Improvements in Tandem-parallel Controllers for Induction Motors.
Year: 1896

page_text: Date of Application, 29th Sept., 1893-Accepted, 6th Feb., 1897
COMPLETE SPECIFICATION.
Improvements in Tandem-parallel Controllers for Induction Motors.
We, THE BRITISH THOMSON-HOUSTON COMPANY, LIMITED, of 38, Parliament
Street, Westminster, in the County of London, Electrical Engineers, do hereby
declare the nature of this invention (which has been communicated to us from
abroad by William B. Potter and Frank E. Case, 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 the regulation of alternating current motors of the
induction type; and has for its object to arrange for the control of such motors by
the so-called tandem-parallel system resembling in some particulars the series
We are aware that this
parallel system of control for continuous current motors.
system is not new, nor is it new to arrange a controller adapted to make proper
changes in the regulation of motors by the systein proposed, such a controller being
illustrated for example in the Patent communicated by Albert H. Armstrong, to
ourselves No. 13264 of A.D. 1896. The controller illustrated in the accompanying
application is substantially of the type described in that patent, the connections
being very slightly changed so as to simplify its construction, but the particular
steps of regulation are the same and are accomplished in substantially the same
manner and order.'
In the system referred to, it is desirable to arrange for cutting out either one of
the motors, should it become disabled for any reason, without affecting the
operation of the other; and it is therefore the special object of our invention, as
described in this application, to provide cut out switches by which this operation
may be effected in a controller of the class described. The problem presented by
such steps as are necessary is, not only to cut out either motor without interfering
with the operation of the other one, but also to change the inductive relation of
the revolving and stationary members of one of the motors, and further, to so
arrange the connections that the motors will come into operation at the same point.
of revolution of the controller. The necessity for this latter provision will be
apparent when it is remembered that in the tandem position (corresponding to the
series position of continuous current motors), the first point of the controller
throws both motors into operation. If the second motor be cut out, ordinarily the
first motor would come into operation as soon as the controller handle was moved.
As, however, the induced member of one motor and the inducing member of the
second motor are the revolving members in this position of the controller and are
connected together, it is necessary that the leads of the revolving members should
be reversed, so that they may act properly. When the first motor is cut out,
therefore, it becomes necessary, not only to reverse these leads, but also to provide
that no current shall flow in the inducing member or field of the first motor.
therefore so arrange the connections of the cut-out switches in the controller that
by the operation of the first cut-out switch the leads to the revolving member of
the second motor will be reversed, and the circuit of the first motor opened. This
adapts the second motor for operation when the controller reaches its first
multiple position. To provide for the operation of the first motor in the same
manner, we so arrange it that when the second cut-out switch is thrown, open-
circuiting the second motor, the connections to the field of the first motor will also
be open-circuited until the controller has reached its first multiple position.
We

page_text: The necessity for open-circuiting the field of the motor is apparent, as it is
necessary not only to provide for avoiding waste of current and the consequent
heating of the field, but also to prevent any false indication in the controller, which
would tend to confuse the operator. If the field of the idle motor should be left
in, when the controller was turned to the off position the spark due to breaking the
circuit would indicate that the current was cn and yet the car would not start;
whereas, if this field be cut out, the first indications of current flowing will be at
the first multiple position of the controller, and the flow of current and the starting
of the car will be simultaneous.
The accompanying drawings show an embodiment of our invention.
Fig. 1 is a diagrammatic representation of a controller of the type described,
with our improved cut out switches, the circuits, motors and resistances being
indicated by conventional signs.
Fig. 2 is a series of diagrams showing the motor combinations effected by the
controller.
Figs. 3 and 4 are detail views of cut out switches, Fig. 3 being a front elevation
and Fig. 4 a section of the line 4-4 of Fig. 3.
Referring by letter, M, M are motors, the field terminals of which are
respectively lettered X, Y, Z and X, Y, Z, the armature terminals being
lettered A, B, C and A2, B2, C2. In this designation we employ the terms
"field" and "armature" in their conventional sense, meaning thereby the fixed
and revolving elements of the motors. In the case of the motor M² the revolving
element becomes, in the first position of the controller, the field or inducing
element, deriving its current from the armature or induced element of the motor M';
but in the multiple position of the controller this arrangement is reversed, and the
revolving element becomes the armature or induced element deriving current only
by induction from the fixed or inducing element, which is connected to line in
parallel with the fixed part of the motor M'. This is all specifically pointed out
in the patent already referred to.
The motor combinations are, as already pointed out, substantially the same as in
the patent above cited. In Fig. 2 the diagrams illustrate these motor combinations.
They are briefly as follows:-
In diagram 1 of Fig. 2, the trolleys feed into the first field, and the armature of
the motor M receives current by induction from that field, feeding the revolving
field of the motor M2 by direct connection, which in turn induces in the stationary
armature of that motor currents which travel in closed circuits through
resistances R', R2, R3. The next step of the controller, illustrated in diagram 2
of Fig. 2, shows the resistances partly cut out or short-circuited. In the next
step, shown in diagram 3, the resistances are entirely short-circuited, and this is
the running tandem position. Diagram 4 is the transition step, the leads of the
second motor being reversed and the motor shunted through a part of the
resistances. In diagram 5 the second motor is open-circuited and the armature of
the first motor is closed through resistances. In diagram 6 the motors are
connected in parallel and their armatures closed through part of the resistances.
In diagram 7 the final running position is shewa, the fields being in parallel, the
armatures being closed-circuited without the resistances.
On referring again to Fig. 1, we do not find it necessary to trace the circuits
entirely, inasmuch as, as already pointed out, they are illustrated and described
fully in the patent already referred to. The trolleys are lettered T, T2. A third
trolley G is also indicated as connected by a dotted line, by which we mean to
indicate that the system may have three metallic circuits instead of having a
ground connection, as illustrated, this forming no limiting feature of our invention.
The contacts of the controller are numbered 1 to 17 respectively; those of the
reversing switch 18 to 25 respectively. The different positions of the controller
are also indicated by the dotted lines 1 to 7, corresponding to the diagrams in
Fig. 2. It will be observed that the current enters from the trolley T', passing to
the contact 25 on the reversing switch, and then around to the contact 1, which is

page_text: the first trolley contact. In order to exemplify the application of our invention
to the controller, we trace the first circuit as follows:-
From the trolley T, through the reversing switch as just pointed out, to
contact 1; thence by cross-connection of the two contact plates to the contact 2;
thence through the cut-out switch at the contact d on that switch, passing to the
terminal Y upon the motor M'. There the current divides, passing through the
field, and leaves the field by two paths, one through the terminal X back to
the lead c of the cut-out switch CO, then to the contact 3 upon the controller, by
cross-connection of the contact-plates to contact 4, and out through the contacts 23
and 22 on the reversing switch to the trolley T. The other path of the current is
from the terminal Z' to ground, and thus back to the generator, or in the case of
a metallic circuit, by a wire directly back to the trolley G. No current passes
directly from the controller to the motor M2, but the induced currents from the
revolving member of the motor M' reach the revolving induced member of the
motor M2, as follows: starting from the terminal A', it passes to the contact a of
the cut-out switch CO, thence to the contact 13 upon the controller by cross
connection of the contact plates to contact 15, thence through the terminal g of
the cut-out switch CO2, directly to the terminal A upon the motor M. Similarly,
the terminal B upon the motor M' is connected to the terminal b of the cut-out
switch CO to contact 16 upon the controller, and by cross connection of the
contact plates to contact 14, through the terminal h to the cut-out switch CO²,
directly to the terminal B of the motor M. The terminals C, C of the
respective motors are connected through the ground ur by a direct metallic
connection. As may readily be seen from an inspection of the connections, the
terminals X, Y, Z are closed through the resistances R', R', R³.
Before describing the operation of the cut-out switches, we will describe their
construction, as illustrated in Figs. 3 and 4. In Fig. 3. N is a base of any suitable
insulating material; the terminals of the switches are lettered a to à respectively.
The upper two terminals constitute the first cut-out switch CO. The four lower
terminals form the cut-out switch CO2. The terminals c, d, with their blades form
the switch CO. Bars of insulating material I, I are shown. The lower cut-out
switch is provided with the bar 1, the upper with the bar I', and each of these bars
is so arranged that by throwing either of the cut-out switches CO', CO, the inter-
mediate switch CO will also be thrown. Back contacts m, n are provided for two
of the blades of the cut-out switch CO2, and these contacts are mounted on the
block O.
Referring again to Fig. 1, the operation of the switch which we have just
described may be deduced from an examination of the circuits. It will be seen
from the description of the first circuit which we have given, that contacts 2 and 3
upon the controller are the starting points for current to the motors, they com-
municating respectively with the terminals Y', X, of the motor M', and therefore
if these contacts are open circuited, no current will flow in either of the motors.
We therefore so arrange our cut-out switches that whichever motor is cut out,
these two contacts shall remain open circuited until the multiple position of the
controller is reached, the reasons for which have been fully pointed out in our
statement of invention. These two contacts connect with the central switch C O,
and it is this switch which the bars of insulation I, 11, open as the other cut-out
switches are thrown. The corresponding parts are indicated in Fig. 1, and the
terminals c, d are the ones which are opened when this intermediate switch is
thrown. The switch is, however, cross-connected to the back contacts m, n, and it
is by this cross-connection that we not only open-circuit the first motor field for the
reasons alrendy, pointed out, but also, when the second cut-out switch is thrown,
reverse the leads of the revolving member of the motor M2. The essential parts
of the controller entering into this operation are the contact plates 5", 7", which
serve to again close the circuit of the contacts 2 and 3, which, until the controller
reaches this (the sixth) position, remain open.
Assume first that the cut-out switch C O is thrown, opening the circuit at

page_text: contacts a, b, c, d respectively; it will he seen that the terminals of the first
motor A, B, X, Y are opened, and the motor is necessarily idle, no current
flowing in either the field or armatures. In this position the motor M' is also cut
out, inasmuch as it can get no current in the tandem position, but as soon as the
controller has been revolved to the sixth position, the contact plates 5, 7, which
are cross connected respectively to the trolleys 1 and 4, complete the circuit
through the contacts 5 and 7, the cirenit from each passing to the contacts e, f
respectively, and from theuce to the terminals X, Y' respectively, of the motor M².
With the first motor cut out, therefore, the second motor takes current only from
the multiple position of the controller.
Assume now that the cut-out switch CO2 is thrown; this open-circuits the
contacts e, f, g, h, thus, as in the case of the motor M', opening the terminals of
the motor M2, and putting it out of action. The bar I also opens the contacts c, d,
and at the same time the back contacts m, n are closed by the switch blades of the
cut-out switch CO2, and thus the current passes directly from the trolley contact 1
to the contact plate 5", then out over the contact 5 and its lead to the switch
blade corresponding to the contacts e on the cut-out switch C 0%, thence to the
back contact n, and thence by the lead to the terminal Y¹ of the motor M',
returning from the terminal X through the lead to the contact m, then se over the
switch blade and by the lead to the contact 7, contact plate 7ª and by cross-
connection of the contact plates to the contact 4, thence by the contacts 23 and 22
upon the reversing switch to the trolley T. The path from the terminal Z of
the motor M is, as before, directly to ground or to the trolley G. As indicated
in diagram 6 of Fig. 2, in the multiple positions only a portion of the resistances
are used, and this is the case when the cut-out switches are thrown.
The paths from the terminals A¹, B, C, of the motor M to the resistances are
as follows: from the terminal A¹ to the cut-out switch C O at the contact a, thence
to contact 13 upon the controller, by cross connection of the contact plates to the
contact 12, to an intermediate point of the resistance R. Again, starting
from tern.inal B₁ of the motor, the lead goes to the contact of cut-out
switch CO, thence to the contact 16 upon the controller, by cross-connection of
the contact plates to contact 17, and to an intermediate point of the resistance R'.
From the terminal C₁ the path is to ground, re-entering the controller at the
contact 10, by cross-connection of the contact plates to contact 9, to an inter-
mediate point of the resistance R, thus closing the circuit of the armature through
the resistances. The next step of the controller is after the dotted line 7 has
been reached, acting to cut out the resistance, and run the armature upon short
circuit.
So far as we are aware, we are the first to devise cut-out switches of any type
for induction motors operated by the tandem parallel system of control.
manifest that other arrangements might be devised which would accomplish the
purpose of our invention, and it is our object to make broad claims.
Having now particularly described and ascertained the nature of this inven-
tion as communicated to us from abroad and in what manner the same is to be
performed we declare that what we claim is :-
1. In a controller for induction motors, contacts and cross-connections adapted
to connect the motors in tandem or parallel at will, and cut-out switches arranged
to cut out part of the motors without affecting the operation of the remainder.
2. In a controller for induction motors, contacts and cross-connections for
regulating the speed and torque of the motors, and cut-out switches adapted to cut
out either one of the motors without affecting the operation of the other.
3. In a tandem-parallel controller for induction motors, contacts and connections
for regulating the speed of the motors in various combinations of tandem and
parallel, and cut out switches adapted to cut out either motor at will, the contacts
being so arranged that the current is turned on at the same point in the operation
of the controller with either motor cut out.

page_text: 4. A tandem-parallel controller for induction motors, comprising contacts and
connections adapted to connect the motors in tandem or parallel, and cut-out
switches in combination therewith arranged to cut out either motor at will, and to
open the circuit until the multiple position of the controller is reached with either-
motor cut out.
5. A tandem-parallel controller for induction motors, comprising contacts and
connections for connecting the motors in tandem or parallel, a cut-out switch for
the first motor acting to disconnect the second motor until the multiple position
of the controller is reached, and a cut-out switch for the second motor disconnecting
the first motor until the multiple position is reached, the cut-out switch for the
first motor acting also to reverse the leads of the inducing element of the second
motor.
J. C. CHAPMAN,
70, Chancery Lane, London, W.C., Chartered Patent Agent.