EP0054784B1 - Overhead cable with tension members - Google Patents

Abstract

In known overhead telephone cables comprising two individual encased and stranded conductors, each consisting of a plurality of copper wires for the transmission of signals, and steel wires for load bearing purposes, the problem of relatively high susceptibility to corrosion at leakage points in the casing due to water penetration is solved by replacing the steel wires with bundles of stretch-resistant synthetic fibres, e.g. aromatic polyamide fibres, and the tendency of spirally wound synthetic fibres, or bundles of fibres, to shift towards the center of the conductor when the cable is under tension, and thus allow the cable to elongate is prevented by arranging the copper wires and bundles of fibres so that they position themselves mutually. The coherency of the bundles of fibres required for this purpose may be obtained, for example, by stranding or twisting the fibres in the bundle or impregnating the bundle with a resin, preferably colophony.

Description

The invention relates to an overhead line cable with a plurality of individually sheathed, stranded wires, each of which comprises a plurality of metal wires provided for signal transmission and essentially at least approximately strain-resistant strain relief means extending in the longitudinal direction of the cable, the sheath covering each wire with a bridge the sheath of each other core of the cable is connected in one piece.

Overhead line cables of this type have become known in particular in the form of two-core cables as telephone lines. Such telephone lines have been used for some time primarily in areas in which individual telephone subscribers are relatively far away from a central switching station or an end point of an underground telephone cable network and underground routing of the telephone lines leading to the subscribers concerned because of the relatively large distance and the Insufficient use of a cable tunnel with only one or a few lines routed through the same would result in excessive costs. In these known telephone cables intended for overhead lines, mainly steel wires were used as strain relief means, which together with the metal wires provided for signal transmission, which mostly consist of tinned copper wire, formed the individual wires of the cable. In these known telephone lines, the two wires were each provided with a polyethylene sheath and an overlying polyamide sheath and connected to one another by a bridge made from the same polyamide and integrally connecting the two polyamide sheaths. However, these known telephone lines have the decisive disadvantage that the steel wires provided as strain relief means in the individual wires lead to a considerably greater susceptibility to corrosion of the wires compared to wires consisting exclusively of copper wires. For example, a number of failures of these telephone lines have been caused by the fact that the polyethylene sheaths enclosing the individual wires are in some places, e.g. Kinks or places of high mechanical alternating stresses have become leaky over the course of time and water could penetrate into the relevant veins at these points, which then led to the formation of local elements at the relevant point and thus finally to corrosion of the vein at this point. In order to avoid this disadvantage of the known telephone lines, attempts have initially been made to reduce the susceptibility to corrosion of the cores consisting of copper and steel wires to the degree of susceptibility to corrosion of cores consisting exclusively of copper wire by not only using the copper wires but also the steel wires tinned. Although these attempts have brought about a certain reduction in the susceptibility to corrosion of the cores consisting of copper and steel wires, it was not possible to reduce them to the extent to which cores consisting exclusively of copper wires are susceptible to corrosion because the tin coatings on the steel wires were not made so tight that the steel wires could have been completely sealed off from the ingress of water by the tin coatings. The effect of a complete elimination of the susceptibility to corrosion, which can theoretically be achieved with completely dense tin coatings on the steel wires and the copper wires, which can almost be achieved with wires consisting exclusively of tin-plated copper wires, could in no way be achieved with wires made of tin-plated copper wires and tin-plated steel wires.

Now it is known from cables other than the type mentioned at the outset, as strain relief means not steel wires arranged inside the wires but within the cable sheath fibers or fiber bundles made of high-strength non-metallic materials such as e.g. Using glass fibers, and when using such non-metallic materials for the strain relief means, of course, the problem of increased susceptibility to corrosion that occurs when using steel wires is eliminated. However, the solution used with these known cables (US-A-2 675 420) to arrange the high-strength fibers parallel to the cable axis and to accommodate them in the form of a fiber layer or individual fiber bundles evenly distributed over the circumference within the cable sheath was not on overhead line cables of the present type transferable because the fiber reinforcement of the cable sheath causes the cable to be much too rigid for overhead line cables. This is primarily due to the fact that the fibers in these known cables are arranged parallel to the cable axis, because if they were arranged parallel to the cable axis, each bend would require the fibers on the outside of the bend to be stretched, which the high-strength fibers are due to their tensile strength oppose.

In the case of an overhead line cable, such a high bending stiffness, due to the fact that overhead line cables are exposed to relatively strong and also constantly changing bending stresses, at least in the areas of their suspension points, would lead to the fibers breaking very quickly in the areas of strong bending stresses and thus no strain relief of the overhead line cable would be more, which would sooner or later lead to the complete breakdown of the overhead line cable due to particularly heavy loads such as a storm. Now it is from the overhead line cables mentioned at the beginning ten kind known how to avoid such bending stiffness caused by axially parallel arrangement of the strain relief means and the resulting consequences in the form of cable breaks, namely by stranding the individual wires, each consisting of copper and steel wires, but such a stranding also brings with it that the total length of the wires within the individual wires is greater than the length of the cable because of their helical course due to the stranding, and that means that the overhead line cable could be extended or extended to the entire length without stretching the wires if the wires would have the possibility of changing from their helical course to a course coinciding with the cable axis. However, such an option is not available for overhead line cables of the type mentioned at the outset, because in each individual wire of the cable the wires enclosed by the associated sheathing fix each other in their position and thus any displacements of the wires when the cable is subjected to tensile loads in the direction of the cable axis are excluded. However, if one would simply replace the steel wires provided there as strain relief means with these overhead line cables of the type mentioned at the beginning by fiber bundles composed of synthetic fibers that run parallel to one another in a strand-like manner, then the individual fibers of these fiber bundles would very well have the option of moving towards the axis center under tensile load move, because the individual synthetic fibers of the fiber bundle are not fixed in position within the core by the copper wires. This can be seen, for example, from FIG. 1 if one imagines that the unshaded circles are either steel wires or synthetic fiber bundles consisting of individual fibers running parallel to one another and the hatched circles are copper wires: in the case of steel wires, the copper and steel wires fix themselves in theirs Mutual position, and a change in this position due to tensile loading of the cable is therefore not possible; in the case of fiber bundles consisting of individual fibers, on the other hand, the individual fibers of the three outer fiber bundles can easily be shifted towards the center, the six cavities grouped around the central fiber bundle being filled in first and the copper wires then being pressed outwards until the Fibers of the outer fiber bundle would have been regrouped into a kind of jacket around the central fiber bundle. Simultaneously with this regrouping, which of course only takes place under tensile load on the cable, the cable would lengthen in accordance with the now smaller mean diameter of the helical course of the three outer fiber bundles, the fibers of the central fiber bundle which would not withstand the tensile load alone, and which would only tear one relative low tensile strength, but stretchable copper wires would be stretched accordingly. Despite the tensile strength of the synthetic fibers under tensile load, the cable would thus be able to be extended to the aforementioned extension due to the regrouping and would therefore no longer be resistant to expansion. The mere replacement of the steel wires in the known overhead line cable mentioned at the beginning with fiber bundles consisting of synthetic fibers would therefore result in the tensile strength of the overhead line cables being lost, and since the tensile strength is one of the basic requirements to be placed on an overhead line cable, the replacement is therefore the Steel wires in the known overhead line cable through high-strength synthetic fibers and thus also the overcoming of the corrosion difficulties mentioned at the outset with steel wires as strain relief means not possible without special measures.

The invention was based on the object of creating an overhead line cable of the type mentioned, in which, on the one hand, corrosion problems such as the known overhead line cables provided with steel wires as strain relief means do not occur, and on the other hand properties comparable to those known with regard to the tensile strength and flexibility with Has steel wires provided as strain relief overhead cables.

According to the invention this is achieved in an overhead line cable of the type mentioned above in that the strain relief means are formed from one or more fiber bundles running parallel to the metal wires and stranded with the same from essentially stretch-resistant synthetic fibers and the individual fiber bundle (s) in their consistency and cross-sectional shape are formed and arranged within the cores in such a way that the metal wires and fiber bundles enclosed by the assigned sheath fix each other in their position in the individual cores and thus caused by tensile loads on the cable, transverse displacements leading to the elongation of the cable under tensile loads due to the stranding being helical running synthetic fibers or fiber bundles in the direction of the core center are excluded, so that each individual core and thus also the cable is essentially stretch-resistant despite the helical shape of the synthetic fibers or fiber bundles .

The advantage of the present overhead line cable compared to the known overhead line cables of the type mentioned at the outset lies in its substantially lower susceptibility to corrosion. This can even be significantly reduced, for example, by completely impregnating the cores with resin, which is susceptible to corrosion in the known overhead line cable under the prerequisite (made practically not possible due to insufficient tensile strength) that it is made exclusively from tinned copper existing metal wires would be achievable. A further advantage of the present overhead line cable compared to the known overhead line cables mentioned can be seen in the fact that the weight of the fiber bundles which act as strain relief means instead of the steel wires is substantially less than that of the steel wires with the same strength properties as when using steel wires, and thus the weight of the present overhead line cable per unit length is 20-40% below that of the known overhead line cables mentioned. This weight advantage is essential for overhead line cables because the tensile load on the cable is mainly caused by the weight of the cable itself.

In a preferred embodiment of the present overhead line cable, the cross-sectional shape of each fiber bundle is essentially circular. In this embodiment, each fiber bundle is preferably stranded in order to achieve a sufficient consistency and a circular cross-sectional shape that is essentially unchangeable even when the cable is subjected to tensile loads. The fiber bundles can expediently consist of simply stranded synthetic fibers. With regard to the consistency and the invariability of the cross-sectional shape, it is more advantageous if the fiber bundles consist of multi-stranded, preferably double-stranded or twisted synthetic fibers.

In another likewise very advantageous embodiment of the present overhead line cable, the cross-sectional shape of each fiber bundle is designed in such a way that in each core the part of the interior space that is not occupied by the metal wires is completely filled by the entire fiber bundle.

In the case of the present overhead line cable, each fiber bundle and / or each wire in its entirety can be particularly advantageously resin-impregnated to achieve a sufficient consistency and thus a cross-sectional shape of the fiber bundles or wires that is essentially unchangeable even when the cable is subjected to tensile loads or to increase this consistency. With regard to the consistency of the individual fiber bundles, such a resin impregnation would not be necessary per se in the cases mentioned above, in which each fiber bundle is stranded in itself, but of course such a resin impregnation further increases the consistency of the individual fiber bundles and also has the resin impregnation, in particular when it encompasses the entire wire, has the advantage that water penetrating into the wire is thereby kept away from the metal wires. On the other hand, such a resin impregnation appears to be necessary in order to achieve a sufficient consistency if the individual fiber bundles consist of synthetic fibers arranged parallel to one another in a strand-like manner. This case of a strand-like parallel arrangement of the synthetic fibers in the individual fiber bundles is particularly suitable for the above-mentioned further advantageous embodiment of the present overhead line cable, because in this embodiment the cross-sectional shapes of the individual fiber bundles are generally not circular and it is therefore not possible for the individual To strand fiber bundles in themselves. The resin used for impregnation can expediently be a resin which disintegrates into powder when subjected to pressure and / or bending stress beyond its breaking limit. This has the advantage that if the overhead line cable is overstressed to bend at the relevant points, the bending stiffness of the cable is reduced by the decomposition of the resin into powder to such an extent that breakage of the cable or individual wires of the cable caused by excessive bending stiffness is avoided. Impregnation with such a resin, which disintegrates into powder when overstressed, comes into consideration in particular if the veins as a whole are impregnated with resin or fiber bundles of relatively large cross-section are provided. The resin used for the impregnation can expediently consist entirely or at least predominantly of natural resin, the natural resin advantageously being rosin.

In the present overhead line cable, the synthetic fibers forming the fiber bundles expediently consist of a plastic, preferably of an organic polymer. This plastic can be an aromatic polyamide with particular advantage. The synthetic fibers can expediently have a tensile strength of at least 250 kg / mm ² , an elastic modulus of at least 10,000 kg / mm2 and an elongation at break of less than 3%. However, the synthetic fibers can also consist entirely or partially of glass fibers, so-called high-strength glass fibers primarily being considered.

In the present overhead line cable, the metal wires of each wire can advantageously be arranged in a centrally symmetrical manner with respect to the axis of the respective wire. With particular advantage, each wire can be provided with a central metal wire, the axis of which coincides with the axis of the wire concerned, and with three outer metal wires of the same diameter as that of the central metal wire, which are arranged at an angle of 120 ° around the central metal wire are and are concerned with this. With this arrangement of the metal wires, each wire can expediently either with three fiber bundles of circular cross-section and at least approximately the same diameter as that of the metal wires, which are arranged between the three outer metal wires and also rest on the central metal wire, or with three fiber bundles of approximately trapezoidal shape Be provided in cross-section, each of which completely fills one of the three cavities, each surrounded by two outer metal wires and the central metal wire, and in this case cylindrical jacket inner wall. In the former case the fiber bundles having a circular cross section expediently stranded in themselves, while in the latter case the fiber bundles having a trapezoidal cross section expediently consist of synthetic fibers arranged parallel to one another in strand-like fashion and are impregnated with resin. Another advantageous possibility of the aforementioned centrally symmetrical arrangement of the metal wires is that each wire is provided with three metal wires of the same diameter, the axes of which are at a distance from the axis of the wire concerned from the simple diameter of the metal wires and which are at an angular distance of 120 ° around the Axis of the relevant wire are arranged around. Each core can advantageously be provided with a central fiber bundle of circular cross-section and the same diameter as that of the metal wires, the axis of which coincides with the axis of the relevant core, as well as with three outer fiber bundles of likewise circular cross-section and the same diameter as that of the metal wires are arranged between the three metal wires and bear against the central fiber bundle; the individual fiber bundles are also expediently stranded in themselves.

Another advantageous possibility of the above-mentioned centrally symmetrical arrangement of the metal wires is that each core with a central fiber bundle, the axis of which coincides with the axis of the relevant core, as well as with a plurality of arranged around the central fiber bundle, adjacent to it and preferably also mutually adjacent metal wires is provided.

The metal wires in the present overhead line cable expediently consist of copper wire, preferably of tinned copper wire. The use of tinned copper wire allows the cable to be extremely susceptible to corrosion. Instead of a tin coating, other corrosion protection coatings such as e.g. multiple paint coats may be provided.

In the case of the present overhead line cable, the sheathing of each wire should expediently engage with its inside in depressions on the outside of the wire and essentially fill these completely. This can be achieved very simply by applying the cable sheath to the cable or the individual wires of the same by extrusion under pressure. A waterproof and preferably also water-repellent polyamide suitably serves as the material for the cable sheath. The sheaths of the individual wires of the cable are expediently connected to one another by bridges between them. These bridges can be formed in the extrusion of the cable sheath by suitable design of the extruder and suitable guidance of the individual wires of the cable through the extruder.

The invention further relates to the use of the present overhead line cable as a telephone line for lines to be laid outdoors. Two-wire overhead line cables according to the present invention are primarily considered.

• Fig. 1 ein Ausführungsbeispiel des vorliegenden Freileitungskabels mit zwei Adern und je vier Kupferdrähten sowie drei in sich verseilten Faserbündeln pro Ader im Querschnitt,
• Fig.2 ein weiteres Ausführungsbeispiel des vorliegenden Freileitungskabels mit zwei Adern und je vier Kupferdrähten sowie drei Faserbündein aus strangartig parallel zueinander angeordneten Kunstfasern pro Ader im Querschnitt,
• Fig.3 ein Ausführungsbeipsiel des vorliegenden Freileitungskabels mit zwei Adern und je drei Kupferdrähten sowie vier in sich verseilten Faserbündeln pro Ader im Querschnitt,
• Fig. 4 ein weiteres Ausführungsbeispiel des vorliegenden Freileitungskabels mit zwei Adern und je drei Kupferdrähten sowie einem Faserbündel aus strangartig parallel zueinander angeordneten Kunstfasern pro Ader im Querschnitt,
• Fig.5 ein Ausführungsbeispiel des vorliegenden Freileitungskabels mit zwei Adern und je sechzehn Kupferdrähten sowie einem in sich verseilten Faserbündel pro Ader im Querschnitt,
• Fig.6 ein weiteres Ausführungsbeispiel des vorliegenden Freileitungskabels mit zwei Adern und je sechzehn Kupferdrähten sowie einem Faserbündel aus strangartig parallel zueinander angeordneten Kunstfasern pro Ader im Querschnitt.

The invention is explained in more detail below with the aid of the following figures using a few exemplary embodiments. Show it

• 1 shows an embodiment of the present overhead line cable with two cores and four copper wires each and three stranded fiber bundles per core in cross section,
• 2 shows a further exemplary embodiment of the present overhead line cable with two wires and four copper wires each and three fiber bundles made of synthetic fibers per wire arranged in parallel to one another in cross section,
• 3 shows an exemplary embodiment of the present overhead line cable with two wires and three copper wires each and four stranded fiber bundles per wire in cross section,
• 4 shows a further exemplary embodiment of the present overhead line cable with two wires and three copper wires each and a fiber bundle made of synthetic fibers per wire arranged parallel to one another in cross section,
• 5 shows an exemplary embodiment of the present overhead line cable with two wires and sixteen copper wires each and a stranded fiber bundle per wire in cross section,
• 6 shows a further embodiment of the present overhead line cable with two wires and sixteen copper wires each and a fiber bundle made of synthetic fibers per wire arranged in parallel to each other in cross section.

In the two-wire overhead line cable 1 shown in FIG. 1, intended for use as a telephone line, the two wires 2 and 3 each consist of four tinned copper wires 4 and 5 of the same diameter and three fiber bundles 6 each of circular cross-section and the same diameter as that of the copper wires 4 and 5, wherein a copper wire 4 is arranged centrally and the three remaining copper wires 5 and the fiber bundles 6 are arranged in an alternating sequence around the central copper wire 4. Each of the fiber bundles 6 consists of a plurality of strands, each of which is stranded and subsequently stranded together, each of a plurality of synthetic fibers or, in short, twisted synthetic fibers. The synthetic fibers consist of aromatic polyamide with a tensile strength of 300 kg / mm ² , a modulus of elasticity of 13400kg / mm ² , an elongation at break of 2.6% and a specific weight of 1.45 g / cm ³ . Synthetic fibers of this type are known, for example, from the information booklet "Keviar 49, Technical Information, Bulletin No. K-1, June 1974" of the Dupont de Nemours Company, page 3, section A and Table I, and in practice they are all commonly referred to as aramid fibers. The wires 2 and 3 are saponified with a lay length of 10 to 15 times the wire diameter or 30 to 45 times the diameter of the copper wires 4 and 5. Each of the two wires 2 and 3 is provided with a sheath 7 and 8 which serves at the same time for electrical insulation and for mechanical protection against weather influences and corrosion, and the two sheaths 7 and 8 together with a bridge 9 integrally connecting them form the cable sheath of the overhead line cable 1. This cable sheath consists of a waterproof and preferably also water-repellent polyamide and is applied to the previously stranded wires 2 and 3 by extrusion under pressure. Because of this type of application, the sheaths 7 and 8 engage with their inside in depressions 10 on the outside of the wires 2 and 3 and essentially fill them completely.

Experiments with the overhead line cable shown in Fig. Have shown that the cable compared to a similarly dimensioned known telephone line cable with the same cable sheath 7, 8, 9, in which instead of the tinned copper wires 4 and 5 tinned steel wires and instead of the fiber bundle 6 tinned copper wires are provided, a 16.4% lower weight per unit length, a 8.1% lower direct current resistance per unit length, a 3.8% higher tensile strength and a significantly greater corrosion resistance and also a significantly more favorable frequency response within the speech frequency range. For example, the attenuation of the known telephone line cable over frequency already increased significantly more in the voice frequency range than that of the cable shown in FIG. 1, which is apparently due to the steel wires provided in the known telephone line cable. Furthermore, the flexural rigidity of the cable shown in FIG. 1 was significantly lower than that of the known telephone line cable, which considerably reduced the risk of a cable break or wire break in the vicinity of the suspension points of the cable, and only in terms of the tensile strength were those with the in Fig. 1 shown cables taking into account a temperature fluctuation range from -30 ° C to + 40 ° C values slightly below the values achievable with the known telephone cable. However, this is not due to the material of the synthetic fibers, the tensile strength of which is even better than that of steel, but rather to the fact that the fiber bundles 6 in the cable shown in FIG. 1 consist of twisted synthetic fibers and the tensile strength of such a “thread”. the tensile strength of the thread material can only be reached with very high pretension. Now, in the manufacture of the cable, correspondingly high pretensions of the fiber bundles 6 could be achieved without great difficulty, but such high pretensions are not desirable because this would have an unfavorable effect on the bending stiffness properties of the cable and the substantially better bending stiffness properties of the cable compared to the known one Telephone line cables are much more important than the slight increase in tensile strength that can be achieved by increasing the pretension of the fiber bundles.

The construction of the overhead line cable shown in cross section in FIG. 2 corresponds essentially to the cable shown in FIG. there are also two wires 12 and 13 and four tinned copper wires 14 and 15, three fiber bundles 16 and a sheath 17 and 18 per wire and also a bridge 19 between the two sheaths 17 and 18, and also the arrangement of the copper wires 14 1, 15 and fiber bundle 16 relative to one another essentially corresponds to that in FIG. 1, but here the fiber bundles 16 do not consist of twisted fibers but rather of strands arranged parallel to one another and are resin-impregnated with rosin, and in addition the fiber bundles 16 here do not have a circular but an approximate one trapezoidal cross-section, and the inner walls 20 of the jackets 17 and 18 are not structured as in FIG. 1, but rather cylindrical. Despite the very similar structure, the cable shown in FIG. 2 differs significantly in its technical properties from the cable in FIG. 1. The tensile strength of the cable in FIG. 2 is the same with the same external dimensions and the same copper wire thicknesses as for the cable in FIG Because of the larger cross-section of the fiber bundles 16 compared to the fiber bundles 6 and because of the fibers arranged parallel to one another in the fiber bundles 16 and the resulting larger effective cross-sectional area per unit area of the fiber bundle cross-section, this is almost twice as large as for the cable in FIG. 1.

However, mainly because of the resin impregnation of the fiber bundles 16, the flexural stiffness of the cable in FIG. 1 is significantly greater than that of the cable in FIG. 1, but this greater flexural stiffness does not lead to an increased risk of cable or wire breaks because the rosin used for the resin impregnation has the property of disintegrating into powder in the event of overstressing in the relevant stressing areas and, with this disintegration into powder, the bending stiffness in these stressing areas is also greatly reduced. Furthermore, the tensile strength of the cable in FIG. 2 is much greater than that of the cable in FIG. 1, mainly because of the strand-like parallel arrangement of the fibers in the fiber bundles 16, and even exceeds the tensile strength in connection with the explanation of FIG. 1 mentioned known telephone line cable. Overall, the mechanical properties of the cable are therefore in FIG. 2 even better than that of the cable in Fig. 1 and much better than that of the corresponding known telephone line cables. In its electrical properties such as DC resistance and frequency response and also in its weight per unit length, the cable in FIG. 2 corresponds completely to the cable in FIG. 1.

The overhead line cable 21 shown in cross section in FIG. 3 corresponds almost completely to the cable shown in FIG. 1 and differs from it only in that the central copper wire 4 in FIG. 1 in the cable in FIG. 3 has a complete structure the central fiber bundle 24 corresponding to the fiber bundles 6 in FIG. 1 is replaced. Otherwise, the two wires 22 and 23 with the outer tinned copper wires 25 and the outer fiber bundles 26 as well as the sheaths 27 and 28 together with the bridge 29 completely correspond in structure and dimensioning to the corresponding parts of the cable shown in FIG. 1. Although the cable in FIG. 1 has a 23.7% higher DC resistance than the known telephone line cable mentioned in connection with the explanation of FIG. 1, like the cable in FIG. 1 it has a smaller increase in attenuation over frequency, so that the attenuation in the voice frequency range for the cable in FIG. 3 is only slightly above the attenuation of this known telephone line cable. In contrast, the tensile strength of the cable in Fig. 3 is almost 40% higher and the weight per unit length by about 25% lower than in the known telephone line cable, and in terms of flexural rigidity and tensile strength, the cable in Fig. 3 has practically the same properties as that Cable in Fig. 1. Overall, the cable in Fig. 3 is thus much better in its mechanical properties than the known telephone line cable, because its higher tensile strength in connection with its lower weight and its significantly lower bending stiffness means that it is much greater loads than the well-known telephone cable such as withstands twice the distance between the masts used to hang the cable. Of the two cables shown in FIGS. 1 and 3, the cable in FIG. 3 is therefore particularly suitable when the line to be laid is subjected to high mechanical stresses, while the cable in FIG. 1 is preferable when the total length of the Cable is relatively large and therefore the lowest possible cable loss per unit length of the cable is important.

The overhead line cable 30 shown in cross section in FIG. 4 essentially corresponds in its construction to the cable shown in FIG. 1 and differs from it only in that instead of the four separate fiber bundles 24 and 26, a cross-sectional shape essentially corresponds to the cross-sectional shape of all of these four Fiber bundle together corresponding common fiber bundle 31 is provided and the fibers of this fiber bundle are not twisted like the fibers of the fiber bundles 24 and 26 in the cable in Fig. 3 but arranged parallel to each other like a strand. In addition, the fiber bundle 31 in the cable in FIG. 4 is resin-impregnated with rosin, while the fiber bundles 24 and 26 in the cable in FIG. 3 are not provided with such resin impregnation. The properties of the cable in FIG. 4 differ from the cable in FIG. 3 in that they have a 20 to 30% higher tensile strength, a somewhat higher tensile strength and a substantially higher bending stiffness. Due to this high bending stiffness, the cable in Fig. 4 is more suitable for use in areas where high tensile strength is less important than bending and resilience, because of course the rosin in the case of the cable in Fig. 4 is also subject to overstressing disintegrates into powder in the stress areas, this cable results in much less favorable strength properties in such areas than, for example, in a corresponding area in the cable in FIG. 2.

The overhead line cables 32 and 40 shown in cross section in FIGS. 5 and 6 have, in principle, a different structure of the wires 33 and 34 compared to the cables in FIGS. 1 to 4, but are correct in the design and dimensioning of their cable sheaths with the cables in 1 to 4 essentially correspond. In the case of the cables in FIGS. 5 and 6, the plurality of individual fiber bundles 6 or 16 or 24, 26 provided for the cables in FIGS. 1 to 3 is a single, essentially circular, centrally arranged fiber bundle 36 or 41 of approximately the same cross section as the total cross section of these individual fiber bundles, and this one central fiber bundle 36 or 41 is of a layer of tinned copper wires of smaller diameter than the diameter of the copper wires 4, 5 or 14, 15 or 25 for the cables 1 to 4, the total copper cross section of which corresponds to the total copper cross section of the copper wires in the cables in FIGS. 1 and 2. The diameter of the copper wires 35 is approximately half the size and the number of the same four times the diameter or number of copper wires in the cables in FIGS. 1 and 2. The lay length of the stranding of the wires 33 and 34 corresponds approximately to the lay length in the 1 to 4. The wires 33 and 34, like the cables in FIGS. 1 to 4, are provided with sheaths 37 and 38 which are connected to one another by a bridge 39. The central fiber bundle 36 in the cable 32 shown in FIG. 5 consists of twisted fibers, while the fiber bundle 41 in the cable 40 shown in FIG. 6 consists of strands arranged parallel to one another and is resin-impregnated with rosin. The fiber material is the same as for the cables in FIGS. 1 to 4. In technical properties, the cable 32 in FIG. 1 corresponds to the properties of the cable in FIG. 1 except for its bending stiffness. The bending stiffness of the cable 32 in FIG. 5 is because the combination of the three fiber bundles 6 provided for the cable in FIG. 1 to form a single fiber bundle 36 and the central arrangement of the latter is still somewhat less than for the cable in FIG. 1. The cable 40 in FIG Fig. 5 because of the larger effective fiber cross-section of its fiber bundle 41, which results from the strand-like parallel arrangement of the fibers, about 25 to 35% higher tensile strength and because of the resin impregnation a somewhat greater tensile strength and also a much greater bending stiffness which, however, as well in the case of the cable in FIG. 2 there is no increased risk of breakage of the cable or individual wires thereof. In all other properties, the cable 40 in FIG. 6 essentially corresponds to the cable 32 in FIG. 5.

In conclusion, it should also be pointed out that the definitions of the fiber arrangement used in the present documents, as well as the arrangement of the metal wires and the fiber bundles relative to one another, in particular in the expression "strand-like arrangement parallel to one another", which is often used for the arrangement of the fibers, as well as that for the Relative arrangement of the fiber bundles to the metal wires used expression "parallel to the metal wires", the stranding of the wires is not taken into account, because otherwise the definitions of the relevant arrangements would have become far too confusing. Accordingly, these definitions only apply to cable sections of relatively short length compared to the lay length of the stranding of the wires.

Claims (22)

1. Overhead cable with a plural number of separately covered and individually twisted cores, each of which comprising a plurality of metal wires provided for signal-transmission and tension-relief means extending substantially in longitudinal direction of the cable and being at least approximately inextensible, wherein the covering of each core is connected with the covering of another core of the cable by a bridge forming a one piece connection, characterized in that the tension-relief means are formed by one or several fiber bundles (6; 16; 24, 26; 31; 36; 41) consisting of substantially inextensible artificial fibers and running in parallel to the metal wires (4, 5; 14, 15; 25, 35) and being twisted together with them, the single fiber bundle or bundles respectively being formed with regard to their consistency and their cross-section form so and being arranged within the cores (2,3; 12,13; 22, 23; 33, 34) in such a manner that, in the single cores, the metal wires and fiber bundles enclosed by the respective covering (7, 8; 17, 18; 27, 28; 37, 38) mutually fix eachother with respect to their position and that therewith transverse shiftings in direction to the core center of said, in consequence of said twisting, helically running artificial fibers or fiber bundles respectively caused by tensile loads on the cable (1; 11; 21; 32; 40) and resulting in extension of the cable under tensile load are excluded, so that each individual core and therewith also the cable is, in spite of said helically running of the artificial fibers or fiber bundles respectively, substantially inextensible.

2. Overhead cable according to claim 1, characterized in that the cross-section form of each fiber bundle (6; 26; 36) is substantially circular.

3. Overhead cable according to claim 1, characterized in that the cross-section form of each fiber bundle (16; 31; 41) is formed so that, in each core (12, 13), that part of the core-inner space enclosed by the covering (17,18) of the core, which part is not occupated by the metal wires (14, 15), is completely filled by the whole of fiber bundles.

4. Overhead cable according to claim 2, characterized in that each fiber bundle (6; 24, 26; 36), for achieving said consistency and a circular cross-section form, is twisted in itself.

5. Overhead cable according to claim 4, characterized in that the fiber bundles consist of single-twisted artificial fibers.

6. Overhead cable according to claim 4, characterized in that the fiber bundles (6; 24, 26) consist of multiple-twisted, preferably double-twisted ortwined, artificial fibers.

7. Overhead cable according to one of the claims 1 to 6, characterized in that each fiber bundle (16; 31; 41) and/or each core in its entirety, for achieving said consistency and an invariable cross-section form of the fiber bundles or cores respectively, is impregnated with resin.

8. Overhead cable according to one of the claims 1 to 3 and claim 7, characterized in that each fiber bundle (16; 31; 41) consists of artificial fibers arranged in a bunch-like form in parallel to eachother.

9. Overhead cable according to claim 7 or 8, characterized in that the resin used for impregnation is a resin desintegrating into powder with compressive and/or bending stresses exceeding its ultimate strength.

10. Overhead cable according to one of the claims 7 to 9, characterized in that the resin used for impregnation consists completely or at least for the predominant part of colophony.

11. Overhead cable according to one of the claims 1 to 10, characterized in that the substantially inextensible artificial fibers consist of a synthetic, preferably of an organic polymer.

12. Overhead cable according to claim 11, characterized in that the synthetic is an aromatic polyamide and, preferably, the fibers have a tensile strength of at least 250 kg/mm², an elasticity module of at least 10000 kg/mm2 and an elongation at rupture of less than 3%.

13. Overhead cable according to one of the claims 1 to 12, characterized in that the metal wires (4, 5; 14, 15; 25; 33) of each core (2, 3; 12, 13; 22, 23; 33, 34) are arranged central-symmetrically to the axis of the respective core.

14. Overhead cable according to claim 13, characterized in that each core (2, 3; 12, 13) is provided with a central metal wire (4; 14), the axis of which coincides with the axis of the respective core, and with three outer metal wires (5; 15) of equal diameter as that of the central metal wire, which are arranged around the central metal wire in an angular distance of 120° and border on the same.

15. Overhead cable according to claims 2 and 14, characterized in that each core (2, 3) is provided with three fiber bundles (6) of at least approximately equal diameter as that of the metal wires, which are arranged between the three outer metal wires (5) and border likewise on the central metal wire (4).

16. Overhead cable according to claims 3, 8 and 14, characterized in that the covering (17, 18) of each core (12,13) is cylindrical on its inner side and has an inner diameter of three times the diameter of the metal wires (14, 15) and each core is provided with three fiber bundles (16), each of which fills completely one of the three hollow spaces, each of these three hollow spaces being enclosed by two outer metal wires (5) and the central metal wire (4) and the inner wall (20) of the covering.

17. Overhead cable according to claim 13, characterized in that each core (22, 23) is provided with three metal wires (25) of equal diameter, the axes of which have a distance of the diameter of the metal wires from the axis of the respective core and are positioned in an angular distance of 120° around the axis of the respective core.

18. Overhead cable according to claims 2 and 17, characterized in that each core (22, 23) is provided with a central fiber bundle (24) of equal diameter as that of the metal wires (25), the axis of which coincides with the axis of the respective core, and with three outer fiber bundles (26) of equal diameter as that of the metal wires, which are arranged between the three metal wires and border on the central fiber bundle.

19. Overhead cable according to claim 13, characterized in that each core (33, 34) is provided with one central fiber bundle (36; 41), the axis of which coincides with the axis of the respective core, and with a plurality of metal wires (35) arranged around the central fiber bundle and bordering on that and preferably bordering also on eachother.

20. Overhead cable according to one of the claims 1 to 19, characterized in that the metal wires (4, 5; 14,15; 25; 35) consist of copper wire, preferably of tinned copper wire.

21. Overhead cable according to one of the claims 1 to 20, characterized in that the covering (7, 8; 27, 28; 37, 38) of each core (2, 3; 22, 23; 33, 34) engages, by its inner side, in deepenings (10) at the outer side of the core and fills substantially completely these deepenings.

22. The use of an overhead cable according to one of the claims 1 to 21 as telephone line.

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