Improvements in Regulating Induction Electric Motors.
Year: 1896

page_text: Date of Application, 16th June, 1896-Accepted, 8th Aug., 1896
COMPLETE SPECIFICATION.
Improvements in Regulating Induction Electric 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 Albert H. Armstrong, Electrical Engineer, of Schenectady, in the
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 regulating alternating current motors, and particularly
to such motors when applied in railway work. It is designed particularly to over-
come a special difficulty arising in the use of alternating current apparatus and in
dealing with which we avail ourselves of the fact that the torque of such motors
is proportioned to the square of the impressed electro-motive forces and not to the
current, as is the case with continuous current machines. In some cases it is
desirable to increase the torque of the motors for a short time to an amount which
is not best adapted for their constant running. This is effected in one particular
class of existing controllers, by the combinations known as "tandem-multiple"
arrangement, which, being well known in the art, we will not further describe;
but on some occasions the maximum torque developed from the two motors in the
tandem position is not sufficient to get the starting effect desired, as when a heavy
load is to be started upon a curve or upon an up grade.
To accomplish the ends thus briefly indicated, we prefer to have the motors
wound with a different number of turns in their inducing and induced members,
which, as is well known in the art, may be interchanged in their relation to the
supply circuit. As an illustrative proposition, we may assume that the stationary
and rotating parts, or, as the motor is commonly used, the inducing and induced
members, are wound in the propcrtion of 5 to 4.
With the parts of the motor connected to line as just described, (that is, with the
inducing member having the higher number of turns) the torque would be 1 of
that obtained from the second connection, in which the part of the motor having
the less number of turns would be connected to line; in this latter case the torque
would obviously be the reciprocal, or of that formerly obtained; if the torque
of the first connection be x, that of the second would be 1.56+ . The motor
acting as a transformer thus impresses upon its secondary or induced member an
electro-motive force corresponding to the line voltage into the ratio of the primary
and secondary turns, omitting minor modifying factors; these constructions are
practically negligible. The torque of the motor as a whole is in direct proportion
to the square of the electro-motive force impressed upon the inducing member and
directly as the electro-motive force in its induced member. Inasmuch as the torque
is the ampere turns of the secondary member into the flux, a rise in the impressed
electro-motive force raising both the flux and the current in the secondary, the
resultant rise in torque would be as the product of these quantities or square of
the electro-motive force.
It is to take advantage of this fact that our present invention has been devised,
and it consists in adapting to a controller of the general type above described, au
emergency switch, so called; by which, when increase of torque is desired, the
switch may be thrown (the controller being of course, at the off position), and
the leads of the rotating and stationary parts may be respectively interchanged, so

page_text: that the line current passes to the part with the greater number of turns, which may
be provided for this purpose with collector rings and brushes, while in the ordinary
operation of the motors, the line current would pass to the part with less turns, and
the brushes would be closed circuited, the motor acting of course in both cases as
an induction motor.
As a specific aspect of the invention thus briefly pointed out, we combine this
emergency switch with the ordinary reversing switch of the controller and
preferably adapt suitable interlocking mechanism to the two; this latter feature,
however, we do not claim, inasmuch as it is old in the art.
The combined reversing and emergency switch consists briefly in four series of
contacts upon a single cylinder having co-operating therewith two sets of fixed
contacts or brushes, one set for each motor. The direction of revolution of the
motors is determined by the first and second rows of contacts respectively; that is
to say, in the middle position of the reversing switch the brushes are out of contact
and the circuit is opened, as is ordinarily the case. In its first position forward
the motors run forward with the current supplied to the stationary member of the
motor or motors; in its second position forward, the motors still run forward, but
the current is supplied to what was before the induced or rotating member of the
motor, and the reversed ratio of transformation referred to in our statement of
invention above is brought into play. In the first backward position of the switch,
the motors run backward with the same ratio as in the first forward position, while
in the last or second backward position, the reversed ratio is brought into effect
with the motors running backward.
The particular combinations just pointed out are additional and auxiliary to
those commonly employed in a tandem multiple controller of the general type
sketched above; and the switch which we have devised is in one sense simply a
torque regulating switch. The various combinations of speed and torque necessary
for the commercial operation of a tram car are supplied by the ordinary controller
cylinder and its connections.
The accompanying drawings show diagrammatic embodiments of our invention,
which may of course be arranged in a great many different ways; but in its
broadest aspect we consider any combination in an induction motor, of a revolving
and stationary part having different numbers of turns or ratio of transformation, or,
to speak more broadly, a ratio of transformation other than 1 to 1, and a switch
adapted to interchange the terminals of the revolving and stationary parts, within
our invention. The more specific aspects of the invention will be pointed out
fully in the specification and in the claims annexed.
Referring now to the drawings more particularly,
Fig. 1 is a general diagram of the circuits, showing a controlling switch
developed, and also a development of our combined reversing and emergency
switch;
Fig. 2 is a plan of the cylindrical switch shown on the right in Fig. 1; and
Figs. 3 and 4 are diagrams illustrative of the particular combinations of motors
effected by the reversing and emergency switch.
A', A2 are the inducing members of the motors; B1 B2 their induced
members; T, 2 the trolleys; C, C, C, the resistances, the motors being shown in
Fig. 3 connected in tandem. The ground at G takes the place of one of the
connections, nothing in our invention however limiting us to the use of ground
circuits, as we may use another trolley T3 (shown in dotted lines) and all the
connections may be metallic. The alternating electromotive forces are furnished
to the inducing member A¹ from the trolleys; the member B₁ has alternating
electro-motive forces induced in it from the field A', which send current over the
lines connecting B' to the inducing member A²; corresponding forces are induced
in the member B2, the circuits of which are closed through the resistances C, C, C,
in ways well understood.
In Fig. 4 the same parts have like letters of reference, but in this the leads
have been interchanged by the action of the switch, and energy is now furnished

page_text: from the trolleys to the member B₁ acting to induce forces in the member A¹
connected directly to the field B2, which acts upon the member A³, the circuits of
which are now closed through the resistances C, C, C, as was before the case with
the member B. It will be seen that the relation of the stationary and revolving
members is thus interchanged and the increase of torque referred to in our statement
of invention is obtained.
Referring now to Fig. 1, the results thus pointed out are obtained by means of
the switch F on the right of that figure, in which four series of movable contacts
are illustrated in conventional ways, and the two sets E, E¹ of brushes a to h
and i to q are illustrated out of contact for the sake of clearness.
Fig. 2 also illustrates the construction of this switch F, it showing the switch in
plan, and the two series of fixed contacts are respectively lettered E, E', the rows
of movable contacts being lettered H₁ to H respectively. It is to be understood
that the brushes can stand upon any of the diametrically opposite contacts in any
desired order. Stated in tabular form, the combinations, of this switch are as
follows
from the trolleys to the member B₁ acting to induce forces in the member A¹
connected directly to the field B2, which acts upon the member A', the circuits of
which are now closed through the resistances C, C, C, as was before the case with
the member B. It will be seen that the relation of the stationary and revolving
members is thus interchanged and the increase of torque referred to in our statement
of invention is obtained.
Referring now to Fig. 1, the results thus pointed out are obtained by means of
the switch F on the right of that figure, in which four series of movable contacts
are illustrated in conventional ways, and the two sets E, E¹ of brushes a to h
and i to q are illustrated out of contact for the sake of clearness.
Fig. 2 also illustrates the construction of this switch F, it showing the switch in
plan, and the two series of fixed contacts are respectively lettered E, E', the rows
of movable contacts being lettered H to H respectively. It is to be understood
that the brushes can stand upon any of the diametrically opposite contacts in any
desired order. Stated in tabular form, the combinations, of this switch are as
follows
E H'
forward
E' H*
E H¹
reverse
E' H'
E H³
emergency forward
E' H¹
E H
:
emergency reverse
E' H²
The circuits in Fig. 1 are as follows.
Starting with the trolley T, the circuit leads to contact 4 upon the controlling
cylinder D, by cross-connection to contact 3, by the lead 3 to contact a on the
switch F, by cross-connection to contact f, by the lead to terminal 1' upon the
inducing member A¹ of the first motor; passing through the coils of this member,
there are two paths,-the first leaving at the terminal I, passing to the ground
wire cr to the trolley T according to whether a grounded circuit or metallic
circuit is used; the other path is from the terminal 13, by the lead b to contact b
upon the switch f, by cross-connection to contact e, and by the lead 2 to contact 2
upon the controller D; by cross-connection to contact 1 and thence to trolley T
Electro-motive forces, being induced in the secondary B' of the motor, send
current to the primary B of the second motor, as follows: Starting with the
terminal L', direct connection is made to the terminal N by the ground wire.
From the terminal L the circuit is by the lead c to contact c upon the switch F,
by cross-connection to contact d, by the lead 13 to the controller, by cross-
connection to the lead 15, to contact m upon the switch F, by cross-connection to
contact k, and by the lead K to the terminal N. Starting again from the
terminal L, pass by the lead g to the contact g on the switch F, by cross-connection
to contact , by the lead 16 to the controller, by cross-connection to the lead 14,
contact Qupon the switch, by cross-connection to contact o, and by the lead o to
the terminal M².
From the primary B² electro-motive forces are induced in the secondary A² of the
second motor, the circuit of which secondary is closed through the resistance C, C, C,
as follows: Starting with the terminal M, the circuit is by the lead I to contact i

page_text: upon the switch F, to contact n, the lead 7 to the controller, thence by lead 8 to
the middle resistance C, thence passing through that resistance, the circuit divides,
passing first through the upper resistance C to the contact 6 upon the controller,
by cross-connection to contact 5, by the lead 5 to contact i, by cross-connection
to contact p, by the lead p to the terminal M. Returning to the resistance as
the dividing point of the circuit, the other branch passes through the lower
resistance C to contact 11 upon the controller, then to contact 10, to the ground
wire, and by the ground wire to the terminal M³.
The circuit just traced is, as will be observed, with the row of brushes E
comprising those lettered a toupou the row of contacts H2; and the brushes E',
comprising those lettered i to q upon the row of contacts H, and is that established
when the switch F is thrown to the first or forward position, which would be by
the rotation of the cylinder (see Fig. 2), from the neutral position in which it is
illustrated, to make the contacts just described.
When the rows of brushes E, E are upon the contacts H, H respectively, the
circuits are in the same condition substantially, except that the first pair of
terminals are reversed, and of course the motors run in the opposite direction.
These circuits will not be particularly described. Each of these running positions
is 45° from the neutral position in which the brushes are illustrated in Fig. 2. At
the next step, however, the switch rotates 90° in whichever direction it may be
thrown, and thus the total revolution of the cylinder is 270°.
The further running positions of the controller D, need not be traced in detail;
it is sufficient to say that they combine the motors in tandem and multiple and
close the circuit of the armatures through resistances, which is not brcadly new
with us.
Referring now to the emergency positions of the switch, it will be sufficient to
describe what we may call the "emergency forward" combination. In this the
row of brushes E is upon the contacts H³, and E' is upon the contacts H', as will
be apparent from Fig. 2. The circuits, as traced in Fig. 1, are as follows:
Starting from the trolley T, it passes to the contact 4, by cross-connection to
contact 3, by the lead 3 to contact a, thence by cross-connection upon the row of
contacts H³ to contact c, thence by the lead e to the terminal L2 upon the member B
of the first motor, thence from the terminal L' to the ground wire or trolley T;
and from the terminal I by the lead g to contact g upon the switch F, thence by
cross-connection to contact e, thence by the lead 2 to contact 2 upon the controller,
by cross-connection to contact 1, and to the trolley T³.
Electro-motive forces, being induced in the member A' of the first motor, send
current from the terminal 12 by the lead 6 to contact 6 upon the switch F, by
cross-connection to contact d, by lead 13 to the controller, by cross connection to
lead 15, thence to contact m, by cross-connection upon the row of contacts H', to
contact l, by the lead to the terminal M' of the second motor.
Starting again from the terminal 1, by the lead to contact f upon the
switch F, by cross-connection to contact L, by the lead 16 to the controller, by
cross connection to the lead 14, to contact 9, by cross-connection to contact p, and
to the terminal M2 of the second motor. The terminal 11 of the first motor is
.connected to the terminal M of the second motor through the ground wire.
The induced electro-motive forces set up in the member B2 of the second motor
send current through circuits closed through the resistances C, C, C; these circuits
are as follows;
Starting from the terminal N, pass by the lead o to contact o upou the switch F,
thence by cross-connection to contact n, by the lead 7 to the controller, by cross-
connection to the lend 8, and to the middle resistance C; there, as before, the
circuit divides, passing through the upper resistance C, to contact 6, by cross-
connection to contact 5, by the lead 5 to contact i, by cross-connection to contact a,
by the lead K to the terminal N. Returning to the middle resistance as the
dividing point, passing through the lower resistance, pass to contact 11 upon the
contruffer, thence to contact 10, by the ground wire back to terminal. N³.

page_text: In the position of the switch in which the brushes E are upon the contact
plates H, and the brushes E' upon the contacts H2, the circuits are made for the
"emergency reverse" position. These are the same as those already described in
connection with the emergency forward position, except that the first two terminals
of the first motor are reversed so that the motors run in a backward position, with
the increase of torque already referred to in our statement of invention.
It is of course manifest that the usual changes, with which those skilled in the
art are conversant, may be made in the arrangements we have pointed out as the
best adapted to our invention, without affecting its essence. The use of
the invention necessarily extends to either one or a plurality of motors, and where
we use the term "a number" in the claims, we mean to include either one or any
other larger number of motors.
Having now particularly described and ascertained the nature of this inven-
tion and in what manner the same is to be performed as communicated to us from
abroad, we declare that what we claim is :
1. In combination, an induction motor having a revolving and stationary part
with a ratio of transformation other than one to one, and a switch adapted to
interchange the terminals of the revolving and stationary parts.
2. In combination, a number of induction motors having a ratio of transformation
other than one to one between their stationary and revolving parts, and a switch
adapted to interchange the terminals of such stationary and revolving parts.
3. In combination, a tandem-multiple controller a number of motors having
revolving and stationary parts with a relation other than one to one, and a switch
adapted to interchange the terminals of the revolving and stationary parts
respectively.
4. In combination, a tandem multiple controller a number of induction motors
operated thereby having revolving and stationary parts with a relation other than
one to one, and a combined emergency and reversing switch adapted to determine
by some of its positions the direction of rotation of the motors, and by its other
positions to interchange the terminals of the revolving and stationary parts of the
motors, in whichever direction they may rotate.
5. A combined emergency and reversing switch for a number of induction
motors having revolving and stationary parts, with a ratio of transformation other
than one to one, such switch composed of four sets of movable contacts and two
sets of fixed contacts or brushes, and having four operative positions, two of which
determine the direction of rotation of the motors and the other two of which
interchange the terminals of the revolving and stationary parts respectively.
Dated this 16th day of June 1896.