IMPROVEMENTS RELATING TO THE ELECTRIC, MAINS EMPLOYED IN DISTRICT LIGHTING
Year: 1884

page_text: I JAMES EDWARD HENRY GORDON of 28 Collingham Place Kensington in the
County of Middlesex Electrical Engineer, do hereby declare the nature of my
Invention for "IMPROVEMENTS RELATING TO THE ELECTRIC, MAINS EMPLOYED IN
DISTRICT LIGHTING" and in what manner the same is to be performed to be
particularly described and ascertained in and by the following statement :-...
This Invention has for its object improvements relating to the electric mains
employed in district lighting.
In district lighting it is important that the electro motive force at each lamp
should be always constant. It is obvious that the electro motive force at points
distant from the dynamo must always be less than at the dynamo itself. The
amount of difference depends upon the relative horse powers expended in the
lamps at the distant points and in the mains respectively. If the number of lamps
at a distant point were always constant then the electro motive force at that
distant point would be a definite number of volts less than the constant electro
motive force at the dynamo. But it occurs that in practice the number of lamps
alight at any distant point are constantly varying and it is the case that as the
Dumber of lamps (in parallel circuit) at a distant point is decreased the electro
motive force at that distant point approaches more and more closely the electro
motive force of the dynamo. If there were only one distant point being fed from
the dynamo this change would cause no difficulty as the electro motive force at
the dynamo could be varied so as to keep the electro motive force at the distant
point always constant. When however two or more distant points are being fed
from the same dynamo as indicated in Figure 1 then it may happen that the full
number of lamps are being used at one distant point (a) and only a fow at the
other distant point (3). If in this case the electro motive force of the dynamo
is adjusted to give the required electro motive force at the first point (a) then the
electro motive force at the other point (B) will be too high and will cause breakage
of lamps, or if on the other hand the electro motive force at the dynamo be
adjusted so as to make the electro motive force at ẞ right then the electro motive
force at a will be too low and the lamps there will burn dimly.
This difficulty has hitherto been partially met by making the conductors which
we may call the "feeders" which lead from the dynamo to the distant points of

page_text: '
very great thickness. The objection to this method is first the great expense of
the copper required and secondly the fact that even with thick conductors it is
only partially successful. (It will be understood that we are assuming the lamps
in different outlying districts, to be supplied by mains or feeders which lead from
the dynamo to a point within each of the outlying districts respectively. These
points are the "distant points" of which we have been speaking from each of these
comparatively short thick conductors radiate to the lamps or groups of lamps in its
district. This method of arrangement is a matter of common knowledge).
My improvements which are illustrated diagrammatically by Figure 2 consist in
making each of these feeders, not of one large cable but of a number of smaller
ones placed side by side, they are permanently connected together into one at the
distant point. Connection to the dynamo pole is made through a plug board or
other suitable apparatus by means of which the cables can be disconnected one by
one and the disconnected ones left idle.
When one or more are disconnected the resistance of the feeding main is of
course increased and the difference of electro motive force between its ends is thereby
increased and therefore if the electro motive force of the dynamo is kept constant,
the disconnecting of some of the cables which go to form the compound main will
reduce the electro motive force at the distant point.
In practice as the lamps fed from the distant point are turned out and so the
total lamp resistance at the distant point increased some of the component cables
of the feeding main will be disconnected one by one until the electro motion force
at the distance point is reduced to the same value which it had when all the lamps
were on, it being understood that the electro motive force at the dynamo is as a
rule kept constant. In order to ascertain when cables require disconnecting a pair
of light wires are brought back from the distant point to the dynamo room or to
a convenient regulating room near it and attached to a voltmeter of any suitable
construction placed there.
•
In practice it will be found convenient to have the number of cables in the
positive and in the negative compound mains respectively each equal to the
difference in the number of volts between the potential at the dynamo and at the
distant point when all the lamps are on. This will enable the electro motive force
at the distant point to be varied in steps of about half a volt each. This
particular proportion is however not essential but is mentioned to indicate one
convenient proportion.
The regulation i.e. the cutting out or the re-inserting of feeding cables may either
be done by an attendant who watches the valtmeter and shifts levers or plugs etc.
accordingly or it may be done by automatic apparatus actuated or controlled by
the voltmeter One of the leads of the main say the positive may be a single cable
and the subdivision described above may be applied to the other one only or both
the positive and negative leads may be subdivided. In the latter case the discon-
nection of cables may be made either in the positive or negative lead or in both.
In Figure 2 only one of these leads is indicated. The. regulation might of course
be done at the distant point instead of in the dynamo room by connecting the
cables permanently at the dynamo or by placing the disconnecting apparatus at
the distant point but it would probably be always most convenient to do it from
the dynamo room.
By the use of this method a very great constancy of electro motive force may be
obtained and it is not necessary that the total section of the main should be great
because it is only necessary to have it of such a size that it shall neither beat
unduly nor waste any undue quantity of horse power--it is no longer necessary as
heretofore to have it large enough to keep the difference of electro motive force at
its two ends very small as is the case when a single cable is used.
With arrangements made in accordance with this Invention there is no objection
to having even this considerable difference of potential between the dynamo and
the distant point because by the use of the Invention that difference is kept always
constant. It is also unnecessary to have the same electromotive force at various

page_text: distant points fed from the same dynamo it being remembered that if different
electro inotive forces are used for different points then different incandescent lamps
have to be used at those points respectively.
When alternating currents are used the arrangement adopted for the purposes of
this Invention may be farther utilized for the dimunition of the self induction and
of the induction in neighboring telegraph or other wires as the small cables forming
the positive main and those forming the negative main may be mixed together in
one trough pipe or bundle and the self induction and external induction will then
be less than it could be when the positive and negative main were earth or single
cable however close to each other they might be laid.
Having now particularly described and ascertained the nature of my said
Invention and in what manner the same is to be performed I declare what
I claim is
In an electrically lighted district in which the lamps are supplied from two or
more centres each in its turn supplied by a feeding main coming from the same
dynamo (or system of connected dynamos) my improved arrangements for keeping
the electro motive force at each centre unchanged in spite of changes in the number
of lamps supplied from it by making each main consist not of one large cable but
of several smaller ones and providing also apparatus for disconnecting these cables
as required substantially as herein described.