Week05 Chapter 2 Electromagnetism and Magnetic Circuit
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Transcript of Week05 Chapter 2 Electromagnetism and Magnetic Circuit
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CHAPTER 2
Electromagnetism and magnetic circuit
5thweek
Introduction, Understanding of magnetic fields,
magnetic relationship
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MagnetismObjective of the
chapterUnderstanding concept basic magnetic field,magnetic flux, magnetic force at the conductor,solenoid and toroid
Identify force on the conductor carryingcurrent in the magnetic field
Identify direction of induce emf on the
conductor in the magnetic field
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Objective of the chapter (Cont.)
Relationship between magnetic and electrical
circuit
Understanding magnetic characteristics and to
analysis simple magnetic circuit
Understanding concept self, mutual and
coupling coefficiences
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Potential to attract other material
Pure, permanence and temporary
magnet
Pure From earth
Permanence
Depended on metal Temporary
electromagnetic
Magnetic material
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Two pole, north and south
Direction of line force outside magnetic material
as shown in figure 2.1
figure 2.1
Magnetic material (Cont.)
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Field Detector can use acompass to map out magneticfield, as shown in (Figure 2.2)
Field forms closed flux linesaround the magnet
Magnetic flux measured inWebers (Wb)
Symbol
Figure 2.2
Magnetic Field/flux
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Magnetic flux lines are assumed to have the following
properties: Leave the north pole (N) and enter the
south pole (S) of a magnet
Like magnetic poles repel each other asshown in figure 2.3 (a)
Unlike magnetic poles create a force ofattraction as shown in figure 2.3 (b)
Magnetic lines of force (flux) areassumed to be continuous loops
Flux lineshort distance
Magnetic Flux or flux line
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Figure 2.3(a) (b)
Properties of magnetism
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Magnetic Field on Conductor
A magnetic field also forms
round a conductor along
which a current is flowing
Field can be described using
right hand screw rule
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Magnetic Circuit
Flux
Force line in the magnetic field
Symbol, Weber (Wb)
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Flux Density
Area,
Flux,
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Magnetomotive Force (mmf)
Coil generates magnetic field in ferrous toroid
Driving Magnetomotive Force (mmf)is neededto overcome toroid reluctance
mmf, proportional to current, I and number of turn, N
mmf = NI, Ampere-turn (AT)
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Magnetic field
intensity/strength Magnetic field strength or Magnetizing force
mmf per length
l
NI
l
mmfH , Unit, At/m
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Permeability
Permeability is a measure of the ease by which amagnetic flux can pass through a material
(Wb/Am)
Permeability of free space o= 4 x 10-7(Wb/Am)
Permeability:
= absolute permeability
o= free space permeability
r= relatif permeability= or
gforcemagnetizin
yfluxdensit
H
B
B = H= orH
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Permeability depend on the material
free space
0= 4 x 10-7(Wb/Am)
Non-magnetic materil i.e. air, vacuum etc
Relative = r= 1
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Reluctance
Reluctance: resistance to flow of magnetic flux
Where,
llength
Across section area
- Permeability
SymbolS
unitAT/Wb or Siemen
Associated with magnetic circuit
flux equivalent to current in electric circuit
A
lS
A
l
r0
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Magnetic leakage and Fringing
Fringing
Occurs at the air gap
Flux intends to bulge outwards
Increasing the effective area Reduce the flux density
As shown in Figure 2.a
(still useful flux)
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