth light is light bright like Sun-light.
— Thiruvalluvar
299

91 Transformer
TRANSFORMER-
INTRODUCTION
6.1
A Transformer is a static device
which transfers electrical energy from one
circuit to another circuit at the same fre-
quency. It works on the principle of mutual
induction. The transformer works only on
A.C supply.
Generating stations generate electric-
ity at a voltage of 11KV. The electric power
from the generating station is to be brought
to the consumers end from 33KV, 66KV etc
through various transmission stages.The
transformer is used to step down (or) step
up the voltage required according to the re-
quirement as shown in fig. 6.1.
Fig 6.1 Transformer in Transmission
Line.
CONSTRUCTION OF
TRANSFORMER CORE
6.2
Based on the construction, it is
classified into 3 types. They are:
i. Core type
ii. Shell type and
iii. Berry type
6.2.1 Core Type
The winding surrounds the core is
called core type transformer. The Figure
6.2 represents the core type.
The magnetic circuit is made up
of laminated iron core. Silicon steels are
used to reduce the hysteresis loss in the
iron core, also laminated sheets are insu-
lated from one another by a layer of var-
nish insulation.
Fig 6.2 Core Type Construction
Advantages
i) Easily handled and maintained.
ii) The coils are in the outside, so it will
get cooled easily.
Disadvantages
i) High magnetic loss.
ii) High leakage flux.

92
6.2.2 Shell Type
The core surrounds the winding
is known as shell type transformer. The
Figure 6.3 represents the shell type.
The primary and secondary wind-
ings are placed on the central limb one
above the other. This gives a better mag-
netic coupling.
Fig 6.3 Shell Type Transformer
Advantages
i) More economical for low voltage.
ii) Low current at the time of no load.
Disadvantages
i) Little complicated to make winding.
ii) Less cooling.
6.2.3 Berry Type
Berry type is similar to shell type. In
berry type magnetic path is placed
around the coil. Normally this type is
not used.
6.2.4
COMPARISON OF CORE
AND SHELL TYPE
TRANSFORMER
Core Type
Transformer
Shell Type
Transformer
1. The winding
encircles the core.
The core encircles
most part of the
winding.
2. It has single mag-
netic circuit.
It has double mag-
netic circuit.
3. The cylindrical
coils are used.
The multilayer disc
(or) sandwichs type
of coils are used.
4. The coils can be
easily removed for
maintenance.
The coils cannot be
removed easily.
WORKING PRINCIPLE
(OR) OPERATION OF A
TRANSFORMER
6.3
A Transformer is a static (station-
ary) apparatus by means of which elec-
tric energy in one circuit is transformed

93 Transformer
into another circuit without changing the
frequency.
Fig 6.4 Construction of an Ideal
Transformer
It consists of two inductive coils
which are electrically separated but mag-
netically coupled to a core as shown in
Fig. 6.4. It operates on the principle of
mutual induction between two (or) more
inductively coupled coils. If the coil is
connected to a AC source, an alternating
flux is setup. Most of the flux is linked
with the other coil. This flux is called
mutual flux.
As per Faraday’s laws of electro-
magnetic induction, an emf is induced in
the second coil. The coil (First coil) which
is connected to the A.C supply is called as
primary winding. The coil (Second coil)
which is connected to the load is called as
secondary winding.
6.3.1
STEP UP/ STEP DOWN
TRANSFORMER:
Step up Transformer – If the out-
put voltage in secondary winding is higher
than the input voltage, it is called step up
transformer. (See Figure 6.5)
Fig 6.5 Step-up Transformer
Step down Transformer – If the
output voltage in the secondary winding
is lesser than the input voltage, it is called
step down transformer as in fig. 6.6.
Fig 6.6 Step-down Transformer
6.3.2 ADVANTAGES OF
TRANSFORMERS
i. The transformer is a static machinery.
Hence there is no wear and tear and
no friction losses in it.
ii. Maintenance cost is low.
iii. As there is no rotating part in it, extra
high voltage can be transferred easily
by providing a good insulation to its
winding.
E.M.F EQUATION OF A
TRANSFORMER
6.4
a) Construction b) Wave Form

94
Fig 6.7 Single Phase Transformer
and Wave Form
No. of turns in primary winding = N1
No. of turns in secondary winding =N2
Maximum value of flux = Øm
webers
Frequency of A.C input = f in Hz
The flux in the core will vary
sinusoidally as shown in the above fig 6.7.
The flux in the core increases from
zero to a maximum value in one quarter
cycle (1/4f second)
i.e, Average rate of change of flux

Øm
f
1
4
Ø
f
4 m
i.e average E.M.F induced per turn
= 4f Øm
volts.
The flux varies sinusoidally. Hence
the, R.M.S value of induced voltage is
obtained by multiplying the average value
by form factor which is equal to 1.11 for a
sine wave.
i.e, R.M.S value of induced E.M.F
per turn= 1.11 × 4f Φm volts.
= 4.44 f Φm volts.
The primary/secondary windings
have N1
/N2
turns respectively,
R.M.S value of induced e.m.f in primary
E1
=4.44 f Φm N1
Volts
R.M.S value of induced e.m.f in second-
ary E2
= 4.44 f Φm N2
Volts
6.4.1 Voltage Transformation
Ratio (k)
The ratio of secondary volt-
age to primary voltage is called voltage
transformation ratio. It is represented
by ‘k’.
E
E
V
V
N
N
k
2
1
2
1
2
1
= =
=
6.4.2 Current Ratio
By neglecting the losses
Input volt ampere = output volt ampere
V I V I
V
V
I
I
1 1 2 2
1
2
2
1
= =
or
I
I
V
V
N
N K
2
1
1
2
1
2
1
= = =

95 Transformer
6.4.3 Application of
Transformer
• It is used to step up
or step down the volt-
ages and currents in
an electrical circuit.
• Used in modern electrical transmis-
sion and distribution systems.
• Itboostvoltagelevelssoastodecrease
line losses during transmission.
TYPES OF INSTRUMENT
TRANSFORMERS
6.5
6.5.1 Potential Transformer
Fig 6.8 Potential Transformers
Potential transformer do not dif-
fer much from the ordinary two windings
transformers (Refer Figure 6.8). These are
step down transformers. The primary wind-
ing is connected directly across the power
circuit. The secondary is usually rated for
110 (or) 220 volts. Voltage ratio is depenting
upon primary voltage .
6.5.2 Current Transformer
Fig 6.9 Current Transformers
The current transformer has a primary
coil of only few turns of thick wire connected in
series with the line whose current is to be meas-
ured. The secondary coil consisting large number
of turns is connected to the terminals of a low
range ammeter (See Figure 6.9). The ammeter is
thus entirely insulated from the line. Mostly the
secondaries of all C.T are wound for 5 amperes.
6.5.3 Auto Transformer (VARIAC)
Fig 6.10 Auto Transformer
An auto transformer is a single
winding transformer which is used to
get varying AC voltage. Consider a single
winding BA of N1
turns wound on an iron
core as shown in Figure 6.10. If core loss,
copper loss, magnetizing current and leak-
age reactance are neglected. If this winding

96
is connected to an A.C Voltage V1, a flux
will set up in the core and e.m.f E1 will be
induced in the winding. Such induced e.m.f
is taken by tapping at point C. There are
N2 turns between B and C, an e.m.f E2 is
induced B and C.
When load is connected across the
terminals B and C a current I2 flows. The
m.m.f due to I2 will be balanced by m.m.f
due to I1. This arrangement is referred as an
Auto transformer. If point C is sliding con-
tact, a continuously variable output voltage
can be made available.
So,
=
V
V
I
I
N
N
2
1
1
2
2
1
= = K
Advantages
1. Copper required is very less.
2. The efficiency is higher.
3. Required less conducting material
and hence cost is less.
4. More smooth continuous varia-
tion of voltage.
Disadvantages
1. Direct link between high voltage
and low voltage sides there is no iso-
lation as in the case of a two wind-
ing transformer.
2. Theshortcircuitcurrentisgreaterthan
that of a two winding transformer.
6.5.4
Applications of Auto
Transformer
1. As a booster of supply voltage to a
small extent.
2. Auto transformers are used to start
the induction motor.
3. It can be used to vary the voltage to
the load, smoothly from zero to the
rated voltage.
LOSSES IN A
TRANSFORMER
6.6
The losses in a transformer consists
of I2
R loss (or) copper loss and iron loss (or)
core loss.
I²R Loss (or) Copper Loss
These losses occur in primary and
secondary windings. Copper loss in a trans-
former is a variable loss. It varies as the square
of the load current (From short circuit test
this can be determined).
Iron Loss (or) Core Loss
Iron loss consists of hysteresis and
eddy current losses. They occur in the trans-
former core due to the alternating flux (from
open circuit test, this can be determined.)
Hysteresis Loss
When the iron core is subjected to an
alternating flux hysteresis loss takes place.
Eddy Current Loss
Eddy current is induced in the cores.
This loss is due to the flow of eddy current.
Thin laminations are used to reduce the eddy
current loss.
6.6.1 Efficiency of a Transformer
The efficiency of a transformer is the
ratio of output power to input power.

97 Transformer
Input = output + losses
% Efficiency ( ) =
output power
input power
η ×100
=
output power
output power + losses
(iron loss + copper los
ss)
×100
=
input power losses
input power
−
×100
6.6.2 Why Transformer Rating in KVA?
As seen Cu loss of a transformer
depends on current and iron loss depends
on voltage. Hence total transformer losses
depends on volt ampere (VA) and not on
phase angle between voltage and current i.e, it
is independent of load power factor. Therefore
rating of transformer is in KVA and not in KW.
cos
KVA
KW
=
θ
6.6.3
Why Transformer does not
Work on DC Supply?
The transformer works on the princi-
ple of mutual induction, for which current in
one coil must change uniformly. If DC sup-
ply is given, the current will not change due
to constant supply and transformer will not
work. This may cause the burning of wind-
ings due to extra heat generated and may
cause permanent damage to the transformer.
Thus DC supply should not be connected to
the transformers.
TESTING METHODS OF
TRANSFORMER
6.7
There are two tests are performed on a
transformer to determine the power. They are:
1. Open circuit test
2. Short circuit test
These two tests are used for finding out
the power loss occurring in the transformer.
6.7.1
Open Circuit Test on
Transformer
The open circuit test on trans-
former is used to determine core losses in
transformer.
Fig 6.11 Open Circuit Test
The connection diagram for open cir-
cuit test on transformer is shown in Figure
6.11. A voltmeter, wattmeter, and an ammeter
are connected in primary side of the trans-
former. The voltage at rated frequency is
applied to the primary side with the help of
a variac (or) variable ratio auto transformer.
The secondary side of the transformer
is kept open. Now with the help of variac,
applied voltage gets slowly increased until
the voltmeter gives reading equal to the rated
voltage of the primary side. After reaching at
rated primary side voltage, all three instru-
ments reading (voltmeter, ammeter and
wattmeter readings) are recorded.
The ammeter reading gives no load
current (Io
) being secondary is open the
transformer draws very less current. Hence
copper loss are negligible. As no load current

98
(Io
) is quite small compared to rated current
of the transformer, the voltage drop due to
this current that can be taken as negligible.
As the transformer is open circuited, there
is no output. Hence the input power consist
of core losses and copper loss in transformer
during no load condition.
6.7.2
Short Circuit Test on
Transformer
The short circuit test on transformer is
used to determine copper loss in transformer.
The connection diagram for short cir-
cuit test on transformer is shown in Figure
6.12. A voltmeter, wattmeter, and an ammeter
are connected in primary side of the trans-
former as shown. A reduced voltage at rated
frequency is applied to the primary side with
the help of a variac of variable ratio auto
transformer.
Fig 6.12 Short Circuit Test
The secondary side of the trans-
former is short circuited. Now with the help
of variac applied voltage is slowly increased
until the ammeter gives reading equal to the
rated current in the primary side. Then three
instruments reading (voltmeter, ammeter and
watt-meter) are recorded. The voltmeter read-
ing is very small compared to the rated primary
voltage of the transformer. Here the core losses
in transformer can be taken as negligible.
Let the, voltmeter reading is Vsc.
. The
input power during test is indicated by watt-
meter reading. As the transformer is short
circuited, there is no output, hence the input
power consist of copper loss in transformer.
William Stanley (1858-1916) was
an inventor and engineer. He developed
the first practical transformer (which
spurred the development of AC power)
as well as other developments; like an
improved electric meter and the first
metal thermos bottle (vacuum flask).
He lived most of his life and ran his busi-
nesses in Western Massachusetts during
the golden age of electric development.
Stanley is one of the most impor-
tant inventors of AC power, his work
puts him on a par with Edison, Westing-
house, Tesla, Elihu Thomson, Charles
Brush and other major personalities of
the time. Like the other great pioneers of
the time he loved to tinker and design,
held a disdain for legal quagmires of
patent proceedings, and had his own set
of friends and rivals in the industry.

99 Transformer
PROTECTIVE DEVICES OF
TRANSFORMER
6.8
The following are the protective devices
in transformer and are explained below:
a) Conservator
b) Breather
c) Explosion vent
d) Buchholz relay
e) Transformer oil
Fig 6.13 Protective Devices of Transformer
a) Conservator
Transformer oil losses its insulating
properties and is oxidised when it is in contact
with the atmosphere. For this reason, the oil
must not come in direct contact with the air
outside. Conservators or oil expansion cham-
bers are provided to prevent this absorption.
The conservator is cylindrical vessel.
It is fitted on the top of the tank. The tank is
entirely filled up with oil. The conservator is
filled with oil partly (about 50%). The trans-
former oil gets heated due to the losses in a
transformer. The volume increases due to heat
and the level of oil in conservator increases.
Air is expelled from the conservator through
the breather. When the coil cools down, the
volume decreases and the level of the oil in
the conservator comes down.
This is referred to a ”breathing”. The
oil surface in the conservator is only exposed
to oxidation. The sludge is thus confined to
the oil surface in the conservator. If there is no
conservator the sludge will stick to the cool-
ing tubes. This will spoil the cooling effort.
Fig 6.14 Buchholz Relay

100
b) Breather
Thebreatherisasmallvessel.Itiscon-
nected between conservator and air outlet.
It contains silica gel. It is a dehydrating
agent. The moisture in the incoming air
is removed. The colour of the silica-gel is
blue and pink, when wet or damp.
c) Explosion Vent
In the event of an accidental inter-
nal short circuit in the transformer, an
arc is formed between the turns of the
winding. Heat is produced by the arc.
Due to this, a large volume of gas is pro-
duced. Provision must be made for rapid
release of gas. Otherwise high pressure
will be built up inside leading to the lip
of the tank blown off. For this reason an
explosion vent is provided on the tap of
the tank. Under normal conditions air is
not allowed to come in contact with the
oil. Under short circuit conditions, the
diaphragon is ruptured due to high pres-
sure. The gas is expelled to atmosphere. If
the high pressure gas releasing a portion
of the hot oil may get splashed and cause
injury to the workers in the transformer
yard. The explosion vent’s mouth is cov-
ered by a glass or aluminium.
d) Buchholz Relay
This is a device which is attached to
an oil immersed transformer. It is fitted in
the pipe connecting the transformer tank
with the conservator.
It consists of two floats as shown in
Fig. 6.14.
Two pairs of electrical contacts are
provided. These contacts may get short
circuited under certain situations.
When an insulation breaks down in
a transformer, gas is generated in the oil.
Quick generation of this gas leads to a seri-
ous fault. The gas rushes through the pipe
and pushes the lower float to the right. The
two lower contacts bridge together and
closes to trip the circuit of circuit breaker.
Now the transformer is disconnected from
the supply. If the fault develops slowly, gas
will also generated slow. This may not be
sufficient to move the lower float. This gas
gets collected gradually in the top of the
relay chamber. The oil level gets lowered.
This causes the upper float to sink. It finally
closes the second pair of contacts. This
trips the circuit breaker or it makes ring
an alarm bell for caution. A fault can thus
be detected and the transformer is discon-
nected from the circuit.
e) Transformer Oil
Transformer oil is a mineral oil. It
is obtained by refining crude petroleum.
It is a good insulator. Its tendency to form,
a sludge is very much less. The dielectric
strength of oil is affected to a great extent
by the presence of moisture. So it should
be kept dry. Transformer oil serves two
functions,
1. Cooling
2. Insulation

101 Transformer
Activities
1. Measure the output voltage of given trans-
former below.
2. Construct 6V transformer with centre tap-
ping connection.
3. Calculate the losses occuring in the trans-
formers by OC and SC tests.
Transformer - மின்மாற்றி
Step-up transformer - உயர்வத்த மின்மாற்றி
Step-down transformer - ைறவத்த மின்மாற்றி
Points to Remember:
1. Transfer electrical energy from one
circuit to another circuit.
2. It works without changing the
frequency.
3. Transformer works on the principle
of mutual induction.
4. Transformer works on AC supply
only, not in DC.
5. E.M.F induced in primary winding
= (E1
) = 4.44 N1
fØm
Volts.
6. E.M.F induced in secondary winding
= (E2
) = 4.44 N2
fØm
Volts.
7. % Efficiency ( ) =
output power
input power
η ×100
8. Voltage transformation ratio (K)
E
E
N
N
k
V
V
I
I
2
1
2
1
2
1
1
2
= = = =

102
1. The transformer may represent as
a) rotating device
b) electronic device
c) static device
d) none of these
2. Transformer operates on the
principle of
a) self induction
b) mutual induction
c) ohm’s law
d) len’s law
3. To find the R.M.S value of trans-
former, E.M.F is to be multiply
with
a) 2.22
b) 1.12
c) 1.11
d) 1.14
4. Transformer core is laminated
to reduce the
a) Copper loss
b) Eddy current loss
c) Wintage loss
d) Hysteresis loss
5. Transformer oil serves the func-
tion of
a) Lubrication
b) Insulation and cooling
c) Only insulation
d) None of these
6. Silicon steel sheets are used to
reduce the
a) Frictional loss
b) Mechanical loss
c) Hysteresis loss
d) Eddy current loss
7. The transformer will work on
a) AC only c) Both AC DC
b) DC only d) None of these
8. The iron core is used to …… of the
transformer,
a) increase the weight
b) provide tight magnetic coupling
c) reduce core losses
d) none of the above
9. The primary and secondary of a
transformer are ….. coupled
a) electrically
b) magnetically
c) electrically and magnetically
d) none of these
10. Conservator is a
a) main tank of transformer
b) protectivedeviceoftransformer
c)
earthing system of transformer
d) none of these
11. The purpose of conducting open
circuit test (O.C) is to determine
a) eddy current loss
b) core loss
c) hysteresis loss
d) copper loss

103 Transformer
1. Explain the constructions of shell type transformer.
2. Explain why transformer not works on DC supply.
3. Compare between core shell type transformer.
4. Explain about auto transformer.
5. Explain losses occur in transformer.
Answer the following questions in briefly:
1. What is transformer?
2. What is meant by step up transformer?
3. What is meant by step down transformer?
4. What are the advantages of transformer?
5. What is the voltage transformation ratio of transformer?
6. Mention the advantages of core type transformer.
7. Write down the types of instrument transformer.
8. Write down the applications of auto transformer.
9. What are the protective devices of transformer?
10. Why transformer is rating in KVA?
11. Define efficiency of a transformer.
12. What are the type of transformer according to cooling method?
3

104
1. Explain the working principle of a transformer.
2. Derive the EMF equation of a transformer.
3. Explain the working principle of potential and current transformer.
4. Explain the procedure to perform various tests conducted in
transformer.
Reference Book
1. ‘A text book of Electrical Technology’ Volume IIand Volume III by B.L. Theraja and

105 DC Generator and DC Motor
DC Generator and DC Motor
7
Letter, number, art and science
Of living kind both are the eyes.
—Thiruvalluvar
L
earning objective of this chapter will enables the student to:
• Understand the various parts of DC machines
• Know the generation of DC voltage
• Understand the expression for the generated voltage
• Know DC motor working principle
• Know the applications of DC motor
392

106
INTRODUCTION
DC machines are electro mechan-
ical energy conversion devices which can
operate as generators converting mechan-
ical energy given to them from a prime
mover to electrical energy. They can also
operate as DC motors, taking electri-
cal energy from DC supply and convert-
ing it into mechanical energy to drive a
mechanical load. Nowadays DC motors
are widely used because of their simpler
and flexible drive systems such as elec-
tric traction, cranes, etc. The extension of
these DC machines leads to the develop-
ment of brushless DC machines which are
mostly used in modern scenario.
As said above, an electrical machine
which converts mechanical energy into
7.1
electrical energy is called an electrical gen-
erator, while the electrical machine which
converts electrical energy into mechanical
energy is called an electrical motor.
The electrical machines which work
on AC supply are AC machines whereas the
electrical energy of direct type are called
DC machines. In this chapter we are going
to study about DC machines.
DC machines are classified into
two types:
1) DC generator
2) DC motor
First, we will study the basic princi-
ple of DC generators.
7.1 Introduction
7.2 Basic principle of operation of DC generators
7.3 Construction of DC machines
7.4 Types of DC generators
7.5 EMF Equation of DC generator
7.6 Applications of DC generator
7.7 DC Motor
7.8 Back EMF of DC motor
7.9 Types of DC motor
7.10 Applications of DC motor

BASIC PRINCIPLE
OF OPERATION DC
GENERATOR
According to Faraday’s law of elec-
tromagnetic induction, ‘when a conduc-
tor is rotated in a magnetic field, to cut
the magnetic lines of flux, dynamically
induced emf is produced in the conduc-
tor. This emf causes a current to flow if
the conductor circuit is closed’. The direc-
tion of the current is found by Fleming’s
Right-hand rule.
Hence, the basic requirements for
the dynamically induced emf to exits are:
1) A steady magnetic field
2) A conductor or coils
3) Relative motion between the mag-
netic field and the conductors.
To understand the principle of
EMF generation, consider the following
Fig 7.1.
7.2
7.2.1 Elementary DC Generator
Consider a single-turn rectangular
copper coil ABCD rotating clockwise in a
magnetic field provided by N and S mag-
nets or electromagnets are shown in fig
7.1. The two ends of the coil are joined to
two split-rings ‘a’ and ‘b’ which are insu-
lated from each other and from central
shaft. Two collecting brushes (of carbon
or copper) press against the split-rings.
Their function is to collect the current
produced in the coil and to carry it to the
external load resistance R. The rotating
coils are called as ‘armature ’ and the mag-
nets as “field magnets” or “poles”. The coil
is rotated in clockwise direction at a uni-
form magnetic field.
Fig 7.1 Principle of EMF Generation

108
At position 1, where θ = 0 degrees,
the plane of the coil is perpendicular to
the direction of lines of the flux. Now, the
flux linked with the coil is maximum, but
the rate of change of the flux linkages is
minimum. So, no emf is induced in the
coil. i.e., is at the starting position the emf
induced is zero.
When the coil is rotated fur-
ther, the rate of change of flux linkage
increases up to the position 3, where
θ = 90 degrees. At this position, the plane
of the coil is parallel to the lines of flux.
Now, the flux linked with the coil is min-
imum, but rate of change of flux linkage
is maximum. Therefore, at this position
emf induced in the coil is maximum. On
further rotation the value of generated
emf continues to decrease from maxi-
mum to minimum value.
At position 5, where θ = 180 degree,
the generated emf is reduced to zero. The
magnitude of emf with respect to the
coil position is represented in fig 7.1.
from position 5 to position 7 (that is 180
degrees to 270 degrees), the induced emf
value starts again from zero to maximum
and from position 7 to positon 1 (from
270 degrees to 360 degrees) maximum to
zero in opposite direction.
In this way the generated emf goes
on one cycle as alternating emf. The two
halved split-rings make the bidirectional
emf into unidirectional emf to behave as
DC generator. This set up is shown in fig
7.2. In the first half revolution current
flows along the path A-B-a-M-L-b-C-
D-A, (fig 7.2a). The coil in the second
half rotation, the induced currents are
reversed. But the positions of brushes
‘a and b’ are also reversed so that cur-
rent through the load remains the same
direction, that is the loop D-C-b-M-L-a-
B-A-D (fig 7.2b). The device making the
alternating supply into unidirectional
supply is by means of a device called
‘commutator’.
Fig 7.2 AC into DC Waveform

CONSTRUCTION OF DC
MACHINES
Invariably speaking, the construc-
tion of the DC generator and DC motor are
same. So any DC generator can be treated
as DC motor. The construction of a 4-pole
DC machine is given in the fig 7.3.
All DC machines have mainly two
parts:
1) Stator (outer stationary part)
2) Rotor (inner rotating part)
The Stator consists of Yoke or
Magnetic frame, poles, pole shoe, field
winding.
Rotor has the following parts:
Armature – Armature core, Armature
winding
Commutator – Brushes, Bearing.
7.3.1 Yoke
The Functions of Yoke are:
1) It provides mechanical support to the
poles and acts as a protecting cover
for the whole machine.
2) It carries the magnetic flux produced
by the poles.
7.3.2 Field System
Field system consist of two main
parts, poles and field winding.
i) Poles
Each pole is divided into two parts,
namely:
1) Pole core
2) Pole shoe
The functions of pole core and pole
shoe are:
1) Pole core carries field winding which
is necessary to produce the flux.
7.3
1. Yoke
2. Pole core
3. Pole winding
4. Pole shoe
5. Pole face
6. Air gap
7. Armature core
8. Slot
9. Tooth
10.Foot
11.Armature winding
12.Commutator
13.Shaft
14.Brush
15.Frame
16.Lifting leg
Fig 7.3 Parts of DC Machines

110
2) Pole shoes spread out the flux in the
air gap uniformly.
3) They support the exciting coils (or
field coils).
4) It is made up of magnetic material
like cast-iron or cast-steel.
ii) Field Winding
The field winding is placed on the
pole core. It is made up of aluminium or
copper. Their functions are to carry the
current to produce the required magnetic
flux. The pole structure of a DC machines
is illustrated in fig 7.4.
7.3.3 Armature System
It is further divided into two parts
namely:
1) Armature core
2)) Armature winding
i) Armature Core
It is cylindrical in shape with slots
on its outer periphery. It is mounted on
the shaft. They are used to house the ar-
mature conductors in the slot. It is made
of cast-steel laminations to reduce the
eddy current loss.
ii) Armature Slots and Windings
The armature windings are placed
into the slots on the armature surface.
When the armature rotates, an emf is in-
duced in the armature conductors in case
of generators. The ends of the coils are sol-
dered with commutator segments. These
segments are made up of copper materials.
7.3.4 Commutator
The emf induced in the armature
conductor is alternating in nature. This al-
ternating emf is made into unidirectional
by means of a device called as commuta-
tor. It is made up of copper segments.
7.3.5 Brushes and Bearings
The function of brushes is to col-
lect current from commutator. They are
usually made up of carbon or graphite and
in the shape of rectangular block. These
brushes are housed in brush-holders usu-
ally of the box-type variety. Ball bearings
are frequently employed because of their
reliability. But for heavy duty machines,
roller bearing is preferable. The complete
structure is shown in fig 7.5.
Fig 7.5 Poles and Armature of DC
Machines.
Fig 7.4 Yoke and Poles

TYPES OF DC GENERATOR
DC generators are classified ac-
cording to the manner in which field
windings are connected. The process of
giving DC voltage to the field winding for
producing magnetic field is called field
excitation. The generators are classified
based on the exciation, as:
1. Separately Excited DC Generator
In separately excited generator,
the exciation to the field winding is giv-
en by an external DC supply as shown in
Fig 7.6.
Fig 7.6 Separately excited DC generator
2. Self-Excited DC Generator
In this type of DC generators, the gen-
eration of emf is due to its property of residual
flux or residual magnetism present in the field
winding. They are mainly of three types:
a) DC series generator
b) DC shunt generator
c) DC compound generator
a) DC Series Generator
In DC series generators the field
winding (Rse
) is connected in series with
the armature winding (Ra
). Therefore, the
series current (Ise
) is equal to the arma-
ture current (Ia
) and the load current (lL
),
as shown in the Fig 7.7.
7.4
Fig 7.7 DC Series Generator
The current equation is Ia
=IL
=Ise
The Voltage equation is Eg
=V + Ia
(Ra
+Rse
)
V=load voltage
b) DC Shunt Generator
In shunt generator the field wind-
ing is across (shunt) the armature wind-
ing. Here the armature current (Ia
) is the
sum of shunt field current (Ish
) and load
current (IL
) as shown in Fig 7.8.
Fig 7.8 DC Shunt Generator
The current equation is Ia
= IL
+Ish
The voltage equation is Eg
= V+Ia
Ra
c) DC Compound Generator
These types of generators are again
classified into long shunt generator and
short shunt generator based on the field
winding connections. In long shunt com-
pound generator, the shunt field winding

112
is connected in parallel with the series
combination of series field winding and
armature winding. (fig 7.9a)
In short shunt compound genera-
tor, the series field winding is connected
in series with the parallel combination
of armature and shunt field winding. (Fig
7.9 b)
Where,
Ia
= Armature current
Ra
=Armature resistance
IL
= Load current
Ish
=Shunt field current
Isc
=Series field current
Rse
=Series field resistance
Rsh
=shunt field resistance
VL
= load voltage
Eg
= Generated voltage from armature.
EMF EQUATION OF DC
GENERATORS
Let Ø = flux in webers.
Z = no. of armature conductors
7.5
N = speed in RPM
P = no of poles
A = no.of parallel paths
(A=P)- for lap winding
(A=2)- for wave winding
According to Faraday’s law of electro-
magnetic induction, the value of generated
EMF, Eg
=
dØ
dt
Flux cut/conductor in one revolu-
tion for ‘P’ poles ‘dØ’=ØP
Thetimeforonerevolution‘dt’=60/N.
The value of induced emf per conductor,
Eg
= = =
dØ Ø Ø
dt
P
N
PN
60 60
Fig 9.(a) DC Long Shunt and Fig 9.(b) Short Shunt Compound Generator
For ‘Z’ number of conductors, and
for ‘A’ parallel paths,
E
ZN
X
P
A
volts
g
=
θ
60

APPLICATIONS OF DC
GENERATORS
1. DC Series Generators
i) They are used for series arc lighting
ii) They are used as boosters, for the
purpose of compensating the drop in
voltage in the lines on loading.
iii) Used for regenerative braking of DC
locomotives.
2. DC Shunt Generators are Used
i) In shunt generator, terminal voltage
is more or less constant. So these are
used for supplying loads needing
constant voltage.
ii) In Electroplating
iii) In Battery charging purpose.
iv) As Exciters for AC generators.
3. DC Compound Generators
i) By means of compound generator it
is possible to give constant voltage at
the line end by proper compounding.
ii) Differentially, compound generator
may be used for welding purpose.
iii) They are used to supply power to
railway circuits, elevator motors etc.
4. Separately Excited Generators
These generators are used for:
i) Supplying DC motors whose speed is
to be varied widely.
ii) Where a wide range of DC voltage is
required for testing purpose.
7.6
Un i v e r s a l
motors are known
to sometimes over-
speed, perhaps
dangerously and
destructively, when run with no load.
This article deals with different meth-
ods of universal electric motor speed
control.
A motor which can be oper-
ated either on DC (direct current)
or on single phase AC (alternat-
ing current) is called a universal
motor. On both AC and DC, it gives
approximately the same speed and
output. Universal motors often run
at dangerously high speed when
operated at no load. This means
that motor speed will be low at full
load, but the speed of the motor will
start increasing as the load on the
motor decreases. Finally at no load,
the motor will run at very high
speed (perhaps about 20,000 rpm
in some cases) and cannot made to
run at less than about 2,000 rpm.
The speed of universal motor varies
just like that of a DC series motor.
Being a series wound motor, it has
a high starting torque and varia-
ble speed characteristics, and if the
motor is started at no load, due to
its high starting torque it will attain
high speed quickly. Thus it is not
advisable to start a universal motor
at no load.

114
DC MOTOR
7.7.1 Motor Principle
An electric motor is a machine
which converts electrical energy into me-
chanical energy. Its action is based on the
principle that when a current-carrying
conductor is placed in a magnetic field,
the conductor experiences a mechanical
force. The direction of this force is given
by Fleming’s left-hand rule and magnitude
is given by:
F = BIl (N)
B =
flux density due to the flux produced
by the field winding
I =
Magnitude of current passing through
the conductor
l = Active length of the conductor
By construction, there is no basic
difference between DC generator and DC
motor. In fact, the same DC machine can
be used interchangeably as a generator or as
a motor. In generator the input is mechani-
cal energy by a prime mover and develops a
voltage, while in a DC motor the input is elec-
trical energy and it develops rotating torque.
7.7.2 Fleming’s Left Hand Rule
Keep the forefinger, middle finger
and thumb of the left hand mutually per-
pendicular to one another. If the forefin-
ger indicates the direction of the magnetic
field (B), the middle finger indicates the
direction of current (I) in the conductor,
and the thumb points to the direction of
motion (F) of the conductor.
7.7
Fig 7.10 Fleming’s Left Hand Rule
7.7.3
Principle of Operation of DC
Motor
A motor is a mechanism by
which electrical energy is converted into
mechanical energy. Both in principle and
design, a DC motor is the reverse process
of DC generator.
Consider a single conductor
placed in a magnetic field as shown in
fig 7.10. The two diagrams indicate the
direction of magnetic fluxes considering
separately.
How the resultant rotation takes
place in a DC motor is clearly understood
from the following descriptions in the
Fig 7.11.
A steady current is passed through
the armature coil from the commutator
and the brushes are so arranged as to re-
verse the current every half revolution.
When a coil, carrying a current is placed
in magnetic field, it experiences forces,
given by Fleming’s left-hand rule, which

turn it about in a direction perpendicular
to both the field and the current.
The fig 7.12a shows the upper side
of the conductor, the magnetizing force
of the field due to the current are addi-
tive while on the lower side these are sub-
tractive. The result is to increase the flux
density into the region directly above the
conductor and to reduce flux density be-
low the conductor.
If the current is reversed in the
conductor, the strengthening of flux lines
occur below the conductor and the con-
ductor will be pushed upwards as shown
in fig 7.12b.
As for the reasons above, one of the
coil side ‘A’ will be forced to move down-
wards while ‘B’ moves upward. These two
forces are equal in magnitude and oppo-
site to each other. (7.12c). These twist-
ing forces make the armature to rotate
through the two ends, that are supported
by bearings.
But practically, a DC machine will
have multiple conductors and each con-
ductor will be experiencing a force F=BI l
newton. These forces collectively produce
a driving torque which sets the armature

rotating. The machine is then said to be
motoring.
Main Flux
Conductor
S
N
N
Flux by
conductor
Current carrying
conductor
S
Fig 7.11 Resultant Force developed
Fig 7.12 Torque Development in DC Motors
(a)
(c)
(b)

116
BACK EMF OF DC
MOTOR (EB
)
When the armature of a DC motor
rotates in the magnetic field, the armature
conductor cuts the magnetic flux. Hence an
EMF will be induced in the conductor. Ac-
cording to Faraday’s law of electromagnetic
induction. This induced EMF acts in oppo-
site direction to the applied voltage and it is
referred as the back emf or counter emf Eb
.
The back emf is given by,
E =
ZN P
A
volts
b
θ
60
×
which is same as that emf induced
in a DC generator.
The relationship between the cur-
rent, back emf and the applied voltage for a
DC shunt motor is given by E V I R
b a a
= − .
Where,
Eb
= back emf in volts
V = supply voltage in volts
Ia
=armature current in amperes
Ra
=armature resistance in ohms.
The back emf Eb
is always less than
that of the applied voltage and hence the
current is flowing against the direction of
back emf.
TYPES OF DC MOTORS
The DC motor is classified into
three types based on the field winding
connection with the armature.
i) DC series motor
ii) DC shunt motor
iii) DC compound motor
DC compound motor is classified as,
a) Long shunt compound motor
b) Short shunt compound motor
7.9.1 DC Series Motor
In DC series motor, the field wind-
ing is connected in series with the arma-
ture as shown in Fig 7.14. The series field
7.8
7.9
Fig 7.13 DC Motor Circuit
Fig 7.14 Equivalent Circuit of DC Series
Motor

winding carries the input current, IL
=Ia
=Ise
.
The series field winding is relatively small
in number to give minimum value of re-
sistance drop.
7.9.2 DC Shunt Motor
In DC shunt motor, the field winding
is connected parallel (shunt) with the arma-
ture as shown in fig 7.15. The field winding
has a large number of turns and relatively
smaller cross sectional area. Therefore, the
shunt field winding has high resistance and
hence shunt field current is relatively small
compared with armature current. The speed
of DC shunt motor is almost constant during
no-load to full-load.
7.9.3 DC Compound Motor
In compound motors both series
and shunt windings are connected accord-
ing to their name of long shunt and short
shunt compound motor.
a) Short Shunt Compound Motor
In short shunt compound motor,
the series field winding is connected in
series with the parallel combination of ar-
mature and shunt field winding. The con-
nection diagram for this compound motor
is as shown in Fig 7.16.
b) Long Shunt Compound Motor
In long shunt compound motor,
the shunt field winding is connected
in parallel with the series combination
of series field winding and armature
winding.
Fig 7.15 Equivalent Circuit of DC Shunt
Motor
Fig 7.16 Equivalent Circuit of DC Short
Shunt Compound Motor
Fig 7.17 Equivalent Circuit of DC Long
Shunt Compound Motor.

118
APPLICATIONS OF DC
MOTORS
Type of Motor Characteristics Applications
1. DC Series Motor i) Variable speed
ii) Speed can be controlled
iii) No load condition is dangerous
iv) High starting torque
i) Electric traction
ii) Cranes hoists
iii) Conveyors Elevators
Trolleys
2. DC Shunt Motor i) Speed is fairly constant
ii) Adjustable speed
iii) Medium starting torque
i) Lathe machines
ii) Blowers and fans
iii) Centrifugal pumps
iv)
Reciprocating pumps
v) Machine tools
vi) Drilling machines
3. DC Compound
Motor
i) Variable speed
ii) Speed can be controlled
iii) High starting torque
i) Punches
ii) Elevators
iii) Shears
iv) Rolling mills
v) Printing presses
vi) Air compressors
Generator - மின்னாக்கி
Motor - மின்ேனா
Magnetic poles - காந்த வங்கள்
Carbon brush - கரிரிைக
Bearings - தாங்கிகள்
Test the DC supply and practice the following
DC motor to rotate.
Activities
7.10

1. Initially the emf generated is an
alternating one. But this alter-
nating emf is converted into
direct emf by
a) Slip-ring
b) Commutator
c) Carbon brush
d) End rings
2. The direction of induced emf in
DC generator is found by
a) Fleming’s left-hand rule
b) Fleming’s Right-hand rule
c) Faraday’s law
d) Kirchhoff’s law
3. The Yoke of a DC machine is
made up of
a) Copper
b) Aluminium
c) Zinc
d) Cast-iron
4. Which of the following is a func-
tion of brushes?
a) To convert AC to DC
b) To convert DC to AC
c)
To collect the current and to
deliver to load
d) None of the above
5. The armature is made up of
a) Solid aluminium
b) Solid steel
c) Laminated aluminium
d) Laminated steel
6. The principle DC motor is based
on
b) Fleming’s Right-hand rule
c) Faraday’s law
d) None
7. For electric traction, the motor
used is
a) DC shunt motor
b) DC series motor
c) DC compound motor
d) AC motor
8. Which of the following motor is
constant speed motor?
a) DC shunt motor
b) DC series motor
c) AC series motor
d) None
9. DC compound motor is having
………… winding
a) series winding only
b) shunt winding only
c) series or shunt winding only
d) series and shunt winding only
10. Commutator is made up of
----------
a) Copper
b) Brass
c) Aluminium
d) Silver

120
1. What are the main parts of DC machines?
2. Write some short notes on commutator.
3. What are the functions of yoke?
4. What are the types of DC generators?
5. State Fleming’s left-hand rule.
6. State the applications of DC series motor.
7. Mention the applications of DC shunt motor.
8. Draw the equivalent circuit diagram of DC shunt motor.
1. Derive the emf generated in DC generators.
2. Give circuit diagram of the different types of DC generators.
3. List out the applications of DC generators.
4. Give circuit diagram of the following types of DC motors.
5. Explain the force developed in case of DC motors.
3
1. Explain the process of emf generation in DC generators.
2. With neat diagrams explain the construction of DC machines.
3. How the rotating force is developed in DC motors?
4. Explain the different types of DC generators with neat diagram.

Reference Book
1. ‘A text book of Electrical Technology’ VolumeII B.L. Theraja and A.K. Theraja, S. Chand
Company Ltd.

122
Basic Electrical Engineering — Theory 122
Alternators and AC Motors
8.1 Alternator (AC Generator) - Introduction
8.2 Basic Principle
8.3 Construction
8.4 Single Phase AC Motor
8.5 Three Phase AC Motor
8.6 Stepper Motor
This chapter enable the students to know about basic principle, construction, operation of single
phase, three phase AC motor and stepper motor.
8
If What is truth? the question be,
It is to speak out evil – free.
— Thiruvalluvar
291

123 Alternators and AC Motors
ALTERNATOR -
INTRODUCTION
8.1
The machine which generates

alternating current is called as alternator
or synchronous generator.
Fig 8.1 Principle of AC Generation
In Power Supply System alternating
current is supplied to a greater
extent that
direct current supplies, because of the fol-
lowing reasons.
1. AC power can be generated in bulk
quantity without much difficulty
2. AC requirements are cheaper in cost
3. AC voltage can be step up or step
down by using transformers
4. AC can be easily converted into DC
8.1.1 Requirement of Alternator
For the generation of AC emf by
the alternator the following basic systems
are required:
1. Magnetic field system to produce
the magnetic field.
2. Armature system which house the
conductor on which emf is to be
induced.
3. A prime mover is required which gives
necessary rotational power for the
generation of emf in the alternator.
8.1.2 Types of Alternator
According to the position of armature
andfield,alternatorsareclassifiedintotwotypes
a) Stationary field and rotating
armature
type.
b) Stationary armature and rotating
field type.
a) Stationary field and rotating
armature type
It is commonly used in small size
generators and for the lower voltages. The
DC supply given to the field windings and
the alternating current generated is delivered
to the slip ring. The mechanical construction
of the revolving armature alternator is sim-
ilar to that of the DC generator except that
there is no commutator.
b) Stationary armature and rotating
field type

Alternator with the stationary arma-
ture and revolving field type is used
in the generation of high voltages.
The main reason for rotating arma-
ture type is the difficulty of using sliding con-
tact brushes on slip rings at high voltages.
With a stationary armature, the power from
the generator is delivered through copper to
copper connections firmly
bolted together.
The revolving fields are supplied with DC
normally at 110V, through a pair of slip rings.
Advantages
1. It is easy to insulate the armature
winding, because they are placed
in the stator.
2. Output Current can be easily

collected and easily supplied to
the load circuit.

124
3. Rotating field system has two slip
rings only and it can be easily
insulated.
4. Rotating field is light in weight
and hence it can run at high
speed.
5. In stationary armature the wind-
ingmaybecooledmoreefficiently.
BASIC PRINCIPLE
8.2
Fig 8.2 Basic Principle of Alternator
An alternator works on the same
fundamental principle of electromagnetic
induction as D.C. Generator i.e. when the
flux linking a conductor changes, an emf
is induced in the conductor. Like a D.C
generator, an alternator has an armature
winding and field winding.
The frequency of output ac voltage
of a synchronous generator is directly pro-
portional to the rotor speed. To maintain
constant frequency, the rotor must always
move at synchronous speed.
CONSTRUCTION OF
ALTERNATOR
8.3
Alternators are constructed in two
types
1. Salient Pole alternator
2. Non – Salient Pole alternator (or)
Turbo Alternator
8.3.1 Salient Pole Alternator
(a) STATOR
It is the stationary part of the ma-
chine and it is built up of silicon steel lam-
inations having slots on its inner periphery
to house the armature conductors. The ar-
mature core in the form of a ring is fitted to
a frame which may be of cast iron or welded
steel frame which is called stator frame.
The armature core is laminated to
reduce the eddy current loss. The lamina-
tions are stamped out and insulated from
each other with paper or varnish. The
stampings also have holes which make ax-
ial and radial ventilating ducts to provide
efficient cooling.
Armature Slot
Slots provided on the stator core
are mainly of three types.
1. Wide-Open Slots
2. Semi-closed slots
3. Closed slots
Fig 8.3 Types of Slots

1. Wide Open Slots
The open slots are more commonly
used because the coils can be form-wound
and pre – insulated before placing in the
slots. This type of slots also facilitates easy
removal and replacement of defective
coils. But this type of slots create uneven
distribution of flux, there by producing
ripples in the emf wave.
2. Semi-Closed Slots
The semi closed type slots are bet-
ter in this respect but don’t permit the use
of forms wound coils, there by complicat-
ing the process of winding.
3. Closed Slots
Totally closed slots don’t disturb
the air gap flux and they are rarely used.
(b) ROTOR
Salient Pole type rotor is used in low
and medium speed alternators. It has a large
number of projecting poles, having their
cores bolted on to a heavy magnetic wheel of
cast iron or steel. The diameter of this kind
of alternator is large and the length is small.
The poles and pole shoes are laminated to
Fig 8.4 Salient Pole Construction
reduce the heat due to eddy currents. In
large machines, field winding consists of
rectangular copper strip wound on edge.
8.3.2
Non-Salient Pole Alternator or
Turbo Alternator
(i) STATOR
The stator diameter of Non salient
pole Alternator is small and the length is
long. Stator is the stationary part of the
machine, and it is built up of silicon steel
laminations having sloth on its inner pe-
riphery to house the conductors. Normal-
ly this type of alternator has double layer
winding. But in high voltage machines,
single layer winding is used in semiclosed
sloth. Lengthy ventilating ducts are pro-
vided for cooling purpose.
(ii) Smooth Cylindrical Type Rotor
Fig 8.5 Cylindrical Pole Rotor
This rotor is used in very high speed
alternators driven by steam turbines. The
rotor of turbo alternator physically is in
the form of smooth cylinder, having long
axial length and smaller diameter.
Poles are not projected out from
the surface of the rotor. The outer periph-
ery of the rotor stampings has radial slots.

126
The field windings are accommodat-
ed in these slots. Generally copper strips are
used for the field winding,
Radial ducts are
provided for ventilation purposes.
8.3.3 Parts of A.C Motors
1. Frame: It is made up of alloy cast iron.
2. StatorandRotorcore:Itisbuiltfromhigh
quality, low loss silicon steel laminations.
3. Stator and Rotor windings: They have
moisture proof insulation embodying
mica and high quality varnishes. They
are carefully spaced for most effective air
circulation.
4. Air gap: The stator is machined carefully
to ensure uniformity of air gap.
5. Shafts and Bearings: The motor shaft is
fixed with in the rotor and rotates with it.
The rotor shaft is held in place by bearings
at either end of the motor casing. Ball and
roller bearings are used.
6. Fans: Light aluminum fans are used for
adequate circulation of cooling air.
SINGLE PHASE AC
MOTOR
8.4
Single phase and three phase sys-
tem is widely used for domestic and com-
mercial purpose. As the single-phase sys-
tem is more economical and the power
requirement in most of the houses, shops,
offices are small, which can be easily met
by three phase system.
Normally single phase motors are
used for domestic purposes. Generally be-
low 1 HP (1HP = 746 watts) motors are used
for domestic purpose and they are called as
fractional Horse Power motors (FHP)
Advantages
i) Simple in construction
ii) Cheap in cost
iii)Very reliable
iv) Easy to repair and maintenance
Applications
Due to all the above advantages, the
single phase motor find its applications in
Comparison of Salient Pole Type Rotor and Smooth Cylindrical Type Rotor
Sl.No Salient Pole Rotor Cylindrical Rotor
1 The diameter of rotor is large The diameter of rotor is small
2 Poles are projecting outside Poles are not projecting outside
3 Length of rotor is short Length of rotor is long
4 Damper winding is required No damper winding is required
5 Runs at slow speed. (100 rpm to
1500 rpm)
Runs at very high speed. (1500 rpm to
3000 rpm)
6 Suitable for hydro generators Suitable for turbo alternators run by steam
turbines

i.mixer
ii.grinders
iii.vacuum cleaners
iv.fans
v.washing machines
vi.centrifugal pumps
vii.egg beaters
viii.Hair drier and
ix.blowers.
8.4.1
Why Single Phase Induction
Motor' is not a Self Starting?
How to Make Single Phase
Induction Motor Self-Starting?
Single phase induction motor has
distributed stator winding and squirrel cage
rotor. When fed from a single phase supply,
its stator winding produces a flux which is
only alternating. It is not a synchronously
revolving (or) rotating flux as in the case of a
two or three phase stator winding fed from a
two or three phase supply. Now, an alternat-
ing or pulsating flux acting on a stationary
squirrel cage rotor cannot produce rotation
(only a revolving flux can produce rotation).
To make itself starting, it can be
temporarily converted into a two phase in-
duction motor while starting. This can be
achieved by introducing an additional start-
ing winding also called as auxiliary winding.
(i) Stator Winding
Stator of a single-phase Induction
motor has two windings
1. Main winding (Running winding)
2. Starting winding (auxiliary winding)
These two windings are connected in
parallel across single phase supply and are
spaced 90º electrical degrees apart, phase
difference of 90º electrical degree can be
achieved by connecting capacitor in series
with the starting winding. Hence the motor
behaves like a two phase motor and the sta-
tor produces revolving magnetic field which
causes rotor to run. Once motor speed, say
up to 80% of its normal speed, the starting
winding gets disconnected from the circuit
by means of a centrifugal Switch and the mo-
tor runs only on main winding.
(ii) Rotor
it consists of a laminated cylindrical
core having parallel slots on its outer periph-
ery. One copper or aluminum bar is placed
in each slot. All these bars are joined at each
end by metal ring called end rings. The en-
tire construction resembles like a squirrel
cage and hence the name called like that.
The rotor is not connected electrically to
the supply but has current induced in it by
transformer action from the stator.
8.4.2
Classification of Single Phase
Motor
a) Split phase induction motor
b) Capacitor start capacitor run motor
c) Universal motor
a) Split Phase Induction Motor
As the starting torque of this type
of motor is relatively small and it’s start-
ing current is high. These motors are most
commonly used for rating up to 0.5 HP
where the load could be starting easily

128
Fig 8.6 Split Phase Induction Motor
CONSTRUCTION
The above figure 8.6 shows the sche-
matic diagram of single phase split phase in-
duction motor. The starting winding is de-
signed to have a higher resistance and lower
reactance than the main winding. The main
winding will have higher inductance when
surrounded by more iron which could be
made possible by placing it deeper into the
stator slots.
WORKING PRINCIPLE
The starting current Is
will lag the
main supply voltage VL
by 15° and the
main winding current Im
lags main sup-
ply voltage by about 80°. Therefore, these
currents will differ in time phase and their
magnetic fields will combine to produce a
rotating magnetic field.
When the motor has come up to
about 75% of synchronous speed the start-
ing winding is opened by a centrifugal
switch and the motor will continue to op-
erate as a single phase motor. At the point
the starting winding is disconnected, the
motor develops nearly as much torque with
the main winding alone as with both wind-
ings connected.
Changing the Direction of Rotation
The direction of rotation of a split
phase motor is determined by the way the
main winding and auxiliary windings are
connected either by changing the main
winding terminals or by changing the
starting winding terminals, the reversal
of direction of rotation could be obtained.
APPLICATIONS
These motors are widely used on
easy starting loads of 1
/3HP or less
1. Washing machines
2. Driving fans
3. Grinders
4. Wood working tools
b) CapacitorStartCapacitorRunMotor
Fig 8.7 Capacitor Start - Run Motor
WORKING PRINCIPLE
This motor starts with a high capaci-
tor in series with the starting winding, so that
the starting torque is high. When a motor
is running, run capacitor is in supply. Both
the running and starting windings remain
in circuit. At the start, when the centrifugal

switch is closed the two capacitors are put in
parallel. After the motor has reached 80% full
load speed, the centrifugal switch opens and
running capacitor remains in the circuit. It
is used to disconnect the starting capacitor
from the supply after attaining almost 75% of
full load speed.Either by changing the main
winding terminals or by changing the start-
ing winding terminals, the reversal of direc-
tion of rotation could be
obtained.
APPLICATIONS
These motors are mainly used for low
noise and high starting torque applications
1. Compressors
2. Pumps
3. Air Conditioners
4. Refrigerators.
c) Universal Motor
The universal motor is defined as a
motor which may be operated on D.C sup-
ply or single phase A.C supply at approxi-
mately the same speed and output.
Fig 8. 8 Universal Motor
CONSTRUCTION
Basically universal motor is similar
to D.C series motor. The universal mo-
tor is usually two poles and a winding of
few turns which gives opposite magnetic

polarity. The armature is of wound type
and it consists of a laminated core hav-
ing either straight (or) skewed slots and a
commutator to which the leads of the ar-
mature winding are connected.
WORKING PRINCIPLE
Universal motor develop unidirec-
tional torque, whether they operate on
D.C or A.C. Supply Universal motor works
on the same principle as a D.C motor, i.e.
force between the main pole flux and the
current carrying armature conductors.
Comparision of various types of single phase motors
Sl. No Types of the
Motor
Starting
Torque
Speed Windings Applications
1 Split – phase
motor
Low Low Main winding
Starting winding
Driving fans, wood
working tools
2 Capacitor
start capacitor
run motor
High Constant Main winding
Starting winding
Compressors,
refrigerators, air
-Conditioners
3 Universal
motor
Very high Varies
according
to load
Field wind-
ing armature
winding
Vacuum cleaners,
mixie, portable drills,
sewing machine

130
In A.C operation, both field and ar-
mature currents change their polarities, at
the same time resulting in unidirectional
torque.
APPLICATION
Universal motor is used in:
1. Vacuum cleaners
2. Food mixer
3. Portable drills and
4. Domestic sewing machines
TYPES OF THREE PHASE
MOTORS
8.5
Three phase induction motors are
widely used in industrial and domestic
drives. The rotor of induction motor re-
ceives the power from the stator by means
of induction. Most of the operating princi-
ples resembles to the working of transform-
er only. So, it can also be treated as a rotat-
ing transformer. That is, primary winding
is stationary part and secondary winding is
rotating part.
According to the rotor construc-
tion, three phase induction motors are
classified as
i) 3-phase squirrel cage induction
motor
ii) 3-phase slip-ring induction motor
8.5.1 Principle of Operation
Three phase supply is given to the
stator winding. Due to this, current flows
through the stator winding and produces
a rotating magnetic field in the space be-
tween stator and rotor. This magnetic field
rotates at synchronous speed given by
Ns
=
120f
p .
Where Ns
= Synchronous speed
f = Supply frequency
p = Number of poles for which the
stator is wound
This rotating magnetic field cuts
the rotor conductors, an emf is induced
in the rotor. This induced emf produces
current and this current produces a rotor
field.
Fig 8.10 Stator and Rotor of 3 Phase Induction Motor

Both these stator and rotor fields
develop a torque. Then the rotor is rotat-
ing in the same direction as the rotating
magnetic field. In an induction motor, the
rotor speed is always less than the syn-
chronous speed.
8.5.2
Construction of 3 Phase
Induction Motor
Stator
Stator
Windings
Shaft
V-Ringer
Slider
Drain
Pugs
Endshields
Rotor
Frame
Nameplate
Eyebolt
Bearings
Fan Cover
Fan
Fig 8.9 Parts of 3 Phase Induction
Motor
Stator
The stator is made up of number
of stamping, with alternate slot and tooth.
Stampings are insulated from each other.
More number of stampings are stamped
together to build the stator core. The sta-
tor core is fitted in a casted or fabricated
steel frame. The slots in the stator, houses
the three phase winding and produces the
required rotating magnetic field.
Rotor
Two types of rotor are used in

Induction motors. They are:
a. Squirrel cage rotor
b. Slip ring (or) Wound rotor
a) Squirrel Cage Rotor
This is made up of a cylindrical
laminated core with slots to carry the ro-
tor conductors. The rotor conductors are
heavy bars of copper or aluminum, short
circuited in both ends by end rings. The
entire rotor resistance is very small. No
supply is given or taken. Motors having
such type of rotors are extremely rugged
in construction. The majority of induc-
tion motors are cage rotors.
Electric motors are used to “actuate” something in your robot: its wheels, legs,
tracks, arms, fingers, sensor turrets, or weapon systems. There are literally doz-
ens of types of electric motors (and many more if you count gasoline and other
fuelled engines), but for amateur robotics, the choice comes down to these three:
In a stepping motor, applying power causes the shaft to rotate a few degrees, then
stop. Continuous rotation of the shaft requires that the power be pulsed to the
motor. As with continuous DC motors, there are sub-types of stepping motors.
Permanent magnet steppers are the ones you’ll likely encounter, and they are also
the easiest to use.

132
Advantages
1. Cheaper
2. Light weight
3. Rugged construction
4. Higher efficiency
5. Requires less maintenance
Disadvantages
1. Moderate starting torque
2. Starting torque cannot be controlled
Applications
1. Lathes
2. Drilling machines
3. Fans
4. Blowers
5. Water pumps
6. Grinders and
7. Printing machines
b) Slip Ring (or) Wound Rotor
In this type of rotor, rotor windings
are similar to the stator winding. The rotor
winding may be star or delta connected,
distributed winding. The rotor is wound
for as many poles as the member of stator
poles and is always wound three phase even
when the stator is wound two phase. The
three phases are brought out and connect-
ed to slip rings mounted on the rotor shaft.
It is possible for introduction of additional
resistance in the rotor circuit during the
starting period for increasing the starting
torque of the motor. By varying the exter-
nal resistance in the rotor circuit, the mo-
tor speed and torque can be controlled.
Advantages
1. The starting torque can be controlled
by varying the rotor circuit resistance
2. The speed of the motor can also be
controlled by varying the rotor cir-
cuit resistance
Disadvantages
1. Slip-ring type motor is heavier.
2. High cost
3. High rotor inertia
4. High speed limitation
5. Maintenanceproblemsduetobrushes
and slip – rings
Applications
These motors are used when
speed control and high starting torque is

required. Mainly used in:
1. Lifts
2. Hoists
3. Cranes
4. Compressors
8.5.3 Slip
The difference between synchro-
nous speed and rotor speed is called the
slip speed. It is usually expressed as a per-
centage of synchronous speed (Ns
) and
represented by the symbol ‘S’.
Slip Speed= NS
– N
Fig 8.11 Stator and Rotor Synchronous
Motor

Slip S =
% Slip = × 100
8.5.4 Synchronous Motor
A motor which is running in its
synchronous speed is called as synchro-
nous motors.
1. For a given frequency, the synchro-
nous motor runs at a constant aver-
age speed, whatever the load.
2. Synchronous motor can be operated
over a wide range of power factors,
both lagging and leading.
3. The synchronous motor is not a
self-starting motor.
4. The changes in applied voltage do not
affect synchronous motor torque.
5. For synchronous motor, D.C excitation
is required.
6. Synchronous motors are usually
more costly and complicated
Applications of Synchronous Motor
1. Power factor correction
2. Constant speed, constant load drives
3. Constant voltage
STEPPER MOTOR
8.6
A stepper motor is an electrome-
chanical device which converts electrical
pulses into discrete mechanical move-
ment.
8.6.1 Step Angle
Step angle is defined as the angle
which the rotor of a stepper motor moves
when one pulse is applied to the input of
the stator.
The position of a motor is
decided
by the step angle and is expressed in degrees
Step angle, (θS
) = 360/mn
m - number of phases.
n – number of rotor teeth.
Stepper motor can be divided into
the following three categories.
1. Variable Reluctance (VR) stepper
motor
2. Permanent Magnet (PM) stepper
motor
3. Hybrid stepper motor
8.6.2
Variable Reluctance Stepper
Motor
It is the most basic type of stepper
motor. The VR stepper motor has stator and
rotor. The stator windings are wound on the
stator poles. The rotor carries no windings.
Rotor poles are of a ferromagnetic material.
The rotor is a salient pole type. This mo-
tor may be single stack or multi stack type.
This is called variable reluctance motor be-
cause the reluctance of the magnetic circuit
formed by the rotor and stator teeth varies
with the angular position of the rotor. The
direction of motor rotation is independent
of the polarity of the stator current.
8.6.3
Permanent Magnet Stepper
Motor
In this motor also stator winding
are wound on the stator poles. The stator
is multipolar. The rotor is generally cy-
lindrical and rotor poles are permanently
magnetized. The direction of motor rota-
tion depends on the polarity of the stator
current.
NS
– N
NS
NS
– N
NS

134
8.6.4 Hybrid Stepper Motor
It combines the features of vari-
able reluctance and permanent magnet
stepper motors. This is the most popu-
lar type of stepper motor. It has wound
stator pole and permanently magnetized
rotor poles.
The important features of the hy-
brid motors are its rotor structure. A re-
cent type motor, a disc rotor is used which
is magnetically, axially to give a small
stepping angle and low inertia.
Advantages of Stepper Motor
1. The rotating angle of the motor is
proportional to the input pulse
2. The motor has full torque at stand
3. Excellent response to starting, stop-
ping and still reversing
Disadvantages of Stepper Motor
1. Resonances can occur if not properly
controlled
2. Not easy to operate at extremely high
speeds
Uses of Stepper Motor
1. It can be held at a particular position
of the shaft
2. Ideal for many autonomous robots
requiring higher precision
Points to Remember
1. A.C. generator is also called as alter-
nator or A.C Synchronous generator.
2. Stationary armature and rotating
field is most advantageous one.
3. Stator is the stationary part and rotor
is the rotating part.
4. Alternator are constructed in two
types
a) Salient pole alternator
b) Non- salient pole alternator
5. Salient pole type the diameter of

stator is large and length is short
6. Non – Salient pole type the diameter
of stator is short and length is long
7. A.C motors are classified into
a) Synchronous motor
b) Induction motor
8. Synchronous motor is running at syn-
chronous speed which is NS
= 1500
9. Synchronous motors are used for
power factor correction
10.Induction motor can also be treated
as rotating transformer
Fig 8.12 Types of Stepper Motor

Alternator (or) AC generator -
Stator -
Rotor -
Slot -
Squirrel cage motor -
1. Construct a small working model by using stepper motor (children toy)
1. Identify the motors which is used in the following domestic appliance.
a) Mixie b) Grinder c) Washing Machine d) Fan
11.Induction motors are widely used in
industrial drives
12.For cooling purpose, light alumi-
num fans are used in three phase A.C
motors
13.No external supply is given or taken
in squirrel cage rotor
14.In a single phase motor, stator wind-
ings are:
1) Main Winding, and
2) Auxiliary Winding
15.Either by changing main winding
terminals or by changing auxiliary
winding terminals, the reversal of
direction of rotation is obtained in
capacitor type motors
16.Stepper motor is an electromechani-
cal device

136
1. The AC generator is also called
as
i) Alternator
ii) DC generator
iii) Synchronous motor
iv) Synchronous generator
(a) (i) and (ii) only
(b) (i) and (iii) Only
(c) (i) and (iv) only
(d) (ii) and (iii) only
2. Armature Core is laminated
a) To reduce hysteresis loss
b) To reduce eddy current loss
c) To reduce copper loss
d) To reduce mechanical losses
3. Slot types in the stator core of an
alternator are
a) Wide – open slots
b) Semi – closed slots
c) Closed slots
d) All of the above
4. Whichtypeofrotorisusedinlow
and medium speed alternators?
a) Salient – pole type rotor
b) Cylindrical type rotor
c) Squirrel cage type rotor
5. Size of stator of an alternator is
small in diameter and large in axial
length, is called as
a) Salient – pole type alternators
b) Turbo alternators
c) D.C. generator
6. Which type of rotors isused for
very high speed in alternators?
a) Salient pole type
b) Smooth cylindrical type
c) Squirrel cage type
7. Axial Ventilating holes are pro-
vided to
a) Increase eddy current
b) Increase cooling effect
c) Reduce eddy current
d) Reduce cooling effect
8. Stationary field and rotating arma-
ture type is used in
i) Small size generators
ii) For low voltages
iii) Large size generators
iv) For high voltages
(a) (i) and (ii)
(b) (ii) and (iii)
(c) (iii) and (iv)
(d) (iv) and (i)

14. Squirrel cage induction motors are
used in
a) Lathes
b) Drilling machines
c) Fans
d) All of the above
15. Slip ring induction motors are used in
a) Lifts
b) Hoists
c) Compressors
d) All of the above
16. One horse power is equal to
a) 736 watts b) 756 watts
c) 746 watts d) 766 watts
17. In India, frequency is
a) 25 Hz b) 50 Hz
c) 60 Hz d) 40 Hz
18. Which one is in correct?
a)
Single phase motors are not self
starting
b)
Single phase motors are self
starting
c)
Three phase motors are not self
starting
19. Normally, which motor is used in
Electric Mixie?
a) Split phase motors
b) Shaded pole motors
c) Capacitor start motors
d) Universal motors
20. Which motor is used in both A.C.
and D.C supply?
a) Split phase motor
b) Shaded pole motor
c) Universal motor
d) Capacitor start motor
9. Stationary armature and rotating
field type is used in
i) small size generators
ii) For low voltages
iii) Large size generators
iv) For high voltages
(a) (i) and (ii)
(b) (ii) and (iii)
(c) (iii) and (iv)
(d) (iv) and (i)
10. A motor which is running in its syn-
chronous speed is called as
a) Synchronous motor
b) Induction motor
c) Three phase motors
d) Single phase motors
11. The rotor used in three phase induc-
tion motor is
a) Squirrel cage rotor
b) Salient – pole type rotor
c) Non- salient pole type rotor
12. Advantage of three phase Induction
motors are
a) Very simple in construction
b) It’s cost is low
c) Very reliable
d) All of the above
13. Slip is designed as
(a) Ns –N
(b)
Ns–N
Ns
(c)
Ns–N
N
(d)
N–Ns
N

138
1. What are the advantages of A.C. generator?
2. State the types of armature slots.
3. What are the types of three phase induction motors?
4. Mention some advantages of three phase induction motor.
5. What are the advantages single phase motor?
6. State the applications of synchronous motor.
7.
Name the two types of rotors used in three phase Induction
motors.
8. Define ‘Slip’.
9. Write some of the applications of squirrel cage Induction motor.
10. State the advantages of slipring induction motors.
11. Write down the few applications of slip ring Induction motor.
12. Why Single phase motor is not a self starting?
13. Name two windings in stator of single phase induction motor.
14. What is meant by ‘Slip speed’?
15.
Write some of the disadvantages of squirrel cage induction
motor?
16. State the different types of stepper motor.
17. What are the advantages of stepper motor?
18. What are the disadvantages of stepper motor?
19. Write down the applications of stepper motor?
3

1. Compare the salient pole type rotor with smooth cylindrical type rotor.
2. Explain the advantages of stationary armature and rotating field system.
3. What are the type of single phase motors?
4. Explain double field revolving theory.
5. Explain the construction of squirrel cage rotor.
6. What are the application of following motors?
a. Spilt phase motor
b. Universal motor
Reference Book
1. ‘A text book of Electrical Technology’ Volume II by B.L. Theraja and A.K. Theraja, S.
Chand Company Ltd.
1. Explain the salient pole and non salient pole alternator with neat sketch.
2. With neat sketch, explain the operation of an alternator.
3. Explain the construction and operation of single phase capacitor start
Induction run motor.
4. Explain with neat sketch about universal motor.
5. Briefly explain the various types of stepper motor.

140
Engineering Materials
If the boys and girls do not learn
discipline in their school days, money
and time spent on their education is so
much national loss.
—Mahatma Gandhiji
T
he learning objective of this chapter is to know about engineering materials,
classifications, electrical, mechanical properties and types of materials.

141 Engineering Materials
Materials Properties
Pencil – Hard, Light, Opaque.
Window – Transparent, Brittle.
Paper – Light, Malleable.
Fork –
Shiny, Hard, Conductor,
Magnetic.
Figure 9.1 Properties of Materials
A material is a substance used to
make physical things. The term property
means quality, which defines the specific
characteristic of a material. Materials have
different properties and characteristics
depending on what they are used for. Exam-
ples of certain materials and their proper-
ties are given below.
Insulation works in both directions: if it is well insulated, a building is more com-
fortable whatever the season, warmer in winter and cooler in summer. It is therefore
more economical as regards heating and air conditioning.
INTRODUCTION–
PROPERTIES OF
MATERIALS
9.1
9.1 Introduction
9.2 Engineering Material
9.3 Classification of Materials and Properties
9.4 Mechanical Properties
9.5 Conducting Materials
9.6 Insulating Materials
9.7 Optical Materials

142
Uses of materials
Materials Uses
Steel - Construction of
Bridges/ Building
Wrought/Cast -
Manufacturing of
iron Tools
Gold, Silver, Copper - Making Coins
Plastic, Wood - Making Chairs
Why copper suitable for wiring?
Copper is a good conductor of electricity,
strong and ductile.
Why cooker is made up of metals?
Metals are good conductor of heat, strong
and does not melt with high temperature.
Hence a detailed study of properties of
materials provide a steady knowledge to select
things depending on their uses and nature.
Thesubstanceswhichareusefulinthe
field of engineering are called Engineering
ENGINEERING
MATERIALS
9.2
Materials. A particular material is selected
on the basis of following considerations.
1. Availability of Material
2. Cost of Material
3. Sustainability
4. Ease of Manufacture
5. Compatibility
6. Reliability
7. Recyclability
9.2.1
Classification of Engineering
Materials
Metals and Non- metals plays an
important role in the engineering industry.
The materials mainly used in practice are
metals which may be divided into ferrous,
non-ferrous and alloy. Non- metals are clas-
sified as polymer and ceramics.
9.2.2 Ferrous Metal
• The metal which contain iron as its
main constituent are Ferrous metal.
• Cast iron, wrought iron and steel are
some examples of ferrous metals.
• Hematite, magnetite, limonite and
siderite are basically iron ores. The
main ore is hematite.
METALS
FERROUS
METALS
CAST IRON
WROUGHT IRON
STEEL IRON
MIXED STEEL
COPPER
ALUMINIUM
LEAD
ZINC
BRASS
BRONZE
NON-FERROUS
METALS
NON-METALS
POLYMER
THERMO- SETTING
PLASTICS
BAKELITE
POLYSTER
REXIN
EBONITE
PVC
POLYTHENE
ACRYLIC
THERMO
PLASTICS
CERAMIC
ENGINEERING
MATERIALS
Fig 9.2 Classification of Materials

• Indians have specialized in metal-
lurgyofironandsteelmanufacturing.
• Ashoka’s pillar at Delhi, Puri tem-
ple’s iron joints speak the glory of
our skill.
9.2.3 NON- FERROUS METAL
• The metal which contains metals
other than iron as main constituent
is non-ferrous metal.
• Copper, Aluminium, Zinc, Lead,
Tin, Platinum, Silver, Gold, Tungsten
are some examples of non- ferrous
metals.
9.2.4 ALLOY METAL
• Combining of two or more metals to
obtain special properties are called as
alloy metal.
• Brass, Bronze, Stainless steel,
Nichrome are some example of alloy
metal.
Properties of materials can be classi-
fied under several heads. As a matter of fact
the following, classification of materials are
important for an engineer, to select a suita-
ble material for a desired purpose.
9.3.1 PHYSICAL PROPERTIES
Physical properties determine the
micro and macro structure of the materials
such as shape, size, colour, lustre , density ,
structure, finish , etc..
9.3.2 MECHANICAL PROPERTIES
Thesepropertiesdealswithbehaviour
of materials while force or load is acting
on it, such as elasticity, plasticity, ductility,
Fig 9.3 Classification of Metals
CLASSIFICATION
OF MATERIALS AND
PROPERTIES
9.3

144
brittleness, strength, stiffness, machinability,
malleability, hardness, toughness etc.
9.3.3 ELECTRICAL PROPERTIES
Electrical properties determine the
ability of material to permit or resist the flow
of electricity. Ex: conductivity, resistivity,
dielectric, insulation, etc..
9.3.4 MAGNETIC PROPERTIES
Magnetic properties determine the
behaviour of the materials with presence
of applied magnetic field. Ex: permeability,
retenativity, hysteresis, curie temperature, etc..
9.3.5 OPTICAL PROPERTIES
Optical properties of a material
determine the behaviour of a material under
the action of light. Ex: emission of light,
absorbance, color luminosity, photo sensi-
tivity, reflecting, refractive index, scattering,
transmission etc.
Fig 9.4 Optical Properties
9.3.6 CHEMICAL PROPERTIES
Chemical properties determine the
corrosion rate, chemical reaction rate of
material. Ex: corrosion resistance, reactivity,
chemical composition, PH, hydroscopy etc.
9.3.7 THERMAL PROPERTIES
Thermal properties determine the
behaviour of the materials when they are
subjected to thermal changes. Ex: specific
heat, thermal conductivity , thermal expan-
sion, thermal stress, thermal shock, latent
heat, specific heat , etc..
Mechanical property defines the
behaviour of material under an act of force
or load.
Fig 9.5 Mechanical Properties
i) Strength
It is defined as the ability of a material
to resist loads without failure and fracture.
ii) Stiffness
It is defined as the ability of a mate-
rial to resist deformation or deflection
under load. Stiffness within the elastic limit
is known as modulus of Elasticity.
MECHANICAL
PROPERTIES
9.4

iii) Elasticity
The ability of a material to deform
under load and return to its original shape
when the load is removed.
iv) Plasticity
The ability of a material to deform
under load and retain its new shape when
the load is removed.
v) Ductility
The ability of a material to be
deformed plastically without rupture under
tensile load. Materials possesing ductility
can be drawn into fine wire.
vi) Brittleness
It is the property of sudden fracture
without any visible permanent deformation.
vii) Machinability
The ease with which a given material
may be worked or shaped with a cutting tool
is called machinability.
viii) Hardness
Theabilityofmaterialtoresistscratch-
ing or indentation by another hard body.
ix) Toughness
The ability of material to absorb
energy up to fracture during the plastic
deformation.
x) Malleability
The ability of material to be deformed
plastically without rupture under compres-
sive load. Malleable metals can be ham-
mered and rolled into thin sheets.
xi) Creep
The slow and progressive deforma-
tion of a material for long time with a con-
stant stress.
xii) Fatigue
Failure of materials under repeated
or reversal stress is called Fatigue.
xiii) Resilience
The capability of a strained body to
recover its side and shape, after deformation
caused. Especially by compressive stress.
Conductivity is the property of a
material by which it allows the flow of elec-
tric current. Conducting materials can be
classified into low resistivity, high resistivity
and zero resistivity.
9.5.1
Conducting Materials and
Its Uses
Silver –
Used in contact surface of
switch gears and circuit
breaker points
Copper –
winding in electrical wires,
and transformer, in wires,
hard drawn copper in trans-
mission lines.
Aluminium –
flexible wires, bus bars,
domestic wiring.
Tungsten – to make filament in bulbs.
Platinum –
thermo couple and constant
material
Manganese –
standard resistances and
shunts.
Constantine –
thermo couples, rheostats
and starters for electric
motors.
Nichrome –
Heating element in Iron box,
(Ni,ch) heater.
CONDUCTING
MATERIALS
9.5

146
Kanthan –
Heating element in furnaces.
(Fe-er-Al)
Carbon –
Brushes in electrical
machines.
9.5.2
Comparison of Copper and
Aluminium
FactorS Aluminium Copper
Colour Silverly
white
Reddish
brown
Density 2700 kg/m3
8900° kg/m3
Melting point 660°C 1085°C
Resistivity 2.65x10–6
Ω-m 1.72x10–6
Ω-m
9.5.3 Advantage of Aluminium
• Cheaper - Low Cost
• Lighter - 1/3 weight of copper.
• Softer.
• Non-Reactive to acids.
• Availability - Aluminium is third most
abundant element in nature. 7.28% of
earth crust is aluminium.
9.5.4 Disadvantage of Aluminium
• Higher Resistivity : Hence aluminium
is not used for winding. If used, the
wire must be of large size to reduce I2
R
losses and machine size also increases.
• High contact Resistance.
• Poor Tensile Strength - Aluminium
cannot be used directly as overhead
transmission line as it cannot be
stretched.
• Possibilities for Loose contacts -
Aluminium cannot be soldered by
conventional method.
INSULATING MATERIALS
9.6
9.6.1 Solid Insulating Materials
A) Plastics
• It is an organic polymer, which can be
moulded into and desired shape and
size with the help of heat, pressure or
both.
Fig 9.6 Application of Plastic
• The plastic in liquid forms is known
as resin.
• There are two types of plastics
namely Thermo plastic and Thermo
set plastic .
• Thermo plastic can be softened and
hardened by heating and cooling by
any number of times. (e.g) Polythene,
PVC, Acrylic.
• Thermo set plastic cannot be softened
once they are moulded. It is formed
by condensation and polymerization.
Eg. Polyester, Bakelite, Epoxy
b) Ceramics
• Ceramics are inorganic, non-
metallic, covalent compounds.
• They are produced from earthy mate-
rial (clay) by the action of fire
• Clay product, refractories and glasses
are types of ceramics.

• Porcealin is (clay product) used
in line insulators. Transformer
bushing pin, switches, Fuse Holder
and socket, discs of Electric stove
Kettle and beads are used to insulate
heating element. Aluminium is an
important refractory material used
in furnances.
Silica glass, Fiber glass, Pyrex are
important glass insulation materials
used in Capacitor, Radio TV tubes,
Lamps, Laminated boards.
c) Rubber
Rubber is an organic polymer, which
elongates on stretching and regains its orig-
inal shapes after the removal of the stress.
Rubber may be classified as natural rubber
and synthetic rubber.
d) Mica
Mica is a mineral compound of
aluminium silicate with soda potash and
magnesium.It has high dielectric strength
and low power loss. Mica is used in tapping
stator coils, electric irons, hotplates,
toasters, motor slot lining and transformer
insulation.
e) Asbestos
• It is natural mineral material of
fibrous structure and low dielectric.
• It has high dielectric loss and low
dielectric strength.
• It is used in electrical machines to
withstand temperature, cloth tape,
Paper boards, covering on wire of
heating element, arcing barrier in
switches and breakers.
9.6.2 Liquid Insulating Materials
A) Mineral Insulating Oils
• These oils are obtained from distilla-
tion of crude petroleum.It has high
oxidation resistance and good ther-
mal stability.
• Transformer oil is used for insulating
and cooling transformer (winding
and core)
• Cable oil and capacitor oil are other
mineral insulating oils.
b) Synthetic Insulating Oils
• Compared to mineral oil, these oils
are very cheap and inflammable.
• Askarel is used as coolant in High
Voltage Transformer (upto 110° C )
• Aroclors,sovoland sovtol are other
synthetic insulating oils.
9.6.3 Gaseous Insulating Materials
A) Air
It is an important insulating material
available in nature. It is used in HT lines and
capacitor as an insulating material.
b) Nitrogen
• It is chemically inert, prevent oxidation
and reduce deterioration.
• It is used in oil filled transform-
ers, capacitors and in cables under
pressure.
c) Inert Gases
• They are used in electronic tubes and
discharge tubes as insulators
Optical materials are becoming
increasingly important for communication.
In communication, an entire network of
optical fibre, LED’S, LASER and detectors
OPTICAL MATERIALS
9.7

148
has already been installed for transmission
of voice and data. Optical disk recording
with semi conductor, laser playback are
replacing the conventional piezo electric
pickups.
Various optical materials and their
Application
Technology Application
1.
Optical
communication
i) Wave guides
ii)
Optical
modulator
iii)
Optical switches
iv) Optical Source
To guide the light
inside the fibre by total
internal reflection (eg.
optic fibre cable)
Tomodulatetheintensity
or phase of light by an
electric field / magnetic
field /ultrasonic waves
To do fast switching
To produce light
2. Energy
convertors
To convert light energy
into electrical energy
(solar panel, silicon,
selenium sulphate)
3
Thermal energy
detectors
To detect thermal
radiation
4 Display device To display electrical
signal in the visual
(eg LED, LASER)
5
Optical Fiber
Sensor
To measure
mechanical quantities
like displacement,
acceleration, pressure
electrical quantities likes
field strength, current
Fig 9.7 Examples of Optical Fibres
1. Collect 15 insulating Materials?

1. Steel is an example for________
a) Non Metal
b) Ferrous Metal
c) Non-Ferrous Metal
d) Alloy Metal
2. Which one of the following is
an alloy__________
a) Cast Iron
b) Copper
c) Brass
d) Platinum
3. Which of the following are the
thermal properties of materials?
i) Fatigue
ii) Specific Heat
iii) Thermal Conductivity
iv) Creep
a) Both (i) and (iv)
b) Both (ii) and (iii)
c) All the above
A 1
Engineering Materials - ப�ொறியியல் ப�ொருட்கள்
Metal Alloy - உல�ோகக் கலவை
Stiffness - விறைப்புத்தன்மை
Elasticity - நெகிழ்வுத்தன்மை
Plasticity - உருமாறும் தன்மை
Ductility - கம்பியாக நீளும் தன்மை
Brittleness - ந�ொறுங்கும் தன்மை
Hardness - கடினத்தன்மை
Toughness - கெட்டிப்புத் தன்மை
Malleability - தகடாகும் தன்மை
Creep - த�ொய்வு
Fatique - ந�ொந்தக் களைப்பு

150
4. Zinc is an example of ________
a) Non Metal
b) Ferrous Metal
c) Non-Ferrous Metal
d) Alloy
5. Refractive index and Reflectiv-
ity are properties of material is
known as ________________
a) Mechanical
b) Thermal
c) Chemical
d) Optical
6. Which of the following are
the chemical properties of
materials?
a) Corrosion Resistance
b) Reactivity
c) Chemical Composition
d) All the above
7. Which one of the following is an
organic material________
a) Zinc
b) Iron
c) Silicon Carbide
d) Wood
8. Shape and density are properties
of materials is known as _____
a) Physical
b) Chemical
c) Mechanical
d) Electrical
9. Which state of material resist Ten-
sion, Compression and shear stress?
a) Gaseous
b) Liquid
c) Solid
10. Which of the following met-
als are both malleable and
ductile_________
a) Copper
b) Cast Iron
c) Porcelain
d) Zinc
11. Which of the following conducto-
ris used in over head distribution
lines?
a) Aluminium
b) Copper
c) ACSR
d) Steel
12. Which of the following is used for
making the resistance of heating
element ________
a) Invar
b) Nichrome
c) Mangani
d) Constantan
13. The following list gives the four met-
als Gold(Au), Silver(Ag), Alumini-
um(Al) and Copper (Cu) increasing
order of resistivity.____
a) Ag, Cu, Au, Al
b) Au, Ag, Cu, Al
c) Ag, Au, Cu, Al
d) Cu, Ag, Au, Al

1. List out the broad classification of the properties of engineering
materials.
2. Write short notes on types of metals.
3. Differentiate Thermo setting plastic and Thermo plastic.
4. State the different properties of material.
5. Write down the thermal properties of materials.
6. What is meant by optical properties and give some examples?
7. Write short notes on optical energy convertor.
8. Name the insulating material available at free of cost and where it is
used.
9. State the factor to be considered for the selection of materials for
engineering applications.
3
14 Aluminium is found ______
percentage of earth crust
a) 7.28
b) 8.27
c) 7.82
d) 8.72
15 Which one of the following is
used as energy convertor in
optical materials____
a) Optic Fibre Cable
b) LED
c) LASER
d) Solar Panel
16 Most widely used conducting
materials are____
a) Gold and Silver
b) Copper and Aluminium
c) Copper and Silver
d) Gold and Platinum

152
1. Explain the various properties of engineering materials.
2. Tabulate the applications of optical materials and technology.
1. Explain the mechanical properties of materials.
2. Explain the types of conducting materials.
3. Compare the properties of copper and aluminium.
4. Explain the types of insulating materials.
Reference Books
1. ‘An introduction to Electrical Engineering Materials’ by Dr. C.S. Indulkar and Dr. S. Thiruven-
gadam, 4th
edition, S. Chand company.

153 Electronics
Electronics
Do all the good you can,
By all the means you can,
In all the ways you can,
In all the places you can,
At all the times you can,
To all the people you can,
As long as ever you can.
—JOHN WESLEY

154
T
his chapter enables the students to study in detail about atomic structure, types of
conductors, classification of rectifiers, filtering circuits. LED, LCD, display, camera and
mobile phone workings.
10.1 Introduction
10.2 Rectifiers-Types
10.3 Filter Circuits
10.4 Zener Diode
10.5 Transistor-NPN and-PNP
10.6 LED(Light Emitting Diode)
10.7 LCD(Liquid Crystal Display)
10.8 Seven Segment Display
10.9 CCTV Cameras
INTRODUCTION
10.1
In the modern era of fast-developing
society, electronics is the most important
branch of Engineering. Electronics is the
branch of engineering which deals with
current flow through a vacuum, gas and
semiconductors.
10.1.1 Atomic Structure
According to modern theory, mat-
ter is electrical in nature. All the materi-
als are composed of very small particles
called atoms. The atoms are the building

155 Electronics
bricks of all matter. An atom consists of a
central nucleus of positive charge around
which small negatively charged particles,
called electrons revolved in different paths
or orbits.
Nucleus is the central part of an
atom which contain protons and neutrons.
A proton is a positively charged particle,
while the neutron has the same mass as the
proton, but has no charge. Therefore, the
nucleus of an atom is positively charged.
So all the materials are in stable condition.
The sum of protons and neutrons consti-
tutes the entire weight of an atom and is
called atomic weight. The number of elec-
trons is equal to the number of protons in
an atom and is called as atomic number.
i.e, Atomic number=number of pro-
tons (or)number of electrons.
Atomic weight=number of protons +
number of neutrons.
10.1.2
Structure of Electron
in An Atom
The electrons in an atom revolve
around the nucleus in different orbits or
paths. The number of electrons in any
orbit is determined by the following rules.
iv) The last orbit cannot have more
than 8 electrons
v) The last but one orbit cannot
have more than 18 electron
10.1.3 Structure of Elements
We have seen that all atoms are made
up of protons, neutrons and electrons. The
difference between various types of ele-
ment is due to the different number and
arrangement of these particles within their
atom. For example, the structure of copper
atom is different from that of carbon atom
and hence the two elements have different
properties. (Ref Fig. 10.1)
The atomic structure can be easily
formed if we know the atomic weight and
atomic number of the element.
Ex:copper→Atomic weight = 64
Atomic number = 29,
Number of protons=Number of
electrons=29,
And Number of neutrons=64–29=35
Fig 10.1 Atomic Structure of Copper
The number of electrons in
any orbit is given by 2n2
where n is
the number of the orbit.
For example
i) First orbit contains = 2 × 12
= 2
electrons
ii) Second orbit contains = 2 × 22
= 8 electrons
iii) Third orbit contains = 2 × 32
= 18 electrons

156
Fig shows the structure of copper
atom.It has 29 electrons which are ar-
ranged in different orbits as follows.
1 orbit = 2 × 12
= 2
2 orbit = 2 × 22
= 8
3 orbit = 2 × 32
= 18
4 orbit will have 1 electron
The atomic structure of all known
elements can be shown in this way.
RECTIFIERS - TYPES
10.2
It has already been discussed in the
previous chapter that a pn-junction con-
ducts current easily when forward bias
and practically no current flows when it is
reverse biased.
“A pn-junction is known as a
semiconductor or crystal diode”
For reasons associated with eco-
nomics of generation and transmission,
the electric power available is usually an
a.c. supply. The supply voltage varies sinu-
soidally and has a frequency of 50 Hz. It is
used for lighting, heating and also in elec-
tric motors.
Mostly all electronic devices require
d.c. power for this proper operation. DC
batteries are used for vehicles and rarely
in commercial appliances. They are costly
and require frequent charging or replace-
ment. So we can get d.c. power from, a.c.
power by using regulated d.c. power
supply. It consists of transformer, rectifier
filter and regulator.
Classification of Rectifiers
The unidirectional characteristic
active element ie., diode is used for this
purpose. The rectifier convert an AC sig-
nal into DC signal. Rectifiers are classi-
fied into two types namely (i) Half wave
rectifier (ii) Full wave rectifier. They are
explained as below
10.2 (i) Half wave Rectifier
In half-wave rectification, the rec-
tifier conducts current only during the
positive half-cycle of input ac supply.
The negative half-cycle of a.c. supply are
suppressed ie., during negative half-cy-
cle, no current is conducted and hence no
voltage appears across the load.
Circuit details
Fig 10.2 shows the circuit where
a single crystal diode acts as a half-wave
rectifier. The a.c. supply is applied in
series with the diode and load resistance
RL
through a transformer.
Operation
The a.c. voltage across the sec-
ondary winding AB changes polarities
after every half-cycle. During the posi-
tive half-cycle of input a.c. voltage, end ‘A’
becomes positive with respect to ‘B’. This
makes the diode forward biased and hence
it conducts current. During the negative
half cycle, end A is negative with respect
to B. Under this condition, the diode is
reverse biased and it conducts no cur-
rent. Therefore, current flows through the
diode during positive half-cycle of inputs
ac voltage only. It is blocked during the

157 Electronics
negative half cycle as shown in fig 10.15.
In this way, current flows through load RL
always in the same direction. Hence d.c.
output is obtained across RL
and this out-
put is pulsating d.c.
Fig 10.2 Half wave Rectifier-wave form
These pulsations in the output are
further smoothened with the help of “Fil-
ter circuit”. The peak inverse voltage of the
diode should be at least equal to Vm
10.2.(ii) Full Wave Rectifier
In full wave rectification, cur-
rent flows through the load is the same
direction for both half-cycle of input a.c.
voltage. This can be achieved with two
diodes working alternately. Therefore,
a full-wave rectifier utilize both half-
cycle of input a.c voltage to produce
the d.c.output. The following two
circuits are commonly used for full wave
rectification.
(i) Centre tap full wave rectifier
(ii) Full-wave bridge rectifier
(a) Centre Tap Full-Wave Rectifier
Circuit Details
The circuit employs two diodes
D1
and D2
as shown in fig 10.16. A cen-
tre tapped secondary winding AB is used
with two diodes connected so that each
uses one half-cycle of input a.c. voltage.
Fig 10.3 Full wave Rectifier-Wave Form

158
Operation
During the positive half cycle of
secondary voltage, the end A of the sec-
ondary winding becomes positive and end
B negative. This makes the diode D1
for-
ward biased and diode D2
reverse biased.
There fore diode D1
conducts while diode
D2
does not. The conventional current
flow is through diode D1,
load resistor Rl
and the upper half of secondary winding
as shown by the dotted arrows.
During the negative half cycle, end
A of the secondary winding becomes neg-
ative and end B positive. Therefore diode
D2
conducts while diode D1
does not. The
conventional current flow is through
diode D2
, load RL
and lower half winding
as shown by solid arrows. Referring to
fig 10.3 it may be seen that current in the
load RL
is in the same direction for both
half-cycle of input a.c. voltage. Therefore
d.c. is obtained across the load RL
. The
peak inverse voltage (piv) of this rectifier
is 2Vm
In recent days center tap full wave
rectifier is not used. It is replaced by full
wave bridge rectifiers. Because of its appli-
cation, full wave bridge rectifier is mostly
used.
(b)Full wave Bridge Rectifier
Circuit Details
The need for a center tapped power
transformer is eliminated in the bridge
rectifier. It contains four diodes D1,
D2
, D3
D4
connected to form bridge as shown
in fig 10.4. The a.c supply to be rectified
is applied to the diagonally opposite ends
of the bridge through the transformer.
Between other two ends of the bridge, the
load resistance RL
is connected.
Fig 10.4 Full Wave Bridge
Rectifier-Wave Form
Operation
During the positive half cycle of sec-
ondary voltage, the end P of the secondary
winding becomes positive and end ‘Q’neg-
ative. This makes diode D1
and D3
forward
biased while diodes D2
and D4
are reverse
biased. Therefore, only diodes D1
and D3
will
conduct. These two diodes will be in series
through the load RL
as shown in fig 10.5 (i).
The conventional current flow is shown by
dotted arrows. It may be seen that current
flows from A to B through the load RL
During the negative half-cycle of
secondary voltage, end P becomes negative
and end Q positive. This makes diodes.
D2
and D4
forward biased whereas diodes
D1
and D3
are reverse biased .Therefore,
only diodes D2
and D4
conduct. These two
diodes will be in series through the load
RL
as shown in fig 10.5(ii). The current
flow is shown by the solid arrows. It may
be seen that again current flows from A to

159 Electronics
B through the load.ie in the same direc-
tion as for the positive half-cycle. There-
fore d.c output is obtained across load RL
The peak inverse voltage (piv) of
each diode is equal to the maximum sec-
ondary voltage of transformer.
FILTER CIRCUITS
10.3
Generally a rectifier is required to
produce pure d.c supply for using at various
places in the electronic circuits. However, the
output of a rectifier has pulsating character.
ie it contains a.c and d.c components. The a.c.
component is undesirable and must be kept
away from the load. So a filter circuit is used
to remove the a.c component.
“A filter circuit is a device
which removes the ac component
of rectifier output but allows the d.c
component to reach the load”
Fig 10.5 Full Wave Bridge
Rectifier
The most commonly used filter cir-
cuits are capacitor filter, choke input filter
and capacitor input filter (or) π Filter.
ZENER DIODE
10.4
Zener Diode is a specially designed
pn-junction diode. The symbol of the
Zener diode in as shown in fig10.6. When
forward biased, its characteristics are just
those of ordinary diode. A Zener diode is
always reverse connected, i.e. it is always
reverse biased. When the reverse bias on a
crystal diode is increased, a critical voltage
Fig 10.20 Zener Diode Characteristics
Fig 10.6 Zener Diode
called breakdown voltage is reached where
the reverse current increase sharply to a
high value. The breakdown region is the
knee of the reverse characteristic as shown
in fig 10.7. Thereforethe breakdown voltage

160
is sometimes called ‘Zener voltage’ and
sudden increase in current is known as
Zener current.
The breakdown or Zener voltage
depends upon the amount of doping.
If the diode is heavily doped, depletion
larger will be thin and consequently the
breakdown of the junction will occur at a
lower reverse voltage. On the other hand,
a lightly doped diode has a higher break-
down voltage. When an ordinary crystal
diode is properly doped, so that it has a
sharp breakdown voltage and it is called a
Zener diode.
“
A properly doped crystal
diode which has a sharp breakdown
voltage is known as a Zener diode”
TRANSISTOR
10.5
“When a third doped element
is added to a crystal diode in such
a way that two pn junction formed,
the resulting device is known as a
transistor
The transistor is a new type of elec-
tronic device and is capable of achieving
amplification of weak signals.
There are two types of transistors,
namely (i) n-p-n transistor (ii) p-n-p
transistor.
Fig 10.8 Transistor Configuration
The n-p-n transistor is composed
of two n-type semiconductors seperated
by a thin section of p-type as shown in
fig 10.8(i). However a p-n-p transistor is
formed by two p-sections seperated by a
thin section of n-type as in fig 10.8 (ii).
A transistor (p-n-p or n-p-n) has
three section of doped semiconductors.

161 Electronics
The section on one side is the emitter and
the section on the opposite side is the col-
lector. The middle section is called the
base and forms two junctions between the
emitter and collector. The above fig 10.8
(i) (ii) shows the symbols of n-p-n
p-n-p transistors.
Note that emitter is shown by an
arrow which indicates the direction of
conventional current flow with forward
bias. For n-p-n connection, it is clear that
conventional current flow out of the emit-
ter as indicated by the outgoing arrow in
fig 10.8(i). Similarly, for p-n-p connec-
tion, the conventional current flows into
the emitter as indicated by inward arrow
in fig 10.8(ii).
Transistor Action
The emitter base junction of a
transistor is forward biased where as col-
lector base junction is reverse biased. If
for a moment, we ignore the presence of
emitter base junction, then practically no
current would flow in the collector circuit
because of the reverse bias. However, if
the emitter base junction is also present,
then forward bias on it causes the emitter
current to flow. It is seen that this emitter
current almost entirely flows in the collec-
tor circuit. Therefore, the current in the
collector circuit depends upon the emitter
current. If the emitter current is zero, then
collector current is nearly zero. However
if the emitter current is 1ma, then collec-
tor current is also about 1ma. This is pre-
cisely what happens in a transistor.
We shall now discuss the transistor
action for npn and pnp transistors.
10.5(i) Working of npn – Transistor
Fig 10.9 shows the npn-transistor
with forward bias to emitter base junction
and reverse bias to collector base junction.
The forward bias causes the electrons in
the n-type emitter to flow towards the
base. This constitutes the emitter current
IE
. As these electrons flow through the
p-type base, they tend to combine with
holes. The base is lightly doped and very
thin. Therefore, only a few electrons less
than 5% combine with holes to constitute
base current IB
. The remainder more than
95% cross over into the collector region to
constitute collector current IC
. In this way,
almost the entire emitter current flows in
the collector circuit. It is clear that emitter
current is the sum of collector and base
currents. ie, IE
=IB
+IC
.
Fig 10.9 n-p-n Transistor
10.5(ii) Working of pnp - Transistor
Fig 10.10 shows the basic connec-
tion of a pnp transistor. The forward bias
causes the holes in the p-type emitter to
flow towards the base. This constitutes
the emitter current IE
. As these holes cross
into n-type base, they tend to combine
with the electrons. As the base is lightly
doped and very thin. Therefore, only a few

162
holes 5% will combine with the electrons.
The remainder 95% cross into the collec-
tor region to constitute collector current
IC
. In this way, almost the entire emitter
current flows in the collector circuits. It
may be noted that current conduction
within pnp-transistor is by holes. How-
ever, in the external connecting wires, the
current is still by electrons.
10.6
LIGHT EMITTING
DIODE (LED)
The Light emitting diode(LED) is
a PN junction device which emits light
when forward biased. In all semiconduc-
tor PN junctions, some of the energy will
be radiated as heat and some in the form
of photons. In silicon and germanium,
greater percentage of energy is given out
in the form of heat and the emitted light
is insignificant. In other materials such
as gallium phosphide (Gap) or gallium
arsenide phosphide (Ga As P) the number
of photons of light energy emitted is suffi-
cient to create a visible light source. Here,
the charge carrier recombination takes
place when electrons form the n-side cross
Fig 10.10 p-n-p Transistor
the junction and recombine with the holes
on the p-side.
Fig 10.11 LED Display
LED under forward bias and its
symbol are shown in the Fig 10.11. When
an LED is forward biased, the electrons
and holes move towards the junction and
recombination takes place. As a result of
recombination, the electrons lying in the
conduction bands of n-region fall into the
holes lying in the valance band of a p-re-
gion. The difference of energy between the
conduction band and the valance band is
radiated in the form of light energy. Each
recombination causes radiation of light
energy. Light is generated by recombina-
tion of electrons and holes where by their
excess energy is transferred to an emit-
ted photon. The brightness of the emitted
light is directly proportional to the for-
ward bias event.
Applications
• LEDs can be switched ‘on’ and ‘off’ at
a very fast speed of one nano second
(1ns).
• They are used in burglar alarm sys-
tems, picture, phones, multimeters,
calculators, digital meters, micropro-
cessors, digital computers, etc.

163 Electronics
• Used in solid state video displays and
optical communication system.
• Used in programmable advertise-
ment boards.
• Used in image sensing circuit.
10.7
LIQUID CRYSTAL
DISPLAY(LCD)
Liquid crystal display (LCDs) are
used for display of numberic and alpha-
numeric character in dot matrix and
segmental displays. The two liquid crys-
tal materials which are commonly used
in display technology are nematic and
cholesteric.
Advantages of LCD
1) The voltage required are small.
2) They have a low power consumption.
A seven segment display requires
about 140W (20W per segment),
whereas LCDs require about 40mw
per numeral.
3) They are economical.
Disadvantages of LCD
1) LCDs are very slow device. The Turn
‘on’ and ‘off’ times are quite large.
2) When used in dc, their life span is
quite small. Therefore, they are used
with ac supplies having a frequency
less than 50 HZ.
3) They occupy a large area.
10.8
SEVEN SEGMENT
DISPLAY
One way of producing an alphanu-
meric display is to make a seven segment
monolithic device as shown in fig 10.12
which can display all numerals. Each seg-
ment contains LED which can be turned
‘on’ or ‘off’ to form the desired digit. Each
segment of the array has to be switched in
response to a logic signal.
Fig 10.12 7-Segment LED Display
Common Anode
For example Fig 10.12 (i) shows the
response to a logic signal corresponding to
2, in which segments a ,b, g, e and d have
been switched ‘on’ and c and f remains
‘off’. Similarly when all segments are ‘on’,
the digit formed is ‘off’ 8. If only the center
segment g is the digit will be zero. Com-
mon anode and common cathode seven
segment LED displays are shown in Fig
10.12 (ii) common anode type LED dis-
plays an active ‘low’ configuration, where
as an active ‘high’ circuitry is necessary for
the common cathode type LED display.
10.9
CCTV CAMERAS
CCTV systems have become
extremely popular over a decade as the
technology has improved and become more
affordable. Themajority of CCTV camera
in use nowdays are usually for surveillance
and security purposes. CCTV systems can
be found in almost every bank, casino,
mall and large departmental store. In fact,

164
CCTV systems have become so afforda-
ble, most smaller mom and pop stores etc.
apartments also have CCTV systems in
them for security purpose.
Different types of CCTV Camera
There are many types of CCTV
camera. Here we run through these types
of camera and what makes them unique
and more suitable for some venues over
others. They are
i) Dome camera
ii) Bullet camera
iii) C-mount camera
iv) Day/night camera
v) PTZ camera
(i) Dome Camera
The dome camera is one of the
most commonly useful for indoor security
and surveillance. The shape of the cam-
era makes it difficult for onlookers to tell
which way the camera is facing, which is a
strong piece of design, deterring criminals
by creating an of uncertainty.
Fig 10.13 Dome Camera
Advantages
a) Ease of installation
b) Vandal proof features
c) Infrared capability
(ii) Bullet Camera
Bullet cameras are long and cylin-
drical in shape, and are ideal for outdoor
use. Their strengths lie specifically in
applications which require long distance
viewing. Installed within protective cas-
ings, the cameras are protected against
dust, dirt and other natural elements.
The cameras can easily be mounted with
a mounting bracket, and come fitted with
either fixed or varifocal lenses depend-
ing on the requirements of its intended
application.
Fig 10.14 Bullet Camera
Advantages
a) Adaptability can use indoors and out
doors
b) Compact size aids installation.
c) High quality image resolution
iii) C-mount Camera
This type of camera Coming with
detachable lenses. C-mount cameras allow
simple lense changes to fit different applica-
tions.C–mountcameras,werestandardCCTV

165 Electronics
lenses can only cover distances of 35-40ft, can
also cover distances beyond 40ft, to the possi-
bility to use special lenses with these cameras.
Fig 10.15 C-mount Camera
Advantages
a) It can support changes in technology.
b) Effective for indoor use.
c) Bulky size makes them noticeable.
iv) Day/Night Camera
Capable of operating in both normal
and poorly lit environment. These cameras
benefit from not requiring inbuilt infrared
illuminators as they can capture clean video
images in the dark thanks to their extra sen-
sitive imaging chips. For this reason, these
cameras are ideal for outdoor surveillance
applications in which IR cameras are unable
to function optionally.
Fig 10.16 Day/Night Camera
Advantages
a) Record in both color and black
white
b) Wide variety of sizes available
c) Infrared capability
How Neon Lamps work!!!
When an electric voltage is applied to the terminals (about 15,000 volts), enough energy
is supplied to remove an outer electron from the neon atoms. If there is not enough volt-
age, there will not be enough kinetic energy for the electrons to escape their atoms and
nothing will happen. The positively charged neon atoms (cations) are attracted to the
negative terminal, while the free electrons are attracted to the positive terminal. These
charged particles, called plasma, complete the electric circuit of the lamp

166
Basic Electrical Engineering — Theory 166
Atomic Structure - அணு அமைப்பு
Valance Electron - இணைதிறன் எலக்ட்ரான்
Free Electron - கட்டுறா எலக்ட்ரான்
Energy Band - ஆற்றல் நிலைகள்
Impurity - மாசு
Forward Bias - முன்னோக்கு சார்பு
Reverse Bias - பின்னோக்கு சார்பு
Emitter - உமிழ்வான்
Collector - ஏற்பான்
Base - அடிவாய்
Depletion Layer - சிதைவு அடுக்கு
Filter Circuit - வடிப்பான் சுற்று
LED – Light Emitting Diode - ஒளி உமிழும் டைய�ோடு
LCD – Liquid Crystal Diode - திரவ படிக காட்சிதிரை
1. How to test the effectiveness of the battery by LED?
2. Identify the types of the transistor using multimeter.
3. Test the LED 7- segment display using the following picture.
Electronics

167 Electronics
1. An atom consist of
a) Proton
b) Neutron
c) Electron
d) All of the above
2. The number of electrons in
any orbit is calculated by the
Formula
a) 2n
b) 2n2
c) 2n3
d) n2
3. In half wave rectifiers, the num-
ber of diodes used as
a) One
b) Two
c) Three
d) Four
4. In bridge rectifier, the number
of diodes used as
a) 1
b) 2
c) 4
d) 3
5. Filter circuit is used to remove
a) dc components
b) ac components
c) combination of these two
d) none of these
6. In forward biasing, the emitter
current in npn
transistor is
a) IB
b) IC
c) IB
+IC
d) none of these
7. The number of segments in seven
segment display is
a) 6
b) 5
c) 7
d) 3
1. What is called atom?
2. What are the types of rectifiers?
3. What are the different types of CCTV camera?
3

168
Answer the following questions not exceeding one page
1. Briefly Explain “Atomic Structure”.
2. Explain the use of Filter circuits.
Answer the following questions not exceeding two page
1. Explain half-wave rectifier with neat circuit diagram.
2. Explain full-wave bridge rectifier with neat circuit diagram.
3. Explain the operation of Zener diode.
4. Explain the working of pnp transistor.
5. Explain the working of npn transistor.
6. What are the advantages of using (i) LED (ii) LCD?
7. Explain seven segment display with diagram.
Reference Books
1. ‘A text book of Electrical Technology’ Volume I and Volume IV by B.L. Theraja and
2. Principles of Electronics by V.K. MEHTA and SHALU MEHTA, S. Chand Company
Ltd.

169 Electronics
169
1. In case of electric fire use
a) dry sand
b) wet sand
c) carbon powder
d) water
2. Good conductor has a property
of
a) low resistance
b) high resistance
c) medium of these two
d) none of these
3. According to ohm’s law I is equal
to
a) V2
/R
b) I2
/R
c) V/I
d) V/R
4. The permanent magnet is not
used in
a) horse shoes magnet
b) energy meters
c) transformers
d) loud speaker
5. Which magnetic field is like a
magnetic field of a bar magnet?
a) Current carrying wire
b) Current carrying ring
c) Current carrying solenoid
d)
Current carrying rectangu-
lar bar
6. Charging and discharging process
in secondary cell is by which law?
a) Ohms law
b) Faradays laws of electrolysis
c) Lenz’s law
d) Current law
7. Advantage of using lithium-ion
battery is
a) high energy density
b) low energy density
c) medium energy density
d) poor energy density
8. Digital energy meters is used for
the following reason
a) High accuracy
b) Small size
c) Long life
d) All the above
9. Transformer operates on the
principle of
a) self-induction
b) mutual induction
c) ohm’s law
d) len’s law
10. The function of DC machine is of
b) Fleming’s right hand rule
c) Faraday’s law
d) Krichhoff’s law
Choose the correct answer:
MODEL QUESTION PAPER
STD:11th
TIME: 3.30 hrs MARKS:90
EMA_English_MQP.indd 169 12/17/2019 5:52:15 PM

170
Basic Electrical Engineering — Theory 170 Model Question Paper
11. Which type of rotor is used for
very high speed in alternators?
a) Salient pole type
b) Smooth cylindrical type
c) Squirrel cage type
12. One horse power is equal to
a) 736 watts
b) 756 watts
c) 746 watts
d) 766 watts
13. Which one of the following is an
organic material
a) Zinc
b) Iron
c) Silicon carbide
d) Wood
14. The number of electrons in any orbit
is calculated by the formula
a) 2n
b) 2n2
c) 2n3
d) n2
15. The Camera which covers a distance
of more than 40 feet is
a) Dome Camera
b) Bullet Camera
c) C Mount Camera
d) Day/Night Camera
1) What are the methods used for production of electricity?
2) Define ohm’s law?
3)
Two resistance 3Ω and 6Ω are connected in parallel voltage of the
circuit in 240V. Find the value of total resistance?
4) What is electro magnetism?
5) Define End Rule?
6) Write short notes on UPS Battery?
7) Define effective value or RMS value?
8) What are the protective devices of transformer?
9) State Fleming’s left hand rule?
10) Why single phase motor is not a self-starting?
11)
State the factor to be considered for the selection of materials for
engineering applications?
12) What are the different types of CCTV camera?
3

171 Electronics
171
1. Explain the method of preventing an electric shock?
2. Explain the properties of a conductor?
3. Compare magnetic and electric circuit.
4. What are the advantages of digital energy meter?
5. Explain about auto transformer?
6. What are the types of single phase motor?
7. Explain the various properties of engineering materials?
1. Explain the Kirchoff’s laws?
(or)
Explain in detail about Lithium ion battery with diagram?
2. Explain the process of emf generation in DC generators?
(or)
Explain Half-wave rectifier with neat circuit diagram.

172
Basic Electrical Engineering — Practical 172
Basic Electrical
Engineering
PRACTICAL
EMA_English_Practical.indd 172 11/9/2020 3:55:47 PM

173
CONTENTS
CLASS XI
1. Study of Hand Tools for Wiring 174
2. House Wiring and Electrical Safety Rules 195
3. Verification of Ohm’s Law. 205
4. Preparation of Appliances Test Board 209
5. One Lamp Controlled by a Regulator 212
6. Wiring Connection of Fluorescent Lamp 216
7. Stair-Case Wiring 219
8. Godown Wiring 223
9. Electric Bell 226
10. Testing of Resistor, Diode, Transistor, and Capacitor 230
Tabulation of Electric Symbols 237
Case Study -1 240
Case Study -2 242

174
Basic Electrical Engineering — Practical
STUDY OF HAND TOOLS FOR WIRING
Do not wait for opportunity. Create it
8th
9th
10th
11th
12th

175 Study of Hand Tools for Wiring
Aim
Usually, in the field of electricity, so many electric tools (both hand and machine
tools) are now-a-days being utilised. A person becomes more efficient, when he knows
the proper way of handling the tools. In domestic side, repairs, maintenance and electrical
wiring work, various types of hand tools are used. In this topic, Line diagram is given to
know about the study of hand tools for wiring purpose.
Cutting Plier
Uses
It is made up of forged steel and is used for cutting, twisting, pulling, holding and
gripping small jobs in wiring assembly and repairing work. Non-insulated plier is also
available. Insulated pliers are used for work on live lines.

176
They are specified with their overall dimensions of length in mm. Mostly, the pli-
ers used for electrical work will be of insulated grip.
Long Nose Pliers
Uses
Long nose pliers are used for holding small objects in places where fingers cannot
reach.

Round Nose Plier
Uses
Wire hooks and loops could be made using the round nose pliers.

178
Cutter
Uses
It is used for cutting copper or aluminium wires having smaller diameter.

Care and Maintenance of Pliers
1. Do not use pliers as hammers.
2. Do not use pliers to cut large size of copper or aluminium wires and hard steel wires of
any size.
3. While using the pliers avoid damage to the insulation of hand grips.
4. Lubricate hinged portions.
Screw Driver
Uses
Screw drivers are used for tightening or loosing screws. The screw driver tip should
snugly fit the grooves of the screw to have maximum efficiency and to avoid damage of the
screw heads. The screw driver is used for electrical works, generally have plastic handles
and the stem is covered with insulating sleeves. As the length of the screw driver is pro-
portional to the turning force, for small work choose a suitable small sized screw driver.

180
Electrician Knife
Uses
It is used for removing the insulation of cables and cleaning the wire surface. One
of the blade having sharp edge is used for skinning the cable and rough edged blade is
used for cleaning the surface of wires.

Line Tester
Uses
It consists of a glass tube filled with neon gas and electrodes at the ends. To limit
the current within 300 micro- amps at the maximum voltages, a high value resistance
is connected in series with one of the electrode. It may have tip like probe or like screw
driver at one end. The presence of supply is indicated by the glow of the lamp. When the
tip is touched on the live supply and the brass contact in the other end of neon tester is
touched by hand, then completes the circuit and the neon bulb will glow.

182
Ball Peen Hammer
Uses
The hammer is made up of special steel and the striking face is tempered and is
used for nailing, straightening and bending work. The handle is made up of hard wood.

Rawl Jumper
Uses
A rawl plug tool has two parts, namely the tool bit and holder. The tool bit is made
of tool steel the holder is made of mild steel. It is used for making holes in bricks, concrete
wall and ceiling. Rawl plugs are inserted in them to fix accessories.
Pipe Jumper
Uses
A pipe jumper is used along with a hammer to make holes in wall which is required
for wiring. The diameter of the pipe jumper depends upon the diameter of the pipe to be
accommodated in wall, and the length depends upon the wall thickness.

184
Mallet
Uses
It is made up of hard wood or nylon. It is used for driving the firmer chisel for
straightening and bending of thin metallic sheets. Also it is used in motor assembly work.

Try Square
Uses
It is used to check whether the object is plane, perpendicular or at right angle. Two
straight blades set at right angle to each other constitute the try square. The steel blade is
riveted to the stock. The stock is made up of cast iron. The stock should be set against the
edge of the job.

186
Measuring Steel Tape
Uses
The measuring tape is made up of thin steel blade, bearing dimensions on it. It is
used for measuring the dimension of the wiring installation and general measurements.

Hacksaw
Uses
It is made up of a sturdy nickel plated steel frame. The frame can be adjusted
between 250mm to 300mm blades. It should be fixed on the frame with its teeth pointing
away from the handle in order to the cutting in forward stroke. It is mainly wood saw (or)
tenon saw.
Generally the length of a tenon saw is 250 to 300mm and has 8 to 12 teeth per
25.4mm and the blade with 10cm. It is used for cutting thin, wooden accessories like
wooden batten, casing capping, boards and round blocks.

188
Pincers
Uses
It is used for extracting nails from the wood. The size is given by its length, e.g.
100mm, 150 mm and 200 mm.

Firmer Chisel
Uses
It has a wooden handle and a cast steel blade of 150mm length. It's size is measured
according to the width of the blade, e.g: 6 mm, 12 mm, 18 mm or 25 mm. It is used for
chipping, scrapping and grooving in wood.

190
Poker
Uses
It is a long sharp tool used for making pilot holes on wooden articles to fix screws.
Spanner - Double Ended
Uses
The size of a spanner is indicated so as to fit on the nuts. They are available in many
sizes and sharps.

The sizes indicated in double- ended spanners are
10 – 11 mm
12 – 13 mm
14 – 15 mm
16 – 17 mm
18 – 19 mm
20 – 21 mm
Spanner sets are used for loosening and tightening of nuts and bolts. It is made of
cast steel. They are available in many sizes and may have single or double ends.
Ring Spanner
Uses
The ring spanner is used in place where the space is restricted.

192
Centre Punch
Uses
The size of the centre punch is given by its length and diameter of body, e.g: 100×8
mm. The angle of tip of the centre punch is 90°.It is used for making and punching pilot
holes on metals. It is made of steel and the ends are hardened and tempered.
Hand Drill
Uses
A hand drill machine is used for making holes in thin metal sheets or wooden
articles.

Electric Drill
Uses
When power is available, power drilling machine is more convenient and an
accurate tool for drilling holes on wooden and metal articles.

194

195 House Wiring and Electrical Safety Rules
HOUSE WIRING AND ELECTRICAL
SAFETY RULES

196
Aim
To study the basic components of house wiring, safety devices, house wiring rules
as per ISI-specification and safety measures of electrical wiring.
Components of Basic Electrical Wiring
Besides safety precautions and regulations, the main thing want to familiarise the
design of house wiring. It consists of three basic components:
¾
¾ Service Entry
This refers to service wire (which brings power supply) from the main grid or pole to
house and the Energy meter. The service entry is critical and there are a few things to keep in
mind. First of all, make sure all service line are at least 10 feet above the ground, inaccessible
from windows, and free of obstructions such as tree limbs. Besides that, make sure your ser-
vice entry is properly installed so that no water can penetrate the access point or meter. Any
changes or fault rectification in this area must be done by the service provider i.e, T.N.E.B.
¾
¾ Panel Board
Panel board is the control centre for electrical wiring. It consists of Main switch
and Distribution fuse board. Now-a-days new safety devices Double Pole MCB instead of
Main Switch and Single Pole MCB instead of distribution fuse were used. While installing
an Air conditioner, Heater, Washing machine or running wiring to a new addition, ensure
electricity is switched off before starting the work, and where you install new breakers.
¾
¾ Branch Circuits
Calculate total load of various electric points used in house, and the wiring should be
carried out on distribution systems with branch circuits. Each branch circuit must have light
circuits not exceeding 10 points or 800 watts, if power wiring circuit not more than 2 points
and AC 1 point. This refers to isolate the areas of house from panel board. For instance, you
cut power to your kitchen while the rest of the house is in operation.

197
Line Diagram of Service Line to Main Switch Connection
Safety Devices
Fuse
Fuse and circuit breaker prevent overheating of wires and protect all electrical
equipments. If the current through fuse is greater than its specified rating, it gets fused.
This breaks the circuit and stops the current, making the equipment safe.
Safety points regarding fuse are:
¾
¾ Always use the correct rating of fuse. For example, if the circuit is of 10 Amp capacity,
the fuse rating must be 150% i.e. 15 amp.
¾
¾ Always use the correct size of fuse, keep the old one to check.
¾
¾ Never replace the fuse with bare wire.It will not be safe.
¾
¾ Do not increase the fuse capacity for preventing or eliminating frequent fuse blow-ups.
Instead it is essential to locate the causes and eliminate the same.
¾
¾ Circuit Breakers are fuses that have buttons or switches for reset.Thus they do not nor-
mally need replacing.
House Wiring and Electrical Safety Rules

198
Wiring of the Distribution Board with RCD (Single Phase Consumer Unit)
(From Energy Meter to the Main Distribution Board)

Miniature Circuit Breakers (MCB)
Miniature Circuit Breakers are gaining increasing prominence in household, labs
and distribution wiring in shops commercial establishments. MCB is an electromagnetic
device that embodies complete enclosure in a moulded insulating material. MCB works as

199
circuit breaker in case of overload/short circuit. It has an advantage since no replacement is
required and it can be reset on elimination of fault and switched ON again. The main function
of an MCB is to switch the circuit, i.e., to open the circuit (which has been connected to it)
automatically when the current passing through MCB exceeds the value for which it is set. It
can be manually switched ON and OFF as similar to normal switch if necessary. MCBs are of
time delay tripping devices, to which the magnitude of over current controls the operating
time. This means, these get operated whenever overload exist long enough to create a danger
to the circuit being protected. Therefore, MCBs doesn’t respond to transient loads and motor
starting currents. Generally, these are designed to operate within 2.5 milli seconds during
short circuit faults and 2 seconds to 2 minutes in case of overloads (depending on the level of
current). MCBs characteristics are:
¾
¾ Rated current up to 100 A
¾
¾ Trip characteristics are not normally adjustable
¾
¾ Thermal or Thermal-Magnetic operation

200
MCCBs
Moulded Case Circuit Breakers are used for commercial purposes. Its characteris-
tics are:
¾
¾ Rated current up to 1000 A
¾
¾ Trip current may be adjustable
¾
¾ Thermal or Thermal-Magnetic operation
ELCBs
Earth Leakage Circuit Breaker works as a circuit breaker in case of only earth
leakage.
¾
¾ Phase (Line), Neutral and Earth wire are connected through ELCB
¾
¾ ELCB is working based on earth leakage current.
RCD/RCCB
Residual Current Device (RCD)/Residual Current Circuit Breaker(RCCB) which
works as a circuit breaker in case of an earth leakage, over load or short circuit. It is used
for protection against electric shocks.
It’s Characteristics:
¾
¾ Phase (Line) and Neutral both wires are connected through RCD.
¾
¾ It trips the circuit when an earth fault occurs.
¾
¾ The amount of current flowing through the phase should return through neutral.Any
mismatch between two currents flowing through phase and neutral is detected by RCD
and trips the circuit within 30 milliseconds.
¾
¾ RCDs are an extremely effective form of shock protection.

201
House Wiring Rules as Per ISI Specification
In construction of a house, the owner should focus on electric works, which need
a lot of attention while laying wiring as well as quality of wiring, specification of electric
appliances and cables/wires. Always plan to work exactly where the outlets, switches
and fixtures are going to be placed. This also allows to check the appropriate tools and
materials are in sufficient quality. Calculate the total load from various items that would
be used in the house and select the proper conductor that is capable of withholding the
total load and distribute accordingly.
Care should be taken while fitting pipes, junction boxes, fan hook boxes in RCC
slab and walls. If any fault happens, it may cause any incident and may require dismantling
of the defective portion. So take proper care to avoid dismantling which is very costly in
comparison to get them fixed properly earlier. To avoid an electric shock, the following
precautions must be kept in mind.Therefore the following rules laid down by the Indian
Standard Institution should be followed. Few of them are listed below for your guidance.
¾
¾ The wiring should be carried out on distribution systems with main and branch
distribution boards.
¾
¾ All conductors should run along walls and ceiling, so that they are easily accessible and
capable of being thoroughly inspected. In any case, wiring should not be run above
ceiling.
¾
¾ Horizontal run of wiring should be at a height of 3 metre.Switch Boards should be fitted
at a height of 1.5 metre.
¾
¾ Fuse wire should be connected with phase only. Connect all switches with phase wire.
Connect the neutral link in neutral wire.
¾
¾ One circuit means, one connection from electrical meter or main fuse board.The
number of points in light circuit should not exceed 10 (or) total load on circuit should
not exceed 800 Watts.
¾
¾ All conductors should be made of copper and should be stranded. They should have a
cross section less than 0.002 square inches, nominal area (3/0.029 inches).
¾
¾ For Power wiring circuit, the size of wire should be 1.5 mm square for copper and
2 mm square for aluminium.[One power circuit = (three 5 amp socket) or (two 15 amp
socket) or (one 15 amp socket + two 5 amp socket) or (one Alternating current circuit)]
¾
¾ Never use damaged insulation, for wiring. It avoid short circuit and overloading, with
the use of MCB and save the electrical appliances.
¾
¾ Burnt element, cut/broken wiring, loose/open connection should be avoided.
¾
¾ Earthing means to connect electrical system to general mass of earth to ensure
immediate discharge of electrical energy without danger. Provide earth connection
to enhance voltage and protect human beings from sudden electric shock.Earth wire
should be 14 SWG in case of copper and 4 mm square in case of Aluminium.

202
¾
¾ All materials used in electrical fitting should be of approved quality of make and from
a reputed manufacturer as per ISI specification.
¾
¾ For low power operations 5 Ampere small size sockets, and for heavy power
operations 15 ampere large size sockets should be used. Multi-plug adaptors are
used for temporary usage only i.e., for a short period of time. No socket or extension
box should be overloaded.
¾
¾ Most of the imported equipments function in two different settings 110-120V and 220-
240V. These equipments have switch for setting the input supply voltage. Hence, make
sure that the switch in equipment is in 220-240V position.
¾
¾ The wiring of a plug is colour coded to help guard against electrical accidents. The
colour codes in India as per Indian Electricity Rules are: Phase (Line) is Red, Blue or
Yellow, Neutral is Black and Earth (Ground) Green or Green with Yellow lines.
¾
¾ If there are only two wires in the power cable, no earth connection is required. If there
are three conductors then the equipment needs to be earthed properly.
¾
¾ Always make sure that the earth wire is longer than the other two so that if the cable is
accidently pulled out of the plug, the earth wire is the last wire to become disconnected.


203

Safe Work Practices
While operating the electrical circuits and handling the hand tools, the following
safety measures should be taken.
1. Avoid contact with energized electrical circuits.
2. Disconnect the power source before servicing or repairing electrical equipment.
Leave a note that you are working. Tape the circuit breaker in OFF position (or) Pull
the fuse carrier, while working.
3. Use Tester to make sure of electrical connection is live or not. Even though fuse is
pulled there may be supply from U.P.S or Auto Generator. So ensure it carefully.
4. Use tools and equipment only with insulated handles when working on electrical
devices. Make sure that all the tools are provided before commencing the wiring.
Example are Tester, Cutting plier, Screw driver, Hammer, Jumper, Electric Drill,
Colour insulation tapes, Wire Stripper etc.,
5. Never use metallic pencils or rulers, or wear rings or metal watchbands when doing
work with electrical equipment.

204
6. When it is necessary to handle equipment that is plugged in, be sure hands are dry
and when possible wear non conductive gloves shoes with rubber soles.
7. If it is safe to do so, work with only one hand, keeping the other hand at your side or
in your pocket, away from all conductive material.
8. Equipment producing a “tingle” should be disconnected and reported promptly for
repair.
9. Drain capacitors before working near them and keep the short circuit on the
terminals during the work to avoid electrical shock.
10.
When it is necessary to touch electrical equipment (for example, when checking for
overheated motors), use the back of the hand. Thus, if accidental shock were to cause
muscular contraction, you would not “freeze” to the conductor.
11.
Do not rely on grounding to mask a defective circuit nor attempt to correct a fault
by inserting another fuse or circuit breaker, particularly one of a larger capacity.
Before replacing a fuse or circuit breaker, check the problem that caused earlier was
rectified.
12.
Insulate all electric contacts and conductors. Never splice wires together and conceal
them within a wall without a junction box. An accessible junction box should always
be used to join wires.
13.
Never use an aluminium or steel ladder while working on any receptacle at height in
your home. An electrical surge will ground and the whole electric current will pass
through the body. Use only bamboo, wooden or a fibre glass ladder for electrification
work.
14.
Do not store highly flammable liquids near electric supply.
15.
Minimize the use of electrical equipment in cold rooms or other areas where
condensation is likely.
16.
Keep the length of extension cords to restricted length.
17.
Unplug cords by gripping the plug and, do not by pulling the cord.
18.
Do not wear loosed clothing or ties near electrical equipment.
19.
If a person was affected by an electric shock, immediately disconnect the power
source of the circuit breaker or pull out the plug using a leather belt.
20.
Never work on live equipment.
21.
De-energize open experimental circuits and equipment to be left unattended.
22.
Never use equipment with frayed cords, damaged insulation or broken plugs.
23.
Be aware that interlocks on equipment disconnect the high voltage source when a
cabinet door is open, but the power for control circuits may remain ON.
24.
Try to cover the live wire with cap while working on circuit panels. The cap acts as an
insulation and helps to prevent electric shock.

205 Verification of Ohm’s Law
VERIFICATION OF OHM’S LAW

206
Aim
To determine the resistance value of two given coils of wire by using Ohm’s Law.
Apparatus Required
S No Name Quantity
1 Battery -12V 1
2 Plug Key 1
3 Rheostat 1
4 Resistances 2
5 Voltmeter - 0-10V 1
6 Ammeter - 0-1A 1
7 Connecting Wires or Cord As Required
Connection Diagram
Ohm’s Law
At constant temperature, the current flowing through the conductor is directly
proportional to the voltage across it and inversely proportional to the resistance of the
conductor.
I =
V
R
V = I × R
R =
V
I
Where
V= Voltage in volts
I = Current in amps
R = Resistance in ohms

207 Verification of Ohm’s Law
Procedure
¾
¾ The first coil R1
is connected as shown in the circuit diagram.
¾
¾ After checking the connection, close the plug key.
¾
¾ Adjust the rheostat.
¾
¾ The corresponding voltmeter and ammeter readings are noted and are tabulated.
¾
¾ By using the formula R1
=
V
I
, the value of resistance is determined.
¾
¾ Similarly, the second coil R2
is connected as shown in the circuit diagram.
¾
¾ After checking the connection, close the plug key.
¾
¾ Adjust the rheostat.
¾
¾ The corresponding voltmeter and ammeter readings are noted and are tabulated.
¾
¾ By using the formula R2
=
V
I
, the value of resistance is determined.
To Find R1
S No Ammeter reading
‘I’ in ampere
Voltmeter reading
in ‘V’ volts
Resistance
R1
=
V
I
Ohms
1.
2.
3.
4.
5.
Mean R1
= ______________

208
To Find R2
S No Ammeter Reading
‘I’ in ampere
Voltmeter reading
in ‘V’ volts
Resistance
R2
=
V
I
Ohms
1.
2.
3.
4.
5.
Mean R2
= ______________
Result
The resistance of two coils of wire R1
= __________________Ohm
R2
= __________________Ohm

209 Preparation of Appliances Test Board
PREPARATION OF APPLIANCES
TEST BOARD

210
Aim
To learn and to prepare an appliances test board and also know, how to test domes-
tic appliances using it.
Tools Required
S.No Name Quantity
1 Screw Driver 1
2 Cutting Plier 1
3 Tester 1
4 Electrician Knife 1
5 Poker 1
6 Drilling Machine 1
7 Ball Peen Hammer 1
8 Hacksaw Frame 1
Materials Required
S.No Name Quantity
1 Wooden Board -12 × 18 1
2 Fuse Unit - 16A, 240V 1
3 Ammeter - 0-5A 1
4 Voltmeter - 0-300V 1
5 Lamp - 200W 1
6 Three Core Power Cord 5 metre
7 1/18 Copper Wire 3 metre
8 Indicating Lamp 1
9 Lamp Holder 1
10 One Way Switch 2
11 Five Pin Socket 2
12 Three Pin Plug 16A, 240V 1
Connection Diagram
Test Board

211 Preparation of Appliances Test Board
Connection Procedure
1. Provide holes in the wooden board at the required places wherever necessary.
2. Fix the switches, socket, fuse indicator, ammeter and voltmeter properly.
3. Give connection to all accessories as per the connection diagram.
4. Connect the power cord properly.
Testing Procedure
1. Connect the given appliances to the test lamp by series.
2. Lamp lighting and faults
S No Lamp Lighting Fault
1 Glows Dimly No fault. Appliance “Good”.
2 Glows Brightly Short circuit fault
3 If not Glow Open circuit fault
3. After rectifying all the faults, connect the appliance parallel to the supply and find out
the value of current and voltage
1 Current = __________
2 Voltage = __________
Result
I have known the method of preparing an appliances test board and also known the
method of testing all the appliances by using test appliance board.
And also I have measured the value of current and voltage by ammeter and volt-
meter respectively. The value of
1. Current = __________
2. Voltage = __________

212
ONE LAMP CONTROLLED BY A
REGULATOR

213 One Lamp Controlled by a Regulator
Aim
To learn about one lamp controlled by one regulator in various position.
Tools Required
S No Name Quantity
1 Screw Driver 1
2 Cutting Plier 1
3 Tester 1
5 Poker 1
8 Hacksaw Frame 1
9 Measurement Tape 1
10 Try Square 1
Materials Required
S No Name Quantity
1 Wooden Board - 3 × 4 1
2 3/4 P.V.C Pipe 1 length
3 1/18 Copper Wire 8 meter
4 One Way Switch 1
5 Regulator 1
6 Lamp Holder 1
7 Three Way Junction Box 1
8 3/4 Clamp 12
9 3/4 Screws 24
10 1 ½ Screws 2
11 Insulation Tape 1
12 60W Lamp 1
Layout Diagram

214
Connection Diagram
Procedure
¾
¾ Study layout diagram and the cable route, distance location of fitting and other
accessories.
¾
¾ Draw the wiring diagram as per the line diagram.
¾
¾ List out the materials required for this wiring.
¾
¾ Confirm how to frame PVC pipe.
¾
¾ Fix the PVC pipe by using clamps, junction box and switch boxes using wooden screws.

215 One Lamp Controlled by a Regulator
¾
¾ Run the cable in the PVC pipe as per the wiring diagram.
¾
¾ Connect the terminals of switches and lamp holder as per the circuit diagram.
¾
¾ Connect the leads of pendent holder by using wire.
¾
¾ Fix the lamp in pendent holder.
¾
¾ Give supply and check the circuit.
Result
I have known the method of one lamp controlled by one regulator. After giving
supply to the circuit through one way switch, turn the regulator in clock wise direction
and find out the brightness of the lamp.

216
WIRING CONNECTION OF
FLUORESCENT LAMP
6

217 Wiring Connection of Fluorescent Lamp
Aim
To know and do the wiring connection method of Fluorescent Lamp.
Tools Required
S.No Name Quantity
1 Screw Driver 1
3 Cutting Plier 1
4 Poker 1
5 Tester 1
Materials Required
S.No Name Quantity
1 Fluorescent Lamp 2
2 LED Tube Light 1
3 Choke 1
4 Starter 1
5 Electronic Choke 1
6 Single Strand Conductor 15 meter
7 Insulation Tape 1
8 Sleeves 10 cm
9 Tube Light Holder 4
10 Starter Holder 1
Connection of tube light with choke and starter
Procedure
Phase supply is given to the pin 1 of the first terminal through switch and choke
(all are connected in series)
Neutral is connected to pin 1 of the second terminal
Pin 2 of the both the terminals are connected to starter.
These connections are shown in the conection diagram

218
Connection of Tube Light with Electronic Choke
Procedure
Phase supply is given to the input side (L) of the choke through switch.
Neutral is given to the input side (N) of the choke directly.
From choke four wire connections are taken and they are connected to both the
terminals as shown in the diagram.
Connection Diagram of LED Tube Light
Procedure
As shown in the diagram, phase and neutral supply is given to the LED tube light
Result
Verified and known the method of doing wiring connection of tube light with
various chokes.

219 Stair-Case Wiring
STAIR-CASE WIRING
7

220
Aim
To learn and know about the method of doing of Stair-case wiring.
Tools Required
S No Name Quantity
1 Screw Driver 1
2 Cutting Plier 1
3 Tester 1
5 Poker 1
8 Hacksaw Frame 1
10 Try Square 1
Materials Required
S No Name Quantity
4 L Bend 1
5 Two Way Switch 2
6 Lamp Holder 1
8 3/4 Clamp 18
9 3/4 Screws 36
10 1 ½ Screws 3
12 60W Lamp 1

221 Stair-Case Wiring
Layout Diagram
Connection Diagram

222
Procedure
¾
¾ Studythelayoutdiagramandthecableroute,distancelocationoffittingofallaccessories.
¾
¾ Draw the wiring connection as per the line diagram.
¾
¾
¾ Confirm how to fix PVC pipe.
¾
¾
¾
¾
¾
¾
Result
I have known the method of doing stair-case wiring. If both switches are in ‘UP’ or
‘DOWN’ position, the lamp glows. Otherwise the lamp does not glow.

223 Godown Wiring
GODOWN WIRING
8

224
Aim
To learn and know about the method of doing Godown wiring.
Tools Required
S No Name Quantity
1 Screw Driver 1
2 Cutting Plier 1
3 Tester 1
5 Poker 1
8 Hacksaw Frame 1
10 Try Square 1
Materials Required
S No Name Quantity
4 One Way Switch 1
5 Two Way Switch 2
6 Lamp Holder 3
8 ¾ Clamp 24
9 ¾ Screws 48
10 1 ½ Screws 6
12 60W Lamp 3
Layout Diagram

225 Godown Wiring
Connection Diagram
Procedure
¾
¾ Study layout diagram and the cable route, distance location of fitting of all accessories.
¾
¾
¾
¾
¾ FixthePVCpipebyusingclamps,junctionboxandswitchboxesbyusingwoodenscrews.
¾
¾ Run the cable in to the PVC pipe as per the wiring diagram.
¾
¾
¾
¾
Result
I have known the method of doing the godown wiring. If we switch ON the first
switch, first lamp only glows. And if we switch ON the second switch, second lamp only
glows. And if we switch ON the third switch, third lamp only glows.

226
ELECTRIC BELL
9

227 Electric Bell
Aim
To know and learn about an electric bell controlled by one way bell switch and its
working.
Tools Required
S No Name Quantity
1 Screw Driver 1
2 Cutting Plier 1
3 Tester 1
5 Poker 1
8 Hacksaw Frame 1
Materials Required
S No Name Quantity
4 One Way Bell Switch 1
5 Electric Bell 1
6 One Way Junction Box 1
8 3/4 Clamp 12
9 3/4 Screws 24
10 1 ½ Screws 2
12 Ceiling Rose 1
Layout Diagram

228
Connection Diagram
Switch
Bell
Procedure
¾
¾ Study the layout diagram, the cable route, distance location of fitting of all other
accessories.
¾
¾
¾
¾
¾
¾
¾ Connect the terminals of switches and ceiling rose by using wire as per the circuit
diagram.
¾
¾ Fix the electric bell in ceiling rose.
¾
Working of an Electric Bell
The image below shows the internal mechanism of an electric bell.

229 Electric Bell
The step by step process of the working of the electric bell is described below:
¾
¾ If the switch is pressed ON and the current will flows through the circuit.
¾
¾ The electromagnet is powered and generates a magnetic field, that attracts the iron strip
towards it.
¾
¾ The striker of the bell strikes the gong (bell)
¾
¾ When the striking arm strikes the gong, the contact is broken and current stops flowing
through the circuit.
¾
¾ This causes the electromagnet to lose its magnetic field.
¾
¾ The connected spring arm returns the striker to its original rest position.
¾
¾ The contact is restored and current flows through the circuit (provided the main switch
is still pressed).
¾
¾ The process is repeated.
Result
I have known the method of preparing an electric bell controlled by one way bell switch
and its working. After giving supply to the circuit, the electric bell will ring.

230
TESTING OF RESISTOR, DIODE,
TRANSISTOR AND CAPACITOR
10

231 Testing of Resistor, Diode, Transistor and Capacitor
Aim
To study and test the conductivity of the components of Resistor, Diode, Transistor
and Capacitor.
Apparatus Required
Sl.No Description Quantity Typical Value
1 Resistors 5 1kΩ, 2kΩ, 3kΩ, 4kΩ, 5kΩ
2 Diodes 2 1N4007, 1N4002
3 Capacitor 2 1mFD, 2mFD
4 Transistors-NPN 2 BC107, BC108
5 Transistors-PNP 2
Testing of Resistor
Objective
To learn the resistor code and identify the value of given resistors.
Consider the following diagram for the better understanding of finding the
resistor values. The first band indicates the first digit, second band is for the second
digit and the third band indicates the multiplier. The numerical value corresponding to
the colour bands are shown below. If the first colour band is brown and the second band
is black then the first two digits are 10. If the multiplier colour is red (value in 2) then
two numbers of zeros added with first two digit.
Tolerance value of Gold = ±5%
Tolerance value of Silver = ±10%

232
Ist Digit 2nd Digit Multiplier Code Resistance
Colour brown Black 2
Value 1 0 00 1000 1kΩ
Likewise, the other types of resistors as four band, five band and sixbands. The tol-
erance is fixed from these bands.(fig)
Testing of Diode
Objective
To test the diode for its forward (conduction) and reverse mode(non-conduction)
of operation.
Description
It is well known that the diodes are unidirectional devices which allow current
in one direction. These are expected to offer very low resistance for the flow of current
under forward biased condition and a very high resistance under reverse biased condition.
In other words, one can undertake diode testing by measuring the resistance across its
terminals by using an equipment like multimeter.
A diode is forward-biased when the positive (red) test lead is on the anode and the
negative (black) test lead is on the cathode.
A diode is reverse-biased when the positive (red) test lead is on the cathode and the
negative (black) test lead is on the anode.

Step 1. Select the switch of the multimeter in resistance mode
Step2. Connect the positive terminal of the diode to Anode and the negative terminal to
the cathode.
Step3. Check the reading of the multimeter.
Under this condition the resistance of the diode is very less that means good conduction
is expected.

234
Step 4. Connect the positive terminal of the diode to cathode and the negative terminal
to the Anode.
Under this condition the resistance of the diode is very high which means open circuit
is expected.
1N4001 diode
Testing of Transistor
Objective
Transistors:
The bi-polar junction transistor (BJT)transistor has three terminals. They are
1. Emitter(E)
2. Base(B)
3. Collector(C)
To identify the above three terminals, keep the flat surface of transistor facing
towards the face of you and mark 1.2 and 3 from left side onwards.
The schematic diagram of BJT is shown below.

Steps to Identify the NPN Type Transistor
1. Keep the Multimeter in the Diode mode.
2. Keep the positive probe to the center pin (Base) of the transistor.
3. Touch the negative probe to the pin-1 (Emitter). You will see some voltage in the multimeter.
4. Similarly, touch the negative probe to the pin-3 (Collector) with respect to the pin-
2. You will see some voltage in the multimeter.
5. It will ensure that, it is a NPN transistor. The logic behind this is, in NPN transistor
Emitter (E) - N type material - Equivalent to cathode of the diodeBase (B) - P type
material - Equivalent to anode of the diodeCollector (C) - N type material - Equivalent
to cathode of the diode
6. If the multimeter positive probe is connected to anode and negative probe is to cathode,
then it will show voltage. If the connections are interchanged it will not show any value.
Steps to Identify the PNP Type Transistor
1. Keep the Multimeter in the Diode mode.
2. Keep the positive probe to the pin-1 (Emitter) of the transistor.
3. Touch the negative probe to the center pin (Base). You will see some voltage in the
multimeter.
4. Similarly touch the negative probe to the center pin (Base) with respect to the pin-3
(Collector). You will see some voltage in the multimeter.
5. It will ensure that it is a PNP transistor. The logic behind this is, in PNP transistor Emitter
(E) - P type material - Equivalent to anode of the diodeBase (B) - N type material
- Equivalent to cathode of the diodeCollector (C) - P type material - Equivalent to
anode of the diode
6. If the multimeter positive probe is connected to anode and negative probe is connected
to cathode, then it will show voltage. If the connections are interchanged it will not
show any value.

236
Testing of Capacitor
Objective: To test the condition of a capacitor.
Test Check a Capacitor By a Digital Multimeter
1. Make sure the capacitor is discharged.
2. Set the meter on Ohm range (Set it at least 1000 Ohm = 1k).
3. Connect the meter leads to the capacitor terminals.
4. Digital meter will show some numbers for a second. Note the reading.
5. And then immediately it will return to the OL (Open Line). Every attempt of Step 2 will
show the same result as was in step 4 and Step 5. It means that Capacitor is in Good
Condition.
6. If there is Change, then Capacitor is dead.
Conclusion
Thus the passive elements of electrical engineering is tested for its values.
Result
In this practical, I have known the method of testing the value of Resistor, Diode,
Transistor and Capacitor.

237 Tabulation of Electrical Symbols
TABULATION OF ELECTRICAL
SYMBOLS
Sl. no Symbols Component Name Description
1 DC Supply Direct Supply
2 AC Supply Alternating Supply
3 1 ϕ (or) 1 Single Phase Supply Single Phase Power
4 3 ϕ (or) 3 Three Phase Supply Three Phase Power
5 Fuse The fuse disconnects when current
above threshold. Used to protect
circuit from high currents
6 Earth/Ground Used for zero potential reference and
electrical shock protection
7 Lamp/Bulb Generates light when current flows
through
8 Connected Wires Connected wires crossing
9 Not Connected Wires Wires are not connectedw
10 Switch Disconnects current when open
11 Resistor Resistor reduces the current flow
12 Variable Resistor/
Rheostat
Variable resistor - has 2 terminals
13 Trimmer Resistor Pre-set Resistor
14 Capacitor Capacitor is used to store electric
charge. It acts as short circuit
with AC and open circuit with DC

238
15 Variable Capacitor Adjustable capacitance
16 Inductor Coil / Solenoid that generates
magnetic field
17 Variable Inductor Inductor value can be varied
18 +
_
+
_
Battery Cell Generates constant voltage
19
G
Generator Electrical voltage is generated by
mechanical rotation of the generator
20
M
Motor Electric motor
21
V
Voltmeter Measures voltage. Has very high
resistance. Connected in parallel
22
A
Ammeter Measures electric current. Has near
zero resistance. Connected serially
23
W
Wattmeter Measures electric power
24
Ω
Ohm Meter Measures resistance
25 Transformer Change AC voltage from high to low
or low to high
26 Star Connection Method of connecting 3ϕ winding in
star connection
27 Delta Connection Method of connecting 3ϕ winding in
Delta connection
28 Electric Bell Rings when activated
29 Buzzer Produces buzzing sound
30 Loudspeaker Converts electrical signal to sound
waves
31
s
M
AC Motor Operater in AC only
32
s
G
AC Generator to produce alternating current

239 Tabulation of Electrical Symbols
33
s
M Universal Motor Operates in both AC DC
34 Push Button (N.O) Momentary switch - normally open
35
s
Single Phase Alternator Produces single phase AC current
36 Fault Identify fault in circuit
37 Over Head Line High tension supply line
38 Diode Diode allows current flow in one
direction only - left (anode) to right
(cathode)
39 Zener Diode Allows current flow in one direction,
but also can flow in the reverse direction
when above breakdown voltage
40
B
C
E
NPN Bi-Polar
Transistor
Allows current flow when high
potential at base (middle)
41
B
E
C
PNP Bi-Polar Transistor Allows current flow when low
potential at base (middle)
42 Antenna/Aerial Transmits receives radio waves
43
P
L
Main Switch Lighting To control the lighting circuit
44
P
Main Switch Power To control the power circuit
45 Change Over Switch Changing supply from one line to
other line
46 Choke Increase voltage for illumination of
tube light
47 Siren Produces sound
48 5-Pin Socket Used for 2-Pin and 3-Pin plug
49 Ceiling Fan Air to Hall/room
50 T Thermostat Set constant heat in heating
appliances

240
Case Study - 1
Name - K.Gunasekar
Fathers Name - K. Kandasamy
EDUCATIONAL QUALIFICATION
Course Year of
Completion
Institution/
School
Board/
University
Percentage
ME (PED) 2016 Sona College of
Technology, Salem.
Anna University,
Chennai
81%
BC (ECE) 2010 Govt. College of Engineering,
Salem.
Anna University,
Chennai
63%
DECE 2002 Annai J.K.K
Samporani Ammal
Polytechnic College
T.N Palayam.
DOTE 75%
HRS 2000 Govt. Hr. Sec. School,
Mettur dam.
Salem (DT)
State Board 67%
SSLC 1998 Govt. Hr. Sec. School,
Nerringipettai.
State Board 57%
EXPERIENCE
CSI Polytechnic College, Salem, as Lecturer in ECE Department from 4th August
2008 to till date.
Thiyagarajar Polytechnic College, Salem, as Instructor in ECE Department from
1st April 2006 to 29th Feburary 2008.

241 Case Study - 1
Bannari Amman Institute of Technology, Sathyamangalam, as Lab Technician in ECE
EEE Department from 24th March 2003 to 2nd January 2006.
Annai J.K.K Samporani Ammal Polytechnic college, T.N.Palayam, as Lab Technician in
ECE Department from 1st May 2002 to 21st March 2003.
AREA OF INTEREST
Digital Electronics.
Mobile Communication.
Micro Processor and Micro Controller.
SOFTWARE SKILLS
Basics of C.
Embedded System.

242
Name - N. Thangavelu
Father Name - A. Naina
EDUCATIONAL QUALIFICATION
Course Year of
Completion
Institution/
School
Board Percentage
HRS 1990 Govt. Hr. Sec. School,
Mettur dam
State Board 73%
SSLC 1988 Govt. Hr. Sec. School,
Mettur dam
State Board 70%
EXTRA QUALIFICATION
Simple Wiring Training Program (3 months) in Vellss Industrial Training Institute under
the Scheme for Training of Nehru Rozgar Yojana from 14/02/1994 to 14/05/1994.
DEPARTMENT OF EMPLOYMENT AND TRAINING – Electric Wireman Helper Com-
petency (WH No. 026337) passed in the year 2000.
SELF EMPLOYMENT IN
Building Wiring
Single phase and Three phase Motor Servicing.
EXPERIENCE
From 1992 to till date.
Case Study - 2

243
Class XI – Basic Electrical Engineering
List of Authors and Reviewers
Academic Coordinators
A.Ilangovan, Lecturer,
DIET, Thirur,
Thiruvallur District.
P.Malarvizhi, BT Assistant,
PUMS, Padiyanallur,
Thiruvallur District.
K.Ravichandran, PG Assistant,
Thanthai Periyar Govt. Hr. Sec. School, Puzhuthivakkam,
Kancheepuram District.
Authors
K. Raja,
Vocational Instructor,
Government Boys Higher Secondary School,
Katpadi, Vellore.
J. Jaya,
Government Higher Secondary School,
Metturdam.
S. Vallinayagam,
Government Higher Secondary School,
Nadupatti.
T. Ashok,
KGS Higher Secondary School,
Aduthurai.
R. Srinivasan,
Government Boys Higher Secondary School,
Walaja, Vellore.
C. Kasinathan,
General Cariyappa Higher Secondary School, Saligramam,
Chennai 600 093
Domain Experts
Dr. R Azhagumurugan Ph.D.,
Associate Professor,
Department of Electrical and Electronics Engineering,
Sri Sairam Engineering College,
West Tambaram, Chennai.

Book Design
(Typing, Pagination, Layout Designing and Illustration)
Student Xerox, Adayar, Chennai.
Wrapper Design
Kathir Arumugam
Quality Control
Manohar Radhakrishnan
Coordination
Ramesh Munisamy
This book has been printed on 80 G.S.M.
Elegant Maplitho paper.
Printed by offset at:
Reviewer
Dr. M. Venkatesh kumar Ph.D.,
Associate Professor,
Department of Electrical and Electronics Engineering,
Arupadai Veedu Institute of Technology,
Payanoor, Chennai.
QR Code Management Team
R. Jaganathan
S.G. Asst., (SPOC)
PUMS Ganesapuram - Polur, Thiruvannamalai Dist.
N. Jagan
B.T. Asst.,
GBHSS Uthiramerur, Kanchipuram Dist.
J.F. Paul Edwin Roy
B.T. Asst.,
PUMS Rakkipatti, Salem Dist.
Acadamic Advisor Expert
Dr. P. Kumar, Joint Director ( Syllabus ),
State Council of Educational Research and Training,
Chennai.

244
NOTES

245
NOTES

246
NOTES

247
NOTES

248
NOTES

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