1 Prof M D Dutt HOD EX Department SRCT Bhopal READING MATERIAL FOR B.E STUDENTS OF RGPV AFFILIATED ENGINEERING COLLEGES SUBJECT BASIC ELECTRICAL AND ELECTRONICS Professor MD Dutt Addl General Manager (Retd) BHARAT HEAVY ELECTRICALS LIMITED Professor(Ex) of EX Department Bansal Institute of Science and Technology KOKTA ANANAD NAGAR BHOPAL Presently Head of The Department ( EX) Shri Ram College Of Technology Thuakheda BHOPAL Sub Code BE 104 Subject Basic Electrical & Electronics UNIT II Magnetic circuits and Transformers
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Prof M D Dutt HOD EX Department SRCT Bhopal
READING MATERIAL FOR B.E STUDENTS
OF RGPV AFFILIATED ENGINEERING COLLEGES
SUBJECT BASIC ELECTRICAL AND ELECTRONICS
Professor MD Dutt
Addl General Manager (Retd)
BHARAT HEAVY ELECTRICALS LIMITED
Professor(Ex) of EX Department
Bansal Institute of Science and Technology
KOKTA ANANAD NAGAR BHOPAL
Presently Head of The Department ( EX)
Shri Ram College Of Technology
Thuakheda BHOPAL
Sub Code BE 104 Subject Basic Electrical & Electronics
UNIT II Magnetic circuits and Transformers
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Prof M D Dutt HOD EX Department SRCT Bhopal
RGPV Syllabus
BE 104 BASIC ELECTRICAL & ELECTRONICS ENGINEERING
UNIT II
MAGNETIC CIRCUITS AND TRANSFORMER
Review of laws of magnetism flux and their relation. Analysis of magnetic circuit and
single phase transformer, Basic concepts and construction feature of transformer.
Voltage , current and impedance transformation,EMF equation, equivalent circuits
and phasor diagrams, Voltage regulation, Losses and efficiency, Open circuit test,
Short circuit test.
INDEX
S No Topic Page
1 Review of laws of magnetism flux and their relation 3,4,5
2 Analysis of magnetic circuit and single phase transformer 6,7,8
3 Basic concepts and construction feature of transformer 9,10,11
4 Voltage , current and impedance transformation EMF equation 11,12,13
5 Equivalent circuits and phasor diagrams 13, to 17
6 Voltage regulation 18,
7 Losses and efficiency 19,20,21
8 Open circuit test 22,23
9 Short circuit test. 23,24
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Prof M D Dutt HOD EX Department SRCT Bhopal
REVIEW OF LAWS OF ELECTROMAGNETISM M.M.F FLUX AND THEIR
RELATION
The space around the poles of a magnet is called magnetic field. The force in the space
around a magnet can be pictured by examining the pattern made by iron fillings. These
chain of iron fillings to the assumption that the region (field) contains invisible lines of
force. The total number of lines of force surrounding a magnet , is called the total flux.
The lines of flux of N and S pole attract each other
The lines of same pole that is N N gives the lines which repel each other
LINE OF INDUCTION
Lines of flux travels from N pole to S pole and continues to travel through the magnet and
finally they reach the N pole again forming closed curves. The portion of the curves within
the magnetic material are called LINES OF INDUCTION
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Prof M D Dutt HOD EX Department SRCT Bhopal
MAGNETIC FLUX
Magnetic flux is the total number of lines of force comprising the magnetic field . It is
represented by ᶲ and is measured in Weber.
MAGNETIC FLUX DENSITY
Magnetic flux density is defined as the magnetic flux passing through per unit area of
material through a plane right angles to the direction of flux. This is also known as magnetic
induction It is represented by B.
B= ᶲ/a Magnetic flux density is scalar quantity.
RELATION BETWEEN MAGNETIC FIELD INTENSITY H AND INDUCTION
DENSITY
The field intensity H is the because of the flux density B ‘s effect . Thus flux density can be
assumed to be proportional to the field intensity in a magnetic field i.e free space
Β =µ0 H
B = Webers per square meter
H= in newton per weber ( amper turn/meter
µ0 = is the magnetic space constant
for free space the value of µ0 = 4π 10¯7 H/M
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Prof M D Dutt HOD EX Department SRCT Bhopal
MAGNETO MOTIVE FORCE
M.MF of the magnetic circuit is defined as the magnetic potential that derives or tends to
derive flux around the magnetic circuit and is analogous to the e.m.f in an electric circuit. It
is measured is ampere turns AT.
MAGNETIC FIELD INTENSITY
M.M F per unit length ( along the path of magnetic flux) is called the magnetic field
intensity H is given by
H = M.M.F /Length AT/mtr
RELUCTANCE
It is the name given to that property of material which opposes the creation of flux in it, It is
analogous to resistance of an electric circuit. It is measured in ampere turn/Wb
PERMEABILITY
It is the measure of receptiveness of material of having magnetic flux developed in it.
Every substance posses a certain power of conducting magnetic flux. For example iron is
better conductor for magnetic flux than air. It is the ratio of flux density B and magnetic
field strength H
µ = B/H
ANALYSIS OF MAGNETIC CIRCUITS SINGLE PHASE TRANSFORMER
Magnetic Circuits with Air Gap
Energy conversion devices which incorporates a moving element have air gaps in heir
magnetic circuits. Airgaps are also provided in the magnetic circuits to avoid saturation. The
length of air gap is Lg is equal to the distance between two magnetic surfaces. When the air
gap length is very smaller than the adjacent core faces, the magnetic flux Φ is constrained
essentially to reside in the core and air gap is continuous through magnetic circuits. Then
configuration A can be analyzed as the magnetic circuit li and air gap permeability µo and
length lg. Since the permeability of the air is constant, the air gap is linear part of the
magnetic circuit and flux density in the air gap is proportional to the m.m.f is calculated
separately for the air gap and iron portion and than added together to determine the total
m.m.f
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Prof M D Dutt HOD EX Department SRCT Bhopal
COMPOSITE CIRCUIT Consider a circular ring made from different material of l1, l2 and
l3 having cross sectional are a1, a2 and a3 and relative permeability µr1,µr2 and µr3 respectively
with a cut of length lg known as air gap. The total reluctance as they are joined in series.