Improvements in Dynamo Electric Machines.
Year: 1896

page_text: Date of Application, 5th May, 1896-Accepted, 13th June, 1896
COMPLETE SPECIFICATION.
Improvements in Dynamo Electric Machines.
I, JAMES DEVONSHIRE, Secretary of The British Thomson-Houston, Limited,
of 38 Parliament Street, Westminster, London, (a communication from abroad by
Charles P. Steinmetz, Electrical Engineer, of Schenectady, in the State of New
York, United States of America), 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 invention relates to dynamo electric machines, especially to those of the
inductor type, now well known in the art; and consists in the general type of
machine, by which I obtain a novel and useful apparatus; as well as, in a more
specific sense, improved details of construction which I have devised, by which the
first cost of the machine may be largely reduced, in that I am enabled to use a less
number of field coils and field-magnet cores, and also to some extent to employ
standard forms of apparatus made from patterns suitable for dynamos of other
constructions.
To this end I employ for my improved dynamo a field-magnet of ordinary type;
that is, having inwardly extending laminated pole-pieces provided with ordinary
windings. The pole-pieces however I somewhat extend circumferentially, and
upon these extended pole faces I mount the armature coils of the machine.
Adjacent to these coils, which may of course be connected in any suitable relation
to obtain current of one or more phases, the inductor revolves. In most inductor
dynamos, the inductor consists of a bobbin-like structure, in section somewhat like
the letter H, composed of two star-wheels connected at their centers by a central
body or shaft about which a coil may be wound to determine the polarity of the
mass. Each of these star-wheels is of different polarity; that is to say, all the
projections on one are of north polarity, and all on the other of south polarity,
each one being provided with its own stationary armature, the two armatures
being mounted side by side in a common frame.
My improved inductor differs from those just described in that the inductor,
although a single unitary structure, is when stationary of north polarity on one
side of its diameter, and of south polarity on the other side, the plane of division
passing through its axis of revolution, or substantially so. Thus the inductor
projections, which in ordinary constructions preserve the same polarity during the
entire revolution, in my improved arrangement reverse their polarity as they
pass from one field to another. I have described the construction as applicable to
a bi-polar structure, but it may be used with even better effect in multipolar
apparatus, and in this particular form I have illustrated it; of course in this case
the inductor would be composed of sectors of different polarity, equal in number to
the pole-pieces.
The accompanying drawings show my invention,
Fig. 1 being a side elevation of my improved machine with one of the bearings
removed, Fig. 2 an end elevation partly in section upon the line 2-2 of Fig. 1 ;
Fig. 3 is a diagram of the electric circuits,
Fig. 4 is a sketch illustrating the magnetic paths of the machine, and Fig. 5 is a
modified form.
A is the base of the machine, B is the field-magnet frame, C, C are the bearings
for the armature; pole pieces D, D, in the case illustrated for a four pole

page_text: machine, are also provided, with suitable field-magnet coils D', D' surrounding the
pole pieces. The polar faces F, F are extended circumferentially partly around
the revolving inductor.
K is the shaft of the machine, to which is keyed a suitable spider carrying the
inductor 1. G, G are the projecting arms of the inductor, by the motion of which
past the armature coil a difference of magnetic condition is produced. Upon the
extended pole-faces F, F, the armature coils a¹, b', c are disposed. In the case
illustrated I have shown a three phase machine, and there are six coils disposed
upon each polar face.
The circuits are best seen in Fig. 3, which a, b, c, are the leads from the
armature coils, and a¹, 61, e' are the armature coils themselves. The order of
connection is best seen by tracing the connection of series of coils, for instance,
that lettered a. The coil a', being most nearly adjacent to the inductor, is
connected to the coil a', which is on the under layer, while a³ is upon the upper
layer; a again is on the under layer, and so around the armature.
These
connected coils give rise to the current of one phase, while the next set b¹, 62, 63
provides the current of another phase, and c', c, c³, &c., the current of the third
phase. All of the coils are connected together at the point Y, although nothing
in my invention excludes the use of the delta winding. The field magnets form a
circuit closed through the exciter E, of the usual shunt type, provided with a
regulating resistance R for determining the output of the machine.
I prefer to have the polar faces provided with projections upon which the
coils may be wound, the effect of these projections being similar to those on my
revolving armature of the toothed type. By mounting the coils in sets upon
these polar face projections, the coils being alternately adjacent to and slightly
removed from the inductor (as for instance, the coils a', a 2, a 3), the total inductance
of each of the circuits is substantially equalized.
In Fig. 4 I show the magnetic paths of the machine. In this case it will be
observed that each of the projections or teeth of the inductor is of polarity corre-
sponding to the polar face opposite which it may be; for instance, suppose four of
the inductor teeth be opposite each of the poles, there then would be four fluxes
across the air gap and through the armature coils, as shown. As the inductor
moves, each of these different fluxes would shift along the polar face of the field
magnet, and thus would cut each of the coils in succession.
In Fig. 5 I illustrate the application of my invention to the bipolar construction,
which for small machines or high speeds might be conveniently done, although
I prefer a multipolar structure.
All of the forms illustrated have the common advantage of providing a single
field magnet winding, which will produce a number of separate magnetic fields;
for instance, suppose the machine to have sixty-four poles, it might still be made
in the form illustrated in Fig. 1, and sixteen coils (in a single-phase machine),
would be disposed upon each polar face, an inductor having a suitable number of
teeth being provided to pass the magnetic flux through the different coils in the
order desired. The economy in copper cost is thus manifest, as a single coil,
necessarily larger than any one of the field-magnet coils, but very much smaller
than the sum of sixteen of such coils, would be sufficient to provide the field
excitation. The machine is not only advantageous in regard to copper cost, but
owing to the smaller resistance of the field-magnet windings, a less amount of
current will be consumed in excitation, and the efficiency thus increased.
I aim to include in the scope of the claims appended variations of form and
other changes of construction not involving departure from the principles of
construction herein set out.
Having now particularly described and ascertained the nature of the said
invention and in what manner the same is to be performed as communicated to me
from abroad, I declare that what I claim is :
1. An inductor dynamo having inwardly projecting pole-pieces provided with

page_text: field-magnet windings, armature coils mounted upon the polar faces, and a revolving
inductor.
2. An inductor dynamo comprising a field magnet having projecting pole-pieces,
pole faces circumferentially extended, the armature coils being mounted upon the
polar faces, and a revolving inductor.
3. An inductor dynamo having inwardly extending pole pieces, polar faces
provided with projections, and armature coils mounted upon the projections of the
polar faces.
4. An inductor dynamo comprising inwardly extending pole-pieces, polar faces
provided with projections, and armature coils mounted in sets upon the projections
of the polar faces, alternate coils in each set being adjacent to and removed from
a revolving inductor.
5. An inductor dynamo comprising a field magnet having inwardly extending
pole-pieces of alternately opposite polarity, armature coils mounted upon the polar
faces of the field-magnets, and a revolving inductor having projections passing
through the fields created by the field magnet poles.
6. A field-magnet structure for an inductor dynamo, comprising field magnet
cores, polar faces having projections upon which the coils may be wound, and
a coil upon each field magnet core, the coil magnetizing all of the projections.
Dated this
this 5th day of May 1896.
Darcu UHS VUTI
For the Applicant,
J. C. CHAPMAN,
70, Chancery Lane, London, W.C., Chartered Patent Agent.