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To enable students to:
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Learn the introduction of DC machines
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Learn how to get a DC voltage out of the
rotating loop
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Overview of Direct Current Machines
Construction
Principle of Operation
Types of DC Motor
Power Flow Diagram
Speed Control
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Direct-current (DC) machines are divided into dc
generators and dc motors
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While dc motors are widely used
in many applications
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A DC generator is a machine
that converts mechanical
energy into electrical energy
(dc voltage and current) by
using the principle of
magnetic induction
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An DC motor is a
machine that converts
electrical
energy
into
mechanical energy by
supplying a dc power
(voltage and current)
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The commutator is connected to the slotted iron core
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The windings of armatures are connected
in different ways depending on the requirements of the
machine
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Loops of wire are wound around slot in a metal core
DC machine armature
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Wave Wound Armatures
◦ are used in machines designed for
high voltage and low current
◦ their windings connected in series
◦ When the windings are connected in
series, the voltage of each winding
adds, but the current capacity remains
the same
◦ are used is in the small generator in
hand-cranked megohmmeters
◦ No of current path, C=2
Lap Wound Armatures
◦ Are used in machines designed for
low voltage and high current
◦ Armatures are constructed with large
wire because of high current
◦ Eg: - are used is in the starter motor
of almost all automobiles
◦ The windings of a lap wound armature
are connected in parallel
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◦ Most large DC machines use frogleg
wound armatures
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The use of square wire permits
the windings to be laid closer together, which increases the
number of turns that can be wound in a particular space
◦ Square and rectangular wire can also be made physically
smaller than round wire and still contain the same surface
area
Most DC machines use wound electromagnets
to provide the magnetic field
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◦ Is constructed with relatively many turns of small
wire, thus, it has a much higher resistance than the
series field
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◦ High resistance is used to limit current flow through
the field
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Both series and shunt field windings are contained in each pole piece
S – series field
F – shunt field
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Winding
armature
field
Self excited
Wave
C=2
Lap
C=2p
Separately
Excited
Frogleg
series
shunt
compound
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