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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


SRM University



India

Dr.C.SUBRAMANI

Assistant Professor


SRM University



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 Supply-

Voltage 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 : B.Tech in Electrical and Electronics Engineering

Semester :

Year :

Name :

Reg. No. :

S.No. Marks Split Up Marks Allotted Marks Obtained

1 Attendance 5

2 Preparation of Observation 5

3 Pre-lab 5

4 In lab Performance 10

5 Post lab 5

Total 30

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. Study the given wiring diagram.

2. Make the location points for energy meter, main witch box, Switchboard, and lamp.

3. The lines for wiring on the wooden board.

4. Place the wires along with the line and fix.

5. Fix the bulb holder, switches, socket in marked positions on the wooden board.

6. Connect the energy meter and main switch box in marked positions on the wooden board.

7. Give a supply to the wires circuit.

8. 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



Evaluation Sheet


Semester :

Year :

Name :

Reg. No. :


1 Attendance 5


3 Pre-lab 5


5 Post lab 5

Total 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) Staircase wiring

(ii) Fluorescent lamp wiring

(iii) Corridor wiring

Apparatus Required:

S.

No.

Tools

required Fluorescent

Lamp Wiring

Staircase Wiring Corridor Wiring

1 Fluorescent lamp with

fitting

Two way switches Switches Screw driver

2 Joint clips Bulb, Bulb holder Bulb, Bulb holder Hammer

3 Wires Clamps Clamps Cutting pliers

4 Screws Screws Screws Line tester

5 Switch board Ceiling rose Ceiling rose

6 Choke Switch board Switch board

7 Switches Connecting wires Connecting wires

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. Components Quantity/Range

1 Incandescent lamp 1 (230V, 40W)

2 Lamp holder 1

3 Two way switches 2 (230V, 5A)

4 Connecting wires As required

Tools Required: Wire mans tool kit – 1 No.

Direct Connection

Circuit Diagram

Tabulation

Position of Switches Condition of lamp

S1 S2

Cross Connection

Circuit Diagram

Tabulation

Position of Switches Condition of lamp

S1 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. Give the connections as per the circuit diagram.

2. Verify the connection

3. Switch on the supply

4. 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. Components Range/Type Quantity

1 Fluorescent lamp fixture 4 ft 1

2 Fluorescent lamp 40W 1

3 Choke 40W, 230V 1

4 Starter - 1

5 Connecting wires - 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. Give the connections as per the circuit diagram

2. Fix the tube holder and the choke in the tube.

3. The phase wire is connected to the choke and neutral directly to the tube.

4. Connect the starter in series with the tube.

5. 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 S2 S3 L1 L2 L3

OFF X X OFF OFF OFF

ON 1-3 1‟-3‟ ON OFF OFF

ON 1-2 1‟-3- OFF ON OFF

OFF 1-2 1‟-2‟ OFF OFF ON

Procedure:

1. Give the corrections as per the circuit diagram

2. Verify the corrections.

3. Switch on the supply

4. Verify the conditions

Result:

Thus different types wiring was completed and tested.

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



Evaluation Sheet


Semester :

Year :

Name :

Reg. No. :


1 Attendance 5


3 Pre-lab 5


5 Post lab 5

Total 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:


1 Voltmeter (0-300)V, MI type 1

2 Ammeter (0-10)A, MI type 1

3 Wattmeter 300V, 10A, UPF/LPF 1

4 Autotransformer 1KVA, 230/(0-270)V 1

5 Resistive, inductive & capacitive load - 1

6 Connecting wire - 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. Connect the circuit as shown in the circuit diagram

2. Switch on the supply and vary the auto transformer to build the rated voltage.

3. Vary the load according to current values are increases linearly for different ratings.

4. Note down the ammeter, wattmeter readings. Voltage will maintain constant.

5. After taking all the reading, bring the voltage back to minimum in the auto transformer.

6. Switch off the power supply. Remove the connections.

7. Calculate the power factor by the given formula.

Tabulation

S.No. Voltage (V) Current(A) Wattmeter Power Factor

Obs Reading Act. Reading

RC – Load

Circuit Diagram

Procedure

1. Connect the circuit as shown in the circuit diagram.


3. Observe the reading of ammeter, voltmeter and wattmeter for various load values.

4. Vary the load according to current readings. Voltage is maintain constant.


6. Switch off the power supply.

7. Calculate the power factor by the given formula

Tabulation



RC-Load

Circuit Diagram

Procedure:

1. Connect the circuit as shown in the circuit diagram


3. Observe the reading of ammeter, voltmeter and wattmeter for various load values.

4. Vary the load according to current readings. Voltage is maintain constant.



7. Calculate the power factor by the given formula.

Tabulation



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



Evaluation Sheet


Semester :

Year :

Name :

Reg. No. :


1 Attendance 5


3 Pre-lab 5


5 Post lab 5

Total 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.

………………………………………………………………………………………………

………………………………………………………………………………………………


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:


1 Voltmeter (0-300)V, MI type 1

2 Ammeter (0-10)A, MI type 1

3 Wattmeter 300V, 10A, UPF/600V,

10A, UPF

½

4 Resistive load 1 / 3 1

5 Energy meter 1 / 3 1

6 Connecting wire - 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)

𝐸𝑖100

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.


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



Evaluation Sheet


Semester :

Year :

Name :

Reg. No. :


1 Attendance 5


3 Pre-lab 5


5 Post lab 5

Total 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.

………………………………………………………………………………………………

………………………………………………………………………………………………


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-

Insulation failure

Accidental contact

Lightning strike

II. 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. Low earth resistance. Highly conductive. Carries high peak current repeatedly.

5. No corrosion. Eco Friendly.

6. Long Life.

7. Easy Installation.

VI. Factors Affecting and Value of Earth Electrode Resistance

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

VII. 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:


1 Megger earth tester – 1 - Hammer – 1

2 Electrode under test – 1 - Glove- 1 pair

3 Electrodes – 2 - -

4 Copper wires – As required - -

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 Resistance

In feet 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



Evaluation Sheet


Semester :

Year :

Name :

Reg. No. :


1 Attendance 5


3 Pre-lab 5


5 Post lab 5

Total 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?

………………………………………………………………………………………………

………………………………………………………………………………………………


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. Appliance Defects Remedies

1 Electric iron box press Does‟t work after supply is on There must be a damage in

wire or there is open circuit.

Check the thermostat for

open circuit

Check the heating element

continuity.

Shock on body Check the continuity of earth

wire to body. If it does not

get continuity dismantle the

cover and connect earth wire

properly.

Iron box has no enough temperature

when knob is placed at one position

Check the heating element.

Adjust the screw below the

knob to produce enough

temperature.

2 Celling fan Doesn‟t work after supply is on Check for switch socket,

capacitor

Wobbling Make sure that all screws and

bolts are tightened

The fan blades aren‟t warped

or damaged

Humming or buzzing Make sure there are no loose

parts that are knocking

together

Airflow Air flow will be less

noticeable if the fan is in

updraft mode

3 Electric heater Shock due to short circuit Remove the short circuit

Troubleshooting Chart

(i) Electric Iron Box

Trouble Possible Causes Corrective Action To Be Taken

No beat No power at outlet Check outlet for power

Defective cord or plug Repair or replace

Loose terminal connections Check and tighten the terminals

Broken lead in iron Repair or replace lead

Loose thermostat control knob Clean and tighten

Defective thermostat Replace thermostat

Defective heater element replace the element if separate

If cast in, replace sole-plate assembly Open terminal fuse replace

Insufficient heat Low line voltage Check voltage at outlet

Incorrect thermostat setting Adjust and recalibrate thermostat

Excessive heat Incorrect thermostat setting Adjust and recalibrate thermostat or

replace

Defective thermostat Replace thermostat

Blisters on sole-plate Excessive heat First repair the thermostat control.

Then replace or repair the sole-plate

Tears Clothes Rough spot, nick, scratch, burn on sole-

plate

Remove these sports with fine emergy

and polish the area with buff.

Iron cannot be turned off Thermostat switch contacts are welded

together

Check the thermostat switch contact.

Open them by force. The contact

points should be in open condition at

off position of the control knob

Power cord Loose connection Clean and tighten

Broken wire Repair or replace

Sticks to clothes Dirty sole-plate Clean

Excessive starch in clothes Iron at a lower temperature. Use less

starch next time.

Wrong setting of the thermostat knob Set the knob to correct temperature

Iron too hot for fabric being ironed Lower the thermostat setting

Iron gives shock Disconnected earth connection Check earth connection and connect

properly

Weak insulation of heating element Check insulation resistance of heating

element; If necessary replace element

Earth continuity with common earth not

available

Check the main earth continuity and

connect properly

(ii) Water Heater

Complaints Causes Remedies

Not hot water No supply Check availability of supply at 3-pin

socket

Blown fuse Replace fuse

Open circuit Check the wiring for broken wire or

loosed connection

Heater element burnt out Check elements for burn-out

Insufficient quality of hot

water

Thermostat setting too low Check the thermostat setting. It should

be 60oC to 65

oC

Lower value of heating element Check the value of heating element

and replace

Capacity of tank is insufficient for one‟s

needs

Check the quantity of water used.

Identify if the tank capacity is too

small

Comstantly fuse blowing Grounded heating element Check the heater element for insulation

resistance and replace if necessary

Grounded lead wire Check wiring for grounds

Steam in hot water Thermostat improperly connected Check the circuit and correct any

improper connections

Thermostat contact welded together Check the thermostat for its operation

Grounded heating element Check the unit for ground

Thermostat set too high or out of

calibration

Reset thermostat

High consumption of power

leading to increased

electricity bill

Leaking faucets Replace washers in all leaking faucets

Excessively exposed hot water pipes Hot water lines should be as short as

possible

Thermostat setting too high Reset thermostat. Setting should be

60oC to 65

oC

Grounded heating element Check element for ground

Scale deposit on the heating units Dismantle the water heater and remove

the scale form the element tube gently

(iii) Mixer

Fault Possible reason Remedy

Motor is not running No voltage or low voltage Check the supply voltage with

multimeter

Either motor field or armature coil

may get open circuited

Do the continuity test. If there is

an open circuit fault, do the service

Supply voltage is correct. But

motor is not running

Overload in the jar and hence

overload protector may get tripped

Press the overload relief button and

remove some materials in the jar.

Now restart.

Motor rotates at same speed in all

speed settings

May be any short circuit in

armature or field coils

Do the continuity test. If there is

an short circuit fault, do the

service.

There may be wear and tear in the

bearings

Check and put lubricating oil at

bearings. If beat persists, replace

it.

(iii) Electric Fan

Fault Cause Remedy

Noise It is due to worn out bearings and

absence of lubricating oil or grease

The bearings must be replace if

worn out; otherwise lubricate with

proper lubricant

Humming or induction noise is due

to non-uniform air gap owing to

the displacement of rotor.

Dismantle and reassemble

properly

Low speed It is due to defective or leaky

capacitor

Replace the capacitor with one of

the same value and voltage

Low voltage applied Check the voltage and adjust it

possible

Jamming of rotor It is due to misalignment Dismantle and assemble property

after proper lubrication

Not starting Low applied voltage Check the voltage and adjust if

possible

Supply failure Check the supply points at switch

regulator ceiling rose and the

terminal of the fan

Open in winding Check for the continuity of

auxiliary and main winding

Condenser open or short Check the capacitor with a megger

Open in regulator resistor Check for open or loose contact in

the resistor or contacts

(v) 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



Evaluation Sheet


Semester :

Year :

Name :

Reg. No. :


1 Attendance 5


3 Pre-lab 5


5 Post lab 5

Total 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?

………………………………………………………………………………………………

………………………………………………………………………………………………


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 𝜑𝜔 𝜍 )𝑝ℎ𝑜 𝑠) 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

𝑁𝑠=

≠ 𝑃𝑟𝑖. 𝐶𝑜𝑖𝑙𝑠

≠ 𝑆𝑒𝑐. 𝐶𝑜𝑖𝑙=

1500

500=

3

1= 3.1

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 𝑜𝑟𝑁𝑝

𝑁𝑠=

≠ 𝑃𝑟𝑖. 𝐶𝑜𝑖𝑙𝑠

≠ 𝑆𝑒𝑐. 𝐶𝑜𝑖𝑙=

240

𝑉𝑠

∴ 𝑆𝑒𝑐. 𝑉𝑜𝑙𝑡𝑠, 𝑉𝑠 =𝑉𝑝

3=

240

3= 80 𝑣𝑜𝑙𝑡𝑠

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 sint, 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 = 𝑁𝑑𝜙

𝑑𝑡

𝐸 = 𝑁 × 𝜔 × 𝑚𝑎𝑥

× cos(𝜔𝑡)

𝐸𝑚𝑎𝑥 = 𝑁𝜔 𝑚𝑎𝑥

𝐸𝑚𝑎𝑥 =𝑁𝜔

2×

𝑚𝑎𝑥=

2𝜋

2× 𝑓 × 𝑁 ×

𝑚𝑎𝑥

∴ 𝐸𝑟𝑚𝑠 = 4.44 𝑓𝑁𝑚𝑎𝑥

Where:

𝑓 − is the flux frequency in Hertz, = 𝜔

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 cost-

effective 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 A-

type standard incandescent lamps.

The traditional tube-type fluorescent lamps are usually identified as T12 or T8 (twelve-

eighths 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



Evaluation Sheet


Semester :

Year :

Name :

Reg. No. :


1 Attendance 5


3 Pre-lab 5


5 Post lab 5

Total 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

………………………………………………………………………………………………

………………………………………………………………………………………………


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

𝑉1=

𝐼1

𝐼2=

𝑁2

𝑁1

The ratio of 𝑁2

𝑁1 is known as transformation ratio K. If the secondary voltage (V2), is more

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

𝑉1× 𝑁1

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

𝑁1× 𝐼1

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

Conductors Size

Amps per sq.mm = 3 Amps/sq.mm

As per the table shown in text book

The size of the conductor = 18 SWG is preferable.

For Secondary Winding

No. of turns per volt = 6 turns

No. of turns per 12 volt = 12 x 6 = 72 turns

Conductor Size

Secondary current 𝐼2 =𝑁2

𝑁1× 𝐼1

=72

1380× 3 = 0.15652𝐴

As per the table shown in the text book,

The size of the conductor 𝑁2 =𝐼2

𝐼1× 𝑁1

=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) No. of

turns

Current

(Amps)

Size of

wire (mm) Winding

Designed value Actual measured

value

Primary

Secondary

Result:

Thus the construction of transformer was completed and tested.

POSTLAB QUESTIONS

1. Explain the various losses in transformer?

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2. Why the core of a transformer in laminated?

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3. What are the various parts of a transformer?

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4. Which winding should be wound first HV or LV? Why?

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5. What is meant by SWG?

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