26 induction motor design
TRANSCRIPT
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Design of Induction Motor
NEMA Class B,
Squirrel-cage Type
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UCF NEMA Design ClassNational Electrical Manufactures Association (NEMA)
breakdown torque: pullout torque
locked-rotor torque: starting torque
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UCF NEMA Rotor Shape
Class B, A Class C Class D
double cage
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Rotor Peripheral Speed
The maximum allowable peripheral speed of the rotor is a central consideration in
machine design. With present-day steel alloys, rotor peripheral speeds of 50,000
ft/min (or about 250 m/s) represent the design limit. 1 ft/min = 0.0051 m/s
This is typically not a problem for low speed motor.
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UCF Maximum FluxExperienced formula is:
in Wattpoweroutput:polesofnumberthe:
08.0)
003.000145.0(
out
outm
PP
f
P
P
Dl
PB
P
DlB mm
mm
2
2
Also
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UCF Number of Turns per Coil on Stator
meffmeff fNfNE 44.421
rD 21.1
wceff
kPqNN sdpw kkkk
where
The denominator 1.1 in Neff is to considering leakage flux.
mw
rated
cfPqk
VN
2
07.1
small)areand(because97.0 11,1 XRVE rated
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UCF Stator Volume and Size
The unit for D and l is inch.
cooled)(watermoreor10hpforlb)ft/(in6~53
0 V
Typically
cooled)(airlessor10hpforlb)ft/(in10~9 30 V
If we design D=l, we have the stator bore (inner)
diameter estimated
3
1
0 )(TVDestimated
coolingondepends1
,(constant) 00
2
sJVV
T
lD
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UCF
Estimated Stator Core diameter (outer diameter):
inch647.0)03.1
175.1(,0 estimatedestimated DPD
Estimated frame outside diameter:
festimatedestimatedf tDD 2,0,
tf is wall thickness, typically 0.5 inch
frameNEMAfromuppickedisfD
Frame Diameter Estimation
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UCF NEMA Standard Frame Size (inch)
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UCF
Stator Core diameter (outer diameter):
03.1175.1
inch647.00
P
DD
Frame outside diameter:
ff tDD 20
tf is wall thickness, typically 0.5 inch
page.lastinframeNEMAfromuppickedisfD
Stator Bore diameter (inner diameter):
Stator Bore Diameter and Length
Stator active region length:
20
D
TVl
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UCF Air GapExperienced formula
gkkg crcseff
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
inch0072.0001.00016.0 lDg
Effective airgap
gDD r 2
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UCF Stator Slot Design
S
Ds
sss bdb 42 1
in5.1in7.0 s
sss b 6.04.0
sss bt Use 0.015-in coil separator and slot liner for 230V motor
Use 0.030-in coil separator and slot liner for 460V motor
NEMA 284T or smaller frames: use 0.06 in slot wedgeLarger than NEMA 284T frames: use 0.125 in slot wedge
6.00.4, ss
s
s rb
r
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UCF Stator Conductor SizeStator current density
a
rated
sa A
I
J,1
where Aa is stator (armature) conductor cross section
area and can be determined from the above formula
together with:
22 A/cm800400A/cm:cooled-Air saJ
pfV
PI
rated
outrated
,
,13
/
sa
rated
a
J
IA
,1
Typical Efficiency :75% for Pout = 1-5 hp
85% for Pout = 5-40 hp
90% for Pout = 50-200 hp
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UCF Number of Slots (Bars) on Rotor
...)3,2,1(
3
)12(
k
kPSS
PkSS
r
r
Certain number of slots (bars) must be avoided because they
can produce detrimental cusps in the speed-torque curve.
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UCF Rotor Effective Winding FactorRotor Coil pitch in electrical angle:
PS
PSfix
r
rr
/
)/(
Rotor Slot pitch in electrical angle:r
rS
P
srdrprwr kkkk
)
2
sin(
)2
sin(
rr
rr
d
q
q
k
)2
(sinc rsrk
PS
q rr3
2sin rprk
Skewed angle in electrical radian:r
rskew
r
S
PS ,
1typicallyskewed,slotsofnumbertheis,rskewS
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UCF
Effective Number of Turns per
Phase for RotorEffective number of rotor slots per phase (may not be integer)
3
rS
Unlike the stator, the single cage rotor has only one conductor per slot
(or equivalent to single layer winding).
6
rwreffr
SkN
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UCF Rotor Bar SizeRated current in rotor bar
ip)relationsher(transform,1, ratedeffr
eff
ratedb IN
N
I
Rotor bar current density ,b ratedsb
b
IJ
S
where Sb is rotor bar cross section area and can be
determined from the above formula together with:
22 A/cm775700A/cm:cooled-Air sbJ
Rotor bars can operate at higher temperatures than stator.
sb
ratedb
b
J
IS
,
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UCF Rotor End Ring
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UCF Rotor End Ring SizeRated current in rotor end ring
ratedb
r
ratedring
IP
SI
,,
Rotor end ring current density
ring
ratedring
ringsA
IJ
,
,
where Aring is rotor end ring cross section area and can
be determined from the above formula together with:
2
,
2 A/cm930775A/cm:cooled-Air ringsJ
Rotor end rings can operate at higher temperatures than rotor bar.
rings
ratedring
ring
J
IA
,
,
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UCF ExampleDesign a 50 hp, 460 V, 60 Hz, 6 pole, Y-connected, 1175 rpm,
NEMA Class B squirrel cage induction motor, pf 0.85 lagging.
Pick up: 54 stator slots, 8/9 pitch, no skew on stator
51 rotor slots (bars), 1 slot skewed
Following the notes discussed, please study the MatLab codeimDesign.m by yourself.