2 Magnetic circuits

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ELECTRICAL SYSTEMS I

STUDY GUIDE FOR

EERI 221

PEC

*EERI221PEC*

FACULTY OF ENGINEERING





ii
























Study guide compiled by:

AJ Grobler




Edited
nn
.

+
Page layout by
Elsabe Strydom
, Graphikos.

Printing arrangements and distribution by Depa
rtment Logistics (Distribution Centre).

Printed by Nashua Digidoc Centre 018 299 2827

Copyright


20
1
3

edition. Date of revision 20
1
3
.

North
-
West University, Potchefstroom Campus.

No part of this book may be reproduced in any form or by any means without w
ritten
permission from the publisher.




iii

MODULE CONTENTS

Welcoming and contact particulars

................................
................................
........................

iv

What is expected of you?

................................
................................
................................
.......

iv

Study icons

................................
................................
................................
............................

v

Module exposition

................................
................................
................................
..................

v

Prerequisites

................................
................................
................................
..........................

v

Yearbook entry

................................
................................
................................
......................

v

Module outcomes

................................
................................
................................
..................

vi

Textbook

................................
................................
................................
...............................

vii

Electrical systems ii

................................
................................
................................
..............

vii

Assessment

................................
................................
................................
..........................

vii

Requirements for examination admission

................................
................................
............

viii

Calculation of final mark

................................
................................
................................
.......

viii

Excuses for

lectures, practicals and semester tests

................................
.............................

viii

Warning against plagiarism

................................
................................
................................
....

xi

Study unit 1

DC and AC circuit theory

................................
................................
.....

1

Study unit
2

Magnetic circuits

................................
................................
..................

3

Study unit
3

Principles of electromechanical energy conversion

.........................

5

Study unit
4

The DC machine

................................
................................
...................

7



iv

WELCOMING AND CONTAC
T PARTICULARS

Welcome to Electrical Systems I. In this module yo
u will build on the knowledge you have
gained in Electrotechnics and Mathematics. While Electrotechnics presented a broad
overview, here we will follow a more focussed approach. You will again use circuit theory (it
is probably the most important set of
techniques that you as Electrical and Electronic
Engineer must be able to use), but in this module it will find greater application.

The module consists of the following main components:



DC and AC circuit theory.

Circuit theory is revised for DC circuits

and treated
extensively for single and three phase AC circuits. This part of the module also covers
the per
-
unit system.



Magnetic circuits.

Magnetic circuits


a concept which will enable you to analyse and
design electromagnetic structures


is introdu
ced. (Magnetic circuits is a technique
which models magnetic fields as electric current circuits.)



Principles of electromechanical energy conversion.

In this part of the module we
will study the way in which electrical energy is converted to the mechanica
l form (and
vice versa
).



The DC machine.
In the last part of the module the DC machine is treated in depth.

The practical part of the module will be conducted by Mr M Trümpelmann in the electrical
engineering laboratory.

The contact particulars of the
lecturer is as follows:

Lecturer:

Dr Andre Grobelr

Consulting time:

Will be indicated on the timetable; otherwise as per appointment.

Office:

Room 22
4

Telephone:

(018) 299 1976

E
-
mail:

andre.grobler
@nwu.ac.za

WHAT IS EXPECTED OF
YOU?

By this time it is ex
pected of you to know how to study. Keep in mind that, to try and "cram"
the evening before a test or examination, will be futile. The only way to achieve success in
this module is by conscientious and regular study. The lecturer has an open door if you

can
demonstrate that you work hard, but still experience problems. Come and discuss your
problems at an early stage. Learners who failed to work diligently during the semester will
not find a sympathetic ear if they, at the end of the semester, approach

the lecturer with a
request to be allowed to write the examination. You are regarded as adults and will be
treated as such. An adult is responsible for the consequences of his/her decisions.



v

STUDY ICONS


Test your current
knowledge/insight


Individua
l exercise


Introductory remarks


Practical example


Study the indicated
material(s) in the
textbook/article, etc


Outcomes


Revision



Preparation for the contact
session/group meeting


Approximate study time




MODULE EXPOSITION

PREREQUISITE
S

EERI 212


Electrotechnics.

YEARBOOK ENTRY

The Yearbook entry for Electrical Systems I reads as follows:

In this module the learner will acquire the skills to solve magnetic circuits with non
-
linear
elements. Also the learner would have consolidated his/
her knowledge of basic units and
derived units. The learner will be able to use the per
-
unit system of measuring as well as the
fundamental principles of electricity, mechanics and heat to solve problems.
Electromechanical energy conversion principles wil
l be mastered. The models of DC
machines are derived in terms of the circuit laws. The operation of machines under steady
state conditions is analyzed by the use of network theory. Electrical network principles and
active, reactive and complex power in sin
gle and three phase linear networks in steady state
will be understood. The steady state operation of single and three phase networks will be
analyzed mathematically.


vi

MODULE OUTCOMES

From the Yearbook entry the following module outcomes are identified (in

the list of
outcomes the term "thorough understanding" is used, indicating that you will have the skills
to solve problems):


1.

DC and AC circuit theory

Thorough understanding of

a)

the analysis of DC circuits;

b)

the analysis of single phase AC circuit
s;

c)

the analysis of three phase AC circuits;

d)

the use of the per
-
unit system; and

e)

the measurement and calculation of three phase power.

2.

Magnetic circuits

Thorough understanding of

a)

the core meaning of Maxwell's equations;

b)

magnetic materials
and their properties (including non linearity and permanent
magnets);

c)

the analysis of magnetic circuits with one flux source;

d)

the analysis of magnetic circuits met more than one flux source; thorough
understanding of magnetic coupling;

e)

the measure
ment and calculation of inductance and mutual inductance; and

f)

the calculation of magnetic losses.

3.

Principles of electromechanical energy conversion

Thorough understanding of

a)

the calculation of energy balance;

b)

the energy conversion process: ele
ctrical energy <=> magnetic field <=> mechanical
energy; skills in the relevant calculations;

c)

the energy conversion process: electrical energy <=> electrical field <=> mechanical
energy; skills in the relevant calculations;

d)

the calculation of magneti
c field energy and coenergy;

e)

the Lorentz force and the Law of Faraday as applied in electrical machines;

f)

the analysis and design of simple linear electromechanical energy converters: relays,
plungers, etc; and

g)

the operation of the DC machine, the

reluctance machine and the synchronous
machine.



vii

4.

The DC machine

Thorough understanding of

a)

the mechanical construction of a DC machine (including the layout of the armature
winding);

b)

the development of electromagnetic torque and induced voltage (c
ounter emf) in the
DC machine;

c)

DC machine magnetization characteristics;

d)

commutation and armature reaction;

e)

the DC machine in generator operation (including voltage regulation, losses, the
criterion for maximum efficiency and the different DC gene
rators: separately exited,
series, shunt and compound);

f)

the DC machine in motor operation (including speed control, losses and the different
types of DC motors: separately exited, series, shunt and compound); and

g)

further DC machine concepts in motor

operation: methods of speed control, the Ward
-
Leonard system, the measuring of torque and the braking of DC motors.

TEXTBOOK



Primary source: BS Guru and HR Hiziroğlo,
Electric Machinery and Transformers
, 3rd
edition, Oxford University Press, New York, 200
1. In the text referred to as "Guru".



Complementary source: AE Fitzgerald, C Kingsley, Jr and SD Umans,
Electric
machinery
, 6
th

edition, McGraw
-
Hill, New York, 2003. In the text referred to as "FKU".

In this module the following chapters in Guru will be
studied: 1, 2, 3, 5 and 6.

ELECTRICAL SYSTEMS I
I

The module following on to this one is Electrical Systems II. You will use the same textbook,
but in that module the transformer (single and three phase) and AC machine types
(synchronous and induction) wi
ll be studied. Electrical Systems I and II form a
comprehensive course on the energy conversion aspects of electrical systems. In the
module Power Systems you will study the transmission and distribution aspects.

ASSESSMENT

In Electrical Systems I your m
astering of the work and achievement of the module outcomes
will be assessed in the following ways:



Practicals (four different practicals).



Two formal semester tests.



Class assignments.



The final examination.

The practicals for this module consist of expe
riments and demonstrations in the machine
laboratory. The dates and practical manuals will be provided during the course of the
module. The practicals will be presented during the course of the module and you must
prepare preliminary reports, as well as
final reports, unless indicated otherwise. You will not
be allowed in the laboratory if you are not adequately prepared and can comply with the
safety standards of the laboratory. Remember: electrical systems are very dangerous!


viii

REQUIREMENTS FOR EXA
MINAT
ION ADMISSION

For

admission to the examination the following requirements must be met:



You must attain a minimum of 50% for each of the practicals.



You must attain a minimum participation mark of 40%.

CALCULATION OF FINAL

MARK

The participation mark is co
mpiled as follows from the practical mark and semester test
mark:



25
%

for practicals


+

55
%

for the semester tests


+

20% for class assignments


=

100%

You require a module participation mark of at least 40% to obtain admission to the
examination.
No exception will be made, eg a
participation mark

of 38% is not an
admission mark.

The final mark is the average of the participation mark and the examination mark.

EXCUSES FOR LECTURES
, PRACTICALS AND SEM
ESTER
TESTS

Class and tutorial attendance is compu
lsory and will be checked from time to time. If you
have a deserving situation, which prevents you to attend a lecture, you must confirm it
by e
-
mail
.

Practicals are compulsory. You must perform a practical on your own and hand in your final
report a w
eek after the completion of the practical. No exchange of reports and results is
allowed.

Requests for excuses from evaluation opportunities must always be accompanied by a
valid
sick note. (In other words, an original copy


plus a photocopy


issued by

a
medical
doctor registered

with the
Health Professions
Council

of South Africa

and must be in
his/her own handwriting and
confirmed

by telephone by the lecturer, followed by
confirmation,
in writing
, by the lecturer that the sick note is accepted. These

measures are
necessary in view of the large number of falsified sick certificates being received. In other
words, a sick note does not provide automatic admission to an additional semester test.

Exemption from class attendance is possible if you have att
ended this module previously.
Apply by submitting full proof of previous attendance. No exemptions are granted for
practicals, class tests and semester tests. In other words, if you do the module a second
time, you must acquire a participation mark in t
he year in which you plan to write the
examination. This is necessary, because changes to the module contents occur from year to
year, making the participation marks of previous years invalid.




ix

MODULE INFORMATION F
ORM


Module code:
EERI 221

Prerequisites
:
EERI 212


Module name:
Electrical Systems I


Module credits:
16

Co
-
requirements:

none

CESM:
080901



Module objectives

The module introduces the electrical engineering student to electrical systems. In particular, the
following themes are covered in
the module: (a) circuit theory is extended to three phase circuits,
the foundation of power systems; (b) the student is introduced to electrical machine principles by
treating magnetic circuits and the fundamentals of electromechanical energy conversion, f
ollowed
by a detailed study of the DC machine.


Module outcomes

After completion of this module the student is
able to:



analyse DC circuits;



analyse single
-
phase and three
-
phase AC

circuits;



analyse simple magnetic circuits;



analyse, design and construc
t simple

electromechanical energy
-
conversion

structures;



analyse the DC machine in motoring and

generating mode.

Assessment criteria

The analysis of DC, AC and magnetic circuits
will be on junior undergraduate level, but more
complex than circuits found i
n the first year. The
designed and constructed electromechanical
energy
-
conversion devices will be very simple,
since the emphasis is on the basic principles. DC
machine theory is treated on a more advanced
undergraduate level, since this is the only time
that this electrical machine type is studied in the
curriculum.


Assessment methods and weights

exams: 50%;

practicals: 15% pass sub minimum;

semester tests: 35%

ECSA Exit Level Outcomes

This module contributes towards the development / demonstrates the

students' achievement of the
following ECSA ELOs: ELO 2: Application of scientific and engineering knowledge.


x

Detailed content

The module consists of four study units: (1) DC and AC circuit theory; (2) magnetic circuits; (3)
principles of electromechanic
al energy conversion; and (4) the DC machine. In study unit 1 the
circuital laws of Ohm and Kirchhoff (well
-
rehearsed in the preceding module EERI 212) are
reviewed and extended to three
-
phase AC circuits. The principles of impedance and apparent
power as
applied to balanced three
-
phase circuits are extensively treated. In study unit 2 the
student is introduced to the flow of magnetic flux in energy
-
conversion structures. The analogue to
electrical circuits is drawn and several exercises follow the treatmen
t of the theory. The treatment
of magnetic circuits naturally flow into study unit 3, where energy conversion principles are
introduced. Simple structures that convert energy bidirectionally from electrical to magnetic form
are studied in detail. The empha
sis is on the use of magnetic coenergy to calculate reluctance
forces in such structures. The module is concluded by studying the DC machine in a fair amount
of detail (only steady
-
state behaviour, however.) The student is now well
-
prepared for Power
Syst
ems I and Electrical Systems

II (where AC machines and transformers will be studied).

Knowledge Areas

Mathematics

Basic sciences

Engineering
sciences

Design and
synthesis

Computers and
IT

Complementary
studies

0

0

13

3

0

0



Prescribed textbook(s)



B.S.

Guru and H.R. Hiziroğlo,
Electric Machinery and Transformers
, 3rd edition, Oxford
University Press, New York, 2001.



Module administration

Prof SR Holm

Weeks per semester

14

Duration of lecture period

50min = 0.83 hr

Number of lectures per week

4

N
umber of tutorials per week

2

Hours of practicals per semester

12

Other contact time per semester (h)

0

Other non
-
contact time per semester (h)

80

Total number of hours per semester

162


Version 10.06



xi

WARNING AGAINST PLAG
IARISM


ASSIGNMENTS ARE INDI
VIDUAL TASKS AND NOT GROUP ACTIVITIES
.
(UNLESS
EXPLICITLY INDICATED AS GROUP ACTIVITIES)

Copying
of text from other learners or from other sources (for instance the study guide,
prescribed material or directly from the internet) is
not allowed



only brief

quotations are
allowed and then only if indicated as such.

You should
reformulate

existing text and use your
own words
to explain what you have
read. It is not acceptable to retype existing text and just acknowledge the source in a
footnote


you should
be able to relate the idea or concept, without repeating the original
author to the letter.

The aim of the assignments is not the reproduction of existing material, but to ascertain
whether you have the ability to integrate existing texts, add your own in
terpretation and/or
critique of the texts and offer a creative solution to existing problems.

Be warned: students who submit copied text will obtain a mark of zero for the
assignment and disciplinary steps may be taken by the Faculty and/or University. It
is
also unacceptable to do somebody else’s work, to lend your work to them or to make
your work available to them to copy


be careful and do not make your work available
to anyone!




xii



Study unit 1


1


1

DC AND AC
CIRCUIT

THEORY







The contents of this Study Unit i
s largely a revision of what was covered in Electrotechnics:
circuit theory is revised for DC and AC circuits. The focus here is on the latter and
applications receive more attention than in Electrotechnics.


The recommended study time for Study Unit 1 i
s 30 hours.


Study material: Guru Chapter 1.


You should have reached outcomes 1(a)


(e) at the end of this study unit.

Study unit 1


2


Guru contains problems marked "exercises" which are integrated in the text of every chapter,
as well as "review questions" and "p
roblems" at the end of the chapter.

You can make use of all these problems to test your knowledge and skills. A
few examples will be worked through in class.



Study unit 2


3


2

MAGNETIC CIRCUITS







In this Study Unit you are introduced to magnetic circuits. This
concept is mainly used to
solve linear magnetic problems, although it is increasingly also used in non
-
linear problems,
for example in transverse flux machines.

Briefly, the technique entails that a "circuit" is set up to model the flow of the magnetic fl
ux.
The different circuit elements are: a flux source (equivalent to a current source in electrical
circuits), an mmf source (equivalent to a voltage source) and a reluctance (equivalent to a
resistance).


The recommended study time for Study Unit 2 is
35 hours.


Study material: Guru Chapter 2 and supplementary notes.


You should have reached outcomes 2(a)


(f) at the end of this study unit.

Study unit 2


4


Make use of the problems in Guru to exercise your problem solving techniques and to test
your knowledge. A
few examples will be worked through in class.


Study unit 3


5


3

PRINCIPLES OF
ELECTROMECHANICAL
ENERGY CONVERSION





In this study unit your aim is to master the principles according to which energy is converted
from the electrical to the mechanical form (and
vice ver
sa
). This conversion is known as
electromechanical conversion. You will discover that the key to this process is the magnetic
field (the electric field is also used sometimes, but to a lesser extent). The conversion
process has the magnetic field energy

(or coenergy) as buffer stage. The conversion
process is completely bidirectional.

At the end of this Study Unit you will also understand the basic operation of the DC,
reluctance and synchronous machines.


The recommended study time for Study Unit 3 is

35 hours.


Study material: Guru Chapter 3 and supplementary notes.


You should have reached outcomes 3(a)


(g) at the end of this study unit.

Study unit 3


6


Make use of the problems in Guru to exercise your problem solving techniques and to test
your knowledge. A

few examples will be worked through in class.




Study unit

4


7


4

THE DC MACHINE







A thorough study of the DC machine is undertaken in this study unit. Electrical machines are
generally completely bidirectional and, therefore, we use the term "machine" instead of

"motor" or "generator". The last two terms are not wrong but are less general. A DC
machine, therefore, can function as generator or as motor, and both these applications are
carefully studied

in this study unit. Guru devotes complete chapters to generator and motor
operation.


The recommended study time for Study Unit 4 is 60 hours.


Study material: Guru Chapters 5 and 6.


You should have reached outcomes 4(a)


(g) at the end of this stud
y unit.


Make use of the problems in Guru to exercise your problem solving techniques and to test
your knowledge. A few examples will be worked through in class.