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Design and Construction of a S911 Sinsle Phase

Cormutator Induction Hotor.

by

.
| A
we wy

H. LS amith

Hichigan Agricultural College

Spring Ter:

1914
THESIS
CONTENTS.

Introduction.

Theory.

Design as a Shunt Commutator Motor.

Redesign as an Induction Motor.
Test Data.

Appendix of Drawings and References.

List of Drawings.

1 Motor Diagrams.

Vector Diagrams.

Circle Diagran.

Preformance Curves.

Stator.

Armature.

End Castings.

Commutator and Brushes.
Shunt Motor Wireing Diagran.
Squirrel Cage Rotor.

Base.

Induction Motor Wireing Diagran.

Photograph of Finished Motor.
SN CT aM ete = Re a Sp Tea eter
INTRODUCTION

There is an increasing demand for small é6lectric
motors. Like large motor practice, there should be mectors with
characteristics, suited tc the worx they area to do.

The Shunt and Series Motors in D. C. will do about
all that is required, but D. C. is net very extersively used on
lighting circuits where the small motor is naturally connected.

Small A. C. motors are zenerally of the single nhase
induction type with squirrel cere motors anda split phase start-
ing windins which is thrown out of service when full sneed is
reached, oy a centrifugal device.

These motors run at only one speed and have a very
small starting torque. Plain A. C. series motors are also used
especially on vacuum cleaners. Such motors have a very bad power
factor and emall capacity for the iron used.

The writer made a number of tests on a small series
motor and tried a compensatins windinz, out still the power fac-
tor was low andi sparking bad.

Series characteristic is hardly whet is wanted in
a small motor, the shunt being greatly preferred. The writer's
attention was next turned to the shunt induction motor for sirgis
yanrss.

Thess have a zood starting torque ania wide speed
variation, with a nower factor near unity. Tne overload capac-
ity ia also hisher than the plain induction rotor. It is true
that the efficisancy is lew, but this is not such an important

iter in a small notor for inter:.ittant use.
Therefore since the writer could find nothing
concerning small rotore of this tyme, it was thought worth

while to experinent along this line.
THEORY

The theory of the gingle phase shunt commutator
motor and the sommon single phase squirrel cage induction mo-
tor is exactly the same.

The shunt motcr consists essentially of a status
with a distributed single phase winding similar to the common
induction motor and an armature and commutator simklar to a
D. C. machine. On the soumutator are four brushes (sreaking
of a two pole machine for simplicity) one set narallel to the
primary winding and the others at right angles. (See Fig. 1).

At steni still the motor is essentially a trans-
fer under short circuit, stator winding primary and rotor wind
ing secondarv, shorted across y y.

Thus the stator current must suprly flux enough
to generate a counter E.M.F. equal to the impressed E.M.F. less
the local stator impedance and balance the M.M.F. of the rotor
current in the transformer axis.

The stator circuit is hiczhly inductive thus the
current I; the Magnitizing current will lag almost 90° behind
the impressed E.M.f., E,. I, causes the flux & which is nearly
in phase with it.

& generates an E.M.F. E,in both the stator and
rotor, lacing 90°. The magnitude of these E.M.F!s varies accord
ing to the ratio of transformation.

Recauses a current I, to flow across axis y y, de-

termined both in magnitude and phase by the local impedance of
v
the rotor. The primary current I,will then be the resultant
of I,the magnetizing current, and I, reversed, or the vectorial
difference, (assuming 1 to 1 ratio of transformation). The
impressed E. M. F. &,will be the resulitart of a corronert equal
and oprosite to E,and of a component i, z,to over core the lo-
cal stator impedance and i,r,.

Now if the motor is brot up to speed, there will
be in E.N.F. EB, (Fig. 3) of line frequency along axis x x, due
to the conductors cutting J. Eis proportional to G and the
speed aniis either in time phase withor in time-phase oprosi-
tion to fluz G@ spending on the direction of rotation. Asswning
it to be in time-phase with _ The rotor current I,along the
transformer axis sets ur a loaxage fieldgin phase with itself.
@ also zensrates an E.M.F. eo, in the speed axis, it is in phase
with I,. Thus B,is the vectorial sum of B,and e. The conditions
€long the snesd axis are tnose of a transformer on oren circuit
since the Counter @.M.F. allows only exciting current to flow.
Thus E,causes a current I, laging heavily, this produces a flux
@, nearly in quadrature with Ky. GD nas line frequency aniis
along x x or risht angles to g mechanically. g by it alterna-
tions induces an E.M.F., Esalong x x, 90° behind @ in phase which
brings it nearly in orposition to Ey: The vectorial difference
between E,and E,is the E.M.F. required to drive I,thru the lo-
cal impedance andj resistance. The rotion of the rotor conduc-
tors thru the spsed field Q senerates an E.M.F. E,in the trans-
former axis, which is in time-phase oprosition to @, and propor-

tional to g,an4 the snsed. Thus Eyis nearly in opposition tof
E,. E,is the counter &.M.F. of ths motor. @,also produces a
WITH.

leakage flux g coazial with @.ana in phase,I,. This with the
speed generates e,in the transformer axis in phase oprosition
to Is. The vector sum of E,, F,and e,give EL, which drives I,
thru the local rotor imredance.

The limiting speed will be when the counter E.M.F.
Fy asd oy e,2nd K,vectorily balance. E,is constant while F de-
pends upon the speed. Now if an external E.M.F. in parse with
E,or ovrosition such as from line ov taps from stator, is intro-

duced across y y, E,will be either increased or decreased and

\

tne esrsolwili neve to increase or decrease to keer ur the bal-

C

ance. This method is used for synsed variation and is used over

wide ranges. See Fi 4.

fe
Again if the speed field can be increased or weak-
' *
ened, E,will be changed and the speed will nave to change to
again sive equalitrhun. This can ve done by inserting a induic-

tance or canacity along x x. A carecity increases I,, thus d,

f
and &, and reduces speed; an inductance decreases I,thus raises

If I,be nade to pass thru stator coils along axis
x x which will either boost or buck g, ) E,can be changed, thus
the speed. (Fic. 4).

# Power factor Compensation.

The power factor may ve imnroved by introducing an
E.M.F. from the line or stator in the sneed axis. This E.M.F.
E is in phase with Isand @ aprroximately and at right angles
with Esand Fy. Thus we have three E.M.F's in speed axis. (Fag. &)
E, causes I,and @, nearly at right angles to it. @,-arerates Fe

# The Inauction Motor--Payley.

 
aging 90° which is a counter F.N.F. to the F intrcedyced.
Thus along axis x x, we have two fluxes D, and G,90° out of
phase with eech other, therefore they cannot react together
to give torque and change the speed. The conductors cutting

, generates another speed E.M.F. BE. along the transformer
axis in phase with the flux. E, being at right angles to
the main speed E.M.F. E.in the y y axis, they corbine to
form a new resultant E.M.F. Taking the acticn of this E.M.F.
Ri causes Io in y y axis to flow lazing heavily, thus causes
flux Bon this exis 90 behind E,. This flux generates E. in
both the rotor and the stator, which lags 90 hehind@ or 90°
behind the counter E.M.F. in the stator equal and crrosite
to E,. Thus E,and E¢ combined to give the stator resultant
E.M.F. &, which can be made to either lead or lag behind the
primary current I,.

All of the theory connected with Fig. 3 holds

for a squirrel cage rotor, the end rings at all times keep
the rotor bars shorted across the respective axis, thus

equavalent to commutator and shorted brushes.
   
 

 

 

i

 

 

 

ale (2)

ae A
 

 

 

 

 

  

(nt

Fig 8

 

—w—— ee eee ee ee ee eS ee

 
SPECIFICATIONS

Out rut about 1 4H. P.

16
Voltace 110 60 cycles
Single Phase

speed near 3600 R.P.M.
DESIGN
Armature

Frou small motor practice an armature about
gi" diam. and 2" long was selected. Standard punchinzs
can be purchased 2 5/16" diam.}2 round slots 3/8" dian.

Standard practice of motors of this size calls
for a 5/16" shaft.

For mechanical detail, see drawinz. Allowance
was made for winding by examining armatures of similar size.
Stator

The stator used is the same as that of any sin-
gle nhase induction motor of two poles.

The area of the air gan is the area of one-half
the armature surface minus the slot area.

As 4 (2x.5x13) = 6 sq. in.

Air gap density 22,500 lines rer sq. in.

(Standard Hand Book 13,000 lines to 26,000 lines)

Thus 6 x 22500 135000 or total flux

Number turnes wire

gs = E x 10%
Kg, f
Where E Line voltage

S nuxbar conductors in stator

K, Form factor |
Ke Distribution constant
g Maximum flux

f Frequency

K,for Sin wave 1.11

K,for 2/3 pole face distribtors .9 (Fi7.52 Sheldon & Mason)

Gg — 110 x 100,000,000 — = 620 ¢
2 X Ll] x. OxLS500OKCO 620 turns

Considering 1/10 H.P. as 74 watts and 50% effic-
iency assumed, the imput should be 158 watts. Assuming Unity
Power factor as this type of motor should sive, the current
would be 1.4 amns. With good ventilation, using 400 cir. mils.
per amp. (Standard Hand Bock)

1.4 x 400 560 cir. rils. area

This is close toagv22 wire, so use No. 22 wire.

With 8 slots,each slot must contain

oe — 85 conductors

D.C.C. wire No. 22 will run 876 turns p3r sq. in.

sie =.l sq. in. aprroximately

.1 sq. in corresponds to a 3/8" hole.

Allowing 1/16" for insulation of slot and extra
roor for winding, makes diameter of slot 7/16".

Round slots are used since they are easier to make
and give greater air gan area thus greater capacity.

The inside diameter of stator is determined so as
to give 1/32" air gap (Standard Hand Bock).

Outside diameter is determined by ond rocm for coils
and castings.

The vunching are clamped by a 3/16" bolt.

( Sée drawing for details.)
Armature Winding

 

Designing the armature winding according to the
transformer E.M.F. Ny actual number of conductors on the
armature, the actual nuber turns is N%,. Since they are dis-
tributed around the armature, the BMP. in each cotl is equal
to the Cos. of the angle of displacenent from the position of
Max. E.M.F. Thus the E.M.F. is the resultant as vectorial sum
of E.M.F. around a circle.

= number turns in one-half the armature or from

Ny

brush to brush, thus the effective turns would be -«

2
Thus, B= @ fe

Assuming 40 volts for the transformer E.M.F.

N= By2 10° _ 40x1.41x100,000,000 —
~ 135 ,000x60

700 Conductors on armature

700

700 =57.5 conductors per slot use 60 conductors
“* 3/8" round slots give an area of .11 sq. in.
Allowing 1/32" for insulation gives a net area of about .1 sq. in.
Thus, 60 x .l 600 turns per sq. in. allowable
D.C.C. wire of this size is between No. 21 and No.22.
Use No. 22 wire.
With 12 slots and 24 commutator segisnts, wakes 4

coil rer slot of 15 turns each.

(See winding diagram dnd drawings for details.)

This motor was built as designed, but did not oper-
ate at all satisfactorily. Sparking at the commutator was at all

times very bad, in fact, the commutator was nearly destrovad. The
excitins current was verv lares, deinz 2.4 amps. the imnut
on no load, 100 watts.

The synchroneous sraesdi was 3660 R.P.M., but the
speei tas only 2400 R.P.M. The motor would carry a heavy load
of about 1/10 H.P., bit the current was excessive, running up

to five armneres.
Standard Ssuirrsl TG.-2 Induction Motor.
4 wo

Using the same stator with four more slots to make
12 slots and with the sa.e flux ner pole 135000 lines. With

6 slots per nols with windins distributed over five slots.

B= 2.29%, e¢f 10"
wheres E line E. M. PF.

§ = nuz.cber conductors

d = flux per role

f = freguency

S- gf 10° 11C x 109000006 = 830 turns

2. DOK Gt mel X 274 KX LE0CUU 2 00

Minimuy. tooth area cf stator.

 

Tidth of slot i", 6 slots ner rcl3 face
6 x 2" x 21/16=3.1 sy. ir. area
Core area of stator depth 2" x 2.1/16"=1 sq. in.
Arvarant coax area ner role sctetor tooth 1"
6x3 x 21/16=6.2 sq. in arosa
maximum corsa densitv. The stator flux divides half coing
around each way.
135000..= 67,500 lines
2x1
Minimum tootn area rer pole of rotor
11 conductors or 53 per rols face

53 x &* x 21/16"=2.35 sq. in.

Maximum tooth density of stator

Le: g

2 tooth area per fo.a

Stator density —=135000 x/ = 74,50C
3.1 x 2

Rotor density—13500U0 x /7 = 74,000
2.89 3

 
830 turns in 13 slots gives

330—83 Condustors per slot or ©3 turns per cecil
The slots will easily hold this anount of No. 22 wire. (See
first Calulation)

Sguirrsl Cage Rotor.

 

Air gap clearance 1/64"

External Diameter 2 3/32"

Length 21/16"

Nurner slots 11
In orier for the rotor not to lock on starting the rotor slots
must ove rrie to the stator slots.
Rotor current I per condutor at full load.

I for fuil load will be 1.5 amps. No. 23 wire has
an area of 545 cir. mils at 4CC cir. mils per amp.

643 21.5 aips. carrying capacity with rood ventilation.
400
Rotor a.ps.—.35 I x total stator conductors

total rotor conductors

I= .75 x 1.6 x 2450 =103 amps.

“il

Amnere conductors per inch 11 x 103 =160
x 3.33

Cir. mils per amp. allowable 500 (Standari Hand Book)
163 x 500 =51500 Gir. Hils.
This area is close to No. 3 B&S wire .229" dia.ster or Drill slots

15/64" diameter.
DATA FOR CIRCLE DIAGRAN

Magnetizineg current.

 

C,=the stator Carter coefficiert

=.135 = 5.1

la
Oo
w

s - slot width = .125

oO

=clesranca = .02

f = from Curve of Carter fringinz constand pase 44
Gray's Electrical Machina Desian

f =.5

C= A slot pitch = .506
t+fs

C, .606 =1.21

 

6 aT e vO x ~L2D

 

C, for rotor = 8 _ .062 25.1
6 a3
tf =,50
Cy =_.54 = 1.92
~539 ~6D x OO
Pole pitch = 2.84 =T L, = Are/ lerrglh of 41-94ap
moaenetizing current Ly = 1 A xXx $C

 

.37 (Sond. per pole) zi,

I, = 1 135000 x.02 x1.02 x 1.31 =1.1 amps. air gap
~37(6x8Q) 35.54 x 2

 

Allow 20% for iron 1.2 x 1.1=1.3 amps. mas. current

Constant Losses

 

Weight of stator teeth in pounds
Volume of stator teeth 5.4 sq. in.
l cu. in. steel .274 F

5.4 x .274=1.47#

Loss in watts ner lo. 7 watts (Fic. 81 nz.102 Gray's
ldachins Design)

1.47 x 7 =10.3 watts loss ir teeth
Volur.e of core 13 cu. in.

Disrecard

Wheres

13 x .274=3. 564

Watts per lb. 7

3.56 x 7=25 watts loss ir core

rotor iron loss since the fr27u210v is verv low.

Total d@oss 35 watts which reucins constant on all loads

Bearing loss=.81 x a2 Vv
160

2
Jeratts
d=bearing dian.

1 =lencth of rubbins surface

vevelocity of ruatcrine in feet per min.

 

81 x .31 x 1.25(3600 x x 51) e= 1.7 watts
12 x 1CC

For 2 beatines 3.4 watts

Assure 1 watt windage

Total loss 40 watts.

Maximun Current

 

Slot Leakage(Paze 2°90 Sheldon & liason)

Where

Stator
| -7
E,= 2 f 1jNn*(.62 a) 10 (For round slots)
We
1l,= length of slot in inches

Ns nur.ber conductors in series per slot

Z
it

nurosr slots ner phase

d,=- depth of saw cut

W, = Width of saw cut in tooth

E¥= 2 x 60«~°%«1L 2x6400( 525 .5)10 =2.7 ohris
Rotor

E.= 2xl0x2xllx1(.625 2) 1077=

Comes out verv small so disrerard
Zig Zag Leakage
Stator and Rotor

X,=3.35 £ 1.Nni(t,, +, -1)107
27 $ » atts -1)
A, x.
Where t, and t,are stator and rotor tooth tip widtns respectively

8

A,and A,are statcr and rotc: tooth pitches

Aaverars or common tooth pitch

 

A radial length of abr var in inches
2 -8

¥=3.35 x60x2x12x6400 .687{.5 .68 - 1)10 -15 ohms
2 tT
2 T. “5

oO

Resistance Primary
Length of sonhictors on stator

2(°2.5 3,.64)x83=85 ft.

 

 

 

12
2(2.5 3) x83 =76 ft.
13
2(2.3 1.5) x 83-52 ft.
12

Total=213 ft.

Resistance ver foot of No. 22 wiras is .0184 ohms
215 x .0184=3.9 ohrs stator resistance

3.9% 2.85 =4.2 ohms apparent resistance

Maximur. current=110 =°23.4 amps.

4.9
110=°8.6 amps. This value is used for dismetsr of the

circle diagram.

22.4 is used to determine the locked position of ths
rotor in the circle diagran:.
Exciting Current

40 =.363 amps. in phase with E.N.F. or a power component
T10 .

R 2
Coprer loss I R=1.3 x 3.9=4.9 watts

4.9=,406 arips. in nhase with E.M.F. or OG ir circle diazreg
Total amps. in phase with E.M.F. =. 769

 

 

Exciting current 76 71.3*=/S amps. or Ol in Circle diagram

Rated Load
Maximum capacity of wire =1.6 amps.
Hagnetizing current =1.5
1.6 =/1.34¢x"
xX =.93 amps.
93 x 110 =103 watts power component
103 =~ 50 watts=50 watts net power
50 =.067 H.P. or 1/15 H.P.
746

Effieiency 50 =48.5%
103
TABULATED DATA

External Diametor
Internal Diameter
Frame Leneth

Air ducts

Net iron

Slots number

Size

Sonductors rar slot
size

Finding tyre
EKinimum slot vitoh
Kinimux tooth wiith
Core ierth
Pole ritch .
Minimum tooth arsa rer pols
Core area

Apparent gay area ,+ar pole
Flux rer pole

“aximunm tooth dansity
haxinum corse dseneity
Anrere conductors rer inch
Circular mills rar anpere
Apparent gar isnsaity

Air sap clearanses

Carter Cosafficisent
hagnetizing current air gan
Total

Reactance rer rhasea

Naximum line osourrant

Stator

4, 5/16"

2 5/16"
21/16"

none

7/16* D
83

#22 D.0.0.
two coil

2506"
Le
>

§
7. 8

<
164
3-1 sq. in.

1 sy. in.

Rotor

2 9732"

3 1/16"

none

2 1/16"

li

15/84"

1

43

squirrel cage
~54*

de

1

2,355q. in.
2 gq. in.
662

1355000
74500

o7 ,500

L160
Rating

Horse Power
Terninal voltags
Anreres full load
Phases

Frequency
synohroneous R.P.K.

Pol4s

Stator Rotor
watts

1/10
110

19

60
3600
 

 

5977 2 My ee EL ek Lp

ELL) aa CLA Oe eS CL
=97 - 7d = (79)

a aie la a hahah i el Oh a Tae
= sp LUCA LA

yea
“SSO7 HYAadOD HOLY
GFHI907 voLl0od sso7 FHial =( 27d)
SAWY DEY = LNILYNI ‘OXF =(/0)

sa . A 1? a. a ee ee 2
= (og)

i Tad
sf cal BOLE
5 eT, AM (AoE SY Ae eee YE OES
= (70)

‘SAWHW L£9°=
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‘SIS9O7 LMHLSNOD = (90)

 

 

 

 

NOILY TNITYWI
AG WYHOVYIT FTIU/D

 

 

 
METHOD OF STARTING.

The Single Phase Motor will not start alone as there
is no torque at standstill. For starting purposes a second
ainding was put on at right anglea to the main winding, as ina
two phase motor. This winding was of fine wire therefore of high
resistance, thus the current was slightly in advance of the
main current. This gives the polyphase effect.

DESIGN. The coil is completely in one slot thus no distribution
factor is needed

Conductors in main winding 830.

Diatribution factor 74

74 x 830= 615 conductors. or 307 turns.
7 x(7/1c)* = .15 oq. in. area of slot.

307 = 2060 turns per sq. in.

This corresponds to a No. 26 8S. ¢ C. wire.

It was found that the motor would not start with the
full voltage on the main winding, s0 an inductance coil was put
in series with it, to reduce the starting current anid the locking
effect. This also caused the main ourrent to lac still nore,
civeing a greater difference in phase.

A 40% reduction in voltage was found to be satisfactory
the motor would then run up to speed with only 3 acps starting

current.
114
113
107
110
107.5
104

Efe.

30.8
41.

49.5
53.2

TEST

El

154
158
161
170
183
203

D A v A e
Wattea Power
Factor
44 . 286
69 438
95 - 59
103 ~605
128 ~69
153 ~75
Torque.
In.
QO
» 563
1.03
1.17
1.6
3216

Speed

3500
3400
35400
3350
33500

3200

jy» Syn. Speed

97.3.

94.5
94.5
93.2
91.6
89

&
°

1

o

ONO Om Gi

Meee ee
on

Load H Pp
03.

0 QO...
13 .0303
22 0555
29 »0625
34 ~0835
46 | » 109

Comparison of calculated data, anitest data.

Capacity

Exc.
Vatts input no load

Current

Efficiency at 1/10 H P
Power Factor at 1/10 H P

Resistance of primary

Paactance

By Calculation By Test.

1/16 HP
1.5 amps.

40
526
~65

3.85 ohms.

1/10 HP
1.35 amps.
44

53%

75

7,5 hin s
 
 
APPENDIX.
Shunt Motor Drawings.
Stator,
Armature.
End Castings.
Commutator and Brushes.

ao -& WF WO FF

Wireing Diagran.
Squirrel Cage Induction Motor Drawings.
Lh Stator as above with four more slots, so as to make twelve

Blots equally spaced.

ed

Squirrel Cage Rotor.

Bearings and 011 Cups as above.

End Sastings as above, both with the short bearing.
Base,

Wireing Diagran.

NIN Do& GH S» W

Photograph of Finished Machine.

References
 

 

 

 

 

 

 

 

 

 

 
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REFERENCES.
Sheldon and Mason, page 262
Standard Handbook, Sect. 8 -=- 99
The Electric Journal Feb. 1912 page 128. Aug. 1912
page 709. April 19123 page 352.
Alternating Surrents by Jackson. $$ page 874.
fhe Induction Motor. by Prof. Bailey U.of M.
Alternating Ourrent Motors. by ModAliister.
Electrical Machine Design. by Gray.
Experimental Electrical Engineering. by Karapetoff. Vol. ii
A. I. BE. E. Proceedings Vol. XXVIII 1909.
(a) Sketch of the Theory of the Adjustable-speed,
Single Phase Shunt Induction Motor. by F.Creedy.
(6) Repulsion Motor with Variable-speed Characteristias
by E. FF. ¥. Alexanderson.
(9) Current Locus of the Single Phase Induction Motor.
by A. 8. Langsdorf.
a _

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