An Improved Method of and Apparatus for Producing Rotating Magnetic Fields and Multiphase Alternating Currents.
Year: 1891

page_text: Date of Application, 6th Nov., 1891
Complete Specification Left, 4th Aug., 1892-Accepted, 15th Oct., 1892
PROVISIONAL SPECIFICATION.
An Improved Method of and Apparatus for Producing Rotating
Magnetic Fields and Multiphase Alternating Currents.
I EMIL ALFRED WAHLSTRÖM of 30 Bad Strasse, Cansstatt in the Kingdom of
Württemberg, German Empire Engineer, do hereby declare the nature of this
invention to be as follows: -
The object of my improvements is to produce rotating magnetic fields and multi-
phase currents by means of one alternating current.
Hitherto a method of economically running self-starting motors by means of
alternating currents was completely wanting. Other problems the solution of which
was desirable were to combine multi-phase currents so as to form a single current,
and to divide a single current into multi-phase currents in a simple and economical
manner.
The invention hereinafter described effects these improvements by means of a
peculiar winding of the exciting and excited coils.
The better to make my meaning clear, I refer to the accompanying drawings, in
which similar letters denote similar parts throughout the several views, and of
which;-
Fig. 1 is a plan showing the manner in which the current flows through eight
consecutive coils wound according to my improvements,
Figs. 2 & 3 are diagrams illustrating the electrical action,
Fig. 4 shows the coils of Fig. 1 arranged on an iron ring,
Figs. 5 & 6 show in section two manners in which the coils may be wound.
A rotating magnetic field consists of a series of consecutive magnetizing coils,
which are disposed to form a ring or a drum and attain their maximum of mag-
netization not all at the same time, but one after the other. The smaller the
interval of time between two adjoining coils attaining their maximum, the better
the effect. The greater the number of coils and the smaller the difference between
single coils situated between coils of opposite magnetization, the more progressively
and uniformly the magnetization proceeds whereby the efficiency is improved.
As is well known, Galileo Ferraris has proved that a rotating field may be
produced by means of alternating currents, the phases of which differ by 90° and
which flow through magnetizing coils placed at half the polar distance from each
other. But Galileo Ferraris has also shown that such a motor cannot be worked
economically.
The invention herein described relates to an arrangement of the coils which are
placed between coils the phase of magnetization whereof differs by 90°; and to the
employment of the same for machines and transformers.
I make the supposition a current be available, which is represented by the
equation y¹ a. sin a, y indicating the ordinate, a a constant and a the arc of a
circle rolling on the X-axis. The curve 1 (Fig. 2) is the graphical representation
of the above equation. If this current be sent through a transformer C-D-A
(see Fig. 1), a current is generated in the secondary bobbin, which is
about y =
b sin (a + 90°), 6 being another constant. If now it be intended to
produce by means of these currents a bipolar rotating magnetic field (consisting for
instance of 8 coils, as indicated in Fig. 1) the magnetization of coils 1 and 5 being
wound or connected so as to produce opposite effects, may be effected by the
current y¹ = a. sin a, and in similar manner the magnetization of coils 3 and 7 by
the current y". b. sin (a + 90°). Supposing, in order to simplify matters, the
constants a and b to be 1 and the turns of the coils to be of equal numbers, the

page_text: curves of Figs. 2 & 3 represent the magnetization of the single coils. Thus
the magnetization effected by the coils 1, 3, 5 & 7 (Fig. 1) is represented by the
curves 1, 3, 5 & 7 (Figs. 2 & 3).
The coils 2, 4, 6 & 8 (Fig. 1) are now to be wound in such a manner, that the
difference of their phases from those of the coils 1, 3, 5 & 7 amounts to 45°. As
will be seen in Fig. 2, an algebraic addition of the curves 1 and 3, having a
difference of phase of 90°, yields a curve 2 having a difference of phase of 45°
from 1 and 3, but a greater constant. That is to say, if two coils having the same
=
number of turns as the coils 1 and 3 be wound into another and if each of them
be excited by one of the currents y¹ = sin a and y¹ sin (90°), the magnetic
action of the coil thus formed is greater than that of each of the coils 1 and 3, and
shows a difference of phase from the latter amounting to 45°. If now the number
of turns of the combined coils be reduced in the same ratio as the magnetic action
of the said coils is greater than that of the coils 1 or 3, a curve 2 (Fig. 2) will be
produced which is equal to the curves 1 and 3, but differs from these in phase
by 45°. It is therefore possible by giving the coil 2 the suitable number of turns
to obtain from it the same magnetic action as from 1 and 3, but intermediate
between these two in phase. The curves 4' and 4 are produced in the same manner
as 21 and 2, with the only difference that the curve 3 must be algebraically
subtracted from 2. The coil 4 is therefore formed of two windings wound in
contrary directions, through each of which flows one of the currents y' = sin a
and y
sin (a+90°). The coils 6 and 8 are formed by winding or connecting
coil 6 so as to produce a magnetic effect opposite to that of coil 2, and coil 8
contrary to coil 4.
=
In Fig. 3 the magnetization of the eight coils is represented by the eight
curves 1-8. In Fig. 4 the coils represented in Fig. 1 are wound upon a ring. By.
comparing Figs. 3 & 4 it will easily be understood that in fact a rotating magnetic
field is produced in this manner.
==== d. sin
If the number of coils pertaining to each pole is to be increased, if for instance
it is intended to have 8 coils instead of 4, as in the example hereinbefore
employed, the coils 2, 4, 6 & 8 of Fig. 1 may be used as primary coils in
transformers, and the secondary currents III: c. sin (a + 45°) and y
(a+135°) thereby produced combined with the currents y a. sin a and y¹¹ = b.
sin (a +90°) in the manner described above; the bipolar field would thus be
composed of 16 coils.
".
The same result can be more easily obtained by conducting the currents y¹ =α.
sin a and y¹¹ b. sin (a + 90°) through two spirals forming one coil in such a
manner, that the magnetizing action of the spirals is different in each. The
maguetization by such a combined coil will the more approach the effect of one or
the other of the mentioned currents, the stronger this current is and the greater the
excess of turns of the corresponding spiral over the number of the turns of the
other spiral.
20¹ and w" indicating the turns of the single spirals, the magnetization. of
the same is:
wo¹ y
= wola. sin a and
w¹¹ y¹¹= w¹¹ b. sin (a + 90°).
--
-
Now the magnetization effected by a combined coil is equal to the algebraic
sum of the single magnetizations, thus = a. sin a + w¹¹ b. sin (a + 90°).
As the addition of two sine-curves always yields a sine-curve, the above quantity
can be written = C. sin (a), C being a constant and the angle by which the
phase of the magnetization of the combined coil differs from the magnetization w² a.
sin a. Thus we have the equation C. sin (a + ) = w³ a. sin a + w¹¹ b. sin (a + 90°).
It is apparent that by varying the quantities on the right side any magnetization of
a combined coil can be obtained, not only in regard to intensity but also respecting
the difference in phase from another coil. Example: A coil is to be formed having
a difference of 30° in phase from another coil excited by the current y¹
= a. sin a.

page_text: The magnetization is not to exceed 100 ampère-turns. We have then the equation :
503 87
100. sin (a+30°) = w¹ a. sin a + w₁l b. sin (a + 90°) the result is: wo¹α =
and: b = 57.
As the constants a and b are known, the number of turns w!
and w is obtained herefrom.
If the coil to be formed shall differ in the phase of magnetization by 135° from
that of the coil excited by the current y₁ = a. sin a, we have again:
100. sin (a+135°) = w¹ a. sin a + w¹¹ b. sin (a + 90°) and consequently
Ine negative sign indicates
to another in both spirals.
01340
In this manner any difference in phase may be obtained.
As already mentioned, the rotating field is produced by the arrangement of coils
of the described kind on a ring or a drum. If multi-phase currents are to be
produced by means of such coils, each of them can be used as primary coil in a
transformer, in which case each of the latter would yield a current.
The coils may also be combined so as to form a rotating field and provided with
a secondary coiling, which can be made continuous or divided into several coils.
From this coiling currents of different phases can be obtained by derivations similar
to those leading to the collector of a continuous current machine. By the reverse
method multi-phase currents can be made to form one current.
Both methods can be employed very advantageously for the transmission of
force.
In order to obtain a motor, the rotating field needs only to be fitted with an
armature the coils whereof are in short circuit.
In order to obtain a machine producing currents, the armature is replaced by a
magnet.
The joining-up of the coiling of the transformer in tension with each of the coils
having different phases, in which coils the spirals excited by the same current are
also joined-up in tension, as shown in Fig. 1, is preferable in certain cases to the
not excluded.
joining-up in quantity, though the latter
Figs. 5 & 6 are sections through the coils of a rotating magnetic field and show
the manner in which the coils may be arranged. If the number of the same is
considerable, the zig-zag lines a-b and b-c will be replaced by curves, so that
there are not many separated coils, but only a few fitting into another. If the
thickness of the coil is small, for instance one layer, one or more turns of one spiral
It has been supposed in the foregoing
would alternate with the turns of the other.
description that the two exciting currents differ in phase by 90°. That is not
necessary, however, and will very seldom occur in practice, unless the second
current be produced by other means than by transformation. The real difference
of phase is easy to ascertain and the coiling can then be made to suit the same.
Dated this 31st day of October 1891.
EMIL ALFRED WAHLSTROM,
By Geo. Thos. "Hyde,
4, Moorfields, Fore Street, London, E.C., Agent for Applicant.

page_text: COMPLETE SPECIFICATION.
An Improved Method of and Apparatus for Producing Rotating
Magnetic Fields and Multiphase Alternating Currents.
I, EMIL ALFRED WAHLSTRÖM of 30 Bad Strasse, Canstatt, in the Kingdom
of Wurtemberg, Germany, 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:-
The object of the improvements constituting my invention is to produce rotating
magnetic fields and multiphase currents, by the means of one alternating current.
Hitherto, a method of economically running self starting motors by the means of
alternating currents has not been attained, although problems have been adduced
(the solution of which were desirable) to combine multiphase currents so as to form
a single current, and to divide a single current into multiphase currents, but these
have always erred upon the side of economy.
My invention as hereinafter explained is intended to effect the improvements
desired and is attained by the peculiar winding of the exciting and excited coils
arranged and employed by me.
In order to make my invention more clear I make reference to the drawings
Sheet 1 which accompanied my Provisional Specification and to Sheet 2 hereunto
annexed in which
Fig. 1 Sheet 1 is a plan view shewing the manner in which the current flows
through eight consecutive coils wound according to my improvements.
Figs. 2 and 3 Sheet 1 are diagrams illustrating the electrical action.
Fig. 4 Sheet 1 shows the coils of Fig. 1 arranged upon an iron ring.
Figs. 5 and 6 Sheet 1 show in section, two methods in which the coils may be
wound.
Figs. 7 and 8 Sheet 2 are details to be hereinafter explained.
A rotating magnetic field consists of a series of consecutive magnetizing coils,
which are disposed so as to form a ring or drum, and attain their maximum of
magnetization, not simultaneously, but one after the other, and the smaller the
interval of time that elapses between two adjoining coils attaining their maximum
the better the effect. The greater the number of coils, and the smaller the
difference between single coils situated between coils of opposite magnetization,
the more progressively and uniformly the magnetization proceeds, whereby the
efficiency is improved.
As is well known Galileo Ferraris has proved that a rotating field may be
produced by the means of alternating currents, the phases of which differ by 90°, and
which flow through magnetizing coils placed at half the polar distance from each
other, but the same authority has also shown that such a motor cannot be worked
economically.
The invention hereinafter described relates to an arrangement of the coils which
are placed between coils the phase of magnetization whereof differs by 90°, and to
the employment of same for machines and transformers.
=
I make the supposition that a current is available, and which is represented by
the equation y=a, sin a, yl indicating the ordinate, a a constant, and a the arc of
a circle rolling on the X axis. The curve 1 (Fig. 2) is the graphical representation
of the above equation. If this current be sent through a transformer C, D, A
(Fig. 1) a current is generated in the secondary bobbin, which is about y¹¹ b sin
(a+90°), being another constant.
b
If now it be intended to produce by means of
these currents a bipolar rotating magnetic field, (consisting for instance of eight
coils, as indicated in Fig. 1) the magnetization of coils ! and 5 being wound or cou-
nected so as to produce opposite effects, may be effected by the current ¹=a, sin α,
and in a similar manner the magnetization of coils 3 and 7 by the current y". b sin,
(a + 90°). Supposing, in order to simplify matters, the constants a and b to be 1

page_text: and the turns of the coils to be of equal numbers, the curves of Figs. 2 and 3
represent the magnetization of the single coils. Thus the magnetization effected
by the coils 1. 3. 5 and 7 (Fig. 1) is represented by the curves 1. 3. 5 and 7 (Figs.
and 3).
The coils 2. 4. 6 and 8 (Fig. 1) are now to be wound in such a manner that the
difference of their phases from those of the coils 1. 3. 5 and 7 amount to 45°. As
will be seen in Fig. 2 an algebraical addition of the curves 1 and 3 having a
difference of phase of 90°, yields a curve 2', having a difference of phase of 45°
from 1 and 3, but a greater constant, that to say, if two coils having the same
number of turns as the coils 1 and 3 be wound into another, and if each of them be
excited by one of the currents y¹ sin a and y sin (a + 90°), the magnetic
action of the coil thus formed is greater than that of each of the coils 1 and 3, and
shows a difference of phase from the latter amounting to 45°. If now the number
=
=
of turns of the combined coils be reduced in the same ratio, as the magnetic action
of the said coils is greater than that of the coils 1 or 3, a curve 2 (Fig. 2) will be
produced which is equal to the curves 1 and 3, but differs from these in phase
by 45°. It is therefore possible by giving the coil 2 the suitable number of turns
to obtain from it the same magnetic action as from 1 and 3, but intermediate
between these two in phase. The curves 4¹ and 4 are produced in the same manner
as 21 and 2, with the only difference that the curve 3 must be algebraically
subtracted from 2. The coil 4 is therefore formed of two windings wound in
contrary directions, through each of which flows one of the currents y' = sin a
and y"
sin (a + 90°). The coils 6 and 8 are formed by winding or connecting
coil 6 so as to produce a magnetic effect opposite to that of coil 2, and coil 8
contrary to coil 4.
=
In Fig. 3 the magnetization of the eight coils is represented by the eight
curves 1-8. In Fig. 4 the coils represented in Fig. 1 are wound upon a ring.
By comparing Figs. 3 and 4 it will be easily understood that in fact a rotating
magnetic field is produced in this manner.
If the number of coils pertaining to each pole is to be increased, such for instance
as when it is intended to have eight coils instead of four, as in the example herein-
before employed, the coils 2. 4. 6 and 8 of Fig. 1, may be used as primary coils in
transformers, and the secondary currents y =c sin (a + 45°) and y¹v=d sin
(a+135°) thereby produced combined with the currents y¹
= a sin a and y" = b sin
(a+90°) in the manner before described, the bipolar field would thus be composed
of sixteen coils.
The same result can be more easily obtained by conducting the currents y¹
= a sin a,
and yb sin (a + 90°), through two spirals forming one coil in such a manner that
the magnetizing action of the spirals is different in each. The magnetization by
such a combined coil will the more approach the effect of one or the other of the
before mentioned currents, if the current be stronger, and if the excess of turns
of the corresponding spiral over the number of the turns of the other spiral be
greater, thus
w and windicating the turns of the single spirals the magnetization of the
same is
w¹ y¹ = w¹, a, sin and
a,
w¹¹ y¹¹ = w¹¹ b sin (a + 90º).

page_text: The negative sign indicates that the direction of the current must be opposite in
both spirals. In this manner any difference in phase may be obtained.
As previously mentioned, the rotating field is produced by the arrangement of
coils of the kind described on a ring or drum. If multiphase currents are to be
produced by means of such coils, each of them can be used as primary coil' in a
transformer, in which case each of the latter would yield a current.
The coils may also be combined so as to form a rotating field, and provided with
a secondary coiling, which can be made continuous or divided into several coils.
From this coiling currents of different phases can be obtained' by derivations
similar to those leading to the collector of a continuous current machine. By the
reverse method multiphase currents can be made to form one current.
I will now describe the construction of transformers embodying my improve-
ments, reference being made to Figs. 7 and 8 Sheet 2.
Fig. 7 represents a series or battery of transformers, which are obtained by
winding a secondary coil on each of the simple coils 1. 3. 5. 7, and of the double
coils, 2. 4. 6 and 8, these coils being constructed as described with reference to
Fig. 1 and constituting the primary coils of the transformers.
The individual transformers are each enclosed within an iron shell or casing C',
but I may employ an iron core in lieu thereof. The ends of the secondary coils are
made fast to contact plates or other conducting metal pieces from which the
currents of different phases may be obtained; in Fig. 7 I have shewn binding
screws S, provided for this purpose.
Fig. 8 represents another form of transformer in which the coils, 1. 2. 3. 4. 5. 6. 7
and 8 are wound upon a ring; these coils are partly simple and partly double' and
constructed substantially as described with reference to Fig. 4. Over these' coils,
constituting the primary coils of the transformer, I wind a continuous secondary
coil from which derivations lead to the binding screws S', similar to the derivations
of a continuous current machine. The whole entire device constitutes a transformer
and currents of different phases may be obtained therefrom by connecting each two
of the binding screws S' with the apparatus or line to which the current is to be
supplied.
These methods can be employed very advantageously for the. transmission
of force.
In order to obtain a motor, the rotating field needs only to be fitted with an
armature, the coils whereof are in short circuit.
In order to obtain a machine producing currents, the armature is replaced by a
magnet.
The joining up of the coiling of the transformer in tension with each of the coils
having different phases, in which coils, the spirals, excited by the same current
are also joined up in tension, as shewn in Fig. 1, is preferable in certain cases to
the joining up in quantity, though the latter is not excluded.
Figs. 5 and 6 are sections through the coils of a rotating magnetic field, and
L

page_text: If the
show the manner in which the coils may be arranged. If the number of the same
is considerable, the zig-zag lines a hand b c will be replaced by curves, so that
there are not many separated coils, but only a few fitting into another.
thickness of the coil is small, for instance, only one layer, one or more turns of one
spiral would alternate with the turns of the other. It has been supposed. in the
foregoing description that the two exciting currents differ in phase by 90°. That
is not necessary, however, and will very seldom occur in practice, unless the second
current be produced by other means than by transformation. The real difference
of phase is easy to ascertain and the coiling can then be made to suit the same.
Having now particularly described and ascertained the nature of my said
invention and in what manner the same is to be performed, I declare that what
I claim is.
1st. Transformers and electrical machines, in which the exciting or excited coils
are formed in part of one, and in part of two spirals, through which flow currents,
the phases of which are displaced towards each other, substantially as hereinbefore
described.
2nd. A transformer, the exciting or excited coil whereof consists of two spirals,
through which flow currents the phases of which are displaced towards each other,
in the manner and for the purpose hereinbefore specified.
A 1000
GEO. THOS. HYDE,
4, Moorfields, Fore Street, London, E.C., Agent for the Applicant.