Electricity: conductors and insulators – Conduits – cables or conductors – Insulated
Patent
1990-03-13
1992-06-09
Nimmo, Morris H.
Electricity: conductors and insulators
Conduits, cables or conductors
Insulated
174131A, H01B 700
Patent
active
051209055
DESCRIPTION:
BRIEF SUMMARY
The present invention concerns an electrocarrier cable, that is to say a cable for conducting electricity, in particular low currents such as those carrying telecommunication signals, or more generally data signals, and for supplying power to measuring instruments or information processing systems.
Currently the electrical conductor or conductors, generally arranged in parallel, have to be strengthened by strength members, generally of steel. These strength members provide the mechanical strength and account for a considerable percentage of the weight and the volume of the electrocarrier. An electrocarrier cable of this kind is heavy and may break under its own weight. The strength/weight relationship is referred to as the self-weight breaking length of the cable.
Thus, for example, an electrocarrier cable comprising 7.times.0.56 mm.sup.2 conductors requires an armouring comprising a first layer of 20 galvanised steel wires with a diameter of 1.4 mm and a second layer stranded with the opposite lay and made up of 35 wires with a diameter of 1.1 mm (steel=1,800 N/mm.sup.2). This cable weighs 680 g/m in air and has a breaking strength of 9,500 DaN; suspended in air, this cable will break under its own weight for a length of: 9,500/680=13.97 km.
In this type of cable the copper conductors inevitably break after stretching by a very small amount, before the overall breaking strength of the cable is reached. These conductors generally break at loads below 50% of the strength of the strength member and the electrocarrier cable then no longer fulfills its electrical function.
Also, it has been observed in the field of hydrolysis, for example, that scientific measurements with an accuracy in the order of 1 ppm were falsified by the presence of micro-particles of zinc or of grease from the galvanised steel carrier member. The problem with conductor cables is that the cable may break under its own weight when suspended in a fluid such as air or water even with no other load applied. When breaking loads are applied to the cable the electrical circuit tends to be broken before the strength members break, with the result that the entire cable must be replaced.
There is known from U.S. Pat. No. 4,034,138 a low-density high-strength electromechanical cable including multifilament fibres of aromatic polyamides covered with a polyurethane protective coating to prevent mutual damage to the aramide fibres by abrasion. However, the conductor wires are parallel to the carrier fibres and have a higher resistance to stretch than the strength members.
EP-A-0,054,784 concerns a telephone cable in which the carrier members are aramide fibres in the form of a central core and strands twisted up with the conductors. DE-A-3,241,425 concerns a conductor cable in which the central conductor members are surrounded by a braided aramide strength member which constitutes the carrier member.
An object of the present invention is an electrocarrier cable that is light in weight and whose conductive part can break only if the carrier members of the cable have already mechanically broken. In accordance with the invention, and differing in this respect from what is observed with conventional cables, the strength members of the cable break before the conductor or conductors. Should the cable break, the conductor or conductors are loaded at the last possible moment, after the carrier member has itself given way.
In accordance with the invention the electrocarrier cable comprising carrier members resistant to traction and electrical conductor members enclosed within an extruded sheath is characterised in that the conductor members are integrated into an elastic central core structure surrounded by an aramide fibre strength member, the conductor members including at least one metal wire wound onto a strand.
The elastic core structure comprises a twisted fibre composite central core. Around this core are disposed two or more conductors in as tight as possible a helical arrangement to constitute a homogeneous strand. There might be, for example, a (1+6
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Cousin Jean-Claude
Delvael Yves
Cousin Freres (S.A.)
Nimmo Morris H.
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