improvements in Systems of Electric Distribut
Year: 1895

page_text: Date of Application, 16th Apr., 1895-Accepted, 8th June, 1895
improvements in Systems of Electric Distribut
I, JAMES DEVONSHIRE, Secretary of The British Thomson-Houston Limited,
of 38 Parliament Street in the County of Middlesex, (a communication to me from
abroad by Edwin W. Rice Junior, residing at Swampscott in the County of Essex,
State of Massachusetts, United States of America), 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 :-
This invention relates to systems of distribution of electric energy, and has for its
object to overcome the differences of potential often existing in such systems where
they cover an extensive territory or where the load upon them is heavy or varies
greatly in distribution from time to time. The solution of the problem of so
distributing electric energy as to maintain uniform potential over a large area has
been attempted in various ways many of them involving disadvantages on account
of expense of installation, and others, which are wasteful of current, involving loss
in running expenses. Some of the disadvantages thus experienced are obviated by
the system which my correspondent has devised, which is briefly to distribute
continuous current over the mains by ordinary methods all of the mains of like sign
being connected as commonly practised, and to connect various points of this
extended distribution system by alternating current lines, establishing at the ends
of such lines motor-generators adapted to convert the current from alternating into
continuous. These motor generators may also be transformer motor generators,
transforming current as well as commuting it, or the transformation may be
performed in separate transformers where high potential is used in the transmission
of the alternating current, as is commonly practised, saving expense in installation.
It is also preferred to use any of the so-called "series-multiple" systems (by
preference the Edison three-wire system), but the method I employ of feeding the
distribution area is equally applicable to a two-wire system or to one involving a
multiplicity of wires."
The accompanying drawings are diagrammatic representations of the improved
system, Figure 1 showing the transmission of ordinary alternating currents, and
Figure 2 showing a modification adapted to three phase alternating current.
At A, A, are dynamo-electric machines operated by any suitable prime mover,
such as the steam engines D, D. As represented, the dynamo-electric machines
are connected to a threephase system of lines a, b, c, the middle or neutral main
being connected to the brushes to form a common return. The machines which it
is preferred have ordinary commutator connections to one side of the armature, and
from the other side connections are taken to collecting rings adapted to furnish an
alternating current.
As pointed out above, a two-wire system of distribution might be employed, and
in that case any suitable connection might be made to the direct current side of the
dynamos; for instance, they may be employed in multiple connected in the ordinary
way to the bus-bars of the station, or may be connected in series if desired. The
alternating current side of the apparatus is shown connected in multiple through
transformers to the system; but this also may be varied at the convenience of the
engineer, and the dynamos may be connected directly to the bus-bars in multiple.
These various connections are all within the scope of this invention, although
I make no special claim thereto, as I consider them rather a matter of engineering
practice than of invention.

page_text: .
At A¹ A¹ are sub-stations, of which there may be as many as occasion may
require, and within these sub-stations are motor-generators E E, preferably similar
in type to the dynamo-electric machines at the main stations A A, that is, having a
single winding upon the armature connected to collecting rings upon one side and
commutators upon the other side; like the generators, these motor generators or
rotary transformers are connected to the supply mains by the three-wire system.
The collecting rings are connected to transformers C, 'C, at the main station and
from these transformers high potential lines de, are carried to the transformers C¹ C¹
at the sub-stations, these transformers being connected to the collecting rings of the
motor generators or rotary transformers. As already indicated, the second step of
the transformation may be omitted, or rather it may be embraced in the construction
of the rotary transformers themselves, and such a construction I aim to include in
the claim.
.
In Figure 2 I have shown a system similar in all respects to that illustrated in
Figure 1, except that I have illustrated threephase connections from the dynamo-
electric machines B, B and threephase transformers at CC, the transformers being
connected by the lines d, e, f. The operation of this arrangement is substantially
identical with that shown in Figure 1.
In starting one of the sub-stations, current from the continuous current mains may
be thrown through the motor generators until they attain a speed approximating
synchronism, and then the switches FF may be thrown, connecting the afternating
mains to the transformers CC, thus operating the motor-generators by the
alternating current. In this method of starting it is important that there should
be no load or a very light load upon the motor generators, so that they may
rapidly attain speed and be driven by the alternating current. In the arrangement
shown in Figure 2, this method may or may not be employed, as the threephase
currents render the alternating motor side of the armature self-starting.
By the arrangement just described, improved economies are effected in the
construction of large plants, because instead of using a number of power stations, at
different points within the distributing system, necessitating a large outlay for land
and for the separate maintenance of so many stations, single stations inay be
employed of large capacity in situations where land is cheap, and by employing
sub-stations of small size and conveying the alternating current to them at high
potential and over 'small conductors, may maintain the current substantially equal
in distribution over the whole system, and keep the potential at a point adapted to
the operation of the translating devices on all of the mains. In many cases only
the basement floor need be used for the sub-stations, and all the upper stories of the
building may be devoted to other purposes whereas in present installations real
estate of great value must be dévoted entirely to the plant located there.
It is manifest that different machines may be employed in the central station for
the generation of the alternating and continuous corrents respectively, afthough it
is preferred to employ a machine such as has been briefly described, because of its
economy in manufacturing and its small size compared to its output, and because of
the convenience of regulation afforded in its construction. But as the leading
feature of this invention is the feeding of continuous distribution systems by the use
of a long distance transmission of alternating currents the operation of separate
machines are intended to be embraced as well as of the composite machine desèribed.
Similarly, although the ordinary single wound motor-generator or rotary trans-
former is preferred, a machine having two windings upon its armature may be
employed, or a separate alternating current motor to run a continuous current
machine furnishing currents of proper potential may even be had. Although two
motor generators are illustrated, it is manifest that only one may be employed in
some cases.
I have not illustrated the translating devices, because these may be of any
approved or convenient form, whether are or incandescent lamps or motors of one
type or another being immaterial in the practice of this invention.

page_text: Having now particularly described and ascertained the nature of my suid inven-
tion and in what manner the same is to be performed I declare that what I
claim is :-
1. The method of maintaining constant potential in the mains of an extended
system of distribution, which consists in supplying such mains at the power
stations with continuous currents, and supplying the outlying portions of the
system with continuous currents derived from alternating currents.
2. The method of operating a motor generator delivering continuous currents
derived from alternating currents to a system of distribution, which consists in
starting the motor generator by means of the continuous currents under no load or
light load, and then running such motor generator by the alternating current.
3. In a system of distribution of electric energy, central stations equipped with
sources of continuous current and with sources of alternating current, sub-stations
adapted to convert alternating current into continuous current, and alternating
current feeder lines connecting the main stations and the sub-stations together, in
combination with mains adapted to supply translating devices connected to all of
the stations, such mains being also interconnected.
4. In a system of distribution of electric energy, sources of continuous current
and of alternating current, mains covering an extended area and connected to the
sources of continuous current, alternating current lines connecting the distant parts
of the system, and means adapted to commute the alternating currents and deliver
them to the continuous current mains at a potential suitable for the translating
devices supplied thereby.
5. In a system of distribution of electric energy, a central station plant composed
of dynamo-electric machines adapted to simultaneously furnish continuous and
alternating currents, a system of mains connected directly to the continuous current
side of such dynamos, alternating current lines taking current from the alternating
side thereof, and motor generators supplied by such alternating current lines and
adapted to furnish continuous currents to the distant parts of the system.
6. In a system of distribution of electric energy, a central station plant provided
with dynamo-electric machines adapted to simultaneously generate continuous and
alternating currents, continuous current mains connected to the commutators of such
dynamo-electric machines, alternating lines connected to the collecting rings of
such machines, step-up transformers in such alternating current lines, lines leading
from step-up transformers to step-down transformers, located at a distant part of
the system, and motor-generators taking alternating current from the step-down
transformers and delivering continuous current of proper potential to the continuous
current mains.
7. In a system of distribution of electric energy, a central station plant provided
with dynamos adapted to generate continuous and alternating currents, a series-
multiple or three wire system taking continuous current from such dynamos, an
alternating current transmission, and motor generators taking current from the
alternating current transmission and delivering continuous current to the three-wire
Bystem.
8. In a system of distribution of electric energy, a central station provided with
dynamos adapted to generate continuous current and alternating current, a three-
wire system connected to the continuous current side of such dynamos, step-up
transformers connected to the alternating current side thereof, alternating current
lines leading from such step-up transformers to step-down transformers at a distant
part of the system, and motor generators adapted to take current from the step-
down transformers and deliver continuous current derived therefrom to the three-
wire system.