Improved Apparatus for Converting Alternating Currents into Continuous Current.
Year: 1899

page_text: Date of Application, 22nd June, 1899-Accepted, 9th Dec., 1899
COMPLETE SPECIFICATION.
Improved Apparatus for Converting Alternating Currents into
Continuous Current.
I, MAX DÉRI, of 1, Reichraths Strasse No. 3, Vienna, Austria, Electrician, 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:-
Various proposals have been made for employing stationary induced coils and
commutators for converting alternating currents into continuous current, by pro-
ducing a rotary field in the magnets and causing the brushes of the commutator
to rotate. Arrangements of this kind offer several advantages both as to con-
struction and action, in particular because with stationary magnets; the magnetic
flux can flow in closed circuits, and only small masses require to be set in motion.
The main reason why this description of converters has not met with material
practical application is mainly that the current must be taken off with considerable
difficulties by means of sliding contacts such as have heretofore been employed
in connection with the revolving brushes.
The present invention relates to a construction of such converters with stationary
magnets and induced coils in which the continuous current produced is taken
from points that are stationary. By this means the importance of the brush
action is reduced, the construction and arrangement of the brushes is simplified
and the use of sliding rings is avoided.
:
In the following this invention will be explained with reference to the accom-
panying drawings.
The Figs. 1 and 2 are diagrams of potentials.
t
The Figs. 3 to 9 shew diagrammatically the arrangements of conductors, wind-
ings and connections in many examples. In these figures the dotted lines
of
represent primary mains
a supply system; the dotted lines
primary windings of transformers; T1 and T2 secondary windings of
transformers; and w² (for simplifying the diagram marked as circles only)
are windings of the converter in ring or drum form, for example in the manner
as explained in Fig. 10. In all the Figs. 3 to 10 the same letters indicate similar
parts.,, are commutators; B1 B2 brushes; a, b, c, d connections of the
alternating current mains to the converter windings; o o, q¹ and q³ connections
of the continuous current mains, which latter mains are marked by thick lines
including between them the sign of D."
I will describe the principles on which the invention is based with reference
to Figs. 1 and 2 of the accompanying drawings.
If in a magnet wound in a similar manner to the armature of a continuous
current dynamo, a rotary magnetic field is produced-for example by exciting the
winding by a polyphase current, then each potential revolves with the rotary

page_text: field round the zero point of the system. The zero point is either ideal or it is
actually formed by a suitable interlinked connection (star connection) of the
sources of current that excite the winding or of self induction resistances combined
with the winding.
The axis of the rotary field is X X, the zero point 0. The circle described
round is the potential circle. The vertical distance of any point from the
axis XX represents the potential of that point for the time being. That point of
the circle will have the highest potential which lies in the radius perpendicular
to XX. Consequently, when a contact such as a commutator brush situated at
that point revolves synchronously with the axis, then the brush potential rela-
tively to the zero point is a constant amount which is equal to the maximum
potential value.
In Figs. 1 and 2 there are shewn two separated winding systems.
Although it is most advantageous to arrange the two windings concentrically on
the same magnet core, so that the same magnetic field rotates in both, yet for the
sake of clearness there are assumed in the diagram to be two separated magnets with
separate rotary fields. In both Figs. X X is the bipolar field axis, and B1 and B2
are the revolving brushes which are always situated in the radius perpendicular
to the axis XX and revolve synchronously with the axis. O and 02 are the
zero points of the two systems. The potential of any point of the winding is
indicated by P and the maximum of the potential by r; the latter is equal to
the radius of the potential circle. The directions or signs of the potential value
are indicated by straight arrows and the direction of rotation by curved arrows.
If the two rotating brushes B¹ and 132 are put in conducting connection as in
Fig. 1, the zero points are put in potential relation to each other, namely, the
sum of the potential values of B1 and B2 appears between 0 and 03, so that the
potential difference D between the zero points is equal to 2r. If terminals be
placed at O¹ and 02, there will exist between these a constant potential difference
and a continuous current can be taken therefrom.
In the Fig. 2 the field axis X X also rotates and the brushes B1 B2 of the two
winding systems revolve synchronously therewith. Also in this case the brushes
are short circuited. If terminals 1 and 2 be applied, one at a certain point in
each of the two systems, the potential difference between the two terminals will
be made up out of the varying potential values P1 and P2 of the points q' and gª
and of the constant potential values of the brushes B¹ and B2.
This sum D is, with reference to the directions = 2 + (P¹-P³).
Each P varies between + and -; consequently, D can never have a negative
sign. D is therefore a pressure of always the same direction but fluctuating
between two values, the difference of which is greater or smaller according to the
relative position of the points q¹ and q².
If the points q¹ and q² have the same relative position as at Fig. 2, then P¹ and P
balance each other and D is = 2r, a constant value.
2.
If on the other hand the terminals lie in opposite potential points as g¹ 92,
Fig. 2, then P and P2 are always of opposite sign and P1 P2 varies between + 2 r
and 2r. The potential difference D is therefore variable between the limit
values 4r and zero. In general the pressure between any two points of the two
circles will fluctuate between 2r + d and 2rd, where can never become
greater than 2 r.
Figs. 3, 4, 5, 6, 7, 8 and 9 shew diagrammatic views of various characteristic
examples of converters constructed according to this invention; Figs. 3 to 6
shew arrangements in which the continuous current is taken from the zero points
of the transformer coils, while Figs. 7 and 8 shew arrangements in which the
continuous current is taken from fixed points of the magnet winding.
In these figs. U denotes the magnets of the converter (the stationary armature);
the circles W and W the two windings which are applied both in the same manner
whether as ring or as drum winding, to the stationary magnet core; and are

page_text: the two corresponding commutators; B¹ and B are the rotating brushes, T¹ and Ta
are the two groups of exciting transformer coils; a¹, a³, b¹, b, c, c, d, d are the
points of connection of the magnet windings with the transformer coils or with the
feed circuits; 01 and 02 are the terminals at the zero points and q¹ and are the
terminals at points of the magnet winding between which the continuous current
pressure is obtained, and (in particular) with the single phase converter Fig. 3)
R is the short circuited armature.
The arrows shew the direction of the momentary, pressures, or of the current.
In all these examples the converter magnet U is represented as a hollow iron
cylinder (as shewn in Fig. 10) in which the two windings w¹ and w³ are imbedded
so that they are surrounded with iron on all sides; only with the single phase con-
verter Fig. 3 are the two windings arranged on the inner surface of the hollow
cylinder, and are separated by an air gap from the revolving armature R which
is provided with a squirrel cage winding.
In Fig. 3 the rotary field is produced by exciting the converter, windings w
and w by means of the two secondary coils T1 and T2 of single phase alternating
transformer and by rotating the short circuited armature R synchronously with
the periods of the alternating current. It is well known if in a stator excited
by single phase alternating currents an armature provided with short circuited
windings be rotated synchronously there is produced, in consequence of the reaction
of the currents induced in the short circuits, a constant magnetic field rotating
with the armature, all other field components being neutralised by the said reaction.
By these means there results a rotary field in the converter magnet of a single.
phase transforming device, shewn in Fig. 3 as well as in the polyphase transform-
ing devices represented in Figs. 4 to 9.
In Fig. 4 the rotary field is excited by two-phase transformer coils T¹ and Ta
which are connected to the windings w¹ and w². In Fig. 5 the rotary field is pro-
duced by excitation from three-phase transformer coils and in Fig. 6 by excitation
from four-phase transformer coils. In all these cases the transformer coils like
the magnet windings are always present in two separate groups. In Figs. 3 and 4.
the zero points to which the terminals are attached are produced by halving and
in Figs. 5 and 6 by star connection of the transformer coils and in all four cases
the continuous current is taken from the zero points o¹ and o².
In an analogous manner any desired higher phase-number may be used, this
being effected the more easily in this case as the larger number of connection
points with these arrangements where there are no sliding contacts but only fixed
terminals, does not cause difficulties, and as the connecting leads need only be of
short length.
Fig. 7 shows the three phase excitation of the armature with two separate groups
of feeders L1 and L2; Fig. 8 shows the same excitation with two separate groups
of transformer coils interlinked in triangular form. In this case the terminals q¹
and are arranged in definite points of the two-magnet windings.
When the terminals are situated at points having the same position in the two-
magnet windings as at a¹ and a³, Figs. 7, 8 and 9, a constant continuous current
will be obtained; if on the other hand the terminals are not in the same position,
a fluctuating continuous current will be obtained. Both kinds of current will in
the following be designated as continuous current."
"
In Fig. 9 the converter magnet is provided with three windings. The primary
winding w marked with dotted line as circle only connected with the primary
mains of alternating current supply, produce the three-phase excitation of the
converter magnet, the secondary windings w¹ and w² arranged with commutators
in the same manner as in the other examples, are not connected with alternating
current mains, but solely with the continuous current supply conductors attached
at q¹ and q³ to these windings. The primary winding generally being excited by
high pressure currents will have a large number of turns. In this way the energy
supplied as high pressure alternating currents will be obtained as low pressure
continuous current from the transforming device, and consequently the pressure

page_text: transformer and the converter for transforming the form of currents are combined
in one apparatus with a magnet common to both.
In the arrangements shewn in Figs. 7, 8 and 9 there is three-phase excitation;
but also in these cases any desired higher number of phases may be used in an
analogous manner.
In all the above described arrangements with single or polyphase excitation, a
bipolar rotary field has been assumed for the sake of simplicity. If the connecting
points be suitably increased, the rotary field can also be made multi-polar, that is,
with any desired greater number of poles.
Fig. 10 shews the winding system of a converter with two drum winding
circuits ¹w and two commutators K¹ and K2 arranged with four poles, the con-
nections a¹, a³, 61, 62, c¹, c², for three phases being present in duplicate in each
circuit. In this case there are provided at the two commutators two pairs of
brushes, which are short circuited with each other, and consequently all have the
same potential.
The brush arrangement can be still farther simplified by shifting the commu-
tator sections of the one circle in the one direction and those of the other circle
in the opposite direction to the extent of half a polar distance, so that the parts
of opposite potential of the two commutators are situated in a radial position. In
that case instead of two brushes only one can be employed which bridges over the
diametrically opposite commutator sections in the shortest connection. Such
double brushes require to be provided in such number as there are pairs of poles
in the system. For example, in the arrangement at Fig. 10 there would only be
two double brushes.
The two winding systems are most advantageously coiled on a magnet core
common to both formed of laminated soft iron, the windings being arranged
concentrically close together and conveniently situated in one and the same set
of channels passing through the armature body at right angles to the iron laminae,
as indicated in Fig. 10. The magnetic flux of the rotary fields, which flows entirely
in iron, passes simultaneously through both the windings, or is excited simul-
taneously by both, so that the contiguous wires have the same potential value.
In the two commutators the potential differences will be equalised at those points
where the rotating brushes are for the time being situated. Therefore the insula-
tion of the brushes relatively to each other is not necessary.
The commutators can be formed cylindrical, and arranged one behind the other,
or they may be arranged as plane commutators and placed concentrically one
within the other. In all the figures the last mentioned arrangement has been
shown by way of example.
In the armature of a' converter constructed according to this invention no cross
fields nor dispersion fields will appear which could 'prejudicially affect the action
of the induction or commutation. Such an apparatus will consequently have a
high degree of effect.
The brushes which for the purposes of this invention can be constructed in a
simple and strong manner must revolve synchronously with the rotary or alter-
nating field. The rotation of the brushes which requires very little power, is
effected in the known manner by a synchronous motor which is actuated either
directly or indirectly from the same source of current as 'the converter.
With the single phase converter the short circuit armature can at the same
time form the rotor of the synchronous motor actuating the brushes; in this case
however, the armature should be provided also with another winding for the
excitation of the armature by continuous currents in the usual
can also be taken from 'the converter itself.
which currents
way,
The motor which actuates the brushes can also be conveniently útilised for
producing artificial' ventilation fór cooling the iron parts and windings of the con-
verter, and when necessary, also those of the feeding transformer, so as to increase
the efficiency of the converter by carrying off the heat' produced.
In Fig. 4 S represents diagrammatically the synchronous motor of the apparatus,

page_text: the continuously excited magnets of which are shown by way of example con-
nected by contacts with the continuous current mains of the converter.
Having now particularly described and ascertained the nature of this inven-
tion and in what manner the same is to be performed, I declare that what I
claim is:
1. Apparatus for converting alternating currents into continuous current
wherein two separate winding systems similar to the armature windings of a
dynamo each with a commutator provided on a stationary magnet and connected
to two separate groups of alternating current generators produce in the magnet
rotary fields common to both windings, while short circuited brushes made to
revolve synchronously with the fields connect such parts of the two commutators
with each other which for the time being have, in the one system, the highest
positive, and in the other system the highest negative potential, and terminals
for the continuous current each being connected to a fixed point of the two systems,
substantially as described.
2. Apparatus for converting poly-phase alternating currents into continuous
current of the kind referred to in the first claim, in which the two winding
systems connected to two separate poly-phase groups of secondary transformer coils
having interlinked star connection, produce in the stationary magnet rotary fields,
the magnetic flux of which common to both windings flows entirely through iron,
the terminals for the continuous current being placed at the zero point of the two
coil groups, substantially as described.
3. Apparatus for converting poly-phase, alternating currents into continuous
current of the kind referred to in the first claim, wherein the two winding systems
connected to two poly-phase groups of feeders produce in the stationary magnet
rotary fields the magnetic flux of which common to both windings flows entirely
in iron, the terminals for the continuous current each being placed at a fixed
point of the two magnet windings, substantially as described.
4. Apparatus for converting single phase alternating currents into continuous
current of the kind referred to in the first claim, in which the two winding systems
connected to two separate single phase groups of secondary transformer coils pro-
duce in the stationary magnets alternating fields, the magnetic flux of which
common to both windings pass from the stationary magnets into a rotor, provided
with short circuited windings which, being rotated synchronously with the
fields, convert the originally oscillating fields into 1otary fields, the terminals
for the continuous current being connected to the points of bisection of the two
secondary transformer coils, that to say, to the zero points of the two circuits
substantially as described.
5. Apparatus for converting single phase alternating currents into continuous
current of the kind referred to in the first claim, wherein the two winding systems
connected to two separate single phase groups of feeders produce in the stationary
magnet alternating fields, the magnetic flux of which common to both windings
passes from the stationary magnets into a rotor provided with short circuited
windings, which being rotated synchronously with the fields, convert the originally
oscillating fields into rotary fields, the terminals for the continuous current each
being placed at a fixed point of the two magnet windings, substantially as
described.