Improvements in and relating to Multipolar Dynamo Machines.
Year: 1894

page_text: PROVISIONAL SPECIFICATION.
Improvements in and relating to Multipolar Dynamo Machines.
I, GEORGE LEONARD ADDENBROOKE, of 21 Lichfield Street, Wolverhampton,
in the County of Stafford, Electrical Engineer, do hereby declare the nature of
this invention to be as follows:-
My improvements relate to the armatures and field magnets of multipolar
dynamo machines, and they have been made with a view to obtain great efficiency.
mechanical strength, and cheapness of construction..
In my improved armature, the armature cores-with their coils-are built up .in
the form of an annulus; fixed for a stationary armature; or mounted and adapted
for rotation before field magnet poles, as the case may be. I employ laminated
iron for the armature cores, which are preferably formed of stamped. plates,
generally oblong in outline, but in some cases (particularly in multiphase machines)
I reduce the sectional area of the core where the armature coil is to be placed.
In either case, the plates are sometimes prolonged, beyond what is absolutely
required for the magnetic circuit, for constructional purposes; but. one object
of my design is to reduce as far as possible the mass of iron subject to magnetic
reversals.
It is well known that loss from eddy currents in the iron is reduced by laminated
cores, but I further reduce the said loss by slitting the core plates at intervals in
lines coinciding with the direction of the magnetic flow, and sometimes cut
transverse slits or slots at certain parts of the core, for the same object. Further-
more, by making the width of the plates less at the centre, (as above stated), and
thus reducing the sectional area of the core at that point, the mass of iron subject
to hysteresis is lessened, all other conditions being considered equal. It is,
however, fully recognized, that by reducing the sectional area of the iron core at
its centre magnetic density is increased; but this reduction of area is only carried
so far that loss therefrom is compensated for by the smaller mass of iron subject
to hysteresis and eddy currents; and by the reduction of the length of each turn
of the armature coils; the winding being upon a smaller core than would otherwise
be the case.
Moreover, the length, cost, and electrical resistance of the conductor.
is also reduced to an important extent; while, in the case of a revolving armature,
the weight to be moved is also lessened. Furthermore, the radial depth or width
of each complete coil is lessened with an advantage described hereinafter.
The armature coils may be wound in any known manner, but in some cases
I wind a double coil of flat or ribbon conductor, placed side by side on one core,
and connect them. together next to the core in what then becomes the centre of
their united length. This enables me to make both connections of each coil to its
neighbours, on the outside of the armature with great facility; and also keeps the
radial depth small.
The core plates extend beyond the width of each coil winding and are adapted
at their ends to be properly secured together and held in a suitable frame. If the
armature is intended to be stationary, the frame is designed to surround and carry
he several cores and their windings in any convenient manner, so as to be clear of
he revolving field inagnets. But if the field magnets are to be kept stationary,

page_text: and the armature made to revolve, the frame itself, which carries the said cores, is
suitably mounted upon the central shaft in any known manner; and in either case
the iron cores lend themselves to good solid mechanical construction. Furthermore,
by my aforesaid construction of armature, the coils thereof are shielded from the
poles, and eddy currents in the conductor are avoided to a considerable extent.
For the field magnets, I construct one or it may be two iron rings, each having
a deep groove in the middle of one of its side faces, in which is placed a single
winding to conduct the exciting current. This arrangement would produce
polarity in each of the annular projections enclosing the recessed winding; one
projection being an anzular north pole, the other a south pole, throughout their
respective circumferential faces; and in this respect they resemble a well known
magnetic coupling, without its keeper. But the said annular projections are
formed into a number of projecting poles in an alternating manner, and crossed
over so as to completely enclose the exciting winding, and also to present, on one
face of each ring, poles alternating in name, and situated much closer together
than other magnets of this type. The two rings (where two are employed) are
arranged with their respective polar faces towards each other, but separated by a
space in which the armature is placed, and with the south pole of each ring placed
opposite the north pole of each ring. Consequently, when the armature is in place
between the several poles, the iron cores of the armature are in close juxtaposition
to the poles of each ring, and serve to conduct the lines of force between the
opposite poles in a manner well understood by electrical engineers.
It is to be seen from the foregoing description that the magnetic circuit is
remarkably short, for a section taken through each field magnet ring discloses only
a sufficient amount of iron, closely surrounding the exciting winding, to avoid
saturation; while the pole pieces are short and close to the winding. The
armature cores also are only long enough to receive each coil, and provide a
sufficient projection on either side of the coil as may be required for constructional
purposes. As conductors are removed from close proximity to the polar faces-
iron being next to iron-the air gaps or clearance on each side of the armature is
reduced to the least possible in practice, and consequently the coils are subjected
to a strong magnetic field. The mass of iron is also kept as small as possible to
avoid losses from: hysteresis, and I sometimes laminate the polar faces to still
further avoid eddy current losses in the iron. In addition to this, I do not employ
masses of iron as in some machines; or form my field magnets with large central
bosses or supporting arms which are directly exposed to the magnetic flux of the
field, as in the Oerlikon, Brown, or Mordey type of multipolar magnets having a
single exciting winding. In all cases, whether revolve the field magnets, or
keep them stationary, I mount them upon a mechanical support which is not
necessarily constructed of a magnetic material. For example, in the case of a
revolving field, I mount my field magnet rings upon the rim of a fly wheel, or
supporting arms which may be of any desired metal or alloy; and therefore I do
not wind my exciting coil immediately around the central boss or core on which
the magnet is mounted as in the above named types.
It has been stated above that the radial depth or width of each armature coil
is lessened with advantage, and that the alternating polar faces are kept close
together. In this way, and by using iron cores for my armature coils, I am enabled
to greatly reduce the distance in the movement from the centre of one polar face
to that of the next one following. This I call the movement of translation; and
in other multipolar machines the poles are spaced with a gap between them of at
least the width of a pole, and in some machines the gap is still wider; thus
increasing the movement of translation. Owing to this fact, the magnetic field is
exposed to great fluctuations, but by reducing the space between the poles to less
than the width of a pole piece, together with small coils and iron cores, I am
enabled to keep the magnetic field in a very uniform or stable condition; and to get
a large number of pole pieces in a comparatively small, or given diameter. Conse-
quently, I am enabled by my invention, to get an increased number of alternations

page_text: of the induced current per revolution of the machine, and this is often of advantage
when the dynamo is coupled directly to the motive power engine.
Dated this 19th day of November 1894.
FAIRFAX & WETTER,
433 Strand, London, Agents for the Applicant.
Improvements in and relating to Multipolar Dynamo Machines.
I, GEORGE LEONARD ADDENBROOKE, of 21 Lichfield Street, Wolverhampton,
in the County of Stafford, Electrical 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:--
My improvements relate to the armatures and field magnets of inultipolar dynamo
machines, and they are made with a view to obtaining great efficiency, mechanical
strength, and cheapness of construction.
In my improved armature, the armature cores-with their coils-are built up in
the form of an annulus, which is suitably mounted and fixed, in the case of a
stationary armature; or mounted and adapted for rotation before the field magnet
poles, in the case of a moving armature. In the further description of the invention,
reference is made to the accompanying drawings, in which
Fig. 1 is an elevation of a portion of an armature showing a part of the
supporting frame in section.
Fig. 2 is a transverse section of Fig. 1;
Fig. 3 is a sectional plan taken on a line about midway of the radial depth of
the laminated core, showing one of the core plates and the coil winding;
Fig. 4 is a plan of the outer segment block at the top of the core, showing one
method of commencing the winding;
Fig. 5 shows in perspective a complete laminated iron core clamped between an
inner and an outer segmental insulating block with its coil winding.
Fig. 6 is a perspective view of a field magnet ring without its winding.
Fig. 7 is a front elevation with one half in section of a multipolar dynamo
machine with a standing armature and revolving field magnets, Fig. 8 is a side
elevation of the same, with part of the field removed;
Fig. 9 is a front elevation with the upper half in section of a multipolar dynamo
machine with a rotatable armature and standing field magnets, and Fig. 10 is a
side elevation of the same, also with part of the field magnets removed to show a
portion of the armature in each case, and how the cores with their coils are
mounted.
Fig. 11 is a detailed plan displayed to show the relative arrangement of poles
and cores, and method of mounting.
In these drawings A indicates a complete armature coil with its core, duly
assembled and mounted in position, or else ready for mounting. The laminated
core is composed of thin iron plates a, generally of oblong form and recessed at
the central portion of each end which is to receive the coil winding, so that the
sectional area of the complete core is reduced at that part where the radial portion
of the coil encloses it. Consequently the width of each plate a is wider than the
width of the coil 6 which, with its insulation, lays within the recesses; while the
extra length of each plate partially or wholly coincides with the depth of the coil
winding, thus forming horns or sides a for the aforesaid recesses, as shown in
Fig. 3. Slits or slots a² are sometimes made in the plates a, for the purpose of
reducing eddy currents.
The laminated core is further provided with inner and outer segments c, of wood
or other insulating material, which are grooved to correspond with the recesses

page_text: formed in the plates a. A groove is thus completed entirely around each core
with the segmental blocks for the reception of the coil winding b, while the sail
inner and outer segments c also serve as clamps between which the core plates a
are secured.
In some cases, (as indicated in Figs. 2 and 3) I connect the inner and outer
segments c; at their ends, by a brass strip, suitably insulated, which assists in
holding the parts of the core more firmly together. A double coil of flat or
ribbon conductor bis wound side by side on the core, and electrically connected
together by means of the brass strip as shown in Fig. 4, which thus becomes
the centre of their united length and forms one complete coil, as will be readily
understood by electricians, and it also tends to keep the radial depth of the coi! A
small.
Bolt holes are sometimes drilled through the assembled core plates a for the
reception of bolts of iron or steel, the bolt holes being located in the marginal
portion of the plates, outside the coil winding b. By means of these bolts, cach
complete armature coil A is mounted and secured in position upon the frame d.
The armature coils A are secured in position upon a suitable frame d, which is
varied to suit the special circumstances of their position or working. If the
armature is intended to be stationary, the frame is designed to surround and carry
the several cores and their windings in any convenient manner, or a double frame,
consisting of an inner and an outer ring, with suitable strengthening ribs, is
employed as shown as Figs. 1 and 2. In this example, a removable annulus plate,
or series of segmental plates d' on one side, is shown to facilitate the insertion or
removal of a coil or coils, as in Fig. 2. The several coils are clamped as shown or
suspended by bolts as may be most convenient, according to the form of frame
adopted.
If, however, the field magnets are to be kept stationary, and the armature
arranged to revolve, the frame d is suitably mounted upon the central shaft in any
known and convenient manner. It will be seen that either with a standing or
revolving armature, the iron cores and sunken winding conduce to good, solid,
mechanical construction; and while the coils are effectually shielded from contact
with the poles, eddy currents in the conductor are avoided to a considerable
extent.
The field magnets B are constructed of two iron or steel rings, each having a
groove or central space in the middle of its side face, in which is placed a single
winding e to conduct the exciting current. This arrangement produced polarity in
each annular projection enclosing the recessed winding, one being an annular north
pole, the other an annular south pole, throughout their circumferences, thus
resembling a well known magnetic coupling, without its keeper. But the said
annular projections are formed into a number of alternate poles by alternate
extensions and g, and crossed over to completely enclose the exciting winding e ;
thus presenting on one face of each ring alternate poles, situated closely together.
The annular projections are preferably cut away opposite, and in the spaces
between, each pole, as shown in Fig. 6, to avoid magnetic leakage, and to lighten
the weight of the magnets.
In the standing armature type of machine, shown in Figs. 7 and 8, the armature
is placed between the two rings which form the respective field magnets, with a
very small air gap between the cross over polar spaces and the iron core of the
armature; the south pole of each ring being placed opposite the north pole of the
opposite ring. Unlike certain other machines which have only half the relative
number of poles, I employ a pair of poles for each armature core and its coil, the
space between being less than the width of their faces, as shown in Figs. 6 and 11.
The field magnet rings are shown in Figs. 6, 7 and 9 as having a central space
just sufficient to enclose the exciting winding e with polar extensions across one side
of the space to enclose the same, the polar faces being parallel with the back or
body portion of the rings as shown, and each ring is mounted upon the periphery of
a. fly wheel, or supporting arms, or a disc as shown in Figs. 7 and 8, which

page_text: mechanical support or mounting is not necessarily of a magnetic material as in
ether types of machines having a single exciting winding for each field magnet.
It will be seen, therefore, from the foregoing description, that the magnetic circuit.
is remarkably short, for a section taken throughout each field magnet ring (as in
Figs. 7 and 9) discloses only a sufficient amount of iron-closely surrounding the
exciting winding- -to avoid saturation; while the pole pieces are short and close to
the winding. The length of the exciting winding is also very short, thus reducing
the cost of conductor, the electrical resistance, and the exciting current required..
The armature cores also are only long enough to receive each coil; and provide a
sufficient projection on either side of the coil as may be required for constructional
purposes. As conductors are removed from close proximity to the polar faces-
iron being next to iron-the air gaps or clearance on each side of the armature is
reduced to the least possible in practice, and consequently the coils are subjected to
a strong magnetic field. The mass of iron is also kept as small as possible to avoid
losses from hysteresis, and I sometimes laminate the polar faces to still further
avoid eddy current losses in the iron.
It has been stated above that the radial depth or width of each armature coil is:
lessened with advantage and that the alternating polar faces are kept close together.
In this way, and by using iron cores for my armature coils, I am enabled to
greatly reduce the distance in the movement from the centre of one polar face
to that of the next one following. This I call the movement of translation; and in
other multipolar machines the poles are spaced with a gap between them of at least
the width of a pole, and in some machines the gap is still wider; thus increasing
the movement of translation. Owing to this fact, the magnetic field is exposed to
great fluctuations, but by reducing the space between the poles to less than the
width of a pole piece, together with small coils and iron cores, I am enabled to
keep the magnetic field in a very uniform or stable condition; and to get a large
number of pole pieces in a comparatively small or given diameter. Consequently,
I am enabled by my invention, to get an increased number of alternations of the
induced current per revolution of the machine, and this is often of advantage when
the dynamo is coupled directly to the motive power engine.
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 ;-
1. An armature for multipolar dynamo machines consisting of a series of
laminated iron cores clamped between inner and outer insulating blocks and
grooved for the reception of their respective coil windings; a suitable frame or
trames adapted to receive and retain the said cores in close proximity to each
other; and a continuous coil winding upon each of the said cores within the said
recess, entirely enclosed within the core plates throughout their radial depth at the
parts directly exposed to the magnetic flux of the poles; substantially as and for
the purpose herein described and shown in the drawings.
2. In an armature for multipolar dynamo machines the combination of a
laminated iron core forming in its depth a radial segment of a circle, composed of
an assemblage of plates of approximately equal width but of variable length
conforming to the radial outline of the core, each plate having recessed ends for
the reception of a coil winding of less width than the said core plates; an inner
and an outer segmental insulating block of similar width to the core plates,
arranged and adapted to clamp the said plates between them and formed with a
corresponding grooved space to receive the winding; an insulated strip conductor
serving to connect and bind the said inner and outer clamping plates between them;
and two coils of copper tape electrically connected to the said strip conductor to
form cne continuous coil winding; substantially as and for the purpose herein
described and shown by the drawings.
3. A multipolar field magnet consisting of an annular ring having an inner
annular projection and an outer annular projection from the face of the ring so as

page_text: to form a groove or space between, with polar extensions having flattened outward
faces parallel with the said ring extending across the said space alternately from
the inner and outer annular projections to form poles of opposite names, and
situated closely together with spaces between the poles less the width of their
faces; and a single exciting winding placed within the said space and enclosed
beneath the said poles; substantially as and for the purpose herein described and
shown in the drawings.
4. A multipolar dynamo machine having in combination the following elements;
an armature comprising a series of laminated iron cores placed in close juxta-
position in the form of an annular ring with parallel side faces, a coil winding
around the central part of each core parallel with the said faces narrower than the
width of the cores and enclosed within recesses on the radial portion of the said
cores; a frame on which the said cores with their coils are mounted, and means to
hold and retain the same in the working position; a field magnet on each face of the
armature having alternating cross over polar faces extending from an annular ring
formed and arranged with a central space between the said ring and the said polar
faces, the latter being situated closely together, corresponding to the armature
cores, with spaces between them less than the width of the polar faces; a single
exciting winding placed within the said central space; and means to rotate the said
field magnets or the said armature relatively to the other substantially as and for
the purpose herein described, and shown in the drawings.
Dated this 19th day of August 1895
FAIRFAX. & WETTER,
433 Strand, London, Agents for the Applicant.