ema241t_eie301t student course guide_20150128s1_dp zikalala

FACULTY OF ENGINEERING AND THE BUILT

ENVIRONMENT

DEPARTMENT OF ELECTRICAL ENGINEERING

NAME OF COURSE

ELECTRICAL MACHINES II

NQF

LEVEL

NQF

CREDITS QUALIFICATION & SAQA ID

COURSE

CODE

6 12 Diploma in Electrical Engineering

SAQA ID No.: 49744

EMA241T /

EIE301T

COMPILED BY: Dr. CG Richards REVISED BY: Mr. AF Nnachi REVISED BY: Dr. AA Yusuff

REVISED BY: Mr. DP Zikalala

2015

STUDENT COURSE GUIDE

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©COPYRIGHT: Tshwane University of Technology

Private Bag X680 PRETORIA 0001

All rights reserved. Apart from any reasonable quotations for the purposes of research criticism or review as permitted under the Copyright Act, no part of this book may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopy and recording, without permission in writing from the publisher.

Printed and distributed by: FACULTY OF ENGINEERING AND

BUILT ENVIRONMENT Tshwane University of Technology

Private Bag X680 Pretoria

0001

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ORGANISATIONAL COMPONENT CONTENTS:

1. Welcome ................................................................................................................ 5

2. Staff ....................................................................................................................... 5

2.1 Contact Details ................................................................................................ 5

2.2 Staff availability ................................................................................................ 6

3. Requirements, resources and recommended material. ....................................... 6

3.1 Requirements for the course ............................................................................ 6

4. Code of conduct .................................................................................................. 9

4.1 Attendance ....................................................................................................... 9

4.2 Classroom behaviour ..................................................................................... 10

4.3 Responsibilities of students ........................................................................... 10

1. Overview of the course ..................................................................................... 11

1.1 Purpose of the course .................................................................................... 11

1.2 Links to other subjects ................................................................................... 11

1.3 Course outcomes ........................................................................................... 12

2. Assessment ...................................................................................................... 12

2.1 Assessment methods and criteria ................................................................. 12

2.2 Assessment rules .......................................................................................... 12

2.3 Marking system .............................................................................................. 13

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2.4 Year mark ...................................................................................................... 13

2.5 Moderation.................................................................................................. 14

2.6 Promotion requirements................................................................................. 15

3. Course content and schedule of tests and assignments ................................... 15

3.1 Course structure and schedule of tests and assignments ............................. 16

3.2 Learning outcomes and assessment criteria.................................................. 20

3.3 Generic outcomes and critical cross-field outcomes ...................................... 23

4. Glossary of terms .............................................................................................. 24

5. Assessment Records ........................................................................................ 24

5.1 Example of a class test .................................................................................. 25

5.3 Example of summative test and examination with memorandum. ................. 26

5.2 Example of a practical report ......................................................................... 43

6. Appendices ....................................................................................................... 44

6.1 Examples of mark sheets used during various assessments during the

course..................................................................................................................... 45

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SECTION A ORGANISATIONAL

COMPONENT

1. WELCOME

Welcome to Electrical Machines II. This is a semester subject which provides an introduction to

electrical machinery. It is offered via compulsory lectures over 14 weeks. The course is structured in

such a way as to provide a sound foundation for further study in Electrical Machines III and IV. Apart

from the theoretical knowledge, the students are exposed to various practical and laboratory work

allowing applying the theoretical comprehension into the practice. We trust you will enjoy the course,

and find it interesting and informative.

2. STAFF

2.1 CONTACT DETAILS

NAME CAMPUS ROOM

NO TEL NO E-MAIL

CONSULTATION

TIMES

ACADEMIC

FUNCTION

Mr. D. P.

Zikalala

Pretoria 6-262 (012) 382 5002 [email protected]

See Timetable Subject Head

& examiner

Mr. A.F.

Nnachi

Witbank

(eMalahleni)

14-

G23

(013) 653 3148

[email protected] See Timetable

Lecturer &

Examiner

mailto:[email protected]


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Mr. P Ntloko Pretoria 6-267 (012) 382 5965 [email protected]

See Timetable Technician

Mr. DR

Shongwe

Pretoria 6-261 (012) 382 5737 [email protected] See Timetable Technician

Mr. PP

Motloung

Witbank

(eMalahleni)

14-

G23

(013) 653 3148 [email protected]

See Timetable Technician

Ms. M.

Mashilo Pretoria Library

(012) 382 5371

[email protected] Always Available

Subject

Librarian

Mr. A.J.S.F. Sliep

External (Private)

N/A

(012) 565 4881 (071) 289 8893 [email protected]

Moderator

2.2 STAFF AVAILABILITY

Normally, the regular and responsible attending of the classes allows students to understand and

perform successfully in the course. However, the teaching staff is available for consultations fixed at a

timetable during the semester. Check lecturers’ timetables pasted against each lecturer’s door for

consultation times. An appointment can also be made, at least one day in advance, at any suitable time

outside of consulting hours. No students will be allowed for consultation outside consulting hours

without an appointment!

3. REQUIREMENTS, RESOURCES AND RECOMMENDED MATERIAL.

3.1 REQUIREMENTS FOR THE COURSE

3.1.1 PRESCRIBED RESOURCES

The following tables indicate what literature and other resources are essential for successful completion

of this course. The book by Stephan J Chapman is the prescribed book for the course, although

students may find the book by Theodore Wildi, B J Le Roux and BL & AK Theraja easier to understand.






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The lecturer will make reference to these books as the topics are covered. Supplementary notes for the

course will also be handed out where it is necessary. You are strongly advised to consult all the

prescribed resources.

PRESCRIBED LITERATURE

CATEGORY AUTHOR NAME PUBLISHER ISBN NO

BOOKS

Ref: 1

Stephen J. Chapman

Electrical Machinery Fundamentals, 5

th edition,

2011

McGraw Hill 007-115155-9

Ref: 2 Theodore Wildi

Electrical Machines, Drives, and Power Systems, fifth edition, 2006

Pearson/ Prentice Hall Columbus, Ohio

0-13-196918-8

Ref: 3 B. L Theraja and A.K Theraja

A textbook of electrical technology, 24

th revised

edition, 2008

S. Chand and company Ltd. New Delhi

81-219-2441-3

NOTES Lecturers’ Notes

PAPERS

OTHER PRESCRIBED RESOURCES

CATEGORY DESCRIPTION WHERE TO FIND COST LEVY

CALCULATOR Sharp DAL 506 W Bookshops ± R 250.00

COMPUTER

HARDWARE

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SOFTWARE Matlab Student Version

MathCad

EQUIPMENT

COMPONENTS

3.1.2 RECOMMENDED RESOURCES

The following recommend resources will enhance your understanding and knowledge in this course,

and you are encouraged to use the following additional resources.

RECOMMENDED RESOURCES

CATEGORY AUTHOR NAME PUBLISHER ISBN NO

1. Theodore Wildi

Electrical Machines, Drives, and Power Systems, fifth edition, 2006

Pearson/ Prentice Hall Columbus, Ohio

0-13-196918-8

2. B J LE Roux

Basic Electrical machines

Lerato

1-919747-07-9

3. B. L Theraja and A.K Theraja

A textbook of electrical technology, 24

th revised

edition, 2008

S. Chand and company Ltd. New Delhi

81-219-2441-3

NOTES

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PAPERS

RECOMMENDED ELECTRONIC MATERIAL & WEBSITES

VIDEO

CD

DVD

WEBSITES http//:myTUTor.tut.ac.za

4. CODE OF CONDUCT

Please take note of the following regulations. These regulations are in addition to the standard rules

and regulations as determined by the TUT. Please familiarise yourself with the TUT rules and

regulations as set out in the student diaries received on registration.

4.1 ATTENDANCE

Regular attendance of all the lectures is of primary importance. It is the learner’s responsibility to sign

the register each week. A minimum attendance of 75% is mandatory for all courses. In a 30 week year,

8 classes that have not been attended and for which you have not furnished a valid doctor’s letter or

other proof of extenuating circumstances, amounts to 25% absenteeism. This level of absenteeism will

lead to exclusion from the final moderation at the end of the year, which means that you will fail the

course and will have to repeat it the following year.

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4.2 CLASSROOM BEHAVIOUR

Students are required to arrive on time for lectures. Students are also required to behave in the

classroom in a way that will not distract other students’ attention from the lecture or distract the lecturer

during the lecture. The lecturer has the right to send any student out of the classroom who continues to

distract lectures or fellow students in class he/she has been warned against it.

4.2.1. USAGE OF CELL PHONES IN CLASSES

Cell phones should be kept ‘off’ during lectures, tests, examinations and consultations.

4.3 RESPONSIBILITIES OF STUDENTS

It is your responsibility to make a success of learning in this course. To this end you are encouraged to

attend class, write set tests and hand in your assignments/projects on the set due dates.

It is also your responsibility to keep up to date with course arrangements (like the time table for the

semester), changes and new information by attending class regularly and visiting the course notice

board and WebCT regularly. The lecturer will take no responsibility for any information that you missed

from any of these resources.

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SECTION B LEARNING COMPONENT

1. OVERVIEW OF THE COURSE

Modern society has adapted during the last hundred and fifty years to embrace the fruits of science.

This trend is even more pronounced in the field of electrical energy. We use it to cook our food, to keep

us warm, to keep us cool during summer and to give us light during night time.

The bulk of electrical energy is however used in the manufacturing sector. Much of the energy is used

to generate heat, where it is in competition with gas systems, think of furnaces, welders and boilers.

The most useful aspect of electricity is however the ease with which it can be transformed to

mechanical energy. This fact becomes clear when you compare the size, complexity and logistical

demands of an electrical machine and a diesel motor. The electrical machine (for the same power

rating) is smaller, less complex and does not require either a fuel tank or constant refueling.

Considering these factors it is hardly surprising to realise that nearly 53% of all electrical energy

produced in the USA is supplied to electrical machines, (The trend in South Africa is not much

different). The use of electrical machines is not however confined to industry. Most appliances in the

home depend on some form of electrical motor. Think for example about refrigerators (compressors),

PC’s (disk drive motors and fans), microwaves (turntable drives) and blow dryers.

1.1 PURPOSE OF THE COURSE

It is clear that the modern electrical engineer/technician can hardly operate without a good working

background of electrical machines. Therefore the purpose of this course in conjunction with electrical

machines III & IV is designed to give students a working knowledge of electrical machines, their

construction, operation and capabilities.

1.2 LINKS TO OTHER SUBJECTS

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Electrical Machines II is closely linked with all fundamental courses of the Power Engineering field. This

course will build upon previous knowledge and some competency is required to understand the

contents of this subject. Students will be expected to have a sound knowledge of Electrical Engineering

I and II and mathematics. Knowledge and skills gained in this subject shall be useful in higher level

subjects such as Electrical Machines III & IV. Skills learned from the mentioned courses which will be

required are:

Understanding of voltage, current, resistivity and their functional relationships ohm’s law.

Understanding of electrical systems.

Understanding of electrical power in both dc and ac systems.

Understanding of complex numbers.

Understanding of three-phase systems.

Thorough knowledge of electrical theorems.

Understanding of phasor diagrams.

Understanding of derivatives and their application in engineering Calculus.

1.3 COURSE OUTCOMES

Students credited with this course should be able to:

Describe and analyse the basic concept of electromagnetism and its application to relays, contactors and single phase transformers

Describe the principle of operation, construction, types, fundamental theory, testing / performance evaluation and analysis of the single-phase transformers.

Analyze the basic concepts, fundamental theories relating to the construction and operation of DC Machines

2. ASSESSMENT

2.1 ASSESSMENT METHODS AND CRITERIA

Assessment of this course will include written tests and assignments, as indicated in the schedule

under Section A. Various assessment methods applied will focus on criteria that will enable the

lecturers to determine whether you have achieved the learning outcomes. The assessment criteria

relevant to each learning outcome are detailed in Section 3.

2.2 ASSESSMENT RULES

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The general rules of TUT regarding assessment apply. You are advised to familiarise yourself with

these rules, as they are applied stringently. It is important for the learner to note that each test or

assignment is very crucial in that his / her year mark (predicate mark) will be formed by the sum of all

tests, assignments, and practical projects.

Should the learner miss one of the official tests, a second chance or sick test shall be given on

condition that the learner furnishes us (lecturers) with a sick note from a doctor confirming his / her

illness. This must be done as soon as possible. Marks will be deducted from students who miss

assignment deadlines.

The contact times, contact details and office numbers for each lecturer is given above in section A.

2.3 MARKING SYSTEM

The learner shall be awarded for his / her good work when it comes to assessments (tests,

assignments, practical and projects). For group work the same amount of points / marks will be

awarded to each member of each group. This is only true for both assignments and practical projects

only.

When it comes to formarive and summative assessments, the learner will be evaluated individually. The

learner must read the instructions carefully and make sure he / she understand exactly what is

expected of them. The leaner must show all his / her workings and he / she should write neatly. Both

positive and negative marking are applicable depending on the type of question asked.

2.4 YEAR MARK

Practicals and tests will contribute to the assessment process. Two formal tests and the practical mark

will complete the final year mark of each student. A sick test will be offered towards the end of the

semester. Individual practical tests will be done at the end of the semester. Each student will be asked

to do one of the practicals done during the semester. The work will be assessed by the lecturer. The

class test component will take the form of either five class tests or two class tests and a task. Any

missed class test will imply a mark of 0%.

Please note this subject is an examination subject, implying all the examination regulations as

published by the TUT applies. Each learner must qualify for exam admission and the exam mark and

year mark will contribute equally to the final mark.

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A minimum mark of 40 % is required by the learner to qualify or gain entry to sit and write the final

examination. The predicate mark is calculated as shown in Table one below.

The following table gives the calculation of the year mark.

Table 1: Year Mark Calculation

Evaluation 1 Class Tests/Assignments 10% -

Evaluation 2 Semester Test 1 & Semester Test 2 60% 40% sub-minimum

Evaluation 3 Project/Practical Work 30% 50% sub-minimum

Predicate Mark 100% 40% sub-minimum

Predicate marks are put on the faculty notice boards. If you have queries about your mark, you must

immediately consult your course lecturer (contact details are given above), before predicate

day. Once the predicate mark is entered on TUT’s mainframe computer, the mark cannot be changed.

NB: See Annexure D: DEE Rules Volume 1.

2.5 MODERATION

At least 50% of the total assessments in Electrical Machines II are subject to external moderation. The

name and the contact details of the appointed moderator are given in Section A. The moderation

process is according to the applicable rules and practices for the institution. The purpose of moderation

is to ensure that justice has been done when marking and awarding marks to the learner and also that

the assessment is at right standard and level as reflected in the study guide and prospectus.

The moderate enjoys the right to change (up or lower) all or some of marks that the lecturer has

awarded to each learner. He can order re-marking of all the scripts when he feels that marking and

allocation of marks were not done properly and satisfactorily. The learner can be assured that whatever

marks that appear in his / her academic record are true and correct. However, the student / learner

reserve the right to apply for re-marking of their scripts in case they are not satisfied by their results.

There is a certain fee that the learner must pay during his / her application for re-marking.

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2.6 PROMOTION REQUIREMENTS

A minimum pass mark of 50 % is needed and is enough for the learner to pass the subject or to be

promoted to the next level and be able to do the other subjects whose pre-requisites is Electrical

Machines III. Such subjects are highlighted in section B paragraph 1.2.

The 50 % is obtained by summing up the predicate mark with the final examination mark and then

dividing the sum by two (2) to get the average or pass mark. The following equation or expression

shows how this is done:

Any final mark ranging from 45 % to 48 % will qualify the learner to sit and write the supplementary

examination / Re-Examination. Please note that the same original predicate mark still stands, i.e. the

learner must get a mark in the supplementary examination that when added to the predicate mark and

the sum divided by 2, the final pass mark is 50 % or more in order to pass the subject. The following

equation or expression shows how this is done:

Should the learner fail to obtain a final mark of 50 % or more after the supplementary examination, the

learner has to repeat the subject the next semester provided that he / she is not excluded.

3. COURSE CONTENT AND SCHEDULE OF TESTS AND

ASSIGNMENTS

This course comprises both a theory and application component. Your mastery of that theory is

assessed at regular intervals. More importantly, the application of theory is assessed through

assignments/projects.

The following table clearly indicates what you have to achieve (the learning outcomes) and how you will

be assessed (assessment criteria) to determine whether you have achieved the required knowledge

and competences.

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3.1 COURSE STRUCTURE AND SCHEDULE OF TESTS AND ASSIGNMENTS

DURATION THEME ASSIGNMENT/ TEST/PROJECT

COMPLETION DATE*

Week 1 Electro-magnetism

Magneto motive force,

magnetic flux, magnetic flux density,

Magnetic field strength

Force on current carrying conductors in a magnetic field

The right hand rule

Magnetic circuit and calculations

Week 2 Electromagnetic induction

Inductance

Factors affecting inductance of an inductor

Relays and contactors Instrument transformers

E.M.F equation of a coil

E.M.F equation of a transformer

Week 3 Transformer

Ideal transformer

Characteristics of ideal transformer

Voltage transformation ratio

Non ideal transformer

Transformer construction

Types of core and their advantages

Flux and flux leakage in a transformer

Practical 1: Transformer Tests Students will be given components with specifications for:

winding of their own transformers

carryout short circuit and open circuit test

Determine the equivalent circuit parameters, voltage regulation and efficiency.

Demonstration of transformer saturation

See Practical Guide

Experiment 1

Experiment 2

Experiment 3

Week 4 Transformer

Equivalent circuit of an ideal and a non ideal transformer

Effect of winding resistance and leakage flux

Referring resistance, reactance and impedance to different sides

Types of transformer test, with explanation (Open

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circuit and short circuit test)

How to determine the parameters of a transformer from transformer tests

Week 5 Transformer

Transformer parameters that can be determined by an open circuit test Rc(LV) and X_(LV)

Transformer loss that can be determined by an open circuit test iron core loss Po

Transformer parameters that can be determined by an short circuit test Re(HV), Xe(HV) and Ze(HV)

Transformer loss that can be determined by an short circuit test copper (Cu) loss core loss Po

Week 6 Transformer

Voltage regulation

Efficiency of transformer

Condition for maximum efficiency

The per unit system measurement

Week 7 Test Week

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Week 8 Auto transformers

Characteristic of auto transformer

Operation of auto transformers

Power distribution in auto transformer

Copper saving of auto transformer compared with a two winding transformer

Week 9 Auto transformers

Advantages of auto transformer

Disadvantages of auto transformers

Usage of auto transformers

Conversion of two winding to an auto transformers

Regulation of auto transformer

Efficiency of auto transformers

Week 10 DC Machines

Generators and Motors operation

Generation of AC voltage

Mechanical rectification

DC generator constructions

Armature reaction

Commutation-Problems and solution

DC Machines

DC generator characteristics

DC motor characteristics

See Practical guide

Experiment 4

Experiment 5

Experiment 6

Experiment 7

Week 11 DC

Equivalent circuit of a generator

Separately excited generator

Shunt excited generator

Output voltage control

Operation and equivalent circuited

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Week 12 DC Motors

Shunt, series, separately excited and compound motors

Performance and operating calculations

Speed control

Week 13 Test 2

Week 14 Performance Characteristics of DC Machines

Performance for different configuration Performance and operating calculation

DC generator characteristics

DC motor characteristics

Week 15 Revision

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Week 14 Revision

*Please note that test dates may be moved on short notice where circumstances require such

change. Also, take particular note of the rules regarding tests and assignments in section B, 2.6

3.2 LEARNING OUTCOMES AND ASSESSMENT CRITERIA

The following tables clearly indicate what you have to achieve (the learning outcomes) and how you will

be assessed (assessment criteria) to determine whether you have achieved the required knowledge

and competences:

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LEARNING OUTCOME 1:

After successful completion of this chapter, the student should be able to describe and analyse the

basic concept of electromagnetism and its application to relays, contactors and single phase

transformers.

Assessment criteria Assessment method

Magnetism

Describe basic principles of magnetism, magnetic flux and lines of flux.

Sketches of magnetic filed a conductor and a solenoid

Calculate forces that exist on a current carrying conductor placed in a magnetic field

Electromagnetic induction, faradays law, e.m.f

Magnetic circuit calculations and application

Principles of operation, application, types, circuit diagram and wiring of Relays and contactors (this will be given to students as an assignment)

Relays and Contactors

Principles of operation, circuit diagram,

types and application (This will be

given to students as assignments 1)

1. SELF ASSESSMENT EXERCISES As per lecturer’s instruction and examples from the text books prescribed in section 3.2.1. above 2. CLASS TESTS According to schedule in Section A and subject to further confirmation during lectures and in compliance with the test time table for the semester. 3. SEMESTER TESTS According to schedule in Section A and subject to further confirmation during lectures and in compliance with the test time table for the semester. 4. EXAMINATION Examination – June / November according to a schedule from Exam department.

Compliance with Critical cross-field

Outcomes

Compliance with Generic Engineering

Outcomes

Collect and critically evaluate

information.

ELO 2: Demonstrate the application of mathematical, science and engineering knowledge in an engineering environment.

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LEARNING OUTCOME 2:

After successful completion of this chapter, the student should be able to describe the principle of

operation, construction, types, fundamental theory, testing / performance evaluation and analysis of

the single-phase transformers.


Single Phase transformers

Describe and analyze ideal and none-ideal single phase transformer, operations and construction.

The derivation of the equivalent circuit.

Transformer tests and its applications.

Voltage regulation, efficiency and per unit systems

Auto-transformer

Analysis, advantages, disadvantages

and applications of auto transformer.

Conversion of two-winding transformer

into auto-transformer.

Instrument transformers Circuit diagrams and application of instrument transformers. (this will be given to students as an assignment 2)

1. SELF ASSESSMENT EXERCISES As per lecturer’s instruction and examples from the text books prescribed in section 3.2.1. above 2. CLASS TESTS According to schedule in Section A and subject to further confirmation during lectures and in compliance with the test time table for the semester. 3. SEMESTER TESTS According to schedule in Section A and subject to further confirmation during lectures and in compliance with the test time table for the semester. 4. EXAMINATION Examination – June / November according to a schedule from Exam department.


Outcomes


Outcomes

Collect and critically evaluate information.


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3.3 GENERIC OUTCOMES AND CRITICAL CROSS-FIELD OUTCOMES

LEARNING OUTCOME 3

After successful completion of this chapter, the student should be able to describe the principle of

operation, construction, types, fundamental theory and analysis of DC machines.


Direct current generators

Generation of an AC voltage

Mechanical rectification

DC generator construction

Commutation - problems and solutions

Equivalent circuit

Separately excited generator

Shunt excited generator

Output voltage control

Performance and operating calculations

Direct Current Motors

Operation and equivalent circuits

Shunt, series, separately excited and compound motors.

Performance and operating characteristics

Speed control

1. SELF ASSESSMENT EXERCISES As per lecturer’s instruction and examples from the text books prescribed in section 3.2.1. above 2. CLASS TESTS According to schedule in Section A and subject to further confirmation during lectures and in compliance with the test time table for the semester. 3. SEMESTER TESTS According to schedule in Section A and subject to further confirmation during lectures and in compliance with the test time table for the semester. 4. EXAMINATION

Examination – June / November according to a

schedule from Exam department.


Outcomes


Outcomes

Collect and critically evaluate information.


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4. GLOSSARY OF TERMS

None.

Sources used for the compilation of the glossary: None.

5. ASSESSMENT RECORDS

The following test and examination are attached to serve as examples of the implementation of the

assessment criteria and assessment method, as listed in the table 3.1, and you should be familiar with

these examples to prepare and orientate yourself of how the various assessment criteria are used and

applied in the various assessment methods.


Outcomes

Compliance with Generic Engineering and

Built Environment Outcomes

Working effectively with others as a member of a team, group, organization, community.

- Especially, when it comes to projects, assignments and practical sessions, students will be and are encouraged to work in groups so that they can share information concerning that particular task.

- E.g. learning outcomes 1, 2 and 3.

Collecting, analyzing, organizing and critically evaluating information.

- Apart from the information appearing on the nameplate of any machine, the students will be required not only to consult their prescribed handbooks but also to browse through websites and other publications in order to have a clear and better understanding of how a particular machine works/operates under various conditions.

- e.g. learning outcomes 1, 2 and 3.

Demonstrate the application of mathematical, science and engineering knowledge in an engineering environment.

Communicate technical, supervisory and general management information effectively, both orally and in writing, using appropriate language and terminology, structure, style and graphical support.

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5.1 EXAMPLE OF A CLASS TEST

Electrical Machines II (EMA241T)

15 August 2008 – Class/Tutorial Test 2 Student Number: _______________________________ Surname & Initials: _____________________________ Marks: 48 for 40 __________________________________________________________________________________

Question 1 [12]

A 100kVA, 2200/440V, 50Hz single phase transformer has 400 turns on the primary and 80 turns on

the secondary. The primary resistance is 0.3Ω and the primary reactance is 1.1Ω. The secondary

resistance and reactance is 0.01Ω and 0.035Ω respectively.

Determine:

1.1 The impedance referred to the primary. (4)

1.2 The induced emf and full load secondary voltage for a lagging power factor of 0.8 lagging. (4)

1.3 The voltage regulation expressed as a p.u. and the secondary voltage. (4)

Question 2 [4]

List four methods for reducing leakage flux in a transformer.

Question 3 [4]

Draw a clearly labeled phasor diagram of an ideal transformer for a leading power factor.

Question 4 [7]

The emf per turn of a 3000/250V 50Hz is 14,73V.

Calculate:

4.1 The net cross-sectional of the core for a maximum flux density of 1,4T. (2) 4.2 The primary and secondary turns for a core type transformer. (5)

Question 5 [3]

A magnetic flux of 360µWb, passing through a coil of 1500 turns, is reversed in 0.05 seconds.

Determine the average value of the induced emf in the coil.

Question 6 [4]

With the aid of a diagram, explain the Hystersis loop of a transformer.

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5.3 EXAMPLE OF SUMMATIVE TEST AND EXAMINATION WITH

MEMORANDUM.

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5.2 EXAMPLE OF A PRACTICAL REPORT

DEPARTMENT OF ELECTRICAL ENGINEERING

ELECTRICAL MACHINES II

PRACTICAL REPORT

Name………………………………………….. Student Number…………………………….. No-Load (Open-circuit) Test and short-circuit Test of Single-phase Transformer Aim: The aim of the experiment is to determine the losses (copper loss and iron loss) of the transformer in order to calculate the efficiency, voltage regulation and that of extracting parameters for the equivalent circuit of the transformer. Apparatus:

Single-phase transformer (100 VA, 230/15.6V)

Variable ac power supply

Voltmeters

Ammeters

Wattmeters

Leads Circuit Diagram

Open-circuit test

Short-circuit test Methods:

Obtain the parameters of the transformer (from the nameplate): VA, V1, and V2.

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Connect the transformer as in the diagram; connect the supply to the high-voltage side

Repeat readings with intervals of 20V after 50V to approximately 140 % of design voltage

Note the readings in table form

Determine the full-load current of the transformer (primary and secondary)

For the short-circuit test connect the supply to the high-current side. Short-circuit the secondary side with an ammeter.

Set the supply current I to the calculated full-load current

Note readings: VSC, ISC1, WSC, and ISC2. Readings

V1 50 70 90 110 130 150 170 190 210 230 250 270

Ioc

W1

V2

Open-circuit test result

VSC1,FL

ISC1,FL

WSC1,FL

ISC2,FL

Short-circuit test result

Assignment 1. Use a graph paper to do the following: 1.1 Draw the magnetizing curve Imag against V1 1.2 Draw V2 against V1 and determine the ration V1/V2 1.3 Give the no-load current Ioc and no-load losses from the table 1.4 Which losses are constant? 1.5 Determine the full-load copper losses 1.6 Determine the full-load efficiency of the transformer at the power factor of 0.8 1.7 Determine the efficiency of the transformer at 75% of full-load at power factor of 0.8 1.8 Determine the load for maximum efficiency as well as the value of maximum efficiency of the transformer at a power factor of 0.8

6. APPENDICES

Appendix A

o A copy of the Semester Test 1 Memorandum. Page 26

Appendix B

o A copy of the Final Examination Memorandum. Page 32

OF 47

6.1 EXAMPLES OF MARK SHEETS USED DURING VARIOUS ASSESSMENTS

DURING THE COURSE.

Appendix C

o A copy of the Mark Sheets.

ema241t_eie301t student course guide_20150128s1_dp zikalala

Documents

course outcomes

faculty of engineering

electrical engineering

student course guide

electrical machines

assessment methods

assessment rules

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