Improvements in Appliances for Reversing the Current in Continuous Current Dynamos.
Year: 1899

page_text: Date of Application, 13th Dec., 1899
Complete Specification Left, 13th Sept., 1900-Accepted, 3rd Nov., 1900
PROVISIONAL SPECIFICATION.
Improvements in Appliances for Reversing the Current in
Continuous Current Dynamos.
We, SIEMENS BROTHERS & Co., LIMITED, of 12, Queen Anne's Gate, West-
minster, in the County of London, Electrical Engineers, do hereby declare the
nature of this invention (as communicated to us from abroad by Siemens &
Halske Aktien Gesellschaft, of Markgrafen Strasse No. 94, Berlin, in the Empire
of Germany, Electrical Engineers) to be as follows:--
This invention relates to that description of continuous current dynamos wherein
special independent magnetic fields are employed between the main field magnets
tor reversing the currents in the armature. We will describe the present improve-
ments in the construction and arrangement of such reversing magnets with
reference to the accompanying drawings in which Fig. 1 shews diagrammatically
the application of such reversing magnets, by way of example to a bipolar shunt-
wound dynamo.
The slotted armature a rotates in the well known manner
between the field magnets f 7 carried by the connecting yoke j; the armature
is assumed to have a drum winding, of which only the connecting leads situated
near the vertical axis are shown the front ones being shewn in full lines while
the back ones are dotted; the middle parts of the front connecting leads are each
connected with a segment of the commutator c. The conductors marked with
crosses in the sections indicate those in which the currents are flowing in the
direction from the front to the back while those marked with dots indicate the
contrary course of the currents.
In the vertical central plane of the machine there are provided the special
reversing electromagnets mm, which extend in the direction of the length of the
armature, and the two poles of which are directed towards the armature. These
poles are narrow in the direction of the armatures circumference and their total
width bears a definite proportion, to be presently referred to, to the pitch of the
armatures teeth or grooves.
On the rotation of the armature clockwise and with the indicated polarity of
the held magnets f, there are produced in the armature windings electromotive
forces or currents having the direction indicated. With the direction of the
currents in the reversing magnets m m similarly indicated by crosses and dots,
there are produced in the cores thereof and also in the opposite parts of the
armature, independent magnetic circuits in the direction indicated by the dotted
arrows:
With the position of the brushes assumed in the drawings the connecting leads
indicated by thick lines, are for the time being, in the short circuit period, the
corresponding parts of the winding being then situated between the limbs of the
reversing magnets m m. The direction of the lines of force of the self-induction
of these parts of the winding is consequently the reverse of the direction of the
magnetic flux of the reversing magnets. If therefore the latter are sufficiently
excited, the magnetic lines of force of the self induction will have their direction
reversed so that the reversal of the current will be effected without sparking.

page_text: The excitation of the reversing magnets m m is made proportional to the
strength of the armature current.
The resistance of the magnetic circuit through the reversing magnet and the
armature is mainly that due to the air gaps. As the independent magnetic circuit
of the reversing magnets is only influenced to a slight degree by the magnetism
of the main field, the magnetic flux of the reversing magnets like that of the
self induction of the armature winding, is very nearly proportional to the strength
of the armature current. The reversal of the current will therefore take place
without sparking and without adjustment of the brushes, no matter what the load
on the machine may be.
The reversing magnets also produce a flux through the armature winding
increasing with the strength of the current, and in the direction of that due to
the contiguous field magnets, as indicated by dotted lines. At the same time,
the dispersed lines of force of the field magnet pole tips (to the left at the top,
and to the right at the bottom) whose magnetism is strengthened by the reaction
of the armature, are led into the armature, so that the fall in pressure in the
machine will be reduced.
If it be desired to increase this action of the reversing magnets, these may have
their poles shaped more or less as shewn at Fig. 2, the exciting current being
correspondingly increased.
The distance apart of the poles of the reversing magnets is dependent as before
stated upon the pitch of the teeth of the armature, as will be seen from their
above described mode of action; it will also to a certain extent be dependent
upon the mode of winding, as with certain variations of the latter the simul-
taneously short circuited parts thereof may not be contiguous to each other.
The excitation of the reversing magnets is generally effected by the armature
current itself; it may however be of advantage under certain circumstances, to
effect such excitation by a suitably regulated independent current.
Should it be desired to damp the magnetic oscillations occuring at the reversal
of the current, which strengthen the tendency to sparking, the reversing
magnets m m may be provided with short circuited windings, in which case their
cores are preferably made of laminated iron.
In the above description it has been assumed that the poles of the reversing
magnets m m extend along the whole width of the armature, parallel with the
axis and teeth thereof.
It has been found however that generally speaking the excitation of the reversing
electromagnets necessary for the reliable reversal of the current must be so great
that the additional flux through the armature windings is thereby made to
increase to a greater extent than is necessary, and that the voltage of the machine
is increased to a considerable extent beyond the pressure of the machine when
without a load.
If on the other hand the polar surfaces of the electromagnets be made very
narrow, their action for the reversal of the current will be insufficient as on the
passage of the teeth and grooves past the polar surfaces, the magnetic resistance
of the air spaces are subject to too considerable variations.
As a means for decreasing as may be required the additional flux through the
armature winding from the reversing electromagnets without interfering with
their beneficial action on the reversal of the currents, it has been found of advan-
tage to arrange the polar surfaces of the reversing magnets in an oblique position
relatively to the armature axis. Such an arrangement is shewn in elevation and
part developed plan at Figs. 3 and 4 of the drawings. The several parts of the
machine are indicated by the same letters as the corresponding parts in Figs. 1
and 2.
The reversing magnets m here have their polar surfaces (indicated by the
sectional lines p in Fig. 4) placed obliquely to the armature axis.
The extent of such obliquity is dependent upon the distance apart of the two

page_text: polar surfaces and is made at least equal to the combined width of one tooth and
one space of the armature; it may however be considerably more, and in the
drawing it is shewn equal to the width of two teeth and two spaces. With this
arrangement the conductor in one of the grooves will at certain times be subject
to the simultaneous action of both poles of the electromagnet. For providing
room for this oblique position the pole tips of the field magnets may be formed
with a corresponding slope.
Dated this 13th day of December 1899
ABEL & IMRAY,
Agents for the Applicants.
improvements in Appliances for Reversing the Current in
Continuous Current Dynamos.
We, SIEMENS BROTHERS & Co., LIMITED, of 12, Queen Anne's Gate, West-
minster, in the County of London, Electrical Engineers, do hereby declare the
nature of this invention (as communicated to us from abroad by Siemens &
Halske Aktien Gesellschaft, of Markgrafen Strasse No. 94, Berlin, in the Empire
of Germany, Electrical Engineers,) and in what manner the same is to be per-
formed, to be particularly described and ascertained in and by the following
statement:-
This invention relates to that description of continuous current dynamos wherein
special independent magnetic fields are employed between the main field magnets
for reversing the currents in the armature. We will describe the present improve-
ments in the construction and arrangement of such reversing magnets with
reference to the drawings accompanying our Provisional Specification in which
Fig. 1, shews diagrammatically the application of such reversing magnets, by way
of example to a bipolar shunt-wound dynamo. The slotted armature a rotates
in the well known manner between the field magnets f f carried by the connect-
ing yoke j; the armature is assumed to have a drum winding, of which only the
connecting leads situated near the vertical axis are shewn the front ones being
shewn in full lines while the back ones are dotted; the middle parts of the front
connecting leads are cach connected with a segment of the commutator c.
The conductors marked with crosses in the sections indicate those in which
the currents are flowing in the direction from the front to the back while those
marked with dots indicate the contrary course of the currents.
In the vertical central plane of the machine there are provided the special
reversing electromagnets m m, which extend in the direction of the length of the
armature, and the two poles of which are directed towards the armature. These
poles are narrow in the direction of the armatures circumference and their total
width hears a definite proportion, to be presently referred to, to the pitch of the
armatures teeth or grooves.
On the rotation of the armature clockwise and with the indicated polarity of
the field magnets f, there are produced in the armature windings electromotive
forces or currents having the direction indicated. With the direction of the
currents in the reversing magnets m m similarly indicated by crosses and dots,
there are produced in the cores thereof and also in the opposite parts of the
armature, independent magnetic circuits in the direction indicated by the dotted
arrows.
With the position of the brushes assumed in the drawings the connecting leads
indicated by thick lines, are for the time being, in the short circuit period, the

page_text: corresponding parts of the winding being then situated between the limbs of the
reversing magnets m m. The direction of the lines of force of the self-induction
of these parts of the winding is consequently the reverse of the direction of the
magnetic flux of the reversing magnets. 11 therefore the latter are sufficiently
excited, the magnetic lines of force of the self induction will have their direction
reversed so that the reversal of the current will be effected without sparking.
The excitation of the reversing magnets m m is made proportional to the
strength of the armature current.
The resistance of the magnetic circuit through the reversing magnet and the
armature is mainly that due to the air gaps. As the independent magnetic circuit
of the reversing magnets is only influenced to a slight degree by the magnetism
of the main field, the magnetic flux of the reversing magnets like that of the
self induction of the armature winding, is very nearly proportional to the strength
of the armature current.
The reversal of the current will therefore take place without sparking and
without adjustment of the brushes no matter what the load on the machine
may be.
The reversing magnets also produce a flux through the armature winding
increasing with the strength of the current, and in the direction of that due to
the contiguous field magnets, as indicated by dotted lines. At the same time,
the dispersed lines of force of the field magnet pole tips (to the left at the top,
and to the right at the bottom) whose magnetism is strengthened by the reaction
of the armature, are led into the armature, so that the fall in pressure in the
machine will be reduced.
If it be desired to increase this action of the reversing magnets, these may have
their poles shaped more or less as shewn at Fig. 2, the exciting current being
correspondingly increased.
The distance apart of the poles of the reversing magnets is dependent as before
stated upon the pitch of the teeth of the armature, as will be seen from their
above described mode of action; it will also to a certain extent be dependent
upon the mode of winding, as with certain variations of the latter the simul-
taneously short circuited parts thereof may not be contiguous to each other.
The excitation of the reversing magnets is generally effected by the armature
current itself; it may however be of advantage under certain circumstances, to
effect such excitation by a suitably regulated independent current.
Should it be desired to damp the magnetic oscillations occuring at the reversal
of the current, which strengthen the tendency to sparking, the reversing
magnets m m may be provided with short circuited windings, in which case their
cores are preferably made of laminated iron.
In the above description it has been assumed that the poles of the reversing
magnets m m extend along the whole width of the armature, parallel with the
axis and teeth thereof.
It has been found however that generally speaking the excitation of the reversing
electromagnets necessary for the reliable reversal of the current must be so great
that the additional flux through the armature windings is thereby made to
increase to a greater extent than is necessary, and that the voltage of the machine
is increased to a considerable extent beyond the pressure of the machine when
without a load.
If on the other hand the polar surfaces of the electromagnets be made very
narrow, their action for the reversal of the current will be insufficient as on the
passage of the teeth and grooves past the polar surfaces, the magnetic resistance
of the air spaces are subject to too considerable variations.
As a means for decreasing as may be required the additional flux through the
armature winding from the reversing electromagnets without interfering with
their beneficial action on the reversal of the currents, it has been found of advan-
tage to arrange the polar surfaces of the reversing magnets in an oblique position
relatively to the armature axis. Such an arrangement is shewn in elevation and

page_text: part developed plan at Figs. 3 and 4 of the drawings. The several parts of the
machine are indicated by the same letters as the corresponding parts of Figs. 1
and 2.
The reversing magnets m here have their polar surfaces (indicated by the
sectional lines p p in Fig. 4) placed obliquely to the armature axis.
The extent of such obliquity is dependent upon the distance apart of the two
polar surfaces and is made at least equal to the combined width of one tooth and
one space of the armature; it may however be considerably more, and in the
drawing it is shewn equal to the width of two teeth and two spaces. With this
arrangement the conductor in one of the grooves will at certain times be subject
to the simultaneous action of both poles of the electromagnet. For providing
room for this oblique position the pole tips of the field magnets may be formed
with a corresponding slope.
Having now particularly described and ascertained the nature of our said
invention and in what manner the same is to be performed, we declare that what
we claim is :-
1. In continuous current dynamos providing in the spaces between the limbs
of the field magnets special bipolar electro magnets for reversing the currents
which magnets are excited by the armature current or by a separate current more
or less proportional thereto, such electro magnets having their narrow poles
directed towards the armature, while the distance apart of such poles being deter-
mined by the number of grooves of the armature, and the description of winding
employed substantially as and for the purpose described.
2. In the arrangement of bipolar electromagnets referred to in the first claim.
providing the magnet cores constructed of laminated iron with short circuited
windings for the purpose of deadening the magnetic oscillations that are caused
by the reversal of the currents, substantially as described.
3. Arranging the bipolar electromagnets referred to in the first and second
claims in oblique positions relatively to the armature conductors for the purpose
of reducing the additional induction produced in the armature conductors by the
said electromagnets, substantially as described.
Dated this 13th day of September 1900.
ABEL & IMRAY,
Agents for the Applicants.