20 induction motor design

7/31/2019 20 Induction Motor Design

1/20

es gn o n uc on o or

NEMA Class B,

-


2/20

NEMA Desi n ClassNational Electrical Manufactures Association (NEMA)

locked-rotor torque: starting torque


3/20

NEMA Rotor Sha e

Class B, A Class C Class D


4/20

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.


5/20

Maximum FluxExperienced formula is:

08.0)

003.000145.0( outm

P

polesofnumberthe:Pin Wattpoweroutput:outP

Dl

PB

P

DlB mm

mm

2

2

so


6/20

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


7/20

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


8/20

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


9/20

NEMA Standard Frame Size (inch)


10/20

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


11/20

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


12/20

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


13/20

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


14/20

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

...,,


15/20

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


16/20

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


17/20

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,


18/20

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


19/20


20/20

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,

,

20 induction motor design

Documents