Improvements in Induction Motors for Alternating Electric Current Circuits.
Year: 1899

page_text: Date of Application, 14th Mar., 1899-Accepted, 22nd Apr., 1899
COMPLETE SPECIFICATION.
Improvements in Induction Motors for Alternating Electric Current
Circuits.
We, THE BRITISHI THOMSON-HOUSTON COMPANY, LIMITED, of 83, Cannon Street,
in the City of London, Electrical Engineers, do hereby declare the nature of this
invention (which has been communicated to us from abroad by Edwin W. Rice,
Jr., and Charles P. Steinmetz, residing at Schenectady, in the County of Schenec-
tady, State of New York, United States of America, Electrical Engineers), and in
what manner the same is to be performed, to be particularly described and ascer-
tained in and by the following statement::—
Our invention relates to induction motors for alternating current circuits, and
has for its object to provide a motor which may be started in a simple and efficient
way, being particularly adapted to motors operated on single phase alternating
current systems.
Prior to the date of our invention it had been customary to construct the
so-called phase-splitting motors with poles displaced from each other by sub-
stantially one quarter of the polar pitch, and to excite one set of the said poles
from the single phase mains, and to excite the other set of poles by deplased
currents derived directly or indirectly from the said.mains. This is objectionable,
for the reason that it is difficult to secure a phase displacement of 90 degrees
between the two currents, and for that reason the rotary field produced by such
motor is unsymmetrical in character.
In the form shown in this application there is one main inducing coil and a
plurality of auxiliary inducing coils, preferably two.
Other features of the invention will be hereinafter more particularly described,
and will be pointed out in the annexed claims.
In the drawings attached to this specification, Fig. 1 is a diagrammatic view of
our improved motor; Fig. 2 is a general view of our improved motor in its pre-
ferred form; and Fig. 3 is a view of the preferred form of armature.
In Fig. 1, B is the main inducing coil, while A and C are auxiliary inducing
coils. It will be seen that the coils A and B are connected in series across the
circuit, while the coil A is shunted by the variable resistance R³ controlled by the
switch F. The coil C is closed on itself through the switch F.
The action of this motor is as follows. In starting the switch F¹ is open, and
the switch is so placed as to short-circuit the coil A, preferably including a
portion of the resistance R³. The action is somewhat complex but we understand
it to be about as follows. The coil A is excited direct from the single phase mains,
and also has induced in it current by the lines of force generated by the coil B
and by the lines of force generated by the current set up in the armature D by
the action of the coil B. The result is to generate in A a resultant current
dephased from the current in B by an angle depending on the amount of resistance
in R³. It will be seen that R³ is a phase shifting device shunting the coil A, 50
that the current passing through B is split into two components, of which the
leading component passes through R³, and the lagging component through A.

page_text: If now the switch F¹ be closed, a current will flow in the coil C, which cur-
rent will be out of phase with the current in each of the coils A and B.
When a speed approaching that of synchronism is attained, the switch F may
be opened, when the coils A and B will be connected in series across the lines and
will generate a resultant Hux passing through the armature and through the
coil C. This resultant Hux will generate in the coil C a current which will tend
to reduce the apparent self induction of the armature, and to keep its current and
electro-motive force in phase.
It is also possible by suitable connections to substitute each for each the
coils A, C, and their functions, and in this way the direction of revolution of the
rotating member is readily reversed. That is, at the start the coil Û can be
closed, and the coil A left open circuited for a time, as will be readily understood.
Referring now to Fig. 2, the mode of operation will be obvious from the
description already given. A, B and C are the three inducing coils, wound in slots
in the face of the ring E, in such a way as to produce a multipolar motor. We
ordinarily prefer to use the multipolar arrangement, as it is more efficacious
than the other forms of alternating current motors, and we particularly prefer
to use a magnetic structure with projecting teeth, or having recesses for the
coils, as shown in the drawings.
Fig. 3 shows the preferred form of the induced member or armature, composed
of a multiphase winding, with the resistances R, R, R2, capable of being cut out
in the usual way. We find that the use of such an armature greatly assists the
action of the motor.
Having now particularly described and ascertained the nature of our said inven-
tion (as communicated to us from abroad) and in what manner the same is to be
performed, we declare that what we claim is :-
-
1-The combination with single phase mains, of an alternating current motor
containing three angularly displaced windings, one of which receives current by
inductive action from the other two, and all of which receive energy derived from
the single phase mains, and means for shunting one winding by a device adapted to
shift the phase of current in said winding.
2 The combination with single phase mains, of an alternating current motor,
containing three angularly displaced windings, one of which receives current by
inductive action from the other two, and all of which receive energy derived from
the single-phase mains, and means for shunting one winding by a device adapted
to retard the phase of current in said winding.
3 The combination with single-phase mains, of an alternating current motor
having a plurality of angularly displaced windings, one of which receives its
energy by induction through the induced member of the motor, and all of which
receive their energy either directly or indirectly from the single phase mains, and
means for shunting one winding by a device adapted to shift the phase of current
in one of said windings.
4 The combination with single-phase mains, of an alternating-current motor
having a plurality of angularly displaced windings, one of which receives its
energy by induction through the induced member of the motor, and all of which
derive their energy either directly or indirectly from the single phase mains, and
means for shunting one winding by a device adapted to retard the phase of current
in one of said windings.
5 The combination of a pair of single phase mains, of an alternating-current
motor having three angularly displaced windings, all of which receive their
energy either directly or indirectly from the single phase mains, means for closing
one winding on itself, and means for shunting another winding by a device adapted
to shift the phase of the current therein.
G-The combination of a pair of single phase mains, of an alternating current
motor having three-angularly displaced windings, all of which receive their energy
ither directly or indirectly from the single-phase mains, means for closing one

page_text: winding on itself, and means for shunting another winding by a device adapted
to retard the phase of the current therein.
7-The combination in an alternating current motor, of an inducing and an
induced member, three angularly displaced windings on the inducing member, two
of which receive energy directly through two supply mains, means for dephasing
the current in the said two windings, and means for short-circuiting the third
winding.
S The combination in an alternating current motor, of an inducing and an
induced member, and a short-circuited winding arranged on the inducing member
and within the inductive influence of current in the induced member and acting
to reduce the self induction of the induced member.
9 The combination in an alternating current motor of an inducing winding
having angularly displaced coils, a short-circuited winding arranged on the
inducing member, in the axis of polarization of the inducing winding, and an
induced member within the influence of currents in said winding.
Doted Lith day of March 1800
THE BRITISH THOMSON-HOUSTON CO., LTD.,
Applicants,
ALFRED CLEMENTS,
Assistant Secretary,
W. MARTINDALE,
A. R. MONKS,
Directors.