Improvements relating to the Regulation of Alternating Current Electric Motors in Electric Railway and other Systems.
Year: 1896

page_text: Date of Application, 14th Apr., 196-4ccepted, 13th June, 1395
COMPLETE SPECIFICATION.
Improvements relating to the Regulation of Alternating Current
Electric Motors in Electric Railway and other Systems.
I, JAMES DEVONSHIRE, Secretary of the British Thomson-Houston Limited,
of 38 Parliament Street, Westminster, London (a communication from abroad by
Charles P. Steinmetz, Electrical Engineer, and Ernst J. Berg, Electrical
Engineer, both of Schenectady in the State of New York and 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 :-
This invention relates to the regulating of alternating electric current motors
used in electric railway and other systems, and particularly to those of the
induction type. The special class of apparatus which I design to regulate by the
invention herein described is induction motors running upon single phase circuits,
and to this end I employ multiphase motors of one type or another, preferably
those of three-phase type, but they are so connected to the single phase circuit as
to run with much larger output and efficiency than by any other method of
operation with which we are familiar; and they are also readily started and run
up to speed by the devices which we have originated, and after attaining their
speed the increased efficiency just referred to is obtained.
It is well known that an ordinary three-phase or two-phase (or, in general, any
poly-phase) motor may be connected to a single phase circuit, and when so
connected will, after it has been run up to synchronism or approximately so,
operate satisfactorily as a motor; but its output in this method of connection is
limited. Ordinarily with a three-phase motor but two of the terminals of the
inducing member or field are connected to line, and this employs therefore in
producing the alternating field only two of the sets of coils which make up the
field-magnet of the motor. Thus the winding of the third coil is wasted. There
is also no starting effect in such a motor, but it must be started mechanically
before the load is put on. The output of motors run in this way is small compared
to that which it is possible to obtain from them as multiphase motors.
By my invention I connect all three terminals of the inducing member to line;
or, to speak more accurately, I connect them to three lines leading from trans-
former secondaries, the primaries of two ordinary transformers being connected in
series between the lines leading from the generator; the secondaries are similarly
connected, but one of these is reversed, and from the point of junction of the two
secondaries the third line is run. To the three lines thus disposed the terminals of
the inducing member or field of the motor are connected. After the motor has
been started with such an arrangement, the single-phase electro-motive-forces are
split by the motor, as more particularly described hereafter, so that the motor
operates approximately as a three-phase motor in the particular arrangement
described; for which could be substituted of course, arrangements adapted to act
as two-phase motors or other polyphase apparatus, as will be manifest to those
skilled in the art.
The drawings accompanying this specification show diagrammatically embodi-
ments of my invention. In these,
Fig. 1 is a diagram showing a three-phase motor connected as just briefly
described; Fig. 2 is a similar diagram showing the means which I have devised for
starting the motor.

page_text: Fig. 3 is a diagram illustrating the combination of apparatus by which single
phase electric railways may be operated by my invention.
A is a generator of single-phase alternating current; a, b are the leads leading
therefrom; C shows the primaries of two transformers connected in series across
the mains; D, D' are the secondaries of these transformers, D' being shown in
reversed relation, as already explained. M is a three-phase motor, of which the
inducing coils are E, E, E; F being its armature.
In Fig. 2 the same parts are similarly lettered, but in this figure I show the
means for starting the motors. In the particular case illustrated this means is
applied to the primaries of the transformer, and this would be the arrangement
where three wires could be conveniently run; as in a mill or factory or other
place; in which case a single phase transmission might be employed and all of the
motors would be supplied with starting current from the means illustrated, which
would, however, ordinarily be cut out after any one of the motors was started,
as in accordance with well known principles such motor would furnish an out-
of-phase electro-motive force adapted to start any of the others. The particular
means which we show consists of a resistance B, and a reactance or inductance B';
the third line (which might represent the teaser of the monocyclic system), is
connected to a neutral point between the reactance and the resistance. Switches S, S¹
are employed, by which the apparatus may be cut out after it has fulfilled its
function of starting one or more of the motors.
In the case of electric railways, however, a different method is desirable. One
great cause of the present success of trolley railways of various types is their
simplicity of wiring, requiring only a single wire above each track, a single
travelling contact, and making direct connection with the track or ground return.
This has been an obstacle in the way of alternating current railways, inasmuch as
three-phase or other self starting roads require a multiplicity of aërial conductors.
By my invention I am, however, enabled as will be apparent, to operate electric
tram cars upon a single-phase system, such cars which are ordinarily not self-
starting being by the arrangements which I have pointed out readily started and
operated, the motors giving good results in output, torque and speed. Single-
phase motors have been impracticable because as already stated, they are not
self-starting, and cannot ordinarily be made so except at very considerable loss of
efficiency and by the use of auxiliary devices, which are in many cases, clumsy and
impracticable.
The arrangement illustrated in Fig. 3 I believe to have special advantages in
accomplishing the ends just pointed out. In that the parts are, as indicated by the
same reference letters, substantially like those of the other figures, a, b representing
the trolley line and the ground return. The car is shown in dotted lines for
clearness of illustration, and is provided with an ordinary trolley. In this case the
switches S, S¹ would be, in the operation of the vehicle, closed until the start had
been effected, and could then be opened and the motors run directly between the
two lines. They are shown connected in multiple, but no particular form of
connection is imperative, and any desirable form of controlling apparatus may be
employed.
An alternative means of furnishing the starting effect necessary in electric
railways is also illustrated in this figure, and consists of a small induction motor,
which, as it is designed to run idle, may be adapted for high speed. This is
illustrated diagrammatically at M2. This motor may be started in any convenient
way, and may. if desired, be started before the car leaves the car house, and the
current is then left on so that the motor constantly runs and furnishes for the
main driving motors M, M' the out-of-phase electro-motive force necessary to
start it.
I believe that the theory of my invention may be briefly stated in ordinary
language as follows: In the three-phase induction motors employed as illustrations
an ordinary field magnet winding is used and the armature of the motor has a
regular three-phase or other suitable winding, which cuts the flux induced by the

page_text: single phase current in the field, each phase of the armature generating a certain
counter electro-motive force. The reaction between the armature electro-motive
force and the impressed single phase electro-motive force displaces the electro-
motive forces at the terminals of the field winding from one another, and
consequently the tendency of the motor is to displace or split the electro-motive
force impressed upon it. If the motor be supplied with single phase current from
one transformer only, there is no possibility of splitting the single phase in this
way, as all the coils are threaded by the same flux; but by employing transformers
connected in the way described in my invention, one being reversed relatively to
the other, the counter electro-motive forces of the motor change the voltages at
the terminals of the transformer by reflection, and this impresses on the motor
itself electro-motive forces of different phase relations tending to increase its
output. As an example, without attempting to state accurately the ratios, I may
say, when the armature is standing still the potentials between the terminals GHI
would be as follows:
G, H 100 volts; I G 100 volts; HI. 0.
As the motor runs up to speed, the voltage between HI becomes larger and
larger, and at full load becomes practically equal to the other voltages, giving a
condition substantially like the three-phase or quarter-phase systems. This
displaced voltage, however, existing only when the motor is running, it cannot be
used to start it, and the starting devices which we have illustrated and described,
or some other means of supplying displaced electro-motive forces to the motor
become necessary.
Nothing in my invention limits me to the use of induction motors, as it will be
manifest that similar effects and advantages may be obtained by the use of multi-
phase synchronous motors. I have therefore illustrated in Fig. 2 both an
induction motor and a synchronous motor M³ running upon the same circuits.
The same advantages of this construction as in the case of the railway car may be
realized in an installation comprising a number of motors, where ordinarily the
starting appliance of our invention would be used at the beginning of the day's
labor or after the noon hour, and as soon as one or more of the motors has been
brought up approximately to speed, it would be cut out; reliance being had for
the starting of other motors upon those already operating, and upon the fact of one
or more motors being always in operation in every large establishment.
In the claims appended hereto 1 have spoken of a connection from the junction
of the reactance and resistance to the motors. It is manifest that this connection
may be direct, as in Fig. 3, where the reactance and resistance are in the
secondary lines, or it may be indirect, or inductive, as in Fig. 2 where they are
included in the primaries; and the starting effect will be equally efficient.
Having now particularly described and ascertained the nature of the said
invention and in what manner the same is to be performed as communicated
to me from abroad I declare that what I claim is :
1. In combination, lines between which single-phase electro-motive force is
maintained, transformers having their primaries connected in series between such
lines and having a secondary in reversed relation to the remaining secondaries of
the transformers, lines leading from the secondaries, and a multiphase motor
connected to such lines.
2. In combination, lines between which single-phase electro-motive force is
maintained, a pair of transformers having their primaries connected in series
between the mains, and their secondaries in reversed relation to one another, lines
leading from the terminals of the secondaries and their junction and a three-phase
motor connected between such lines.
3. In combination, lines between which single-phase electro-motive force is
maintained, transformers connected in series across such lines and having their
secondaries in reversed relation to each other, a reactance and resistance connected

page_text: between the lines, lines leading from the secondaries to a motor or motors and a
connection between the junction of the reactance and resistance and the motor.
4. In combination, a single-phase electric railway comprising outgoing and
return conductors, a travelling vehicle making contact with such conductors, trans-
formers upon the vehicle having their primaries connected in series and their
secondaries in reversed relation to one another, and poly-phase motors taking
current from the transformers.
5. A single-phase electric railway comprising outgoing and return conductors, a
vehicle making travelling contact therewith, transformers carried upon the vehicle
and having their primaries connected in series between the conductors, and their
secondaries in reversed relation, polyphase electric motors taking current from
such secondaries, and means for splitting the phase supplied to the motors.
6. A single-phase electric railway comprising outgoing and return conductors, a
vehicle making travelling contact therewith, transformers having their primaries in
series between the conductors, and their secondaries in reversed relation to each
other, a reactance and resistance connected between the lines, and a connection
from the junction of the reactance and resistance to the motors.
Dated this 14th day of Anil 1906
For the Applicant,
J. C. CHAPMAN,
70 Chancery Lane, London, W.C., Chartered Patent Agent.