Improvements in Single Phase and Multiphase Alternate Current Motors.
Year: 1895

page_text: Date of Application, 12th Aug., 1895
Complete Specification Left, 12 h May, 1896-Accepted, 4th July, 1896
PROVISIONAL SPECIFICATION.
Improvements in Single Phase and Multiphase Alternate Current
Motors.
I, LLEWELYN BIRCHALL ATKINSON, of Bank Buildings, St. Mary Street,
Cardiff, in the County of Glamorgan, Civil Engineer, do hereby declare the
nature of this invention to be as follows:-
This invention relates to improvements in single phase and multiphase alternate
current motors, and has for its object the improvement of the power of such
motors, particularly at starting and when overloaded during running.
It is well known that multiphase alternate current motors do not start well
against a load without the insertion of resistance in the circuit of the induced
windings. The reason of this is that there is a leakage of magnetic induction
between the rotating part and the fixed part, so that all the induction threading the
inducing winding does not thread the induced winding, and vice versa, and hence the
magnetic field acting on the current in the rotating winding is limited whilst further
its maximum value is not in phase with the maximum value of the induced current.
To obviate these difficulties it is necessary to decrease the leakage of magnetic
induction and this I do in my present invention by bounding the areas through
which the induction should pass, by copper or other highly conductive plates or
surfaces, in which currents are induced opposing the leakage, not however closed in
themselves so as to oppose the induction in its proper magnetic circuit.
In order to diminish the co-efficient of self induction of the induced winding, I
divide or slit the polar surfaces of the inducing magnetic ring either partly or right
through and if necessary fill the slot or aperture with a plate of conducting metal
and in order to enable this to be carried out without increasing the magnetic
resistance of the magnetic circuits 1 provide independent magnetic circuits for the
windings of each phase. These improvements are also applicable to single phase
alternate current motors of that class in which the magnetic field acting on the
induced current in the rotating part to produce rotation, is produced at right angles
to the main inducing field and set up in the induced winding by the rotation; this
E.M.F. being in phase with the primary magnetic field.
In this class of motor my further improvements relate to the production of the
This is at
said magnetic field when the motor is at rest so as to enable it to start.
present done by applying to a winding at right angles to the inducing winding,
an E.M.F. differing in phase by period or nearly so from the E.M.F. applied to
the inducing winding. In my improved method I produce this magnetic field by a
winding which may be at starting only or is permanently in circuit with the
inducing winding and which therefore produces a magnetic field nearly in phase
with the current in the induced winding differing therefore by nearly a phase from
the main magnetic field and to enable this to be done I provide brushes which only
short circuit those coils of the armature in which the working current is required
until the motor attains its full speed after which all the coils are short circuited and
the subsidiary exciting coil may be cut out. My improvements further relate to
the method of winding the inducing circuits of single phase and multiphase motors.
As usually wound the coils encircle the iron core after the manner of the winding
of a Gramme" ring which has the disadvantage of increasing the magnetic
leakage before referred to, or if the winding is of the drum type the inducing

page_text: winding is symmetrical, having end connections with cross one another and which
are connected at intermediate points, to the supply circuits.
In my improved winding, each winding corresponding to each pole is complete in
itself and may be described as a spiral drum winding, so that no winding crosses
another winding, and whilst all the coils thus constructed are symmetrical the
winding as a whole is not symmetrical, but divided into groups. It is to be under-
stood that though the language used above in explanation of my invention applies
when the inducing winding is fixed and the induced winding rotates, my invention
is applicable when these relations are changed.
It is further to be understood that whilst the terms used are applicable to motors,
having one pair of poles to each phase, my invention is applicable to motors having
any number of pairs of poles to each. phase. It is also to be understood that
although I only describe the application of the winding in circuit with the
inducing winding of a motor of the class last described I consider the combination
produced; that is, an alternating generator producing currents of one phase with a
motor having an inducing winding, and an induced winding adapted for relative
rotation, with a second magnetic field produced wholely when in a state of rest,
and wholely, or partly when rotating by a winding in series with the inducing
winding, to be a novel combination for the purpose of transmitting power, by
alternating currents of one phase by means of asynchronous motors.
Dated this 12th day of August 1895.
FELL & WILDING,
1 Queen Victoria Street, London, E.C., Agents for the Applicant.
Improvements in Single Phase and Multiphase Alternate Current
Motors.
İ, LLEWELYN BIRCHALL ATKINSON, of Bank 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 particularly
described and ascertained in and by the following statement :-
This invention relates to improvements in single-phase and multiphase alternate
current motors, and has for its object the improvement of the power of such
motors, particularly at starting and when overloaded during running.
It is well known that multiphase alternate current motors do not start well
against a load without the insertion of resistance in the circuit of the induced
windings. The reason of this is that there is a leakage of magnetic induction
between the rotating part and the fixed part, so that all the induction threading
the inducing winding does not thread the induced winding, and vice versu; and
hence the magnetic field acting on the current in the rotating winding is limited,
whilst, further, its maximum value is not in phase with the maximum value of the
induced current.
To obviate these difficulties it is necessary to decrease the leakage of the
magnetic induction, and this I do in my present invention by bounding the areas
through which the induction should pass, by copper or other highly conductive
plates or surfaces, in which currents are induced opposing the leakage, not however
closed in themselves, so as to oppose the induction in its proper magnetic circuit.
In order to diminish the co-efficient of self-induction of the induced winding,
I divide or slit the polar surfaces of the inducing magnetic ring, either partly, or
right through, and if necessary fill the slot or aperture with a plate of conducting
metal; and in order to enable this to be carried out without increasing the magnetic
resistance of the magnetic circuits I provide independent magnetic circuits for the

page_text: windings of each phase. These improvements are also applicable to single phase
alternate current motors of that class in which the magnetic field acting on the
induced current in the rotating part to produce rotation is produced at right angles
to the main inducing field, and set up in the induced winding by the rotation;
this E.M.F. being in phase with the primary magnetic field.
In this class of motor my further improvements relate to the production of the
said magnetic field when the motor is at rest, so as to enable it to start. This is
at present done by applying to a winding, at right angles to the inducing winding,
an E.M.F. differing in phase by period, or nearly so, from the E.M.F. applied to
the inducing winding. In my improved method I produce this magnetic field by a
winding, which, may be, at starting only, or is permanently, in circuit with the
inducing winding, and which therefore produces a magnetic field nearly in phase
with the current in the induced winding, differing therefore by nearly a phase
from the main magnetic field; and to enable this to be done provide brushes,
which only short-circuit those coils of the armature, in which the working current
is required until the motor attains its full speed; after which all the coils are short
circuited, and the subsidiary exciting coil may be cut out. My improvements
further relate to the method of winding the inducing circuits of single phase and
multiphase motors. As usually wound the coils encircle the iron core after the
manner of the winding of a "Gramine" ring, which has the disadvantage of
increasing the magnetic leakage before referred to; or if the winding is of the
drum type, the inducing winding is symmetrical, having end connections which
cross one another, and which are connected at intermediate points, to the supply
circuits.
In my improved winding, each winding, corresponding to each pole, is complete
in itself, and may be described as a spiral drum winding, so that no winding crosses
another winding, and whilst all the coils, thus constructed, are symmetrical, the
winding as a whole is not symmetrical, but divided into groups.
And in order that my invention may be the better understood, I will now proceed
to describe it in relation to the drawings hereunto annexed, reference being had to
the letters and figures marked thereon.
Figure 1 shows in cross section the laminated iron core A of the inducing
winding, and B of the induced windings of a multiphase motor. The normal path
of the induction is from the face a a to the face bb, but a certain amount of
magnetic leakage takes place as represented in diagram in Figure 2, the arrowed
circles showing the path of the leakage. I provide copper or other highly
conductive plates, as CC in Figure 3, completely enclosing the iron surfaces of
the cores, except on the faces where normally the induction should pass; the
currents set up in these conductive plates oppose the leakage of induction, and
confine it to its proper path between a a and b b.
Figure 4 shews in diagram a two-phase motor with one pair of poles to each
phase.
The diagram represents the condition of the motor when the magnetic field
on the axis a a is at its maximum. At the same time the secondary current in the
shaded helt of the armature conductors n is a maximum. The direction of
notation being as shown by the external arrow, and the direction of the magnetic
field as a a, this belt of current tends to produce a magnetic field in the direction
of the arrow bb, and there being a closed path through the polar surfaces carrying
the coils A A, there is a leakage field established through these polar surfaces.
Figure 5 shows by the full lines one pair of poles carrying the coils B B of one
phase, and the poles are divided as at dd.
The poles carrying the coils A A of the other phase are shown by dotted lines,
and are divided as at d¹ d'. The openings or gaps thus produced, may have sheets
of copper or other conductive metal inserted in them, and the magnetic cores may
be enclosed or surrounded by conductive metal bounding sheets as in Figure' 3.
Similar arrangements may be adopted when there are any other number of phases,
a separate magnetic core being provided for each phase.

page_text: Figure 6 shows diagrammatically a single phase motor, in which AA are the
inducing coils, the path of the maguetic field producing rotation, which when
running is set up by the rotation of short circuited coils in the field of the coils A A,
being shown by the arrows.
My improvement consists in providing coils BB, connected in series with A A,
and in the use of a collector e, to which the conductors of the induced winding are
connected, and of short-circuiting brushes or contacts cc dd, which at starting
short circuit only those coils through which the magnetic induction due to AA
passes. It results from this arrangement that the phase of the magnetic field due
to B is e incident with the current in B, that is with the current in A, which is
phased half a period in advance of the phase of the current in the coils under the
brushes; in other words the induced currents are at a maximum at the same time
as the magnetic field in which they are immersed, and hence rotation is set up.
When the motor has started, the conductors embraced by the arcs c d and c¹ d¹
may also be short circuited by similar brushes, and the coil B cut out of circuit,
when the motor will work in the usual manner.
The particular method of short circuiting shown in Figure 6, that is by the use
of wide brushes of flexible material, embracing an are on the collector, is not the only
method, but is applicable more particularly when a winding of the squirrel-cage
type is used, ending at one end in a collector instead of a short circuited ring. Ii
a continuous winding is adopted it may be connected to an ordinary collector, and
ordinary brushes applied at the points cd, c' d', and the brushes c c¹ being connected,
as also d d', at starting, the brushes cd c¹ d' are connected when the motor has ran
up to speed, or instead of this last operation, contact rings may be provided,
connected to four points on the induced winding at right angles, which, when the
motor is up to speed, are short circuited, when the brushes cc dd may be lifted
off the collector, or cut out of circuit.
Figure 7 shows a diagram of the electrical connections of this class of motor,
and shows the supply circuit passing through A and B in series. A switch is
provided as at S by which the coil B may be cut out of circuit, the connections
of the brushes c, d, c', d¹, are as has been already described.
Figures 8, 9 and 10 relate to my improved method of winding the induced and
inducing windings.
Figure 8 shows a development on the plane of the paper of one part of a
winding, carried out after the manner of a Gramme ring, in the ordinary method
producing a pole at A, each line marked with an arrow representing a conductor
passing across the face through a slot or hole.
Figure 9 shows part of a drum winding producing a pole at A, with symmetrical
but crossing end connections.
Figure 10 shows my improved spiral drum winding, producing a pole at A, the
coil in itself being symmetrical with other coils, but each coil or winding being
complete in itself without crossing of wires.
It is to be understood that though the language used above, in explanation of
niy invention, applies when the inducing winding is fixed and the induced winding
rotates, my invention is applicable when these relations are changed.
It is further to be understood that whilst the terms used are applicable to motors
baving one pair of poles to each phase, my invention is applicable to motors having
any number of pairs of poles to cach phase. It is also to be understood that
although I only describe the application of the winding in circuit with the inducing
winding of a motor of the class last described I consider the combination produced;
that is, an alternating generator producing currents of one phase with a motor
having an inducing winding, and an induced winding, adapted for relative rotation,
with a second magnetic field, produced wholely when in a state of rest, and wholely,
or partly when rotating, by a winding in series with the inducing winding, in
combination with the arrangement of brushes described, to be a novel combination
for the purpose of transmitting power, by alternating currents of one phase by
means asynchronous motors.

page_text: Having now particularly described and ascertained the nature of my inven-
tion and in what manner the same is to be performed, I declare that what I
claim is :-
1st. In multiphase or monophase alternate current induction motors, the arrange-
ment of plates of highly conductive metal, bounding the surfaces through which
the magnetic induction is desired to pass, for the purpose of diminishing magnetic
leakage, substantially as described and illustrated in Figure 3 of the accompanying
drawings.
2nd. In multiphase alternate current induction motors, having inducing and induced
windings, the arrangement of separate magnetic circuits or cores corresponding
to each phase of the inducing winding, having slots or gaps dividing the poles,
with or without conductive metal filling pieces, substantially as and for the
purpose described and illustrated in Figure 5 of the accompanying drawing.
3rd. In single phase or monophase motors, in combination, a principal or main
inducing winding, a secondary or subsidiary magnetising winding, an induced
winding having the coils acted on by the main inducing winding, adapted to be
short circuited by brushes, and devices for cutting out the subsidiary winding, and
short-circuiting all the coils, substantially as and for the purposes described and
illustrated by Figures 6 and 7 of the accompanying drawings.
4th. In multiphase or mono-phase motors, the arrangement of inducing or induced'
windings in the form of a distributed drum winding, with spiral non-crossing end
connections, substantially as described and illustrated in Figure 10 of the
accompanying drawings.
De 10th day of M 1906
FELL & WILDING,
1 Queen Victoria Street, London, E.C., Agents for the Applicant.