induction motor fundamentals.pdf
TRANSCRIPT
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Induction Motor Fundamentals
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UCFInduction Machine - Introduction
A 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 and
generator. 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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UCFIM Stator
Stator for a 2hp induction machine
http://www.ece.ualberta.ca/~knight/ee332/induction/basics/construction.html
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UCFIM Rotor
Two types of rotors for induction machine:Cage Rotor
Wound Rotor
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UCFCage Rotor
A 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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UCFWound 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 rotors shaft, where
extra resistance can be inserted into rotor circuits for control.
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UCFWound Rotor (2)
skewed
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UCFIM Basic Concepts
statesteadyatfollowsspeed,
ssynchronouatrotatesfield,magneticinducedsrotor':
speedssynchronouatrotatesfield,magneticsstator':rotortheofspeedorspeedmechanical:
rpminspeedssynchronou120
statoronfrequencyelectrical:
S
R
S
m
esyn c
e
n
P
fn
f
B
B
B
But rotor will not follow BS.
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UCFConcept of Rotor Slip
%100
sync
msync
f
ff
s
syncm nsn )1(
)1(
)1(
syncm
syncm
fsf
s
Pfn
P
fnf
esyn c
esyn c
syn
120
2/60
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UCFRotor Electrical Frequency
rotorthetorelativeofspeed:2/
frequencyelectricalrotor:
Rr
r
P
f
f
B
Since BRfollows BS, we have:
2/P
fff rmsync
esyncmsyncr sfPsfPfff 22
)(
)(120
msyncr nnP
f
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Induction Motor Equivalent
Circuit
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UCFEquivalent Circuit of Induction Motor (1)
1 4.44 e eff mE f N
stator copper loss
0
0
4.44
4.44
4.44
R r effR m
e effR m R
R e effR m
E f N
sf N sE
E f N
effR
eff
R
eff N
N
E
E
n 0
1
RI
FromB
net
leakage
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UCFEquivalent Circuit of Induction Motor (2)
ReR
RReRrRrR
LfXsXLsfLfLX
222
0
0
0
0
0 / RR
R
RR
R
RR
RR
jXsRjsXRjXR
EEEI
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UCFEquivalent Circuit of Induction Motor (3)
1:eff
n
per phase equivalent circuit
0
2
2
2
2
Reff
Reff
XnX
RnR
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UCFThevinin Equivalent Circuit
Thevinin equivalent circuitMc
McMcM
jXR
XjRjXRZ
//
11
11
11
)(
)//(
jXRZ
jXRZjXRZZ
M
M
MTH
THTHTH jXRZ
VV
11 jXRZ
Z
M
MTH
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UCFInduction Motor Power Flow
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UCFPower and Torque (1)
2
2
2
InI
RnR
effR
Reff
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UCFPower and Torque (2)
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UCFPower and Torque (3)
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UCF
Per Phase Equivalent Circuit with Rotor Loss and
Converted Power Separated
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Induction Motor Torque Speed
Characteristics
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UCFInduced Torque from Physical Standpoint (1)
netRind k BBT sinnetRind BkBT
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UCFInduced Torque from Physical Standpoint (2)
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UCFInduced Torque from Physical Standpoint (3)
)()()()( dcba
sin
sinnetRind BkBT
s
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UCFThevinin Equivalent Circuit
Thevinin equivalent circuitMc
McMcM
jXR
XjRjXRZ
//
11
11
11
)(
)//(
jXRZ
jXRZjXRZZ
M
M
MTH
THTHTH jXRZ
VV
11 jXRZ
Z
M
MTH
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UCFInduced Torque Equation
])()/[(
/32
2
2
2
22
XXsRR
sRVT
THTHsyn c
THin d
syn c
AGind
PT
])()[(
322
2
2
2
2
2
sXXRsR
sRVT
THTHsyn c
THind
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UCFTorque Speed Characteristic (2)
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UCFConverted Power vs Speed Characteristic
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UCFEffect of R2
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UCFMaximum (Pullout)Torque
])()/[(
/32
2
2
2
22
XXsRR
sRVTTHTHsyn c
THin d
2222
2)(0)/( XXRs
R
sR
TTHTHin d
])([2
32
2
2
2
max
XXRR
VT
THTHTHsyn c
TH
2
2
2
2max
)( XXR
Rs
THTH
has no relationship with R2and s
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Appendix - Examples
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UCFExample 1
details in im1.m
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UCFExample 2
details in im2.m
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UCFExample 3
details in im3.m
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UCFExample 5
details in im5.m
cR