Improvements in Three wire Electric Railways
Year: 1895

page_text: Date of Application, 22nd Oct, 1895-Accepted 23rd Nov., 1895
COMPLETE SPECIFICATION.
Improvements in Three wire Electric Railways
I, JAMES DEVONSHIRE, Secretary of The British Thomson Houston Limiti
ol No 38 Parliment Street, Westminster, London do hereby declare the nature
of this invention (a communication to me from abroad by William B Potter,
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 tollowing statement
The present invention relates to three-nne electric railways, and has for its
object to provide a specific arrangement of conductors from which derive
advantages not heretofore obtainable with the ordinary aangement of such
10ads
As ordinarily constineted, three-we electic always have two trolley lines
serving for the plus and minus conductors, and the rails or earth return form the
Beutral of the system. In tiamway work where a single trolley is used, the out-
going and return conductors are respectively at five hundred volts positive and
negative potential, and the neutral is at zero. In long distance electric rail-roading,
at is sometimes desuable to use positive and negative conductors with two trolleys
upon each cal o locomotive, and m such cases the ground has been gencially
taken as the neutral The present system, however, differs from that I have
found that m a system in which the ground is the nential, the conducting capacity
of the neutial may be far greater than that of the feeders and hues of the positive
and negative conductors. In the case of a double-track road having the standard
steel rail construction, the conducting capacity of the rails is equivalent to five
million circular mills of copper The current flowing in the neutial is only that
due at any time to want of balance in the system, as where the motor upon one
side of the system should take a little more curient than the one upon the other.
As motors are ordinarily designed to be as nearly as possible alike in then con-
struction, these small differences tend to balance up, so that practically but very
little current will ever return to the station though the neutral The very large
canying capacity of the track is thus wasted.
In the system which forms the present invention there is employed a track
return at zero potential, a positive conductor at a thousand volts difference of
potential from the track, and a neutral intermediate conductor at hve hundred volts
above the track and below the positive conductor By this specific arrangement of
conductors it is possible to use a very small conductor for the neutral, limited in
size to that requisite to support the stiam of its suspension, the ordinary trolley
The wire
we being ample for this purpose, of number on number 1 size
might be even smaller if it were strong enough to stand the strain.
The accompany mg diawing shows in diagiam an exemplification of the present
Dvention Therein, A, B are the dynamos connected in series, as in any ordinary
three-wire system, C is the track, in this stance connected to the immus side of
the system, D is the positive conductor, and E is the neutral, F is a car travelling
upon the trach, and provided with trolleys. All of these parts are in themselves
old and well known, and no special claim is made herein for any method or mode
of control. The essence of the present invention is in employing the track as oue
side of the system, and two suspended conductors for the neutral and the other
side; but in many cases, as in the rase of elevated railway work or condit
construction, I may still employ the three-wire system, using the earth or ground

page_text: return as one side of the system, and having the nential and the other side of the
system composed of metal. Such an arrangement would be within the scope of
the present invention.
Having now particularly described and ascertained the nature of the said inven-
tion and in what manner the same is to be performed as commumcated to me
fiom abroad I declare that what I claim is
1 A three-wie electric railway system composed of two dynamos in series, a
track or ground return forming one side of the system; and metallic conductors
forming the neutral and the other side of the system.
2. A three-wire electric ailway system comprising a source of electro-motive
force, a positive conductor feiming a trolley line and one side of the system, a
neutral also forming a trolley line, and a track or ground return forming the negative
or other side of the system
3. A three-wire electric railway system comprising a divided source of electro-
motive force, a track or ground return forming a negative at zero potential, a
neutial conductor at five hundred volts positive potential, and a positive conductor
at a thousand volts positive potential.
Dated this 22nd day of October 1805