Improvements in Systems of Distribution of Electricity.
Year: 1896

page_text: Date of Application, 15th June, 1897-Accepted, 24th July, 1897
COMPLETE SPECIFICATION.
Improvements in Systems of Distribution of Electricity.
We, THE BRITISH THOMSON-HOUSTON COMPANY, LIMITED, of 83, Cannon Street,
in the City of London, Electrical Engineers, do hereby declare the nature of this
invention (which has been communicated to us from abroad by Edwin W. Rice,
Junior, of Schenectady, in the county of Schenectady, 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 systems of distribution of electricity, particularly to
those of the three-wire type, in which a plurality of sources of electro-motive force
are connected in series, with a neutral wire running from the intermediate con-
nection, as in various well-known systems. The particular adaptation of our
improved system which we hereinafter illustrate and describe is to an electric
railway having peculiar features. We do not however mean to exclude its appli-
cation to other systems, as it might be used under some circumstances; but its
most extended application will be found in electric railways.
In a three-wire system as applied to electric railways, (for example, as illustrated
and described in the Patent to James Devonshire (W. B. Potter) No. 19861 dated
October, 1895) it is sometimes desirable to divide up the road into sections, some
of which are operated on the two-wire system; for instance, in suburban or inter-
urban traffic the three-wire system as described in that patent would be employed,
but where the road was extended within municipal limits, it would be more
convenient to operate by the two-wire or single trolley system, and avoid the com-
plications of numerous wires in the overhead structure, where two trolleys were
used. In such a system it will be most convenient ordinarily to put the divided
source of electro-motive force in some place where land is cheap and the station
can be conveniently enlarged from time to time. This being the case, there would
necessarily be a drop in voltage between the station and city lines. It is the object
of the present invention to compensate for the drop in voltage between the station
and the two-wire part of the line, and at the same time to reduce the unbalancing
of the system so that as the load increases, the percentage of unbalancing becomes
less.
To this end we have devised the present method and apparatus for effecting
the proper distribution of load in such a system as that which we have indicated;
the method consisting briefly, in feeding the two-wire part of the line from both
sides of the three-wire system, for which purpose we prefer a combination of
apparatus such as is indicated diagramatically in the accompanying drawing, which
represents a three-wire system and a two-wire extension thereof, supplied with
current at proper potential from both sides of the three-wire system.
Referring by letter, A, A' are two generators connected in series, supplying
the mains a, b, c with current, these being respectively the positive, neutral and
negative lines of the system; it, being understood that in the case illustrated
the ordinary railway potentials would be used and that the neutral wire would be
intermediate between the positive and negative, as is customary. The three-wire
part of the system extends as far as the section insulator D, shown in the positive

page_text: wire. Upon this part of the system a double-trolley railway car E is diagram-
matically indicated, making travelling contact with both sides. Upon the two-
wire part of the system beyond the insulator D, a tram car E having a single
trolley is shown, the other trolley being held down out of engagement with the
wire.
It is of course immaterial what form of car is used, as a separate system
of tram cars suited for street travel may be operated within the city and long
distance trains of larger cars run without.
So far the description of our invention.conforms substantially to that in the
patent already referred to. The improved means which we have provided for
feeding the two-wire system, as illustrated, consists of two dynamo electric
machines (using the term in its general sense), B and C. B. is a shunt wound
machine or motor coupled between the negative wire c and the neutral and having
a resistance R in its field magnet circuit to determine its output. Upon the same
.shaft is fixed the armature of the series machine C, the field magnet of
this machine being, as is understood, in series with its armature, and the
machine itself being in series in the main a: the feeder passing
from this main to the two-wire part of the system upon the other side
of the insulator D. By adjusting the resistance R, the effect of the com-
bination of machines just described may be determined so as to supply the two-wire
part of the system with current at any desired potential necessary to compensate
for the drop; and as will be observed, the two armatures being connected together,
the machines are run from both sides of the system, the current passing from
machine A through the series machine, and being raised in potential, the series
machine acting as a "booster" in well-known ways, while part of the work
necessary to perform this operation is done by the shunt motor B, which operates
upon the side of the system supplied by the machine A.
A feature of our invention is that the two-wire part of the line may be operated
at any desired potential, the combination of machines being adjusted to suit
required conditions; the potential might be higher or lower than the three-wire
portion of the system, and the load would divide, as herein pointed out.
If the machines be located in the power house or near the generators, they
tend to assist the compounding, as the speed of the shunt motor is proportional
to the potential at its terminals; when the load rises, the potential also rises
(from the usual over-compounding of the main generators), thus accelerating the
motor, which in turn speeds up the booster, raising the voltage in accordance
with well-known principles.
Having now particularly described and ascertained the nature of our said in-
vention (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 method of maintaining potential upon a two-wire system of distribution
connected with a three-wire system, which consists in supplying the two-wire
system with energy from both sides of the three-wire system.
2. In a system of distribution, a divided source of electro-motive force, positive,
negative and neutral wires, forming a three-wire system, a two-wire distribution,
and means interposed between the systems for supplying the two wire system with
energy from both sides of the three-wire system.
3. In a system of distribution, a divided source of electro-motive force, positive,
negative and neutral mains forming a three-wire system, a pair of dynamo electric
machines connected one on one side of the system, the other upon the other side,
and a two-wire system connected with the three-wire through the dynamo electric
machines; whereby the energy supplied to the two-wire system is derived from
both sides of the three-wire.
4. In a system of distribution, a three-wire system, a two-wire system, a booster
in one side of the three-wire system supplying current to the two-wire distribution,
'and a motor in the other side of the three-wire system, the motor driving the
booster.

page_text: 5. A three-wire distribution, a two-wire system connected therewith, a series
machine in one side of the three-wire system feeding the two-wire distribution,
an a motor in the other side of the system driving the series machine.
6. A three-wire distribution, a two-wire system connected therewith, a dynamo
electric machine in one side of the three-wire system feeding the two-wire dis-
tribution, a motor in the other side of the system mechanically connected with and
driving the dynamo, and means for regulating the output of the machines.
UNIS
Jou may
1001.
For the Applicants,
J. C. CHAPMAN,
70 Chancery Lane, London, W.C., Chartered Patent Agent.