EP0277157B1 - Self-supported cable for overhead electric lines - Google Patents

Abstract

Metal wires (1) are twisted into several layers (7, 8, 9) around a core (2) in order to obtain a cable for overhead lines. Reinforcing elements (3, 4) are located between the wires (1) and are twisted with them at the same pitch. The reinforcing elements (3, 4) are non-distortable bars having a rigid structure and consist of reinforcing fibres and a hardening reactive resin. The reinforcing elements (3, 4) are completely surrounded by metal wires (1) and are protected against ultra-violet radiation.

Description

The invention relates to a self-supporting overhead line cable with a plurality of metallic wires stranded in layers and at least one strain relief element made of a plurality of reinforcing fibers arranged in the manner of a strand, the reinforcing fibers being impregnated with a binding material and forming a composite element.

An overhead line cable of this type is known from European Patent No. 25 461. In this overhead line cable, the metallic wires and the strain relief element are each arranged in an independent cross section. The strain relief element consists of synthetic fibers which run approximately parallel to one another and are surrounded by a protective sheath, this protective sheath simultaneously enclosing the metallic wires and establishing the connection between the two cross sections. The protective jacket is also necessary to protect the synthetic fibers from ultraviolet rays, for example as a result of sunlight. With overhead line cables of this type, large spans can be bridged between the suspension masts, since the synthetic fibers can absorb a much higher tensile stress than the metallic wires. Fibers made from organic polymers are described as suitable synthetic fibers. The synthetic fibers are impregnated with a binder material, for example a natural resin, which resin is said to disintegrate into powder when overused. Since overhead line cables of this type are a sheathing for connecting the strain relief element to the metallic wires need, the structure is complicated and time-consuming. In practice, they are mainly used for special applications, for example as transmission lines for control signals, but are not particularly suitable for high-voltage overhead lines because of the high manufacturing costs. In the case of high-voltage overhead lines, there is also a demand for an optimal ratio between the total cross-section of the overhead line cable and the cross-sectional area available for power transmission.

According to British Patent No. 838 494, it was proposed to arrange the strain relief element in the center of the rope as the core. According to the solutions described, up to 50% of the cable cross-section is lost at the strain relief element. For the production of ropes with a larger cross-section, it is proposed here to manufacture bundled ropes. The rope consists of a strain relief element that forms the core and several bundles stranded around this core. Each bundle in turn has a core made of a strain relief element, metal wires with a specific lay length being stranded around this core. The metallic wires always have a different lay length in relation to the strain relief elements, which additionally leads to voluminous or large rope cross sections. With tensile loads on the rope, there are different stretching movements of the wires and the strain relief elements, which can lead to overloading and destruction of individual strain relief elements. Both with simple as well as with stranded ropes of this type, considerable problems also arise in the final fastening of the ropes, since the reinforcing element forming the core can only be gripped and clamped with great technical effort. This problem is multiplied in the case of stranded ropes because each of the bundles has a core in the form of a strain relief element. These difficulties are apparently also the reason why such overhead line cables have not yet been used have reached and only solutions for EP 25 461 B1 are used for special applications.

An electrical conductor is known from US Pat. No. 2,675,420, in which loose glass fiber strands are inserted between the outer insulation and the metallic wires. With such loose glass fiber strands, a pressure-resistant cross-sectional structure of the conductor cannot be formed, since the loose glass fiber strands have a tendency to move into the center of the conductor or to shift in another way with respect to the wires. The final attachment of the conductors is hardly possible, since no bond is possible between wires and loose glass fiber bundles and the loose glass fiber bundles can only be clamped or gripped with great effort.

The cables used for high-voltage overhead lines today mostly consist of a combination of steel and aluminum wires or of high-strength aluminum alloys. The aluminum wires are used because of their low weight and the relatively good conductivity. Since they have a low tensile strength, overhead line ropes made of pure aluminum wires have to be reinforced with steel wires, which, however, considerably increase the weight of such overhead line ropes. Heavy ropes require reinforced masts. The steel wires are also not suitable for power lines and are susceptible to corrosion. The use of two different metallic materials increases the risk of corrosion. Due to the dense population, it is exceptional today difficult to find suitable routes for overhead lines. Due to the increasing demand for electricity, new routes should be built, which is difficult for the reasons mentioned. An attempt is therefore made to make better use of the existing routes by using larger masts with different ropes, ie ropes with a higher transmission capacity. In many cases, however, further consolidation of the existing overhead line routes is also no longer possible for various reasons, and the increase in the transmission capacity therefore reaches its limits.

It is an object of the present invention to provide an overhead line cable which has a larger conductor cross-section for power transmission and thus a higher transmission capacity than steel-aluminum cables with the same weight and as the known cables with non-metallic strain relief elements with the same diameter, which is simple and If possible, it can be produced on the known stranding machines for spiral-stranded ropes, in which the strain relief elements and the metallic wires perform the same stretching movements under tensile loads, which means no additional means for establishing the connection between the reinforcing elements and metallic wires during the guyings and no additional sheathing as protection against ultraviolet radiation. Furthermore, it is also an object of the invention to provide a spirally stranded overhead line cable which, with the same transmission power, enables larger spans between the masts and has a high level of corrosion resistance and thus greater operational reliability.

This object is achieved by the features defined in the characterizing part of patent claim 1. Advantageous further developments result from the features of the dependent claims.

The overhead line rope according to the invention has essentially the same structure as an overhead line rope made of steel and aluminum wires or, for example, the aluminum alloy Aldrey. Purely aluminum wires are expediently used for the conductors, since these cost represent the cheapest solution. Depending on the application, wires made of copper or another conductive material can also be used. The strain relief elements consist of composite elements which consist of reinforcing fibers embedded in binding material, preferably a curable synthetic resin. In principle, all fibers which can be used in composite materials can be used as reinforcing fibers. Fibers made from aromatic polyamides, glass fibers or so-called Kevlar fibers have proven particularly suitable. These fibers are arranged in a strand-like manner and approximately parallel to one another and embedded in a hardened reactive resin in such a way that a rod-shaped element with a solid structure and a fixed cross section is formed. The cross-sectional shape of these composite elements is determined by the desired type of reinforcement of the overhead line cable according to the invention. A particularly simple manufacture of the overhead line cable according to the invention is possible if the composite elements serving as strain relief elements have the same cross-sectional area and shape as the metallic wires. Such composite elements can be stranded with the metallic wires without difficulty, the number of composite elements embedded between the metallic wires being determined by the desired tensile strength of the overhead line cable. Due to the incorporation of the fibers in hardened synthetic resin, the composite elements have a dimensionally stable cross-section, which cannot be compressed by the metallic wires during stranding. In contrast to previous tests with strain relief elements made of reinforcing fibers, this gives the possibility of producing a dimensionally stable overhead line cable without additional measures being necessary. The overhead line rope formed in this way can be clamped at the ends with the known devices, since the strain relief elements are arranged between the conductors and are spirally stranded with them. The composite elements point as Strain relief elements compared to those made of steel depending on the selected fiber material the factor 1.5 to 4 less weight. With the same tensile strength of the relief elements, the weight and thus the conductive cross section of the metallic wires can be increased. This results in a higher transmission performance for a cable of the same weight. With a suitable combination of reinforcing fibers with the synthetic resin, higher strength values can also be achieved. This results, for example, when using aramid fibers in combination with unsaturated polyester resins or with epoxy resins.

An even more compact overhead line cable results if the desired conductor cross section is produced in a conventional manner entirely from metallic wires, in particular the inexpensive pure aluminum wires or strands, and the composite elements are inserted into the cavities between the wires which are formed during the stranding. Depending on the required strength, the composite elements in this solution have the largest possible round cross-section, or their cross-sectional area corresponds to the cross-section of the cavity. Such ropes can also be compressed by smoothing and pressing them together in the stranding matrix.

In the case of overhead line cables according to the invention, the risk of corrosion is practically eliminated, since only wires made of the same material are present. The materials aluminum or copper mostly used for the wires are inherently corrosion-resistant. This increases the operational and long-term safety of the overhead line cables.

The arrangement with a waveguide in the core is easy to manufacture and is used in particular as an earth rope. If necessary, an optical cable can be pulled into the waveguide, which is freely movable in relation to the metallic wires. The optical cable is not a component the supporting structure and is therefore well protected against deformation.

Spiral-stranded overhead line cables according to the invention have an approximately 70% higher transmission capacity than conventional aluminum steel cables of the same weight per unit length. Compared to the known bundled ropes with a reinforcing element as the core, they have a much smaller diameter with the same conductive cross section. This makes it possible to transmit higher outputs on existing routes when using the ropes according to the invention. With the same transmission performance, an overhead line cable of the type according to the invention becomes lighter, and the associated supporting masts and guy lines can be made lighter and simpler, or larger spans can be provided between the individual masts. As a result, the construction costs of such overhead lines are reduced and the further advantage that smaller masts can be better fitted into the landscape.

Fig. 1

einen Querschnitt durch ein erfindungsgemässes Freileitungsseil mit in die Hohlräume eingelegten Verstärkungselementen mit rundem Querschnitt,

Fig. 2

einen Querschnitt durch ein erfindungsgemässes Freileitungsseil mit Verstärkungselementen, welche den gleichen Querschnitt wie die metallischen Drähte aufweisen,

Fig. 3

einen Querschnitt durch ein Freileitungsseil mit Verstärkungselementen, welche unterschiedliche Querschnitte aufweisen,

Fig. 4

einen Querschnitt durch ein Freileitungsseil mit einem als Hohlkörper ausgebildeten Kern und gleichem Querschnitt der Verbundelemente und der metallischen Drähte.

Exemplary embodiments and further advantages of the invention are explained in more detail below with reference to the drawings. Show it:

Fig. 1

1 shows a cross section through an overhead line cable according to the invention with reinforcing elements with a round cross section inserted into the cavities,

Fig. 2

3 shows a cross section through an overhead line cable according to the invention with reinforcing elements which have the same cross section as the metallic wires,

Fig. 3

3 shows a cross section through an overhead line cable with reinforcing elements which have different cross sections,

Fig. 4

a cross section through an overhead line cable with a core formed as a hollow body and same cross-section of the composite elements and the metallic wires.

The spiral stranded overhead line cable shown in Figure 1 consists of metallic wires 1, which are stranded in three layers 7, 8 and 9. The core 2 is also formed from a metallic wire 1. In the cavities 5, between the first layer 7 and the second layer 8 and in the cavities 6 between the second layer 8 and the third layer 9, composite elements 3 and 4 are arranged. These composite elements 3, 4 consist of polyaramid fibers, which are embedded in a hardened synthetic resin. In this example, an unsaturated polyester resin dissolved in styrene is used as the synthetic resin. Such resins are known under the name Leguval from Bayer. The composite elements 3, 4 have a circular cross section, which is firm and dimensionally stable. The metallic wires 1 of all layers 7, 8, 9 and the core 2 have a diameter of 3.36 mm and consist of pure aluminum. Overall, the overhead line cable shown consists of 37 metallic wires 1, which results in a conductive cross section of 328 mm². The composite elements 3 have a diameter of 1.17 mm and the composite elements 4 of 1.07 mm. As further characteristic values for the rope, this results in a weight of 907 kg / km and a breaking strength of approx. 80,000 N. The copper cross-section with the same conductance value in this example, which is important for the comparison of overhead line ropes and the calculation of the transmission power, is 201 mm².

A conventional spiral-stranded overhead line cable made of steel / aluminum wires with the same weight per km length only has a cross-section of 119 mm² with the same conductance value. The conductive cross section of the overhead line cable according to FIG. 1 is thus 69% larger than that of the conventional steel / aluminum cable. If overhead cables of the conventional type on an existing route are replaced by ropes according to FIG. 1, a correspondingly higher power can be transmitted on the same route.

Figure 2 shows a cross section through an overhead line with metallic wires 1 and composite elements 10, which are also arranged between the metallic wires 1 and have the same cross section as these. Polyaramide fibers, which are processed together with the hardened synthetic resin to form the rod-shaped composite element 10 with a circular cross-section, also serve as reinforcement elements. These composite elements 10 are as dimensionally stable as the metallic wires 1 and can therefore be stranded with these metallic wires 1 in a known manner without difficulty. Two composite elements 10 are arranged in the first layer and three in the second layer. There are no composite elements 10 in the third and outer layer 9, since the material used is not resistant to ultraviolet radiation. The metallic wires 1 arranged in the outermost layer 9, which cover the overhead line cable along the entire circumference, form an effective protective layer against ultraviolet rays for the composite elements 10 arranged in the lower layers. It is therefore not necessary to arrange an additional protective sheath around the overhead line cable, since the protection that can be achieved by the outer position of the metallic wires 1 is sufficient. If the overhead line rope shown is formed from metallic wires made of pure aluminum with a diameter of 3.54 mm, the rope contains 32 metallic wires 1. The copper cross-section of the same conductance value for this rope is 193 mm². The rope also has a weight of 912 kg / km. A conventional overhead line cable made of steel-aluminum wires, which has the same weight per km as mentioned above, has a copper cross-section of 119 mm² with the same conductance. The conductive cross section of the overhead line cable according to FIG. 2 is therefore also substantially larger here, namely 63%. It is obvious that even in this embodiment according to the invention, significantly higher outputs can be transmitted with the same weight load on a route. At the same time, the rope according to the invention has a higher one Strength by the breaking strength being approx. 55% higher than with the steel-aluminum rope mentioned. This results in the possibility of reducing the distance between support masts and / or the sag of the overhead line cables with increased transmission power. If the strength of the rope is even higher, it can be increased further by inserting additional composite elements 3, 4 into the cavities 5, 6 in accordance with the arrangement in FIG. 1. Since the rope structure and the conductor cross-section are not changed as a result, the rope designer has a considerably greater scope for the calculation than was possible with conventional ropes.

The overhead line cable shown in cross section in FIG. 3 shows an embodiment which can be produced on a stranding machine with a limited number of wire feeds. If, for example, the stranding machine has only 48 wire feeds, a rope according to FIG. 1 cannot be produced in one operation. The overhead line cable according to FIG. 3 has a total of four composite elements 10 as core 2 and in the inner layer 7, which have the same cross-section as the metallic wires 1. In the cavities 5 of the inner layer 7, six additional composite elements 3 are inserted with a smaller cross section and stranded with the wires 1. This combination of thirty-three wires 1, four composite elements 10 and six composite elements 3 can be produced in one operation on a stranding machine with 48 wire feeds. The composite elements 10 and 3 are also made of polyaramide fibers, which are embedded in a hardened synthetic resin. Depending on the needs, different combinations of arrangements of the different cross sections of the composite elements 3 and 10 can be selected. If you compare this rope with overhead line ropes of a conventional type, you can see that a steel-aluminum rope with a copper cross-section of the same conductance value has a weight per km is about 64% higher. With a rope made of Aldrey, a well-known and frequently used aluminum alloy with a copper cross section with the same conductance, the weight per km is still approx. 53% higher. For the same transmission performance, routes that are equipped with ropes of the conventional type must be equipped with much more massive masts and stronger guy lines.

In the overhead line cable shown in Figure 3, the composite elements 3 and 10 are completely surrounded by metallic wires 1 and thereby protected from the action of harmful ultraviolet radiation. If necessary, additional layers of wire can be applied to the rope shown here and stranded into a larger rope.

The construction of the overhead line rope shown in FIG. 4 corresponds to the overhead line rope according to FIG. 2 in the construction of the metallic wires 1 and the composite elements 10. However, the inner layers in the rope shown are replaced by a hollow body 16 which has a cavity 17. In addition, the rope has an outer layer 15 of metallic wires 1, and the composite elements 10 are all arranged in the inner layer 9 here. The rope shown is used in particular as a grounding rope. If necessary, optical conductors can be inserted into the cavity 17 of the hollow body 16. These optical conductors advantageously have a waveform, as a result of which any changes in length or deformations of the overhead line cable can be compensated for. This version is a particularly simple and inexpensive combination of an overhead line cable with metallic wires and an integrated optical conductor.

Claims (9)

1. Self-supporting cable for overhead transmission lines with several metal conductors laid up in layers and at least one strain relief element made from a number of rope-type reinforcing fibres, whereby the reinforcing fibres are impregnated with a binding material and form a composite element, characterised in that in the spirally-wound cable, in a common laid-up layer (7, 8, 9) with metallic conductors (1), at least one composite element (3, 4, 10) is arranged between the metallic conductors (1) in this laid-up layer (7, 8, 9), all composite elements (3, 4, 10) and the metallic conductors (1) which are arranged in the same layer (7, 8, 9), are laid up parallel to each other at the same pitch, and each composite element (3, 4, 10) in the cable is surrounded on all sides by metallic conductors (1) or a combination of metallic conductors (1) and other composite elements (3, 4, 10) and the outermost laid-up layer consists exclusively of metallic conductors.
2. Self-supporting cable for overhead transmission lines according to claim 1, characterised in that the binding material is a hardenable, reactive synthetic resin and the hardened reactive synthetic resin and the reinforcing fibres embedded in this form flexible, rod-shaped composite elements (3, 4, 10).
3. Self-supporting cable for overhead transmission lines according to claim 1 or 2, characterised in that each of the composite elements (3, 4, 10) has a solid structure and a dimensionally-stable cross-section.
4. Self-supporting cable for overhead transmission lines according to one of the claims 1 to 3, characterised in that each of the composite elements (10) has the same shape and cross-sectional area as the metallic conductors (1).
5. Self-supporting cable for overhead transmission lines according to one of the claims 1 to 3, characterised in that the composite elements (3, 4) have a cross-sectional area whose maximum dimensions are equal to or less than the dimensions of the cross-sectional area of the hollow space (5, 6) between each adjacent conductor (1) of the same and adjoining laid-up layers, and the composite element (3, 4) is arranged in this hollow space.
6. Self-supporting cable for overhead transmission lines according to one of the claims 1 to 3, characterised in that several composite elements (3, 4, 10) with cross-sectional areas of differing size or shape are incorporated in one cable.
7. Self-supporting cable for overhead transmission lines according to one of the claims 1 to 6, characterised in that the reinforcing fibres of the composite elements (3, 4, 10) are aramide fibres.
8. Self-supporting cable for overhead transmission lines according to one of the claims 1 to 6, characterised in that the reinforcing fibres of the composite elements (3, 4, 10) are glass fibres.
9. Self-supporting cable for overhead transmission lines according to one of the claims 1 to 8, characterised in that a hollow space (17) is formed in the core of the cable for overhead transmission lines and this hollow space (17) is bounded by a hollow body (16) and the metallic conductors (1) and the composite elements (10) are laid up around this hollow body.

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