DE2548371A1 - ELECTRIC SEMI-CONDUCTIVE SHIELDING FOR POWERFUL CABLES AND COMMUNICATION CABLES WITH PLASTIC INSULATION - Google Patents

Description

Swiss cable, rubber

and plastics factories

Altdorf / Switzerland

Electrically semiconducting shielding for power and communication cables with plastic insulation

The invention relates to an electrically semiconducting shield for power and communication cables with plastic insulation, an insulation layer made of a thermoplastic or crosslinked polyethylene or thermoplastic or crosslinked copolymers of ethylene, the shielding being a polymer layer with an additive of conductive fillers

The application of shields for the limitation of the electrical Field and for the suppression of partial discharges directly on the insulation layer of a cable, in particular a high-voltage cable, is known.

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Thus, electrically conductive or made conductive tapes and fabrics of synthetic or natural material are used for this purpose proposed, these wrapped around the insulation layer will. In those that inevitably arise at the points of overlap In the air, glow discharges occur even at low field strengths, which destroy the cable insulation to lead.

The creation of these air spaces is avoided if graphite or soot itself or in dispersion on the insulation surface is applied and, if necessary, dried. Graphite is to be applied to the insulation layer by means of rotating brushes known and belongs to the common good in the cable production. Dispersions of carbon black or graphite in solvents are used in the DT-AS 1,011,948 and 1,490,625. In order to give these dispersions film-like properties that are intended to help that the graphite or soot after drying does not immediately come off the insulation surface with the slightest vibration various binders are used. For example, in GB-PS 724.850 (Pittsburgh Plate Glass Comp.) Alkaline Carboxymethyl cellulose and, in U.S. Patent 2,933,457 (General Cable Corp.), polyamide. The DT-AS 2.131.822 (Telefonaktiebolaget LM Ericsson) recommends the use of an aqueous dispersion of carbon black and polyethylene for the generation of an electrical semiconducting mixture on an olefinically insulated cable. It should be noted that the presence of conductive and insulating particles in the dried state next to each other never achieve the shielding effect of a homogeneous layer, because the Contact of the conductor particles with one another is worsened, if not prevented at all, by the presence of the insulation particles will. As can be seen from the text, their only advantage is based on the fact that they are thin-walled concentric Layers are obtained, as they cannot be obtained by extrusion, but in other ways long before Notice of this writing were generated.

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All publications mentioned in this section are What they have in common is that the cables, after they have been manufactured, produce satisfactory results in terms of partial discharge properties have to show, which, however, deteriorate considerably soon after the corresponding cable has been put into operation, so that a sufficient service life is no longer guaranteed. This is due to the fact that the initially sufficient low electrical resistance of the layer when the cable is operated with switching on and off the power supply very strong in the first heating-cooling cycles that occur increased and can no longer fulfill its intended purpose. (Compare Fig. 2)

Dispersions of carbon black, graphite or a metal powder in the solution of an organic binder, i.e. an electrical one Using conductive paint to limit the field lines in medium and high voltage cables is also sufficient known; almost all paint binders on the market are used. For example in GB-PS 1,109,095 (Coal Industry Ltd.) and GB-PS 1,144,325 (Dow Chemical Comp.) natural rubber latex or synthetic polymer latex based on polyvinyl chloride, polyvinylidene chloride, polyvinyl acetate, polyvinyl alcohol or polyvinyl propionate called. GB-PS 1.44.189 (Minnesota Mining and Manufacturing Comp.) Also names polyvinyl chloride in addition to a butadiene acrylonitrile copolymer for the production of conductive tape and lacquer. Silicone, styrene-butadiene polymer and polyamide used for this by Chomerics Inc. in GB-PS 1,266,422. Alkyd, epoxy, polyester, polyurethane and silicone resins can be found in CH-PS 399.560 (Allmänna Svenska Elektrisa Aktiebolaget) use, while in DT-OS 1.765.994 (Japan Glas-Chemical Co., Inc.) an amide, which during the Temperature increase during curing is converted into the imide, which is given preference. Because these binders are chemically

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clearly differ from those on which this writing is based, it should only be stated that when using all binders listed so far there is no adhesion to a untreated polyolefin surface is done, which is sufficient would be enough to permanently take over its task as a boundary layer of the electric field. This also applies to the DT-OS 2.340.881 (VEB Kabelwerk Oberspree), which contains a copolymer of ethylene and vinyl acetate as a binder component, to which either peroxides, drying resins or oils, or materials with free isocyanate groups are added to harden it will. This should create a firmly adhering, void-free, semiconducting mixture. That this is not the If this is the case, it can be inferred from the remark that the mixture can be easily pulled off the insulation like a hose. In the case of medium-voltage cables with a nominal voltage of up to 20 kV, where this relatively low operating voltage means that there is no partial discharge does not play a major role, this procedure can certainly be used successfully, but not with olefin-insulated cables for voltages in the range between 30 and 220 kV and above.

The application of semiconducting compounds that fuse with the insulation onto cable surfaces in an extrusion process has been known since 1945 (GB-PS 604.695; Automatic Telephone and Electric Comp.). While in the beginning In medium and high voltage cable production, pure polyethylene, filled with graphite and / or carbon black, is used for this purpose later, due to the development of new products in the plastics industry, other polymers or Copolymers of ethylene with acrylic acid esters, vinyl acetate, propylene and similar compounds for the production electrically semiconducting compounds are used. The use of copolymers of ethylene with vinyl acetate as a binder in electrically semiconducting mixtures according to known methods

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describe both U.S. Patents 2,200,429 and 2,703,794. In US Pat. No. 3,629,154 (Martin H. Johnson), an electrically semiconducting, non-porous, thin film is made by extrusion of a Material based on ethylene vinyl acetate with up to 10% by weight polyisobutylene and electrically conductive filler material obtained, which is used for electrical conductors in batteries. A similar blend of polyethylene and polyisobutylene is used specifically for cables according to GB-PS 828.334 (British Insulated Callender's Cables Ltd.). The DT-OS 2.051.268 (Sumitomo Electric Industries Ltd.), but a crosslinking agent is also added to the mixture. The use of copolymers of ethylene DT-PS 1.219.674 (Union Carbide Corp.) recommends using ethyl acrylate. oC ^ -monoethylenically unsaturated carboxylic acid and The DT-OS 1,669,970 (Dow Chemical Comp.) Contains copolymers of ethylene with a carboxylic acid ester. According to the US-PS 3,709,835 (Esso Research and Engineering Comp.) Are polyethylene, butyl rubber, ethylene-propylene copolymers and terpolymers, Styrene-butadiene rubber, polyvinyl chloride and mixtures of these polymers for the purpose of making extruded Tapes that are wound at their splice points when connecting two cables and also for extruded ones Layers are suitable used. Ethylene-propylene terpolymer, as well as other copolymers of an olefin with a Rubber and carbon black are also the basis of the concept of the invention in DT-OS 2.120.197 (Allied Chemical Corp.). from The same inventors mentioned almost identical material in DT-OS 2.161.076 as film material for Leclanche batteries suggested. Blends of polyethylene with rubber materials are disclosed in U.S. Patent 2,597,197 (Goodrich Comp.) Called. Finally, semiconductor compounds for cable shielding are based on crosslinkable, chlorinated Polyethylene with carbon black is described in DT-OS 2.235.075 (Siemens AG).

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All of these electrically semiconducting mixtures mentioned for the shielding, i.e. for the interference suppression of communication cables and for the limitation of the electrical field in medium and high voltage cables, have the following behavior in common: If the shielding is produced by simply adding the polymer used to form a layer with a If conductive filler is added and extruded onto the cable insulation, this and the shield weld together. In terms of the cable construction and the life expectancy of the cable, this would be an optimal condition, because the welding of both parts mentioned does not only occur when the absolutely identical insulation polymer is used in semiconductor mixtures, but can also occur when mixed and copolymers are used Ethylene alone or in combination with polyethylene. This depends solely on how much ethylene is present in the other component (eg propylene, vinyl acetate, ethyl acrylate, carboxylic acid) in the end polymer or in the mixture. A statement as to the weight ratio of ethylene to the copolymer component in order to ensure this welding cannot be given, since it depends on many other factors in addition to the factor which material is used for the copolymerization. The decisive disadvantage of welding such a known semiconductor layer to the insulation layer, however, is that the necessary undamaged, smooth insulation surface can hardly be achieved in order to detach the semiconductor layer during cable assembly, as is the case with cable sleeves and cable terminations of central and high-voltage cables are required. However, the removal of the semiconductor layer is mechanically simple tools can be made at an installation of the cable \ in peeling of the semiconductor layer but grooves and small, barely visible injuries in the insulation can not be avoided. Be part of such a

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The cables commonly used today, made of an elastic material (ethylene propylene terpolymer, RTV silicone rubber, etc.) existing clip-on terminations or terminations wound from insulating tapes of various materials, see above When the operating voltage is applied, leakage paths are formed which soon lead to failure of the cable due to a flashover at this end to lead. If the known semiconductor mixtures are adjusted by combining one or more polymers so that they After the extrusion, not welded to the polyolefin of the insulation surface, but only more or less strongly stick to this, so occur (as with graphite, dispersions and lacquers) when the cable is in operation after a few heating-cooling cycles Partial discharges of higher magnitude and lead to Destruction of the cable. This is because the semiconducting layer becomes detached from the insulating layer as a result of various Elongation, different coefficients of expansion and because of the lack of adhesion for this purpose, and back there remain air gaps in which the glow discharge takes place.

The object of the invention is therefore to produce a shield from an electrically semiconducting mixture, which is at Welding with the insulation of a communication or power cable by common solvents is easy again and can be completely removed without causing the slightest damage to the insulation surface, and which can subsequently be used universally.

According to the invention, such a shield is the one mentioned at the beginning Type obtained that the semiconducting mixture contains at least one polymer based on acrylic acid, acrylic acid ester, butene-1, Propylene, vinyl acetate, vinyl ethers alone and / or in copolymerization, especially terpolymerization, with ethylene and / or Copolymers, especially terpolymers of the same with styrene, carboxylic acids, carbon monoxide, cyclopentene, cyclohexene or

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Vinyl chloride and also a resin based on unsaturated hydrocarbons of low molecular weight with a Contains softening point of 70 - 200 C. This mixture is optionally halogenated, sulfohalogenized and / or Pure polyethylene added.

The electrical conductivity is achieved by adding carbon black and / or graphite and / or metal powders, depending on the specific Purpose of use, received and depends entirely on the desired specific conductivity of the coating. Carbon black and / or graphite are preferably used in the mixtures where a specific resistance of 10-100ji cm can be accepted. The mix should have smaller resistances present, metal powder is used. Metals of groups Ib, 2 B, 3, 4 and 5 proved to be here of the periodic system of the elements according to CH-PS 515 (British Petroleum Comp., Ltd.) are most suitable. Also surface silver-plated Metal powder, in particular copper powder, can advantageously be used as electrically conductive fillers in the Mixture are used.

The invention is illustrated by way of example with reference to the accompanying drawings explained in more detail, it show:

1 shows the composition of the polymer mixture,

2 shows the resistance behavior of various semiconducting shielding materials as a function of temperature,

3 shows the same behavior as a function of elongation,

4 shows a cross section through a cable provided with a shield, and

5 Results of partial discharge measurements on medium-voltage cables with different shields.

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The polymer mixture is preferably composed so that that, as can be seen from Fig. 1, the proportion of polymer Ethylene is between 20 and 66 wt .-% and this still, according to the description in the previous section, between 8 to 35% by weight of other polymers or copolymers and / or terpolymers plus 5 to 68% by weight of an unsaturated hydrocarbon resin can be added. The high proportion of polyethylene that is to be striven for causes the welding to take place in the mixture the same with the olefinic insulation of the cable. The addition of the other polymers or copolymers, especially the Terpolymers, serves several purposes. It creates an extremely high degree of flexibility and a reduction in value the solvent resistance of the polymer mixture obtained, in addition to a mediation of the compatibility between the polyethylene and the hydrocarbon resin. Hydrocarbon resin must be contained in the polymer mixture in the stated amounts, in order to ensure solubility in chlorinated aromatic and / or aliphatic Hydrocarbons (e.g. gasoline and toluene) improve so much that they can be easily and completely at temperatures takes place between 0 and 20 C. The mixture of these components is called polymer mixture in the following text.

To achieve electrical conductivity, the polymer mixture, based on its weight, can contain up to 150% by weight Carbon black, up to 200 wt .-% graphite or mixtures of this material with carbon black, up to 900 wt .-% of a metal powder and up to 500 wt .-% of a surface silver-plated metal powder are added. As particularly suitable for the manufacture · electrical The Ketjenblack carbon black types have become semiconducting mixtures EC (Ketjen-Carbon NV, Holland), Vulkan XC-72 (Cabot Corp., USA) and Corax L (Degussa, FRG). Depending on the chosen procedure The production of the cable coating with a semiconductor mixture takes place in different ways and should therefore are described in more detail below.

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Semiconductor mixtures according to the invention which are produced by extrusion to be applied as an electrically conductive layer on the cable insulation, are either in special mixing extruders {such as the transfer mix from Paul Troester, Hanover, the Ko-Kneter from Buss KG, Pratteln or the ZSK twin-shaft kneader from Werner & Pfleiderer, Stuttgart) or made in a well-known internal mixer. If the latter is used, the hot mixture will arrive onto a rolling mill and from there into a strainer / granulator device, while it, manufactured in mixing extruders, is fed directly to the granulator in the form of strings. That The electrically conductive mixture granulate obtained in this way is then suitable for extrusion onto the core insulation.

Starting from the granules or that obtained by mixing the polymers with the conductive fillers on a rolling mill For the time being, the skins are coarsely crushed mechanically. The small pieces of mixture obtained are then dissolved in aromatic and / or aliphatic and / or chlorinated hydrocarbons and are in this Form as paint ready for coating.

Another way of producing solvent-based paints is to mix the polymers in a suitable one Solvent by heating the same in a heated stirred tank, this solution the conductive Add fillers and the desired degree of fineness of the latter by comminution in one, in the lacquer and paint industry the usual equipment (e.g. dissolver, bead mill, three-roller mill, etc.). Dispersions in water or Another nonsolvent can be obtained by dispersing an ultrafine powder of the semiconducting mixture by means of a slight Addition of a wetting agent based on surface-active substances can be obtained. A semiconducting powder is obtained if such large amounts of a non-solvent v (e.g. alcohols, ketones or acetic acid esters) are added to the paint while stirring

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adds that the dissolved materials precipitate completely in a homogeneous mixture. If the filtration residue is washed and dried, a powder suitable for use as a powder coating is present. This can, however, also be obtained by mechanical comminution of the granulate or the skin to the desired degree of fineness, the comminution taking place either at room temperature or according to the Linde process by supercooling by means of liquefied gases. According to all of the processes mentioned, it is in principle possible to produce ultra-fine powders with particle sizes between 5 and 20 μm.

As a coating process for the semiconductor mixtures according to the invention all known for this can apply to the olefinic insulation of a communication or power cable Procedure to apply. Granules can be processed with screws suitable for polyethylene (e.g. PE and BM screws) in conventional extruders in tandem extrusion or in a separate operation to obtain so-called "extruded semiconductor layers" on olefin-insulated Cores are processed. Paints and dispersions are made by dipping, spraying, brushing or spraying (in printing or Airless process; with or without electrostatics) to the Insulation surface applied. Paint in combination with spray propellant in spray cans with one or more metal or Filled porcelain balls for the homogeneous distribution of settled fillers, helps the fitter with the assembly of Terminations and cable sleeves at the deposition point of the semiconductor coating one around the circumference of the wire to obtain symmetrical deposition of the semiconductor layer, with a drying of the lacquer layer after the spraying an industrial blow dryer or an open flame. The process that has recently become more and more successful the so-called "powder coating" can also be used for the

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Core coating with the semiconductor mixture in powder form be used; Both the fluid bed process, in which the powder is blown by means of an air stream (such as Chalk in water) is kept in a homogeneous suspension as a mixture of air / powder, as well as the spraying process with or be used without electrostatics. Such a coating process should preferably be based on a heated one Vein surface take place.

Depending on the type of coating process used either an after-treatment of the applied layer takes place in the heat, or it is unnecessary. No heat treatment require the coating process of extrusion and all those processes in which the order is direct is applied to the hot core insulation leaving the extrusion head. For all other procedures, at those who have a relatively cold insulated wire available, must be dried after coating with the known Heat sources such as heated air, infrared dry rays, MICOR heat emitters, but preferably with High-frequency dryers, whereby the temperature on the insulation surface should be briefly high enough to allow it softens and on this way with the then also present as a melt semiconductor layer in such a way what connects with each other is that after cooling, both layers are welded together. Then this is the This is the case when, during a mechanical tensile strength test, the breakage occurs very rarely or not at all at the connection points this two layers occurs. When coating with paints, dispersions and powders, compared to extrusion result in thin coatings, special care must be taken during the heat treatment that the coated The surface does not get too hot because, in the special case of a pure polyethylene-insulated surface, it becomes one very quickly

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The material flows away, and so does the semiconductor layer Cracks can occur, which impair the functionality of the cable.

The chemical resistance of the semiconducting polymer mixture to alcohols and water allows it where there is a coating the wire takes place directly after the insulation extrusion and thus a relatively slow cooling must be done to work in all cooling media used for this purpose, such as in ethylene or triethylene glycol, in order to prevent the occurrence of internal stresses caused by too rapid a cooling process in the end product.

The welding of the semiconducting polymer mixture also occurs all olefin-containing or olefin surfaces (e.g. polyethylene, Polypropylene, ethylene-propylene copolymer, ethylene-propylene terpolymer, Ethylene methyl acrylate). Very good adhesion will be to paper, wood, polystyrene, plasticizer-free or-poor polyvinyl chloride, polyacrylates, natural rubber and styrene-butadiene rubber. No liability takes place too soft polyvinyl chloride, polyamide and many types of synthetic rubbers. This is particularly important because electrically semiconducting upholstery tapes, based on these materials, are used to protect the core from damage caused by overlying copper wires or tapes and on which the semiconducting layer, even under thermal stress, must not adhere under any circumstances in order to avoid damage to these cores of central and avoid high-voltage cables by gluing them to the tape.

During further processing, cable cores are very often subject to mechanical abrasion loads, such as those caused by trains occur through caterpillars, stranding points and on pulleys.

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Is it not possible for any manufacturing reason to wrap the semiconducting coated wire? To protect this with an electrically semiconducting cushioning tape from the effects of this stress, the semiconductor layer becomes partially mechanically damaged, with the use of glow discharges at these points during commissioning this cable can come. Therefore, it was also the aim of the invention to obtain a coating that the possible Abrasion loads has grown.

To assess the abrasion resistance, a test device such as that described in Publication No. MW 15-1955 of National Electrical Manufacturers Association, New York (NEMA) recommended for testing enamelled wires and from Rudolf Herbeck, Wuppertal-Elberfeld is produced, modified in such a way that it is suitable for the use of flat test objects and automatically when the insulation value increases

2
1 cm large test area switches off to over 100 kA. For the test, polyethylene plates 2 mm thick, 10 mm wide and 50 mm long were coated on one side with a wide variety of semiconducting materials to a thickness of about 50 μm. Graphite could only be tested in a much thinner layer. The abrasion test was carried out with a steel needle with a diameter of 0.40 mm, which was loaded with a weight of 1 kg. With semiconductor lacquers and dispersions of known composition, as well as with graphitization, the abrasion resistance with values below a double stroke proved to be extremely dubious for the core coating. Which ^- on the market semiconductor blends for extrusion coating moving with values between 5 and 15 double strokes, depending on the composition and manufacturers, in useful limits. The semiconductor mixtures according to the invention withstand over 100 double strokes and can therefore be described as optimal for the wire coating.

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When stressed by the operation of medium and high voltage cables, for example, the olefinic core insulation expands as a function of the operating temperature. The temperature at which the cable can be operated depends on the one used Insulation material from and is 70 C for polyethylene and for peroxidically crosslinked ^ polyethylene and ethylene-propylene terpolymer 90 C. What is the resistance behavior in the semiconductor layer surrounding the insulation (called radiation protection) occurs when graphitization is used, is illustrated in FIG. 2. Already after four heating-cooling cycles the surface resistance increases to such an extent that the task of coating is no longer given. In the case of the semiconductor layers according to the invention, on the other hand, there is only an insignificant increase in the surface resistance with increasing temperature, which is, however, absolutely reversible. For the operational safety of the radiation protection a surface resistance that is as unchanged as possible when stretched is required. The behavior of some common ones Semiconductor coatings is plotted in FIG. Here graphite behaves as it did before found bad and inadequate. Commercially available dispersions and lacquers lie between the curve for graphite and the one called HL-Lack. The latter is a commercially available high-flexibility paint based on of ethylene-vinyl acetate copolymer on olefin surfaces adheres well and can be described as the best known semiconductor lacquer in terms of elongation properties. The mixture according to the invention, in FIG. 3 for comparison purposes also applied to the test specimen in lacquer form, is close to the values for extruded semiconductor layers and shows an almost analogous behavior to these. The advantage of the mixture according to the invention over the known extrudable Semiconductor mixtures are based on a significantly higher elasticity of the material, which is about 70% compared to only 25% with conventional extrusion compounds.

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Medium and high voltage cables with the inventive Mixtures are coated, can be with cables that are coated with known semiconductor mixtures, compare qualitatively as follows:

The layer according to the invention has in comparison to an extruded, a semiconductor layer welded to the insulation equivalent behavior in the case of partial discharges and better in terms of removability of the layer. Compared to the mixture according to the invention is a semiconductor mixture which is likewise extruded but is only glued to the insulation better with partial discharge and with regard to elongation and adhesion, while the removability is about the same. In comparison It is much better than graphite and known paints in terms of partial discharge, elongation and adhesion, only the removability is about the same.

The difference between welding and gluing in this context is that there is a glued layer loosens from the insulation in the event of mechanical stress, while a welded layer (e.g. during expansion under the influence of the heating of the thermally highly stressed cable) maintains its original, close adhesion to the insulation. The bonding is often implemented in such a way that deliberately chemically different materials for semiconductors and Insulation can be used (e.g. rubber-like semiconductors on olefin insulation), while chemically similar ones are used for welding Materials to be chosen.

A single-conductor medium-voltage cable constructed according to FIG. 4

20 kV / 50 mm should be used as an example for all other cables Cross-sections, insulation materials and higher voltage series speak with analogous results. The middle-

2
voltage cable has a 50 mm conductor 1 made of copper, on which in tandem a peroxide layer filled with soot

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Containing polyethylene existing Leiterschirra 2 and a polyethylene insulation mixture 3 mixed with peroxide were extruded, whereupon the crosslinking took place in the steam. The cable core formed in this way was then cut into three lengths. Part length 1 was provided with a graphite layer by means of rotating brushes, part length 2 was extruded and crosslinked with a customary cal lead, so that a bond between the semiconductor layer and insulation resulted and part length 3 was coated with a semiconductor mixture according to the invention. The three partial lengths provided with the above-mentioned different coatings serving as radiation protection 4 were completed with a semiconducting rubber padding tape 5, a wire screen 6, a copper tape 1, wrapped cover tape 8 and extruded thermoplastic material 9 as test cable. The partial discharge measurement was carried out on five test items of each of these three variants. The values found are shown in curves A (FIG. 5) for the individual variants. The test items were then subjected to the load cycle test with heating to a conductor temperature of 130 C (which corresponds to the permissible emergency operating temperature of this cable type) and on - ■ ■

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final cooling to room temperature over a total of Subjected to 300 such cycles, after which the partial discharge values of curves B were obtained for the individual variants. The poor elongation behavior typical of graphite was confirmed by the initially very good partial discharge threshold voltage dropped from 55 kV after exposure to 15 kV. The conventional behavior showed a different behavior and semiconductor mixtures according to the invention, with only one deterioration in the partial discharge threshold voltage after their loading of 3 kV. In detail, the values fell from 20 to 17 kV (known semiconductor mixture) and from 37 to 34 kV (semiconductor mixture according to the invention). That The hatched rectangle in Fig. 5, bottom left, indicates the impermissible partial discharge threshold voltage and level of a 20 kV cable according to the regulation Conzept 5, 1974 of the Dutch Keuring Electrische Materialen Arnhem (KEMA).

The semiconductor mixture according to the invention is thus all known dispersions and lacquers in addition to the commonly used graphitization with regard to adhesion and abrasion resistance and far superior to the functional reliability of the coating on a cable. With regard to known semiconductor mixtures for the extrusion process has the semiconductor mixture according to the invention the advantages of easy detachability when welded to the insulation, higher flexibility, better Abrasion resistance and the higher partial discharge voltage due to these properties. One use Powdery semiconductor mixtures for the powder coating of olefinically insulated cables were not previously known.

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Claims (12)

Claims 1. 'Electrically semiconducting shielding for heavy current and Communication cable with plastic insulation that has a layer of insulation made of a thermoplastic or crosslinked polyethylene or of thermoplastic or crosslinked Have copolymers of ethylene, the shielding a polymer layer with the addition of conductive Contains fillers, characterized in that this semiconducting mixture is based on at least one polymer Acrylic acid, acrylic acid ester, butene-1, propylene, vinyl acetate, vinyl ethers alone and / or in copolymerization, especially terpolymerization, with ethylene and / or copolymers, especially terpolymers of the same Styrene, carboxylic acids, carbon monoxide, cyclopentene, cyclohexene or vinyl chloride and also an unsaturated hydrocarbon-based resin having a softening point from 70 - 200 ° C. 2. Shielding according to claim 1, characterized in that the proportion of polymeric ethylene is between 20 and 66% by weight, the proportion of other polymers or copolymers, in particular terpolymers, between 8 and 35% by weight and the proportion of unsaturated Hydrocarbon resin is between 5 and 68% by weight. 3. Shielding according to claims 1 to 2, characterized in that that the polymer mixture contains up to 150% by weight of carbon black, up to 200% by weight of graphite or mixtures of this material with carbon black, up to 900% by weight of a metal powder or up to 500% by weight of a surface-silvered metal powder are added to achieve electrical conductivity, each based on the weight of the polymer mixture. 7 0 9 81 8/0107 4. Shielding according to claim 1, characterized in that the resin has a softening point of 100-150C. 5. Shielding according to claim 1, characterized in that its halogenated, sulfohalogenized and / or pure polyethylene powder is added. 6. shield according to one of claims 1 to 5, characterized in that that the semiconducting mixture in aromatic, aliphatic, cycloaliphatic and / or chlorinated Hydrocarbons at temperatures between 0 and 20 C. is easily soluble. 7. A method for producing the shield according to claims 1 to 4 on a cable insulation with a surface olefinic plastic, characterized in that the shielding is achieved by continuously applying the semiconducting mixture to the cable insulation and then subsequently Welding is formed with the latter. 8. The method according to claim 7, characterized in that the semiconducting mixture is applied by extrusion. 9. The method according to claim 7, characterized in that the semiconducting mixture by dispersion or in solution to the Surface is applied. 10. The method according to claim 7, characterized in that the semiconducting mixture by applying a fine powder is obtained on the surface. 11. The method according to claim 9, characterized in that the semiconducting mixture by spraying a varnish or a dispersion with a propellant, e.g. dichlorodifluoromethane, takes place together from a pressurized spray container. 709818/0107 12. The method according to any one of claims 9 and 10, characterized in, that the semiconducting mixture with the insulation by drying with preferably high-frequency dryers is welded. Sb / dh / 10/23/1975 709818/0107