ELECTRICAL ENGINEERING
PRACTICE
LAB MANUAL
Dr.SUBRANSU SEKHAR DASH
Professor
Department of Electrical and Electronics Engineering
SRM University
Kattankulathur – Chennai
Tamilnadu – 603 203
India
Dr.K.VIJAYAKUMAR
Professor and Head
Department of Electrical and Electronics Engineering
SRM University
Kattankulathur – Chennai
Tamilnadu – 603 203
India
Dr.C.SUBRAMANI
Assistant Professor
Department of Electrical and Electronics Engineering
SRM University
Kattankulathur – Chennai
Tamilnadu – 603 203
India
Preface
v
Acknowledgements
vii
Safety Precautions
ix
Electrical Symbols
xi
Experiment 1
Residential House Wiring Using switches, Fuse, Indicator, Lamp
and Energy Meter
Experiment 2
Types of Wiring
Experiment 3
Measurements of Electrical Quantities – Voltage, Current, Power
and Power Factor in RLC Circuit
Experiment 4
Measurement of Energy Using Single Phase / Three Phase energy
Meter
Experiment 5
Study of Earthing and Measurement of Earth Resistance
Experiment 6
Study Troubleshooting of Electrical Equipment
Experiment 7
Study of Various Electrical gadgets
Experiment 8
Assembly of Choke of Small Transformer
Graph Sheets
About the Authors
Dr.Subharansu Sekhar Dash is Presently working as Professor in the Department of Electrical
and Electronics Engineering, SRM University, Chennai. He has completed his under graduation
in Electrical Engineering and M.E in Power Systems Engineering from University of College of
Engineering, Burla, Orissa. He obtained his Ph.D degree from College of Engineering, Guindy
Anna University. He is a visiting research scholar at University of Wisconsin, Milwaukee, USA
and has worked as visiting professor at Polytech University, Tours, France. He has visited many
foreign countries like Singapore, Spain, USA, France Hong Kong, etc. His research interests
include FACTS, Power Quality, Power System Stability and Computational Intelligence
Techniques. He has more than sixteen years of research and teaching experience and has
published more than 150 papers in reputed international journals and conferences.
Dr.K.Vijayakumar is presently working as Professor and Head in the Department of Electrical
and Electronics Engineering, SRM University, Chennai. He has completed his B.E degree in
Electrical and Elecgtronics Engineering and M.E in Power Systems Engineering from Annamalai
University. He obtained his Ph.D degree from SRM University, Chennai. His research interests
include FACTS, Power System Modelling, Analysis, Control and Optimization, Modern
Optimization Techniques like GA, EP etc. He has more than fifteen years of research and
teaching experience and has published more than 40 papers in reputed international journals and
conferences.
Dr.C.Subramani
is presently working as Assistant Professor in the Department of Electrical
and Electronics Engineering, SRM University, Chennai. He has completed his B.E degree in
Electrical and Electronics Engineering from Bharathiyar University, Coimbatore and M.E in
Power Systems Engineering from Anna University. He obtained his Ph.D degree from SRM
University, Chennai. His research interests include FACTS, Power Systems Stability, Voltage
Stability, Soft Computing Algorithm for Power System Applications. He has more than ten
years of research, teaching and industrial experience and has published more than 40 papers in
reputed international journals and conference.
Preface
Electrical Engineering Practices is a basic subject offered to the undergraduate
engineering students of electrical and non-electrical streams. Its gives a fair knowledge about
the various electrical gadgets used in day to day life and troubleshoots them. Also it provides the
basic knowledge of the various electrical symbols, safety precautions, types of wiring, earthing
etc.
Despite several lab manuals being available on the subject, we felt that there is still a
need for a book that would make the learning and understanding of the principles of Electrical
engineering, an enjoyable experience.
This book presents comprehensive coverage of all the basic concepts in electrical
engineering practices/ Beginning with the electrical symbols, residential wiring using energy
meter, fuses, switches, indicator, lamps, etc., the book also covers various types of wiring such as
fluorescent lamp wiring, staircase wiring godown wiring, study of earthing and measurement of
earth resistance etc.
This book deals with definitions of voltage, current, power, power factor etc., and the
measurement of these electrical quantities in RLC circuits. It gives comprehensive idea about
the measurement of energy using single phase and three phase energy meter. It also covers the
working and troubleshooting of the various electrical equipments used in home applications such
as fan, iron box, mixer-grinder, etc.
The book gives a details design and assembly of small choke/transformer used in
stabilizers. It also deals with the study of various electrical gadgets like induction motor,
transformer, CFL, LED, PV cell, etc.
Written in straightforward style with a strong emphasis on primary principles, the main
objective of the book is to bring an understanding of the subject within the reach of students.
We hope that students will discover that their learning and understanding of the subject
progressively increases while using this book.
Dr.Subharansu Sekhar Dash
Dr.K.Vijayakumar
Dr.C.Subramani
Acknowledgements
We are very grateful to our reveredChancellor, Dr.T.R.Pachamuthu, President,
Prof.P.Sathyanarayanan and Vice Chancellor, Sir.Dr.M.Ponnavaikko of SRM University,
Chennai. They have been a source of inspiration and encouragement in all our academic efforts
and to bring out this book.
We sincerely thank our respectable Pro-vice-Chancellor, Prof.T.P.Ganesn and Director
(E&T), Dr.C.Muthamizhchelvan who have been very kind to us in all aspects.
We are thankful to Dr.R.Jegatheesan, Professor, Department of EEE, SRM University,
Chennai for his support and guidance.
We would like to especially thank all the faculty members, Department of EEE for their
support in editing this book.
We would like to thank Mr.Paduchuri Chandra Babu, Research Scholar, Department of
EEE, SRM University, for rendering support in bringing out this book.
A special thanks to our parents and family members for their encouragement and
wholehearted support.
We are sincerely thankful to the entire team of Vijay Nicole Imprints for prompt
execution of the book.
Dr.Subharansu Sekhar Dash
Dr.K.Vijayakumar
Dr.C.Subramani
Safety Precautions
1. SAFETY is of paramount importance in the Electrical Engineering Laboratories.
2. Electricity NEVER EXCUSES careless persons. So, exercise enough care and attention
in handling electrical equipment and follow safety practices in the laboratory.
(Electricity is a good servant but a bad master).
3. Avoid direct contact with any voltage source and power line voltage. (Otherwise, and
such contact may subject you to electrical shock).
4. Weat rubber-soled shoes. (To insulate you from earth so that even if you accidentally
contact a live point, current will not flow through your body to earth and hence you will
be protected from electrical shock)
5. Wear laboratory-coat and avoid loose clothing. (Loose clothing may get caught on an
equipment/instrument and this may lead to an accident particularly if the equipment
happens to be a rotating machine)
6. Girl students should have their hair tucked under their coat or have it in a knot.
7. Do not wear any metallic rings, bangles, bracelets, wristwatches and neck chains. (When
you move your hand/body, such conducting items may create a short circuit or may touch
a live point and thereby subject you to electrical shock).
8. Be certain that your hands are dry and that you are not standing on wet floor. (Wet parts
of the body reduce the contact resistance thereby increasing the severity of the shock).
9. Ensure that the power is OFF before you start connecting up the circuit. (Otherwise you
will be touching the live parts in the circuit)
10. Get you circuit diagram approved by the staff member and connect up the circuit strictly
as per the approved circuit diagram.
11. Check power chords for any sign of damage and be certain the chords use safety plugs
and do not defeat the safety feture of these plugs by using ungrounded plugs.
12. When using connection leads, check for any insulation demage in the leads and avoid
such defective leads.
13. Do not defeat any Safety devices such as fuse or circuit breaker by shorting across it.
Safety defices protect YOU and your equipment
14. Switch on the power to your circuit and equipment only after getting them checked up
and approved by the staff member.
15. Take the measurement with one hand in you pocket. (To avoid shock in case you
accidentally touch two points at different potentials with your two hands)
16. Do not make any change in the connection without the approval of the staff member.
17. In case you notice any abnormal condition in your circuit (like insulation heating up,
resistor heating up etc). switch off the power to your circuit immediately and inform the
staff member.
18. Keep hot soldering iron in the holder when not in use.
19. After completing the experiment show your readings to the staff member and switch off
the power to your circuit after getting approval fro the staff member.
Electrical Symbols
Single-pole Single-throw
(SPST) Switch
Single Pole Double-throw (SPDT) Switch
Double-pole, Single Throw (DPST) Switch
Fuse
Two Conductors Crossing
(No Connection)
Two Conductors Connected
Cell
Power Supply
(Usually identified by voltage & type)
Polarity would indicate DC Power SupplyVoltage Source
AC Power Supply-Voltage Source
Capacitor
Inductor
Constant Current Source
Meter
The letter in the center identifies the type
V = Voltmeter, A = Ammeter
 = Ohmmeter, MA = Milliameter
W = Wattmeter, G = Galvanometer
Resistor or Resistance (Fixed value)
Transformer
Variable Voltage Transformer
(Autotransformer / Variac) Iron Core
Relay Contacts
Normally Open (NC)
Normally Closed(NC)
Relay (Energizing) Coil
SRM UNIVERSITY
FACULTY OF ENGINEERING AND TECHNOLOGY
DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINEERING
Evaluation Sheet
Program Name
:
Semester
:
Year
:
Name
:
Reg. No.
:
S.No.
B.Tech in Electrical and Electronics Engineering
Marks Split Up
Marks Allotted
1
Attendance
5
2
Preparation of Observation
5
3
Pre-lab
5
4
In lab Performance
10
5
Post lab
5
Total
30
Marks Obtained
PRELAB QUESTIONS
1.
Define: Energy?
………………………………………………………………………………………………
………………………………………………………………………………………………
2.
What is the use of energy meter?
………………………………………………………………………………………………
………………………………………………………………………………………………
3.
What is the unit of Energy?
………………………………………………………………………………………………
………………………………………………………………………………………………
4.
I Unit = ……………. kWhr
………………………………………………………………………………………………
………………………………………………………………………………………………
5.
What do the three holes in a socket represent?
………………………………………………………………………………………………
………………………………………………………………………………………………
6.
Why is the earth pin bigger in size?
………………………………………………………………………………………………
………………………………………………………………………………………………
7.
What is the difference between earth and neutral?
………………………………………………………………………………………………
………………………………………………………………………………………………
8.
How does the tester work?
………………………………………………………………………………………………
………………………………………………………………………………………………
9.
Why the tester glows in line not in neutral?
………………………………………………………………………………………………
………………………………………………………………………………………………
10
What is the use of fuse?
………………………………………………………………………………………………
………………………………………………………………………………………………
11.
Fuse is made up of……………………
………………………………………………………………………………………………
………………………………………………………………………………………………
12.
Mention the type of fuses.
………………………………………………………………………………………………
………………………………………………………………………………………………
Date :
Experiment : 1
RESIDENTIAL HOUSE WIRING
USING SWITCHES, FUSE INDICATOR,
LAMP AND ENERGY METER
Aim:
To implement residential house wiring using switches, fuse, indicator, lamp and energy meter,
Apparatus Required:
S.No.
Components equired
Range
Quantity
1
Switch
SPST
3 Nos.
2
Incandescent lamp
40W
2 Nos.
3
Lamp Holder
-
2 Nos.
4
Indicator
-
1 No
5
Socket
10A
1 No
6
Wires
-
As per required
7
Energy Meter
1-phase, 300V, 16a, 750rev, 50Hz
1 No.
Tools required: Wire mans tool Kit-1 No.
Precautions:
1. The metal covering of all appliances are to be properly earthed in order to avoid electrical
shock due to leakage or failure of insulation.
2. Every line has to be protected by a fuse of suitable rating as per the requirement.
3. Handle with care while giving connections and doing experiments.
Circuit Diagram
Theory:
Conductors, switches and other accessories should be of proper capable of carrying the
maximum current which will flow through them. Conductors should be of copper or aluminum.
In power circuit, wiring should be designed for the load which it is supposed to carry current.
Power sub circuits should be kept separate from lighting and fan sub-circuits. Wiring should be
done on the distribution system with main branch distribution boards at convenient centers.
Wring should be neat, with good appearance. Wire should pass through a pipe or box, and
should not twist or cross. The conductor is carried in a rigid steel conduit conforming to
standards or in a porcelain tube.
A switch is used to make or break the electric circuit. It must make the contact finely.
Under some abnormal conditions it must retain its rigidity and keep its alignment between switch
contacts. The fuse arrangement is made to break the circuit in the fault or overloaded conditions.
The energy meter is used to measure the units (kWh) consumed by the load should not twist or
cross. The conductor is carried in a rigid steel conduit conforming to standards or in a porcelain
tube.
Procedure:
1.
2.
3.
4.
5.
6.
7.
8.
Study the given wiring diagram.
Make the location points for energy meter, main witch box, Switchboard, and lamp.
The lines for wiring on the wooden board.
Place the wires along with the line and fix.
Fix the bulb holder, switches, socket in marked positions on the wooden board.
Connect the energy meter and main switch box in marked positions on the wooden board.
Give a supply to the wires circuit.
Test the working of light and socket
Result:
Thus the simple house wiring by using switches, fuse, indicator, filament lamps and
energy meter was studied.
Exercises:
1.
For the circuit diagram given below draw the electrical layout using the required
components.
The layout diagram of the circuit given is shown below
2.
Draw the electrical plan for a sample residential building
3.
Draw the connection diagram from the service main to the distribution of loads.
Main and Distribution Board
To Fan Circuit
Incoming Cable
4.
Electrical layout for residential building – A sample
5.
Draw the electrical layout for your class room
Result:
Thus the single-phase wiring diagram has been constructed, tested and the results are verified.
POSTLAB QUESTIONS
1.
The filament in a lamp is made up of ……………………. Material
………………………………………………………………………………………………
………………………………………………………………………………………………
2.
Mention the types of lamps
………………………………………………………………………………………………
………………………………………………………………………………………………
3.
What is meant by CFL?
………………………………………………………………………………………………
………………………………………………………………………………………………
4.
What are the advantages of CFL?
………………………………………………………………………………………………
………………………………………………………………………………………………
5.
What is meant by LED?
………………………………………………………………………………………………
………………………………………………………………………………………………
6.
How does an LED work?
………………………………………………………………………………………………
………………………………………………………………………………………………
7.
What type of supply is given to houses?
………………………………………………………………………………………………
………………………………………………………………………………………………
8.
What type of meter is energy meter?
………………………………………………………………………………………………
………………………………………………………………………………………………
9.
Explain the working of energy meter
………………………………………………………………………………………………
………………………………………………………………………………………………
10.
Explain the working of incandescence lamp
………………………………………………………………………………………………
………………………………………………………………………………………………
11.
What is meant by neutral link?
………………………………………………………………………………………………
………………………………………………………………………………………………
12.
What is meant by earthing?
………………………………………………………………………………………………
………………………………………………………………………………………………
13.
Which shock is more severe?
………………………………………………………………………………………………
………………………………………………………………………………………………
SRM UNIVERSITY
FACULTY OF ENGINEERING AND TECHNOLOGY
DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINEERING
Evaluation Sheet
Program Name
:
Semester
:
Year
:
Name
:
Reg. No.
:
S.No.
B.Tech in Electrical and Electronics Engineering
Marks Split Up
Marks Allotted
1
Attendance
5
2
Preparation of Observation
5
3
Pre-lab
5
4
In lab Performance
10
5
Post lab
5
Total
Marks Obtained
30
Staff Signature
PRELAB QUESTIONS
1.
What is the use of choke?
………………………………………………………………………………………………
………………………………………………………………………………………………
2.
What is the use of starter?
………………………………………………………………………………………………
………………………………………………………………………………………………
3.
What is present inside the starter?
………………………………………………………………………………………………
………………………………………………………………………………………………
4.
Name the gas present inside the tube light.
………………………………………………………………………………………………
………………………………………………………………………………………………
5.
What types of switches are used for staircase wiring?
………………………………………………………………………………………………
………………………………………………………………………………………………
6.
Explain the operation of Fluorescent lamp wiring.
………………………………………………………………………………………………
………………………………………………………………………………………………
7.
Explain the function of staircase with truth table
………………………………………………………………………………………………
………………………………………………………………………………………………
8.
Explain the working of godown wiring
………………………………………………………………………………………………
………………………………………………………………………………………………
Date :
Experiment : 2
TYPES OF WIRING
Aim:
To study different types of wiring and to prepare the following wiring:
(i)
(ii)
(iii)
Staircase wiring
Fluorescent lamp wiring
Corridor wiring
Apparatus Required:
S.
No.
1
2
3
4
5
6
7
Fluorescent
Staircase Wiring
Lamp Wiring
Fluorescent lamp with Two way switches
fitting
Joint clips
Bulb, Bulb holder
Wires
Clamps
Screws
Screws
Switch board
Ceiling rose
Choke
Switch board
Switches
Connecting wires
Corridor Wiring
Tools
required
Switches
Screw driver
Bulb, Bulb holder
Clamps
Screws
Ceiling rose
Switch board
Connecting wires
Hammer
Cutting pliers
Line tester
Types of Wiring
There are various types of wiring used in the residential and commercial buildings. They are
1. Cleat Wring
2. Batten Wiring
(a) PVC Batten Wiring
(b) TRS/CTS Wiring
(c) Lead Sheath Wiring
3. Casing Capping Wiring
(a) Wood Casing Capping Wiring
(b) PVC Casing Capping Wiring
4. Conduit Wiring
(a) Surface Conduit Wiring
Metal Conduit Wiring
PVC Conduit Wiring
(b) Concealed Conduit Wiring
1.
Cleat Wiring:
Cleat wiring is recommended only for temporary installations. The cleats are made in pain
having bottom and top halves. The bottom half is grooved to receive the wire and the top half is
for cable grip. Initially the bottom and top cleats are fixed on the wall loosely according to the
layout. Then the cable is drawn, tensioned and the cleats are tightened by the screw. Cleats are
of three types, having one, two or three grooves, so as to receive one, two or three wires. This
system uses insulated Cables sub protected in porcelain cleats. This is of wiring suitable only for
temporary wiring purpose. In lamp or wet location the wire used should be moisture proof and a
weathering proof.
2.
Batten Wiring
Tough rubber-Sheathed (T.R.S) or PVC – Sheathed cables are suitable to run on teak wood
battens. Varnishing of teak wood batten Method of securing the battens Suitability of tough
rubber-sheathed cable Suitability of PVC sheathed cable.
3.
Wood Casing Wiring System
Wood casing wiring system shall not be used in damp places or in ill-ventilated places, unless
suitable precautions are taken. This system of wiring is suitable for low voltage installation, I
this wiring, cables like vulcanized rubber, insulated cables or plastic insulated cables are use and
carried within the wood casing enclosures. The wood casing wiring system shall not be use in
damp places and in ill-ventilated places, unless suitable precautions are taken.
Material and Pattern of Casing
All casing shall be of first class, seasoned teak wood or any other approved hardwood
free from knots, shakes, saps or other defects, with all the sides planed to a smooth finish, and all
sides well varnished, both inside and out side with pure shellac varnish. The casing shall have a
grooved body with a beaded or plain-molded cover as desired.
4.
Tough rubber-Sheathed or PVC Sheathed Wiring System
Wiring with tough rubber sheathed cables is suitable for low voltage installations and shall not
be used in places exposed to sun and rain nor in damp places, unless wires are sheathed in
protective covering against atmosphere and well protected to withstand dampness.
5.
Metal-Sheathed Wiring System
Metal-sheathed wiring system is suitable for 1GW voltage installations, and shall not be used in
situations where acids and alkalis are likely to be present. Metal-sheathed wiring may be used in
places exposed to sun and rain provided no joint of any description is exposed.
6.
Conduit Wiring System
This uses a conduit pipe for the mechanical protection of wire. In this system of wiring, wires
are carried through P.V.C conduit pipe for giving converging to pipes conduit pipe has certain
advantages like it is moisture proof and durable.
STAIRCASE WIRING
Aim:
To control a single lamp from two different places.
Apparatus Required:
S.No.
1
2
3
4
Components
Incandescent lamp
Lamp holder
Two way switches
Connecting wires
Quantity/Range
1 (230V, 40W)
1
2 (230V, 5A)
As required
Tools Required: Wire mans tool kit – 1 No.
Direct Connection
Circuit Diagram
Tabulation
Position of Switches
S1
Condition of lamp
S2
Cross Connection
Circuit Diagram
Tabulation
Position of Switches
S1
Condition of lamp
S2
Theory
1. A two way switch is installed near the first step of the stairs. The other two way switch is
installed at the upper part where the stair ends.
2. The light point is provided between first and last stair at an adequate location and height
if the light is switched on by the lower switch. It can be switched off by the switch at the
top or vice versa.
3. The circuit can be used at the places like bed room where the person may not have to
travel for switching off the light to the place from where the light is switched on.
4. Two numbers of two-way switches are used for the purpose. The supply is given to the
switch at the short circuited terminals.
5. The connection to the light point is taken from the similar short circuited terminal of the
second switch. Order two independent terminals of each circuit are connected through
cables.
Procedure:
1.
2.
3.
4.
Give the connections as per the circuit diagram.
Verify the connection
Switch on the supply
Verify the conditions
Result:
Thus the circuit to control the single lamp from two different places is studied and verified.
EXERCISE
Draw the electrical layout diagram using the required components.
FLUORESCENT LAMP WIRING
Aim:
To make connections of a fluorescent lamp wiring and to study the accessories of the same.
Apparatus Required:
S.No.
1
2
3
4
5
Components
Fluorescent lamp fixture
Fluorescent lamp
Choke
Starter
Connecting wires
Range/Type
4 ft
40W
40W, 230V
-
Quantity
1
1
1
1
As per required
Tools Required : Wire mans tool kit – 1 No.
Circuit Diagram:
Theory:
1. The electrode of the starter which is enclosed in a gas bulb filled with argon gas, cause
discharge in the argon gas with consequent heating.
2. Due to heating, the bimetallic strip bends and causes in the starter to close. After this, the
choke, the filaments (tube ends) to tube and starter becomes connected in series.
3. When the current flows through the tube end filaments the heat is produced. During the
process the discharge in the starter tube disappears and the contacts in the starter move
apart.
4. When sudden break in the circuit occur due to moving apart of starter terminals, this
causes a high value of e.m.f to be induced in the choke.
5. According to Lenz‟s, the direction of induced e.m.f in the choke will try to opposes the
fall of current in the circuit.
6. The voltage thus acting across the tube ends will be high enough to cause a discharge to
occur in the gas inside the tube. Thus the starts giving light.
7. The fluorescent lamp is a low pressure mercury lamp and is a long evacuated tube. It
contains a small amount of mercury and argon gas at 2.5 mm pressure. At the time of
switching in the tube mercury is in the form of small drops. Therefore, to start the tube,
filling up of argon gas is necessary. So, in the beginning, argon gas starts burning at the
ends of the tube; the mercury is heated and controls the current and the tube starts giving
light. At each end of the tube, there is a tungsten electrode which is coated with fast
electron emitting material. Inside of the tube is coated with phosphor according to the
type of light.
8. A starter helps to start the start the tube and break the circuit. The choke coil is also
called blast. It has a laminated core over which enameled wire is wound. The function
of the choke is to increase the voltage to almost 1000V at the time of switching on the
tube and when the tube starts working, it reduces the voltage across the tube and keeps
the currents constant.
Procedure:
1.
2.
3.
4.
5.
Give the connections as per the circuit diagram
Fix the tube holder and the choke in the tube.
The phase wire is connected to the choke and neutral directly to the tube.
Connect the starter in series with the tube.
Switch on the supply and check the fluorescent lamp lighting.
Result:
Thus the fluorescent lamp circuit is studied and assembled.
Electrical Layout of Fluorescent Lamp Circuits
CORRIDOR WIRING
Theory
Corridor wiring is meant for switching on the lamp one by one while going forward into the go
down or the corridor and switch off the lamp one by one while returning back.
Circuit Diagram
S1
OFF
ON
ON
OFF
Procedure:
1.
2.
3.
4.
S2
X
1-3
1-2
1-2
S3
X
1‟-3‟
1‟-31‟-2‟
Give the corrections as per the circuit diagram
Verify the corrections.
Switch on the supply
Verify the conditions
Result:
Thus different types wiring was completed and tested.
L1
OFF
ON
OFF
OFF
L2
OFF
OFF
ON
OFF
L3
OFF
OFF
OFF
ON
POSTLAB QUESTIONS
1.
Mention the types of wiring used in homes
………………………………………………………………………………………………
………………………………………………………………………………………………
2.
Choke is made up of
………………………………………………………………………………………………
………………………………………………………………………………………………
3.
Mention the types of lamps
………………………………………………………………………………………………
………………………………………………………………………………………………
4.
What is the power consumption of commonly called zero watt lamp?
………………………………………………………………………………………………
………………………………………………………………………………………………
5.
What is the usual power factor of Fluorescent lamp and incandescence lamp?
………………………………………………………………………………………………
………………………………………………………………………………………………
6.
What is the type of wiring used in homes nowadays?
………………………………………………………………………………………………
………………………………………………………………………………………………
7.
Mention the types of switches
………………………………………………………………………………………………
………………………………………………………………………………………………
SRM UNIVERSITY
FACULTY OF ENGINEERING AND TECHNOLOGY
DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINEERING
Evaluation Sheet
Program Name
:
Semester
:
Year
:
Name
:
Reg. No.
:
S.No.
B.Tech in Electrical and Electronics Engineering
Marks Split Up
Marks Allotted
1
Attendance
5
2
Preparation of Observation
5
3
Pre-lab
5
4
In lab Performance
10
5
Post lab
5
Total
Marks Obtained
30
Staff Signature
PRELAB QUESTIONS
1.
Define charge
………………………………………………………………………………………………
………………………………………………………………………………………………
2.
Define voltage
………………………………………………………………………………………………
………………………………………………………………………………………………
3.
Define current
………………………………………………………………………………………………
………………………………………………………………………………………………
4.
Define resistance
………………………………………………………………………………………………
………………………………………………………………………………………………
5.
Define power
………………………………………………………………………………………………
………………………………………………………………………………………………
6.
Define power factor
………………………………………………………………………………………………
………………………………………………………………………………………………
7.
What is meant by potential and potential difference?
………………………………………………………………………………………………
………………………………………………………………………………………………
Date:
Experiment : 3
MEASUREMENT OF ELECTRICAL QUANTITIES
– VOLTAGE, CURRENT POWER AND POWER
FACTOR IN RLC CIRCUIT
Aim:
To measure the electrical quantities – voltage, current, power and to calculate power factor for
RLC circuit.
Apparatus Required:
S.No.
1
2
3
4
5
6
Components
Voltmeter
Ammeter
Wattmeter
Autotransformer
Resistive, inductive & capacitive load
Connecting wire
Range/Type
(0-300)V, MI type
(0-10)A, MI type
300V, 10A, UPF/LPF
1KVA, 230/(0-270)V
-
Quantity
1
1
1
1
1
As per required
Theory:
Power in an electric circuit can be measured using a wattmeter. A wattmeter consists of two
coils, namely current coil and pressure coil or potential coil. The current coil is marked as ML
and pressure coil is marked as CV. The current coil measures the quantity that is proportional to
the current in the circuit and the pressure measures quantity that is proportional to voltage in the
circuit. An ammeter is connected in series to the wattmeter to measure the current. A voltmeter
is connected in parallel to wattmeter to measure voltage. The power factor of the circuit is
calculated using the relation given below:
Formulae:
Actual power
=
OR x multiplication factor
Apparent power
=
VI watts
Power factor, Cos  =
(Actual power) / (Apparent power)
R-Load
Circuit Diagram
Procedure:
1.
2.
3.
4.
5.
6.
7.
Connect the circuit as shown in the circuit diagram
Switch on the supply and vary the auto transformer to build the rated voltage.
Vary the load according to current values are increases linearly for different ratings.
Note down the ammeter, wattmeter readings. Voltage will maintain constant.
After taking all the reading, bring the voltage back to minimum in the auto transformer.
Switch off the power supply. Remove the connections.
Calculate the power factor by the given formula.
Tabulation
S.No. Voltage (V)
Current(A)
Wattmeter
Obs Reading Act. Reading
Power Factor
RC – Load
Circuit Diagram
Procedure
1.
2.
3.
4.
5.
6.
7.
Connect the circuit as shown in the circuit diagram.
Switch on the supply and vary the auto transformer to build the rated voltage.
Observe the reading of ammeter, voltmeter and wattmeter for various load values.
Vary the load according to current readings. Voltage is maintain constant.
After taking all the reading, bring the voltage back to minimum in the auto transformer.
Switch off the power supply.
Calculate the power factor by the given formula
Tabulation
S.No.
Voltage (V)
Current(A)
Wattmeter
Obs Reading Act. Reading
Power Factor
RC-Load
Circuit Diagram
Procedure:
1.
2.
3.
4.
5.
6.
7.
Connect the circuit as shown in the circuit diagram
Switch on the supply and vary the auto transformer to build the rated voltage.
Observe the reading of ammeter, voltmeter and wattmeter for various load values.
Vary the load according to current readings. Voltage is maintain constant.
After taking all the reading, bring the voltage back to minimum in the auto transformer.
Switch off the power supply.
Calculate the power factor by the given formula.
Tabulation
S.No.
Voltage (V)
Current(A)
Wattmeter
Obs Reading Act. Reading
Power Factor
Result:
Thus the electrical quantities – voltage, current and power are measured for RLC load and
corresponding power factor is calculated.
POSTLAB QUESTIONS
1.
What is the unit for voltage current and resistance power?
………………………………………………………………………………………………
………………………………………………………………………………………………
2.
Define volt, ampere, ohm and watt.
………………………………………………………………………………………………
………………………………………………………………………………………………
3.
What is the power factor of pure R, pure L and pure C circuits?
………………………………………………………………………………………………
………………………………………………………………………………………………
4.
Draw impedance triangle
………………………………………………………………………………………………
………………………………………………………………………………………………
5.
Draw power triangle
………………………………………………………………………………………………
………………………………………………………………………………………………
6.
Mention the types of power in ac circuit
………………………………………………………………………………………………
………………………………………………………………………………………………
7.
Name the unit for real reactive and apparent powers.
………………………………………………………………………………………………
………………………………………………………………………………………………
8.
Name the device used to measure voltage current power factor and resistance.
………………………………………………………………………………………………
………………………………………………………………………………………………
SRM UNIVERSITY
FACULTY OF ENGINEERING AND TECHNOLOGY
DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINEERING
Evaluation Sheet
Program Name
:
Semester
:
Year
:
Name
:
Reg. No.
:
S.No.
B.Tech in Electrical and Electronics Engineering
Marks Split Up
Marks Allotted
1
Attendance
5
2
Preparation of Observation
5
3
Pre-lab
5
4
In lab Performance
10
5
Post lab
5
Total
Marks Obtained
30
Staff Signature
PRELAB QUESTIONS
1.
Define energy
………………………………………………………………………………………………
………………………………………………………………………………………………
2.
Mention the unit for energy
………………………………………………………………………………………………
………………………………………………………………………………………………
3.
What type of instrument is energy meter?
………………………………………………………………………………………………
………………………………………………………………………………………………
4.
Explain the working of energy meter.
………………………………………………………………………………………………
………………………………………………………………………………………………
5.
Mention the types of energy meter.
………………………………………………………………………………………………
………………………………………………………………………………………………
Date:
Experiment : 4
MEASUREMENT OF ENERGY USING SINGLE
PHASE / THREE PHASE ENERGY METER
Aim:
To measure the energy consumed in a single phase circuit and 3 phase circuit
Apparatus Required:
S.No.
1
2
3
4
5
6
Components
Voltmeter
Ammeter
Wattmeter
Resistive load
Energy meter
Connecting wire
Range/Type
(0-300)V, MI type
(0-10)A, MI type
300V, 10A, UPF/600V,
10A, UPF
1 / 3
1 / 3
-
Quantity
1
1
½
1
1
As per required
Theory:
Energy meters are interesting instruments and are used for measurements of energy in a circuit
over a given period of time. Since the working principle of such instrument is based on
electromagnetic induction, these are known as induction type energy meters. As shown in fig.1,
there are two coils in an induction type energy meter namely current coil (CC) and voltage coil
(VC), the current coil is connected in series with the load while the voltage coil is connected
across the load. The aluminum disc experiences deflecting torque due to eddy current induced in
it and its rotation are counted by a gear train mechanism (not shown in figure).
The rating associated with the energy meter are:
1. Voltage rating
2. Current rating 3. Frequency rating 4. Meter constant
Formulae Used (1 Energy Meter)
1. Using energy meter constant 750 revolutions = 1kWh
1 revolution = 1  1000  3600 / 750 = 4800 W-s
For n revolution energy is n 4800 W-s
2. Calculated energy E = (V  I)  T W-s
Where V – load voltage
I – load current
T – Time taken for n revolution in seconds
3. % Error =
(𝐸𝑖 −𝐸𝑐 )
𝐸𝑖
100
Formulae Used (3 Energy Meter)
1. Energy meter constant 240 revolutions = 1kWhr
1 revolution =
1×1000 ×3600
240
= 1500 𝑊 − 𝑠
Ei = Energy for n revolution = n x 1500 (W-s)
2. Total power (P) = W1 + W2 (W)
3. Ec – Calculated energy = P  t (W-s)
4. % Error =
(𝐸𝑖 −𝐸𝑐 )
𝐸𝑖
× 100
Procedure:
1. Connect the circuit as shown in the circuit diagram.
2. Switch on the supply.
3. Load is increased in steps and each time the meter readings are noted and also the time
for one revolution is also noted down.
4. Repeat the step 3 till the rated current is reached.
5. Switch off the power supply.
6. Calculate the necessary value from the given formula
Model Graph:
POSTLAB QUESTIONS
1.
What is meant by creeping?
………………………………………………………………………………………………
………………………………………………………………………………………………
2.
What is meant by phantom loading?
………………………………………………………………………………………………
………………………………………………………………………………………………
3.
What does one unit refer to?
………………………………………………………………………………………………
………………………………………………………………………………………………
4.
How is energy meter connected?
………………………………………………………………………………………………
………………………………………………………………………………………………
5.
What may be the reason for the energy meter to rotate too fast or too slow?
………………………………………………………………………………………………
………………………………………………………………………………………………
SRM UNIVERSITY
FACULTY OF ENGINEERING AND TECHNOLOGY
DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINEERING
Evaluation Sheet
Program Name
:
Semester
:
Year
:
Name
:
Reg. No.
:
S.No.
B.Tech in Electrical and Electronics Engineering
Marks Split Up
Marks Allotted
1
Attendance
5
2
Preparation of Observation
5
3
Pre-lab
5
4
In lab Performance
10
5
Post lab
5
Total
Marks Obtained
30
Staff Signature
PRELAB QUESTIONS
1.
What is meant by earthing?
………………………………………………………………………………………………
………………………………………………………………………………………………
2.
How can we avoid shock?
………………………………………………………………………………………………
………………………………………………………………………………………………
3.
Mention the types of earthing?
………………………………………………………………………………………………
………………………………………………………………………………………………
4.
Explain the process of earthing.
………………………………………………………………………………………………
………………………………………………………………………………………………
5.
What is megger?
………………………………………………………………………………………………
………………………………………………………………………………………………
6.
Explain the use of megger.
………………………………………………………………………………………………
………………………………………………………………………………………………
7.
Explain the working of megger.
………………………………………………………………………………………………
………………………………………………………………………………………………
Date:
Experiment : 5
STUDY OF EARTHING AND MEASUREMENT OF
EARTH RESISTANCE
5. (A) STUDY OF EARTHING
Aim:
To study about earthing and their types
I. Earthing / Grounding
Earthing or grounding is the term used for electrical connection to the general mass of earth.
Equipment or a system is said to be „earthed‟ when it is effectively connected to the ground with
a conducting object. Earthing provides protection to personal and equipment by ensuring
operation of the protective gear and isolation of faulty circuit during


II.
Insulation failure
Accidental contact
Lightning strike
Importance of Earthing
Earthing is necessary for proper functioning of certain equipments. Earthing is done also for
preventing the operating personal from hazardous shocks caused by the damage of the heating
appliances. Consider an electric heater connected to the supply using two-pin plug and socket.
If by some chance the heating element comes in contact with the metallic body of the heater, the
body of the heater being a conducting material will be at the same potential as the heating coil.
If a person comes and touches the body of the heater, current will flow through his body, which
will result in an electric shock.
To avoid unnecessary accident, it is recommended that electric heater be connected to a
3-pin socket using a 3-core cable. (Note: To see a three-core cable, open a plug of an electric
iron. There will be three wires, red, blue and green. The green wire connected to the body of the
iron is the earth wire) In this case the body of the electric heater is connected to the green wire of
the cable, which is connected to the earth through the earth terminal. Besides the body of the
electric heater, bodies of hot plates, kettles, toasters, heaters, ovens, refrigerators, air
conditioners, coolers, electric irons etc could be earthed using three pin plugs. The resistance of
the path to the earth terminal through the earth wire is very low. Hence, even if the heating
element comes in contact with the metallic body and a human being comes in contact with the
metallic body, major part of the current will flow only through the earth wire (usually the green
wire in a 3 core cable). Moreover because of the low resistance path, a large current will flow
through the phase wire and the fuse will blow off. For large current to flow, earth resistance
should be low. To achieve this proper earthing has to be done.
III.
Need of Good Earthing
1. To save human life from danger of electrical shock or death by blowing a fuse i.e. to
provide an alternative path for the fault current to flow so that it will not endanger the
user.
2. To protect buildings, machinery & appliances under fault conditions i.e. To ensure that
all exposed conductive parts do not reach a dangerous potential.
3. To provide safe path to dissipate lighting and short circuit currents.
4. To provide stable platform for operation of sensitive electronic equipments i.e. to
maintain the voltage at any part of an electrical system at a know value so as to prevent
over current or excessive voltage on the appliances or equipment.
5. To provide protection against static electricity from friction.
Main Objectives of Earthing Systems are:
1. Provide an alternative path for the fault current to flow so that it will not endanger the
user.
2. Ensure that all exposed conductive parts do not reach a dangerous potential.
3. Maintain the voltage at any part of an electrical system at a known value so as to prevent
over current or excessive voltage on the appliances or equipment.
IV.
Some Definitions
Earthing: A tower / equipments connecting to the general mass of earth by mans of an electrical
conductor.
Earth Electrode: Connection to earth in achieved by electrically connecting a metal plate, rod
or other conductors or an array of conductors to the general mass of earth. This metal plate or
rod or conductor is called as “Earth electrode”.
Earth Lead: The conductor by which connection to earth is made.
Earth Loop Impedance: The total resistance of earth path including that of conductors, earth
wire, earth leads and earth electrodes at consumer end and substation end.
V.
Types of Earting:
There are various ways of doing Earthing:
1. Conventional Earthing
 Pipe Earthing
 GI Plat Earthing
 Cast Iron plat Earthing
 Copper plat Earthing
2. Maintenance Free Earthing
1.
Conventional Earhing:
The Conventional system of earthing calls for digging of a large pit into which a GI pipe
or a copper plate is positioned amidst layers of carcoal and salt. It is cumbersome to install only
one or two pits in a day.
The Conventional system of GI pipe Earthing or copper plate Eathing requires
maintenance and pouring of water at regular interval.
2.
Maintenance free earthing:
It is a new type of earthing system which is ready made, standardized, and scientifically
developed.
Advantages of Maintenance Free Earthing:
1. Maintenance Free: No need to pour water at regular interval-except in study soil.
2. Consistency: Maintain stable and consistent earth resistance around the year.
3. More Surface Area: The conductive compound creates a conductive zone, which provides
the increased surface area for peak current dissipation. And also get stable reference
point.
4.
5.
6.
7.
VI.
Low earth resistance. Highly conductive. Carries high peak current repeatedly.
No corrosion. Eco Friendly.
Long Life.
Easy Installation.
Factors Affecting and Value of Earth Electrode Resistance






VII.
Electrode material
Electrode size
Material and size of earth wire
Moisture content of soil
Depth of electrode of underground
Quantity of dust and charcoal in earth pit
Shapes of Earth Electrodes
Earth electrodes can be following shapes









Driven Rods of pipes
Horizontal Wires
Four Pointed Stars
Conductive Plates
Buried Radial Wires
Round Vertical Plates
Spheres made of metal
Square Vertical Plates
Water Pipes
VIII. Water Pipe as Earth Electrode
As water pipes exist extensively and these are most of the time embedded in earth, they can
make a good earth electrode. Such earthing is not objectionable with alternating currents. But
with direct currents, the flow of fault currents in pipes produces electrolysis and results in heavy
corrosion of pipes. This electrolysis process makes the water also harmful to certain extent. If
water pipes are proposed to be used as earth electrode, then only main water supply pipe should
be used as an electrode. The water supply main pipe should have metal-to-metal joints between
its segments. A perfect electrical connection should be made between water pipe & earth
conductor. Pipe should be cleaned thoroughly with emery paper. Earth conductor also should be
cleaned thoroughly. The cleaned conductor should be wrapped 4 to 5 times and ends clamped by
nuts & bolts. The earth resistance achieved by such an arrangement is usually a fraction of an
ohm. Low resistance of such system is due to long length of water pipe and the fact that it
mostly embedded below earth. This method is mostly used for grounding in telephone services.
Electrodes should be made of a metal, which has a high conductivity. Normally copper is used.
The size of the electrode should be such, that it is able to conduct the expected value of stray
equipments. For example a 3 phase star wound generator must have its neutral point at earth
potential.
The salts commonly used for chemical treatment of soil are




Sodium Chloride
Calcium Chloride
Sodium Nitrate
Magnesium Sulphate
Other factors, which affect the soil resistivity, are
1. Temperature of soil: the resistivity increases when temperature falls below the freezing
point. If the temperature falls from 20 degrees C to O degree C, soil resistivity goes up
from 700-ohm cm to 400-ohm cm.
2. Moisture content of Soil: small changes in moisture content seriously affect the
resistivity. For example if the moisture content changes from 25% to 30%, soil resistivity
drops from 250000-ohm cms to 6400-ohm cm. It is important that earth electrodes
should be in contact with moist soil. It should be ensured that the electrodes are deep in
soil and if possible below the permanent water level.
3. Mechanical Composition of soil: finer the grading, lower the resistance.
IX.
Methods of Placing Earth Electrodes in Soil
1.
Pipe Earthing
Pipe earthing is done by permanently placing a pipe in wet ground. The pipe can be made of
steel, galvanized iron or cast iron. Usually GI pipes having a length of 2.5m and an internal
diameter of 38mm are used. The pipe should into be painted or coated with any non-conducting
material.
The figure shows an illustration of a typical pipe electrode. The pipe should be placed
atleast 1.25m below the ground level and it should be surrounded by alternate layers of charcoal
and salt for a distance of around 15cm. This is to maintain the moisture level and to obtain
electrode and it should be carried in a GI pipe at a depth of 60cm below the ground level. A
funnel with a wire mech should be provided to pour water into the sump. Three or four bucket of
water should be poured in a few days particularly during summer season. This is to keep the
surroundings of the electrode permanently moist.
2.
Plate earthing
A typical illustration of plate earthing is shown in figure. The plate electrode should have
a minimum dimension of 600 x 600 x 3.15mm for copper plate or 600 x 600 x 6.3mm for GI
plates. The plate electrode should be placed atleast. 1.5m below the ground level. Bolts and
nuts should be of the same material as that of the plate by means of bolts and nuts. The bolts and
nuts should be of the same material as that of the plate. The earth conductor should be carried in
a GI pipe buried 60 cm below the ground level. The plate electrode should be surrounded by a
layer of charcoal to reduce the earth resistance. A separate GI pipe with funnel and wire mesh
attached is provided to pour water into the sump.
5 (B) MEASUREMENT OF EARTH RESISTANCE
Aim
To measure the earth resistance using megger earth tester
Apparatus Required:
S.No.
1
2
3
4
Components
Megger earth tester – 1
Electrode under test – 1
Electrodes – 2
Copper wires – As required
Range/Type
-
Quantity
Hammer – 1
Glove- 1 pair
-
Formula Used:
Depth of insertion of electrode into the soil = (Distance between two electrode / 20) in feet.
Theory:
The megger is a portable instrument used to measure insulation resistance. The megger consists
of a hand-driven DC generator and a direct reading ohm meter.
The moving element of the ohm meter consists of two coils, A and B, which are rigidly
mounted to a pivoted central shaft and are free to rotate over a C-shaped core. These coils are
connected by means of flexible leads. The moving element may point in any meter position
when the generator is not in operation.
As current provided by the hand-driven generator flows through Coil B, the coil will tend
to set itself at right angles to the field of the permanent magnet. With the test terminals open,
giving an infinite resistance, no current flows in Coil A. Thereby, Coil B will govern the motion
of the rotating element, causing it to move to the extreme counter-clockwise position, which is
marked as infinite resistance.
Coil A is wound in a manner to produce a clockwise torque on the moving element. With
the terminal marked “line” and “earth” shorted, giving a zero resistance, the current flow through
the Coil A is sufficient to produce enough torque to overcome the torque of Coil B. The pointer
then protect Coil A from excessive current flow in this condition.
When an unknown resistance is connected across the test terminals, line and earth, the
opposing torques of Coils A and B balance each other so that the instrument pointer comes to
rest at some point on the scale. The scale is calibrated such that the pointer directly indicates the
value of resistance being measured.
Procedure:
1. Connection are given as per the circuit diagram
2. Connect together the terminals PI and CI by closing the switch provided and connect
them to the electrode or metal structure to be tested.
3. Keep the lead used for this connection as short as possible, as its resistance is included in
the measurement.
4. Connect terminals marked P2 and C2 to two temporary earth spikes driven into the
ground.
5. Rotate the handle provided in the megger at about 160 rpm.
6. Measure the resistance of the electrode under test.
7. Repeat the test by placing the electrodes at different spacing.
Tabulation:
S.No.
Distance between wo earth electrodes
In feet
Resistance
ohm
Model Graph:
Result:
Thus the resistance of the test electrode was found using megger.
POSTLAB QUESTIONS
1.
What is the normal value of earth resistance?
………………………………………………………………………………………………
………………………………………………………………………………………………
2.
What is the resistance of human body?
………………………………………………………………………………………………
………………………………………………………………………………………………
3.
How much current or voltage can a normal human withstand?
………………………………………………………………………………………………
………………………………………………………………………………………………
4.
How the earth electrode is made up of?
………………………………………………………………………………………………
………………………………………………………………………………………………
5.
On what factors does earth resistance depend?
………………………………………………………………………………………………
………………………………………………………………………………………………
6.
Why is charcoal/salt used in earth pit?
………………………………………………………………………………………………
………………………………………………………………………………………………
7.
How can we minimize the earth resistance?
………………………………………………………………………………………………
………………………………………………………………………………………………
8.
Which type of earthing is used in homes?
………………………………………………………………………………………………
………………………………………………………………………………………………
SRM UNIVERSITY
FACULTY OF ENGINEERING AND TECHNOLOGY
DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINEERING
Evaluation Sheet
Program Name
:
Semester
:
Year
:
Name
:
Reg. No.
:
S.No.
B.Tech in Electrical and Electronics Engineering
Marks Split Up
Marks Allotted
1
Attendance
5
2
Preparation of Observation
5
3
Pre-lab
5
4
In lab Performance
10
5
Post lab
5
Total
Marks Obtained
30
Staff Signature
PRELAB QUESTIONS
1.
Mention the various parts in iron box
………………………………………………………………………………………………
………………………………………………………………………………………………
2.
Name the type of motor used in fan, mixer, grinder, etc.
………………………………………………………………………………………………
………………………………………………………………………………………………
3.
Explain the working of fan
………………………………………………………………………………………………
………………………………………………………………………………………………
4.
What is the difference between ceiling fan and pedestal fan?
………………………………………………………………………………………………
………………………………………………………………………………………………
5.
What are the problems encountered in fan?
………………………………………………………………………………………………
………………………………………………………………………………………………
Date:
Experiment : 5
STUDY OF TROUBLESHOOTING OF
ELECTRICAL EQUIPMENTS
Aim:
To study about the trouble shooting of electrical equipments like fan, iron box, mmixer-grinder
etc.
S.No.
1
Appliance
Electric iron box press
Defects
Does‟t work after supply is on
Shock on body
Iron box has no enough temperature
when knob is placed at one position
2
Celling fan
Doesn‟t work after supply is on
Wobbling
Humming or buzzing
Airflow
3
Electric heater
Shock due to short circuit
Remedies
There must be a damage in
wire or there is open circuit.
Check the thermostat for
open circuit
Check the heating element
continuity.
Check the continuity of earth
wire to body. If it does not
get continuity dismantle the
cover and connect earth wire
properly.
Check the heating element.
Adjust the screw below the
knob to produce enough
temperature.
Check for switch socket,
capacitor
Make sure that all screws and
bolts are tightened
The fan blades aren‟t warped
or damaged
Make sure there are no loose
parts that are knocking
together
Air flow will be less
noticeable if the fan is in
updraft mode
Remove the short circuit
Troubleshooting Chart
(i)
Electric Iron Box
Trouble
Excessive heat
Possible Causes
No power at outlet
Defective cord or plug
Loose terminal connections
Broken lead in iron
Loose thermostat control knob
Defective thermostat
Defective heater element
If cast in, replace sole-plate assembly
Low line voltage
Incorrect thermostat setting
Incorrect thermostat setting
Blisters on sole-plate
Defective thermostat
Excessive heat
No beat
Insufficient heat
Tears Clothes
Iron cannot be turned off
Power cord
Sticks to clothes
Iron gives shock
Rough spot, nick, scratch, burn on soleplate
Thermostat switch contacts are welded
together
Loose connection
Broken wire
Dirty sole-plate
Excessive starch in clothes
Wrong setting of the thermostat knob
Iron too hot for fabric being ironed
Disconnected earth connection
Weak insulation of heating element
Earth continuity with common earth not
available
(ii)
Corrective Action To Be Taken
Check outlet for power
Repair or replace
Check and tighten the terminals
Repair or replace lead
Clean and tighten
Replace thermostat
replace the element if separate
Open terminal fuse replace
Check voltage at outlet
Adjust and recalibrate thermostat
Adjust and recalibrate thermostat or
replace
Replace thermostat
First repair the thermostat control.
Then replace or repair the sole-plate
Remove these sports with fine emergy
and polish the area with buff.
Check the thermostat switch contact.
Open them by force. The contact
points should be in open condition at
off position of the control knob
Clean and tighten
Repair or replace
Clean
Iron at a lower temperature. Use less
starch next time.
Set the knob to correct temperature
Lower the thermostat setting
Check earth connection and connect
properly
Check insulation resistance of heating
element; If necessary replace element
Check the main earth continuity and
connect properly
Water Heater
Complaints
Not hot water
Causes
No supply
Blown fuse
Open circuit
Insufficient quality of hot
water
Heater element burnt out
Thermostat setting too low
Lower value of heating element
Remedies
Check availability of supply at 3-pin
socket
Replace fuse
Check the wiring for broken wire or
loosed connection
Check elements for burn-out
Check the thermostat setting. It should
be 60oC to 65oC
Check the value of heating element
Capacity of tank is insufficient for one‟s
needs
Comstantly fuse blowing
Grounded heating element
Steam in hot water
Grounded lead wire
Thermostat improperly connected
High consumption of power
leading
to
increased
electricity bill
Thermostat contact welded together
Grounded heating element
Thermostat set too high or out of
calibration
Leaking faucets
Excessively exposed hot water pipes
Thermostat setting too high
Grounded heating element
Scale deposit on the heating units
(iii)
Replace washers in all leaking faucets
Hot water lines should be as short as
possible
Reset thermostat. Setting should be
60oC to 65oC
Check element for ground
Dismantle the water heater and remove
the scale form the element tube gently
Mixer
Fault
Motor is not running
Possible reason
No voltage or low voltage
Supply voltage is correct.
motor is not running
Either motor field or armature coil
may get open circuited
Overload in the jar and hence
overload protector may get tripped
But
Motor rotates at same speed in all
speed settings
May be any short circuit in
armature or field coils
There may be wear and tear in the
bearings
(iii)
and replace
Check the quantity of water used.
Identify if the tank capacity is too
small
Check the heater element for insulation
resistance and replace if necessary
Check wiring for grounds
Check the circuit and correct any
improper connections
Check the thermostat for its operation
Check the unit for ground
Reset thermostat
Remedy
Check the supply voltage with
multimeter
Do the continuity test. If there is
an open circuit fault, do the service
Press the overload relief button and
remove some materials in the jar.
Now restart.
Do the continuity test. If there is
an short circuit fault, do the
service.
Check and put lubricating oil at
bearings. If beat persists, replace
it.
Electric Fan
Fault
Noise
Low speed
Cause
It is due to worn out bearings and
absence of lubricating oil or grease
Humming or induction noise is due
to non-uniform air gap owing to
the displacement of rotor.
It is due to defective or leaky
capacitor
Low voltage applied
Remedy
The bearings must be replace if
worn out; otherwise lubricate with
proper lubricant
Dismantle
and
reassemble
properly
Replace the capacitor with one of
the same value and voltage
Check the voltage and adjust it
possible
Jamming of rotor
It is due to misalignment
Not starting
Low applied voltage
Supply failure
Open in winding
Condenser open or short
Open in regulator resistor
(v)
Dismantle and assemble property
after proper lubrication
Check the voltage and adjust if
possible
Check the supply points at switch
regulator ceiling rose and the
terminal of the fan
Check for the continuity of
auxiliary and main winding
Check the capacitor with a megger
Check for open or loose contact in
the resistor or contacts
Vaccum Cleaner
Repairing of Vaccum Cleaner
When a vacuum cleaner fails to clear the dirt effectively, we think of replacing it with a
new one. But troubleshooting a vacuum cleaner is not a so difficult task. When a vacuum
cleaner begins to perform ineffectively there are three main areas that need to be considered
namely poor suction, still brush and no power supply.
Other than these three areas, there are other parts of the vacuum cleaner which is worth
considering. These are the vacuum cleaner belt, clogging of the hose, vacuum filter etc. now
before you start troubleshooting your vacuum cleaner, it is very important to detect what actually
is wrong with your vacuum cleaner. Once we are aware about the faulty pars ha are causing the
problem then repairing it is easy. As most of the vacuum cleaners problem are not problems at
all.
Following are some steps that will guide us on troubleshoot/repair the vacuum cleaner:
1. If the faulty is in the belt then we have no other choice rather than to replace it with a new
belt. It is not possible to repair a belt. Installing a new belt is not a difficult task. Turn
over the vacuum cleaner and unscrew the plate so that you face the brush. Remove the
old belt which connects the agitator brush and the drive shaft and install the new one.
2. Check the agitator brush for any thread or hair that could be tangled in the brush. Use a
scissor to cut them out. And make sure that it is spinning properly with ease.
If the
brush in worn out then replace it with a new one.
3. If your vacuum cleaner is not sucking up the dirt effectively then it could be due to a
clogged filter or hose or a moist bag. Cleaning the filter and the hose can increase the
cleaning efficiency of the cleaner. If required replace the filter that will enhance the
efficiency of the vacuum cleaner.
4. If there is no power supply to the vacuum cleaner then check of any discontinuity along
the wire. Replace the breakers if required and mend and discontinuity along the line.
Another reason for no supply of power could be due to a burned out motor. In this case
we will have to replace the motor.
5. Check the vacuum hose for any holes. A vacuum hose with a hole will face suction
problem. So if there is any hole on the hose than repair it by parting a tape on it.
(vi)
Washing Machine
Washing Machine problems and remedies: Washing machine problems are of various types.
However, there are certain common washing machine problems which many people have to face.
If the problem is a different one, it is necessary to call the repair, because diagnosing washing
machine problems is not an easy task. Washing machine troubleshooting is no child‟s play.
Let‟s see the different problems with washing machines and how we can deal with them.
Washing Machine doesn’t Spin: This problem can occur if we stuff too many clothes at one
time. Remove some clothes out and then try the spin cycle again with a less number of clothes.
The other reasons can be broken lid switch and the tab on the lid, broken or loose belt or control
problem. If we are good at home repair, we can remove the switch or belt and replace them if
needed, otherwise we would need to call an expert.
Washing Machine doesn’t Drain: This problem may occur if the water pump is clogged, the
belt is loose or the drainage hose is kinked. We can replace the belt or call an appliance repair
person to deal with this problem.
Washing Machine doesn’t fill with water: We might face this problem if the inlet hoses are
clogged, fault in the timer, and the lid switch or the water level switch which is located in the
control panel with a clear tube attached to it. With the VOM on Rx1 (Volt-oym-meter set on
resistance mode), examine the three terminals and all the optional pairings to see whether you are
getting a 0 reading on one infinity reading on the others.
Washing Machines doesn’t Run: Recjheck if the washing machine is plugged in (receiving
electrical power). If it is plugged in and still does not work then check the outlet with the VOM
for the voltage and power cord (if it is damaged). If all the devices are fine then the lid switch or
timer may have a problem. Call the appliance repair person and replace the parts if necessary.
Leakage in washing machine: The leakage might take place due to damaged hoses or loose
connections. Check the water pump in case of a leakage.
Washing machine doesn’t Agitate: Check the lid switch belt timer or bad transmission )spin
solenoid). There is a possibility that any cloth must have got wrapped around the agitator
resulting in this problem.
Washing Machine Makes Noise: This problem might occur due to unbalanced/heavy Load.
Dot not stuff too many clothes in the machine. Remove some of the clothes and try again. If the
problem does not get solved, then there might be a bad transmission or the agitator might be
broken. Call the home appliances repair person to get it repaired.
STUDY OF VARIOUS ELECTRICAL EQUIPMENTS
Parts and its working of the following devices.
1.
IRON BOX
2.
FAN
3.
MIXIE
Result:
Thus the troubleshooting of electrical equipments is studied.
POSTLAB QUESTIONS
1.
Name few problems in iron box
………………………………………………………………………………………………
………………………………………………………………………………………………
2.
What is the power consumption of various electrical gadgets?
………………………………………………………………………………………………
………………………………………………………………………………………………
3.
Mention the various parts of fan motor
………………………………………………………………………………………………
………………………………………………………………………………………………
4.
What is the use of capacitor in fan?
………………………………………………………………………………………………
………………………………………………………………………………………………
5.
When a low voltage is supplied to fan, what happens and why?
………………………………………………………………………………………………
………………………………………………………………………………………………
SRM UNIVERSITY
FACULTY OF ENGINEERING AND TECHNOLOGY
DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINEERING
Evaluation Sheet
Program Name
:
Semester
:
Year
:
Name
:
Reg. No.
:
S.No.
B.Tech in Electrical and Electronics Engineering
Marks Split Up
Marks Allotted
1
Attendance
5
2
Preparation of Observation
5
3
Pre-lab
5
4
In lab Performance
10
5
Post lab
5
Total
Marks Obtained
30
Staff Signature
PRELAB QUESTIONS
1.
Explain the construction and working of induction motor.
………………………………………………………………………………………………
………………………………………………………………………………………………
2.
Explain the working of transformer.
………………………………………………………………………………………………
………………………………………………………………………………………………
3.
Mention the types of transformer.
………………………………………………………………………………………………
………………………………………………………………………………………………
4.
List the application of transformer.
………………………………………………………………………………………………
………………………………………………………………………………………………
5.
Name few application of induction motor in home.
………………………………………………………………………………………………
………………………………………………………………………………………………
6.
Why are CFL preferred?
………………………………………………………………………………………………
………………………………………………………………………………………………
7.
What is LED?
………………………………………………………………………………………………
………………………………………………………………………………………………
8.
How does an LED work?
………………………………………………………………………………………………
………………………………………………………………………………………………
Date:
Experiment : 7
STUDY OF VARIOUS ELECTRICAL GADGETS
Aim:
To study various electrical gadgets of Induction motor, transformer, CFL, LED, PV cell.
Light Emitting Diodes
A light-emitting diode (LED) is a semiconductor light source. LEDs are used as indicator lamps
in many devices and are increasingly used for other lighting. Appearing as practical electronic
components in 1962, early LEDs emitted low-intensity red light, but modern versions are
available across the visible, ultraviolet, and infrared wavelengths, with very high brightness.
When a light-emitting diode is switched on, electrons are able to recombine with holes
within the device, releasing energy in the form of photons.
This effect is called
electroluminescence and the color of the light (corresponding to the energy of the photon) is
determined by the energy band gap of the semiconductor. An LED is often small in area (less
than 1 mm 2), and integrated optical components may be used to shape its radiation pattern.(8)
LEDs present many advantages over incandescent light sources including lower energy
consumption, longer lifetime, improve physical robustness, smaller size, and faster switching.
However, LEDs powerful enough for room lighting are relatively expensive and require more
precise current and heat management the compact fluorescent lamp sources of comparable
output.
Light-emitting diodes are used in applications as diverse as aviation lighting, digital
microscopes, automotive lighting, advertising, general lighting, and traffic signals. LEDs have
allowed new text, video displays, and sensors to be developed, while their high switching rates
are also useful in advanced communications technology. Infrared LEDs are also used in the
remote control units of many commercial products including televisions, DVD players and other
domestic appliances. LEDs are also used in seven-segment display.
Light emitting diodes, commonly called LEDs, are real unsung heroes in the electronics
world. They do dozens of different jobs and are found in all kinds of devices. Among other
things, they form numbers on digital clocks, transmit information from remote controls, light up
watches and tell you when your appliances are turned on.
Basically, LEDs are just tiny light bulbs that fit easily into an electrical circuit. But
unlike ordinary incandescent bulbs, they don‟t have a filament that will burn out, and they don‟t
get especially hot. They are illuminated solely by the movement of electrons in a semiconductor
material, and they last just as long as a standard transistor. The lifespan of an LED surpasses the
short life of an incandescent bulb by thousands of hours. Tiny LEDs are already replacing the
tubes that light up LCD HDTVs to make dramatically thinner televisions.
The LED consists of a chip of semiconducting material doped with impurities to create a
p-n junction. As in other diodes, current flows easily from the p-side, or anode, to the n-site, or
cathode, but not in the reverse direction. Charge-carriers-electrons and holes-flow into the
junction from electrodes with different voltages. When an electron meets a hole, it falls into a
lower energy level, and releases energy in the form of a photon.
The wavelength of the light emitted, and thus its color depends on the band gap energy of
the materials forming the p-n junction. In silicon or germanium diodes, the electrons and holes
recombine by a non-radiative transition, which produces no optical emission, because these are
indirect band gap materials. The materials used fro the LED have a direct band gap with
energies corresponding to near-infrared, visible, or near-ultraviolet light.
LED development began with infrared and red devices made with gallium arsenide.
Advances in materials science have enabled making devices with ever-shorter wavelengths,
emitting light in a variety of colors.
LEDs are usually built on an n-type substrate, with an electrode attached to the p-type
layer deposited on its surface. P-type substrates, while less common, occur as well. Many
commercial LEDS especially GaN.InGaN, also use sapphire substrate.
Most materials used for LED production have very high refractive indices. This means
that much light will be reflected back into the material at the material/air surface interface. Thus,
light extraction in LEDs is an important aspect of LED production, subject to much research and
development.
Photovoltaic Cells
Photovoltaic (PV) cells are made up of at least 2 semi-conductor layers. One layer containing a
positive charge, the other a negative charge.
Sunlight consists of little particles of solar energy called photons. As a PV cell is
exposed to this sunlight, many of the photons are reflected, pass right through, or absorbed by
the solar cell.
When enough photons are absorbed by the negative layer of the photovoltaic cell,
electrons are freed from the negative semiconductor material. Due to the manufacturing process
of the positive layer, these freed electrons naturally migrate to the positive layer creating a
voltage differential, similar to a household battery.
When the 2 layer are connected to an external load, the electrons flow through the circuit
creating electricity. Each individual solar energy cell produces only 1-2 watts. To increase
power output, cells are combined in a weather-tight package called a solar module.
A solar cell (also called a photovoltaic cell) is an electrical device that converts the
energy of light directly into electricity by the photovoltaic effect. It is a form of photoelectric
cell (in that its electrical characteristics-e.g. current, voltage, or resistance-varu when light is
incident upon it) which, when exposed to light, can generate and support an electric current
without being attached to any external voltage source.
The term “photovoltaic” comes from the Greek 𝜑𝜔𝜍 )𝑝ℎ𝑜𝑠) meaning “light”, and from
“Volt”, the unit of electro-motive force, the volt, which in turn comes from the last name of the
Italian physicist Alessandro Volta, inventor of the battery (electrochemical cell). The term
“photo-voltaic” has been in use in English since 1849.(1)
Photovoltaics is the field technology and research related to the practical application of
photovoltaic cells in producing electricity from light, though it is often used specifically to refer
to the generation of electricity from sunlight. Cells can be described as photovoltaic even when
the light source is not necessarily sunlight (lamplight artificial light, etc.) In such cases the cell
is sometimes used as a photo detector (for example infrared detectors), detecting light or other
electromagnetic radiation near the visible range, or measuring light intensity.
The operation of a photovoltaic (PV) cell requires 3 basic attributes:
1. The absorption or light, generating either electro-hole pairs or exactions.
2. The separation of charge carriers of opposite types.
3. The separate extraction of those carriers to an external circuit.
In contrast, a solar thermal collector collects heat by absorbing sunlight, for the purpose of
either direct heating or indirect electrical power generation. “Photo electrolytic cell” (photo
electrochemical), on the other hand, refers either a type of photovoltaic cell )like that
developed by A.E. Becquerel and modern dye-sensitized solar cells) or a device that splits
water directly into hydrogen and oxygen using only solar illumination.
Photovoltaic Cell
Induction Motor
An induction or asynchronous motor is an AC electric motor in which the electric current in
the rotor needed to produce torque is induced by electromagnetic induction from the
magnetic field of the stator winding.
An induction motor therefore does not require
mechanical commutation, separate-excitation or self-excitation for all or part of the energy
transferred from stator to rotor, as in universal, DC and synchronous motors. An induction
motor‟s rotor can be either wound type or squirrel-cage type.
Three-phase squirrel-cage induction motors are widely used in industrial drives because
they are rugged reliable and economical. Single-phase induction motors are used extensively
for smaller loads, such as household appliances like fans. Although traditionally used in
fixed speed service, induction motors are increasingly being used with variable-frequency
drives (VFDs) in variable speed service.
Induction motor is a generalized transformer. Difference is that transformer is an alternating
flux machine while induction motor is rotating flux machine. Rotating flux is only possible
when 3 phase voltage (or poly phase) which is 120 degree apart in time is applied to a three
phase winding (or poly phase winding) 120 degree apart in space then a three phase rotating
magnetic flux is produced whose magnitude is constant but direction keeps changing. In
transformer the flux produced is time alternating and not rotating.
There is not air gap between primary and secondary of transformer whereas there is a
distinct air gap between stator and rotor of motor which gives mechanical movability to
motor. Because of higher reluctance (or low permeability) of air gap the magnetizing current
required in motor is 25-40% of rated current of motor whereas in transformer it is only 2-5%
of rated primary current.
In an alternating flux machine frequency of induced EMF in primary and secondary side
is same whereas frequency of rotor EMF depends on slip. During starting when S = 1 the
frequency of induced EMF in rotor and stator is same but after loading it is not.
Other difference is that the secondary winding and core is mounted on a shaft set in
bearings free to rotate and hence the name rotor.
If at all secondary of a transformer is mounted on shaft set at bearings the rate of cutting
of mutual magnetic flux with secondary circuit would be different from primary and their
frequency would be different. The induced EMF would not be in proportion to number of
turns ratio but product of turn ratio and frequency. The ratio of primary frequency to the
secondary frequency is called slip.
Any current carrying conductor if placed in magnetic field experience a force so rotor
conductor experience a torque and as per Lenz;s Law the direction of motion is such that it
tries to oppose the change which has caused so it starts chasing the field.
Transformer
A Typical Voltage Transformer
The transformer is very simple static (or stationary) electro-magnetic passive electrical
devices that works on the principle of Faraday‟s law of induction. It does this by linking
together two or more electrical circuits using a common oscillating magnetic circuit which is
produced by the transformer itself.
A transformer operates on the principals of
“electromagnetic induction”, in the form of Mutual Induction.
Mutual induction is the process by which a coil of wire magnetically induces a voltage
into another coil located in close proximity to it. Then we can say that transformers work is
the “magnetic domain”, and transformers get their name from the fact that they “transform”
one voltage or current level into another. Transformers are capable of either increasing or
decreasing the voltage and current levels of their supply, without modifying its frequency, or
the amount of electrical power being transferred from one winding to another via the
magnetic circuit.
A single phase voltage transformer basically consists of two electrical coils of wire, one
called the “Primary Winding” and another called the :Secondary Winding” that are wrapped
together around a closed magnetic iron circuit called a “core. This soft iron core is not solid
but made up of individual laminations connected together to help reduce the core‟s losses.
These two windings are electrically isolated from each other but are magnetically linked
through the common core allowing electrical power to be transferred from one coil to the
other.
In other words, for a transformer there is no direct electrical connection between the two
coil windings, thereby giving it the name also of an Isolation Transformer. Generally the
primary winding of a transformer is connected to the input voltage supply and converts or
transforms the electrical power into a magnetic field. While the secondary winding converts
this magnetic field into electrical power producing the required output voltage as shown.
Transformer Construction (single-phase)
Where:
Vp
-
is the Primary Voltage
Vs
-
is the Secondary Voltage
Np
-
is the Number of Primary Windings
Ns
-
is the Number of Secondary Windings
 (phi) -
is the Flux Linkage
Notice that the two coil windings are not electrically connected but are only linked
magnetically. A single-phase transformer can operate to either increase or decrease the
voltage applied to the primary winding. When a transformer is used to “increase” the voltage
on its secondary winding with respect to the primary, it is called a Step-up transformer.
When it is used to “decrease” the voltage on the secondary winding with respect to the
primary it is called a Step-down transformer.
However a third condition exists in which a transformer produces the same voltage on its
secondary as is applied to its primary winding. In other words, its output is identical with
respect to voltage, current and power transferred. This type of transformer is called an
“Impedance Transformer” and is mainly used for impedance matching or the isolation of
adjoining electrical circuits.
The difference in voltage between the primary and the secondary windings is achieved by
changing the number of coil turns in the primary winding (Np) compared to the number of
coil turns on the secondary winding (Ns). As the transformer is a linear device, a ratio now
exists between the number of turns of the primary coil divided by the number of turns of the
secondary coil. This ratio, called the ratio of transformation, more commonly known as a
transformers “turns ratio”, (TR).
This turns ratio value dictates the operation of the
transformer and the corresponding voltage available on the secondary winding.
It is necessary to know the ratio of the number of turns of wire on the primary winding
compared to the secondary winding. The turns ratio, which has no units, compares the two
windings in order and is written with a colon, such as 3:1 (3 to 1). This means in this
example, that if there are 3 volts on the primary winding there will be 1 volt on the secondary
winding, 3 to 1. Then we can see that if the ratio between the number of turns changes the
resulting voltage must also change by the same ratio, and this is true.
A transformer is all about :ratios”, and the turns ratio of a given transformer will be the
same as its voltage ratio. In other words for a transformer: “turns ratio = voltage ratio”. The
actual number of turns of wire on any winding is generally not important, just the turns ratio
and this relationship is given as:
A Transformer‟s Turns Ratio
𝑁𝑝
𝑁𝑠
=
𝑉𝑝
𝑉𝑠
= 𝑛 = Turns Ratio
Assuming an ideal transformer and the phase angles: p = s
Note that the order of the numbers when expressing a transformers turns ratio value is
very important as the turns ratio 3:1 expresses a very different transformer relationship and
output voltage than one in which the turns ratio is given as: 1:3
Example No.1
A voltage transformer has 1500 turns of wire on its primary coil and 500 turns of wire for in
secondary coil. What will be the turns ratio (TR) of the transformer.
𝑇. 𝑅. =
𝑁𝑝 ≠ 𝑃𝑟𝑖. 𝐶𝑜𝑖𝑙𝑠 1500 3
=
=
= = 3.1
𝑁𝑠
≠ 𝑆𝑒𝑐. 𝐶𝑜𝑖𝑙
500
1
Ans:
This ratio of 3:1 (3to1) simply means that there are three primary windings for every one
secondary winding. As the ratio moves from a larger number on the left to a smaller number on
the right, the primary voltage is therefore stepped down in value as shown.
Example No.2
If 240 volts are applied to the primary winding of the same transformer, what will be the
resulting secondary no load voltage.
𝑇. 𝑅. = 3: 1 𝑜𝑟
𝑁𝑝 ≠ 𝑃𝑟𝑖. 𝐶𝑜𝑖𝑙𝑠 240
=
=
𝑁𝑠
≠ 𝑆𝑒𝑐. 𝐶𝑜𝑖𝑙
𝑉𝑠
∴ 𝑆𝑒𝑐. 𝑉𝑜𝑙𝑡𝑠, 𝑉𝑠 =
𝑉𝑝 240
=
= 80 𝑣𝑜𝑙𝑡𝑠
3
3
Again confirming that the transformer is a “step-down transformer as the primary voltage
is 240 volts and the corresponding secondary voltage is lower at 80 volts. Then the main
purpose of a transformer is to transform voltages and we can see that the primary winding has a
set amount or number of windings (coils of wire) on it to suit the input voltage. If the secondary
output voltage is to be the same value as the input voltage on the primary winding, then the same
number of coil turns must be wound onto the secondary core as there are on the primary core
giving an even turns ratio of 1:1 (1to1). In other words, one coil turn on the secondary to one
coil turn on the primary.
If the output secondary voltage is to be greater or higher than the input voltage, (step-up
transformer) then there must be more turns on the secondary giving a turns ratio of 1:N (1toN),
where N represents the turns ratio number. Likewise, if it is required that the secondary voltage
windings much be less giving a turns ratio of N:1 (N to 1)
Transformer Action
We have seen that the number of coil turns on the secondary winding compared to the primary
winding, the turns ratio, affects the amount of voltage available from the secondary coil. But if
the two windings are electrically isolated from each other, how is this secondary voltage
produced?
We have said previously that a transformer basically consists of two coils wound around
a common soft iron core. When an alternating voltage (Vp) is applied to the primary coil, current
flows through the coil which in turn sets up a magnetic field around itself, called mutual
inductance, by this current flow according to Faraday’s Law of electromagnetic induction. The
strength of the magnetic field builds up as the current flow rises from zero to its maximum value
which is given as
𝑑𝜙
𝑑𝑡
.
As the magnetic lines of force setup by this electromagnet expand outward from the coil
the soft iron core forms a path for an concentrates the magnetic flux. This magnetic flux links
the turns of both windings as it increases and decreases in opposite directions under the influence
of the AC supply.
However, the strength of the magnetic field induced into the soft iron core depends upon
the amount of current and the number of turns in the winding. When current is reduced, the
magnetic field strength reduces.
When the magnetic lines of flux flow around the core, they pass through the turns of the
secondary winding, causing a voltage to be induced into the secondary coil. The amount of
voltage induced will be determined by: N.
𝑑𝜙
𝑑𝑡
(Faraday‟s Law), where N is the number of coil
turns. Also this induced voltage has the same frequency as the primary winding voltage.
Then we can see that the same voltage is induced in each coil turn of both windings
because the same magnetic flux links the turns of both the windings together. As a result, the
total induced voltage in each winding is directly proportional to the number of turns in that
winding.
However, the peak amplitude of the output voltage available on the secondary winding
will be reduced if the magnetic losses of the core are high.
If we want the primary coil to produce a stronger magnetic field to overcome the cores
magnetic losses, we can either send a larger current through the coil, or keep the same current
flowing, and instead increase the number of coil turns (Np) of the winding. The product of
amperes times turns is called the “ampere-turns”, which determines the magnetizing force of the
coil.
So assuming we have a transformer with a single turn in the primary, and only one turn in
the secondary. If one volt is applied to the one turn of the primary coil, assuming no losses,
enough current must flow and enough magnetic flux generated to induce on voltage in the single
turn of the secondary. That is, each winding supports the same number of volts per turn.
As the magnetic flux varies sinusoidally,  = max sint, then the basic relationship
between induced emf, (E) in a coil winding of N turns is given by:
emf = turns x rate of change
𝐸=𝑁
𝑑𝜙
𝑑𝑡
𝐸 = 𝑁 × 𝜔 × 𝑚𝑎𝑥 × cos⁡
(𝜔𝑡)
𝐸𝑚𝑎𝑥 = 𝑁𝜔 𝑚𝑎𝑥
𝐸𝑚𝑎𝑥 =
𝑁𝜔
2
× 𝑚𝑎𝑥 =
2𝜋
2
× 𝑓 × 𝑁 × 𝑚𝑎𝑥
∴ 𝐸𝑟𝑚𝑠 = 4.44 𝑓𝑁𝑚𝑎𝑥
Where:
𝜔
𝑓 − is the flux frequency in Hertz, = 2𝜋
N – is the number of coil windings
 - is the flux density in webers
This is known as the Transformer EMF Equation: For the primary winding emf, N will
be the number of primary turns, (Np) and for the secondary winding emf, N will be the number of
secondary turns, (Ns)
Also please note that as transformers require an alternating magnetic flux to operate
correctly, transformers cannot therefore be used to transform DC voltages or currents, since the
magnetic field must be changing to induce a voltage in the secondary winding. In other words,
Transformers DO NOT Operate on DC Voltages.
Compact Fluorescent Lamps
Fluorescent lamps use 25% - 35% of the energy used by incandescent lamps to provide the same
amount of illumination (efficacy of 30-110 lumens per watt). They also last about 10 times
longer (7,000 – 24000 hours).
The light produced by a fluorescent tube is caused by an electric current conducted
through mercury and inert gases. Fluorescent lamps require a ballast to regulate operating
current and provide a high start-up voltage.
Electronic ballasts outperform standard and
improved electromagnetic ballasts by operating at a very high frequency that eliminates flicker
and noise. Electronic ballasts also are more energy-efficient. Special ballasts are needed to
allow dimming of fluorescent lamps.
The two general types of fluorescent lamps are:

Compact fluorescent lamps

Fluorescent tube and circline lamps
Compact Fluorescent Lamps
CFLs come in a variety of sizes and shapes, including (a) twin-tube integral, (b and c) triple-tube
integral, (d) integral model with casing the reduces glare, (e) modular circline and ballast, and (f)
modular quad-tube and ballast varieties. Compact fluorescent lamps (CFLs) combine the energy
efficiency of fluorescent lighting with the convenience and popularity of incandescent fixtures.
CFLs can replace incandescent that are roughly 3-4 times their wattage, saving up to 75% of the
initial lighting energy. Although CFLs cost 3-10 times more than comparable incandescent
bulbs, they last 6-15 times as long (6,000 – 15000 hours).
CFLs work much like standard fluorescent lamps. They consist of two parts: a gas-filled
tube and a magnetic or electronic ballast. The gas in the tube glows with ultraviolet light when
electricity from the ballast flows through it. This, in turn, excites a white phosphor coating on the
inside of the tube, which emits visible light throughout the surface of the tube. CFLs with
magnetic ballasts flicker slightly when they start.
They are also heavier than those with
electronic ballasts. This may make them too heavy for some light fixtures. Electronic ballasts
are more expensive but light immediately (especially at low temperatures). They are also more
efficient than magnetic ballasts. The tubes will last about 10,000 hours and the ballast about
50,000 hours. Most currently available CFLs have electronic ballasts.
CFLs are designed to operate within a specific temperature range. Temperatures below
the range cause reduced output. Most are for indoor use, but there are models available for
outdoor use. A CFLs temperature range is usually listed on its package. CFLs are most costeffective and efficient in areas where lights are on for long periods of time. Because CFLs do
not need to be changed often, they are ideal for hard-to-reach areas.
Types of Compact Fluorescent Lamps
CFLs are available in a variety of styles and shapes. They may have two, four, or six tubes or
circular or spiral-shaped tubes. The size or total surface area of the tube(s) determines how
much light is produced. In some CFLs, the tubes and ballast are permanently connected. Other
CFLs have separate tubes and ballasts. This allows the tubes to be changed without changing the
ballast. There are also types enclosed in a glass globe. These look somewhat similar to
conventional incandescent light bulbs, except they are larger.
Sub-CFLs fit most fixtures designed for incandescent lamps. Although most CFLs fit
into existing three-way light sockets, only a few special CFL models can be dimmed.
Fluorescent Tube and Circline Lamps
In fluorescent tubes, a very small amount of mercury mixes with inert gases to conduct electrical
current. This allows the phosphor coating on the glass tube to emit light. Fluorescent tube
lamps-the second most popular type of lamps-are more energy efficient than the more popular Atype standard incandescent lamps.
The traditional tube-type fluorescent lamps are usually identified as T12 or T8 (twelveeighths or eight-eighths of an inch tube diameter, respectively). They are installed in a dedicated
fixture with a built-in ballast. The two most common types are 40-watt, 4-foot (1.2-meter) lamps
and 75-watt, 8-foot (2.4-meter) lamps. Tubular Fluorescent fixtures and lamps are preferred for
ambient lighting in large indoor areas. In these areas, their low brightness creates less direct
glare than incandescent bulbs. Circular tube-type fluorescent lamps are called circline lamps.
They are commonly used for portable task lighting.
POSTLAB QUESTIONS
1.
What is meant by PV cell?
………………………………………………………………………………………………
………………………………………………………………………………………………
2.
Explain the working of PV cell.
………………………………………………………………………………………………
………………………………………………………………………………………………
3.
Write the advantages and disadvantages of CFL
………………………………………………………………………………………………
………………………………………………………………………………………………
4.
List the merits and demerits of PV cell.
………………………………………………………………………………………………
………………………………………………………………………………………………
5.
What will happen if DC supply is given to transformer?
………………………………………………………………………………………………
………………………………………………………………………………………………
6.
Mention the types of Induction motor.
………………………………………………………………………………………………
………………………………………………………………………………………………
7.
Name few applications LED and CFL.
………………………………………………………………………………………………
………………………………………………………………………………………………
Result:
Thus the various electrical gadgets are studied successfully.
SRM UNIVERSITY
FACULTY OF ENGINEERING AND TECHNOLOGY
DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINEERING
Evaluation Sheet
Program Name
:
Semester
:
Year
:
Name
:
Reg. No.
:
S.No.
B.Tech in Electrical and Electronics Engineering
Marks Split Up
Marks Allotted
1
Attendance
5
2
Preparation of Observation
5
3
Pre-lab
5
4
In lab Performance
10
5
Post lab
5
Total
Marks Obtained
30
Staff Signature
PRELAB QUESTIONS
1.
What is a choke?
………………………………………………………………………………………………
………………………………………………………………………………………………
2.
Where is choke used?
………………………………………………………………………………………………
………………………………………………………………………………………………
3.
Explain the detailed design of choke.
………………………………………………………………………………………………
………………………………………………………………………………………………
4.
Mention few applications of choke
………………………………………………………………………………………………
………………………………………………………………………………………………
5.
Explain the difference between core and shell type transformer
………………………………………………………………………………………………
………………………………………………………………………………………………
Date:
Experiment : 8
ASSEMBLY OF CHOKE OR SMALL
TRANSFORMER
Aim:
I.
To wind the single phase 230V/12V-0-12V, 3A shell type transformer
II.
To check the continuity and operation without vibration.
III.
To measure the rated voltage and rated current on full load in secondary winding.
Related Information
A transformer is a static device which transforms power from one circuit to another circuit at the
same frequency. It consists of two coil windings on a core made of magnetic material. AC
voltage is applied to one of the coils is called the primary coil. The other coil, from which output
is taken, is known as the secondary coil.
The relation between primary and secondary voltage (V1,V2); currents (I1,I2), number of
turns (N1,N2) respectively, is given by,
𝑉2 𝐼1 𝑁2
= =
𝑉1 𝐼2 𝑁1
𝑁
The ratio of 𝑁2 is known as transformation ratio K. If the secondary voltage (V2), is more
1
than the primary voltage (V1), then it is know as a step-up transformer. If the secondary voltage
is less than the primary voltage, then it is called a step-down transformer.
Core
AC supply voltage is applied to the primary winding; therefore, the flux flowing through the core
is alternating. To reduce the eddy current loss, the core is made of lamination. The thickness of
laminations or stamping varies from 0.35mm. To 0.55 mm. The laminations are insulated from
each other by the thin coat of insulating varnish. For good magnetic characteristics, cold rolled
silicon steel is used. Silicon content may be of the order of 3 or 4%.
There are two types of transformer, from the construction point of view.
Shell Type
In this type, the iron core surrounds the winding, as shown in fig.1.3 of (a) and (b) various types
of laminations and stampings are shown in figs.1.4 and 1.6. In figs. 1.4(a) and (b) two L-shaped
laminations are shown, indicating their mode of placement in the alternate layers. They are
placed together to give the rectangular lamination of core. The complete laminated core consists
of rectangular laminations placed alternately, one over the other as shown in fig.1.4(c), so that
the joints are staggered. The joints are staggered to avoid a continuous air gap which increases
the magnetizing current.
Further, if the joints are not staggered, the core will have less
mechanical strength and there would be an undue humming noise during operation.
The core could also be assembled out of U and T types of laminations as shown in fig.1.5
(a) and (b). The L and U-T laminations are generally used for the core type transformer. For
making the shell type transformer, generally the combination of U and T laminations is used, as
shown in figs.1.6(a) and (b).
Windings
In the case of small transformers, coils are usually would with round wire in the form of a
bobbin, in the same ways as cotton thread wound on a spool.
For small transformers of low voltage such as 230V, about 5 to 8 turns per volt may be
taken for primary winding, depending on the size of the transformer. Secondary number of turns
can be obtained by the relationship.
𝑁2 =
𝑉2
× 𝑁1
𝑉1
The primary current can be calculated with the help of the given volt-ampere rating of the
transformer.
Primary current I1 = Volt-ampere rating / V1
Secondary current I2 can be calculated from the relation:
𝐼2 =
𝑁2
× 𝐼1
𝑁1
The area of the cross-section of the winding conductor depends upon the current.
Normally, the size of the primary and secondary conductors will be different. Top select the
cross sectional size of the winding, conductor tables of the manufactures may be consulted.
Normally, the current density of 3 amperes per sq.mm. may be assumed for determining the size
of the conductor.
Equipment and Materials

Stampings/laminations

Malinex insulating sheet

Thin insulating paper

Plastic or Bakelite former

Small bolts and nuts for clamping stampings

Super enameled copper winding wire

Cotton and empire tapes

Coil winding machine
Calculations
For Primary Winding
No. of turns per volt
=
6 turns
No. of turns per 230V
=
230 x 6
=
1380 turns
=
3 Amps/sq.mm
Conductors Size
Amps per sq.mm
As per the table shown in text book
The size of the conductor
=
18 SWG is preferable.
No. of turns per volt
=
6 turns
No. of turns per 12 volt
=
12 x 6 = 72 turns
For Secondary Winding
Conductor Size
𝑁
Secondary current 𝐼2 = 𝑁2 × 𝐼1
1
72
= 1380 × 3 = 0.15652𝐴
As per the table shown in the text book,
𝐼
The size of the conductor 𝑁2 = 𝐼2 × 𝑁1
1
=
0.1562
3
× 1 = 0.0.152𝐴 = 32𝑆𝑊𝐺
Procedure
1. Select the size of the core and the type of the stamping (i.e.) for the shell type
transformer, the combination of „E‟ and „I‟
2. Select the suitable size of the conductor for windings, as explained above.
3. Select / make a transformer of suitable size.
4. Wrap the transformer with malinex insulation sheet.
5. Wind the primary winding or the transformer preferably with the help of winding
machine.
6. After every 2 or 3 layers of primary winding, use a layer of thin insulating paper.
7. After completing the primary winding, warp with malinex sheet.
8. Wind the secondary turns.
9. Bring out taps at suitable number of turns for 12-0-12 volts.
10. Wrap with empire or cotton tape for insulation and mechanical protection.
11. Assemble the core with winding as shown in the figures
12. Clamp / bolt the core.
Precaution
While winding, the enamel wire should not come into contact with sharp metallic edges.
Voltages (Volts)
Winding
Designed value
Primary
Secondary
Actual measured
value
No. of
turns
Current
(Amps)
Size of
wire (mm)
Result:
Thus the construction of transformer was completed and tested.
POSTLAB QUESTIONS
1.
Explain the various losses in transformer?
………………………………………………………………………………………………
………………………………………………………………………………………………
2.
Why the core of a transformer in laminated?
………………………………………………………………………………………………
………………………………………………………………………………………………
3.
What are the various parts of a transformer?
………………………………………………………………………………………………
………………………………………………………………………………………………
4.
Which winding should be wound first HV or LV? Why?
………………………………………………………………………………………………
………………………………………………………………………………………………
5.
What is meant by SWG?
………………………………………………………………………………………………
………………………………………………………………………………………………