Electricity: conductors and insulators – Conduits – cables or conductors – Conductive armor or sheath
Patent
1985-02-21
1986-11-04
Grimley, Arthur T.
Electricity: conductors and insulators
Conduits, cables or conductors
Conductive armor or sheath
174 23C, 174102SC, H01B 728
Patent
active
046211691
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a new electric cable construction wherein the conductor is covered by several successive layers of materials comprising a hydrophobic and semiconducting moistureproofing gel disposed between a likewise semiconducting polymer layer and a metallic shield.
The invention further relates to the use of said construction for the continuous grounding of electric conductors and for the radial distribution of the field in power cables.
As is known, the advent of semiconducting polymeric materials has brought great improvements to the manufacture of electric cables with respect to both communications cables and power transmission cables. Such known cable constructions will now be described with reference to FIG. 1a and 1b of the accompanying drawings, wherein:
FIGS. 1a and 1b are cross sections of two types of prior-art cables;
FIGS. 2a and 2b are similar sections of the same cables embodying an improvement in accordance with the invention, FIG. 2c being a section of a coaxial cable in accordance with the invention; and
FIG. 3 is a perspective view, cut away to illustrate a cable construction in accordance with the present invention.
The cable construction shown in FIG. 1a is that of a conventional communications cable. Said cable comprises, for example, a plurality of conducting wires 1, made of a conducting material such as copper or aluminum and covered by an insulating jacket 2. The assembly of conducting wires so jacketed is enclosed in a conducting metallic sheath 3 forming a shield, which in turn is surrounded by a protective layer formed of a semiconducting polymer 4 which makes good physical contact with the metallic surface 3. The space 5 left free between the insulating jacket 2 and the metallic surface 3 may be filled conventionally with a sealant.
The power transmission cable shown in FIG. 1b, which is also of a known type, comprises a strand of conducting wires 6 which is surrounded by a semiconducting polymer sheath or layer 7. Around this sheath 7 there is disposed an insulating material 8 which in turn is surrounded by a second semiconducting polymer layer 9 that is sheathed with a layer of conducting metal 10 forming a shield and consisting of copper, steel or aluminum, for example. The outer covering 11, in turn, may consist of an insulating or semiconducting polymer sheath.
However, the usual cables of the type of those illustrated by FIGS. 1a and 1b or consisting of an assembly of strands, such as multipolar cables, have the drawback of not being perfectly moisture-tight and of not assuring perfect contact between the semiconducting sheath and the metallic surface. In fact, as a result of shock to or twisting or cracking of the cable, or of condensation occurring at the level of the free spaces, or of longitudinal propagation starting at cable joints or splices, the region between the semiconducting polymer (reference numerals 4 in FIG. 1a and 9 in FIG. 1b) and the metallic shield (reference numerals 3 in FIG. 1a and 10 in FIG. 1b) is always apt to allow traces of moisture to come in contact with the metal, thus causing the latter to deteriorate by a process of disintegration, oxidation and/or corrosion. This drawback can be partially limited by incorporating between the metallic sheath and the semiconducting polymer a layer of a hydrophilic material such as carboxymethylcellulose or of a hygroscopic material such as a semiconducting clay whose swelling in the presence of moisture will prevent the water from spreading along the conducting metal. However, these products will not prevent local corrosion of the shields.
The object of the present invention thus is to provide an effective moisture barrier between the metallic shield and the semiconducting polymer layer of such electric cable constructions.
To this end, the invention has as its object an electric cable construction of the type comprising at least one metallic shield and at least one semiconducting polymer layer which surround at least one cable conductor, characterized in that between said metallic shie
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Bertier Dominique
Petinelli Jean-Claude
Acome, Societies Anonyme
Compagnie Francaise de Raffinage
Grimley Arthur T.
Nimmo Morris H.
S. Safford A. Thomas
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