Improvements in Single Phase Induction Motors.
Year: 1898

page_text: Date of Application, 11th Jan., 1898
Complete Specification Left, 5th Oct., 1898-Accepted, 3rd Dec., 1898
Improvements in Single Phase Induction Motors.
I, LLEWELYN BIRCHALL ATKINSOx, of Western Mail Buildings, St. Mary Street,
Cardiff, in the County of Glamorgan, Civil Engineer, do hereby declare the nature
of this invention to be as follows:-
My invention relates to improvements in single phase or monophase induction
motors, and relates to the means of starting the same.
The present means of starting induction motors designed to be operated by
currents supplied from a source of supply of one phase only consists in relatively
displacing the phases of the currents in the inducing circuits thus producing a
difference of phase between the magnetic fields successively surrounding the short
circuited armature, producing in fact by means of condensers or self induction
coils in the inducing circuits, a multiphase magnetic system, the resistance and
self induction of every armature or secondary coil being the same.
In my present invention, the phase of each of the successively surrounding
magnetic fields is substantially the same being one fourth of a period or there-
abouts displaced from the phase of the supply E. M. F. The resistance of all the
armature conductors is the same but the self induction of each armature circuit
is made to differ on different magnetic axes.
Thus dealing with a motor having two pairs of poles at right angles to each
other. I wind each of the pairs of poles, in the manner usual, say with an
ordinary two phase motor, so that with as little magnetic leakage as possible each
produces a secondary E. M. F. on the short circuited coils on the armature.
The armature however is arranged relatively to the magnetic system so that on
one axis the magnetic leakage of the secondary circuits is small, on the other
axis at right angles it is large.
Calling the axis on which the secondary magnetic leakage is small A, and that
on which it is large B, the following description explains the action:-
Premising that the inducing magnetic fields on A and B are substantially in
phase, the secondary E. M. F. on Ä sets up a secondary current quarter period
displaced from either of the magnetic fields and therefore producing no magnetic
effect. The secondary E. M. F. on B produces a current which owing to the
presence of self induction in the armature circuits on this axis, is a quarter period
behind the E. M. F. that is in all half a period behind the inducing magnetic
field, that is (omitting algebraic sign) in phase with the magnetic field in
which it is immersed, and hence rotary movement results.
It is to be observed that when the motor has been started the coils on B may
be suppressed, the motor will then run as an ordinary monophase motor, and
the secondary magnetic leakage becomes in part the useful magnetic field.
It will be observed that whereas at starting the current on axis B reacts with

page_text: the magnetic field on A to produce rotation, when running as a monophase motor
it is the current on axis A which reacts with the magnetic field on B.
Several constructions may be made to carry my invention into effect.
For example the short circuited armature may extend beyond the inducing
frame, and be surrounded by a second magnetic system which either by its
shape or by being wound with shading coils offers in one direction a magnetic
circuit of low and in one of high magnetic resistance, or one frame only may be
wound with two sets of coils, the first of these is arranged so that all the induc-
tion produced by it passes into the armature, and the windings of the armature
cannot produce induction along any leakage path, the second is also arranged
so that all the induction passes into the armature; but enclosing in its area a
smaller width than the coil just described, the induced armature currents have
in part an alternative path outside of the coil and thus produce a magnetic field
in other words on this axis axis the armature coils have a large co-efficient of
self induction.
In starting the motor it is desirable except for small sizes to insert resistance
in the armature circuit by means of slip rings in manner well understood.
Dalth 1141 dov of Tonuo 1808
FELL & JAMES,
1, Queen Victoria Street, London, E.C., Agents for the Applicant.
Improvements in Single Phase Induction Motors.
I, LLEWELYN BIRCHALL ATKINSON, of Western Mail Buildings, St. Mary Street,
Cardiff, in the County of Glamorgan, Civil Engineer, do hereby declare the nature
of this invention and in what manner the same is to be performed to be particu-
larly described and ascertained in and by the following statement:-
My invention relates to improvements in single phase or monophase induction
motors, and relates to the means of starting the same.
The usual means at present adopted of starting induction motors designed to
be operated by currents supplied from a source of supply of one phase only con-
sists in relatively displacing the phases of currents in the inducing circuits
thus producing a difference of phase between the magnetic fields successively
surrounding the short circuited armature, producing in fact by means of con-
densers or self induction coils in the inducing circuits, a multiphase magnetic
system, the resistance and self induction of every armature or secondary coil
being the same.
In my present invention, the phase of each of the successively surrounding
magnetic fields is substantially the same, being one fourth of a period or there-
abouts displaced from the phase of the supply E. M. F. The resistance of all the
amature conductors is the same but the self induction of the armature circuit
is made to differ on different magnetic axes.
Thus dealing with a motor having two pairs of poles at right angles to each
other. I wind each of the pairs of poles in the manner usual, say with an
ordinary two phase motor so that with as little magnetic leakage as possible each
produces a secondary E. M. F. on the short circuited coils on the armature.
The armature however is arranged relatively to the magnetic system so that on
one axis the magnetic leakage of the secondary circuits is small, on the other
axis at right angles it is large.

page_text: Calling the axis on which the secondary magnetic leakage is small A, and
on which it is large B, the following description explains the action:-
Premising that the inducing magnetic fields on A and B are substantially in
phase, the secondary E. M. F. on A sets up a secondary current a quarter period
displaced from either of the magnetic fields and therefore producing no magnetic
effect. The secondary E. M. F. on B produces a current which owing to the
presence of self induction in the armature circuits on this axis, is a quarter period
behind the E. M. F. that is in all half a period behind the inducing magnetic
field, that is (omitting algebraic sign) in phase with the magnetic field AA in
which it is immersed, and hence rotary movement results.
It is to be observed that when the motor has been started the coils on B may
be suppressed, the motor will then run as an ordinary monophase motor and the
secondary magnetic leakage becomes in part the useful magnetic field.
It will be observed that whereas at starting the current sheets surrounding
the axis B react with the magnetic field on A to produce rotation, when running
as a monophase motor it is the current sheet surrounding the axis A which
reacts with the magnetic field on B.
Several constructions may be made to carry my invention into effect.
For example the short circuited armature may extend beyond the inducing
frame, and be surrounded by a second magnetic system which either by its
shape or by being wound with shading coils offers in one direction a magnetic
circuit of low and in one of high magnetic resistance, or one frame only may be
wound with two sets of coils, the first of these is arranged so that all the induc-
tion produced by it passes into the armature, and the windings of the armature
cannot produce induction along any leakage path, the second is also arranged
so that all the induction passes into the armature, but enclosing in its area a
smaller width than the coil just described, the induced armature currents have
in part an alternative path outside of the coil and thus produce a magnetic field
in other words on this axis the armature coils have a large co-efficient of
self induction.
In order that my invention may be better understood, I will now proceed to
describe it with reference to the drawings hereto annexed and to the letters and
figures marked thereon.
Figure 1 is a diagrammatic elevation of an induction motor with short
circuited armature and fixed induction frame, having working and subsidiary
starting coils.
Figure 1 is a back elevation showing an added starting magnetic frame
hidden from view in Figure 1.
Figure 1 is a modified form of added induction starting frame when used in
conjunction with the usual fixed induction frame of Figure 1.
Figure 2 shows diagrammatically the arrangement where only one induction
frame is used and
Figure 3 shows diagrammatically the connection of the working and subsid-
iary starting winding to the supply terminals.
or
Figure 1 shows the case when the armature is extended and shows diagram-
matically an induction motor with short circuited armature (a) having its coils
winding in holes near the surface. The stationary inducing frame (b) sur-
rounding it has a main inducing winding (w) shown in clear and shaded slots
of circular section surrounding the axis AA which is hereafter termed the axis
of the main winding. There is a second winding shown in slots of oblong
section surrounding the axis B B which is hereafter termed the axis of the
starting winding.
The short circuited armature is extended in the direction of the shaft (0)
beyond the width of the inducing frame (b) and the extended part enters on a
magnetic frame C unwound with any coils built like but of the form shewn
in Fig. 1, that is to say the interior surface approaches the exterior surface of

page_text: the armature for half the surface of the armature corresponding to the magnetic
axis BB, whilst half the surface corresponding to the magnetic axis AA is
removed.
It results from this that the magnetic resistance on the axis BB is low,
on AA high.
A simalar result is obtained, leaving the frame C uncut, and winding in slots
on its inner surface, the closed coils dd', e e¹, etc. as shown in Figure 1".
Figure 2 shows the case where one frame only is used and this is wound with
two sets of coils, those constituting the main or working winding shown by
clear and shaded holes of circular section wwe surrounding the axis AA, and so
arranged, as shown, that all the induction passing into the armature threada
both these coils and the coils on the armature, and those constituting the sub-
sidiary or starting winding surrounding the axis B B and shown by oblong
holes, so arranged that all the induction due to BB passes into the armature,
but those parts of the windings as KK on the armature circuit have an
independent magnetic circuit hh as shewn, in other words the coils KK have a
large co-efficient of self induction.
Though the coils rr are shown not coming to the interior surface of the
inducing frame, they preferably may do so being in the same holes as the
winding ww or interspaced with it.
Figure 3 shews the connection of coils and to the supply terminals .ry
at starting, and when run up to speed the circuit is disconnected and the
motor runs as a monophase motor in the usual manner, in the circuit ww.
In starting the motor it is desirable except for small sizes to insert resistance
in the armature circuit by means of slip rings in manner well understood.
It will be understood that allthough this description refers to a motor with
two pairs of poles only-and with a revolving armature and stationery inducing
winding, there may be any number of pairs of poles, and the armature may be
stationary and the inducing winding revolve in manner well understood.
Having now particularly described and ascertained the nature of this
invention and in what manner the same is to be performed, I declare that what
I claim is:-
1st. An alternating current nonsynchronous induction motor adapted for supply
circuits of one phase only, having the known short circuited induced or armature
winding and a main or inducing winding in combination with a starting wind-
ing, having a magnetic circuit closer so arranged in reference to the armature
that the magnetic leakage of the armature winding is greater on the axis of the
starting winding, than on the axis of the main winding.
2nd. An alternating current motor as claimed in Claim 1, having a short
circuited armature, in combination with a frame surrounding it and carrying
the main and starting windings and a second frame having poles adapted to
give a greater magnetic leakage to the armature windings on the axis of the
starting winding, than on the axis of the main winding, substantially as
described in relation to Figures 1 and 1.
3rd. An alternating current motor as claimed in Claim 1 having a short cir-
cuited armature in combination with a frame surrounding it carrying the main
and starting windings and a second frame having short circuited shading coils,
adapted to give a greater magnetic leakage to the armature windings on the
axis of the starting winding than on the axis of the main winding substantially
as described in relation to Figs. 1 and 1".
4th. An alternating current motor as claimed in Claim 1 having a short
circuited armature and a main winding arranged on the armature so that the
magnetic induction threading the main or inducing winding also threads the
induced or armature winding, in combination with a starting winding arranged
so that the magnetic induction threading it all enters the armature, but only 5

page_text: enclosing part of the surface of the armature, leave a specific path for the leakage
magnetic induction of the uncovered part of the armature winding substantially
as described in relation to Figure 2.
Dated this 5th day of October 1898.
FELL & JAMES,
1, Queen Victoria Street, London, E.C., Agents for the Applicant.