MGM’s Jawaharlal Nehru Engineering College

Aurangabad

Laboratory Manual

Electrical Engineering Materials

For

Second Year (EEP) Students

Manual made by

Prof. S. B. Ghodke Prof. C.B. Ingole

Author JNEC, Aurangabad.

FORWARD

It is my great pleasure to present this laboratory manual for second year Electrical, electronics & Power engineering students for the subject of Electrical Engineering

Materials. Keeping in view the vast coverage required for visualization of concepts of Electrical Engineering Materials with simple language.

As a student, many of you may be wondering with some of the questions in your

mind regarding the subject and exactly what has been tried is to answer through this manual.

Faculty members are also advised that covering these aspects in initial stage itself, will greatly relived them in future as much of the load will be taken care by the

enthusiasm energies of the students once they are conceptually clear.

HOD (EEP)

LABORATORY MANNUAL CONTENTS

This manual is intended for the second year students of Electrical, electronics & Power engineering branch in the subject of Electrical Engineering Materials. This manual typically contains practical/Lab Sessions related electrical Engineering

materials covering various aspects related the subject to enhance understanding.

Although, as per the syllabus, only descriptive treatment is prescribed, we have made the efforts to cover various aspects of electrical machine subject covering

types of different electrical Engineering Materials & their characteristics and Applications will be complete in itself to make it meaningful, elaborative understandable concepts and conceptual visualization.

Students are advised to thoroughly go through this manual rather than only topics mentioned in the syllabus as practical aspects are the key to understanding and conceptual visualization of theoretical aspects covered in the books.

Good Luck for your Enjoyable Laboratory Sessions

Prof. S.B. Ghodke

Prof. C.B. Ingole

SUBJECT INDEX

1.Do’s and Don’ts

2. Lab exercise:

1) To Measure Electric strength of solid Insulating Materials.

2) To Measure Electric strength of Liquid Insulating Materials.

3) To Measure Electric strength of gaseous Insulating Materials.

4) To Measure KVAR capacity of Power Capacitor.

5) To Measure Resistivity of high Resistive Alloys.

6) To Understand the Principle of Thermocouple & to obtain the Characteristics of Different

thermocouples.

7) To study the Hysteresis loop of ferromagnetic materials.

8) Measurement of insulation resistance using megger.

3. Quiz on the subject

4. Conduction of Viva-Voce Examination

5. Evaluation and Marking Systems

DOs and DON’T DOs in Laboratory: 1. Understand the equipment to be tested and apparatus to be used.

2. Select proper type (i.e. A. c. or D. C.) and range of meters.

3. Do not touch the live terminals.

4. Use suitable wires (type and size).

5. All the connection should be tight.

1. Do not leave loose wires (i.e. wires not connected).

2. Get the connection checked before switching ‘ON’ the supply.

3. Never exceed the permissible values of current, voltage, and / or speed of any machine, apparatus,

wire, load, etc.

4. Switch ON or OFF the load gradually and not suddenly.

5. Strictly observe the instructions given by the teacher/Lab Instructor

Instruction for Laboratory Teachers:

1. Submission related to whatever lab work has been completed should be done during the next lab

session. The immediate arrangements for printouts related to submission on the day of practical

assignments.

2. Students should be taught for taking the observations /readings of different measuring instruments

under the able observation of lab teacher.

3. The promptness of submission should be encouraged by way of marking and evaluation patterns that

will benefit the sincere students.

2. Lab Exercises: [Purpose of this exercise is to introduce the students to different Electrical Engineering Materials.]

Exercise No1: (2 Hours) – 1 Practical

To Measure Electric strength of solid Insulating Materials.

AIM: To Measure Electric strength of solid Insulating Materials.

APPARATUS:

1) Test cell For Solid Breakdown.

2) Single Ph 230v 50 Hz AC supply.

3) MCB

4) High Voltage Transformer

THEORY:

1. Which is the basic Breakdown Mechanism in solid dielectric materials?

2. Which are the different factors upon which the breakdown strength depends?

3. What is the need of High voltage transformer?

PROCEDURE:

1) Ensure that the oil level should be high enough so that both electrodes completely immersed

in the oil.

2) Ensure that there is physical contact of H.V. Electrode with solid insulating material.

3) Ensure that there is no sharp point at the point of connection between H.V. bushing & H.V.

electrode of the test cell set up.

4) Ensure that the test cell is properly connected to the ground.

5) Gradually increase the voltage at appropriate rate of 2KV/sec. note down the exact value of

break down voltage.

OSERVATION TABLE:

Sr. No. Solid

Dielectric

Break Down

Voltage(KV)

Thickness(mm) Breakdown

strength(KV/mm)

1.

2.

3.

4.

5.

Result: The Breakdown strength of solid insulating materials is…………….. KV/mm

Exercise No2: ( 2 Hours) – 1 Practical

To Measure Dielectric strength of Liquid Insulating Materials.

AIM: To Measure Dielectric strength of Liquid Insulating Materials.

.

APPARATUS:

1 Test cell For Liquid Breakdown.

2 Single Ph 230v 50hz AC supply.

3 MCB

4 High Voltage Transformer

THEORY:

1. Which is the different theory for liquid breakdown?

2. Which are the different factors upon which the breakdown strength depends?

3. What is the effect of gap distance upon break down strength of oil?

PROCEDURE:

1 Ensure that the oil level should be high enough so that both electrodes completely immersed

in the oil.

2 Apply high voltage to HV terminal of test cell.

3 Ensure that the test cell is properly connected to the ground.

4 Gradually increase the voltage at appropriate rate of 2KV/sec. note down the exact value of

break down voltage.

OSERVATION TABLE:

Gap between the electrodes is 2.5mm

Sr. No. Liquid

Dielectric

Break Down

Voltage(KV)

Breakdown

strength(KV/mm)

Mean

dielectric

Strengh

1.

2.

3.

4.

5.

Result: The Breakdown strength of Liquid insulating materials is…………….. KV/mm

Conclusion:

- Break down strength of oil increases with increase in gap distance between electrodes. Impurities such as gas bubbles, solid fibrous particles reduce the breakdown strength of oil.

Exercise No3: ( 2 Hours) – 1 Practical

To Measure Dielectric strength of Gaseous Insulating Materials.

AIM: To Measure Dielectric strength of gaseous Insulating Materials.

.

APPARATUS:

1 Test cell for gaseous Breakdown. sphere gap unit)

2 Single Ph 230v 50 Hz AC supply.

3 MCB

4 High Voltage Transformer

THEORY:

1. Which is the different mechanism for breakdown in gases?

2. Which are the different factors upon which the breakdown strength depends?

3. What is the effect of gap distance upon break down strength of gases?

PROCEDURE:

1) Connect HV terminal of transformer to the upper sphere of sphere gap unit& connect earth

terminal corresponding to lower terminal.

2 Apply high voltage to Upper terminal.

3 Here the hissing noise due to ionization of air. At perticuler voltage depending on

atmospheric condition there appears sparks that i.e. breakdown occurs between two

spheres. Note this voltage

4 Repeat this procedure & note down the readings.

OSERVATION TABLE:

Gap between the electrodes is 2.5mm

Sr. No. Gap between spheres in mm Dielectric strength

(KV/mm)

1.

2.

3.

4.

5.

Result: The Breakdown strength of gases insulating materials is…………….. KV/mm

Exercise No4: ( 2 Hours) – 1 Practical

To Measure KVAR capacity of Power Capacitor.

AIM- To Measure KVAR capacity of Power Capacitor.

APPARATUS-

1) 3Ph AC Supply.

2) AC Ammeter……………………..01 No.

3) AC Voltmeter…………………01 No.

4) Autotransformer ………..01 No.

5) Capacitor Bank………………01 No.

THEORY:

1. Explain the different test carried out on Power capacitors?

2. Write the formula for KVAR capacity?

3. State the industrial Applications Power capacitors?

PROCEDURE

1) Make the connection as per circuit diagram.

2) Connect the Capacitor Bank in Delta, as shown in circuit diagram.

3) Give the supply to capacitor bank through Auto transformer.

4) Increase the voltage gradually through autotransformer.

5) Take the reading of Ammeter & voltmeter.

6) Calculate the KVAR capacity of capacitor by using the formula.

SAMPLE CALCULATION-

KVAR capacity =√3*Vl *Il* Sin ɸ*10^-3

OBSERVATION TABLE:

Sr. No. Line Voltage Vl (Volt) Line current Il (Amp)

1.

2.

3.

4.

5.

CONCLUSION-

Exercise No5: ( 2 Hours) – 1 Practical

To Measure Resistivity of high Resistive Alloys AIM: Resistivity of high Resistive Alloys To Measure.

APPARATUS : -

1. Variable DC power supply

2. DC voltmeter

3. DC Ammeter

4. High resistive material such as nicrome, tungsten etc

THEORY:

1. What is the significance of resistivity of the material?

2. Which are the different parameters affecting the resistivity of material?

3. State the different applications of high resistive alloys?

PROCEDURE :

1) Measure the gauge of given specimen with the help of SWG.& note down the diameter & area

from given table

2) Measure the length of given specimen with the help of measuring tape.

3) Make the connection as shown in diag.

4) Switch on the DC power supply with suitable voltage range

5) Note down the readings of voltmeter &ammeter.

6) Select another suitable voltage range& note down the reading of voltage & current

7) Calculate R for each specimen using ohms & take the mean of these values to calculate Rmean.

8) Reapt the same procedure for other specian.

OBSERVATIONS:

Specimen V volts I amp R ohm Rmean ohm

Nicrome 1.

2.

3.

1.

2.

3.

R1=

R2=

R3=

Maganim 1.

2.

3.

1.

2.

3.

R1=

R2=

R3=

Tungsten 1.

2.

3.

1.

2.

3.

R1=

R2=

R3=

Sample calculation:

Resistivity =Rmean*A/L

Result: Resistivity of the material is ………..Ohm.m

CONCLUSION:

Exercise No6: ( 2 Hours) – 1 Practical

To Understand the Principle of Thermocouple & to obtain the Characteristics of Different thermocouples.

AIM: To Understand the Principle of Thermocouple & to obtain the Characteristics of Different

thermocouples

APPARATUS: -

1. Electric Hot plate

2. Vessel

3. Thermometer

4. Thermocouple

5. DC voltmeter

THEORY

1) What is the working principle of thermocouple?

2) State the Industrial Applications of thermocouple?

3) Explain different types of thermocouples?

PROCEDURE:

1) Make the connections of two terminals of thermocouple to the volt meter as shown in fig.

2) The volt meter should have mili voltmeter range.

3) Keeps the stainless steel vessel containing water on the electric hot plate.

4) Dip the thermocouple & thermometer in vessel.

5) Switch on the supply of electric hot plate & allow the water in vessel to boil up to its boiling

point.

6) Note down the reading of temp. of water with the help of thermometer & corresponding

readings of voltmeter.

OBSERVATIONS:

Sr No. Temp. in °C Reading of Digital multimeter in mili volt

Thermocouple1 Thermocouple2

1 -

2

3

4

Conclusion:

Exercise No7: ( 2 Hours) – 1 Practical

To study the Hysteresis loop of ferromagnetic materials.

AIM: To study the Hysteresis loop of ferromagnetic materials.

THEORY:

Ferromagnetism is the basic mechanism by which certain materials (such as iron)

form permanent magnets, or are attracted to magnets. In physics, several different types

of magnetism are distinguished. Ferromagnetism (including ferrimagnetism) is the strongest

type; it is the only type that creates forces strong enough to be felt, and is responsible for

the common phenomena of magnetism encountered in everyday life. Other substances respond

weakly to magnetic fields with two other types of

magnetism, paramagnetism and diamagnetism, but the forces are so weak that they can only be

detected by sensitive instruments in a laboratory. An everyday example of ferromagnetism is

a refrigerator magnet used to hold notes on a refrigerator door. The attraction between a

magnet and ferromagnetic material is "the quality of magnetism first apparent to the ancient

world, and to us today".

Permanent magnets (materials that can be magnetized by an external magnetic field and

remain magnetized after the external field is removed) are either ferromagnetic or

ferrimagnetic, as are other materials that are noticeably attracted to them. Only a few

substances are ferromagnetic. The common ones are iron, nickel, cobalt and most of their

alloys, some compounds of rare earth metals, and a few naturally-occurring minerals such

as lodestone.

Ferromagnetism is very important in industry and modern technology, and is the basis for many

electrical and electromechanical devices such as electromagnets, electric

motors, generators, transformers, and magnetic storage such as tape recorders, and hard

disks.

The most important parameters of the ferromagnetic material constitute its magnetic

hysteresis loop.

Hysteresis is the dependence of the output of a system not only on its current input, but also

on its history of past inputs. The dependence arises because the history affects the value of

an internal state. To predict its future outputs, either its internal state or its history must be

known. If a given input alternately increases and decreases, a typical mark of hysteresis is

that the output forms a loop as in the figure.

Such loops may occur purely because of a dynamic lag between input and output. This effect

disappears as the input changes more slowly. This effect meets the description of hysteresis

given above, but is often referred to as rate-dependent hysteresis to distinguish it from

hysteresis with a more durable memory effect.

Hysteresis occurs in ferromagnetic materials and ferroelectric materials, as well as in

the deformation of some materials (such as rubber bands and shape-memory alloys) in

response to a varying force. In natural systems hysteresis is often associated with irreversible

thermodynamic change. Many artificial systems are designed to have hysteresis: for example,

in thermostats and Schmitt triggers, hysteresis is used to avoid unwanted rapid switching.

Hysteresis has been identified in many other fields, including economics and biology.

The phenomenon of hysteresis in ferromagnetic materials is the result of two effects:

rotation of magnetization and changes in size or number of magnetic domains. In general, the

magnetization varies (in direction but not magnitude) across a magnet, but in sufficiently small

magnets, it does not. In these single-domain magnets, the magnetization responds to a

magnetic field by rotating. Single-domain magnets are used wherever a strong, stable

magnetization is needed (for example, magnetic recording).

Larger magnets are divided into regions called domains. Across each domain, the magnetization

does not vary; but between domains are relatively thin domain walls in which the direction of

magnetization rotates from the direction of one domain to another. If the magnetic field

changes, the walls move, changing the relative sizes of the domains. Because the domains are

not magnetized in the same direction, the magnetic moment per unit volume is smaller than it

would be in a single-domain magnet; but domain walls involve rotation of only a small part of the

magnetization, so it is much easier to change the magnetic moment. The magnetization can also

change by addition or subtraction of domains .

There are a great variety of applications of the hysteresis in ferromagnets. Many of these

make use of their ability to retain a memory, for example magnetic tape, hard disks, and credit

cards. In these applications, hard magnets (high coercivity) like iron are desirable so the

memory is not easily erased.

Soft magnets (low coercivity) are used as cores in electromagnets. The nonlinear response of

the magnetic moment to a magnetic field boosts the response of the coil wrapped around it.

The low coercivity reduces that energy loss associated with hysteresis.

Exercise No 8: ( 2 Hours) – 1 Practical

Measurement of insultion resistence.

AIM: Direct measurement of insulation resistance of i) Complete installation

ii) between conductors

Apparatus: Megger.

.

Procedure:

Part1:

1. Switch off the supply of the circuit.

2. Put all fuse links and lamps in the position.

3. Turn on all switches

4. Short the live and neutral wire connect it to the line terminal of the megger

5. Connect earth terminal of megger to either earth continuity conductor or earth electrode

6. Measure the insulation resistance

The value must not be less than 50Mohm/no. of outlets (points switches)

Part 2:

1. Switch off the main supply of the circuit.

2. Remove all the lamps and electric appliances from holders and plugs

3. Turn on all the switches

4. Connect line terminal of megger to neutral terminal of circuit

The vallule must not be less than 50Mohm/no. of outlets (points+switches).

Conclusion:

The value of insulation resistance of complete installation is…………ohm

The value of insulation resistance Between the conductor is…………ohm

3. Quiz on the subject:

1. Define loss tangent?

2. Explain the dielectric loss?

3. Define dielectric strength? Dielectric constant?

4. What is difference between Dielectric and insulators?

5. Enlist the Dielectric materials and insulating materials.

6. What is mean by polarization of dielectric?

7. Enlist the liquid and gaseous insulating materials?

8. Classify the solid, liquid and gaseous insulating materials?

8. State the different factors affecting the breakdown strength of solid, liquid and gaseous insulating

materials?

9. Define the breakdown voltage and breakdown strength?

10. What do you understand by 1) contaminated liquid 2) technically pure liquid 3) highly purified liquid?

11. State different properties of ferromagnetic materials?

12. Define hysteresis loss and query temp for ferromagnetic materials

13. Enlist the most commonly used thermocouples in industries?

14. State the see becks effect.

15. state the different factors affecting the resistivity of materials.

16. Enlist the different test to measure the KVAR capacity of he capacitor.

17. What is the use of megger?

4. Conduction of Viva-Voce Examinations:

Teacher should oral exams of the students with full preparation. Normally, the objective questions with

guess are to be avoided. To make it meaningful, the questions should be such that depth of the students

in the subject is tested Oral examinations are to be conducted in co-cordial environment amongst the

teachers taking the examination. Teachers taking such examinations should not have ill thoughts about

each other and courtesies should be offered to each other in case of difference of opinion, which should

be critically suppressed in front of the students.

5. Evaluation and marking system:

Basic honesty in the evaluation and marking system is absolutely essential and in the process impartial

nature of the evaluator is required in the examination system to become popular amongst the students.

It is a wrong approach or concept to award the students by way of easy marking to get cheap popularity

among the students to which they do not deserve. It is a primary responsibility of the teacher that

right students who are really putting up lot of hard work with right kind of intelligence are correctly

awarded.

The marking patterns should be justifiable to the students without any ambiguity and teacher should

see that students are faced with unjust circumstances.