Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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The present invention relates to improvements in
elongated bodies that are adapted to be suspended between a
pair of supports, such elongated bodies including overhead
power cables and uninsulated cables containing telecommuni-
cation elements in the form of optical fibers.
As is known, overhead power cables are suspended by
means of insulators, on supports that are spaced apart, one
from the other. The uninsulated cables that are known in the
art as "earth conductors" can, in their turn, be suspended to
run above the overhead power cables. The earth conductors are
directly secured to the supports in a non-insulated way.
The purpose of the earth conductors is to protect
overhead power cables from lightning strikes. The latter, in
fact, are guided so as to hit the earth conductor itself.
In the past, it has been known to use overhead power
cables, or earth conductors, as a path for telecommunication
elements, in particular, for co-axial pairs used for trans-
mitting signals by means of the pulse code modulation system.
As already known, this co-axial pair can be realized with an
outer diameter of only a few millimeters. It is due to this
size characteristic that it has been possible to dispose said
co-axial pair, singly or in a plurality, inside overhead power
cables, or inside earth conductors constituted by an assembly
of elongation resistant and/or conductive elements.
The elongation resistant elements are generally steel
wires, whereas the conductive elongate elements are, for
example, made of aluminum. The use of optical fibers, in the
field of telecommunications has become widespread. Due to the
similarity of what takes place with the co-axial pairs and in
view of the small transversal dimensions that even more so
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characterize the optical fibers, there is foreseen that the
optical fibers themselves may be disposed in a path inside the
overhead power cables and inside the earth conductors.
The structures known until now for the overhead
power cables and for the earth conductors containing tele-
communication elements comprising optical fibers does not sub-
stantially differ from that in use for the co-axial pairs. See,
for example, the description of the British application No.
2,029,043A. In said British application, optical fibers are
10 loosely disposed inside an aluminum hermetically sealed tube
which is surrounded by elongation resistant, cylindrical elements
of steel or of an aluminum alloy. In other words, in the state
of the art, the resistant elements and the conductive elements
are always realized out of metallic alloys that are different
from each other.
This characteristic of the state of the art can
produce large drawbacks. In fact, as is well-known to those
skilled in the art, owing to electro-chemical effects, corrosive
processes are encountered. These corrosion effects, by giving
rise to the formation of perforations, will permit water to
penetrate in-between the optical fibers. The water also spreads
along the entire length of the fibers themselves.
The water, in getting into the micro-fissures of the
optical fibers, particularly when the fibers are under stress
conditions, causes these micro-fissures to widen, and hence, the
optical transmission characteristics become worse. Deteriorations
in the characteristics of the optical fibers, or even breakages
in the fibers themselves, can also be encountered in the operations
involving the stretching, in the course of installation, of the
fibers themselves, should the helices of the resistant and of
the conductive elements unwind owing to the "puIl" thereon.
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With such unwinding, there is a consequent elongation of the overhead power
cable or of the earth conductor to beyond permissible values for optical
fibers, said value of elongation being, itself, very small.
It is an object of the invention to obviate the drawbacks stated
above. In particular, it is proposed that the elongate bodies intended
for being suspended, and containing optical fibers should have elongation
resistant reinforcing elements and conductive elements, both tubular as
well as wire-shaped, constituted of materials that are electro-chemically
compatible with each other. By "optical fibers", it is intended to include
the bare fibers, or else, the fibers covered by at least a primary coating.
The elongate bodies intended for being suspended, which form the
object of this invention, will moreover, be highly inextensible, for pre-
venting any excessive elongations during the stretching which occurs in
the course of installing them, but will still retain their good flexibility
characteristics.
More precisely, the present invention provides a cable for use
in a moisture-containing ambient, said cable comprising a fluid-tight
metal tubular element, at least one optical fiber within said tubular ele-
ment, a plurality of elongation resistant, elongate reinforcing elements
around and extending lengthwise of said tubular element, said reinforcing
elements contacting said tube to provide metal-to-metal contact between
the exterior surface of said tubular element and surfaces of said reinfor-
cing elements and a plurality of elongate conductive, metal elements
around said tubular element and extending lengthwise thereof, said conduc-
tive elements contacting at Ieast said reinforcing elements to provide
metal-to-metal contact between surfaces of said conductive elements and
said reinforcing elements and each of said elements being made, at least at
their peripheries, of a metal which is electro-chemically compatible with
the metal of the elements with which it is in contact.
In a preferred embodiment of the invention the reinforcing ele-
ments are made of rods or wires having a steel core clad with aluminum and
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the tubular conductive element as well as the conductive elongate elements
are made of aluminum.
Instead of aluminum, an aluminum alloy can be used to cover the
steel cores, and the tubular element and conductive elements can also be
made of an aluminum alloy.
In a further preferred embodiment of the invention the reinforcing
elements and the conductive elongate elements constitute, together, an
anti-torsional structure.
Other objects and advantages of the present invention will be
apparent from the following detailed description of the presently preferred
embodiments thereof, which description should be considered in conjunction
with the accompanying drawing in which the single figure illustrates an
embodiment of the invention schematically and in perspective.
In the embodiment illustrated in the drawing, there is an elongate
body 10 intended for being suspended either as an overhead power cable or
as an earth conductor. The elongate body 10, comprises one or more optical
fibers 11 which are enclosed in the longitudinal cavity of a fluid-tight,
tubular conductive element 12. The element 12 can be realized in any oppor-
tune manner, for example, by extrusion or else, by longitudinally folding
a tape of conductive material and welding its edges together. Moreover,
the tubular conductive element 12 is surrounded by a first covering 13 of
elongation resistant reinforcing elements 14, which, in this particular
case, are cylindrical in shape.
Said first covering 13 is, in its turn, surrounded by a second
covering 15 of elongate conductive elements 16, which, in this particular
case, are also cylindrical. Said tubular conductive element 12, elonga-
tion resistant cylindrical reinforcing elements 14, conductive cylindrical
elements 16, are realized, at least with respect to their outermost thick-
ness, with electro-chemically compatible metals, such electro-chemically
compatible metals being known in the art.
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I'he resistant elongate elements and the conductive
elongate elements could be disposed, with respect to each
other, in a way which is different from that indicated in the
drawing. For example, said elements could be disposed alter-
nately at the same raclius.
A preferred embodiment comprises conductive cylindrical
elements 16 and a conductive tubular element 12 made entirely
of aluminum while the resistant cylindrical elements 14 are
made of steel rods 17, covered with an outermost layer 18 of
aluminum. Wires which have a steel core and an aluminum
covering and which are available in the market under the
trademark "Allumoweld" have proven to be particularly suitable
for the rods 17.
Of course, even all the elements 14 can also be con-
stituted, for their entire thickness, out of a single material
that is equivalent, or else electro-chemically compatible with
that of the elements 12 and 16. For example, the elements 12,
14, 16 could be made entirely of aluminum alloy or else they
could have only an outermost layer of aluminum alloy.
Moreover, the first covering 13 and the second
covering 15 are, as indicated in the drawing, helicoidally wound.
The resistant cylindrical elements 14, and the conductive
cylindrical elements 16, are wires wound helicoidally. The
outer helicoid 15, is wound on the inner one 13, with more or
less the same pitch with respect to the axis X-X of the cable,
but in the contrary sense. The system, constituted by the inner
helicoid 13 and by the outer helicoid 15 is, according to the
invention, an anti-torsional system.
This anti-torsionality is achieved, as those skilled
in the art already know, by properly equalizing the following
parameters:
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S = (section of each single wire of the helicoids)
~ = (helix pitch)
0m= (avexage diameter of the helices)
E - (YOUNG's modulus)
G = (Modulus of tangential elasticity).
This allows for providing the elongate cylindrical body lO,
which is to be suspended, with the desired characteristics of
inextensibility together with a good flexibility, and it
facilitates the capability of withstanding twistings without
incurring any damage.
Although preferred embodiments of the present invention
have been described and illustrated,it will be apparent to those
skilled in the art that various modifications may be made without
departing from the principles of the invention.
