Improvements in Alternating Current Electric Motors.
Year: 1898

page_text: Date of Application, 9th Sept., 1898-Accepted, 12th Nov., 1898
COMPLETE SPECIFICATION.
Improvements in Alternating Current Electric Motors.
A communication by CHARLES S. BRADLEY, a citizen of the United States, and
resident of Avon, County of Livingston, State of New York, United States
of America, Electrical Engineer.
I, WILLIAM PHILLIPS THOMPSON, F.C.S., M.I.M.E., of the Agency for Foreign
Patent Solicitors, 6, Lord Street, Liverpool, and 6, Bank Street, Manchester,
both in the County of Lancaster, 118, New Street, Birmingham, in the County
of Warwick, and 322, High Holborn, in the County of Middlesex, Civil Engineer,
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
This invention relates to electric motors, and has for its object the construction
of a motor which may be operated from a single-phase alternating-
current circuit, that is to say, one in which but two supply wires are used,-
and which will have a strong running and starting torque and may be capable
of operation at different speeds. In carrying out the invention a winding on
one element of the motor is provided by which a rotary magnetic field may be
developed when the winding is connected to a single-phase supply-circuit.
may be accomplished in several different ways, as by having two or more sets
of co-operating coils in which a phase-difference is established, or by having an
auxiliary closed winding on the motor element displaced with reference to a
companion winding on the same element which connects with the single phase
circuit. The secondary element of the motor is provided with a winding with
which is connected an external circuit including one or more adjustable electric
condensers, the capacity of which may be regulated by a controlling switch.
With this organization the capacity may be changed and the speed of the motor
will accordingly change. The condensers should have such a capacity that a con-
sonous relationship may be established between the waves of the supply circuit
and the induced waves in the secondary element of the motor, so that the latter
will be in a resonant relationship to the supply currents. When the motor
circuits are thus arranged and the capacity of the condensers so adjusted as to
produce the consonous relationship just referred to, a strong current will flow,
as in this condition of adjustment the motor inductance is neutralized and the
analogy of a resonant electric circuit is established. The establishment of this
relationship by means of the adjustable condensers in the secondary circuit
effects a very important result, namely, it permits the phase-difference of the
currents of the primary winding to be increased which is a very important con-
sideration where a single alternating current is to be split up into two currents
of different phase at a point remote from the supply generator, since a more
perfect rotary magnetic field can thus be established. With adjustable condensers
in the secondary circuits, therefore, good conditions are established for the

page_text: development of an effective rotary magnetic field, and therefore a better operation
of the motor is possible. The condensers should be of sufficient capacity to pro-
vide more than enough electro-static capacity than is necessary to establish
electrical consonance and thus the inductance of the motor system will not only
be neutralized but a lead of phase produced in the motor circuits with relation
to the supply circuit as the condenser acts as a phase-advancing device. It has
also an important practical result in preventing a disturbance of the line current
by the operation of the motor and counteracting the production of lagging
currents in the lines. Two plans for operating this invention are shown in the
accompanying drawings.
In Figure 1 the rotary field is established in the outside or stationary element
of the motor by means of two coils, one of which is connected with the line
through an inductance, and the revolving element is connected with the adjust-
able condenser.
In Figure 2 the revolving element is connected to the supply circuit and a
phase-difference to establish the rotary magnetic field is produced by a closed
coil set at an angle with reference to the principal coil. The secondary circuit
is similar to the arrangement in Figure 1, except that it is here shown on the
stationary element of the motor and a single condenser is used in place of three
separate condensers.
The
In both drawings A-B are the supply wires of a single-phase alternating
current; in Figure 1 two sets of coils on the primary element of the motor are
supplied from this circuit as indicated by the wires 1, 2, 3, 4. The windings
of the primary motor element 5 may be spaced any suitable distance apart on
the core, the inductance 6 being sufficient to produce a phase displacement in
the two windings corresponding to their difference of position on-the.core.
secondary element 7 is provided on its shaft with three ring-contacts insulated
from one another and connecting with three symmetrical points on the secondary
windings 7; from these rings three brushes a, b, c, connect with three condensers
over which switches 8, 8ª, 8b, metallically connected together by a controlling
lever 9, may be shifted, thus permitting the amount of condenser surface to be
varied by moving the switches so as to cover more or less of the contact-points
with which one set of condenser plates connect. Instead of three separate con-
densers a single condenser might be employed, such as is shown at 11 in Figure 2,
the successive condenser plates connecting with the groups of contacts corre-
sponding to the switch-arms 10ª, 10b, 10°; the first plate of the condenser in
this organization connects with the first contact-point of switch 10", the
second plate of the condenser with the first contact-point of the switch 10b, and
the third plate of the condenser with the first contact-point of the switch 10°.
The fourth, fifth and sixth plates of the condenser connect with the second
point of the switches 10", 10b, 10°, respectively; the seventh, eighth and ninth
plates with the third point of the switch-arms and so on, each group of three
plates connecting with the respective contacts of the controlling switch. When
the switch in Figure 2 is moved upon the contacts the amount of surface may
be adjusted in a manner similar to Figure 1. The three switch arms 10°, 10° 10°,
should be insulated from one another and from the handle-bar in the system
of Figure 2 and the connections with the secondary winding may be made with
the first contact point of each switch, as shown. In the form of motor shown in
Figure 2, the phase displacement of the primary element, here shown as 7a
is established by connecting one set of coils through the brushes with the supply
circuit A-B and placing on the same core a coil system d, d¹ closed upon itself
and placed at an arc or angle of about 45° with relation to its companion coil-
system. By means of the two coil-systems, in which the current phases will
differ, a rotary magnetic field is developed in the element 7 and by a proper
adjustment of the condenser connecting with the secondary element the motor
may be rendered self-starting and of strong running torque. The secondary
circuit is shown in the two figures of drawings as three phase in character; of course,
any number of connections may be made acording to the number of phases

page_text: desired. This invention is to be distinguished from others heretofore described
by my correspondent and others, the novelty consisting in supplying the motor
from a single-phase circuit and placing an adjustable condenser in the secondary
circuit of the motor. The relationship called electrical consonance takes places
when the capacity in microfarads multiplied by the inductance in henries of the
secondary circuit becomes equal to 25,300 divided by the square of the rate of
alternation.
Having now particularly described and ascertained the nature of this inven-
tion, 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 :-
1. An electric motor having one core or element wound to produce a rotary
magnetic field when supplied from a single phase alternating-current circuit, and
a secondary core or element having its winding connected with an adjustable
phase-advancing device such as an electric condenser.
2. An electric motor having on its primary element a rotary field winding,
the several coils of which are arranged for connection with a single-phase
alternating-current circuit and include inductance or inductances to produce a
phase-difference of current, and on its secondary element a winding connecting
with one or more adjustable electric condensers of sufficient capacity for the
purpose described.
Doted this 20th
בז'
1000