Note: Descriptions are shown in the official language in which they were submitted.
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The invention relates to high--tension overhead lines
and, in particular, to methods of increasing the power handling
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capacity and economy thereof.
.. Conventional overhead lines cannot be operated above alimiting temperature of about 40~, and consequently cannot be
overloaded by the power to be transmitted, on account of the
d need to avoid excessive sagging brought about the thermal
expansion of stretches suspended between supportin~ towers.
Although such overhead lines, which usually consist of materials
of high coefficient of thermal expansion, are loaded beyond
- their "natural" or surge impedance, this can only be done up to the limit of their thermal capacity.
A further drawback of a conventional overhead line
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resides in the fact that the electric current heat losses
inseparable from power transmission are dissipated in the
_ surrounding atmosphere and can therefore no longer be made use
of. The continually increasing need for energy gives rise
however to the requirement for high power transmission over long
~ distances, which can no longer be met by the conventional
overhead lines.
An object of the invention is to enable transmission
-. of a high power energy level exceeding the power handling
capacity of conventional overhead lines to be obtained,
whilst at the same time increasing the economy of power trans-
mission b~ overhead lines.
The present invention consists in a method of
increasing the power handling capacity and the economy
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of a high-tension overhead line, in which a coolant is passed
through the overhead line so as to remove a substantial portion
of the heat dissipated therein, the heat removed by the coolant
being usefully employed.
Owing to the coolant flowing through the overhead
line the power handling capacity thereof can be increased to a
multiple of the previous level, without the risk of any expansion
beyond the prohibited limiting value~ At the same -time the
economy of such an installation is increased by a not inconsid-
erable amount owing to the fact that the heat taken up by thecoolant is employed for a useful purpose. It has been found to
be particularly advantageous to use a liquid coolant, and
particularly water, since liquids in general have better heat
transfer characteristics and particularly a higher heat
absorbing capacity than vapours or gases, and water not only
_ ~ possesses the requisite properties but in addition is easily
accessible everywhere and i5 particularly cheap. ~evertheless
it may be of advantage in special circumstances to use gases or
vapours as the coolant, and particularly such as have vapour-
izing temperatures which lie within the operational range of the
overhead line, such as for example that supplied under the
trademark Freon-12 (C C12 F2).
The coolant may be supplied to or taken from the high-
tension overhead line at intervals of at least 5 kilometres, is
fed to a consumer installation, for
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example a heating plant, is cooled do~n therein and
then passed on to the next stretch of overhead line.
~he coolant may be supplied or withdrawn in this
manner through earthed connecting lines, which are
- 5 suitably insulated from the conductor itself, so that
there is no risk of any appreciable current flow to
earth. The spaclng apart of the feed and take off
points of -the coolant may be selected having regard to
the effective utilization of the hea-t and can be a
multiple of the specified value, provided always that
the particular coolant flow rate selected and therefore
~ the velocity~ pressure thereof is so adapted to the
- prevailing conditions that the thermal limits of the
coolant, and therefore the permissible sag of th0 line,
are not exceeded and that inadequate heating up of the
coolant, which would nullif`y the economy of the heat
utilization plar-t, is avoided~
~he invention also consists in a high-tension over~
head line for carryi~g out the method according to the
i~ention, comprising ~or the passage of coolant
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di~posed within a flexible or ~endable electric
conductor. It is of vital i~!portance to the practical
usefullness of the conductor that the latter should
~ be sufficiently flexible, i~9. that considerable
! 25 length thereof must be adapted after manufacture to be
wo-~nd onto a drum for the purpose of transport to -the
assembly site where it can be unwound again without
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damage, which procedure must if necessary be capable
of being repeated several times, for example during
subsequent alterations to the stretch of cable. It
must moreover be capable of withstandin~ the not
inconsiderable bending and tensile stresses due to
its o~ weight and to sagging which are set up during
assembly and in operation, and also due to the forces
acting externally thereon.
In a preferred embodime~t of the overhead line the
duct comprises a thin-walled flexible pipe of corrosion-
and erosion-resistant material, for example of
stainless steel or the like or of a plastics material
having a high resistance to abrasion, said duct being
surrounded by the electrical conductor. In this
connection the flexibility of the overhead line for
the purpose of tra~sport on a drum is ensured both by
suitable dimensioning of the electrical conductor and
in particular to the duct having regard to the
mechanical strength of the materials employed, so that
; 20 both the resistance to abrasion a~d the stability to
corrosion of the material selected for the duct are
of special and vital importarr,e to the useful life
of the overhead line.
Preferably the electrical condùctor consists at least
partly of a solid conductor, of for example aluminium
or the like, the coolant duct being made use o~ in
such case as the member withstanding tensile stresses.
This affords the advantage inter alia o~ a considerably
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.. simplified method of manufacturin~ the overhead line,
which can be done by extruding the electrical
conductor around the duct, since by this means the
custom.ary arrangement of special tension members of
steel wire or the like in overhead cables is unnecessary,
as the duct particularly when it consists of alloy steel
is dimensioned so as to wi~thstand all tensile and
. bending stresses that can occur. ~he flexibility of
the overhead line for the purpose of drum transport is
ensured in this case, apart from the dimensioning of
the conductor and of the duct by the fact that the
electrical conductor is not rigidly fixed to the duct~
~: so that the forces set up during the bending and
specially during the coiling of the line around a
drum can be suitably distributed a~d very considerably
reduced by movement of the conductor relatively to the
duct.
The inner side of the electrical conductor ac~.jacent
the pipe includes recesses substantially uniformly
. 20 distributed around its periphery and extending in the
longitudinal direction of the conductor, the total
surface area of the inner lands of the conductor
between the recesses ill contact with the pipe amounting
to at least one third of the surface area of the duct.
This feature of the invention very considerably reduces
- the adhesion of the conductor to the duct and especially
the mutual friction during the rel~tive movement of the
two parts described above, whilst ~t the same time
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retaining the contact surfaces sufficient for the
requisite heat transfer from the conductor to the duct
or from the latter to the coolant. At the same ti.me
the recesses in the inner surface of -the conductor
extending longitudinally through the entire length
: thereof afford the advantage that any damage to the
duct can be detected in time and obviated by replacement
: of the section of overhead line concerned, before the
conductor itself is exposed to any perceptible degree
to the action of the coolant.
~he electrical conductor may consist at least partly
;. of plain wires or braided or stranded bundles of wires,
-~ at least one concentric layer of which is twistad
: together leaving a central cavity or is braided with a
suitable length of lay around the duct enclosing the
coolant cha~nel or around the .solid tubular conductor.
. ~hese embodiments are particularly suitable for overhead
lines having an internal duct consisting for example of
an abrasion resistant plastics material, the tensile
strength of which is relatively low and which is not
:~ - strong enough to withstand the ~oroes concerned, In
this case the stranded portion of the conductor,
consisting of elements of high tensile s-trength, for
example a layer of so-called stalcu (copper-clad steel)
wires, constitutes the element of the overhead wire
withstanding the bulk of the tensile forces to be met
with. ~'he arrangement of stranded wire elements, al.one
or in conjunction with a solid conductor may also be of
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advantage when a conductor of specially large cross-
section or a particularly flexible conductor is
required.
A preferred embodiment of the inve~tion will be
described with reference to the accompanying drawings,
in which:
Figure 1 shows diagrammatically the la~out of a
high-tension overhead line working at a high power
e~ergy level in accordance with the me-thod of the
invention; and
~igure 2 is a cross-section through the pverhead
line of Figure 1.
As shown in Figure 1, an overhead line 1 is secured
to supporting structures 2 or 3, which are suitably
spaced apart. ~he spacings are as large as possible
consistent with the weight to be supported and the
permissible sag of the line and also with the nature
of the particular terrain involved, ~nd may be spaced by
up to several hundred metres. A single suitably
insulated suspension device 4 for the line 1 is
provided on supporting structures 2 arranged along the
line. At points for supplying and -taking o~f the
coolant and for cooling it down, supporting structures
3 with two suspension devices 4 fixed to insulators 5
o~ a supporting arm are required for supporting an end
section 6 of line through which flows coolant to be
withdrawn or for an end section 7 o~ the high-tension
overhead line 1 for the supply of cooled coolant.
Provision is made in the neighbourhood of the cross-
over po~nt of the end sec-tions 6 and 7 for the
uninterrupted tr~nsmission of the high-tension and
high power energy, while by-passing the supply or take
off points of the coolant, by means for example of a
contact bridge 8. ~he coolant is fed via a terminal
insulator 9 to a pump 10 ~Ihich feeds it directly or
indirec-tly to a heat utilizing device 11 that cools
the medium down and renders the heat contained therein
a~ailable. A further pump 10 feeds the cooled coolant
likewise via an interposed terminal insulator 9
; through the next successive section of the high-
tension line. The heat utilizing device 11 may, if
desired, be e~uipped with a heat exchanger 12 traversed
by a coolant and connected to a separately thermally -
insulated circulating system. This mode of utilizing
the abstracted heat is recommended particularly n
cases where no heating requir~ment exists in the
immediate vicinity of the stations ~or the supply or
- 20 withdrawal of coolant. In such cases~ the heat trancifer
medium such as water is circulate-l by a special pump 13
in a closed cycle from the heat exchanger 12 to the
actual consumer statio~ 14, such as a number of space
heating radiatorci of a building, the heating coil
system of a hot-house or an industrial or commercial
heating consumer~ and whence it is returned in a coo;ed
condition to the heat exchanger 12.
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With reference to Figure 2, the high power energy-
- high-tension overhead transmission line 1 comprises
a conductor 15, enclosing a thin walled tube 16, which
defines a duct 17 for the passage of a coolant, and
particularly water. The conductor 15 is preferably
designed as a solid conduetor with a substantially
smooth surfaee. It may however also consist at least
partly of stranded wires or plain wires braided around
the solid conductor. These wires are denoted by 20.
~he internal surface of the conductor adjacent the
tube, which COIlSiStS for example of alloy steel,
ineludes a number of groove-like recesses 18
uniformly distributed around the periphery of the tube,
the dimensions of the groove being such that the
intervening la~ds 19 collectively ensure adequate
heat transfer from the conductor to the tube~ which
transfers the electric heat absorbed from the
conductor to the coolant flowing through its duct 17.
Various modifications may be made within the scope
of the invention.
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