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

page_text: Date of Application, 4th June, 1891-Accepted. 11th July, 1891
COMPLETE SPECIFICATION.
Improvements in Alternating Current Electro-magnetic Motors.
We WILLIAM STANLEY Jr., of Pittsfield County of Berkshire and State
of Massachusetts Post Office address. Pittsfield, Massachusetts, Electrician, and
JOHN FORREST KELLY, of New York, County and State of New York,
Post Office address 29 Plane Street, Newark, New Jersey, Electrician both of
United States of America 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 :-
The object of this invention is to render practicable and efficient the operation of
an electro-magnetic motor of ordinary character, such as are now used on continuous
current circuits, by an alternating current, so that the motor may have the full
capability of starting and regulation common to the corresponding forms of direct
or continuous current motors.
It is a well-known fact that any ordinary electro-magnetic motor provided with
a commutator may be operated by an alternating current, but far less efficiently,
for various reasons, than by a continuous current, for it is a common characteristic
of all such motors that the lag or retardation of the current behind the impressed
electro-motive force reduces their efficiency to a comparatively low point.
The present application has to do with series as well as shunt wound motors, in
fact with any motor provided with a cominutator and in which the electro-motive
force in the field and armature circuits or coils is directly and not inductively
impressed by the generator, the object of the invention being to neutralize the self-
induction of such motors.
The invention is based on the well-known property or feature possessed by a
condenser of neutralizing or counteracting the effects of the self-induction of a
circuit with which it may be connected, and it consists in the combination with
a motor of a condenser in series with one or both of its circuits, which condenser
has sufficient capacity or value, according to the conditions of the circuit, to
neutralize or overcome the self-induction of the same.
In the case of a series motor the condenser is placed in the circuit in series
with both the armature and field coils, so that the self-induction of the motor being
neutralized the current through the same will meet with no other opposition than
that of dead resistance.
In the case of a shunt wound motor, however, the self-induction is mainly in the
field circuit, and when such a motor is operated by an alternating current, a loss is
occasioned by the higher self-induction of the field circuit, which retards the phase
of the current imparting magnetism to the field magnets, and, as a consequence, the
maximum magnetic effects of the armature and the field are not coincident, a
condition which impairs the efficiency of the motor. In order to counteract this and
bring the maximum magnetic conditions of the two elements, armature and field,
more nearly into coincidence, the condenser is introduced into the field circuit or is
placed preferably in series with the coil of the field magnets only and not with those
of the armature. This has the effect of bringing the phase in the field circuit nearer
to that of the impressed electro-motive force of the source of current.
The efficiency and economy of this disposition will, of course, depend upon the
electro-motive force, rate of change of the current and other well understood
conditions, but these are matters which are now well-known to electricians.
It may be stated that the motors, of whatever kind employed, will be adapted
in other well-known respects than those herein specified for use and operation
with a source of alternating current. For example, the cores of the field

page_text: magnets as well as of the armature should be magnetically subdivided or
laminated.
are
The invention is illustrated in the accompanying drawings, which
diagrams illustrating several of the more usual ways of applying or utilizing
the invention.
In Figure is illustrated the general plan of connecting a condenser in series
with the motor, the motor in this figure being diagrammatically shown as a series
motor.
G is a generator of alternating currents, and A, A, the conductors of the main
linc.
B is one of any number of parallel branches between these conductors.
In any
branch, as B, is a series motor of which E represents the armature and F the
field. In series with such motor is a condenser C of a capacity or value that
neutralizes the electro-motive force of the self-induction of the motor, so that when
the latter is at rest no opposition is offered to the passage of the current but that of
dead resistance.
R is a variable resistance in series with the motor for adjusting the current on
the start.
In Figure 2 the arrangement is based on the same principle. Each motor,
however, is in this case connected directly in the line, and around each is a shunt S
containing a rheostat or variable resistance. These shunts may be completely
interrupted when the motor is running. In series with the motor, in this arrange-
ment as in the other, is a condenser C capable of neutralizing the self induction of
the motor.
In Figure 3 is shown in diagram an ordinary form of shunt wound motor having
a commutator II, brushes I, I, armature E and a field circuit F. In the said
circuit is the condenser C, capable of neutralizing the self induction of
said field.
By the means above described, the operation of any form of commutating motor
by an alternating current is rendered practicable.
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 :-
First. The combination with a generator of alternating currents and a motor,
the field and armatures cores of which are energized by the directly impressed
electro motive force of the generator, of a condenser in series with such motor and
adapted to neutralize its self-induction, as herein set forth.
Second. The combination with a generator of alternating currents and a series
wound motor connected therewith, of a condenser in series with such motor and
of a capacity or value capable of neutralizing the self-induction of the motor, as set
forth.
Third. The combination of an electro-magnetic motor provided with a
commutator and having its field and armature circuits in derivation, of a
condenser included in the field circuit or that having the higher self-induction, as
set forth.
Dated this 4th day of June 1891
HASELTINE, LAKE & Co.,
45, Southampton Buildings, London, Agents for the Applicants.