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DESIGN & CONSTRUCTIONOF A

BOUCHEROT INDUCTION MOTORBY

R. L GRAYR. HAY

ARMOUR INSTITUTE OF TECHNOLOGY

1911

IHInois Institute

of TechnologyUbrarln

AT 219Gray, R. L.

Design and construction of a

Boucherot Induction Motor

' I. ''I I'

(

U (I Ml

ULilbxGJN AND CONSTRUCTION OF

A BuUCaaRoT INDUCTION I-IOTOR,

A THESIS("RESENTED BV

R. L. GRAY and R. HAY.

PRESIDENT AND FACULTY

OF

ARMOUR INSTITUTE OF TECHNOLOGYFOR THE DEGREE OF

BACHELOR OK SCIENCE IN ELECTRICAL ENGINEERING

HAVING COMPLETED THE PRESCRIBED COURSE OF STUDY IN

ELECTRICAL ENGINEERINGILLINOIS INSTITUTE OF TEGHNQtOGY

PAUL V. GALVIN LIBPA!^

35V»eSJ33FJOi7i^'T

CHICAGO, IL mi^':yi^l.rZr<^

DESIGN & CONSTRUCTION OF A BOUCHEHOT

INDUCTION MOTOR.

The object of this work is to design a Boucherot rotor

to be used in a 10 HP, G.E. 25 Cycle, 80 Volt, 4 Pole, 2-3

Phase Induction Motor.

The only difference between a Boucherot Induction Motor

and the ordinary squirrel cage type is in the rotor. Instead

of having one squirrel cage, the Boucherot Motor has t?;o or

more placed one inside the other. The object of the two squir-

rel cages is to give the rotor a better starting torque with

less current consumption and also to give a better running

characteristic.

FIGURE I. shows the method of placing the two sets of

windings. The outer winding has a high resistance and relative-

ly low inductance. The inner winding has a low resistance and

high inductance due to the greater leakage surface. At the

start the frequency of the flux in the rotor equals the stator

frequency, hence the high inductance cage will carry practical-

ly no c^orrent. The outer winding or low inductance winding

will furnish the torque, and since the resistance of this wind-

ing is high and practically equal to the reactance, we will

get maxiimua torque at the start. Under running conditions

the frequency of the flux in the rotor will be proportional

to the slip and since the slip is snaall the frequency will be

sinall and the reactance of the inner winding will be small.

The impedance of the inner winding will therefore be small under

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^ tampinjsfor lOhP Tnductlorr. Motor.

Double Rotar CorLdLuctorj

.

^-^

X"^"-

%.. ^\

\ \ \

\ \ ^

ThLCknes3 of S ta.-m,pi-n.g3

rvinnlng conditions and It will furnish the torque or the

greater portion of the torque at a minimum slip.

the total characteristic is shown Dy curve 3, FIG. ?,

which is the resultant of curves 1 and 2. Where 1 is the curve

for the high resistance winding and 2 is the curve for the low

resistance winding.

An idea of the running and starting characteristics

of the Boucherot Rotor can also he obtained from the circle

diagram of each winding. The inner winding will have a smaller

circle than the outer winding, because the reactance of the inner

winding is greater. The resultant quantities can be obtained

by the vecter addition of these two circles, i.e., we would

have to know the phase and magnitude of the curre(^nt8 in each

one at the same tii^e and by adding them vectorially we would

obtain the resultant circle diagram. The diameter of the re-

sultant circle would be equal to

E^_X/ - x^

Where E - impressed E M F of primary

X/ - primary reactance

X^ - secondary " reduced to primary reactance.

X^ is ^he reeulatant reactance of the two winding. The windings

may be considered as in parallel because the current In any wind-

ing is proportional to the impedance of that winding. The easiest

way to find the impedance of the two windings would be to find

the admittance and taKe th^^ reciprocal as the iropedance.

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In designing the rotor our object was to obtain a

maximum torque at starting and rainiimTin slir at normal full

load. This being our object ve found it would be easier to

obtain the conqponent circles first and then determine the

resultant circle diagram.

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C a.LcvLu.t ioiinS

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Rotor Blocked . zs ^£ - /4>'!r VoLh^ Rf,^ o6/^y<^. PCZfy ' &^ Am-^los

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Rotor Blochf,cL 3o V. £^. Scix^U<f>

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-1 "—

CONSTRU C TION

Owing to the peculiar form of the stamping that would

"be required to maXe up the laminated core of this rotor. It

was found necessary to form them by another method than stamp-

ing. For this reason and the difficulty entailed in cutting

and fitting the laminations, it was decided to do without a

spider and fit the laminations directly on the shaft.

The laminations where cut from sheet Iron and placed

on a specially made arbor with a shoulder on one end and a

thread on the other. In orddr to drill the hole in the lamin-

ations to fit on the arbor, a special drill the required size had

to be nade. Two cast iron flanges, PIG. 4, were made to fit

the arbor and the laminations screwed up between them, placed

in a lathe and turned down to size.

Before putting the laminations on the arbor one flange

vras laid off and holes drilled 1/I6" larger than the conductors

as in Pig. 1. This was used as guide in drilling the holes in

the laminations. For this drilling extra long drills had to be

obtained. After drilling the work was placed in a milling machine

and slots cut. It was then taken apart, the laminations cleaned

up and placed on the shaft made similar to the one in Pig. 3,

with the exception that a thread was cut on one end. One flange

was fastened in position with set screws and the laminations

tightened up on the shaft.

The flanges were cut off to allow the end rings Fig. 5,

to be placed in position. The copper bars were cut to allow a

preelection of I-1/4" on either side. The 1/2" bars were cut

down to 3/3" diameter for this distance of 1-1/4".

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^7^oU9f\y

^ HoU

Up of Stiri/bs

\ "<?:je<

// /tcn^ made,//up of CQppenr

/ 3trip s

-13-

Ordlnary paper was used for Insulation. The end rln^s, the

inner one of brass to provide a low resistance, and the outer

of cast Iron for the high resistance, were faatenod on "/1th

brass nuts. The completed rotor v/as then filed to pxact sine

and placed in the stator virhere it ran satisfactorily.

Eue to the fixed dimensions of the rotor it was

necessary to change the calculated values to the valup>s nhown

on the blue prints.

After the completion of the new rotor ttb ran a test on

it to obtain the exciting and rotor blocked current, (which ia

a measure of the instantaneous staitiiig current.

Data obtained for new rotor.

Motor running no load. - Exciting currerit.

E = 80, I - S3-5/10, average

r^ - 1300 W^ = 540, V = 960 watts.

Kotor blocked

E = 25, I = 72.5 avera,-^e

W/ - 1650, W^ - 200, W = 1850 watts.

As seen from the data the exciting c\irrent in imieh smaller for

the nev7 rotor than the old; this is probably due to the errialler

iron lop;s and slightly less air gap. 71ie power consumed is

greater, but this might be due to the newness of the movixig rarts,

The rotor blocked quantities are about 50<;*^ scialler for

the new rotor than for the old.

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