•
Introduction.
•
Direct Current (DC) Machines construction.
•
DC Machines operation and control.
•
DC Drives using power electronics.
•
Alternating Current (AC) Machines construction.
•
AC Machine operation and control.
•
AC Drives using power electronics.
•
Transformer construction.
•
Transformer operation.
•
Hard wiring control.
•
Programmable logic controller (PLC).
Electrical Machines and Power
Electronics
4
Torque
:
Torque
is
a
twisting
or
turning
force
that
tends
to
cause
an
object
to
rotate
.
A
force
applied
to
the
end
of
a
lever,
for
example,
causes
a
turning
effect
or
torque
at
the
pivot
point
.
Torque
(τ)
=
Force
x
Radius
of
rotation
If
10
lbs
of
force
were
applied
to
a
lever
1
foot
long,
for
example,
there
would
be
10
lb

ft
of
torque
.
(lbs=
0
.
453
kg),(
1
foot=
30
.
48
centimeters,)
Introduction
5
Introduction
Speed
If an object in motion travels a given distance in a given time.
Speed is the ratio of the distance traveled to the time it takes
to travel the distance.
6
Introduction
Linear Speed
The
linear
speed
of
an
object
is
a
measure
of
how
long
it
takes
the
object
to
get
from
point
A
to
point
B
.
Linear
speed
is
usually
given
in
a
form
such
as
feet
per
second
(f/s)
.
For
example,
if
the
distance
between
point
A
and
point
B
were
10
feet,
and
it
took
2
seconds
to
travel
the
distance,
the
speed
would
be
5
f/s
.
(f=
0
.
3048
meters)
7
Introduction
Angular
(Rotational)
Speed
The
angular
speed
of
a
rotating
object
is
a
measurement
of
how
long
it
takes
a
given
point
on
the
object
to
make
one
complete
revolution
from
its
starting
point
.
Angular
speed
is
generally
given
in
revolutions
per
minute
(RPM)
.
An
object
that
makes
ten
complete
revolutions
in
one
minute,
for
example,
has
a
speed
of
10
RPM
.
8
Introduction
Acceleration
When
an
object
changes
speed,
an
increase
in
speed
is
called
acceleration
.
Acceleration
occurs
when
there
is
a
change
in
the
force
acting
upon
the
object
.
An
object
can
also
change
from
a
higher
to
a
lower
speed
.
This
is
known
as
deceleration(negative
acceleration)
.
A
rotating
object,
for
example,
can
accelerate
from
10
RPM
to
20
RPM,
or
decelerate
from
20
RPM
to
10
RPM
.
9
Introduction
Work
Whenever
a
force
of
any
kind
causes
motion,
work
is
accomplished
.
For
example,
work
is
accomplished
when
an
object
on
a
conveyor
is
moved
from
one
point
to
another
.
Work is defined by the product of the net force (F) applied and
the distance (d) moved.
W = F x d
10
Introduction
Power
Power
is
the
rate
of
doing
work
,
or
work
divided
by
time
.
In
other
words
,
power
is
the
amount
of
work
it
takes
to
move
the
package
from
one
point
to
another
point,
divided
by
the
time
.
11
Introduction
Horsepower
Power
can
be
expressed
in
foot

pounds
per
second,
but
is
often
expressed
in
horsepower
(HP)
.
One
horsepower
is
equivalent
to
500
foot

pounds
per
second
or
33
,
000
foot

pounds
per
minute
.
when torque (lb

ft) and speed (RPM) are known.
Power in an electrical circuit is measured in watts (W) or
kilowatts (kW). One horsepower = 746 W=0.746 kW.
12
Introduction
Review 1
1. If 5 lb of force were applied to a radius of 3 feet, the torque would
be ____________ lb

ft.
2. Speed is determined by ___________ .
a. dividing Time by Distance
b. dividing Distance by Time
c. multiplying Distance x Time
d. subtracting Distance from Time
3. Work is accomplished whenever ____________ causes motion.
4. A twisting or turning force that causes an object to
rotate is known as ____________ .
13
14
15
Introduction to Electrical Machines
•
An
electric
machine
is
a
device
which
converts
electrical
power
(voltages
and
currents)
into
mechanical
power
(torque
and
rotational
speed),
and/or
vice
versa
.
•
A
motor
describes
a
machine
which
converts
electrical
power
to
mechanical
power
;
a
generator
(or
alternator)
converts
mechanical
power
to
electrical
power
.
16
Introduction to Electrical Machine
•
To
understand
how
an
electrical
machines
works,
the
key
is
to
understand
how
the
electromagnet
works
.
•
The
principles
of
magnetism
play
an
important
role
in
the
operation
of
an
electrical
machines
.
17
Review of Electromagnetism
•
The
basic
idea
behind
an
electromagnet
is
extremely
simple
:
a
magnetic
field
around
the
conductor
can
be
produced
when
current
flows
through
a
conductor
.
•
In
other
word,
the
magnetic
field
only
exists
when
electric
current
is
flowing
•
By
using
this
simple
principle,
you
can
create
all
sorts
of
things,
including
motors
,
solenoids,
read/write
heads
for
hard
disks
and
tape
drives
,
speakers
,
and
so
on
MZS
FKEE, UMP
18
Magnetic Field
•
Unlike
electric
fields
(which
start
on
+q
and
end
on
–
q),
magnetic
field
encircle
their
current
source
.
The
field
weakens
as
you
move
away
from
the
wire
Ampere’s
circuital
law

the
integration
path
length
is
longer
i
d
H
.
A
circular
magnetic
field
develops
around
the
wire
follows
right

hand
rules
field
is
perpendicular
to
the
wire
and
that
the
field's
direction
depends
on
which
direction
the
current
is
flowing
in
the
wire
MZS
FKEE, UMP
19
Example of Electromagnetic
•
An
electromagnet
can
be
made
by
winding
the
conductor
into
a
coil
and
applying
a
DC
voltage
.
•
The
lines
of
flux,
formed
by
current
flow
through
the
conductor,
combine
to
produce
a
larger
and
stronger
magnetic
field
.
•
The
center
of
the
coil
is
known
as
the
core
.
In
this
simple
electromagnet
the
core
is
air
.
MZS
FKEE, UMP
20
Adding an Iron Core
•
Iron
is
a
better
conductor
of
flux
than
air
.
The
air
core
of
an
electromagnet
can
be
replaced
by
a
piece
of
soft
iron
.
•
When
a
piece
of
iron
is
placed
in
the
center
of
the
coil
more
lines
of
flux
can
flow
and
the
magnetic
field
is
strengthened
.
MZS
FKEE, UMP
21
Strength of Magnetic Field (Cont)
•
Because
the
magnetic
field
around
a
wire
is
circular
and
perpendicular
to
the
wire
,
an
easy
way
to
amplify
the
wire's
magnetic
field
is
to
coil
the
wire
•
The
strength
of
the
magnetic
field
in
the
DC
electromagnet
can
be
increased
by
increasing
the
number
of
turns
in
the
coil
.
The
greater
the
number
of
turns
the
stronger
the
magnetic
field
will
be
.
Magnets
–
A magnet is an object that possesses a magnetic field,
characterized by a North and South pole pair.
–
A
permanent magnet
(such as this bar magnet) stays
magnetized for a long time.
–
An
electromagnet
is a magnet that is created when
electricity flows through a coil of wire. It requires a
power source (such as a battery) to set up a magnetic
field.
A Simple Electromagnet
•
A Nail with a Coil of Wire
•
Q
–
How do we set up a magnet?
•
A
–
The battery feeds current through the coil of wire.
Current in the coil of wire produces a magnetic field (as long
as the battery is connected).
A Simple Electromagnet
•
A Nail with a Coil of Wire
•
Q

How do we reverse the poles of this
electromagnet?
•
A
–
By reversing the polarity of the battery!
+

S
N
The Electromagnet in a Stationary
Magnetic Field
•
If we surround the electromagnet with a stationary magnetic field, the
poles of the electromagnet will attempt to line up with the poles of the
stationary magnet.
•
The rotating motion is transmitted to the shaft, providing useful mechanical
work. This is how DC motors work!
OPPOSITE
POLES
ATTRACT!
26
Faraday’s Law
•
The effect of magnetic field:
–
Induced Voltage from a Time Changing
Magnetic Field
–
Production of Induced Force on a Wire
–
Induced Voltage on a Conductor Moving in a
Magnetic Field
MZS
FKEE, UMP
27
Voltage Induced from a time changing
magnetic field
28
Voltage Induced in a conductor moving in a
magnetic field
•
Faraday’s Law for moving conductors :
For coils in which wire
(conductor) is moving thru the magnetic flux, an alternate approach is
to separate the voltage induced by time

varying flux from the voltage
induced in a moving conductor.
•
This situation is indicates the presence of an electromagnetic field in a
wire (conductor). This voltage described by Faraday’s Law is called as
the flux cutting or
Electromotive force
, or
emf
.
•
The value of the induced voltage is given by
E =
Blv
where
E
= induced voltage (V)
B
= flux density (T)
l
= active length of the conductor in the magnetic field (m)
v
= relative
speed
of the conductor (m/s)
The polarity of induced
voltage is given by the
right

hand rule.
29
Induced Force (Cont)
•
The motion of the bar
produces an
electromagnetic
force.
The polarity of the
emf
is
+
ve
where the current
enters the moving bars. The
moving bar
generates a
‘back’
emf
that opposes the current.
•
The instantaneous electrical power into the bar = mechanical
output power
TRANSFORMERS
Badariah Bais
KKKF163 Introduction to EE Sem II
2006/07
31
Transformer
•
Made up of inductors.
•
Not electrically connected.
•
An ac voltage applied to the primary induces an ac voltage in the secondary.
32
Types of Transformer
Step

up transformer

provides a secondary voltage that is
greater than
the primary voltage.
Step

down transformer

provides a secondary voltage that is
less than
the primary voltage.
Isolation transformer

provides a secondary voltage that is
equal
to
the primary voltage.

to isolate the power supply electrically from
the power line, which serves as a
protection.
33
Transformer
–
secondary voltage
The turns ratio of a transformer is equal to the voltage ratio of the component:
)
(
)
(
1
2
1
2
t
v
t
v
N
N
or
)
(
)
(
1
1
2
2
t
v
N
N
t
v
For example:
ac
ac
V
V
t
v
N
N
t
v
30
)
120
(
4
1
)
(
)
(
1
1
2
2
34
Transformer
–
secondary current
Assuming the transformer is 100% efficient, then
or
1
2
P
P
)
(
)
(
)
(
)
(
1
1
2
2
t
i
t
v
t
i
t
v
)
(
)
(
)
(
)
(
1
2
1
2
t
i
t
v
t
v
t
i
)
(
)
(
1
2
1
2
t
i
N
N
t
i
35
Example
Consider the source, transformer, and load shown in the circuit below. Determine
the rms values of the currents and voltages (a) with the switch open and (b) with
the switch closed.
36
Example
Consider the source, transformer, and load shown in the circuit below. Determine
the rms values of the currents and voltages (a) with the switch open and (b) with
the switch closed.
V
rms
V
110
)
(
1
Solution
Voltage applied to the primary,
V
rms
V
N
N
rms
V
22
)
110
(
5
1
)
(
)
(
1
1
2
2
(a) With the switch open, the secondary current is zero. Hence, the primary
current is also zero.
(b) With the switch closed,
A
R
rms
V
rms
I
L
2
.
2
10
22
)
(
)
(
2
2
A
rms
I
N
N
rms
I
44
.
0
)
2
.
2
(
5
1
)
(
)
(
2
1
2
1
Badariah Bais
KKKF163 Introduction to EE Sem II
2006/07
37
Transformer Rating
•
The rating of a transformer is stated as Volt
Ampere (VA) that it can transform without
overheating.
•
The transformer rating can be calculated as
either V
1
I
1
or V
2
I
2
where I
2
is the full load
secondary current.
DC Motor Construction
DC
motors
provide
very
precise
control
for
industrial
applications
.
DC
motors
can
be
used
With
:
conveyors,
elevators,
robots
marine
applications,
material
handling,
paper,
plastics,
rubber,
steel,
and
textile
applications
.
38
DC Motor Construction
Construction
DC motors are made up of the
following components :
• Frame
• Shaft
• Bearings
• Main Field Windings
(Stator)
• Armature (Rotor)
• Commutator
• Brush Assembly
39
40
DC Machine Construction
Figure 8.3 Details of the commutator of a dc motor
.
41
DC Machine Construction
Figure 8.4 DC motor stator with poles visible.
42
DC Machine Construction
Figure 8.5 Rotor of a dc motor.
43
DC Machine Construction
Figure 8.6 Cutaway view of a dc motor.
DC Motor Construction
Basic Construction
Field windings are mounted on pole pieces to form electromagnets.
In smaller DC motors, the field may be a permanent magnet.
The armature is inserted between the field windings.
The armature is supported by bearings .
Carbon brushes are held against the commutator.
44
DC Motor Construction
Armature
The armature rotates between the poles of the field windings.
The armature is made up of a shaft, core, armature windings, and
a commutator.
The armature windings are wound and then placed in slots in the
core.
45
DC Motor Construction
Brushes
Brushes
ride
on
the
side
of
the
commutator
to
provide
supply
voltage
to
the
motor
.
Dirt
on
the
commutator
can
inhibit
supply
voltage
from
reaching
the
armature
.
The
action
of
the
carbon
brush
against
the
commutator
causes
sparks
which
may
be
problematic
in
hazardous
environments
.
46
DC Motor Operation
Magnetic Fields
In small DC motors, permanent magnets can be used for the stator.
However, in large motors used in industrial applications the stator is
an electromagnet.
When voltage is applied to stator windings an electromagnet with
north and south poles is established.
The resultant magnetic field is static (nonrotational).
47
DC Motor Operation
Magnetic Fields
A
DC
motor
rotates
as
a
result
of
two
magnetic
fields
interacting
with
each
other
.
The
first
field
is
the
main
field
that
exists
in
the
stator
windings
.
The
second
field
exists
in
the
armature
.
Whenever
current
flows
through
a
conductor
a
magnetic
field
is
generated
around
the
conductor
.
48
DC Motor Operation
Right

Hand
Rule
for
Motors
A
relationship,
known
as
the
right

hand
rule
for
motors,
exists
between
the
main
field,
the
field
around
a
conductor,
and
the
direction
the
conductor
tends
to
move
.
If
the
thumb,
index
finger,
and
third
finger
are
held
at
right
angles
to
each
other
and
placed
as
shown
in
the
following
illustration
so
that
the
index
finger
points
in
the
direction
of
the
main
field
flux
and
the
third
finger
points
in
the
direction
of
electron
flow
in
the
conductor,
the
thumb
will
indicate
direction
of
conductor
motion
.
49
DC Motor Operation
Right

Hand
Rule
for
Motors
As
can
be
seen
from
the
following
illustration,
conductors
on
the
left
side
tend
to
be
pushed
up
.
Conductors
on
the
right
side
tend
to
be
pushed
down
.
This
results
in
a
motor
that
is
rotating
in
a
clockwise
direction
.
We
will
see
later
that
the
amount
of
force
acting
on
the
conductor
to
produce
rotation
is
directly
proportional
to
the
field
strength
and
the
amount
of
current
flowing
in
the
conductor
.
50
DC Motor Operation
CEMF
Whenever
a
conductor
cuts
through
lines
of
flux
a
voltage
is
induced
in
the
conductor
.
In
a
DC
motor
the
armature
conductors
cut
through
the
lines
of
flux
of
the
main
field
.
The
voltage
induced
into
the
armature
conductors
is
always
in
opposition
to
the
applied
DC
voltage
.
So
it
is
known
as
CEMF
(counter
electromotive
force)
.
The
amount
of
induced
CEMF
depends
on
the
number
of
turns
in
the
coils,
flux
density,
and
the
speed
of
the
motor
.
51
DC Motor Operation
Commutation
In
the
following
illustration
of
a
DC
motor
only
one
armature
conductor
is
shown
.
Half
of
the
conductor
has
been
shaded
black,
the
other
half
white
.
The
conductor
is
connected
to
two
segments
of
the
commutator
.
In
position
1
the
black
half
of
the
conductor
is
in
contact
with
the
negative
side
of
the
DC
applied
voltage
.
Current
flows
away
from
the
commutator
on
the
black
half
of
the
conductor
and
returns
to
the
positive
side,
flowing
towards
the
commutator
on
the
white
half
.
52
DC Motor Operation
Commutation
At
position
3
current
flows
away
from
the
commutator
in
the
white
half
and
toward
the
commutator
in
the
black
half
.
Current
has
reversed
direction
in
the
conductor
.
This
is
known
as
commutation
.
53
DC Motor Operation
Types
of
DC
Motors
The
field
of
DC
motors
can
be
a
permanent
magnet,
or
electromagnets
.
Permanent
Magnet
Motors
The
permanent
magnet
motor
uses
a
magnet
to
supply
field
flux
.
Permanent
magnet
DC
motors
have
excellent
starting
torque
capability
with
good
speed
regulation
.
A
disadvantage
of
permanent
magnet
DC
motors
is
that
these
motors
can
be
found
on
low
horsepower
applications
only
.
Another
disadvantage
is
that
torque
is
usually
limited
to
150
%
of
rated
torque
to
prevent
demagnetization
of
the
permanent
magnets
.
54
DC Motor Operation
Series
Motors
In
a
series
DC
motor
the
field
is
connected
in
series
with
the
armature
.
The
field
must
carry
the
full
armature
current
.
The
series
motor
develops
a
large
amount
of
starting
torque
.
However,
speed
varies
widely
between
no
load
and
full
load
.
Series
motors
cannot
be
used
where
a
constant
speed
is
required
under
varying
loads
.
Additionally,
the
speed
of
a
series
motor
with
no
load
increases
to
the
point
where
the
motor
can
become
damaged
.
Some
load
must
always
be
connected
to
a
series

connected
motor
.
Series

connected
motors
generally
are
not
suitable
for
use
on
most
variable
speed
drive
applications
.
55
DC Motor Operation
Shunt
Motors
In
a
shunt
motor
the
field
is
connected
in
parallel
(shunt)
with
the
armature
windings
.
The
shunt

connected
motor
offers
good
speed
regulation
.
The
field
winding
can
be
separately
excited
or
connected
to
the
same
source
as
the
armature
.
An
advantage
to
a
separately
excited
shunt
field
is
the
ability
to
provide
independent
control
of
the
armature
and
field
.
56
DC Motor Operation
Compound
Motors
Compound
motors
have
a
field
connected
in
series
with
the
armature
and
a
separately
excited
shunt
field
.
The
series
field
provides
better
starting
torque
and
the
shunt
field
provides
better
speed
regulation
.
57
DC Motor Operation
Review
2
1
.
The
field
in
larger
DC
motors
is
typically
an____________
.
2
.
Whenever
____________
flows
through
a
conductor
a
magnetic
field
is
generated
around
the
conductor
.
3
.
Voltage
induced
into
the
conductors
of
an
armature
that
is
in
opposition
to
the
applied
voltage
is
known
as____________
.
4
.
Identify
the
following
motor
types
.
58
DC Motor Operation
DC
Motor
Ratings
The
nameplate
of
a
DC
motor
provides
important
information
necessary
for
correctly
applying
a
DC
motor
with
a
DC
drive
.
The
following
specifications
are
generally
indicated
on
the
nameplate
:
•
Manufacturer
•
Horsepower
at
Base
Speed
•
Maximum
Ambient
Temperature
•
Insulation
Class
•
Base
Speed
at
Rated
Load
•
Rated
Armature
Voltage
•
Rated
Field
Voltage
•
Armature
Rated
Load
Current
•
Winding
Type
(Shunt,
Series,
Compound,
Permanent
Magnet)
•
Enclosure
59
DC Motor Operation
Typically
armature
voltage
in
the
U
.
S
.
is
either
250
VDC
or
500
VDC
.
The
speed
of
an
unloaded
motor
can
generally
be
predicted
for
any
armature
voltage
.
For
example,
an
unloaded
motor
might
run
at
1200
RPM
at
500
volts
.
The
same
motor
would
run
at
approximately
600
RPM
at
250
volts
.
60
Review
3
1
.
One
way
to
increase
motor
speed
is
to
____________armature
voltage
.
a
.
increase
b
.
decrease
2
.
CEMF
is
zero
when
the
armature
is
____________
.
a
.
turning
at
low
speed
b
.
turning
at
max
speed
c
.
not
turning
d
.
accelerating
3
.
A
____________

connected
motor
is
typically
used
with
DC
drives
.
61
Σχόλια 0
Συνδεθείτε για να κοινοποιήσετε σχόλιο