Improvements in Alternating Electric Current Motor Systems.
Year: 1899

page_text: Date of Application, 22nd Dec., 1899-Accepted, 7th Apr., 1900
COMPLETE SPECIFICATION.
Improvements in Alternating Electric Current Motor Systems.
We, THE BRITISH THOMSON-HOUSTON COMPANY, LIMITED, of 83, Cannon
Street, in the City of London, Electrical Engineers, do hereby declare the nature
of our said invention (which has been communicated to us from abroad by
Albert G. Davis, residing at Schenectady, in the County of Schenectady, State of
New York, United States of America, Electrical Engineer), and in what manner
the same is to be performed, to be particularly described and ascertained in
and by the following statement:-
The present invention relates to alternating-current motor systems, and parti-
cularly to those of the tandem and tandem-multiple types, and is designed to
provide an arrangement whereby such a motor system may be started with
full torque and run efficiently at various speeds.
One important function of this invention consists in connecting in tandem
with a single-phase alternating-current motor, actually driving a load, a multi-
phase alternating-current motor also driving a load, which may be the same load
as that driven by the first motor. For example, both motors may be connected
to the same or different axles of a street car. Further, this invention contem-
plates regulating the speed of the system thus formed in various ways, and
thereafter connecting the motors in multiple across the single-phase mains.
In this way we are able to drive a regulable and self starting motor system,
possessing the advantages of a multi-phase tandem-multiple system, from a
source of single-phase current, which is particularly available in connection
with railway work.
This invention also comprises certain means for varying the resistance of the
induced member of one or more of the motors, which is particularly useful
when the change from tandem to multiple is made. This invention also com-
prises a method and apparatus for neutralizing or adjusting the phase displace-
ment in the intermediate circuits of a tandem or tandem-multiple system or in
any multiphase system whatever, and various other combinations and arrange-
ments of parts and connections to be hereinafter more fully described and claimed.
We have illustrated various embodiments of our invention in the accompanying
drawings, in which-Fig. 1 is a general diagrammatic view of a motor system
constructed and arranged in accordance with our invention and applied to
railway work; Fig. 2 is a section on the line 2-2 of Fig. 3, and Fig. 3 is a
section on the line 3-3 of Fig. 2, both sections showing details of the means
for varying the armature resistance in its preferred form; Fig. 4 is a develop-
ment of the induced member of one of the motors showing diagrammatically
the resistance varying means; Figs 5, 6, 7, 8, 9, 10 and 11 are diagrams
illustrating the circuit relations of our improved system of various controller
positions, and Fig. 12 shows one form of our improved means for neutralizing
the self induction and regulating the phase of the intermediate circuits. Refer-
ring more particularly to Fig. 1, A B are the two motors shown as connected
to a common shaft S, A¹, B' are the inducing members and A2, B2 are the
induced members, the relations of the parts being reversed in the two motors,

page_text: His a generator of single-phase alternating currents, shown as feeding current
through a tension raising transformer T, transmission lines 1, 1, and a tension
reducing transformer T¹ to the trolley or third rail L,-and the track. rail R.
Connection to the car is made through the trolley and the wheels Was
usual, though obviously any other suitable arrangement may be substituted.
The motor A is provided with a flux screen A³ independently rotatable in the
air-gap, and containing. a short circuited winding, as shown. As is well known
in the art, if the flux screen be set in rotation it will so distort the flux set
up by the current flowing in the primary single-phase circuit shown on the
member A¹, as to produce in the induced member A2 a rotary field. This rotary
field generates dephased electromotive forces in the winding of the induced
member A2; which winding may be of any well known type, and should ¨pre-
ferably be similar in arrangement to the windings of any ordinary multiphase
generator armature. The electromotive forces so generated cause multiphase
current to flow in the circuit leading from the rings and brushes. These currents
are led through condensers C, C¹ to the inducing member B¹ of the motor B,
in which member they produce a rotary field. This rotary field in turn generates
current in the induced member 132, which reacts to create torque.
It will thus be seen that both motors produce a rotary effort at the start, and
tend to run to such a speed that the frequency of the current in the intermediate
circuit in which the phase advancing devices are preferably interposed, is merely
one half of the frequency of the current fed to the primary of the first motor A.
To start the flux screen A³ we provide a small auxiliary motor M, which, as
it is of insignificant output, may be of the split-phase type, as shown; that is to
say, it may be wound like an ordinary two-phase or three-phase motor, and
provided with a monocyclic starting device, consisting of a self-induction M' and
a condenser or resistance M2 as shown. The armature M³ of this motor drives the
flux screen A³, through a belt D, pulleys E, F, and a second belt G.
The magnets Mª, M serve, when energized by the battery or other source of
current, to reduce the resistance of the induced members of the motors A and B
respectively, preferably by the arrangement to be hereinafter described.
To start the motors the controller K, here shown in development only, is shown
so that the brushes 10 to 36, inclusive, bear upon the line 1. Current then
flows from the trolley through the brush 13, to contact plate 13ª and brush 15,
to the motor M, and thence to brush 12, by contact 10 to brush 10, and to
ground through the wheels W. It will be seen that this position simply acts
to start the small motor M and the flux screen A³. The connections are in-
dicated in diagram in Fig. 5, in which it will be seen that the primary of the
motor M is energized and the secondary short-circuited upon itself, while the
windings of the other members A1, A2, B1, B2, are de-energized
When the flux screen has attained a sufficient speed, the controller is moved
to the second position 2. Here contacts 13ª and 10ª are energized as before by
the brushes 13 and 10, so that current flows from contact 13ª, through brush 14,
to the primary winding A¹, through brush 11, and to the contact 10ª. This
generates a reciprocating flux in the member A', which is converted into a rotary
flux by the action of the flux screen A³, which now, since it has no appreciable
load, runs up to a speed approaching that of synchronism.
The rotary field thus induced in the secondary A causes dephased currents to
be generated in the multiphase winding of that member, supposed in this case
to be a two-phase winding. Current then flows from the brush a¹ to the
condenser C, and thence, through the first section of the condenser, to the
contact 16 and brush 19, thence to the brush of the motor B and, through
the winding B¹, to the brush 3, to brush 21, to the controller contact 20, and
brush 20, back to the motor A, at the brush ³.
The other intermediate circuit is from the brush a² to the condenser C¹,
brush 22, contact 22ª, brush 25, motor brush 62, through the induced member B¹,
to the brush 74, brush 27 and contact 26, and thence to the brush at on the

page_text: motor A. The current passing in these paths will create a rotary field in the
inducing member B', which may be wound as shown, with a ring_winding topped
at four equidistant points, or, with two independent circuits, or in any other
suitable way. This rotary field will produce electromotive forces in the bars
of the winding B2, which, in turn, will produce currents in these bars, which
bars are arranged in two circuits, and constitute an ordinary multiphase secondary.
The terminals of these two circuits lead respectively to brushes 28, 29, and 30, 31,
which brushes are united together in pairs by the resistances R', R.
It will thus be seen that in this position, which is illustrated in diagram in
Fig. 6, the motor M is energized, the primary A¹ is also energized with single
phase current, and the primary B₁ of the motor B is fed with quarter phase
current from the secondary A2 of the motor A through the condensers C. C¹,
while the secondary 12 of the motor B is closed on itself through resistances R' R².
The position above described, is the starting position.
The current flowing in the intermediate circuits of the tandem system is in
general of a frequency equal to the slip of the motor A, which slip is, before
the motor starts, equal to the frequency of the original current. But as the
motor starts, the frequency of the current in the intermediate circuit falls,
as is well understood.
When a small speed has been attained, the controller is moved to the
position 3, in which the motor M is cut out, since the brushes 12 and 15 leave
the segments 10, 13ª, an additional section of each of the condensers C, C¹ is
cut in by the contact of the brushes 17 and 23 with the segments 16 and 22ª,
and the resistances R1, R2 are cut out by the action of the segment 28b. This
position is shown in diagram in Fig. 7, and obviously corresponds to a slightly
higher speed in the motor.
In the next position, in which the brushes rest upon the line 4, the whole
capacity is cut in, since all of the brushes 16, 17, 18, 22, 23, 24 are in the seg-
ments 16ª, 22, respectively, and in addition it will be observed that the brushes 32
and 33 rest upon the segments 32ª. This makes the circuit from battery b.
through the magnet Mb, to the brush 32, contact 32ª, brush 33, and back to the
battery. This energizes the magnet Mb, and short circuits on itself the whole
winding B in small sections instead of simply connecting together the terminals
of this winding, so that its resistance is considerably diminished. This position,
which is indicated in Fig. 8, is, obviously, the full tandem position, in which
the motors will run to nearly half of their synchronous speed. In position 5
it will be noticed that the brush 34 also rests upon the segments 32ª, so that
the magnet Ma is energized. This short circuits on itself the winding A2, which
practically cuts off current from the intermediate circuits and from the motor B,
owing to the low resistance of the short circuit. It is now safe to open the
intermediate circuits, which is, accordingly, done, in the sixth position, illus-
trated in diagram in Fig. 9.
The seventh position connects the motors in multiple. Current enters at the
brush 13, as before, and passes to the segment 13ª, where it divides, a portion
passing by brush 14, through the primary A¹ of the motor A, and then through
the brush 11, to the segment 10ª. A second path, however, is found from cross
connection to the segment 21ª, and brush 21, to brush 3 of the motor B, thence
through the primary B¹ of the motor B, out by the brush 6, to brush 19,
segment 19ª, and cross connection, to the segment 10ª. This connects the two
motors in multiple, as single-phase machines. The brush of the motor A is
connected through the brush 20 on the controller to the contact 20b, thence
through the resistance R³, to the contact 35ª, and by brush 35, to the brush a¹.
A second circuit leads from the brush 2, through the brush 36 to segment 36ª,
resistance R, contact 26, brush 26, to the brush at of the motor A. These con-
nections short circuit the secondary A² on itself through the resistances R³, R+.
The secondary B2 of the motor B is short circuited on itself through resistances,

page_text: as in the second position, since the segments 28°, 29°, 30°, 31°, are cross con-
nected to the contacts 28, 29, 30, 31. This connection is shown in Fig. 10,
and is simply a multiple connection of single-phase motors but running at
half speed with resistance in their secondaries. In such circumstances, the
two motors will evidently tend to run up to synchronism, by an amount depend-
ing merely on the magnitude of the resistances.
:
. In the eighth position the connections are the same, except that the resis-.
tances R1, R2, R3, R, are displaced by short circuiting leads.
The ninth and last position, shown in Fig. 11, omits the contacts. 20°, 20°, etc.
and short circuits both secondaries on themselves by. means of the magnets M Mb
energized from the battery. 6 through the contact 32b. In this position the motors
will tend to approach very near to synchronous speed.
We have illustrated our short-circuiting arrangement in Figs. 2, 3 and 4, as
applied to the rotor A2 of Fig. 1, though a similar arrangement will obviously
be applied to the stator B2 of the same figure. In these drawings A4, A; are
the bars of the winding, shown developed in Fig. 4, connected together, as shown,
to form an ordinary two-phase winding having free terminals at a¹, a², a³, at,
corresponding to the brushes a¹, a², a³, a², of Fig. 1. The magnets Ma, M³,
Fig. 4, serve to attract the short-circuiting bar A, which are furnished with
spring contacts 6, 6, against various segments a; connected to the bars A+.
It will be seen that while the magnets Ma -are de-energized, the spring A7, A7,
will draw down the short-circuiting bar A³ against the stops A8, A8, and the
bars A will be connected like tlie bars of an ordinary two-phase winding. If,
however, the magnets Ma, Ma, are energized, the short-circuiting bar A will be
attracted, and the bars will be short-circuited on themselves in pairs or singly,
according to connections.
In practice we prefer to replace the short-circuiting bar A by the plate A
(shown in Fig. 3) which serves the same function, sliding directly upon the
shaft of the machine. The disk A is preferably formed of two portions, an inner
and an outer, insulated from each other, as shown, and is pulled away from the
bars A by springs A7, A7..
A magnet coil Ma is energized by current led in through a suitable ring A
and out by the shaft. This magnet coil serves to energize a cup-shaped core A10,
which attracts the inner magnetic portion of the disk -A, whose outer portion is
preferably made of copper to short circuit the bars A¹.
We have shown in Fig. 1 condensers interposed directly in the circuits, but
we prefer in most instances to interpose the condensers inductively. We have
illustrated such an arrangement in Fig. 12, in which P1, P2, P3 are the three leads
of the intermediate circuits of a three-phase tandem motor system, or of any
other three-phase system, which may obviously be substituted for the two-phase
motor system shown in Fig. 1.
In each one of these leads we place a very coarse transformer primary lettered
Q1, Q2, Q3, respectively. The secondaries Q, Q, Q, of these transformers are
connected at one end to a common point through a three-phase condenser V, and
at the other end are connected to brushes 31 6¹ 9¹. From intermediate points
of these secondaries are taken out leads to the brushes 21 51 81 and to the brushes
14. The condenser switch. is shown at X, and consists of an arrangement
which first connects together the brushes 1' 41 71, then the brushes 21 51 8¹, and
finally the brushes 31 6 91. This varies the voltage upon the condenser and thus
varies the effect upon the phase displacement. This method of neutralizing or
adjusting the lag in the intermediate circuits of a tandem system is not confined
to the particular system shown, or to any particular number of phases, but is
applicable generally to tandem systems, and, in some respects, to multiphase
systems generally.
It is obvious that various changes may be made without departing from the
spirit and scope of our invention.

page_text: Having now particularly described and ascertained the nature of our said
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 obtaining mechanical work from the energy of a single
phase alternating current, the rotation of an armature at a lower speed than
synchronous rotation, converting thereby a portion of the energy of the current
into mechanical work, and another portion into low frequency multiphase
currents; transmitting said low-frequency multiphase currents to a multiphase
motor, producing a rotary field in said motor by the multiphase currents, and
causing by said rotary field a rotation of the second motor.
2-The method of converting the energy of singlephase alternating currents
into mechanical work, which consists in causing said currents to create a rotary
field in a member of an alternating current motor, causing said rotary field to
expend its energy, partly in maintaining the motor in rotation, and partly, in
generating in said motor multiphase alternating currents of a frequency lower
than the original frequency, and utilizing part or all of the energy of said low
frequency alternating currents in causing a second alternating current motor
to perform mechanical work.
The method of converting the energy of single phase alternating currents
into mechanical work, which consists in causing said currents to create a rotary
field in a member of an alternating-current motor, causing said rotary field to
expend its energy partly in maintaining the motor in rotation, and partly in
generating in said motor multiphase alternating currents of lower frequency,
and utilizing part or all of the energy of said low-frequency alternating currents
in causing the second motor to assist the first motor in driving its load.
4 The method which consists in generating single-phase current, trans-
mitting the same, generating by said single-phase current a single-phase magneto-
motive force, deforming the Hux due to the magneto-motive force in such a
manner as to produce a rotary field, generating by the action of said rotary
field multiphase currents, and transmitting said multiphase currents to a multi-
phase motor.
5-The method of reducing the spark on opening the intermediate circuits of
a tandem motor system, which consists in sort circuiting the induced winding of
the first motor, and then opening the circuits.
6-The combination with a source of single-phase current, of a motor driven
by electric energy from said source, a multiphase winding on the secondary of
said motor, leads from said secondary to the primary of a second motor, and a
secondary for said second motor, the two motors being coupled to perform
mechanical work.
-The combination with a source of single-phase current, of a motor driven
by electric energy from said source, a multiphase winding on the secondary_of
said motor, leads from said secondary to the primary of a second motor, and a
secondary for said second motor, the two motors being arranged to drive the
same load.
8-The combination with a source of single-phase current, of a motor driven
by electric energy from said source, a multiphase winding on the secondary
of said motor, leads from said secondary to the primary of a second motor, the
two motors being coupled to perform mechanical work, and means for neutraliz-
ing or adjusting the phase displacement in the intermediate circuits.
9-The combination with a single phase motor driving a load, of a multiphase
motor connected in tandem with the single-phase motor, and also driving a load.
10 The combination with a single-phase motor, a multi-phase motor in
tandem therewith, and adjustable means for neutralizing the phase displacement
of the intermediate circuits.
11—The combination with a single-phase motor, of a multiphase motor, and
a switch for connecting the two motors in tandem and for varying the resistance
in the secondary of the second motor.

page_text: 12 The combination with a single-phase motor, of a multiphase motor, and
a switch for connecting the two motors in tandem and for varying the resistance
in the secondary of the second motor and the reactance of the intermediate
circuits.
13 The combination with an alternating current motor, of means for pro-
ducing a rotary field therein by energy derived from a single-phase alternating
current, a load for each motor, connections from the secondary of said motor,
to a multiphase motor also driving a load, and a secondary for said multi-phase
motor.
14 The combination with a single-phase motor, of a multi-phase motor, a
switch arranged to connect the two motors in tandem to a source of single-
phase current, to vary the speed of said motors, and finally to connect the two
motors in multiple to the said source.
15 The combination with a single-phase motor of a multiphase motor, a
switch arranged to connect the two motors in tandem to a source of single-phase
current to vary the speed of said motors, and finally to connect the two motors in
multiple to the said source, the switch being also arranged to vary the reactance
of the intermediate circuits.
16 The combination with two motors connected in tandem, of means for
reducing the effective resistance of a winding on the secondary of the first
motor.
17 A tandem motor system in which the first motor is provided with a
secondary wound with a multiple winding, with means for short circuiting the
conductors of said winding singly, or in small groups, to reduce the resistance of
the winding.
18-The combination with leads carrying multi-phase current, of transformers
having their primaries fed from said leads, the secondaries of the transformers
being concatenated with the condenser.
19 The combination with a source of multi-phase leads, of transformers each
having its primary inserted in series in one of the leads, the secondaries the
transformers being connected together at one end, and connected at the other end
to different portions of a single condenser.
20 The combination with a set of multiphase leads of transformers each having
its primary inserted in series in one of the leads, the secondaries of the transformers
being connected together at one end, and connected at the other end to different
portions of a single condenser, and means for varying the effective length of said
secondaries.
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11
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