Electricity: conductors and insulators – Overhead – With messenger cable
Patent
1991-06-25
1998-08-04
Sough, Hyung S.
Electricity: conductors and insulators
Overhead
With messenger cable
174 40R, 174 43, 385113, 2541343R, 2541344, H01B 718
Patent
active
057897018
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to suspended cables and the like, and in particular but not exclusively to suspended transmission lines.
2. Description of Related Art
For above ground routes, a cable, known in this context as a drop cable, may be suspended from poles so that the cable hangs between each adjacent pair of poles in a catenary. Typically, a drop cable comprises a strength member made of tensile steel which supports the load, and a carried member, which may for example be a more delicate transmission line or lines. The carried member is attached, either continually or at intervals, to the strength member. For transmission lines, the typical distance between poles is 200 feet, that is 69 metres. Between the poles, the drop cable sags due to its own weight, the extent of the sag on installation being determined by the tension in the drop cable, and being designed to be within a range of values determined by the acceptable drop cable tension and the acceptable extent of eventual sag to avoid hazard. In addition to the suspension load of the weight of the drop cable itself, an externally-mounted drop cable is subject to additional variable loading due to wind force and settling of moisture or ice formation. This additional loading results in strain in the drop cable which will affect all the elements of the cable including the carried line(s).
Optical fibre or other lightweight transmission lines may be conveniently installed in a previously-suspended drop cable the strength member of which supports a duct along which a lightweight package can be installed by the technique known as fibre blowing, this technique being described in our European Patent specification No. 108590.
This technique involves blowing compressed fluid, usually gas, along a duct into which the transmission line is to be installed, and feeding the transmission line into the duct at the same time, so that it is urged along by the viscous drag of the fluid flow. A particular feature of this technique is that it enables sensitive transmission lines, especially those containing optical fibres, to be installed after the laying, or suspending, of the duct, and the transmission line is, therefore, free from any stress resulting from installation or suspension of the duct itself. Alternatively, the carried line may be lashed to a previously-suspended strength member, but this is less convenient. However, even if a transmission line is installed after suspension of the strength member, it is in present systems still subjected to the additional, variable strains resulting from ice and/or wind loading on the drop cable.
SUMMARY OF THE INVENTION
An aim of the invention is to provide a convenient means for suspending a carried member from a strength member in a catenary and to inhibit environmentally-produced strain on sensitive elements. Another aim is to provide a means for reducing the strain experienced by sensitive elements in a catenary system.
The present invention provides a drop cable arrangement for a catenary, the arrangement comprising a tensile, load-supporting, strength member, a carried member, and a tubular member supporting the carried member, the strength member being mounted within the tubular member, and the tubular member being of a sufficient internal size to enable relative longitudinal movement between the strength member and the tubular member.
The invention also provides a drop cable arrangement for a catenary, the arrangement comprising a tensile, load-supporting, strength number and a carried member, wherein an elastic linkage is provided in the strength member, the elastic linkage having an extension rate per unit length substantially greater than the extension rate of the strength member, and wherein the carried member is provided with sufficient slack to take up the extension of the elastic linkage without strain.
BRIEF DESCRIPTION OF THE DRAWING
The invention will now be described, by way of example, with reference to the accompanying drawings in which:
FIG.
REFERENCES:
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patent: 3063860 (1962-11-01), Gemmer
patent: 4195192 (1980-03-01), Hackney et al.
patent: 4409429 (1983-10-01), Gaylard
patent: 4686325 (1987-08-01), Marsico et al.
patent: 4695677 (1987-09-01), Ruth et al.
patent: 4832442 (1989-05-01), Pappas
patent: 4892442 (1990-01-01), Shaffner
Philips Telecommunication Review, vol. 46, No. 1, 1988, Hilversum NL pp. 14-28, R. Herff: `optoflex optical overhead cable for use on high-power lines`.
Journal of Lightwave Technology, vol. 6, No. 2, 1988, New York US pp. 186-190. S. Tomita: `suppression of galloping oscillation for a self-supporting opticl fibre c cable`.
Bell Laboratories, "Undulated Core Makes Self-Supporting Cable Practical", Nov. 1964, Electronic Industries, p. 28.
Ishihara et al., "New Self-Supporting Cable for Overhead Subscriber Distribution Use", Apr. 1980, Japanese Telecommunications Review, vol. 22, No. 2, pp. 135-140.
Jenkins Peter David
Wettengel Paul Frederick
British Telecommunictions public limited company
Sough Hyung S.
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