CH672031A5 - - Google Patents

Description

DESCRIPTION The present invention relates to an air cable with a core containing optical waveguides, a covering surrounding the core made of a thermoplastic or elastomeric material.

In the area of energy supply through high-voltage overhead line networks, [ETZ Nd. 106 (1985) Issue 4, p. 154 ff.) Air cables with fiber optic cables are provided for the transmission of messages. In the case of so-called wide-span air cables, spans of up to 435 m could be bridged. The problems encountered with such aerial cables can be mechanical, such as vibration or load difficulties, which depending on the type of reinforcement provided by metallic or non-metallic, i.e. metal-free, kind could at least be reduced.

However, problems of an electrical nature which result from the insulating sheath are also already known. In the electrical field of the phase conductors of a high-voltage overhead line, the sheath is charged on the surface, and the induced charge cannot flow off due to the high surface resistance of up to 1012 Q / cm. Different soiling and moisture on the surface of a sheathing have the result that potential differences occur on the metal-free air cable even within the span of a high-voltage overhead line, which lead to leakage current discharges. In addition, the surface of the casing on each mast is forced to zero potential by the metallic suspension, which is connected to the mast in an electrically conductive manner. As is known, this leads to high voltage differences in the region of the sheathing-suspension transition, which are always reduced by discharges which are harmful to the aerial cable.

On the basis of this prior art, the object of the invention is to increase the operational reliability of the cables described at the outset and used in the area of high-voltage overhead lines.

The aerial cable is characterized in that the thermoplastic or elastomeric material of the sheath is crosslinked after the grafting of silane compounds under the influence of moisture and contains an additive which effects the creep resistance of this material. The particular advantage lies in the fact that the additive is integrated evenly over the entire cable length and cross-section of the sheathing in an equally cross-linked polymer matrix. This leads to a cable that is operationally reliable for the purposes mentioned, since damage or even destruction of the cable by leakage currents is not to be expected even if it is simultaneously influenced by dirt and moisture in the electrical field.

The tracking resistance of the sheath-like sheathing of the cable over the entire length also has the advantage of simple assembly compared to designs in which one tries to protect known cables only at the points of the mast suspension against leakage currents, but also greater operational reliability because of the extensive independence from the Quality of assembly work.

The additive can consist of metal oxides or carbide.

It has proven to be advantageous if the additive according to claim 3 consists of aluminum oxide hydrate and iron oxide, the material of the covering expediently containing 30 to 80 parts by weight of aluminum oxide hydrate and 3 to 7 parts by weight of iron oxide per 100 parts by weight of polymer. The ready-to-use casings have the required tracking resistance, the production of the casings, their extrusion as well as the subsequent cross-linking is smooth.

According to claim 5, the additive can also contain titanium dioxide or zinc oxide.

According to claim 6, it is also advantageous if the material for the covering contains a linear polyethylene (LLDPE) with a density of 0.88-0.95 g / cm3 or one of its copolymers alone or as a blend with other polymers. Linear polyethylene (LLDPE - linear low density polyethylene) is a polyethylene polymer that combines the characteristic properties of linear low pressure polyethylene (HDPE = high density polyethylene) with those of highly branched high pressure polyethylene (LDPE = low density polyethylene). Like the HDPE, the structure of this material, which is produced using different processes at comparatively low pressures, contains only very short-chain branches. As with HDPE, the polymer main chain is therefore decisive for some essential properties of the macromolecule. As a result, the melting range of the LLDPE at 120 - 125 ° C is close to that of the HDPE. Deviating from the HDPE and thus again similar to the LDPE, the number of branches is much higher. This means that the density and crystallinity are significantly reduced. The term LLDPE summarizes the traditionally contradictory properties, namely linear molecular structure and low density.

Envelopes made of such a material draw5

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e.g. characterized by increased abrasion resistance, heat resistance and cold resistance. In addition, when producing such a cable, smaller amounts of silane and peroxide for the purpose of crosslinking than usual are to be expected; after the silane compounds have been grafted onto the base molecules of linear polyethylene, the crosslinking process takes place more rapidly in the presence of moisture. If the air humidity is sufficiently high, saturated steam or water storage can even be dispensed with. The manufacture of such a cable is therefore also more cost-effective.

To manufacture an aerial cable, one can proceed according to claim 7, that the base material is first mixed with the silane component and then the silane is grafted onto the base polymer, that the additive is incorporated and homogeneously distributed in the base material thus prepared, and that finally Sheathing formed and exposed to moisture for the purpose of crosslinking. The base polymer must first be made crosslinkable in order to ensure later even crosslinking even of different cross sections, before the material essential for the improvement of the tracking resistance is mixed into this preprogrammed material for the crosslinking process.

Further quality improvements of the end product can still be achieved during the production process by mixing the additive according to claim 8 into the base material grafted with silanes at temperatures between 100 ° and 140 ° C.

It is also expedient according to claim 9 if the crosslinking catalyst for the crosslinking under the action of moisture is only mixed in immediately before the shape of the crosslinkable casing. Pre-crosslinking after adding the additive is avoided in this way.

The invention will be explained in more detail with reference to the following mixture example and the embodiment shown in FIGS. 1 and 2.

Mix example

Polyethylene copolymer (copolymer content approx. 20% vinyl trimethoxysilane peroxide

(e.g. dicumyl peroxide)

Polyethylene copolymer (copolymer content approx. 30%) aluminum oxide hydrate (Martinal OL 104 X from Martinswerke)

Iron oxide (Fe304) stabilizer (Anos HB)

Polyethylene copolymer (copolymer content approx. 15%) catalyst (Naftovin S)

100 parts 1.7 parts

0.006 parts

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Parts parts

0.5 parts

100 parts 0.85 parts

The polyethylene component in the blend example can also e.g. be replaced with an ethylene-propylene rubber or the above-mentioned LLDPE.

To produce a sheath current-resistant sheath for 5 aerial cables, one proceeds, for example, by first entering the polymer material together with the silane and peroxide dissolved in it into a so-called graft extruder in its insertion funnel and grafting the silane onto the PE copolymer is made crosslinkable, io The PE base material treated in this way is extruded and granulated.

At the same time, a highly concentrated “batch” mixture is produced according to B, which contains aluminum oxide hydrate and iron oxide as an additive to improve the tracking resistance, lì A suitable kneader is used to mix the individual components. A batch corresponding to (C), which contains the crosslinking catalyst, is also advantageously produced on a kneader.

After the crosslinkable base mixture (A) 20 has been granulated, it is mixed with the highly concentrated mixture (B) e.g. mixed in a suitable kneader or a corresponding mixing unit and the mixture is then fed to the feed hopper of an extruder for the continuous production of the casing. At the earliest, the mixture corresponding to (C) is also introduced into the Ausform-25 extruder, while the crosslinking catalyst is distributed sufficiently homogeneously during the mixing and homogenization phase in the extruder.

1 shows a metal-free air cable with optical waveguide (LWL) constructed according to the invention, while in FIG. 2 the arrangement thereof is illustrated in the course of a high-voltage overland overhead line.

The hollow cores 2, in which the optical waveguides 3 are guided, are distributed around an insulating core 1. This stranding is surrounded by the insulating, jacket-like covering 4, which consists of a polymer material which is crosslinked by moisture after grafting on silanes by moisture. A e.g. Reinforcement 5 made of high-strength plastic threads, for example based on aromatic homo- or copolyamides, serves to absorb tensile forces.

The practiced arrangement of an air cable with optical waveguide in the energy supply area is shown schematically in Fig. 2. Here, between the e.g. 45 masts 6 and 7, 400 m away, clamped the earth rope 8 and the three phase ropes 9. At a distance of e.g. 6 m to the phase conductors 9 there is an air cable 11 constructed in accordance with FIG. 1, which is fastened to the mast 6 or 7 via the metallic and grounded suspensions 10. Particularly in the area of these suspensions, increased stress due to leakage currents induced on the surface of the sheathing 4 can be expected with a metal-free aerial cable. With corresponding, additional inevitable electrical stress due to dirt and moisture, vibrations of the cable, special construction, etc., other cable sections are also at risk of leakage current. The invention also provides a remedy here due to the special jacket structure.

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1 sheet of drawings

Claims (9)

672 031 1. Air cable with a fiber optic (3) containing core, a sheath enclosing the core (4) made of a thermoplastic or elastomeric material, characterized in that the thermoplastic or elastomeric material of the sheath is crosslinked after grafting on silane compounds under the influence of moisture and one has the tracking resistance of this material causing additive. 2. Air cable according to claim 1, characterized in that the additive consists of metal oxides or carbide. 2nd PATENT CLAIMS 3. Air cable according to claim 2, characterized in that the additive consists of aluminum oxide hydrate and iron oxide. 4. Air cable according to claim 3, characterized in that the material of the sheath contains 30 to 80 parts by weight of aluminum oxide hydrate and 3 to 7 parts by weight of iron oxide per 100 parts by weight of polymer. 5. Air cable according to claim 2, characterized in that the additive contains titanium dioxide or zinc oxide. 6. Air cable according to claim 1, characterized in that the material for the sheath contains a linear polyethylene (LLDPE) with a density of 0.88 - 0.95 g / cm3 or one of its copolymers alone or as a blend with other polymers. 7. The method for producing an aerial cable with a creep-current-resistant sheath according to claim 1, characterized in that the base material is first mixed with the silane component and then the silane is grafted onto the base polymer, that the additive is incorporated and homogeneously distributed in the base material processed in this way , and that the casing is finally molded and exposed to moisture for the purpose of crosslinking. 8. The method according to claim 7, characterized in that the mixing of the additive into the silane-grafted base material takes place at temperatures between 100 ° and 140 ° C. 9. The method according to claim 7, characterized in that the crosslinking catalyst for the crosslinking under the action of moisture is only mixed in immediately before the shape of the crosslinkable envelope.