Improvements relating to Electro-motors and Transformers.
Year: 1895

page_text: Date of Application, 8th Oct., 1895
Complete Specification Left, 29th May, 1896-Accepted, 11th July, 1896
Improvements relating to Electro-motors and Transformers.
We, WALTER LANGDON-DAVIES, of 57 Comeragh Road, West Kensington in
the County of Middlesex, and THE ALTERNATE CURRENT ELECTRO MOTOR
SYNDICATE LIMITED of 2 and 4 Penywern Road, Earls Court, in the said County
of Middlesex, do hereby declare the nature of this invention to be as follows:-
In the Specification No. 19364 in the year 1894 there is described means by
which an alternating single phase current may be made to produce a rotary
magnetic field suitable for a self starting alternating current motor and suitable
also for a transformer which is required to transform a single phase current into two
approximately equal currents differing from one another in phase.
For these purposes, whether it be to obtain the greatest starting moment in an
electromotor or the greatest efficiency in a transformer the magnetic field should
rotate as uniformly as possible and should not vary in strength.
The means described in the said specification approximately satisfy these
conditions, but greater uniformity may be obtained by the following means:-
When two fields are used to produce the rotating field the coils should be so set
that the axes of the two fields, forming the resultant rotating field, are at an angle
to each other which is the supplement of the phase angle of the coils; thus, suppose
the phase difference of the currents in the coils to be 45°, the coils should be so set
upon the core that the north pole of one field is 135° from the north pole of the
other field. Thus two fields having simple harmonic variations, which are not in
phase with one another are combined to produce a rotary field of which both the
strength and the velocity of rotation are constant.
Similarly three or more fields may be combined to produce a like resultant
field.
It is also important that the magnetic flux should be as evenly distributed over
the polar surfaces as possible. Now suppose an annular field magnet and a
cylindrical rotor mounted within it, the axis of the field generated by the field
magnet through the rotor, being vertical, then this field may be represented by a
number of vertical lines drawn across the annular field space, and these lines, which
will decrease in length from the centre line or diameter, to either side, will
approximately represent the reluctances of the magnetic paths across the various
elements of the field. If now the same magneto motive force be applied over the
whole field, by surrounding the field space with a single coil, a stronger magnetic
field will be generated through the regions of lesser reluctance, and as a result the
field generated by the above described field magnet will be considerably denser at
the two sides than in the centre. Therefore to produce an approximately uniform
distribution of the magnetic field we make up the coils of each of our component
fields, of windings not uniformly distributed but so disposed upon the core, that the
magneto motive forces generated by the several windings vary approximately
inversely as the reluctance of the portions of the field they respectively energise.
A further advantage may be obtained by placing the coils so that the entire

page_text: core is not enveloped by them, leaving properly proportioned neutral spaces; in
the above described field magnet these spaces would be at the two sides.
In some cases there may be air spaces in the neutral positions.
Dated this 7th day of October 1895.
We, WALTER LANGDON-DAVIES, of 57 Comeragh Road, West Kensington,
in the County of Middlesex, and THE ALTERNATE CURRENT ELECTRO MOTOR
SYNDICATE LIMITED, of 2 and 4 Penywern Road, Earls Court, in the said
County of Middlesex, 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 :-
In the Specification No. 19364 in the year 1894, there is described means by
which an alternating single phase current may be made to produce a rotary
magnetic field suitable for a self starting alternating current motor and suitable
also for a transformer which is required to transform a single phase current into
two approximately equal currents differing from one another in phase.
For these purposes, whether it be to obtain the greatest starting moment in an
electro-motor or the greatest efficiency in a transformer the magnetic field should
rotate as uniformly as possible and should not vary in strength.
The means described in the said specification approximately satisfy these
conditions but greater uniformity may be obtained.
We have demonstrated that when two fields are used to produce the rotating
field the coils should be so set that the axes of the two fields, forming the resultant
rotating field, are at an angle to each other which is the supplement of the phase
angle of the coils, thus-suppose the phase difference of the currents in the coils
to be 45° (which is about the maximum difference of phase which is suitable and
is readily obtained from one electro-motive source) the coils should be so set upon
the core that the north pole of one field is 135° from the north pole of the other
field. Thus two fields having simple harmonic variations, which are not in phase
with one another are combined to produce a rotary field of which both the strength
and the velocity of rotation are constant.
The law is general that when the axes of two simple harmonic fields are inclined
to one another at an angle which is the supplement of the phase angle between the
fields they produce a uniformly rotating resultant.
It is therefore correct to place the axes of these fields at 90° when the phase
difference is 90° between the two fields.
In general the difference of phase to be taken into consideration for the above
purpose will be that which exists initially. But if it is intended that the motor
shall run asynchronously as well as to be thus set in motion it may be found
advantageous to take the difference of phase when the motor is at or about its
normal work.
It is also important that the magnetic flux should be as evenly distributed over
the polar surfaces as possible. Now suppose an annular field magnet and a
cylindrical rotor mounted within it, the axis of the field generated by the field
magnet through the rotor, being vertical, then this field may be represented by a

page_text: number of vertical lines drawn across the annular field space, and these lines which
will decrease in length from the centre line or diameter to either side will approxi-
mately represent the reluctances of the magnetic paths across the various elements
of the field. If now the same magneto-motive force be applied over the whole field
by surrounding the field space with a single coil, a stronger magnetic field will be
generated through the regions of lesser reluctance and as a result the field
generated by the above described field magnet will be considerably denser at the
two sides than in the centre.
Figure 1 shows an end view of an iron cylinder such as would be used in a
motor wound with a single coil to produce a field perpendicularly across the interior
diameter.
The conductors are wound through the holes at the sides of the cylinder say up in a
direction parallel with the axis through the hole on the left hand side A across the
end of the cylinder in a semi circle and down through the right hand hole B, again
in a direction parallel with the axis.
Now with such a winding when the current passes polarities N and S are obtained
but the field is not at all uniformly distributed for the reason already given namely
the different reluctances of the paths, and the field is very dense at the two sides
near A and B and diminishes very considerably towards the centre as is indicated
by the figure.
Now it is a fact (as might indeed be anticipated) that a uniform rotating field
cannot be obtained by superposing as in Figure 2 two fields such as Figure 1
indicates which are not individually uniformly distributed.
Figure 3 illustrates our method of winding by which we obtain approximately
uniform distribution in cach of the individual component fields.
We distribute the winding so as to compensate the different reluctances of the
paths. A portion only of the winding is threaded through the holes A B, whilst
another portion is threaded through holes C, D, and it may be a third portion
Then the
through holes E, F, and a fourth portion through holes G, H.
windings CD, E F, G H will successively reinforce the magneto motive force
in those sections of the field which need reinforcement in consequence of the
progressive increase in the reluctance. The dotted lines indicate the directions
taken by the winding wires in passing from hole to hole.
The number of the sections into which the winding is divided may be varied,
three will be sufficient for the smallest class of two pole motors, and four or more
sections will be used in two pole motors of larger size.
The cylinder is built up of thin discs of soft iron having sixteen holes in each
and is adapted to receive two similar windings each in four sections and diametrically
opposite, one above and the other below the horizontal diameter of the cylinder as
it appears in the figure. These windings above and below may be regarded as
parts of a single coil. It is not essential however that the windings should be thus
arranged, there need be no winding on the lower part of the cylinder, or the lower
part of the cylinder may be reserved to receive a winding for a current differing in
phase to produce with the first winding a rotatory field, or again the winding may
be disposed as in Figure 4 partly on the upper and partly on the lower half of the
cylinder.
The rule by which we apportion the turns in the several sections for a cylinder
such as Figure 3 is the following
--
Draw a figure, such as Figure 34, in which the points A, B, C, D, E, F, G, H,
on the circumference of a circle, correspond to the equally spaced holes similarly
lettered in Figure 3.
Bisect the intervals between the holes in points 1, 2, 3, 4 and 5 marked on the
circle.
From the neutral point 1 draw a radius and from the point 5 at the centre of
the polar surface draw another radius, they meet at the centre O in a right angle.
Draw a line 2, 6 so that the angles at 6 are right angles.
Draw right angles 6, 2, 7-2, 7, 3-7, 3, 8-3, 8, 4-and 8, 4, 9.

page_text: Thus we find for example that if we wind through A B 19 turns, we should wind
these being the nearest whole numbers.
advantages of fractional parts.
وو
CD 16
EF 10
"
"
"
GH 5
"
99
We give to the winding G H the
Similarly we calculate when the number of sections is less or greater than four.
The rule given above is readily deduced from the fact that the reluctance of two
paths represented in Figure 5 by lines y and z varies approximately as the sines of
the angles Y and Z. We therefore apply a proportionately greater magnet-
motive-force about z than along y.
2
It will be observed that neutral intervals occur between the upper and the lower
windings, it is expedient to provide in this manner for neutral areas between the
polar surfaces.
When the total number of turns to be wound on is but smail, sufficient accuracy
cannot be obtained with equally spaced holes, we then prefer to wind an equal
number of turns in each section and to vary the distances between the holes.
Such a field magnet may be set out in the manner shewn in Figure 6 the
diameter of the armature space coinciding with the axis of the field is divided into
twice as many parts as there are coils to be wound (in this case 16) at right angles
to the axis of the field are drawn parallel lines through the points 2, 4-6, 8, 10,
12, 14, 16 cutting the diameter of the armature space, through the points where
these lines cut the diameter are drawn radii, and the holes for winding are punched
upon these radii; as shewn these holes are bisected by the radii.
+
We can in a similar manner wind a cylindrical magnet core so as to obtain four
or more poles. Figure 7 shews a cylinder prepared to receive a four pole
winding.
In the case of a four pole magnet when the holes are equally spaced and the
number of turns on the coils differ from one another as in Figure 3 we ascertain
the proportions to be given to the several sections of the windings by drawing
a diagram such as Figure 7.
It is very similar to Figure 3A but now the radii 5, 0 and 0, 1 meet in an angle
of 45 degrees, in other respects the description of Figure 3A applies.
We have so far described the winding for obtaining one uniform field. To yield
a rotating field a second winding is required separated from the first winding by an
angular distance dependent on the difference of phase in the two windings as
already explained. We can apply the second winding over the first, using the
same holes or some of them to accommodate both the windings. Thus in Figure 8
the full lines show a cylinder set out with holes for winding as in Figure 6 except
that in this case the windings are to be each in five sections.
The dotted lines show the holes repeated at 90° distance from the holes
represented by the full lines. The phase difference between the currents in the
coils is in this case assumed to be 90°. It is obviously impracticable to punch the
double set of holes as they occur in this diagram. Figure 9 shows the arrangement
of holes suitable to receive two windings, the one over the other and at right
angles.
The dotted lines crossing the central space represent diagrammatically one pair
of windings and the dotted lines outside the central space represent the other pair
of windings.
Figure 10 shows the arrangement which is suitable for a motor in which the
difference of phase in the two component fields is 45° and in which the current in
the two coils is derived from the same source, the coils being adjusted to equal
amjère turns in the manner described in our before mentioned patent.
Figures 11, 12 and 13 show a rotor which is suitable for use with field magnets

page_text: such as herein described, it consists of a series of iron discs threaded upon a shaft A
and clamped fast between screw nuts B. A feather C, prevents the discs from
turning on the shaft. A series of copper rods D, are passed through the discs and
at their ends are fixed into massive copper rings E. Saw cuts are made in the
edges of the discs parallel to the axis and penetrating into the holes which receive
the copper rods. These slits are seen in Figure 13. The thick black lines in
Figure 11 indicate insulating material.
For transformers the field coils are wound as described in respect to Figure 12
of our former Specification No. 19364% with the modifications to produce a more
uniform rotating field as described herein.
The secondary coils are applied as shewn in the above specification.
Having now particularly described and ascertained the nature of our said inven-
tion and in what manner the same is to be performed we declare that what we
claim is :-
1. In electro-motors, transformers and the like, a rotating field derived from
a single alternating source, such field being the resultant of component fields, the
axes of which are inclined to each other at an angle the supplement of that by
which the component fields differ in phase, as hereinbefore set forth.
2. In electro-motors, transformers and the like, a rotating field, the resultant of
component fields, the axes of which are inclined to each other at an oblique angle,
the supplement of that by which the fields differ in phase as hereinbefore set
forth.
3. In electro-motors, transformers and the like, a magnetic field obtained within
the central space of a cylindrical magnet core by windings substantially as
described, encircling more or less of the central space, and distributed upon the
cylinder in due relation as herein explained to the magnetic reluctance to be
overcome.
4. In electro-motors, transformers, and the like a rotating field, the resultant of
two component fields obtained in the manner stated in Claim 3.
5. In electro-motors, transformers, and the like, a rotating field the resultant of
two component fields obtained in the manner stated in Claim 3 the axes of such
fields being inclined to each other at an angle, the supplement of that by which
the fields differ in phase, as hereinbefore set forth.
Dated this 28th day of May 1896.
W. LANGDON-DAVIES.
THE ALTERNATE CURRENT ELECTRO MOTOR
SYNDICATE, LTD.,
G. W. DE TUNZELMANN,
Managing Director.