Improvements in Dynamo Electric Machines.
Year: 1899

page_text: Date of Application, 29th May, 1899
Complete Specification Left, 28th Feb., 1900-Accepted, 31st Mar., 1900
Improvements in Dynamo Electric Machines.
A communication from abroad by the ACTIEN-GESELLSCHAFT ELEKTRICITÄTSWERKE
vormals U. L. AUMMER & Co., of Dresden, Germany.
I, WILLIAM LLOYD WISE, of 46, Lincoln's Inn Fields, in the County of London,
Consulting Engineer and Chartered Patent Agent, do hereby declare the nature
of this invention to be as follows:
-
To explain the undesirable occurrences caused by the reaction of the rotating
armature in an electric machine, it is usually stated that a distortion of the
magnetic field of the poles or pole pieces occurs as a result of the intiuence of
the said armature-in other words, that in consequence of the rotation of the
armature there is caused a concentration of the lines of force of the field at that
horn of each pole at which the armature coils emerge from the magnetic field
(hereinafter called the leading horn) while at the other horn (hereinafter called
the trailing horn) where the armature coils enter the magnetic field, there is
a weakening of the lines of force.
To prevent this distortion of the field, which is the principal cause of sparking,
many suggestions have been made, some of which, for example, are described
in the well known text-book of Sylvanus Thompson "The Dynamo-electric
Machines," chapt. XVI., 5th German edition. They consist, inter alia, in the
employment of auxiliary coils, which create a field of force of their own in such
a position as to counteract the shifting forwards of the lines of force of the main
field. But this arrangement of such auxiliary coils complicates the machines and
increases their cost, so that none of these auxiliary methods have come into
general use.
Various simple and purely mechanical means or solutions have been suggested.
The one that has been most employed is the arrangement of slots or cuts in
the poles or their shoes, running parallel to the direction of the field or to the
axis of the core of the magnet, in a plane perpendicular to the cross section of
Such cuts or slits
the armature that is, parallel to the armature winding.
should cause a resistance to the concentration of the lines of force at one of the
horns, by preventing them from going beyond one half of the core into the other
half thereof.
This certainly very simple means could, however, from the nature of the case,
have no favourable effect. For it is clear that the lines of force, in consequence
of the necessarily occurring magnetic bridges, can distribute themselves in the
already described unfavourable manner if the cuts do not run entirely through;
and this, for practical reasons, is not feasible and would cause other disadvantages.
Also the adoption of cuts where steel castings are used for the pole-pieces, is
especially difficult.
The effect of the cuts is improved (see German Patent Specification No. 97697)
by giving the pole pieces or shoe an unsymmetrical shape, for the purpose of
favorably influencing the lines of force at its surface.

page_text: The result of this arrangement may, perhaps, be satisfactory, but it is very
complicated and therefore not suitable for general use.
Another suggestion is made in the German Patent Specification No. 42164
(Fig. 10). It consists in combining with the cast field-magnet core, at the side
at which the armature-coils enter the magnetic field, a suitably formed piece of
a material which has a greater magnetic permeability than the material of the
core itself. This arrangement has, however, the disadvantage that the applied
piece lies entirely outside of the path of the ragnetic lines of torce. It can serve
as a conductor only for those lines that are generated in the said piece by reason
of the surrounding coil, while the lines of force of the closed magnetic circle
pass through the core.
This arrangement has also had no practical application, as is indicated by the
short life of the German Patent No. 42164.
Now this invention has for object, inter alia, to prevent the concentration of
lines of force at the leading horn of the pole in the simplest imaginable manner.
The pole, according to this invention, has in it on one side only one or more
cuts or slits, which does or do not run in the direction of the axis of the pole
but run at right angles thereto and are only made in that side of the pole or core,
at which the armature coils emerge from the magnetic field. These cuts or
slits, which can be made to serve as air spaces or be merely parting slits, increase
the magnetic resistance of the pole or pole-core only at that side at which they
are placed and then compel the lines of force at the opposite entrance or leading
side to concentrate. A strengthened field is thus produced and sparking is con-
sequently prevented.
The action of this device can be increased in several ways. The extreme ends
of the pole may consist of two parts, one being in one piece with the core or the
pole body and the other being mechanically attached to the core or pole body by
a screw. The plane of separation between the detachable piece and the pole body
or core increases the magnetic resistance at this side (the emergence or leading
side) of the path of the force lines and prevents concentration of the force-lines.
The most widely differing proportions of the magnetic conductibility can be
reached by altering the ratio of the dimensions of the surfaces where the two parts
join the core or pole body or by shifting to the right or to the left the plane of
separation between the two parts.
Furthermore, the proper ratio between the number of lines of force and the
field density of the surfaces of the two portions of the pole end facing the
armature can be easily attained by making the contact surfaces or planes of or
between the two parts of the extreme end of the pole oblique to the direction of the
pole, pole core, or core. The more oblique these separating surfaces are, the
smaller, in relation to the pole, is the entrance or trailing surface of the lines of
force in proportion to the emergence or leading surface-that is to say, the greater
the field-density will become at the horn at which the armature coils enter the
magnetic field.
This oblique arrangement of the planes of separation of or between the two
parts of the extreme ends of the pole (which can at the same time form one or
more air spaces) makes it possible to make the part of the extreme end of the
pole that is at the side at which the armature coils enter the field, separate from
the core or pole body and to attach it mechanically, which from the practical
point of view is desirable. While the desired ratio between the magnetic resist-
ance of both parts can be attained by suitable proportions of the two surfaces in
contact with the core or pole body, this can be effected within considerable limits
by obliquity to the axis of the core or pole body) of the separation or adjacent
surfaces of or between the two detachable parts of the pole.
The device may be further improved by the adaptation of the ideas embodied
in the German Patent Specification No. 42164 (Fig. 10); the part of the extreme
or face and which lies at the side of exit of the armature winding is then not made
of the same material as the other part and the core or pole body, but of a material

page_text: of less permeability, as for example cast iron, if the core or pole body and the
other part of the extreme or face end of the pole are steel castings. But this
arrangement is distinguished from that described in the German Patent Speci-
fication No. 42164 in that the attached piece of different permeability is a part
of the face portion of the pole and not a part of the core or pole body so that no
more lines of force are excited therein, but it serves only as a conductor for
the lines of force that are excited in the pole body or bodies or core or cores-
as far as permitted by the resistance of the surfaces of the slit or slits, which
are at right angles to the direction of the lines of force.
In all cases in which both parts of the extreme end or face portion of the pole
are mechanically attached to the core or pole body they can without difficulty
be made symmetrical or symmetrically attached. They can, furthermore, be
interchangeable with each other if the direction of rotation of the machine has
to be reversed an advantage that none of the other devices offers in so simple a
manner.
The device is intended principally to prevent sparking in continuous current
machines; but it can however so far be applied to alternate current machines
as to lessen self-induction and improve the current-curve under varying loads.
1000
W. LLOYD WISE,
46, Lincoln's Inn Fields, London, W.C.,
Chartered Patent Agent.
A communication from abroad by the ACTIEN GESELLSCHAFT ELEKTRICITÄTSWERKE
vormals O. L. KUMMER & Co., of Dresden, Germany.
I, WILLIAM LLOYD WISE, of 46, Lincoln's Inn Fields, in the County of London,
Consulting Engineer and Chartered Patent Agent, do hereby declare the nature
of this invention, and in what manner the same is to be performed, to be particu-
larly described and ascertamed in and by the following statement:
-
To explain the undesirable occurrences caused by the reaction of the rotating
armature in an electric machine it is usually stated that a distortion of the
magnetic field of the poles or pole pieces occurs as a result of the influence of
the said armature-in other words, that in consequence of the rotation of the
armature there is caused a concentration of the lines of force of the field at that
horn of each pole at which the armature coils emerge from the magnetic field
(hereinafter called the leading horn) while at the other horn (hereinafter called
the trailing horn) where the armature coils enter the magnetic field, there is
a weakening of the lines of force. Fig. 1 of the accompanying drawings illustrates
such a combination of lines of force.
To prevent this distortion of the field, which is the principal cause of sparking,
many suggestions have been made, some of which, tor example, are described
in the well known text-book of Sylvanus Thompson Dynamo-electric
Machinery," chap. XVI., 5th German edition. They consist, inter alia, in the
employment of auxiliary coils, which create a field of force of their own in such
a position as to counteract the shifting forwards of the lines of force of the main
field. But this arrangement of such auxiliary coils complicates the machines and
increases their cost, so that none of these auxiliary methods have come into
general use.

page_text: Various simple and purely mechanical means or solutions have been suggested.
The one that has been most employed is the arrangement of slots or cuts in
the poles or their shoes, running parallel to the direction of the field or to the
axis of the core of the magnet, in a plane perpendicular to the cross section of
the armature that is parallel to the armature winding. Such cuts or slits
should cause a resistance to the concentration of the lines of force at one of the
horns, by preventing them from going beyond one half of the core into the other
half thereof.
"
This certainly very simple means could, however, from the nature of the case,
have no favorable effect. For it is clear that the lines of force, in consequence
of the necessarily occurring magnetic bridges," can distribute themselves in the
already described unfavourable manner if the cuts do not run entirely through;
and this, for practical reasons, is not feasible and would cause other disadvantages.
Also the adoption of cuts where steel castings are used for the pole-pieces, is
especially difficult.
The effect of the cuts is improved (see German Patent Specification No. 97697)
by giving the pole piece or shoe an unsymmetrical shape for the purpose of
favorably influencing the lines of force at its surface.
The result of this arrangement may, perhaps, be satisfactory, but it is very
complicated and therefore not suitable for general use.
Another suggestion is made in the German Patent Specification No. 42164
(Fig. 10). It consists in combining with the cast field-magnet core, at the side
at which the armature-coils enter the magnetic field, a suitably formed piece of
a material which has a greater magnetic permeability than the material of the
core itself. This arrangement has however the disadvantage that the applied
piece lies entirely outside of the path of the magnetic lines of force. It can serve
as a conductor only for those lines that are generated in the said piece by reason
oi the surrounding coil, while the lines of force of the closed magnetic circuit
pass through the core.
This arrangement has also had no practical application, as is indicated by the
short life of the German Patent No. 42164.
Now this invention has for object, inter alia, to prevent the concentration of
lines of force at the leading horn of the pole in the simplest imaginable manner.
The pole, according to this invention, has in it on one side only one or more
cuts or slits, which does or do not run in the direction of the axis of the pole
but run at right angles thereto and are only made in that side of the pole or core,
at which the armature coils emerge from the magnetic field. These cuts or
slits, which can be made to serve as air spaces or be merely parting slits, increase
the magnetic resistance of the pole or pole-core only at that side at which they
are placed and then compel the lines of force at the opposite or trailing side to
concentrate. A strengthened field is thus produced and sparking is consequently
prevented. Fig. 2 shows an example of a pole treated in this way.
The action of this device can be increased in several ways The extreme end
of the pole may consist of two parts (as shown in Fig. 3), one being in one
piece with the core or pole body and the other being mechanically attached to the
core or pole body by a screw. The surfaces of separation between the detachable
piece and the pole body or core increases the magnetic resistance at this side
(the emergence or leading side) of the path of the lines of force and prevent con-
centration of the lines of force. The most widely differing proportions of the
magnetic conductibility can be reached by altering the ratio of the dimensions
of the surfaces where the two parts a and b join the core or pole body or by
shifting to the right or to the left the plane of separation between the two parts a
and b (Fig. 3).
Furthermore, the proper ratio between the number of lines of force and the
field density of the surfaces of the two portions of the pole tip facing the armature,
can be easily attained by making the contact surfaces or planes of or between
the two parts a and 6 of the extreme end of the pole oblique to the direction of

page_text: the pole, as shown in Fig. 4. The more oblique these separating surfaces are,
the greater the field-density will become at the horn at which the armature coils
enter the magnetic field.
This oblique arrangement of the plane of separation of or between the two
parts of the extreme end of the pole shoe (which can at the same time form one or
more air spaces) makes it possible to make the part of the extreme end of the
pole shoe that is at the side at which the armature coils enter the field, separate
from the core or pole body and to attach it mechanically, which from a practical
point of view is desirable. While the desired ratio between the magnetic resist-
ance of both parts can be attained by suitable' proportions of the two surfaces
in contact with the core or pole body, this can be effected within considerable
limits by obliquity (to the axis of the core or pole body) of the separating or
adjacent surfaces of or between the two detachable parts of the pole (Fig. 5).
The device may be further improved by the adaptation of the ideas embodied
in the German Patent Specification 42164 (Fig. 10); the part of the extreme or
face end, which lies at the side of exit of the armature winding is then not made
of the same material as the other part and the core or pole body, but of a material
of less permeability, as for example cast iron, if the core or pole body and the
other part of the extreme or face end of the pole are steel castings. But this
arrangement is distinguished from that described in the German Patent Speri-
fication No. 42164 in that the attached piece of different permeability is a part
of the face portion of the pole and not a part of the core or pole body so that
no more lines of force are excited therein, but it serves only as a conductor for
the lines of force that are excited in the pole body or core as far as permitted
by the resistance of the surfaces of the slit or slits, which are at right angles to
the direction of the lines of force.
In all cases in which both parts of the extreme end or face portion of the pole
are mechanically attached to the core or pole body they can without difficulty
be made symmetrical or symmetrically attached. They can, furthermore, be
interchangeable with each other if the direction of rotation of the machine has
to be reversed—an advantage that none of the other devices offers in so simple a
manner.
The device is intended principally to prevent sparking in continuous current
machines; but it can however so far be applied to alternating current machines
as to lessen self-induction and improve the current-curve under varying loads.
Having now particularly described and ascertained the nature of the said
invention and in what manner the same is to be performed I declare that what
I claim is:-
1. Dynamo poles provided with cuts or slits transverse to the lines of force
(to which a suitable path is offered) for preventing or reducing sparking by
avoiding or reducing the concentration of the lines of force at the sides of the
poles at which the armature coils emerge from the fields, and the corresponding
weakening of the fields at the trailing side
2. A dynamo pole according to the preceding claim in which the face portion
of the pole consists of two parts of which the one at the trailing side is in one
piece with the core, whilst the one at the leading side is mechanically attached
to the core so that a cut or slit for the purpose mentioned is formed by the surfaces
of separation of the core and the piece attached thereto.
3. A dynamo pole according to Claim 2. in which the plane of separation
between the two parts of the face of the pole does not run in the direction of
the axis of the pole or core but obliquely thereto as to obtain the desired ratio
between the densities of the lines of force on the two parts of the face of the
pole.
4. A dynamo pole according to Claim 2, in which for the purpose of further
concentrating the lines of force at the trailing side of the face of the pole part
of the face of the pole that is mechanically attached to the pole core on the

page_text: leading side consists of a material which has less magnetic permeability than
that of the pole core itself or of the other part of the face of the pole."
5. A dynamo pole according to Claim 2 in which the part of the face of the
pole at the trailing side is mechanically attached to the pole core and the desired
distribution of lines of force is secured by a suitable arrangement of the surfaces
of separation of the two parts of the face of the pole.
6. A dynamo pole according to Claim 5. in which the two parts of the face of
the pole are symmetrically formed or attached, so that they can be interchanged
for the purpose of reversing the direction of rotation of the machine.
7. Dynamo poles constructed, arranged, and operating as hereinbefore described
with reference to and shown respectively in Fig. 2, in Fig. 3, in Fig. 4 and in
Fig. 5 of the accompanying drawings.
Dated thi, 20th dov of Tahmam 1000
W. LLOYD WISE,
46, Lincoln's Inn Fields, London, W.C.,
Chartered Patent Agent.