Improvements relating to Electric Motors.
Year: 1892

page_text: COMPLETE SPECIFICATION.
[Communicated from abroad by WILLIAM STANLEY, Junior, and JOHN FORREST
KELLY, both c/o Stanley Laboratory, Pittsfield, in the County of Berkshire
and State of Massachusetts, United States of America, Electricians.]
Improvements relating to Electric 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 :-
When an electro-magnetic motor, which requires for its operation alternating
currents differing in phase, which are caused to flow through separate or
independent energizing circuits, is run by currents derived from a single source,
and the difference of phase obtained by inserting in one of the derived or
branched energizing circuits a condenser, or what may be described as a polarizer
or polarization cell, a difficulty is met with due to the following conditions:
The condenser or polarizer is so adjusted with reference to the particular con-
ditions of the circuit that the current in the circuit in which it is included may have
a negative lag, or in other words, so that the phases of the current shall be ahead of
the impressed electro-motive force, or the electro-motive force due to capacity shall
exceed that due to self-induction, but this adjustment is made for the condition of
full load, of the motor.
At full load, however, the self-induction is largely neutralized by the reactive
action of the motor armature, but since this effect is reduced as the load on the
motor is lessened, the self-induction and capacity effects become more nearly equal.
The reduction of the reactive action of the armature, moreover, brings about a
reduction of the effective resistance of the field circuit, and hence it follows that
as the load is lessened the current in the branch circuit possessing negative lag,
increases in amount and decreases in lag, thus causing a great waste of energy.
To obviate this difficulty we have devised the following arrangement: Instead
of simply dividing a main or single circuit of alternating currents into the two
branch circuits for the field coils of a motor, and in parallel as heretofore has
been generally done, we include the primary coil of a transformer in circuit with
one of the field or energizing coils of the motor and connect its secondary through
a condenser or polarizer to the other energizing coil or set of coils. The impressed
electro-motive force in the secondary circuit in this case will be dependent upon
the current in the primary circuit and this latter will be kept from rising by the
increased self-induction when the armature load is lessened.
Transformers, however, as ordinarily constructed are not well adapted for this
purpose, for reasons which are hereinafter explained, and our invention also includes
a transformer of special construction as an element of the invention or combination
In transformers as ordinarily constructed and worked the ampere turns in the
primary and secondary coils are nearly equal, the number in the secondary being
if anything, rather less. In consequence of this it is usual to put into the two coils
the same weight of copper.
We have found that, when a transformer is used in conjunction with a polarizer
or condenser to produce two currents differing in phase by 90° this proportion
between the ampere turns is objectionable, for, when the current in the secondary
of the transformer lags 90° behind the primary current, it is just in phase with the
electro-motive force impressed by the primary current, and its total reaction on the
primary circuit is in the nature of creating in the latter a resistance or a counter
electro-motive force directly in opposition to the primary current.
The magnitude
of the electro-motive force thus set up is a measure of the work done in the

page_text: secondary circuit while the reaction produces no effect on the self-induction of the
primary.
Now when the number of ampere turas is the same in both coils, the counter
electro-motive force due to the reaction of the secondary circuit will be equal to
to the electro-motive force of self-induction in the primary, and these two electro-
motive forces will be at right-angles, since one is in opposition to the primary
current and the other at right angles to it. The current, therefore, neglecting the
resistance of the primary coil, which is small in comparison with the secondary
reaction, will be caused to lag 45° since the impressed electro-motive force at the
terminals of the primary circuit must be equal to the vector sum of the two
counter electro-motive forces and these latter, as shown are equal in magnitude
and at right angles.
The effective energy delivered will be equal to the impressed electro-motive force
multiplied by the current and this by the cosine of the angle of lag which in the
case under consideration would be about 7 of the apparent energy.
But if the number of ampere turns in the secondary be increased, say to twice
the number in the primary, much better conditions will be secured, for with the
ampere turns of the secondary twice those of the primary, the secondary reaction
on the primary will, in magnitude, be twice the electro-motive force of self-induction
in the primary although in the same direction as before.
By this means the lag of the current in the primary behind the impressed electro-
motive force would be materially reduced and the effective energy would become
equal to about 9 of the apparent energy, so, with a still higher ratio of ampere
turns in the secondary the results would be still better.
The greater number of ampere turns in the secondary does not necessarily require
a greater mass of copper in that coil, but if only the same mass be employed the
loss of energy due to the heating of the secondary coil will become considerable and
the efficiency of the transformer will be lowered. We therefore prefer in practice
to employ a greater mass of copper in the secondary circuit than in the primary,
say, in proportion to the number of ampere turns in the secondary.
The invention as far as it may be illustrated diagrammatically is shown in the
accompanying drawing, in which:
A A represent the conductors of an alternating circuit; B the armature and
M, N, the two energizing or field coils of any ordinary two-phase motor.
The primary coil P, of a transformer of which C represents the core, and one
of the motor coils, as M, are included in series in the main circuit. The circuit of
the secondary coil S includes the other energizing coil N and a condenser or
polarization cell D adjusted to the requirements of the system so as to produce
between the currents in the two motor circuits an approximate difference of 90°.
The use of a condenser in this connection is now well understood, and in view of
the present public information on the subject it need only be said of the polarization
cell that it consists of conducting plates or couples in an electrolyte by which the
plates are not chemically attacked, and included in the circuit in the usual way.
Having now particularly described and ascertained the nature of the said inven-
tion and in what manner the same is to be performed, as communicated to me
by my foreign correspondents, I declare that what I claim is :-
1. The combination with a circuit from a source of alternating currents, of a
transformer, and a motor having independent energizing coils or circuits, the
primary of the transformer and one of the energizing coils of the motor being
included in the said circuit, and the other energizing coil of the motor being in the
secondary circuit of the transformer, and a condenser or its equivalent in the said
secondary circuit, as set forth.
2. The combination with an alternating current two-phase motor having
independent energizing circuits, a main circuit from a source of alternating currents,
a transformer the primary and secondary coils of which are in circuit with the
motor coils respectively, and a condenser or its equivalent in series with the

page_text: secondary coil and one of the motor coils, the transformer being constructed or
designed with a greater number of ampere turns in the secondary than in the
primary circuit.
3. The combination with an alternating current two-phase motor having
independent energizing circuits, a main circuit from a source of alternating currents,
a transformer the primary and secondary coils of which are in circuit with the
motor coils respectively, and a condenser or its equivalent in series with the
secondary coil and one of the motor coils, the transformer being constructed or
designed with a greater number of ampere turns in the secondary than in the
primary and having a mass of copper in the secondary greater than that in the
primary in proportion to the number of ampere turns.
Dated this Third day of August 1892.
HASELTINE, LAKE & Co.,
45, Southampton Buildings, London, W.C., Agents for the Applicant.