Improvements in and connected with the Transmission of Energy by Alternating Currents.
Year: 1897

page_text: Date of Application, 7th Sept., 1897--Accepted, 6th Nov., 1897
COMPLETE SPECIFICATION.
Improvements in and connected with the Transmission of Energy by
Alternating Currents.
I, CHARLES SCHENCK BRADLEY, of No. 48 High Street, Avon, in the County
of Livingston, and State of New York, United States of America, Electrical En-
gineer, 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 the removal of the difficulties experienced on long
lines conducting alternating currents of high voltage and considerable frequency.
It is well known to electrical engineers that the electrostatic capacity of such
lines causes a large idle current to flow through the generator and also on the
line, interfering with successful and economical transmission of electrical energy.
The capacity may be reduced by placing the conductors far apart, but such an
arrangement greatly increases the inductance which is very low when the con-
ductors lie close together, by reason of their mutual induction. I overcome the
difficulty by placing the outgoing and return conductor in close mutual inductive
relation, as by making them concentric or placing them close together side by
side, thereby rendering the line inductance nil or very low since this inductance
is in series relation to the circuit, whereas the capacity is in multiple arc relation,
it has no effect in neutralising said capacity, and the latter must be overcome
by other provisions in order to permit free propagation of energy over the line.
I place a series of inductances in parallel relation to one another between the
two conductors, distributing them at different points along the line, and these
inductances are so calculated that they will render the sections into which they
divide the circuit resonant with the rate of alternation of the generator. It is
known that in a circuit adjusted or tuned to electrical resonance, current is
in phase with the applied electromotive force, so that by placing inductances of
the proper value in parallel I render each section of the line resonant, and the
difficulties of idle currents and uneconomical transmission are eliminated. The
value of the inductance required to produce the proper adjustment may be deter-
mined by the following formula:
*
K. 1 =
25300
R2
in which K represents the capacity of any part or section of the line, 1 the
required inductance and R the rate of alternation of the generator. Suppose for
example that we have a line 100 miles in length, and we divide it into three mile
sections, and suppose the rate of alternation of the generator to be 60 cycles
per second, the line then might have a capacity of 1/3 of a microfarad per mile:
each section having a capacity of one microfarad can be rendered resonant, or
completely balanced, by placing across the line at the middle of each section an
inductance of 7 1/36 henrys as derived from the above formula. The line, leaving
aside the inductance of generators and transformers, which is rory
small

page_text: It has been proposed to transmit speech telegraphically throught an ocean cable
by interpolating inductances at definite intervals between the outgoing and
return conductors: with such an organization, however, the result aimed at and
attained by me are impossible: the rates of vibration due to speech are widely
different for the different parts of speech both in the fundamental sounds and in
the overtones which determine their quality or timbre, so that any adjustment
which would be resonant for one would be far from resonance for others, and it
would be impossible to render the line resonant at all: thus some would pass
freely, and others would be greatly obstructed or almost entirely shut off: in my
system however there is but a single rate and the line may be easily adjusted to
reasonance with that rate. The best results are attained when the several sections
of the line are adjusted for perfect resonance with a definite rate and that rate is
maintained uniform in service: it must be understood, however, that a responsive
vibration of the line to the alternations of the generator will take place over a
small range of variation from the resonant rate, so that if the generator varies
somewhat in speed, practical though not the most perfect results may be attained.
My invention comprises an alternating system of transmitting energy for
whatever application said transmission may be intended, comprising a generator
of practically uniform rate of alternation, and a line in which the capacity-induct-
ance product is adjusted for substantial resonance with that rate: it comprises
also a line rendered sectionally resonant by making a plurality of sections resonant
to the rate of the generator: it comprises also other features more or less generic
which will be hereinafter more fully described and will be definitely indicated
in the claims.
In the accompanying drawings which illustrate diagrammatically my inven-
tion, A is an alternating current generator and 1, 2, a circuit for transmitting
the energy developed by said generator over a long distance. B is a terminal
plant supplied by the generator, and C and D are intermediate plants which may
be supplied. The consumption circuits may be directly or indirectly supplied
from the line, and may contain translating devices of any character which may
be operated or controlled by periodic currents. The conductors 1, 2 are placed
close together and may be made concentric with an intervening tube of insulating
material, such a disposition will reduce the inductance to almost nothing, so that
currents may be propagated with almost no drop of electromotive force resulting
from inductance. As current in the two conductors is in opposite directions, one
carrying outgoing and the other return current, the induced electromotive forces
oppose one another, so that the inductance is obliterated. E. E and E* are
inductances, which may be made of wire wound on a laminated core of iron. The
terminals of each coil are connected with the line conductors.
As an example of the economy of a system organized in accordance with my
invention, let us assume it to be required to transmit 400 kilowatts over a line 100
miles in length at a voltage of 30,000 and at 60 alternations per second. Sup-
pose the line is formed of two No. 4 copper wires, supported on poles and 12 inches
from each other. The resistance of the lines (200 miles) would be 260 ohms.
The inductance of a loop 12 inches wide 100 miles long would be :3 henry. The
current necessary at 30,000 volts to give 400 kilowatts is 13.3 amperes. The
drop due to resistance alone is 3460 volts; the drop due to resistance and in-
ductance is 3800 volts; or a little over 12 per cent. The capacity of the lines
for 100 miles is 1.26 microfarad; the capacity. per mile is therefore 0126 micro-
farad. The total amount of charging current that would flow into the con-
ductors from the generating end would be 14 amperes. 14 multiplied by 30,000
or 420 kilowatts represents the apparent energy flowing in and out of the lines
when they are open at the further end. The loss due to heating by this
14 amperes can easily be found; the effect would be practically the same as if a
condenser of 1.26 microfarad be placed 50 miles from the station. The loss
would then be that due to 14 amperes for 100 miles. The resistance for
100 miles is 130 ohms; therefore CR equals (14)³ 130 equals 25,480 watts or in

page_text: round numbers 25.5 kilowatts. Therefore at no load 420 kilowatts apparent
energy leaves the station and causes 25 kilowatts of heating on the lines, giving
a power factor of 6 per cent. At full load, that is to say 400 kilowatts at the
receiving end, 450 kilowatts (real) must leave the station to get 400 at the
receiving end, due to legitimate losses-25 kilowatts (real) to heat the lines, and
420 kilowatts (idle) to change the lines. Combining these vectorially, as 420 kilo-
watts is wattless, gives 635 kilowatts as the necessary capacity of generators
to supply 400 kilowatts at the receiving end, giving a power factor of 70 per
cent.
Now let us assume the same case, all conditions remaining the same except
that the system is made sectionally resonant by placing inductances across the
lines at distributed points. The inductances must be so planned that they will
be in resonance with the capacity of that section of the line in which they are
placed for the given frequency. Let us suppose they are placed every three
miles. The capacity of three miles is 0378 microfarad; the inductance necessary
25,300
to produce resonance is
[frequency (60) and K the capacity (0378)]
or 183 henrys, which will admit 43 ampere at 30,000 volts. By using No. 22
or No. 23 wire, a calculation will show that to give the required inductance
about 30 pounds of wire and 50 pounds of iron must be employed. Since 33 in-
ductances must be employed, one for each section, the total weight of wire
will be 990 pounds and of iron 1650 pounds. The loss in copper of all 33 is
2750 watts and the loss in iron 4356 watts or a total loss of 7106 watts in the in-
ductances. The current to supply this loss sent from the generating station would
be 8.5 watts. The 43 ampere flowing through the inductances 21 from each
side along the line also causes a slight loss of 6 watts. Hence 7120.5 watts or
about 7 1/8th kilowatts supplied from the station will when the system is made
sectionally resonant avoid 25 kilowatts of loss on the lines and 420 kilo-
watts apparent at the generating end which would be necessary were no pre-
cautions taken. The power factor would be nearly 100 per cent. At full load
as before we have 450 kilowatts necessary to give 400 kilowatts at the distant
station with 12 per cent. drop and 7 kilowatts to supply inductances, thus making
the required capacity of the generator 457 kilowatts as against 635 kilowatts in
the first case; that is to say the generator might be less than three fourths as
large. With lines possessing more capacity, such as underground systems of con-
centric conductors, the saving would be a great deal more.
Two other very important functions of the inductances placed in my system
are, that by keeping idle currents off the line they improve the regulation of the
system, getting rid of all drops in voltage caused by these currents; and they
prevent the formation of high local voltages at points along the line which are
liable to break down the insulation. The resulting advantages of decreased
size of apparatus applies not only to the generator but also to the transformers. The
great apparent energy at no load is almost as much of a disadvantage at the
generating end as if it were real energy, as the heat losses, the strains on the
machines, insulation, etc., are just as great. In fact this enormous load would
make transmission over the supposed line at 60 alternations per second almost
prohibitive by the ordinary plan, and a much lower frequency would have to be
employed requiring heavier and more expensive apparatus and thus interfering
with a successful operation of lamps by reason of flickering.
Having now particularly described and ascertained the nature of my said
invention, and in what manner the same is to be performed, I declare that what
I claim is:-
1. As a means for transmitting periodic currents of uniform rate, a generator
of definite frequency, and a circuit containing a plurality of inductances in
multiple arc, said inductances being proportioned to render the line resonant
with the periodic electromotive force.

page_text: 2. A system of transmission for alternating currents comprising an alternating
current generator of definite fundamental rate, and a circuit containing in-
ductances connected in parallel at intervals, said inductances being proportioned
to produce resonance of the circuit with the generator.
Dated this 6th day of September AD 1897.