Improvements in Electric Railways Systems, Worked with Alternating Currents.
Year: 1899

page_text: Date of Application, 30th Dec., 1899-Accepted, 7th Apr., 1900
COMPLETE SPECIFICATION,
Improvements in Electric Railways Systems, Worked with
Alternating Currents.
We, THE BRITISHI THOMSON-HOUSTON COMPANY, LIMITED, of 83, Cannon Street,
in the City of London, Electrical Engineers, do hereby declare the nature of
our said 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:-
In supplying current to third rail or other electric railway systems equipped
with alternating current motors, it has been proposed to use a central generating
station, producing multiphase current of high tension, and to transmit this
current to various step-down transformers along the line of the road, and to
connect the secondaries of each transformer, or set of transformers, to the track
rails and to one or more third rails or trolley wires. Third rails are in general
preferable, as railways which it is proposed to operate by alternating current
are usually long distance, high-speed roads, owning their own right of way.
In any case, this arrangement involves either an enormous number of trans-
formers, or the transmission of current to the motors through a considerable
length of conductor. With the preferred construction, two iron third rails in
two sides of a three-phase or two-phase system, and the two track rails in
multiple in the other side, each car will receive current on the average through
a heavy iron conductor, in each leg of the circuit, of a length equal to about
one quarter of the distance between transformers, while in some positions the
path through iron will be equal to half the distance between transformers for
each leg of the circuit.
Now alternating current railways commonly employ induction motors, which
themselves have more or less self-induction, and which are particularly sensitive
to self-induction in the line. The passage of the low tension currents, neces-
sarily of some considerable volume, through any considerable length of iron,
produces an inductive drop such as to sometimes partially wipe out the impressed
voltage as the car starts, and in all cases to seriously interfere with the operation
of the motors.
This difficulty may be corrected by the use of a large number of transformers,
but this arrangement is very expensive, and introduces large losses due to the
magnetizing current, etc., of the transformer, so that in practice it cannot be
carried very far.
Even if third rails of copper or other non-magnetic material, or trolley wires
sufficiently. heavy to carry the large currents needed, should be employed, there
would still be an inductive drop in the track rails which would, with this
arrangement, seriously unbalance the system.
Obviously, each transformer in the system above set forth may be replaced
by a generating station, an "inverted rotary' or any other source of alter-
33

page_text: nating current, but the difficulties above set forth will still persist, usually in
an even greater degree.
We are able to avoid these troubles by employing only a reasonable number
of sources of current, and connecting each of them to the track rails and to
the third rails, or, speaking more generally, to the inductive conductors, at
a number of different points, by heavy leads of copper or other non-magnetic
conducting metal, preferably arranged in a triple non-inductive cable. In our
improved system, in its best form, we use one or more multiphase generating
stations, leads or feeders extending therefrom, reasonable number of step-
down transformers in multiple from the leads, and iron or steel conductors
(which are best adapted to withstand heavy strains and rough usage) connected
to the secondaries of the transformer by non-inductive cables, each secondary
feeding the line at a number of different points. In this way, we may use only
a limited number of transformers, sufficient for the most economical distribu-
tion, first cost and losses being considered, and yet reduce the maximum
inductive path through which current must pass to a mimimum.
In the drawings attached to this specification, Fig. 1 is a diagram of a railway
system, or a portion thereof, embodying our invention and Fig. 2 is a cross
section of a triple cable.
Referring more particularly to Fig. 1A is a generator or generator station
capable of supplying three-phase currents to the lines B1, B2, B3. We have shown
in this application three-phase currents, since they are particularly well adapted
to railway work, but obviously single-phase currents, two-phase currents, or
any other desired alternating currents may be employed. C, C are the track
rails of a railway system, and D¹ D2 are the third rails, or conductors, extending
along the line of the road. In order to supply current to the third rails D1, D2,
and to the track rails C, C, we carry the conductors B1, B2, B3, substantially
the whole length of the railway, and connect these conductors by feeders or
otherwise, to points at which we wish to locate the transformers T1, T2, T3, etc.
Each of these transformers is here shown as of the open-delta type, but obviously
three transformers connected in Y or in delta, or with their primaries in Y
and their secondaries in delta, or arranged in any other way to transform the
particular currents employed, may be used in place of each of the trans-
formers T1, T2, T3. The primaries of these transformers are supplied, as shown,
from the generator A through the lines B1, B2, B³. The secondaries are cach
connected at a plurality of points to the third wires D1 and D2 and to the track
rails C, C. As the best and simplest way of accomplishing this result we carry
along the line of the road three heavy conductors of non-magnetic
metal E, E, E³. These conductors are preferably arranged in a triple cable,
as shown in Fig. 2, in order to reduce their inductance as much as possible.
This cable is connected to the secondary of each of the transformers T¹, T², T³,
and is also connected to the track rails C, C, and to the third rails D1, D2 at a
number of points of conductors F, F, F.
In this way we are enabled to supply current to the car, irrespective of where
it may be located on the road, in such a way that no appreciable reactive
electromotive force shall be created outside of the motor itself.
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 combination with an electric railway equipped with alternating-
current motors, and with rails, or conductors, one or more of which is formed
of magnetic material, of one or more sources of electromotive force, and con-
nections from each of said sources of electromotive force to a plurality of points
on said wires or conductors.
2-The combination with a source of alternating currents, of lines extending
therefrom, transformers connected across said lines, an electric railway adapted

page_text: to be operated by alternating currents, and supplied with current through
supply conductors formed in part or in whole of magnetic metal, and connections
from the secondary of each of the transformers to a plurality of points on said
supply conductors.
3 The combination of a generator of alternating currents, a plurality of
transformers supplied in multiple arc therefrom, an electric railway adapted to
be operated by alternating currents and equipped with induction motors, iron
or steel supply conductors for said railway, and a non-inductive, or substan-
tially non-inductive, feeding conductor extending along the line of the road,
and connected to the secondary of each of the transformers, and connected at
a large number of points to the supply conductors.
Dated this 28th day of December 1899
THE BRITISH THOMSON-HOUSTON CO. LTD.,
ALFRED CLEMENTS,
Assistant Secretary.
A. R. MONKS,
Managing Director.