Improvements in Arrangements for Exciting the Magnets of Dynamo Machines.
Year: 1898

page_text: Date of Application, 11th July, 1898-Accepted, 10th Sept., 1898
COMPLETE SPECIFICATION.
Improvements in Arrangements for Exciting the Magnets of
Dynamo Machines.
nature
I, MAX DÉRI, of I, Reichsrath Strasse, No. 3, Vienna, Austria, Electrician, do
hereby declare the
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 the excitation of the magnets of dynamo machines having
armatures with commutators in such a way that the resulting field has a constant
direction, even when the current of the armature, as generator or motor, varies
between wide limits or the direction of rotation of the armature changes. In this
way sparking at the commutator is avoided when any desired regulation of pressure,
current or speed is made, the brushes being retained in a certain invariable
position.
For this purpose, the field is arranged in the form of a shell or a cylinder (for
external or internal pole machines respectively) with the iron equally distributed
around and equi-distant from the armature, similarly to the armatures used in
alternate current induction motors; but it is not necessary to construct the iron
core in laminar form for continuous current excitation. Pole pieces or poles of
special construction are not used. In contrast with usual field constructions.
The cross section of iron and the air space for the flow of magnetic force are
uniform over the whole circumference.
The surface of the field magnet turned towards the armature is wound either in
ring or drum windings in two different groups of coils in notches or grooves or
through holes.
Fig. 1 shews a field magnet F (of an external pole machine) in the form of a shell
with ring winding. A is the armature, C the commutator and BB are the brushes.
The coils S S' form in the series a-b and c-d the one winding and are arranged
for example, as a shunt to the brush circuit which supplies the external leads; the
coils which form the second winding e-f and g-h, are wound in series with
the brush circuit. Both groups of coils are arranged to be bipolar in such a way
that the mean poles of the one group are turned halfway between those of the other
group, just as in a two phase winding of an induction apparatus. The layers of
wire of both windings can be placed over or near to one another. It is also
perinissible to wind the coils of one group as ring windings and those of the other
group as drum windings. The number of windings on the coils S2 S2 is independent
of that on the coils S₁ S¹; it is advisable to make the number equal or nearly equal
to the number of active armature windings. Both groups of coils act together to
excite the field magnets-the coils S¹ S¹ effecting the chief excitation and the coils
S² S² the compensating excitation--and create a field the axis of which coincides
with that of the shunt circuit field (x¹¹) when no current is flowing in S² S², but
when a current is flowing in S2 S² it is inclined to the axis xx¹ on the one side or
the other at a certain angle dependent on the direction and strength of the current.
The coils S2 S2 are so arranged in the main circuit that they excite in the field a flow
of magnetic force in a direction contrary to that of the armature field (³ ³),
whether the armature operates as generator or as motor. The coils S² S² are

page_text: invariably connected with the armature circuit so that the circuits of the armature
and the coils S² S² are reversed together when the direction of rotation of the
armature is altered.
In the diagram Fig. 2 the line o a represents in magnitude and direction the
field (f) excited by the shunt circuit, and the line ab represents the field (f) excited
by the compensating coils; together they constitute the components at right angles to
each other of the field, which must be regarded as the field created by the sum
of the exciting coils of the armature; this together with the armature
field (measured by the line o c) constitutes the resulting field, that is the total
field of the dynamo-machine which determines the induction of the rotating
armature windings. If the number of the windings of the compensating coil is made
equal to the number of effective armature windings, then, since the current in both
always changes equally, oc = - a b (as in Figure 2) and consequently the total
resulting field is always equal to f¹.
According to the arrangement shewn in Figure 1, where the main excitation is
effected in the shunt circuit the armature at a constant speed of rotation yields a
constant pressure, and when actuated by a constant pressure develops a uniform
speed.
By resistances in the shunt circuit the strength of the resulting field can be
varied as may be necessary. The field strengthened or weakened in this way
romains, however, in its direction, always independent of the variation of the
armature current. The strengthening or weakening of the field can be similarly
effected by compound winding the main excitation. In this manner over. or
under-compounding or even counter-compounding is obtained; all these methods
of working are brought about with a constant direction of the resulting field.
When the main excitation coils S¹ S₁ are arranged in series with the armature
instead of in shunt circuit, the direction of the resulting field still remains
constant, although the strength of the armature current or the direction of rotation
of the armature varies. On the other hand the strength of the resulting field in
such an arrangement may vary within wide limits. Even in this case the.
compensating coils S2 S² as in Figure 1 must be coupled in series with the armature,
and if a reversal is necessary, the armature must remain in un-changed series
with the compensating coils and both must have their currents reversed
together.
In all the cases mentioned it will be obvious that the neutral zone, that is the
zone in which no induction is exerted on the armature windings remains fixed in
place as well as the resulting field axis; the most essential cause of sparking at the
commutator is removed and the brushes do not spark even when kept in the same
position and with large changes of armature current.
As
To achieve the desired purpose by this arrangement, it is an important condition
that the masses of iron on the armature be equally distributed. Only thus-in
contrast with the compensation windings elsewhere proposed for overcoming the
reaction does the flow of force excited by the compensating coils meet with equal
magnetic resistance as the flow of force produced by the main excitation coils.
a result the current in the compensating coils is as effective for excitation of the
field as is the current in the main excitation coils; in this manner the two fields are
combined in the desired manner. Contrary to what is the case in the compound
field winding heretofore usual, the currents in the compensating coils have always
a positive effect, since by this current the field in the machine whether as a generator
or as a motor becomes always stronger but never weaker. It is thus possible by
the arrangement herein described to charge accumulators with compensated
armature currents without fear of a reversal of the poles. It is further possible
under equally advantageous working conditions to change the direction of rotation
of the dynamo-machine without shifting the brushes.
The arrangements above described for exciting the magnets of dynamo-machines
having commutator armatures are applicable to the different constructions of such
machines with any number of poles.

page_text: Having now particularly described and ascertained the nature of this
invention and in what manner the same is to be performed, I declare that what I
claim is :-
1. In a dynamo-machine having a commutator armature, a field magnet arranged
round the armature in such a way that the iron of the magnet is equally distributed
around and equidistant from the armature there being two groups of excitation
coils having an equal number of poles and the polar divisions being displaced
inutually through half a pole distance, substantially as and for the purpose set
forth.
2. In a dynamo-machine for constant pressure having field magnets as set forth
in the preceding claim, the arrangement wherein one of the two windings of the
field magnets excites a field having a contrary direction to that of the armature
field and is in unchanged series connection with the armature, while the other
winding effects the main excitation and is in a shunt circuit, so that the fields
excited in community by both groups of windings added to the armature field form
a field constant or nearly constant in strength and direction, substantially as and
for the purpose set forth.
3. In a series motor or generator having field magnets as set forth in Claim 1,
the arrangement for exciting the magnets wherein one of the two windings
of the field magnet excites a field having a contrary direction to that
of the armature field and in unchanged series connection with the
armature, while the other winding effects the main excitation and may be in
changeable connection with the armature, so that the field excited in community
by both groups of windings added to the armature field forms a field variable in
strength relatively to the armature current, but constant or nearly constant in
direction even when the direction of rotation is altered, substantially as and for the
purpose set forth.
Dated this 11th dow of 1.1 1000