Improvements in Method of and Apparatus for Controlling Alternating Electric Current Motors,
Year: 1899

page_text: Date of Application, 30th June, 1899-Accepted, 27th Jan., 1900
COMPLETE SPECIFICATION.
Improvements in Method of and Apparatus for Controlling Alternating
Electric 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 Albert H.
Armstrong, 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, broadly speaking, relates to the control of alternating
current motors, and in some of its more limited aspects has more particular
reference to the control of alternating current induction motors by the now
well-known tandem multiple system.
a
It has been discovered that the torque of an induction motor with its inducing
coils connected in Y or gamma may be greatly increased by shifting the con-
nections so as to change the winding to the closed or delta form. When the
windings are connected with one terminal of each coil to a common point commonly
known as a Y or gamma_connection, the electromotive force impressed on each
coil bears the ratio of √3 to the electromotive force impressed on the individual
coils when connected in delta. Since the torque on an induction motor is pro-
portional to the square of the impressed electro-motive force it follows that the
operation of changing the windings of the motor from gamma to delta results in
increasing the torque of the motor three times. The application of this principle
is found to be useful in connection with the regulation. of single induction
motor, and it is also of particular value in connection with the control of induc-
tion motors by the tandem multiple system. In the latter case when induction
motors operate in tandem it has been found that their torque is reduced to a
value materially lower than that which they would have were the motors con-
nected in multiple, and the same current flowing in each motor. The torque of
the first motor is reduced because of the fact that its secondary is connected to
a reactive circuit furnished by the primary of the second motor, while the torque
of the second motor is reduced because of the diminished electro-motive force
impressed thereon from the secondary of the first motor. By connecting the
inducing or primary winding of the first motor in delta when the motors are running
in tandem the torque of the combination is reduced three times, thus more than
making up for the inherent lessening of the torque due to the tandem connection.
In addition to the broader features outlined above this invention includes certain
minor details all of which will be hereinafter described. The scope of the
invention, both in its broader and its more limited aspects will be particularly
pointed out in the appended claims.
Fig. 1 is a diagram of the connections employed in carrying out the invention.
Fig. 2 illustrates diagrammatically two induction motors connected in tandem.
Fig. 3 shows the motors connected in multiple, and, Fig. 4 represents a detail.
In Fig. 1 is shown a developed view of the contacts on a controller cylinder em-
ployed in changing the connections of induction motors, according to this invention,

page_text: The contacts indicated collectively at K¹ are those which correspond to the
first controller position. The contacts indicated at K2 correspond to the second
controller position, while the contact shown at K³ represents the last or extreme
position of the controller cylinder. The contact fingers, operating in conjunction
with these contacts, are indicated by the numerals 1 to 14 inclusive.
The controller thus briefly indicated is intended to be used in connection with
two induction motors, preferably of the three phase type. The fixed members
of the two motors are indicated at 1 and 12, and are each provided with three
coils. The movable members of the motors corresponding to the fixed members
are shown at A1 and A2. In describing this invention it is preferable to designate
the members of the motors in this manner, rather than refer to them as inducing
and induced members, because of the fact that in changing the connections of the
motors from tandem to multiple or rice versa the members of one of the motors
are reversed in character, thus giving a chance for ambiguity if the members of
the motors be designated according to their electrical functions.
Suppose now that the controller is moved to its first position and that the
contact fingers 1 to 14 bear upon the corresponding contacts 1 to 14'. In this
position of the controller the motors are connected in tandem as shown in
diagram in Fig. 2, the fixed member F of the first motor having its coils con-
nected in deita. The contacts 11, 21 connect together the coils 002, the con-
tacts 3, 6 the coils C2, C3, and the contacts 41, 5 the coils C₁, C. The windings
on the fixed member of the first motor are thus connected in delta and receive
current through the supply connections E E and G as will readily be seen.
The connections El E2 represent trolleys or contact shoes and the connection G,
the ground return or rails of a three phase railway system, but it will be evident
that the invention, while thus illustrated as applied to a railway system, is in
no sense limited thereto but is equally available where ever it is desired to secure
variations in speed and torque of induction motor.
The contact fingers 11 and 12, together with the corresponding contacts and
cross connections on the controller cylinder, act to connect two of the windings
of the movable member A' with corresponding windings of the movable
member, the terminal T being connected to T and the terminal S
to S¹ An electrical conductor Z permanently connects together the
remaining terminals UU The two movable members of the motors
are thus connected in series, the member A acting as a primary
for the secondary motor, while the member A acts as a secondary to
the first motor. The coils of the fixed member F2 of the second motor are per-
manently connected with one terminal of each coil with a common point,
as indicated, and in the first controller position this winding is connected to
the resistance R, the connections being as follows: One terminal V of the
winding is permanently connected to the common conductor % to which one
leg of the resistance R is also permanently connected. The contact fingers 7
and operating in conjunction with the corresponding contacts and cross-con-
nections on the controller cylinder serve to connect the two remaining terminals
of the windings of the fixed member with the contact fingers 9, 10 which form
the two remaining terminals of the resistance R.
From the diagram of connections shown in Fig. 2, it will be seen that the
second motor receives its energy from the movable or secondary member of the
first and that for the purpose of increasing the starting torque of the com-
bination, a non-inductive resistance is shown as inserted in the induced or
stationary member of the second motor.
The common conductor Z is indicated in Fig. 2 in dotted lines, and its object
is to lessen the number of contact fingers and contacts on the controller, the
connections being made, as far as possible, between two sides of the three phase
conductors, the third conductor Z being unbroken. With the motors connected
as shown the maximum starting torque is obtained by reason of the delta con-
nection of the primary winding of the first motor and because of the non-inductive

page_text: esistance in the secondary of the second motor. If the motors be geared to run
the same speed they will reach a speed corresponding to one-half that which
hey would attain if connected individually to the supply conductors. When this
speed has been reached the delta connection of the first motor may, if desired,
be changed to gamma and the resistance R of the second motor short-circuited.
It has not, been considered necessary to illustrate these minor details.
common
In the second position K2 of the controller the motors are connected in
multiple, with the induced windings on the movable members closed circuited
upon the common resistance R. In this position of the controller the coils on
cach member of each motor are connected in gamma or Y, a mode of connection
already explained and clearly indicated in Fig. 3. Referring to the drawings,
the contacts 211, 31, 4" connect three terminals of the coils of the fixed member FI
to a common point. The remaining terminals of these coils are connected directly
to the supply conductors E, E and G. The coils of the fixed member of the
second member are connected, in parallel with the first, the coil being
conductor Z, with the supply ter-
connected, through the
minal ; the coil W to the supply connection G: and the remaining coil X
with the terminal E. The movable armis A1, A2 of the motors are connected in
multiple the connections being reversed from those corresponding to the first
controller position, in order to preserve the same direction of rotation in the
two motors. The coils U, U of the members A', A2 are, as before, permanently
connected together by the conductor Z, the remaining terminals, however, being
reversed, the coil T being connected to the coil S' and the coil $ to the coil T₁.
The resistance R has one of its terminals permanently connected to the conductor Z
and by consequence, to the terminals U, C' of the movable members A', A2, while
its remaining terminals are connected through the contact fingers 9, 10 and the
corresponding controller contacts, with the two remaining terminals of the wind-
ings of A and A2, thus being in parallel therewith. From the connections
shown in Fig. 3, it will be seen that the motors are connected in multiple, with
the windings of the fixed or primary member of the first motor connected in gamma
rather than in delta, as in the first controller position. The object of this change
of connections of the windings of the first motor has already been set forth. The
connection of the motors in multiple operates to increase their speed, as is well
understood.
The resistance in the secondaries of the motors reduces the speed at which
the motors attain their maximum torque. This resistance is therefore chiefly
useful while the motors are being gotten up to speed, and is intended to be cut
out as the speed rises in order to prevent waste of energy and to secure close
speed regulation with varying load. The third controller position, indicated at
OK, differs from the second controller position only in that the resistance Ris
short-circuited. The connections are obvious from the drawings. In this position
however it should be stated that the contact fingers 9, 10 bridge over the spaces
between the contacts 9", 10" and 9111 10 respectively.
When the controller is at the last controller position large currents flow through
5 the windings of the induced or movable members of the motors. If, under these
conditions, the controller were to be moved back toward its original position so
as to cut out the short-circuiting connections of the resistance R, large and
destructive arcs would be formed on the contacts 11, 9, 10, which ares are
difficult to blow out or extinguish, owing to the fact that they are formed by
In order to overcome this
50 alternating currents and not by direct currents.
difficulty a supplemental short-circuiting switch is used, the contacts of which
are arranged on a small cylinder and adapted to be operated from the main
controller cylinder. Fig. 4 illustrates the co-operative relation between these
two cylinders. The main controller cylinder is indicated at L and its contacts
5 are shown at K¹, K², K³. The supplemental cylinder is shown at L' and is
provided with contacts K. Suitable controller fingers operate, as shown, in
conjunction with these contacts. The relative position of the parts shown corre-

page_text: sponds to the off position of the controller. When the main controller is turned
from its first and second positions no movement is communicated to the short-
circuiting cylinder L'. When however, the main controller has been moved
to its last position the lug on the main cylinder engages the lug P on the
supplemental cylinder thus causing the latter to turn until its contacts K are
brought under the corresponding contacts fingers C and so short-circuiting the
resistance R. On the return movement of the controller the short-circuiting
contacts on the main cylinder are withdrawn from beneath their co-operating
contact fingers without the production of arcs owing to the fact the short-
circuiting cylinder L' still remains with its contacts short-circuiting the resis
tance R. Just before the main cylinder has reached its off position, and when
the motors have been entirely disconnected from line, the lug 0¹ on the main
cylinder engages the lug P on the short-circuiting contacts K+. It is obvious that
under these conditions no arcing will be produced on the short-circuiting contacts.
In some cases the short-circuiting contacts on the main controller cylinder may
be omitted, the supplemental short-circuiting switch being depended upon
entirely for short-circuiting the resistance.
Although a supplemental short-circuiting switch is shown in connection with
a tandem multiple system of control, it is obvious that it may appear in many
other relations than that shown, and in its broader aspects the function of the
supplemental switch need not be that of a short circuiting device but may make
any other desired connections.
Although the system of control for induction motors above described is particu-
larly valuable in connection with railway work, it will, he obvious to any one
skilled in the art that the various features which go to make up this invention,
are equally applicable whether the system be employed in connection with
electric railway or for other purposes to which it may be adapted, as, for example,
in electric hoisting, elevator work or the like.
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 controlling a plurality of induction motors at least one of
which has angularly displaced windings on one of its members, which consists
in connecting the motors in tandem and in multiple and connecting the said
angularly displaced windings either in closed circuit or with one terminal of
each of said windings to a common point.
2. The method of controlling a plurality of induction motors which consists
in changing the connections of the motors from tandem to multiple or the reverse,
connecting the windings of one of the motors in closed circuit wlien the motors
are connected in tandem, and connecting one terminal of each of said windings
to a common point when the motors are connected in multiple.
3. The method of controlling a plurality of induction motors which consists
in connecting the motors in tandem with the windings of one member of the
motors arranged in closed circuit and connected to line, and then changing the
aforesaid connection of said windings to one in which one terminal of each
winding is connected to a common point.
4. The method of controlling a plurality of induction motors which consists
in connecting the motors in tandem, connecting the windings on one member
of one of the motors to line, and varying the electro-motive force impressed on
the individual coils of said windings, independent of any variation of the electro-
motive force impressed on the terminals of the first motor of the series.
5. The method of controlling a plurality of induction motors which consists
in connecting the motors in tandem, then in multiple, and when in multiple con-
necting the induced windings to a resistance, then short-circuiting the resistance
and maintaining the short circuit until the motors have been disconnected from
line.

page_text: 6. The combination of a plurality of induction motors, means for connecting the
motors to line in tandem or in multiple, means for connecting the induced winding
of one of the motors to a resistance, means for short-circuiting said resistance and
for maintaining said short-circuit until the connection to line is broken.
means
7. The combination of a plurality of induction motors, means for connecting
the motors in tandem or in multiple, and
for connecting one
terminal of each of the angularly displaced coils of one member of one of
the motors to a common point and means for connecting the said coils in closed
circuit.
8. The combination with a plurality of induction motors, of means for con-
necting the motors in tandem or multiple, and means for changing the winding
of one member of one of the motors from gramme to delta, or the reverse.
9. The combination with a plurality of induction motors, of means for con-
necting the motors in tandem or in multiple, and means operating simultaneously
therewith for connecting the windings of one member of one motor in delta when
the motors are connected in tandem and for connecting said windings in gramme
when the motors are connected in multiple.
10. The combination with a plurality of induction motors, of controller for
a connecting the motors to line in tandem or in multiple, for connecting the
induced winding of one of the motors to a resistance, and for short-circuiting
said resistance and maintaining said short-circuit until the connection to line
is broken.
11. The combination of an induction motor, a controller for connecting the
motor to a source of supply, for connecting the induced member of the motor
to a resistance and for short-circuiting said resistance and maintaining said
short-circuit until the connection to line is broken.
12. The combination of an induction motor, a main controller for connecting
and disconnecting the motor from a source of supply, and for connecting the
induced member of the motor to a resistance, and a supplemental switch actuated
from said main controller and operating to short circuit said resistance and
maintain said short-circuit until the connection to the source of supply is broken.
0012 doy of Tuno 1899
THE BRITISH THOMSON-HOUSTON Co. LTD.
W. MARTINDALE,
A. R. MONKS,
} Directors.
ALFRED CLEMENTS,
Assistant Secretary.