Improvements in Method of and Means for Operating Alternating Current Motors.
Year: 1897

page_text: Date of Application, 3rd Aug., 1897-Accepted, 11th Sept., 1897
COMPLETE SPECIFICATION.
Improvements in Method of and Means for Operating Alternating
Current Motors.
We, THE BRITISH 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
Charles P. Steinmetz, of Schenectady, County of Schenectady, State of New
York, United States of America) 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 electric motors, especially those
commonly known as induction motors, and has for its object to provide an
improved method of and means for operating such motors. It comprises a com-
bination of circuits with a plurality of motors fed from the same source of power
supply whereby they are adapted to run at a speed below that which either one
would have if connected directly into the supply circuit; and also a series of
combinations of circuits whereby the said motors may be run at varying speed
also in the use of a non-inductive resistance which is arranged to be included in
the secondary of the ultimate motor or motors of a series in starting, or in changing
the speed. By our invention we are enabled to run alternating current motors
at full efficiency and at different speeds, or at full efficiency when fed with
currents of a periodicity much higher than would be permissible were the. motors
connected directly to the line in the usual manner; and also to obtain the same
good results in regulating the power and speed of a number of alternating current
motors as are obtained by the use of the "series-parallel" method of control: used
with continuous current motors.
To these ends we employ two or more motors, one of which must be an induction
motor, and the other of which is supplied with current from the induced or
secondary winding of the first motor; in case a third motor is used in the same
motor series, it is supplied with current from the secondary winding of the
second motor, and so on. In other words, for any number of motors the primary
winding of the first motor is connected directly into the supply circuit; the
induced winding becomes the source of supply for the inducing winding of the
next succeeding motor, whose induced winding in turn becomes the source of
supply for the next. In this manner in such a motor-series, each motor has a
two-fold function; first, as a motor converting a part of the supplied electrical
energy into mechanical work, and, second, as a transformer, transforming part
of the supplied electrical energy into electrical energy of the same or of different
electro-motive force and of lower frequency suitable for the next following motor.
In this arrangement the speed of the second motor, if two motors are used, will
correspond to the lower frequency of the current supplied by the secondary.winding
of the first motor, while the speed of the first.. motor will correspond to the
difference between the line frequency and the frequency of the current supplied to
the second motor, so that if both motors have the same number of poles the sum
of their speeds is substantially equal to the speed which each motor would have

page_text: or
when connected or running alone on the main circuit; if one of the motors has a
greater or less number of poles than the other its speed will be increased
reduced proportionately.
The speed which one motor would assume if connected directly in the circuit
in the usual way is, by this arrangement, divided up between the two, so that
both may run at half speed, or the one at one third and the other at two thirds
speed, or in any other desired proportion. In this same manner the speed may
be divided up amongst three or four motors, and each motor will run at fuil
efficiency at one half, one third, and one fourth speed, or at any other fraction of
the speed at which it would run if connected directly to the line. It is known
that an induction motor can be run at a speed below its normal by inserting a
non-inductive resistance into its secondary circuit; but this practice would result
in a loss of efficiency due to the waste of energy in the resistance. Our present
invention substitutes a second motor for this non-inductive resistance, by which
the energy is utilized for doing mechanical work in the second and other following
motors instead of being wasted in the resistance. Our invention comprises also
means for changing the speed of each motor by varying the number of motors
constituting the group, or by changing the manner in which they are coupled in
circuit. Starting, for example, with the motors connected tandem-wise, that is
to say, with the secondary member of one motor in circuit with the primary
member of a second motor, the primary members are, for a higher speed, thrown
into multiple and their secondaries closed. In many cases, where the number of
motors in the series is sufficient, the motors are also connected at times in what
we term "Multiple tandem" groups, meaning thereby two or motors with their
primaries connected in multiple to the supply mains and their secondaries
respectively in circuit with the primary members of other motors, as illustrated
in diagram b, Fig. 5.
17
SO
When two or more induction motors mechanically coupled together are con-
nected in tandem, in the manner described, the speed at which the motors will
run is determined by the frequency of the main current applied to the leader of
the series of motors and the number of motors. For example, two motors
connected will run at substantially half the speed of a single motor, while if the
motors are thrown into multiple the speed will be doubled. In this manner,
changes of speed may be readily secured by changing the number of motors in
circuit or the order in which they are connected, and the control thus secured may
be rendered even more flexible by the use of resistances as herein pointed out.
In the accompanying drawings, herein referred to and made a part of this
specification, Figs. 1 and 2 are diagrammatic illustrations of our invention applied
to two multiphase induction motors; Fig. 3 is a similar illustration applied to
four multiphase motors, all of these figures showing a suitable controller;
Fig. 4 shows our invention in modified form, with a synchronous motor; Fig. 5
is a diagram illustrating its application to single phase alternating apparatus,
and Fig. 6 shows two motors connected to a common load, which is here
represented as an ordinary street car.
In Fig. 1, the motor M is a three-phase induction motor of the usual type, the
inducing field-magnet winding of which is fed by three-phase currents from any
suitable source of power, as from a three-phase transformer T. The secondary
member or induced winding instead of being directly closed upon itself, or closed
through a resistance in the usual manner, is connected to three collector rings,
and the three-phase currents taken up by the collector rings are fed to the primary
or inducing winding of the motor M, which is also a multiphase induction motor.
The induced secondary winding of the armature or revoluble member A is closed
through resistances R, R¹, R. At C we represent the development of a controller
cylinder. The brushes a, d, g are connected to the three brushes of the secondary
member A of motor M', while the brushes b, c, e, f, h, i, lead to the resistances
mentioned. In the first position of the cylinder the current is interrupted. In
position 2 the brushes a b, de, and 9 h, rest upon and are electrically connected

page_text: by the contacts S, S1, S2 upon the controller cylinder, whereby, as will be seen
from the drawing, the resistance R, R1, R2 are included in the different branches
of the circuit of the secondary member of the motor M. The switching con-
nections between the transformer and the motor M are omitted for clearness. In
position 3 the brushes abc, def, and ghi, respectively, rest upon the controller
contacts, whereby a portion of the different resistances is cut out, and in position 4
the secondary winding of motor M is entirely short-circuited, since the
brushes a d rest upon contacts which are electrically connected, as is
indicated in dotted lines.
The action is as follows: At starting, position 2, the rotary magnetic field set
up by the primary winding of the motor M acts upon the, winding of A and sets
up corresponding secondary currents in its conductors, producing a torque in the
movable member. To limit the current at starting it has been customary hereto.
fore to short circuit the induced winding through a resistance, which is necessary
to get the maximum starting torque. But this plan wastes energy in the
resistance, and instead of following such a method we use the induced currents of
the winding of A as the source of supply for the primary winding of a second
motor M', which is also provided with a secondary member; and the resistance
we place in the closed circuit of the secondary member. In this manner we
obtain a starting torque from both motors, which is nearly double that which
would be produced by the motor M alone. Both motors now begin to rotate; it
is to be noted, however, that when the induced member A is standing still the
induced currents are of the same frequency as those coming from the transformer
while this frequency is reduced when the member A is in rotation, and becomes
less and less until at synchronous speed the frequency of the induced currents
would be zero. The frequency of the currents supplied to the motor M¹ will
therefore depend upon the rate of revolution of the secondary member A; and it
is further evident that if the member A is run at half synchronous speed, the
currents supplied to the motor M¹ are of half frequency, and under these conditions
both of the secondary members A, A', will run at maximum efficiency at half the
speed either would tend to have if connected alone in the primary circuit. This
is what takes place when two induction motors coupled in tandem are geared to
a common load by gearing having the same ratio of reduction.
The energy
supplied to the leader of the series is consumed partly by the mechanical work
performed by the first motor, and partly by the secondary currents delivered by
the first to the second motor, which, in this instance, will have substantially half
the frequency of the main currents. It is likewise evident that if the member A
runs at one third speed the member A¹ will run at two thirds speed, and vice
versa; or, generally stated, the total initial frequency may be divided up between
the two machines in any desired proportion and is then represented by the sum
of the speeds, it being understood that the number of poles of both the inducing
and induced elements in the two motors, are the same; if not the same, then the
speeds would bear an inverse ratio to the number of the poles of the respective
machines. The resistances R, R1, R2, may be cut out in order to increase the
speed of both machines, as in the case of ordinary multiphase motors, by advanc-
ing the controller cylinder to the positions 3 and 4.
:
In Fig. 2 we show connections for two multiphase induction motors according
to our invention, whereby their speed and power may be further varied. T is a
three-phase transformer with leads to the brushes à, c, e, the terminals of the
inducing or primary winding of the motor M being the brushes b, d, f; h, k, n,
are the brushes for the ends of the resistance leads, the resistance coils being
shown at R, R1, R2; and i, 1, o, are the brushes including a portion only of this
resistance. p, q, r are brushes to which lead connections from the respective
conductors uniting the secondary members A, A¹ of the motors. In Fig. 1 the
current from the member A is taken up by collector rings and fed to the inducing
element of the motor M', that is, the stationary element; but as either the
stationary or revoluble member may be the inducing element one set of the

page_text: collecting rings may be dispensed with by connecting the 1, 2, 3 leads from the
members A, A¹ together, A¹ becoming now the inducing element of the motor M',
and the outer member the induced element. As indicated in the drawing, the
1 leads of the motor members A, A¹, are connected to a collector ring r; the
2 leads to a ring r, and the 3 leads to a ring Position 1 of the controller is
the idle position as before. In position 2 the brushes a b, c d e f g h, jk,
and' m n, are united by the contacts S, S1, S2, S3, S, S³, on the switch cylinder
and the motors bear the same relation as in position 2, Fig. 1, that is, both motors
have about the same starting torque. In position 3, one half of each of the
resistances R, R1, R2, is cut out or short-circuited from the closed circuited
induced winding of the motor M', increasing the speed of each machine In
position 4 the resistance is entirely short-circuited, and the speed of the
motors M, M is still further increased. In position 5, a distinct change is made
in the order of connections. Both motors now have their primary windings fed
in multiple from the transformer T, current from a passing to brushes 6 and g,
fiom c to d and j, and from e to f and m. The functions of the stationary and
movable members of the motor M are thus reversed, the outer member becoming
now the inducing and the inner member the induced element. A corresponding
change is made as regards the resistance, which must of course be included in the
induced circuit. Therefore, in this position, the brushes h, k, n.of the resist-
ances R, R1, R2, are now connected by the switch contacts to the
brushes q, r, P, respectively, which latter connect to the three conductors uniting
the members A, A¹, by the brushes and collector rings r, rl, 3. We thus have the
motors M, M running in multiple from the transformer T, and, manifestly, both
will now tend to reach the normal speed of an induction motor connected to the
circuit. In this position, the resistance R may be gradually reduced in amount
until it is entirely cut out, as is illustrated respectively in positions 6 and 7.
In position 6 the resistance is decreased and the speed accelerated, and finally in
position 7, the resistance is entirely short-circuited and the motors run at full
speed connected in multiple to the transformer T. It will be seen that if the
motors M, M, are connected to the same work, as for instance in propelling
railway vehicles, the series of connections above described affords & very efficient
and useful of changing their torque and speed, giving, in effect, a series of con-
nections for alternating current motors having the advantage of what is known
as the "series parallel" control of continuous current motors.
By referring to the development of the switch cylinder in Fig. 2, it will be seen
that the first four positions correspond with the similar positions of the switch
shown in Fig. 1, the only difference being, that the switch not only controls the
connections between the motors, but also, in the first position, breaks circuit
between the transformer T and the first of the motors, additional contacts S³, S+, S,
being provided for this purpose.
In position 5 the brushes g, j, m, rest respectively upon contacts ³, st, s5 which
are connected with S3, S4, S5, so that the inducing windings of the motors are in
multiple with the source of power supply; the brushes p, q, r, rest upon
contacts 6, 7, 8 and the brushes h, k, n, on contacts 9, 10, 6. The contact sis
connected to so and 8 to 10, so that the circuit from ring r, for example, may be
traced as follows: from contacts 8 to $10, brush and resistance R₁, where the
current may divide, part passing through resistance R, brush n, contacts so,
brush p and ring; the other path being through resistance R8, brush h,
contacts 9, 87, brush and ring r¹.
In position 6 part of the resistances are short-circuited, and in position 7 the
resistances are entirely short-circuited, since the brushes p, q, r, are all connected
by the contact $18.
This method of control may be applied to any number of motors, as in Fig. 3,
which shows its application to four induction motors M, M, M3, M³, each of the
last three motors receiving its energizing current from the induced winding of
the preceding motor; if these motors have the same number of poles and are con-

page_text: nected to the same work they will run at maximum efficiency at one fourth the
speed they would have connected singly into the supply circuit. As either winding
of the induction motor may act as the induced member, they are illustrated inter-
changeably in the figure, this arrangement allowing us to dispense with one set
of sliding connections, as already explained in connection with Figure 2. A
series of connections similar to that shown in Fig. 2 may be carried out in the
case of the four motors here shown, and evidently the combinations for different
speeds which may be effected are largely increased. Thus, the motors may all
be placed in series at the start with the resistances R, R1, R2, in the induced
winding of the last motor of the series; the resistance may then be reduced, and
finally cut out, short-circuiting the secondary or induced conductors of the last
motor. The primary windings of motors M, M³, may then be placed in multiple
with the transformer T with their secondaries closed respectively through the
primary windings of the motors M³, M. All the motors will now run at one half
their highest speed. After this they may be placed in multiple for the final and
highest speed. Throughout these different arrangements of connections the
resistances R, R1, R2, may be used or not, as desired; it may be found advisable
to use the resistances at the start. It is obvious that when the motors are con-
nected to the same work the connections of the primary and secondary circuits
must always be such as will cause the movable members to revolve in the desired
direction.
In
In Fig. 4 we show that the second motor may be a synchronously running
machine with its field magnets excited by a continuous current from any suitable
source, as from an exciter E, regulated in the usual way by a resistance R.
this case one of the induction motors of the former figures is replaced by a
synchronous motor to which currents are delivered from the induced winding A;
it will consequently run at a speed corresponding to this frequency as does the
induction motor above mentioned. One advantage of this arrangement is that
the second motor M¹ may be regulated to control the phase relation of current
and electro-motive force, this regulation being effected in the induced circuit of
the first motor and thereby in the inducing circuit and main linc.
While we have so far shown the invention as used with multiphase currents,
it is equally applicable to alternating currents of any character, whether of one
or more phases, and in Fig. 5 we show a series of four motors, fed by single phase
alternating currents, in various connections for changing their speed in accordance
with our invention. In diagram 1, four motors M, M1, M2, M3, are shown as
supplied with single-phase alternating currents from a dynamo D and inter-
mediate transformer T, the motors being arranged as in Fig. 3, that is, each
inducing winding of the motors M1, M2, M3, is fed by the secondary winding of
the preceding motor, and in the last induced winding is included a resistance 1,
as before. This gives the lowest speed. In diagram 2, the secondary winding of
the motor M is short-circuited and the motors now run at one quarter full speed.
In diagram 3, the fourth motor is cut out and the secondary winding of the third
motor is closed through the resistance. In diagram 4, this winding is short-
circuited and the motor series runs at one third speed, one motor being entirely
cut out. In diagram 5, the inducing windings of the first and third motors are
joined in parallel and their induced windings feed into the inducing windings of
the motors M, M³, respectively, the induced windings of these motors being
joined in parallel and closed through the resistance R. In diagram 6, the induced
windings of the motors M, M³, are closed circuited, and the motors are thus
placed in two groups, each of two motors in tandem, whereby the speed is made
one half the highest speed; and in diagram 7 the inducing members of all the
motors are joined in parallel and each induced winding is 'short-circuited or closed
on local circuit, whereby the motors are run at full speed.
The diagrams above described show different arrangements in which the motors
can be coupled in order and obtain varying speeds and torques. Thus in
liagrams 1 and 2, a number of motors are connected in tandem, and in diagram 3

page_text: it is indicated that different speeds may be secured by cutting one or more motors
out of circuit; and finally in diagram 7 the position of highest speed is represented
with the motors in multiple. We do not, however, make a specific claim to the
invention of changing motors from tandem to multiple, by first cutting out one of
the motors and then reconnecting the cut out motor or motors in multiple.
In all of the above combinations of circuits between alternating current motors
arranged in the manner described we prefer that they shall also be mechanically
connected or geared together in the ratio of their desired speeds, reference being
had to the relative number of poles of the different motors; where this is not done,
a tendency to oscillation may exist or one motor may revolve at a sneed out of
proportion to the other.
Gearing the motors together ensures a proper division of the speed of the motors,
that is to say, of the speed at which alternating currents of given frequency
would drive a single motor when connected in circuit in the ordinary manner.
The invention, therefore, is specially applicable to installations where two or
more motors are required to drive a common load, and where variable speeds of
the driven load are desirable, as, for instance, in electric railways.
In Fig. 6 two alternating motors of the type hereinbefore specially mentioned,
are shown mounted on the truck of a railway car Q. The motors are respectively
geared to the two axles of the truck. The motors are supplied with current in
any desired manner, and the circuit wires leading to their primary and secondary
parts are shown as wrapped into an insulating cable Q', which extends to con-
trolling switches at the opposite end of the car. The only part of this arrangement,
however, material to the present invention is the gearing of two motors to a
common load. By the controlling switches, the motors may be coupled in tandem,
as already explained, so as to drive the car at substantially half synchronous
speed and other combinations of circuits, such as already described, may be
effected.
"
So far as we are aware, we are the first to devise a method and means of
operating alternating current motors, in tandem, and we are also the first to
combine alternating current motors with a controller by means of which they
may be connected in various combinations, in tandem or in multiple, to obtain
various speeds and torques. We therefore wish to claim broadly such com-
binations as we have herein indicated. Where we employ the term "multiphase
in describing our invention we do not mean to limit ourselves to those cases
wherein a multiphase effect is obtained by means external to the motor, but we
also mean to include all methods of obtaining rotary magnetic fields by a
succession of phases in the motor however they may be obtained; whether by
windings in the motor itself, or by a phase splitter, or directly from the
transformer or generator.
Having now particularly described and ascertained the nature of our sail
invention (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 method of operating alternating current motors, which consists in
feeding alternating currents to one member of one such motor from a source of
power supply, converting the energy so supplied to the motor partly into
mechanical energy expended in driving a driven mechanism and partly into
electrical energy in the form of alternating currents induced in the secondary
element of the motor, and supplying a second alternating motor with the said
secondary currents, as set forth.
2. The method of operating alternating current motors, which consists in
feeding alternating currents to one member of such a motor, converting that
portion of the energy so supplied, which is not utilized as mechanical work per-
formed by the motor, into electrical energy in the form of alternating currents
induced in the secondary member of the motor, and applying such currents to

page_text: a second translating device directly or indirectly in circuit with the induced
member of the motor, as set forth.
3. The method of operating alternating current motors of the induction type,
which consists in feeding alternaung currents to the primary or induced member
of one such motor, inducing secondary currents of different frequency in the
secondary member of the motor, and feeding such secondary currents to the
inducing member of a second induction motor, provided with a closed-circuited
secondary member.
4. The method of operating alternating current motors of the induction type,
which consists in feeding multiphase currents to the primary member or n
Induction motor, inducing secondary currents of different frequency in the
secondary member of the motor by its rotation in the magnetic field of the primary
member, and closing the circuit of the secondary member through the primary
of a second induction motor provided with a closed-circuited secondary.
5. The method of operating alternating current motors of the induction type,
which consists in supplying the primary member of one such motor with alterna-
ting currents from a source of power supply, and the primary members of one or
more other motors in succession with current induced in the secondary member
of the preceding motor, and regulating the motors by varying the resistance of
the circuit of the secondary member of the last motor.
6. The method of operating a plurality of alternating current motors of the
induction type, which consists in coupling them in tandem, as described, with the
secondary of one motor in circuit with the primary of another motor, then coupling
them in multiple tandem groups, and finally, for a still higher speed, coupling
them in multiple, as set forth.
7. The method of operating alternating current motors of the induction type,
which consists in connecting them in circuit tandem-wise with a resistance in
the local circuit of the last induced member, then reducing and cutting out the
resistance, then connecting the motors in multiple tandem groups, and finally
connecting them all in multiple.
8. The method of regulating alternating current electric motors of the induc-
tion type, which consists in connecting the secondary or induced element of one
motor with the inducing element of a second motor, and then connecting the induc-
ing elements of the inducing motors in multiple with the same source of current
supply, as set forth.
9. The method of regulating alternating current electric motors of the induction
type, which consists in connecting the secondary or induced element of one motor
with the inducing element of a second motor, and with the secondary of the
second motor closed-circuited, and then connecting the inducing elements of the
different motors in multiple with the same source of current supply, and closing
the secondary elements of the two motors, as set forth.
10. The method of regulating alternating current electric motors, which con-
sists in connecting the induced element of one motor with the inducing element
of a second motor and with a resistance in circuit with the induced element of
the second motor, then cutting out the resistance, and finally coupling the induced
elements of the motor in multiple, and closing the circuits of their secondary
elements.
11. The method of regulating alternating current motors of the induction type,
which consists in feeding the inducing element of one motor with alternating
currents connecting the induced element of the motor with the inducing element
of a second motor and with a resistance in the circuit of the secondary element
of the last mentioned motor, varying the resistance, coupling the inducing
elements of the motors in parallel and closing the induced elements through a
resistance, and finally cutting out the resistance, as set forth.
12. The combination of two alternating current motors each geared to a driven
mechanism, of which the inducing element of one is in circuit with the induced
element of the other.

page_text: 13. In combination; a plurality of alternating current motors, each geared to
a driven mechanism, having relatively revolving inducing and induced members,
the induced member of each motor except the last connected to the inducing
member of the next. succeeding motor, and a resistance included in the induced.
circuit of the last motor, whereby alternating current motors may be operated
in tandem, as set forth..
14. The combination of a plurality of alternating current motors, each geared
to a diven mechanism, having relatively revolving primary and secondary
member, and a resistance, with a switch, contacts and electrical connections
for coupling the secondary element of one inotor in circuit with the primary
membe of a second motor, and for coupling the whole or a desired portion of
the resistance in circuit with the secondary member of the last named motor.
15. The combination of two or more alternating current motors geared together
or mechanically connected to a common driven mechanism, and having the
induced element of one motor in circuit, with the inducing member of a second
motor, as set forth.
16. The combination with two or more alternating current induction motors
having relatively revolving. inducing and induced members, and mechanically
connected to a common driven mechanism, with means for supplying multiphase
alternating currents to the inducing members of one motor, and connections between
the induced member of the motor and the inducing member of a second motor,
as set forth.
17. The combination of a plurality of alternating. current induction motors,
and a switch. for coupling the induced member of one motor to the inducing
member of a second motor, and for connecting the inducing members. of the two
motors in multiple, as set forth.
18. The method of varying the speed of driven mechanism connected to a
plurality of alternating motors of the induction type, which consists in connecting
the motors in tandem, that is to say, with the induced element. of one motor con-
nected to the inducing member of another, and changing the number of the motors:
so connected, by cutting one or more motors into and out of the series so connected,
as set forth.
19. The method of operating alternating current motors of the induction type
mechanically coupled together or geared to a common driven mechanism, which
consists in supplying to one such motor energy in the form of alternating electric:
currents from a source of power supply, and supplying to a second motor the excess
of energy not expended in mechanical work performed by the first motor, in the
form of alternating currents induced in the secondary member of the first. motor.
20. The method of operating alternating current motors of the induction type,
which consists in connecting them to a source of power supply in tandem, in the
manner described, then throwing the inducing element of one motor and the
induced element of a second motor into multiple with the source of supply, and
closing the circuit of the remaining elements of such motors, as described.
21. In combination, a plurality of alternating current motors having inducing
and induced members, and circuit connections from the induced member of each
motor except the last feeding current into the inducing member of a succeeding
motor, the induced member of the last motor being closed-circuited.