Improvement in the Regulation of the Speed and Power of Alternating Current Motors.
Year: 1890

page_text: Date of Application, 15th Dec., 1890-Accepted, 31st Jan., 1891
BIL MEDIUITIATION,
Improvement in the Regulation of the Speed and Power of
Alternating Current Motors.
We, MICHAEL VON DOLIVO-DOBROWOLSKY, Electrician, and the Company
"ALLGEMEINE ELEKTRICITATS-GESELLSCHAFT," both of No. 22, Schiffbauer-
damm, Berlin, Prussia, 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 :-
Our invention relates to alternating current motors driven by currents of
respectively differing phases, and its object is to provide new means for regulating
the speed and power of such motors.
Among the motors of this kind there are many arrangements in which no
current is supplied to the rotative part or armature, and the operation whereof
depends solely upon the excitement of magnetism in the armature by the current
circulating in the exciting part. Conformably to this circulating or circumrotative
current, the magnetic field of the exciting part also rotates in a circle, and a solid
iron body, the armature, placed movably in the field, is drawn along by the same.
If, however, the iron constituting the armature, is divided into disks, whereby the
passage of the Foucault or eddy-currents is intercepted, the armature remains at
rest. But, if coils of wire are arranged upon the divided body of iron, the outer
field excites, in the said coils, currents which magnetize the iron and produce a
rotation thereof corresponding to the circumrotation of the outer field. The strength
of this magnetism and the propelling power produced by the same, depends upon
the strength of the excited current, which, if there is a given invariable resistance,
is in turn dependent upon the electro-motive force induced. This force attains its
highest value if the armature is stationary, and the value zero if its number of
rotations is equal to the number of rotations of the outer field. The latter state
can, however, never occur, as the friction always present, prevents the armature
from attaining the said highest speed. For the intermediate speeds the electromotive
force induced in the coils of the armature is dependent upon the difference of the
two numbers of rotations. The more considerable this difference is, the greater
will be the propelling power. The variation of rotative speed of the outer field
therefore presents a means often employed for regulating the propelling power.
The new method which we employ for the same purpose is based upon the
regulation of the induced current. If, at the commencement of working, the induced
coils of the armature are short-circuited, the motor does not start, because the
electro-motive force being at its maximum, generates in the armature a very strong
current, which as it were annihilates the outer exciting field. The short circuited
coils are, however, very efficient when the motor is running at full speed, that is
when it rotates nearly uniformly (synchronously) with the outer field. Now,
between these limits any desired speed and propelling power may be produced by
means of interposed resistances formed by metals, liquids, lamps, induction-coils, &c.,
and in this mode of regulating the speed and power of the motor our invention
consists.
Under the said conditions the armature runs non-synchronously and it acts in a
manner as current-producing part in which the strength of current may be regulated
at will from outward, the resistances serving at the same time as well for starting
the motor as for regulating it while at work. The number of coils on the armature
and the arrangement of their connections is variable, and besides the number of
coils is entirely independent, as regards the number of currents of respectively
differing phases, from that of the exciting field. The more currents, however, are

page_text: derived from the armature, the better and the more uniform the regulation
will be.
The
In the annexed drawing is shown a motor comprising our improvement.
exciting field of the same has twelve coils b to be supplied with a corresponding
number of alternating currents of different phases. In view of simplifying the
drawing the armature is shown provided with but two coils d and d', but ordinarily
a greater number will be employed. The said coils are connected at their respective
ends a a¹ by means of wires to the contact-ring a³, while coil d is connected at its
other end, e, to the ring e², and coil d' at its other end, e¹, to the ring e³. ff¹ are
vessels containing the liquid whereby the resistance is to be created and into which
are introduced the conductors g g' and h, the latter dipping into the liquid and being
arranged to lead the currents from the vessels f to the vessels f'. The conductors g
are connected by the wire a and brushes to the ring a³, the conductors g¹ by the
wires ee and brushes to the rings e' e³, so that a current passing outward through
wire as to the conductors g first traverses the liquid in vessels f, thence passes
through conductors to vessels f¹ and traverses the liquid contained therein, and
finally returns through conductors g¹ and wires et e to the armature-coils.
regulating the resistance, the conductors are attached to a bar i provided with a
mechanism for lowering and raising the same in view of causing the conductors h
to dip more or less deeply into the liquid. This is, however, only one example of
the resistance-device, which may be arranged in various manners.
For
Moreover, as regards the form of the inducting field and of the induced armature,
it is immaterial what kind of coils are applied thereto. The substance of the
invention lies solely in this that the circuits of the armature, instead of being
closed in themselves, are connected to resistances capable of being regulated.
Having now particularly described and ascertained the nature of this inven-
tion and in what manner the same is to be performed, we declare that what we
claim is :-
In alternating current motors propelled by currents of respectively differing
phases and having an armature provided with coils that are not supplied with
current, the combination, with the armature-coils, of resistances and means for
regulating the same, substantially as described.
Dated the 15th day of December 1890.
J. H. JOHNSON & Co.,
Agents.