DE9218351U1 - Electrical cables - Google Patents

Description

OUR ZHCHENiOUR REF DATUMA)ATE

D7 68-9-T 93 Gbm ; 20 October 1993

Tu/fi :

- Applicant:

Daetwyler AG

Cables and systems

CH-6460 Altdorf

Electrical cables

The invention relates to an electrical cable, in particular an electrical power cable, which in cross-section has at least the following elements arranged from the inside to the outside in the following list in the corresponding order:

- a leader;

an inner conductor layer;

- an insulator;

- an outer conductor layer;

- an umbrella; and i

- pine outer shell.

Such a cable structure is particularly well-known in electrical cables in medium and high voltage technology and has an external plastic insulation in the case of a so-called three-layer insulation consisting of semiconductor-insulation-semiconductor. The semiconductor layers ensure that, on the one hand, the electrical field pattern within cylinders that is favorable in terms of energy technology is optimally approximated. Surrounding the conductor, the semiconductor layers also serve to better smooth its outer circumference or, at a distance, as an insulation shield. Between the inner and outer semiconductors,

An insulator is preferably made of PE, XLPE or ethylene-propylene rubber elastomer.

It has been shown that the plastic insulation of the cable is extremely sensitive to water and allows water to diffuse into the interior of the cable even with the slightest amount of water vapor; this process occurs even at relatively high humidity. If the water molecules penetrate through the outermost plastic protective cover into the insulator during diffusion, they destroy or change its structure when a high electric field is simultaneously applied. Such structural changes, which vary from place to place, are known as so-called water trees due to their branched shape and ultimately lead to premature aging of the material and, accordingly, to a shortened service life of the cable. They cause different conductivities and dielectric properties and initiate a potentially destructive breakdown.

To counteract this problem, the following solutions have been applied to high voltage cables:

- the use of an outer lead sheath:

However, such a lead sheath has the disadvantage that it is very heavy and makes laying the cables more complicated. At the same time, such a lead sheath is expensive and tends to develop microcracks if there are even the slightest deviations from the optimal alloy composition, which in turn lead to the previously described disadvantage of water diffusion. In addition, lead, like other heavy metals, places excessive strain on the environment.

- the use of a shaft jacket made of metal, for example aluminium or copper:

In addition to the properties already described in the context of the disadvantages of the lead sheath, with such a corrugated sheath there is the fact that the increased diameter of the entire cable with the same winding drum diameter only allows shorter overall cables on this usually standardized drum. In addition, such a corrugated sheath is associated with known installation difficulties.

- a layered jacket is installed under the outer protective cover, i.e. the jacket, as a polyethylene-coated metal foil (CU or AL) running lengthwise with an overlap and longitudinal seam. This is an extremely expensive construction method. At the same time, major problems arise during assembly and in equipotential bonding in the event of a fault.

Such a layered jacket is known, for example, from EP 0 380 929 A1. The composite film described in this publication consists in a complex manner of four layers of very different consistencies.

All the solutions described above have the common problem that the so-called "longitudinal watertightness ^{" 11} must be ensured under the plastic sheath, but also in the case of metallic protective covers (such as corrugated sheaths or lead sheaths). Otherwise, even the slightest damage or assembly errors could cause water molecules to enter the cable, spread longitudinally and thus endanger not only the damaged area, but the entire cable.

However, additional construction elements for this "longitudinal watertightness", such as a transverse fleece, further increase the effort as well as the material requirements and also the costs.

In addition, common source materials are hygroscopic; they

··

contain water already during installation and lead to water reaching the insulation directly.

Windings made of metal strips - for example made of the materials AL, CU or BL - similar to those used in EP 0 380 929 Al may make water diffusion more difficult, but they cannot guarantee a sufficient protective effect. In the event of bending, such strips loosen locally, which means that their bond and the corresponding barrier effect are broken. In all previously known designs, metal could not fit directly on the insulation due to the different thermal expansions; an integrated layer of padding was required. In addition, such strips must be extensively padded due to their sharp edges. Such padding is usually finely structured HI materials, such as foam, fleece, crepe paper, etc. They are naturally hygroscopic and increase the water content in the layers adjacent to the insulation during installation. In the event of damage, they serve as an undesirable water reservoir.

However, with an electrical cable with the known type of structure, there is not only the problem of water molecules entering the insulator from the outside through the sheath into the interior of the cable. Water diffusion from the inside, i.e. from the conductor, is also possible. This occurs, for example, when water gets into the conductor when the cable is pulled in, or when there is mechanical damage (for example from an excavator) or electrical damage (breakdown) during operation. Water can also penetrate the cable undesirably at cable ends that are not properly sealed.

To counteract this problem, the following solutions have been offered for high-voltage cables:

a solid conductor, which, however, has the disadvantage of compromising flexibility and causing great difficulties in processing and installation.
the introduction of swelling powders between individual wires; however, such a construction method is expensive and complicated, and at the same time there is the disadvantage that water can get into the interior of the cable, which is something that should be avoided. In addition, the assembly is problematic.

- a pipe ladder; however, this is extremely expensive and complex.

Such solutions, which usually have major disadvantages, have so far only been able to prevail for cables for higher voltages or for direct submarine water use. However, for so-called mass-produced medium-voltage cables such solutions were usually far too complex. However, the common features of the solutions so far are that they can at best inhibit water diffusion, but not eliminate it.

The aim of the invention is to improve generic cables in terms of

Shielding against water diffusion at least

to improve the consistent electrical properties of the cable.

This objective is achieved in an electrical cable of this type by arranging a metallic layer or foil on and/or in at least one conductor layer.
dadu:

This ensures that not the entire cable, but (mainly) the water-sensitive insulation system is protected against water diffusion - regardless of whether it comes from

inside or from the outside - is shielded. Since the conductor layers form the immediate surroundings of the insulator, the invention prevents, for example, additional layers or gaps formed with them, which are further away from the insulator, from filling with water molecules. At the same time, the coaxial field pattern of the cable can be improved by arranging metallic layers or foils directly on and/or in the conductor layers, without providing a direct charge carrier injection. In a particularly preferred embodiment of the electrical cable according to the invention, a cushioning layer is arranged between the outer conductor layer and the wire shield (claim 2). This cushioning layer serves as a buffer for the wire shield. It prevents the wires of the wire shield from undesirably penetrating the outer conductor layer or damaging it when external forces are applied to the cable.

Another particularly preferred embodiment of the electric cable according to the invention is designed in such a way that the metallic layer or foil is arranged at least partially adjacent to the inner surface of the inner conductor layer and/or the outer conductor layer (claim 3). Since the conductor usually consists of individual conductors which, when packed tightly together, do not represent a smoothed outer surface, since they form free spaces on the outside due to their spacing from one another, the metallic layer or foil can simulate such a smoothed surface, electrically speaking. In particular, a foil is stretched onto the upper, outwardly projecting sections of the outermost individual conductors in a point-by-point manner. The structure of the foil then does not follow the recesses caused by the dimensions of the individual conductors. Of course, the advantage of smoothing the outer surface of the conductor also applies to a composite of conductor layer and foil/metallic layer arranged on this outer surface. The conductor layer can be used as

first applied to this outer surface, for example as part of a spraying process. In general, the higher conductivity of the applied metal compared to the conductivity of the usual conductor smoothing layers allows for better smoothing of the field. The special structure also makes it possible to avoid undesirable direct metal-to-metal contact.

In a particularly preferred embodiment of the electrical cable according to the invention, the metallic layer or foil is integrated into the inner conductor layer and/or the outer conductor layer (claim 4). This results in particular in manufacturing advantages, since the respective metallic layer or foil is automatically introduced during the manufacture of the electrical cable as part of a predetermined process step. At the same time, its position within the conductor layer, which is usually sprayed, is precisely defined, which has positive effects in particular with regard to the geometry of the field. The conductor layers advantageously consist of semiconducting material, which is preferably provided with soot particles (claim 5). The conductor layer therefore has only a low resistance and therefore a high conductivity, which in turn is advantageous for the electrical conditions within the cable, and in particular between semiconductor layers and the insulator arranged between them.

In a particularly preferred embodiment of the electric cable according to the invention, the metallic layer or foil has a lower electrical resistance than the conductor layer on and/or in which it is arranged (claim 6). The difference in the resistances can be in the order of magnitude of at least a power of ten. In such a design, the metallic layer or foil acts as an equipotential surface, through which essentially no current flows. Between the metallic layers on and/or in mutually

An electric field of a coaxial capacitor can form between spaced conductor layers.

It is particularly advantageous for the metallic layer 5 or foil of the cable according to the invention to have properties of a vapor barrier (claim 7). Water or water vapor diffusion is prevented in this way. It is particularly advantageous for the metallic layer to be an atomically thin layer with a thickness of preferably a few angstroms to 20 μm (claim 8). In order to act as a water vapor barrier, no particular thickness of the metallic layer is required. Even a layer thickness in the atomic range means that the hydrogen molecules are prevented from migrating. From this point of view, it is particularly advantageous if the metallic layer consists of a material that can be vapor-deposited onto the respective surfaces of the conductor layers (claim 9). Such a design leads to the most cost-effective, minimal material consumption while at the same time providing optimal effect as a vapor barrier. In addition, the vapor-deposition process step in the manufacture of the electrical cable can be carried out in the shortest possible time.

Particularly thin metal layers are very sensitive and not self-supporting. For this reason, a force transmission or a relief element is necessary.

In a particularly preferred embodiment of the electric cable according to the invention, the metallic foil or layer has a carrier material for these purposes (claim 10). Further processing then takes place together with the carrier material. Since the conductor layer consisting of semiconductor material is sprayed, the introduction of a metallic foil with carrier material offers improved mechanical strength. During the spraying process for the conductor layer, material collapses can therefore be reduced or avoided. Arranged on the inner conductor layer

a previously explained, mechanically stronger carrier or holding material can help to avoid geometric errors, in this context, material collapses and gusset shapes are particularly mentioned. 5

Particularly preferably, the metallic layers or foils in the respective conductor layers are arranged concentrically around the conductor (claim 11). The field distribution within the cable is thereby optimal. The field distribution is further improved in particular from the point of view that, according to a further preferred embodiment of the electrical cable according to the invention, the metallic layers or foils in the respective conductor layers are arranged in such a way that their surfaces run concentrically to one another (claim 12). This ensures that the area of conductor layer-insulator-conductor layer is optimally aligned in terms of field distribution.

The metallic layer or foil is particularly preferably part of the cushioning layer (claim 13). For example, the metallic layer can be applied to the inside of the cushioning layer and applied together with the cushioning layer to the outer conductor layer (semiconductor layer). In another preferred embodiment of the electrical cable according to the invention, the metallic foil or layer has an anti-corrosive layer (claim 14). In particular, the anti-corrosive layer can be designed as a conductive paint layer and ensures that the property of the metallic layer or foil to act as a water vapor barrier according to the invention is not impaired by corrosion processes.

Embodiments of the invention are illustrated in the drawings and are described in more detail below.

Show it:

Fig. 1 a 1/4 cross section of the cable according to the invention and

Fig. 2 shows a half or full cross section of further embodiments of the cable according to the invention.

The following is an explanation of the invention and its further advantages based on the drawings according to the structure and, if applicable, also the mode of operation of the invention shown.

Fig. 1 shows an energy cable 1 according to the invention, which is suitable for both high voltage and medium voltage. This energy cable 1 has the following components from the inside to the outside in the cross section shown in Fig. 1:

A conductor 2 that runs coaxially through the power cable 1 in the longitudinal direction of the axis consists of one or more conductor wires 3 that are packed tightly together. The surface of the circumferentially outermost conductor wires 3 is, viewed as a whole, corrugated in that the geometric distances between the individual conductor wires 3 form successive gaps 4 due to their approximately circular geometry. These gaps 4 on the surfaces of the outermost conductor wires 3 cause the field within the power cable 1 to become non-uniform on the surfaces that form the gaps 4. The conductive (semi-conductive) interstices filling that is currently used and is generally known can only smooth the field to a limited extent.

According to the invention, a metallic foil 5 is now arranged in a point-by-point arrangement on the outermost conductor wire sections. As explained later, a metallic layer 5 can also be suitable instead of the metallic foil, depending on the surface to be influenced and/or shielded. This metallic layer 5

The metallic foil 5 forms, so to speak, the outward-facing, smoothed outer surface of the conductor 2. It is clear from Fig. 1 that the stretched metallic foil 5, as an outer surface of the conductor 2, has significantly smaller valleys and peaks (almost circular) than an outer surface of the conductor 2 that would be created by the outwardly projecting peripheral surfaces of the conductor wires 2. Consequently, the application of a metallic foil 5 according to the embodiment according to Fig. 1 as a quasi-artificial outer surface of the conductor 2 has a field-calming and field-smoothing effect. This effect is significantly improved by the resistance ratios.

The metallic foil 5 rests at least partially against the inner surface of an inner semiconductor 6, preferably over a large area, in order to avoid the possibility of gaps between the metallic foil 5 and the inner semiconductor 6. The formation of longitudinal water at this point can thus be counteracted. As already explained above, the metallic foil 5 has the effect of a vapor barrier, which prevents the diffusion of water molecules.

An insulator 7, which preferably consists of PE, XLPE or ethylene-propylene rubber elastomer, is directly connected to the inner semiconductor 6. According to the invention, the insulator 7 is prevented from being damaged, i.e. weakened, by forming branched shapes, the so-called "water trees", due to the penetration of water molecules 0. An outer semiconductor 8 is again directly connected to the insulator 7.

In the embodiment of Fig. 1, a further metal layer 9 is applied or introduced into or onto the outer semiconductor 8. Fig. 1 shows how the metal layer 9 is integrated into the outer semiconductor 8. For this purpose,

A further semiconductor layer 10 is applied to the metal layer in a process that is advantageous, in particular by spraying. The outer semiconductor 8, 9 with the integrated metal layer forms a better field limitation of the power cable 1.

A cushioning layer 11 is arranged on the outer surface of the semiconductor layer 10. This cushioning layer 11 ensures that the shielding wires 12 arranged on their outer surface cannot influence or damage the geometrically exact arrangement of the outer semiconductor 8, 10 with the metal layer 9 located therein, coaxial to the conductor 2, due to the effect of external forces on the power cable 1. An external force on the power cable 1 and consequently on the shielding wires 12 is absorbed by the cushioning layer 11. Finally, a sheath 13, for example made of polyethylene or PVC protective sheath, is arranged completely around the shielding wires 12.

Finally, it should be noted with regard to Fig. 1 that, of course, the metallic foil 5 or a metallic layer 5 can be embedded in the inner semiconductor 6 in the same way as was explained in connection with the outer semiconductor 8, 10. The innermost outer layer of the semiconductor 6 is then used to smooth the outer surface of the conductor 2, which then virtually replaces the metallic foil 5 of Fig. 1. The metallic foil or metallic layer 5 is then represented in the embodiment according to Fig. 1 by the white line in the inner semiconductor 6.

In the embodiment of Fig. 2, which corresponds in principle and in its essential elements to the embodiment of Fig. 1 - accordingly, the same components are provided with the same reference numerals - the multiple function of the field-limiting layers, in particular the

metallic layers 5 and 9 are further optimized. In the case of identical components, their function and arrangement will not be explained in more detail again, since this has already been done with reference to Fig. 1.
5

In contrast to Fig. 1, however, the inner surface of the inner semiconductor 6 is completely vapor-deposited with a metallic layer 5. The coaxial formation of the field-limiting layers in the manner of a capacitor around the coaxial conductor 2 is clearly visible. The metallic layers or foils 5, 9 acting as vapor barriers are geometrically aligned exactly coaxially to one another. The metallic layers 5, 9 preferably consist of Cu, Al, Pb, Zn and, due to their direct arrangement on the insulator 7 to be protected against water diffusion, provide optimal protection while simultaneously limiting the field due to their function as conductive layers. The field distribution is optimized.

Claims (14)

SAMSON & Aip^ f PATENT ATTORNEYS · EUROEÜBÄtf PATtNTATTORNEYS OUR REF DATE/OATE D768-9-T 93 Gbm 20 October 1993 Tu/fi Claims 5 1. Electrical cable, in particular electrical power cable, which has in its cross-section at least the following elements arranged from the inside to the outside in the following list in the corresponding order: - a leader; - an inner conductor layer; - an insulator; - an outer conductor layer;
an umbrella; and - an outer shell, characterized,
that a metallic layer or foil (5;9) is arranged on and/or in at least one conductor layer (6;8,10). 2. Electric cable according to claim 1, characterized in that a cushioning layer (11) is arranged between the outer conductor layer (10) and the shield (12). 3. Electric cable according to claim 1 or 2, characterized in that the metallic layer or foil (5; 9) is arranged at least partially adjacent to the inner surface of the inner conductor layer (6) and/or the outer conductor layer (8). 4. Electric cable according to one of the preceding claims, characterized in that the metallic layer or foil (5; 9) is integrated into the inner conductor layer (6) and/or the outer conductor layer (8, 10). 5. Electric cable according to one of the preceding claims, characterized in that the conductor layers (6; 8, 10) consist of semiconducting material, which is preferably provided with soot particles. 6. Electric cable according to one of the preceding claims, characterized in that the metallic layer or foil (5; 9) has a lower electrical resistance than the conductor layer (6; 8, 10) on and/or in which it is arranged. 7. Electric cable according to one of the preceding claims, characterized in that the metallic layer or foil (5;9) has properties of a vapor barrier. 8. Electric cable according to one of the preceding claims, characterized in that the metallic layer (5;9) is an atomically thin layer, preferably with a thickness of a few Å (Angstroms) to 2θμδα. 9. Electric cable according to one of claims 1-7, characterized in that the metallic layer (5; 9) consists of a material that can be vapor-deposited onto the respective surfaces of the conductor layers (6; 8, 10). 10. Electric cable according to one of claims 1-8, characterized in that the metallic foil or layer (5; 9) has a carrier material. 11. Electric cable according to one of the preceding claims, characterized in that the metallic layers or foils (5; 9) in the respective conductor layers are arranged concentrically around the conductor (2). · 12. Electric cable according to one of claims 1-10, characterized in that the metallic layers or foils (5; 9) in the respective conductor layers (6, 8, 10) are arranged in such a way that their surfaces are concentric with one another. 13. Electric cable according to one of the preceding claims, characterized in that the metallic layer or foil (5; 9) is part of the cushioning layer (11). 14. Electric cable according to one of the preceding claims, characterized in that the metallic foil or layer (5; 9) has a corrosion protection layer.