Improvements in the Distribution of Electricity by Alternate Currents.
Year: 1892

page_text: Date of Application, 19th Apr., 1892
Complete Specification Left, 18th Jan., 1893-Accepted, 25th Feb., 1893
PROVISIONAL SPECIFICATION.
Improvements in the Distribution of Electricity by Alternate
Currents.
We, WILFRID L. SPENCE, of The Elms, Seymour Grove, Manchester, Civil
Engineer, and BENJAMIN DEAKIN, Electrical Engineer of 2 Raeburn Street
The Avenue, Brixton, London, S. W., do hereby declare the nature of this inven-
tion to be as follows:-
In a well designed central electric light station, according to our view, the
arrangement should be such that the generating machines are all coupled in parallel
on to omnibus bars from which the feeding mains are tapped also in parallel. Such
a plan necessitates compensating devices in the different feeders to make up for the
varying losses of pressure. The best known method being to use regulating
transformers.
Our improved method will be best explained by taking the hypothetical case of
a station in the centre of the district of supply, having a large demand for light in
the immediate vicinity and a smaller demand in the outside districts.
In this case
we would prefer the following plan, (the generators being of the type hereafter
described):-
A three wire distributing network to be laid round the station supplying all
consumers within a radius of, say, of a mile. This system to be supplied at
200 volts by feeders direct from the alternators whose exciting coils form the only
means of adjustment.
Now as the whole plant is in parallel a certain amount of regulation in addition
will be required in the long-distance feeder circuits (which are fed at high pressure
by step-up transformers). This we get by tapping the terminal coils on the
armature at two or three points before the full number of turns is reached. Hence
we have a supply at two, three or more pressures differing from one another by the
required percentage. These points we connect to a series of multiple-way switches,
one for each feeder (or group of feeders of the same length), by which any desired
pressure may be communicated. Long feeders are given the higher pressures,
medium ones get somewhat less and the short feeders a still lower one.
It will be obvious that very little further regulation is necessary, for the load at
all points increasing and decreasing approximately at the same time, adjustment in
the alternator exciting coils for the direct supply district at once adjusts the
pressures on the distant feeders as required.
In order, however, to make sure we provide a small adjustable dead resistance or,
it may be, a choking coil in the feeder circuits.
Thus we are enabled to use similar step-up transformers for the feeders with the
attendant advantages of uniformity and interchangeability.
As ordinary alternators will not run in series, as required for our three wire
system, we build the generators with two separate armatures aud two separate fields
but all mounted together in one machine so as to be co-phasally synchronized. We
are thus able to regulate the E.M.F. of each half of our alternator independently
when the two circuits are out of balance.
We also employ this double armature alternator in all machines, whether for two
or three wire distribution, of over 200 electrical horsepower. Our reason for this
somewhat more expensive construction being the unwieldy size which a high-power
single armature alternator attains when the frequency is, say, over 60 periods per
second and the speed reasonably low, and also on account of the much greater
stability with which relatively small armatures may be built. Hence we design
each armature to give the required frequency but only one-half the output, and

page_text: then couple the two armatures in series or parallel according to the winding
adopted.
It will be understood that we do not limit ourselves to two armatures only-a
larger number may be used if desired. We would also have it understood that we
do not limit ourselves to the three wire system of distribution.
From the foregoing the drawings will be self-explanatory.
Figure 1 shows the general arrangement. N.D.N. and D.D.N. are respectively
the near and distant distributing networks, L.F. and H.F. the corresponding low
and high pressure feeders. One alternate current dynamo, A.D., is shown with the
armature coils opened out, the connections being as indicated.
The omnibus bars are shown to the number of four with a corresponding number
of points on the multiple switches M.S. V.R. is the variable resistance in the
primary circuit of the step-up transformer T.U., and T.D. is the corresponding step-
down transformer in the sub-station.
The relative length of each feeder is indicated by the position of the switch.
The other figures show several methods of obtaining different pressures from the
same alternator.
In Figure 2 the variation is got from the terminal coils. Fig. 3 shows a plan
giving E.M.Fs. differing by that due to a whole coil. Separate circuits which are
intended to be put in series with the feeder primary are shown in Figures 4 and 5,
and separate circuits throughout, one for each group of feeders of the same length
are shown in Figure 6.
Dated this 19th day of Anril 1892.
WILFRID L. SPENCE.
BENJAMIN DEAKIN.
COMPLETE SPECIFICATION.
Improvements in the Distribution of Electricity by Alternate
Currents.
We, WILFRID L. SPENCE of The Elms, Seymour Grove, Manchester, Civil
Engineer, and BENJAMIN DEAKIN of 2 Raeburn Street Brixton, London, S.W.,
Electrical Engineer 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 :-
In a well designed central station, according to our view, the arrangement should
be such that the generating machines are all coupled in parallel on to omnibus bars
from which the feeding mains are tapped also in parallel. Such a plan necessitates
compensating devices in the different feeders to make up for the varying losses of
pressure. The best known method for the purpose being the use of regulating
transformers which give slightly differing ratios of transformation according to the
length of the feeder and to the number of lamps in use on that feeder.
Our improved method will be best explained by taking the case of a station in
the centre of the district of supply having a large demand for light in the
immediate vicinity and a somewhat smaller demand in the outside districts.
In this case we would prefer the following plan (the generators being of the
type hereinafter described). A three wire distributing network to be laid round
the station to supply all consumers within a radius of say one-third of a mile.
This system to be supplied direct at 200 volts by feeders from the circuit of the
alternators whose exciting coils form the only means of adjustment. Now as the
whole plant, i.e., machines, transformers (each with its own feeder), distributing
mains and lamps is in parallel a certain amount of additional regulation will be
required in the long distance feeder circuits. This we get by tapping the terminal
coils on the armatures at two or three points before the full number of turns is
reached, Thus we have a supply at two, three or more pressures differing from one

page_text: another by one or two per cent. These points we connect to a series of multiple-
way switches, one for each feeder, by which any desired pressure may be com-
municated to that feeder. Long feeders are given the higher pressure, medium
ones get somewhat less, and the short feeders a still lower one.
This method is applicable both to the low pressure feeders and to those supplying
at a higher pressure more remote districts. A step-up transformer being used in
the latter but not in the former case. Thus it will be obvious that very little
further regulation is necessary, for the load at all points increasing and decreasing
approximately at the same time adjustment in the alternator exciting coils for the
direct supply district at once adjusts the pressure on the distant feeders as required.
In order, however, to meet extreme cases we provide a small adjustable dead
resistance or it may be a choking coil in the feeder circuits. By the combined use
of this resistance and of the multiple-way switches we are enabled to use similar
step up transformers for all the long distance feeders with attendant advantages in
the
way of uniformity and interchangeability.
As the ordinary alternator will not run in series with another similar machine we
build the generators with two separate armatures and two separate fields but all
mounted together in one machine so as to be co-phasally synchronized. We are
thus enabled to regulate the E.M.F. of each half of this alternator independently
when the two circuits are out of balance. It is convenient also to use this double
armature generator in sizes over 200 h.p. whether for two or three wire distribution
on account of the greater stability of relatively small machines.
Although we have particularly stated the type of alternator which we consider
to be most suitable we would have it understood that we make no claim to this
machine nor do we limit ourselves thereto. In all cases a single armature machine
may be employed with two transformers having their primaries in parallel and their
secondaries in series on the three wire system.
From the foregoing the drawings left with the Provisional Specification will be
self explanatory.
Figure 1 shows the general arrangement, which may be adopted in whole or in
part, applicable to a case such as that already described. N.D.N. and D.D.N.
are respectively the near and distant distributing networks, L.F. and H.F. the
corresponding low and high pressure feeders. One alternate current dynamo A.D.
is shown with the armature coils developed, the connections being as indicated.
Omnibus bars are shown to the number of four with a corresponding number of
points on the multiple-way switches M.S.V.R. is the variable resistance in the
primary circuit of the step-up transformer T.U., and T.D. is the corresponding
step-down transformer at the distributing centre. The relative lengths of the
feeders may be gathered by the position of the switch, each one being assumed
equally loaded.
The other figures show several methods of obtaining different pressures from the
same alternating generator. In Figure 2 the variation is got from the terminal
coils. Figure 3 shows a plan giving E.M.Fs. differing by that due to a whole coil.
Separate circuits which are intended to be put in series with the feeder primaries,
or with the feeders themselves on a low pressure system, are shown in Figures 4
and 5; separate circuits throughout, one for each group of feeders of the same
length being shown in Figure 6.
Having now particularly described and ascertained the nature of our said inven-
tion and in what manner the same is to be performed we declare that what we
claim is:
1. In a parallel system of electricity distribution by alternating currents at
constant potential obtaining slightly differing electro motive forces from the same
generator substantially as described.
2. In a parallel system of electricity distribution by alternating currents at
constant potential supplying different feeders each with its appropriate electro

page_text: motive force from the same generator by means of connections and multiple-way
switches substantially as described and illustrated.
3. In a parallel system of electricity distribution by alternating currents at
constant potential an alternator armature having connections and circuits substan-
tially as described and illustrated with reference to Figure 1 at A.D. and to
Figures 2, 3, 4, 5 and 6.
1000
WILFRID L. SPENCE.
BENJAMIN DEAKIN.