21 im equivalent circuits
TRANSCRIPT
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Induction Motor Introduction
and Equivalent Circuit
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UCF Induction Machine - IntroductionA machine with only armortisseur windings is called an
induction machine.
No DC field current is required to run the machine. Rotor
voltage is induced in the rotor windings rather than being
physically connected by wires.
Induction machine has the same physical stator as a
synchronous machine with a different rotor construction.
Induction machines can be operated as either motors andgenerator. However, they are primarily used as induction motors.
Induction machines are by far the most common type of motor
used in industrial, commercial or residential settings.
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UCF IM Stator
Stator for a 2hp induction machine
http://www.ece.ualberta.ca/~knight/ee332/induction/basics/construction.html
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UCF IM RotorTwo types of rotors for induction machine:
Cage Rotor
Wound Rotor
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UCF Cage RotorA cage (or squirrel-cage) rotor consists of a series of conducting bars
laid into slots carved in the face of the rotor and shorted at either end
by large shorting rings.
skewed
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UCF Wound Rotor (1)A wound rotor has a complete set of three phase windings usually Y-connected.
The ends of three rotor wires are tied up to slip rings on the rotor’s shaft, where
extra resistance can be inserted into rotor circuits for control.
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UCF Wound Rotor (2)
skewed
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UCF IM Basic Concepts: electrical frequency on stator
synchronous speed in revolution/second/ 2
120 synchronous speed in rpm
60: mechanical speed or speed of the rotor
: stator's magnetic field,
e
esync
sync esync
m
S
f
f f P
f f n
Pn
B rotates at synchronous speed
: rotor's induced magnetic field, rotates at synchronous
speed, follows at steady state
R
S
B
B
But the rotor will not follow BS.
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UCF Concept of Rotor Slip
%100
sync
msync
f
f f s
syncm nsn )1(
)1(
)1(
syncm
syncm
f s f
s
P
f n
P
f n f
esync
esync
syn
120
2/60
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UCF Rotor Electrical Frequency
: rotor electrical frequency
: speed (rev/s) of relative to the rotor/ 2
r
r slip R
f
f f P
B
Since BR follows BS, we have:
sync m slip f f f
slip sync m sync f f f sf
60
slip
slip
n f
2 2r slip sync e
P P f f sf sf
2 120
slip
r slip
n PP f f
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UCF Example 1
details in im1.m
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UCF Equivalent Circuit of Induction Motor (1)
meff e N f E 44.41
stator copper loss
meffRe R
RmeffRe
meffRr R
N f E
sE N sf
N f E
44.4
44.4
44.4
0
0
effR
eff
R
eff N
N
E
E n
0
1
RI
From Bnet
leakage
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UCF Equivalent Circuit of Induction Motor (2)
Re R
R Re Rr Rr R
L f X
sX Lsf L f L X
2
22
0
0
0
0
0 / R R
R
R R
R
R R
R R
jX s R jsX R jX R
EEE
I
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UCF Equivalent Circuit of Induction Motor (3)1:eff n
per phase equivalent circuit
0
2
2
2
2
Reff
Reff
X n X
Rn R
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UCF Thevinin Equivalent Circuit
Thevinin equivalent circuit M c
M c M c M
jX R
X jR jX R Z
//
11
11
11
)(
)//(
jX R Z
jX R Z
jX R Z Z
M
M
M TH
TH TH TH jX R Z
VV
11 jX R Z
Z
M
M TH
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UCF Induction Motor Power Flow
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UCF Example 2
details in im2.m
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UCF Power and Torque (1)
2
2
2
I n I
Rn R
eff R
Reff
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UCF Power and Torque (2)
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UCF Power and Torque (3)
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UCF
Per Phase Equivalent Circuit with Rotor Loss and
Converted Power Separated
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UCF Example 3
details in im3.m