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7/31/2019 20 Induction Motor Design
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es gn o n uc on o or
NEMA Class B,
-
7/31/2019 20 Induction Motor Design
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NEMA Desi n ClassNational Electrical Manufactures Association (NEMA)
locked-rotor torque: starting torque
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NEMA Rotor Sha e
Class B, A Class C Class D
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Rotor Maximum Diameter
With present steel alloys, rotor peripheral speeds of 50,000 ft/min
represent the design limit.
rev/min)in(2.1
)length/minin(
2.1
length/s)in(max
m
r
m
r
r
n
v
f
vD
This is typically not a problem for low speed motor.
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Maximum FluxExperienced formula is:
08.0)
003.000145.0( outm
P
polesofnumberthe:Pin Wattpoweroutput:outP
Dl
PB
P
DlB mm
mm
2
2
so
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Number of Turns er Coil on Stator
meffmeff fNfNE 44.421
small)areand(because97.0 11,1 XRVE rated
wckPqN kkkk 1.1
e spw
where
. e .
ratedV07.1mw
cfPqk 2
7/31/2019 20 Induction Motor Design
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Stator Volume and Size
coolingondepends1
,(constant) 00
2
VVlD
Typically
s
cooled)(watermoreor10hpforlb)ft/(in6~53
0 V
coo ea ressorporn~0
The unit for D and l is inch.
=
diameter estimated
3
1
0estimated
7/31/2019 20 Induction Motor Design
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Frame Diameter EstimationEstimated Stator Core diameter (outer diameter):
inch647.0)03.1
175.1(,0 estimatedestimated DPD
Estimated frame outside diameter:
tDD 2 ,,
tf is wall thickness, typically 0.5 inch
frameNEMAfromuppickedisfD
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NEMA Standard Frame Size (inch)
7/31/2019 20 Induction Motor Design
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Stator Bore Diameter and Len thFrame outside diameter:
Stator Core diameter (outer diameter):
.f
ff0
tf is wall thickness, typically 0.5 inch
inch647.00DD
Stator Bore diameter (inner diameter):
.175.1P
20
D
TVl
7/31/2019 20 Induction Motor Design
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Air GaExperienced formula
...
gDD r 2
gkkg crcseff
Effective airgap
where the Carters coefficients
2)5()5(
sss
sscs
bbgbgk
2
22
2
)75.04.4(
)75.04.4(
rrs
rscr
bbg
bgk
NEMA Class B
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Stator Slot Desi nD
s
in5.1in7.0 s
sss 1
sss b 6.04.0 6.00.4, s
s
s
s rb
r
sss bt Use 0.015-in coil separator and slot liner for 230V motor
. -
NEMA 284T or smaller frames: use 0.06 in slot wedgeLarger than NEMA 284T frames: use 0.125 in slot wedge
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Stator Conductor SizeStator current density
a
rated
saAJ,1
where a is stator (armature) conductor cross section
area and can be determined from the above formula
to ether with:
22 A/cm800400A/cm:cooled-Air saJ
P /
pfV ratedrated
,
,13
yp ca c ency :75% for Pout = 1-5 hp
85% for Pout = 5-40 hp
sa
rated
a
J
A,1 90% for Pout = 50-200 hp
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Number of Slots (Bars) on RotorCertain number of slots (bars) must be avoided because they
can pro uce e r men a cusps n e spee - orque curve.
3 kPSSr
r
...,,
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Rotor Effective Winding FactorRotor Coil pitch in electrical angle:
PS
PSfix rr
/
)/(
Rotor Slot pitch in electrical angle:r
rS
P
Skewed angle in electrical radian:r
rskew
r
S
PS ,
srdrprwr kkkk
1typicallyskewed,slotsofnumbertheis,rskewS
)2
sin( rrq
k
rSr r
)
2
sin( rrq
2srP
r3 2
pr
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Effective Number of Turns per
Effective number of rotor slots per phase (may not be integer)
3
rS
n e e s a or, e s ng e cage ro or as on y one con uc or per s o
(or equivalent to single layer winding).
6
rwreffr
SkN
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Rated current in rotor bar
ip)relationsher(transform,1, ratedeffr
eff
ratedb INI
Rotor bar current density
b
ratedb
sbS
J,
w ere b s ro or ar cross sec on area an can e
determined from the above formula together with:
22- s
Rotor bars can operate at higher temperatures than stator.
sb
ratedb
b
J
S,
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Rotor Slot Desi n:ratiowidthdepth to
21 rr dd ~
1
rb
2b bwddS
b
inch045.001.02 Dbr
2wd
22 667.0 rr bd
221 rcr ddd
Area is Sb
)( 211 rrrb ddbS 21 r
r
rr b
N
Dt
21212 rrcrc dddbb 11
2 r
r
rrr b
N
t
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7/31/2019 20 Induction Motor Design
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Rated current in rotor end ring
ratedb
r
ratedring
IP
I,,
IRotor end ring current density
ring
ra er ng
ringsA
J,
,
w ere ring s ro or en r ng cross sec on area an can
be determined from the above formula together with:
22- ,r ngs
Rotor end rings can operate at higher temperatures than rotor bar.
rings
ratedring
ring
J
A,
,