Transmission of Power by High Potential Direct Currents of Electricity.
Year: 1893

page_text: Date of Application, 7th Feb., 1893-Accepted, 29th Apr., 1893
COMPLETE SPECIFICATION.
Transmission of Power by High Potential Direct Currents of
Electricity.
We, CHARLES SCHENCK BRADLEY Electrician of Avon, State of New York,
RANALD TREVOR MCDONALD Manufacturer of Fort Wayne, State of Indiana,
and ROBERT STEWART TAYLOR Attorney at Law of Fort Wayne, State of
Indiana, 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 electric transmission of power over long distances by
direct currents. Transmission of power by direct currents has heretofore been
limited to short distances, for the reason that the electric potential necessary to
overcome the resistance of long lines is destructive to commutators and the
insulation of the machines could not successfully withstand high voltage, and as no
mode of dynamically generating continuous electric currents of high tension without
the use of a commutator has yet been discovered, large conductors must be used in
order to economically convey the low tension currents. The great expense of the
conductors has rendered it commercially impossible to use direct current machines
for long distances. The advantages of a direct current system in which high
potentials could be transmitted are striking in that the efficiency of both generator
and motor is very high and a very large return of the power expended at the
transmitting station could be recovered at the delivery station; and high potentials
permit the use of small line conductors without great losses. It is the object of
our invention to organize a system in which direct currents may be used and high
potentials transmitted. To that end the invention consists in placing a large
number of generators in series relation and thoroughly insulating them both from
earth and from one another and transmitting the combined electro-motive force of
all the machines to line; the invention also comprises a system in which the
generators are arranged in series at the transmitting station and highly insulated
and motors are similarly arranged at the receiving station, the generators being
driven by and the motors driving a single power shaft so that they act as a unit.
By such an arrangement the difference of potential across any pair of brushes is
only that due to the electro-motive-force developed by a single armature, and by
making this electro-motive-force of a degree which can be safely withstood by a
commutator the objectionable feature hereinbefore noted is overcome. The inven-
tion also comprises a number of generators and motors coupled in series relation,
all being highly insulated, the frames of the machines being brought to a potential
approximating that of any part of the winding so as to insure the safety of the
insulation. The invention comprises other features which will be more particularly
hereinafter described and the novelty of which will be hereinafter indicated in the
appended claims.
In the accompanying drawings which illustrate the invention,
Figure 1 illustrates a series of generators all actuated by a single shaft and
thoroughly insulated from ground and from each other;
Figure 2 illustrates a series of motors similarly arranged and all acting upon a
single driven shaft ;
Figure 3 is a diagrammatic illustration showing a mode of coupling the
generators, and the switches for cutting them out, showing also the arrangement of
the generator circuits;
Figure 4 is a diagram showing a similar arrangement for the motor station ;
Figure 5 shows in enlarged view the details of mounting the generators or

page_text: motors, the left and portion of the ngure showing a compounded machine used at
the generating station, and the right hand portion showing a simple series
machine;
Figure 6 illustrates a detail of a switch for cutting in or out the motors or
generators;
Figures 7 and 8 are further details of the switch.
As shown in the drawings fifteen generators and fifteen motors are connected in
series relation. A larger number might be used if greater electro-motive-force
were desired. Supposing that each armature delivered a current of five hundred
volts, the whole number of machines would deliver a current of seven thousand
five hundred volts. The difference of potential between the brushes of machine
No. 1 would then be five hundred volts, and the left hand brush of machine No. 2
would have a potential of five hundred volts, while the right hand brush of
machine No. 2 would have a potential of one thousand; in machine No. 4 the left
hand brush would have a potential of fifteen hundred, the right hand brush a
potential of two thousand, and so on through the series. It will thus be seen that
the difference of potential between the brushes of any generator is simply five
hundred volts, while the difference of potential of the line terminals connected
respectively with the positive brush of one terminal machine and the negative
brush of the other will be fifteen times five hundred or seven thousand five hundred
volts. The line terminals are connected with a series of motors arranged also in
series relation, so that supposing a potential of seven thousand and five hundred
volts to be delivered at the left hand brush of motor No. 1, if the counter-electro-
motive-force of its armature were five hundred volts the potential of the right
hand brush would be seven thousand, so that the drop of potential between the
brushes would be only five hundred volts; and so with the other motors of the
series, but a fractional drop of the entire electro-motive-force occurring in any
motor, which the commutator can easily be made to withstand. While such
provision enables the machines to be operated with safety to the commutator the
connections to the machines are at a very high potential, dangerous to human life
and it is necessary in order to make the system commercially feasible that means
should be provided for thoroughly insulating the system so that an attendant in
controlling or repairing the machines will be subjected to no risk of shock. To
this end each entire machine is thoroughly insulated from ground and the machines
are preferably set apart a sufficient distance so that an attendant in moving about
them can by no possibility come in contact with parts of two or more machines at
the same time. The foundation is preferably formed of glass brick cemented
together by sulphur or some other insulating and non-hydroscopic cement, forming
a highly insulated flooring which an attendant must mount before he can touch any
machine. Such a foundation is shown at. A in Figure 5. The bolts or other
anchorage devices by which the bed plates of the machines are secured in position
pass through glass insulators B anchored in the foundation walls. The glass
flooring should be given a sufficient area to prevent possibility of leakage by
reason of moisture deposited on its surface. The several machines are connected
with the common shaft with which they co-operate by insulating belts, thus providing.
against any discharge of potential between the machines except over the connecting
wire. It is very desirable to provide against breaking down the insulation of the
windings in case of accidental grounding of the frame of the machine. The frame
of each machine is therefore placed in good electric connection with one of its
brushes, as indicated at L, so that the dielectric strain on the insulation can at no
point of the winding be greater than the voltage of a single machine. In case a
ground occurs an easy path to earth will exist from a brush which will result in
blowing a line fuse but cannot disable a machine. A very important incident of
this construction is that the wire insulation need not be made higher than to
withstand the voltage of a single machine. Moreover the attendant if by accident
he touches a brush and the frame of the machine simultaneously will be affected by
the voltage of a single machine only: Each machine is provided with a number

page_text: of switches for regulating or cutting it in or out of circuit. The regulating switch
may open or short circuit the field-magnet circuit and may be mounted on the
machine, while the controlling switch is adapted to short circuit the entire machine
when it is designed to repair it or when it becomes necessary to handle the
metallic parts. This controlling switch is mounted at some distance from the
machines and highly insulated. At the generating station we prefer to use chiefly
compound-wound dynamo electric machines, thus rendering the system self-
regulating and delivering a constant potential and a current suitable to the load.
A few series-wound machines are included at the generating station in addition to
the compound-wound machines, thus tending still further to make the electro-
motive-force delivered constant. The motors are preferably all shunt wound and
provided with a switch for first opening the shunt circuit and then short circuiting
the armature, D representing the field-magnet winding and E the switch for opening
the field magnet circuit and closing the short circuit around the armature, see
Figure 4. The series generators as indicated in Figure 3, machine 14, at F, and
in Figure 5, are provided with a switch for short circuiting the field-magnet
circuits. The compound-wound generators are provided with a switch C,
see Figures 3 and 5, by which the shunt circuit on the field-magnet may be first
opened and the series coils then short circuited. In the positions shown in
Figures 3 and both the series and shunt windings are active. When the switch
is thrown the shunt winding will be opened and when it reaches the other contact
the series coils will be short circuited. The line switches as indicated in Figures 3
and 4 are mounted upon switch boards S1, S2, S3, etc., a switch lever Genabling
any motor or generator to be short circuited and switch levers H, I, permitting
both sides of the line to be entirely disconnected from the motor. The switch
board should be highly insulated and is preferably enclosed in a glass casing, as
indicated in Figures 6 and 7, a glass or other insulating stem K, K', projecting
through the glazing and being provided with handles by which the switches may
be thrown. The motors and generators are as before stated belted or otherwise
connected with a single shaft so as to equalize the effect of fluctuations in load
upon all of the machines. The battery of generators and motors will of course be
located at single terminal stations and the power delivered by the common motor
shaft may be applied to the operation of a large distribution plant, or may drive.
low tension dynamo electric machines for any desired number of distribution
We are
circuits. The battery of machines at each station thus acts as a unit.
thus enabled to raise the tension of a direct current to a point by which it may be
made to economically traverse long distances and can then be converted into power.
As the efficiency of direct current dynamo electric machines and motors may be
made ninety-six per cent.. it will be seen that excluding the heating losses in over-
coming the resistance of the line the efficiency of such a system would be ninety-
two per cent. at the motor shaft, or allowing for another conversion by means of
low tension generators and motors eighty-five per cent.
We desire to have it understood that parts of this invention as herein described
may be used without other parts; for example, although we have described the
system as composed of a certain number of generators and motors acting as units
at two stations, and co-operating with a shaft common to all of the generators or
all of the motors, it is possible to have part of the generators acted upon by one
shaft and part by another, and all of the motors act upon a common shaft, or to
have the motors act upon independent shafts. The mode herein described is
however, the preferable, when its adoption is available.
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. A system for electrically transmitting power by direct current comprising a
multiplicity of generators coupled in series relation, and highly insulated from
earth, a series of motors similarly arranged, a connecting line, and a highly

page_text: insulated flooring or platform about the machines, upon which an attendant must
stand to gain access to any machine.
2. A generating station for high tension direct current comprising a multiplicity
of generators coupled in series and highly insulated from earth, and a highly
insulated floor over which an attendant must pass to gain access to a machine, the
several machines being highly insulated from each other and spaced a sufficient
distance apart to prevent an attendant establishing accidental connection between
them.
3. A system of apparatus for generating and transmitting a direct electric
current of high electro-motive-force, comprising a multiplicity of generators
coupled in series relation and highly insulated from earth, the winding of each
generator being electrically connected with its frame.
4. A. system of apparatus for transforming a high potential direct electric current
into mechanical energy, comprising a multiplicity of motors coupled in series
relation and highly insulated from earth, the winding of each motor being
electrically connected with its frame.
5. A system of apparatus for electrically transmitting power by direct electric
current, comprising a multiplicity of generators coupled in series relation and
highly insulated from earth, the winding of each generator being electrically
connected with its frame, a multiplicity of motors in circuit with the generators,
said motors being coupled in series relation and highly insulated from earth, the
winding of each motor being electrically connected with its frame.
6. A system for electrically transmitting power by direct current comprising a
multiplicity of generators coupled in series relation and connected with a common
driving shaft, a series of motors similarly arranged, and a controlling switch for
short circuiting any machine, said switch being highly insulated and located at a
sufficient distance from any machine to prevent an attendant forming an accidental
contact between the machine and any part of the switch.
7. A battery of direct current dynamo electric machines or motors coupled in
series mounted upon a floor of glass or other insulating material, said floor
surrounding the machines for the purpose described, the several machines being
spaced a sufficient distance apart to prevent an attendant from forming an accidental
contact with any two machines simultaneously.
Dated this Seventh day of February 1893.
S. S. BROMHEAD,
97, Newgate Street, London, Agent for Applicants.