IMPROVEMENTS IN THE CONSTRUCTION OF DYNAMO ELECTRIC MACHINES AND IN BOBBINS OR GRAMME-RINGS THERE
Year: 1883

page_text: LETTERS PATENT to William Phillips Thompson of the firm of W. P Thompson
& Boult Agents for Foreign Patent Solicitors 6 Lord Street Liverpool in the
county of Lancaster for an Invention of "IMPROVEMENTS IN THE CONSTRUCTION
OF DYNAMO ELECTRIC MACHINES AND IN BOBBINS OR GRAMME-RINGS THEREfor
a communication to him from Monsieur l'Ingénieur Bartolomeo Cabella of
Milan in the kingdom of Italy
.
PROVISIONAL SPECIFICATION left by the said William Phillips Thompson
at the Office of the Commissioners of Patents on the 19th April 1883:
WILLIAM PHILLIPS THOMPSON of the firm of W P Thompson & Boult Agents
for foreign Patent Solicitors 6 Lord St Liverpool in the County of Lancaster
"IMPROVEMENTS IN THE CONSTRUCTION OF DYNAMO-ELECTRIC MACHINES AND IN
BOBBINS OR GRAMME-RINGS THEREFOR." a communication to me from Monsieur
l'Ingenieur Bartolomeo Cabella of Milan in the kingdom of Italy
This invention has for its object the great reduction of resistance of the
armatures in the secondary or induction coils of the Pacinotti or Gramme machines,
and others of the same genus-the length of the circuit directly submitted to
induction remaining always constant.
These improvements permit also of the simplification of the construction of said
coils or rings, and of forming special coils in which the secondary or induced
conductor acts as a core. Lastly it gives the possibility of constructing machines
furnishing a practically constant current. In all coils or rings of the Pacinotti-
Gramme order, as well as all those of derived types, and even in the Siemens
coil-the portion of the circuit submitted directly to the action of the magnets of
the magnetic field, is less that half that directly necessary to form the coils
themselves Thus fifty percent or more of the wire, employed in forming the
coils, plays no other part than that of giving a passive resistance diminishing the
out-put of the machine and causing deleterious heating.

page_text: -
:
In the construction of all these induction coils, the core of soft iron is first
prepared upon which is wound the wire duly isolated. The present invention―
enables one to greatly diminish the resistance of the part of the circuit, which is
not submitted to induction, yet which the construction of the machine makes
necessary. It is carried out in the following manner; that part of the circuit
which does not serve directly to produce the induced current; is formed first, then
the core is formed, and lastly the coil is completed by completing the circuit in
which the current is induced. The power of the machine being limited by the
quantity of energy it is capable of transforming-one can determine the length
of the circuit which it is most profitable to place in the magnetic field.
To form the part of the circuit not in the magnetic field, bars of copper with two
projecting pieces at right angles-all cut out of sheet copper or formed in other
manner, are placed round a non conducting sleeve on the revolving axle. The one
end of the bars project beyond the second projecting arm so as to form the series
as in the ordinary Gramme machine for the brushes to collect the currents between
the pairs of projections all projecting radially-and isolated from each other by
isolating strips; the insulated soft iron wire core is wound till level with the top
of the projections Thin connecting strips of. copper are now soldered to the
projecting pieces, the strips being arranged so as to connect them in series—one
end of one copper piece to the opposite projecting end of the next, and so on-
or if desired they can be connected in multiple arc. Usually however they are
connected so as to give as many elements as there are copper pieces round the axis.
The length of the small connecting pieces-which are made with much greater
resistance than the copper pieces afforesaid, being equal to the length of useful
circuit originally determined on. The advantages of this arrangement are stated
by M Cabella as follows.
.
1st It reduces to a minimum the distance between the induction coil and the
magnets of the magnetic field, since the exterior surface of the coil is parallel to
that of the magnet
2nd It enables one to bring the core of soft iron very near the field magnets, and
thus render the lines of force more active.
3rd One can better utilize the space between the interior surface of the primary
and the core, because of the suppression of the usual cylindrical section of the
induction coil and its isolating envelope.
4th One can augment to the furthest limit the number of collector blades or
bars, and diminish consequently the sparks which pass between the collectors and
brushes.
5th One reduces the resistance of the coil or bobin so as to render it little
greater than the resistance of its useful part,-by augmenting the dimensions of the
copper pieces inside the core circle compared with those of the small copper
junction pieces.
6th The lines of force are rendered more active, since one can augment the
volume of core without increasing the resistance of the passive part, like one has
to when increasing the size of the core in the ordinary arrangements.
7th It is possible to construct the bobbins of great size, without augmenting the
resistance, a point hitherto not obtained with Siemens, or Gramme-Pacinotti,
bobbins hitherto.
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8th One can augment the axial length of the bobbins without augmenting the
useless resistance.-another point hitherto uneffected in Gramme machines
9th The apparatus is easy to construct in a very solid manner by winding the
core on the central portions-the same facility is not experienced in the Pacinotti-
Gramme bobbin.
10th One obtains the cooling of the armature by means of circulation of air,
since the little plates can be soldered to the copper pieces without isolating
material.
In adopting the system described above, it is easy to construct a bobbin having
no core properly so called. One can employ for the useful conductor a magnetic

page_text: metal, such as iron or nickel, which in this case acts as a conductor, and also fulfils
the office of attracting the lines. of force.
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Since then there would be no core, the space between the radial arms would be
empty. One could replace the little conducting pieces by thicker or higher pieces
of magnetic metal, and greatly reduce in size the space between the arms. As
however some core is useful as a diaphragm to destroy the induction action upon
the "passive" portion of the circuit, it is better to wind a shallow core on. The
conducting pieces can then be very high radially, the side pieces being corre-
spondingly short, and thus being joined up as before from one copper piece to the
next, it is possible to use as a conductor a magnetic metal, spite of the augmentation
of resistance that it offers.
The system described above renders possible the construction of a machine with
continuous current engendered by the movement of a conductor in a uniform field.
The following is a convenient arrangement. A uniform annular magnetic field
of northern polarity is maintained by a tubular electro-magnet, or by a series of
ordinary bobbins having their cores inserted in a ring. A bobbin similar to that
already described, but turned, on its side so that the active conducting pieces come
opposite the before mentioned ring-is fixed on the axis of the magnet and close
alongside the same; one of the conducting pieces is omitted, and wires are brought
down from the ends of the broken circuit to two insulated bars on the axes, which
project to a collecting apparatus at another part of the shaft. A similar but
reversed arrangement of magnet and bobbin is also placed on the same shaft,
and connected to same collector. The union of supports of the two magnets, so as
to bring them into magnetic connection with eachother increases the activity of
the lines of force.
SPECIFICATION in pursuance of the conditions of the Letters Patent filed.
by the said William Phillips Thompson in the Great Seal Patent Office on
the 19th October 1883.
WILLIAM PHILLIPS THOMPSON, of the firm of W. P. Thompson and Boult, Agents
for Foreign Patent Solicitors, 6 Lord Street, Liverpool, in the county of Lancaster,
"IMPROVEMENTS IN THE CONSTRUCTION OF DYNAMO-ELECTRIC MACHINES, AND IN
BOBBINS OR GRAMME RINGS THEREFOR"-A communication to me, from Monsieur
l'Ingénieur Bartolomeo Cabella, of Milan, in the kingdom of Italy
The following is the description of the invention exactly as communicated to me
by my foreign correspondent.
"The object of my invention is to greatly reduce the resistance of the induced
armatures in dynamo-electric machines, while the length of the circuit submitted
directly to the induction remains the same. My invention enables me to simplify
the construction of rings of the Pacinotti-Gramme type, and to make special

page_text: rings or armatures in which the induced conductor takes the place of the soft iron
core.
" In all the rings of the Pacinotti-Gramme kind, as well as in all those of the
desired types and in a Siemens armature, the portion of the circuit submitted
directly to the action of the magnets of the magnetic field is less than half what
is strictly necessary for the formation of the rings or armatures themselves; thus
fifty per cent of the wire employed in making the rings or armatures, and even
more, plays no other part than that of passive resistance, diminishing the useful
effect of the machine and causing a prejudicial heating.
"In the construction of all these armatures a core of soft iron is used on which
the insulated wire is wound.
"Now I construct dynamo machines in such manner as to diminish the
resistance of the part of the circuit which is not submitted to induction, a part
which it is necessary to preserve in order to complete the circuit, and my invention
essentially consists in making the non-useful part of the induced body of much
larger section than the useful part of such body; by the expression non-useful
part, I mean that part of the induced body which is furthest from the exciting
magnets, or in the weakest part of the magnetic field.
"I first establish a part of the circuit and precisely that which does not serve
directly to produce the induced current, then I form the soft iron core and next I
complete the coil by means of the circuit in which the induced current is generated.
The power of the machine to be constructed having been determined with reference
to the amount of energy to be transformed, the section of the induced body and
the length of the useful circuit which should move in the magnetic field can be
fixed.
"I first make small copper plates (hereinafter referred to) Fig 1. a, b, whose
section has been previously fixed and which when added together will give a length
equal to that required. Their number represents the number of elements of which
the armature is to be composed. I then take an equal number of sheets of copper,
which I cut by preference of the contour seen at c, d, e, f, g, h, i, k, Fig. 2, of the
annexed drawings, or approximately so; I then unite them side by side interposing
between every sheet and its neighbour a sheet of insulating material. I thus
obtain by their connection the solid body engendered by the rotation of the
figure c, d, e, f, g, h, i, k, around the axis x, y. Fig 3, which is the axis of the
armature. The solid thus obtained is fixed to the shaft, an insulating sleeve,
k, i, m, n, m, n¹, i, k¹, Fig 3, being placed between them.
"
By the combination above described, I obtain a sort of pulley or grooved
wheel, composed of elements in the form of plates insulated from each other. In
the groove of this pulley I wind insulated iron wire up to the line d, g, d², g', .
Fig 3, and I thus form the soft iron core. I next take the small copper plates
berein before mentioned, Fig 1 a b and Fig 3 a b, and place them as seen at a bo, p,
Fig 3. soldering thein or otherwise uniting them to the lateral projections of the
elements c d e f g h i k Fig 3, so as to form a continuous circuit. (see Fig 4).
"Thus the essential arrangement of a Pacinotti-Gramme ring or a Siemens
armature is reproduced, that is to say, there is a conductor forming a continuous
helix wound on a ring of soft iron and having insulated derivations p q r Fig 3,
constituting the elements of the collector; the number of these elements can be
equal to that of the elementary plates of the armature, or it may be less, in which
case a single element of the collector may be made to correspond to a certain
number of the elements of the armature connected in series. As in Fig 5. where A
bas connection to commutator and Ahas not.
"It will be seen that the section of that portion of the plates c d e f g etcetera,
which is farthest from the exciting magnets N and S, Fig. 3, and which is the
non-useful part and serves only to complete the circuit, is much larger than the
section of that part which is nearest the exciting magnets and which is the
useful part. Although I prefer to make the plates of the shape shown, it is
evident that various other shapes will answer the purpose of my invention, the

page_text: essential feature of which is as already explained the making of the non-useful part
of much larger section than the useful part.
"In applying my invention it would be easy to construct an armature without
an inducing core. I can for example employ as the useful conductor a magnetic
metal such as iron, which in this case while acting as the conductor would also
excite the lines of force, and the so-called Foucault currents, which in ordinary
machines heat the soft iron core and are thus a source of loss, would in this
manner be giving an electro-motive force in the required direction and instead of
being harmful would become useful. Since therefore there would be no inducing
core, the space d e f g Fig 3, would be free. In this modification, I substitute for
the small conducting plates a b, plates of greater height, as shown at abop
Fig 6, and made of a magnetic material. The armature is constructed in the
manner already described, that is to say, I begin by forming the solid body
engendered by the rotation of the profile cdefghik Fig. 6; then I apply a
small core of iron if I wish to take advantage of it as a diaphragm to destroy the
inducing action on the conductor ef Fig 6. If this property of iron is not to be
taken advantage of, any other suitable material may be substituted. The armature
is completed by means of the plates abop Fig 6. which are united from angle to
angle, as indicated in Fig 4.
"The suppression of the inducing core will allow of the dimension a p being
much increased, and a magnetic metal can therefore be employed as the induced
part of the conductor notwithstanding the resistance which it offers. It must
however be understood that the non-useful part of the conductor must be of much
larger section than the useful part as already explained, or in this modification it
may be made of a metal of greater conductivity than that of the useful part, and
then a larger section is not necessary."
Having now described the invention as communicated to me, I wish it to be
understood that what I claim is, (also in the words of my correspondent):-
"First. In a dynamo-electric machine, an armature or ring in which the
non-useful part, that is to say, the part which is farthest from the exciting magnets
or in the weakest part of the magnetic field, is of much larger section or made of
a metal of greater conductivity than the useful part, or that part which is nearest
the exciting magnets and in which the useful induction actually takes place,
substantially as and for the purpose set forth."
"Second. In a dynamo-electric machine, an armature or ring comprising a
number of copper plates of comparatively large section, separated by insulating
material and united together, a soft iron core around said plates, and a number of
copper plates of comparatively small section connecting the outer edges of the said
plates of larger section, substantially as set forth."
In witness whereof I the said William Phillips Thompson have hereunto set
my hand and seal this fifteenth day of October, in the year of our Lord one
thousand eight hundred and eighty three.
TIM D THA