Improvements in Controlling Electric Motors by the Three Wire. System.
Year: 1895

page_text: Date of Application, 5th Nov., 1895-Accepted, 11th Apr., 1896.
COMPLETE SPECIFICATION.
Improvements in Controlling Electric Motors by the Three Wire.
System.
I, JAMES DEVONSHIRE, Secretary of the British Thomson-Houston »Limited
of 38 Parliament Street, Westminster, London (a communication from abroad by
William B. Potter, Electrical Engineer of Schenectady in the State of New York,
United States of America) do hereby declare the nature of this invention' 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 the control of electric motors especially those
operated by continuous currents; and has for its object 'to' provide a system of
control and an apparatus for carrying 'out the system by which the two motors may
be regulated from rest to their highest speed, employing at the same time the
commercial economies of the now well-known "series multiple or three wire
system.
In my Patent No. 19860 dated October 22nd, 1895 bearing the title: Improve-
ments in Regulating Electric Motors, I have illustrated and described a system
especially adapted for an electric railway in which four motors are "employed,
divided into two groups of two; one group upon each side of the three wire system
in which the positive and negative conductors are represented by trolley lines and
the neutral by the track or ground return.
In the present system I aim to employ the same arrangement except that in' this
case I ordinarily use only two motors. In the application filed October 22nd 1'895
above referred to I have made claims which are sufficient in scope' in their broadest
aspect to include the subject matter of the present case,' but in the latter I'aim to
claim specifically the arrangement and method" of operating two motors, and
therefore the claims which I make herein are not to be considered as broad enough
to cover matter shown in the application referred to except in the more particular
aspect of my invention presently to be referred to.
The accompanying drawings illustrate my invention, Figure 1 being a develop-
ment of a cylindrical switch adapted to carry out its purpose, the motors; resistances"
and trolleys being indicated diagrammatically;
Fig. 2 is a series of diagrams showing the different combinations of motor and
resistance.
I have not illustrated the mechanical arrangement of the controller inasmuch as
cylindrical'switches of the type herein shown are now well known in the art'and do
not require extended description.
The broadest aspect of my present invention is that improvement' in the art of
controlling continuous current electric motors by the three wire system' which
consists in connecting one of them between the positive conductor and the ground,
which is taken as the neutral and the other between the negative conductor and
ground, and then regulating the motors simultaneously or successively, it being
understood that the ground connection is maintained at all times (wherein the
present improved system differs from any now in use) and also that the motors are
preferably connected or geared to a common load. In its more particular aspect,
however, to which reference has been made, the present consists also in a particular
combination of the two motors and especially in the fact that before making the
'change and connecting the two motors between the ground and the respective

page_text: outside lines I first shunt one of the motors and then break the connection between
it and the other, establishing a connection between that motor and the second
outside line. I do not mean however to limit myself to the use of the ground
return as a neutral by this statement of invention, for it is manifest that another
arrangement might be adopted in which some other conductor would take the place
of the ground as a neutral. In some classes of stationary work particularly this
would be preferred.
Referring now to Fig. 1, in the first position of the controller K (the two trolleys
being respectively marked T' and T', the motors, A and B, and the resistance R),
the current would enter from the trolley T' to contact 1, by cross-connection to
contact 2, through the motor A, to contact 3; by cross-connection to contact 4 and
through the motor B and the resistance R to ground, at G, being the combination
shown in the diagram a, Fig. 2, corresponding to the dotted line a upon the
controller K. The diagram b, c, d indicate the next three steps of the controller
respectively until the contact-plate 5 is reached, which short-circuits the resistance
as shown in diagram d, the intermediate steps being to cut out portions of the
resistance and thus increase the speed. At position e a shunt is thrown around the
motor B, and preferably including a part of the resistance R; the entire resistance
being in series with the motor B, but only a part of it in shunt thereto or in series
with the motor A. The path of the current in this case is from the trolley T¹ to
contact 1, to contact 2, through the motor A, contact 3, by cross-connection to
contact 4, and the resistance R to ground at G.
The second path is from the trolley T" through the contact plates 1 and 2 and
the motor A, as before, but branching out at the contact 3, it passes by the lead r
to contact-plate 9 upon the controller, thence by cross-connection to contact plate 7
and out through a part of the resistance R to ground at G. This is the shunt
around the motor B. The path through that motor is, as before, through the first
motor to contact-plate 3, thence by cross-connection to contact-plate 4, then
through the motor and through the entire resistance to ground at G.
In position of the controller, the counection between the two motors is opened
by the brushes passing off the contact-plates 3 and 4. The path through the
motor A is, however, still complete, as shown in the diagram, because the lead r is
connected by its brush to the contact-plate 9, thence by cross-connection to the
contact-plate 7, and through part of the resistance to ground. The motor B is,
however, open-circuited, because its terminals in this position are disconnected
from the trolley.
In the position 9 the motor is connected to the minus side, indicated by the
trolley T, by means of the contact-plates 10 and 11, which at this point connect
their respective brushes by means of the cross-connection. The path of the
current then is from the trolley T, through the contact-plates 1 and 2 and the
motor A and lead x, to contact-plate 9, by cross-connection to contact-plate 7,
thence through a part of the resistance to ground; and from trolley T2 to contact-
plate 10, by cross-connection to contact-plate 11, hence by the lead y through the
motor B and through the entire resistance to ground. The next two steps of the
controller are resistance steps, as indicated in the diagrams h, i, that is, the resistance.
is first partly and then completely short-circuited, so that, in the last position the
two motors are running in series between the two trolleys with an intermediate
ground connection, giving, as is well understood, five hundred volts difference of
potential between their terminals.
Having now particularly described and ascertained the nature of the said inven-
tion and in what manner the same is to be performed as communicated to me
from abroad, I declare that what I claim is :
1. The art of controlling electric motors by the three-wire system, which
consists in connecting the two motors between an outside main and the neutral,
shunting one of the motors, and then connecting the motors between the two
outside mains, preserving the connection to the neutral between the two motors.

page_text: 2. The art of controlling electric motors by the three-wire system, which
consists in connecting two motors between an outside main and the neutral, and
then connecting them between the two outside mains, preserving the connection to
the neutral between the two motors.
3. The art of controlling electric motors by, the three-wire system, which
consists in connecting the two motors between an outside main and the neutral,
with a resistance in series with the motors, cutting out the resistance, then
reinserting the resistance and shunting one of the motors, and then connecting
them respectively between the two outside mains and the neutral.
4. The art of controlling electric motors by the three-wire system, which
consists in connecting the two motors in series with a resistance between an outside
main and the neutral, then cutting out the resistance, then reinserting the resistance
and shunting one of the motors, then connecting them respectively between the two
outside mains and the neutral, and cutting out the resistance.
5. The art of controlling electric motors by the three-wire system, which
consists in connecting them in series between an outside main and the neutral, with
a resistance in series with the motors, cutting out the resistance, then reinserting
the resistance and shunting one of the motors, opening the circuit of the shunted
motor, then connecting them respectively between the outside mains and the neutral
with a resistance between the motors and the ground or neutral connection, and
then gradually cutting out the resistance.
6. A three-wire system of electric supply, motors geared to and simultaneously
driving a common load and connected one between the positive conductor and the
neutral, and the other between the negative conductor and the neutral, and means
for regulating the motors.
7. A controlling mechanism for two electric motors provided with contacts and
connections arranged to connect both the motors between an outside main and the
neutral in a series-multiple or three-wire system, and then to connect them each
upon one side of the system, between an outside main and the neutral.
8. A controlling mechanism for a number of electric motors geared to a common
load, provided with contacts and connections arranged to connect them in series
between an outside main and the neutral in a series-multiple or three-wire system,
and then to connect them each upon one side of the system, between an outside
main and the neutral.
9. In combination, a pair of motors geared to a common load, a three-wire
system of supply for the motors, and means arranged to connect one motor between
the positive conductor and the neutral, and the other between the negative
conductor and the neutral, to regulate the motors.
10. The combination of electric motors, a three-wire system of supply therefor,
and means for connecting the motors between an outside main and the neutral,
shunting part of the motors, and connecting them between the two outside mains
with a connection to the neutral between them.
11. The combination of a pair of motors, a three-wire system of supply therefor,
and means arranged to connect the motors between an outside main and the neutral,
with a resistance in series with the motors, to cut out the resistance, to reinsert the
resistance and shunt one of the motors, and then to connect them respectively
between the two outside mains aud the neutral.
1007
Dated this 5th day of October 1895.
For the Applicant,
J. C. CHAPMAN,
70, Chancery Lane, London, W.C., Chartered Patent Agent.