Improvements in Alternate-current Dynamos.
Year: 1893

page_text: Date of Application, 15th Sept., 1893
Complete Specification Left, 15th June, 1894-Accepted, 21st July, 1894
Improvements in Alternate-current Dynamos.
I, GISBERT KAPP of 31 Parliament Street Westminster in the County of
Middlesex, Electrical Engineer, do hereby declare the nature of this invention to
be as follows:-
This invention relates to alternate-current dynamo electric machines of the
multi-polar type, and its object is to secure the advantages in construction and
arrangement hereinafter set forth.
In a dynamo constructed according to my present improvements the armature is
constructed with an annular core composed of thin wrought iron plates insulated
from each other, the inner surface of the core being smooth or nearly smooth and
concentric with the field magnet system which revolves within it. The armature
winding is embedded in suitable grooves formed near the inner surface of the
annular core, which is not continuous but divided circumferentially into as many
truncated wedge shaped sections as there are poles in the field, each of the sections
being separate and distinct, and the radial divisions between them being made as
small as practicable, so that the condition of a magnetically continuous core is
approached as nearly as possible. The thin wrought iron plates of each section of
the core may be secured together by means of end plates and bolts or by other
equivalent devices so that each of the sections may be separately handled and
dealt with. Near to the radial ends of each section the herein before mentioned.
grooves are formed for the reception of the armature winding. These grooves
may be lined with insulating material in the shape of troughs or otherwise, and the
copper conductor is wound therein before the several sections are assembled to
form the armature. By these means I obtain the advantages of a smooth armature
core with buried conductors, combined with that of being able to wind the
conductor into grooves instead of threading them through holes, which greatly
facilitates the construction. The assembled sections are supported and secured in
a metallic shell or framing which may surround the completed armature. The
method and means of securing the sections to the support, are such as to enable
each section to be separately removed with its coil without disturbing any other
section.
The internal surface of the annular armature core is a practically true cylindrical
surface interrupted only by the radial joints between contiguous sections which
may be made to fit so closely that the construction is magnetically equivalent to a
smooth and unbroken surface. I thus obviate or greatly reduce the deleterious
effects produced by armature cores having projections or teeth, and I still further
promote this result if desired, by surrounding each pole-piece of the field magnet
system with a closed copper ring, or by attaching copper plates to the polar
surfaces.
I obtain the exciting current either partly or wholly from the secondary winding
of a transformer the primary winding of which is connected with the armature.
The alternating current obtained from the secondary terminals of the transformer
is rectified in the usual well known manner by means of a commutator and suitable
brushes, and to avoid or minimise sparking at the brushes 1 connect a suitable
inductionless resistance to the exciting circuit in such a manner as to divert a part
of the current given from the transformer through this resistance, or a storage
battery. The transformer may be provided with two primary coils, one coupled in
parallel and the other in series with the armature or with part of it, or I may use
two distinct transformers for this purpose in combination with either one or two

page_text: exciting circuits. The brushes are arranged so as to be capable of backward and
forward adjustment, whereby the amount of excitation and consequently the E.M.F.
produced in the armature may be varied.
Although I have described the armature surrounding the revolving field magnet
system, as being the arrangement which I at present prefer to adopt, I do not now
limit myself thereto as it will be obvious that without materially varying the
construction described, the positions of armature and field magnet system may be
reversed.
Dated this 14th day of Sentember AD 1893
COMPLETE SPECIFICATION.
Improvements in Alternate-current Dynamos.
I, GISBERT KAPP of 31 Parliament Street Westminster in the County of
Middlesex, 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:-
This invention relates to alternate-current dynamo-electric machines of the
multi-polar type, and its object is to secure the advantages in construction and
arrangement hereinafter set forth.
In a dynamo constructed according to my present improvements, the armature
has an annular core composed of thin wrought iron plates insulated from each
other, the inner surface of the core being smooth or nearly smooth and concentric
with the field-magnet system. The armature winding is embedded in suitable
grooves formed near the inner surface of the annular core, which is not continuous
but is divided circumferentially into as many truncated wedge-shaped sections
as there are poles in the field, each of the sections being separate and distinct, and
the radial divisions between them being made as small as practicable, so that the
condition of a magnetically continuous core is approached as nearly as possible.
The thin wrought iron plates of each section of the core may be secured together
by means of end plates and bolts or by other equivalent devices, so that each of
the sections may be separately handled, and dealt with. In the radial ends of each
section the hereinbefore mentioned grooves are formed for the reception of the
armature winding. These grooves may be lined with insulating material which may
take the form of troughs or other suitable shape, and the copper conductor may be
wound or placed therein before the several sections are assembled to form the
armature. By these means I obtain the advantages of a smooth armature core
with buried conductors, combined with that of being able to arrange the conductor
in grooves instead of threading them through holes, which greatly facilitates the
construction. The assembled sections are supported and secured in a metallic
shell or framing which may surround the completed armature. The method of and
means for securing the sectious to the support are such as to enable each section to
be separately removed with its coil without disturbing any other section.
The internal surface of the annular armature core is a practically true cylindrical
surface interrupted only by the joints between consecutive or contiguous sections,
which may be made to fit so closely that the construction is magnetically equivalent
to a smooth and unbroken surface. I thus obviate or greatly reduce the deleterious
effects produced by armature cores having projections or teeth, and 1 still further
promote this result, if desired, by surrounding each pole-piece of the field-magnet
system with a copper ring, or by attaching copper plates to the polar surfaces.
I will more particularly describe my invention with reference to the accom-
panying drawings, in which :-
Figure 1 is a perspective view of one of the truncated wedge shaped armature
sections, the wire coil being omitted for the sake of greater clearness.

page_text: Figure 2 is a plan of the same section with its wire coil in position.
Figure 3 shews, partly in elevation and partly in section, a portion of the field-
magnet system and several of the armature sectious assembled in position.
Figure 4 is a partial longitudinal section of Figure 3.
Figure 5 shews partly in elevation and partly in section, part of a machine
differing from the construction represented by Figures 3 and 4, in the field magnet
system, and in the method of attaching the armature sections to the shell.
Figure 6 represents a section taken at right angles to that shewn in Figure 5.
In the arrangements and constructions represented by Figures 3, 4, 5, and 6, the
field-magnet system, rotates within the armature. A modification of this arrange-
ment wherein the field-magnet system surrounds the armature is also represented
by the drawings, in which:
Figure 7 is an elevation, and
Figure 8 a section at right angles to Figure 7 of one of my improved armature
sections as arranged in a machine having an external field-maguet system.
Figure shews on an enlarged scale, the arrangement and insulation of the
armature coil.
Figure 10 illustrates in plan and end view respectively, a method of applying a
closed copper circuit to the pole pieces.
In winding each section of the armature core I may employ either of two almost
equally convenient methods. First, I may wind the armature coils in the grooves
or troughs formed in the radial ends of the armature sections, after insulating the
latter; or, second, I may form the coils separately and build up the sections within
the coils. In the first case, which I generally prefer, I embed the insulating
material in the trough V and wind the coils therein. In the second case I may
wind the coils separately upon a suitable mandrel or former, and afterwards, insert
the core plates into the coil one by one until the required length of the section has
been built up. This has the advantage of enabling a higher degree of insulation to
be secured. Having built up the section of the armature core, I apply the gun-
metal end plates X and bolt the whole firmly together with insulated bolts. Under
this method of construction the whole surface of the coil may be very thoroughly
insulated by lapping insulating tape over it in several layers. To prevent abrasion
of the insulating material during the insertion of the core plates, I may protect
each longitudinal side of the coil by placing over it from the inside, one or more
U-shaped troughs of vulcanised fibre, ebonite or other suitable insulating material.
In Figure 9 P is part of the armature plate, C the coil, and I the insulation
applied over its whole surface.
One method of assembling the sections to form a complete armature is illustrated
by Figure 3. The core plates P may be stampings of sheet iron, of the shape
shewn the end plates X being of gun metal and provided with strengthening ribs.c.
The plates Pare insulated from each other by paper or varnish in the usual manner
and the bolts which hold them together are insulated. The heads of two of these
bolts in each section are left sufficiently long, as shewn by Figure 4, to engage in
suitable aud corresponding holes H, formed in the inner flange of the cast iron
supporting shell S. The gun-metal plate on the other side is provided with lugs L,
by means of which the section is bolted to the corresponding outer flange of the
shell, which may be conveniently made in halves bolted together by the flanges A.
The lower half of the shell may be provided with suitable feet B for attachment
to the bed-plate of the machine. M is the field-magnet system provided with
polar claws p, and energised by a single coils.
To remove any armature section it is only necessary to disconnect the wires a b
Figure 2 from the rest of the circuit, remove the nuts N and draw the section out
in a direction parallel with the spindle of M.
The modified construction represented by Figures 5 and 6 is
the field-maguet system consists of a yoke-ring y, provided with
pole shoes p'. Each pole is provided with an exciting coil s.
similar, except that
radial plates p and
The front plate of

page_text: each armature section is bolted by means of the bolt N, to flanges F, projecting
inwards.
Figures 7 and 8 illustrate the construction and arrangement of my armature
when surrounded by the field-magnet system, which is not shewn. In this case the
end plates are prolonged inwards by the lug T on the back plate and the two
lugs TT on the front plate. The section is bolted to the supporting ring R by
means of bolts N passing through these lugs as shewn. By removing the nuts from
these bolts, the section can be drawn out in a direction parallel with the spindle,
the electric conductors having first been disconnected.
The dividing spaces between two consecutive sections of the armature, is
exaggerated in Figures 3, 5, and 7, for the sake of greater clearness. In practice
shape the armature plates in such a fashion that contiguous sections of the
armature core almost touch each other in situ, the clearance left being just
:sufficient to enable the withdrawal of a section when required, for repairs or
renewal. The armature, although built up of sections distinct from each other, is
thus, magnetically, almost equivalent to an armature with a continuous core.
The
surface of the armature being practically continuous, there is very little change in
the magnetic flux for different relative positions of armature and field. To still
further minimise the change in magnetic flux, I sometimes provide the polar faces
with a copper sheet covering, or alternatively, I may apply stout copper conductors
to the polar faces as shewn by Figure 10, where d d d are three copper bars
dovetailed into suitable grooves formed in the pole face, and e e are transverse
conductors of the same metal joining the ends of d d d. The effect of this
arrangement is to prevent any sensible change in the magnetic flux emanating from
the pole by reason of the stray currents which a very slight change of the flux
induces in the conductors d e.
I have in my Provisional Specification described a method of excitation which
may be employed, but on further experiment I do not find from it all the
advantages anticipated and at present I prefer to employ the ordinary and well
known means.
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed, I declare that what I
claim is :-
1. An armature for alternating current dynamos built up of distinct wedge
shaped core sections so as to form a continuous cylindrical armature core each section
having its own coil embedded in suitably insulated troughs, constructed and
arranged substantially as herein before described and as illustrated by the
accompanying drawings.
2. In an alternating current dynamo, a device for minimising variations in the
magnetic flux, consisting of a closed copper conductor or conductors arranged upon
the polar faces, substantially as hereinbefore described with reference to the
accompanying drawings.
3. An alternating current dynamo constructed and arranged substantially as
herein before described and as illustrated by Figures 3 and 4 of the accompanying
.drawings.
Dated this 14th day of June A.D. 1894.
WILLIAM E. HEYS,
Agent for the Applicant.