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 BRIrish 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
Schenectady, 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 ascertained in and by the following statement: —
Our invention relates to alternating current motors, particularly to that class
adapted to be operated by single phase alternating currents, and it embodies
certain improvements enabling such motors to be started from rest under load,
with a large torque.
Our invention also comprises arrangements for modifying the character of
the motor, or altering the relations of its parts so that when a speed approaching
the normal has been attained the motor may, if desired, be thereafter operated
as a single phase alternating motor of the induction type.
To this end we arrange a field magnet coil, or an inducing coil, which may or
may not be wound on the moving member, and in inductive relation thereto,
at such an angle as to produce a rotary effect, we provide a second coil which
we may close on itself by means of a switch, inserting preferably an adjustable
resistance, or which we may supply with the primary currents, as hereinafter
explained.
We prefer to leave a third portion of the circumference of the inducing member
without any winding, or to provide it with a winding which is open circuite.
while the motor is starting. As far as the starting action is concerned, we regard
these two arrangements as practically equivalent.
Within the field of the coils thus arranged, we provide an induced member.
preferably a closed circuited winding on a revolving armature, although as
above indicated either the inducing or the induced member may be the revolving
part.
Although we have spoken in this statement of invention of a coil, in the
singular, it is to be understood that we may adapt our invention to a multi-
polar arrangement, and such an arrangement we ordinarily prefer, for various
reasons, and we particularly prefer to use a magnetic structure with projecting
teeth, having recesses for the coils. On such a structure we place two windings.
spaced as if they were to form two of the windings of a three phase motor, one
of said windings being fed from the inducing circuit, and one being short cir-
cuited. It will be seen that this arrangement will leave a third portion of the
field core unwound. This portion we may wind with a third coil or series of
coils. but in this case, as stated above, the third coil or series of coils should be
open circuited while the motor is starting.
In the accompanying drawings, which show various embodiments of our inven

page_text: tion, Figs. 1, 2, and 3 are explanatory diagrams; Figs. 4 and 5 are views, partly
diagrammatic, of a multipolar motor arranged according to our invention; Fig. 6
is a diagram of an armature winding which we may employ, having resistances;
and Fig. 7 shows our improved motor in a different form.
In Fig. 1, which is inserted simply to explain the principles of our inven-
tion, A, B and C are field or inducing coils, arranged at an angle of 120 degrees
from each other around a short circuited armature 1). Rª is a variable resist-
ance in the circuit of the coil C. B is the primary coil, and is fed from the
single phase mains.
Suppose that the resistance R³ is cut out, that is to say, that the coil C is short
circuited, and the current is admitted to B. The coil B will set up lines of
force which will induce secondary currents in both the armature 1) and the
cails A and C. The secondary currents in I will also induce currents in both A
and C. The result will be that the currents in D, will lag behind the currents
in B, and that the currents in A and in C will lag by a different and usually be
a greater angle. But owing to the symmetry of the system there will be no
torque, or the torque in one direction will be equal to that in the other.
If now the resistance R be adjusted to some considerable value, the motor will
tend to start. The reason for this we undertsand to be that the currents in C,
owing to the action of the resistance, will lag behind the impressed electro-
motive force less than do the currents in A, so that we have what may in general
be regarded as an unsymmetrical three phase system. We find that the result-
ing torque is a maximum when the resistance R becomes infinite, in other words
when the coil C is open circuited or removed altogether.
This results in the form shown in Fig. 2, which is a simple elementary dia-
gram of the motor shown in Figs. 4 and 5. The mains are connected to the
extremities of the coils A and B. and a switch F is arranged which acts to short
circuit A on itself when desired. This switch Facts also to cut in a variable
resistance. If current be supplied to the motor, and the switch F be closed, the
machine will start under load. We understand the action to be somewhat as
follows. The current in B induces a field of force, which induces secondary
currents in D and in A. lagging behind the primary currents. I also induces
in A tertiary currents, lagging still further. If now the resistance controlled
by the switch F is actually zero. the current flowing in A will be the resultant
of the two currents induced in it by B and D, and the phase of this resultant will
depend on the character of D and of the magnetic circuits, as well as on its own
self induction, etc. Suppose that the armature D is of very high resistance, and
few turns, so that its inducing power is small. Then the current in A will be
practically due to the action of B only, and will have the usual transformer lag.
which may be perhaps 150 degrees behind the current and 120 degrees behind
the magnetism of B. The motor will thus start and run left-handedly. If ou
the other hand, as we prefer should be the case, D) is so constructed as to have
a high inducing power, there will be three magneto motive forces acting to pro-
luce rotation, instead of two, as in the case where the inducing power of the
armature is small. The motor will start and run right-handedly.
The phase relations of currents and magneto-motive forces in this case, where
the inducing power of the armature is high, may be more clearly explained by
reference to the diagram, Fig. 8 of the drawings. In this diagram the line B
represents in magnitude and phase the primary current in the inducing mem-
her of the motor, while the line D represents the current induced thereby in
the closed circuited winding on the armature or induced member D) of the motor.
The resultant 4 represents in magnitude and phase the resultant magneto-motive
force due to the action of the primary current and the current in the induced
member. In addition to these currents there is a third current which is genera-
ted in the accelerating or closed-circuited coil A on the primary member. This
tertiary current is due to the combined action of the currents in B and D), and
lags in phase behind their resultant by an angle equal to nearly 180 degrees,

page_text: and therefore behind the current in the primary coil B by an angle greater than
180 degrees, which is equivalent to a lead. This tertiary current lags behind
the resultant 4 in the same manner that the secondary current 1) lags behind
its inducing current B. The tertiary current may therefore be represented
by the vector A, and lags something over 90 degrees behind the magneto-motive
force 5, which is the resultant, as will be seen, of the tertiary current A+, and the
resultant 4, which latter, as previously stated, is the resultant of the original
primary current B and the current D in the induced member.
It will of course be understood that the phase relations and magnitudes shown
in the diagram referred to illustrate, the conditions existing in the case of one
particular design of motor; and it will further be understood that these magni-
tudes and phase relations vary with different designs of motor, and that even for
the same design of motor the values vary with different values of load. The
diagram is not to be taken as illustrating a fixed and unalterable condition of
affairs, but it is to be considered as indicating one relation only of the large
number which may exist between the currents and magneto-motive forces acting
in motors constructed in accordance with our invention.
It will be seen that the starting effect depends on the fact that A is set at an angle
to B, for if it were parallel to it, or one half of the polar pitch from it, there
would be no shifting or rotary field, and no torque,
The resistance controlled by the switch F serves to vary the volume and lag
of the current in A, and to control the starting torque. When this resistance
becomes fairly large, a considerable portion of the primary current will flow
through A, instead of flowing through the short circuit as before, which serves
to still further adjust and control the phase of the magnetism induced by A.
When the motor attains a speed which will vary with the particular machine
and with the load, but which should preferably be nearly equal to that of syn-
chronism, the switch F may be opened altogether. The action will then be that of
a simple single phase induction motor, which, as is well known will run in
either direction with good efficiency, if it is once started.
In Fig. 8 we have shown the connections of another form. In this case the
coil C is not omitted, but is open circuited by a switch F1 during the starting,
and is closed on itself at about the time when the switch F is opened. It then
tends to add to the torque of the machine by keeping the currents of the arma-
ture 1 more nearly in phase with the electromotive force, the action being the
usual action of a short-circuited secondary.
Referring now to Figs. 4 and 5, which show our improved motor in a more
practical form, A, A are one set of field magnet coils, and 13, B are another set.
These two windings or sets of coils correspond to the coils A and B of Fig. 2,
and are wound at an angle to each other, but as in this form the motor has four
polar lines, the angle is 30 degrees instead of 120 degrees. These two coils each
fill one third of the circumference of the inducing member; the remaining por-
tion being unwound, in order to produce the unsymmetrical relation necessary
to starting torque.
As shown more clearly in Fig. 5. each winding consists of four coils A. A
A, A and B, B1, B3, B³, the coils of each set being 90 degrees from each other,
and the two sets being displaced by 30 degrees. All of the coils are connected
in series, being the entrance point, 2 the common point of the two windings,
and 3 the exit terminal. For convenience of comparison, the same numbers
are inserted at the corresponding points in Fig. 2. The current enters at the
point marked 1, passes to the point a, thence around the coil B, thence out at b.
thence to the point a¹, thence around the coil B¹, thence out at 61, thence to a²,
around the coil B2, out at point 2. to a³, around the coil B³, out at 63, to the
point 2. A similar cycle, starting from point 2 and ending at point 3, is repeated
with the coils A, A1, A2, A³. The switch F serves to short circuit the coils A,
A A, A during the period of starting, with or without resistance.
D is the armature, shown in this case as the rotor, though it will be evident,

page_text: as stated above, that either member may rotate. The preferred, form is shown
in diagram in Fig. 6, and consists of several circuits which may be short cir-
cuited upon themselves when a speed approaching synchronism is attained, but
which in starting have resistances R. R, R², in circuit so as to reduce the lag
of the armature currents and to prevent them from attaining excessive values.
The action of this motor is the same as that of the elementary form shown in
Fig. 2. In starting the switch is adjusted in such a manner that the phase
and volume of the current in A is such as to give a maximum torque, which is
in general attained by cutting in a portion of the resistance. It will be seen
that by the use of a resistance in this manner, a portion of the primary current
passes through the coil A, the proportion so passing depending upon the resist-
ance in the local circuit of the coil A; and that its superposition upon the short
circuited current displaces the phase of the latter. Furthermore, if the resist-
ance interposed in the local circuit of the coil A is increased, the short circuited
current is reduced and the primary current modified, and nice cersa. At the same
time the actual lag of the short circuited current is varied. That resistance is
of course selected which will give the desired difference of phase in any case.
It is also evident that any number of field magnet coils may be used in series
and several of such coils may be shunted individually by short circuiting or
through resistances, so as to give a gradual and progressive difference of phase
between adjacent sets of field magnet coils.
It is also possible to run a motor constructed in accordance with our inven-
tion without the use of a switch F, and such an application we aim to embrace
in our claims but ordinarily the commercial efficiency of such a motor would be
very much below that of one operated in the manner already described. In such
a construction the inducing coils would be connected in series, as shown; but
part of them would be permanently short circuited by a permanent electrical
connection used in place of the switch F. In fact, the switch I may be said
to illustrate such a construction when it is kept permanently closed.
Fig. 7 shows the practical embodiment of the form shown in Fig. 3. and need
not be further explained.
With the three sets of coils. Figs. 3 and 7, it is also possible to substitute.
each for each, the coils A; C and their functions, and in this way the direction
of rotation of the motor is readily reversed, that is, at the start the coil C can
he closed circuited, as described, and the coil A left open circuited until speed
is attained, when B and C may be thrown in circuit with each other as described,
and A may be short circuited to suppress the lag of the armature currents.
We have used in this application the expression polar pitch. By that
expression we means to signify the angular distance, at any desired instant, from
one north pole to the next north pole in the same phase; for example in a two-
pole motor or a motor having one resultant polar line, the polar pitch is
360 degrees, in a four-pole motor 180 degrees etc.
".
The improvements described above may be applied to motors of various types.
and may be varied in many ways. We therefore do not restrict ourselves to the
specific forms shown and described.
.
Having now particularly described and ascertained the nature of our said in-
vention (as communicated to us from abroad) and in what manner the same is
to be performed, we declare that what we claim is:-
The combination in an alternating current motor device, of an inducing
or primary element, comprising coils or sets of coils connected in series and
angularly displaced so as to have different axes of magnetization, an adjustable
resistance connected in multiple with one of said coils or sets of coils whereby
the magnitude and phase of the current therein may be varied, and a secondary
or induced element in inductive relation to the primary coils, as set forth.
An induction motor, comprising an induced part, a primary member com-

page_text: prising a closed ring iron core, a plurality of inducing coils arranged in recesses
in the face of the core, some of such coils being set at an angle to and overlap-
ping the others, and means adapted to short-circuit some of such coils at will.
An induction motor comprising an induced part, a plurality of inducing
coils in inductive relation to each other, some of such coils being set at an angle
to others so as to develop polarization in a different direction, and means sub-
stantially as described, whereby said coils are connected in series or partly short-
circuited at will.
4-An induction motor comprising a revolving short circuited armature, a field
magnet or induced core having recesses or slots some of which contain main
circuit inducing coils, some of which contain other inducing coils in mutual
inductive relation to said first coils, and the remainder of which slots or recesses
contain no winding and means, substantially as described, for producing a differ-
ence of phase of the currents in said inducing coils.
An induction motor comprising a short-circuited revolving armature, an
inducing coil in the main circuit, a second coil also in the main circuit at an
angle to and in infuctive relation to the first, and a switch adapted to wholly
or partially short circuit one of the inducing coils.
6-An induction motor comprising a revolving armature, a field magnet core
carrying main circuit inducing coils, other inducing coils disposed upon the same
core overlapping the first, and in series therewith, an unwound portion of said
core, and means, substantially as described, adapted to short circuit some of such
coils through a resistance.
7-An induction motor comprising a revolving armature, a closed ring field
magnet core carrying main circuit inducing coils in recesses in its face, other
inducing coils disposed in recesses upon the same core and in mutual inductive
relation to the first, an unwound portion of said core, and means, substantially
as described, and whereby such coils are connected in series or are partly short-
circuited at will.
S-In an induction motor for alternating currents, an inducing element com-
prising a ring core having recesses in its face having a portion wound with an
exciting coil or coils connected in the main circuit, another portion wound with
a secondary coil in inductive relation to the main circuit, and a third portion
without any active winding in combination with an induced element comprising
coils connected in closed circuit, said coils being situated in inductive relation
to the inducing element, and a resistance in circuit with the coils of the induced
element and reducing the lag of current therein.
9-In an induction motor for alternating currents, an inducing element com-
prising a ring core having recesses in its face with an exciting coil in the main
circuit, and with a secondary coil in inductive relation to said exciting coil and
at an angle therewith, and an induced element comprising coils in inductive
relation to the coils of the inducing element and connected in closed circuit.
such closed circuit being of relatively high resistance, so as to cause the current
therein to be substantially in phase with the electro-motive force.
10-lu an alternating current motor, the combination of relatively movable
inducing and induced elements, the inducing element comprising a ring core
having recesses in its face, having a portion wound with an exciting coil or coils,
another portion wound with a coil which is closed circuited when the
motor is started and a third portion having no winding which is active when the
motor is started, and an induced element comprising coils connected in a closed
circuit so designed that the current and electromotive force therein are main-
tained approximately in phase with each other.
11-The method of starting an alternating current motor which consists of
passing an alternating current through a primary winding on the inducing mem-
ber, generating thereby a current in a relatively rotatable armature, inducing.
by the joint action of said primary winding and armature winding, current in a
second winding on the inducing member, artificially regulating the phase of

page_text: the current in the said second winding, and producing rotation of the armature
by the joint action of the two windings on the inducing member.
12-The method of operating a single phase alternating current motor, which
consists in generating by the action of a current due to a single phase alter-
nating electro-motive force, a plurality of alternating magneto-motive forces
displaced from each other by phase angles each equal approximately to one third
of a period, and causing by said magneto-motive forces a relative rotation between
the inducing and induced members of the motor.
13 The combination in a single phase alternating current motor, of an induced
member and means for generating by the action of a current due to a single
phase electro-motive force, a plurality of alternating magneto-motive forces dis-
placed from each other in space by angles, each equal approximately to one
third of the polar pitch.
Dated 14th day of March, 1899.
THE BRITISH THOMSON-HOUSTON CO, LTD.,
ALFRED CLEMENTS,
Assistant Secretary.
A. R. MONKS } Directors.
W. MARTINDALE,