Improvements in Alternating Current Electro-magnetic Motors.
Year: 1891

page_text: Date of Application, 6th July, 1891-Accepted, 22nd Aug., 1891
[Communicated from abroad by NIKOLA TESLA, of Astor House, New York,
United States of America, Electrician.]
Improvements in Alternating Current Electro-magnetic Motors.
I, HENRY HARRIS LAKE, of the firm of Haseltine Lake & Co., Patent
Agents, 45 Southampton Buildings, in the County of Middlesex, 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 :-
This invention relates to electric motors, the action or operation of which is
dependent upon the inductive influence upon, and magnetization of a rotating
armature by independent field magnets or coils traversed by alternating or similar
currents, which produce their effect upon said armature not simultaneously but
successively, as would result from said currents being of different phase.
The improvements consist in a novel arrangement applicable to motors, in which
the current for one of the energizing circuits is obtained by induction from the
other, and also in a means for increasing the flow of current in the closed induced
armature coils of any form of alternating current motor in which such coils may
be present, particularly, in what are now known as the Tesla motors.
The first feature above referred to is the placing in the secondary or induced
field or energizing circuit of the motor a condenser, adjusting it so as to neutralize
the self induction to the desired extent, and to secure between the primary and the.
secondary currents the proper difference of phase for the most economical operation
of the motor; and the second is the interposition of a condenser in the induced
or what is otherwise the closed circuit of the armature.
In the accompanying drawings
Figure 1 is a form of induction motor to which the improvements are applied.
Figure 2 is a diagram of a modification of a part of the improvements.
The motor is composed of two or more pairs or sets of field magnets, A and B,
mounted in or forming part of a suitable frame and a rotary armature wound with
a coil C.
In the particular motor, here shown, the coils on two opposite poles, as A, are
connected directly to a main or branch circuit D from a generator of alternating
currents. Over, or in any other inductive relation to these coils, secondary coils E
are wound, and in the circuit of these are included the energizing coils of the
other pair of field poles B. Hence, the alternating currents that energize the
poles A, induce currents that energize poles B, but no means have heretofore been
proposed that would secure between the phases of the primary or inducing and the
secondary or induced currents that difference of phase, theoretically ninety degrees,
that is best adapted for practical and economical working.
To more perfectly secure this object, I interpose in the secondary circuit, or
that which includes the coils E, F, a condenser G, adjusting it as to capacity in
well-known ways so as to neutralize or overcome the retarding effect of self
induction and bring the phase more nearly to the proper point of difference.
As the required capacity of this condenser is dependent upon the rate of alter-
nation or the potential or both, its size and cost may be brought within economical
limits, for use with the ordinary circuits by raising the potential of the secondary
circuit in the motor. Many turns of fine wire are therefore used for the coils E,
so as to convert to a current of very high potential.
This improvement is equally applicable to motors of this type, that is to say,-

page_text: those in which the currents for one energizing circuit are induced from the other
when a distinct transformer outside of the motor is used. In the illustration, the
two energizing circuits are brought into inductive relation inside the motor, but it
is evident that they may be brought into the same relation outside the motor by
means of a transformer.
In this, as well as in all other forms of motor in which a closed armature coil is
used, in which currents are induced by the action of the field magnets or coils,
the most efficient working conditions require, that, for a given inductive effect
upon the armature there should be the greatest possible current through the
armature or induced coils, and, also, that there should always exist between the
currents in the energizing and the induced circuits, a given relation or difference of
phase hence, whatever tends to decrease the self-induction and increase the current
in the induced circuit. will, other things being equal, increase the output and
efficiency of the motor, and the same will be true of causes that operate to
maintain the mutual attractive effect between the field magnets and armature at its
maximum.
These results are secured by connecting with the induced or armature circuit H
of the armature a condenser L. This coil or coils H have no connection with the
outside circuit and are closed upon themselves through the condenser. In ordinary
cases, the terminals of the coils lead to collecting rings M, M, upon which
brushes N, N, bear, and the condenser is inserted between these brushes. But
the armature core may be hollow and the condenser carried within it, or the sheet-
iron plates, of which the core is composed, may be carefully insulated so as to
constitute a condenser, and the coils may be connected to the plates. In such cases
no brushes would be required.
The condenser should be of such character as to overcome the self-induction of
the armature, so that when the motor is in operation the impedence of the said
coils to the passage of the induced currents is not only neutralized, but the phases
of the induced currents are brought more nearly into proper accord with those in
the field coils.
In motors in which the armature coils are closed upon themselves, as, for example,
in any form of alternating current motor in which one armature coil or set of coils
is in the position of maximum induction with respect to the field coils or poles,
while the other is in the position of minimum induction, the coils are preferably
connected in one series and two points of the circuit thus formed are bridged by a
condenser. This is illustrated in Figure 2, in which P represents one set of
armature coils and P¹ the other. Their points of union are joined through a
condenser G.
It will be observed that in this disposition the self-induction of the two branches P
and P varies with their position relatively to the field magnet, and that each
branch is alternately the predominating source of the induced current, hence the
effect of the condenser G is two-fold. Firstly, it increases the current in each of the
branches alternately and secondly it alters the phase of the currents in the branches,
this being the well-known effect which results from such a disposition of a condenser
with a circuit as above described.
This effect is favorable to the proper working of the motor because it increases
the flow of current in the armature circuits due to a given inductive effect, and
also because it brings more nearly into coincidence the maximum magnetic effects
of the co-acting field and armature poles.
Although this feature of the invention has been illustrated herein, in connection
with a special form of motor, it will be understood that it is equally applicable to
any other alternating current motor in which there is a closed armature coil wherein
the currents are induced by the action of the field, and, furthermore, I would state
also that the feature of utilizing the plates or sections of a magnetic core for
forming the condenser, regard as applicable, generally, to other kinds of alter-
nating current apparatus.

page_text: Having now particularly described and ascertained the nature of the said
invention and in what manner the same is to be performed, as communicated to
me by my foreign correspondent, I declare that what I claim is :-
First. In an alternating current motor in which one energizing circuit is in
inductive relation to the other and closed upon itself, the combination with such
closed or secondary circuit of a condenser interposed in the same, as described.
Second. In an alternating current motor, the combination of two energizing
circuits, one connected or adapted for connection with a source of alternating
currents, the other constituting a secondary circuit in inductive relation to the first
and adapted to convert to currents of high potential, and a condenser interposed
in the said secondary circuit, as set forth.
Third. In an alternating current motor, the combination with the armature and
an energizing circuit formed by a coil or conductor wound thereon in inductive
relation to the field, of a condenser connected to the said coil or conductor.
Fourth. In an alternating current motor, the combination with armature coils
in inductive relation to the field and connected in a closed circuit, of a condenser
bridging said circuit, as set forth.
.
Fifth. In an alternating current motor, the combination with the induced
energizing coil or coils of the armature of a condenser connected therewith and
made a part of the armature or rotating element of the motor.
Dated this 4th day of July 1891.
HASELTINE, LAKE & Co.,
45, Southampton Buildings, London, W.C., Agents for the Applicant.