Improvements in and relating to Alternating Current Electro-Motors.
Year: 1897

page_text: Date of Application, 5th Oct., 1897-Accepted, 22nd Jan.,
1898
COMPLETE SPECIFICATION.
Improvements in and relating to Alternating Current Electro-Motors.
I, CHARLES SCHENCK BRADLEY, of Avon, in the County of Livingston, in the
State of New York, United States of America, Electrical Engineer, do hereby
declare the nature of this invention, and in what manner the same is to be per-
formed, to be particularly described and ascertained in and by the following state-
ment:-
-
This invention relates to alternating current motors and its chief object is to
dispense with brush contacts. The invention is especially applicable to motors of
the induction type in which a rotary field is established in one element, preferably
the fixed or stationary element and the other element is inductively charged by
the rotary field. I connect the revolving element at a plurality of points with a
winding enclosing an independent core rigidly secured to the same shaft which
carries the rotary element; this winding forms the primary of a transformer the
secondary of which is wound upon an annular core surrounding the primary. Thus
the induced currents set up in the motor armature act inductively upon the
secondary of the transformer and deliver current to a stationary part of the
apparatus. The transformer secondary is connected with an external regulating
circuit including devices by which the capacity inductance product may be varied
to vary the torque and speed of the motor. I prefer to employ adjustable con-
densers for this purpose, though the inductance may be varied with less convenience
by making the secondary of the transformer sectional and coupling the sections
in different relations.
is a
In the accompanying drawings which illustrate the invention, Figure
sectional side elevation of a motor embodying my improvements; Figure 1' is a
partial side elevation; Figure 2 is a diagram of one mode of regulating the speed
and torque; Figure 3 is a diagram of another mode of regulating the speed and
torque.
Crepresents a field magnet which is preferably provided with a rotary field
winding adapted for polyphase currents, which currents may be of any order.
Figure 2 shows at P1, P2, the two branches of a quarter phase winding; Figure 3
shows a tri-phase winding. When other induction motors are connected in the
same distribution circuit, a single phase winding may be employed. The armature S
is provided with a winding preferably polyphase, shown as quarter-phase in
Figure 2 and as tri-phase in Figure 3. The winding connects at a plurality of
symmetrically distributed points with corresponding coils S1, S2, wound on an
annular iron core fixed to the armature shaft and revolving with it. Surrounding
the annular iron core is another core wound with a plurality of coils T, T³,
numbered from 1 to 6, provided respectively with independent terminals at B
and C (see Figure 2) and connected with switches D, E, by which they may be
grouped in various relations to vary the inductance. A condenser K¹, K2, of con-
stant value is included in circuit with each switch. In lieu of adjusting the
inductance the latter may be a constant factor, changing slightly only with changes
of load, and the condenser may be variable; such an organisation is illustrated in
Figure 3, where K', K³, K³ are condensers included in the polyphase circuit of the

page_text: transformer and provided with a controlling switch L by which a single movement
of an operating handle graduates all of the condensers simultaneously and similarly
by cutting in or out more surface. It will be understood from the construction
thus described that no brushes whatever are employed on the motor; a rotary or
progressive magnetic field is set up in the element C which inductively develops
currents in the winding of the armature S and consequently delivers alternating
currents differing in phase to the primary windings S1, S2, of the transformer;
thus electromotive forces differing in phase are developed in the coils T, T
Evidently by adjusting the switches D, E, or L the relations of capacity and in-
ductance are varied in these circuits, which by varying the phase differences of
current and electromotive force and permitting the greater or less flow of current
graduate the speed and torque of the motor. The best condition of adjustment will
he obtained when the circuits T, T¹ are electrically consonous "with relation to
the supply current, that is to say when the inductance and capacity of the said
circuits are so adjusted that the inductance will be neutralised; this will occur
when the adjustment is such that the capacity in microfarads multiplied by the
inductance in henries equals 25,300 divided by the square of the rate of alternation
in the circuits T", T. The rate of alternation is a variable factor dependent on
the "slip" of the armature, since evidently it depends upon the difference in speed
of the armature and the rotary field. As the largest current flows when the con-
sonous adjustment is obtained, the speed of the armature may be held at any point
desired by making the adjustment of the condenser or inductance such that the
capacity-inductance product will be such as to produce electrical consonance for
that speed. As the torque begins to fall off on departure from consonance, this
also may be varied by adjustment of the switches.
Any suitable form of switch may be provided; that for the condenser depicted
in Figure 3 will be understood upon inspection of the drawing; that of Figure 2
may require a brief description. D represents a series of concentric annular
segments insulated from one another and mounted upon a suitable arbor to turn
as a whole. Upon these segments may bear a series of radially disposed contacts B
corresponding in number to the number of annular segments. The switch is sub-
divided into four parts a, b, c, d, which are so arranged as to connect the contacts B
(which connect with coil terminals T₁, Tn) in different relations. Alternate
segments of this group a connect with opposite plates of the condenser. Let us
suppose that contacts B are placed on group a; each coil will then be connected
with opposite sides of the condenser, and the coils will be in multiple arc relation,
offering a minimum inductance. If placed on group the second and third con-
tacts, the sixth and seventh, and the tenth and eleventh will be connected together
by the broad faced segments, thus placing the coils in three groups of two each in
series. Similarly, if the contacts be placed on group c, the second and third, the
fourth and fifth, the eighth and ninth, and the tenth and eleventh will be connected
together, the other terminals connecting alternately with opposite sides of the con-
denser, thus connecting the coils in two groups of three each in series; and when
the contacts are placed on the group d all coils will be connected in series giving a
maximum inductance. In each of these adjustments a different capacity induct-
ance product will be given, thus changing the consonous speed of the motor. I
prefer to make the condenser the adjustable factor, as shown in Figure 3, on account
of the simplicity of construction and ease of management; and although the
polyphase system of connection is the most advantageous and efficient, it is not
absolutely essential, as a single phase motor when once started will run under load;
my invention is therefore applicable to induction motors of all kinds.
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed, I declare that what I
claim is-
1. An alternating current induction motor having a revolving element induc-
tively related to a rotary magnetic field and inductively related also to an auxiliary

page_text: stationary circuit including current regulating devices, substantially as herein-
before described and as illustrated by the accompanying drawings.
2. An alternating current induction motor having a field core provided with a
rotary field winding, a rotary armature electrically connected with the revolving
primary coil of a transformer, and a stationary secondary coil of the transformer
connected with a regulating switch, substantially as hereinbefore described and as
illustrated by the accompanying drawings.
3. An alternating current induction motor having a stationary element provided
with a rotary field winding and a rotary element in fixed connection with a poly-
phase circuit including the primary coils of a transformer, and stationary secondary
coils for the transformer including devices for regulating the capacity inductance
product of the circuit including it, substantially as herein before described and as
illustrated by the accompanying drawings.
Dated this 4th dow of Catalin 1907
W. E. HEYS & SON,
Agents for the Applicant.