GB2164171A

GB2164171A - Overhead electric conductor wrapped in optical fibre ribbon

Info

Publication number: GB2164171A
Application number: GB08521842A
Authority: GB
Inventors: Kenneth Albert Austin
Original assignee: BICC PLC
Current assignee: Balfour Beatty PLC
Priority date: 1984-09-06
Filing date: 1985-09-03
Publication date: 1986-03-12
Also published as: AU4705385A; GB8422545D0; GB2164171B; AU579403B2; GB8521842D0

Abstract

In an overhead conductor 1 mechanically supporting a plurality of optical fibres, an optical fibre ribbon 5, comprising a plurality of optical fibres 6 embedded side by side with their axes lying in a common plane in a plastics material 8, is helically wrapped around the conductor so that, at any transverse cross-section of the conductor, the optical fibres of the helically wound optical fibre ribbon lie on an imaginary circle concentric with the outer periphery of the conductor. The optical fibre ribbon is preferably helically wound under a constant tension around the conductor when the conductor is in situ. <IMAGE>

Description

SPECIFICATION Overhead electric transmission or distribution systems This invention relates to overhead electric transmission or distribution systems in which at least one overhead electric conductor, comprising at least one layer of helically wound bare elongate elements of metal or metal alloy, is freely supported in long lengths from towers, pylons, poles or other upstanding supports spaced along the length of the system. The invention is particularly concerned with systems of the kind in which at least one of the overhead electric conductors includes at least one of the overhead electric conductors includes at least one optical fibre for use in the communications field adapted for transmission of light having a wavelength within the range 0.8 to 1.9um.

In the Complete Specification of our British Patent No: 1598438 there is described and claimed an overhead electric conductor comprising at least one layer of helically wound bare elongate elements of metal or metal alloy, at least one elongate compartment within and extending throughout the length of the conductor and, loosely housed in the elongate compartment or in at least one of the elongate compartments, at least one separate optical fibre and/or at least one optical bundle.

The overhead electric conductor incorporating an optical fibre and/or optical bundle of the aforesaid patent is especially suitable for incorporation in a new overhead electric transmission or distribution system that is to be installed, or for replacement of an overhead conductor in an existing overhead electric transmission or distribution system.

When it is required to incorporate an optical fibre and/or optical bundle in an existing overhead conductor of an overhead electric transmission or distribution system, it has been proposed to wind a lightweight optical fibre cable helically under a controlled tension around an overhead conductor in situ using a conventional catenary cable spinning machine appropriately modified.

It is an object of the present invention to provide, in an overhead electric transmission or distribution system, at least one improved overhead conductor which comprises at least one layer of helically wound bare elongate elements of metal or metal alloy and which mechanically supports a plurality of optical fibres.

According to the invention, at least one of the overhead electric conductors of the overhead electric transmission or distribution system has helically wrapped around the conductor, an optical fibre ribbon structure comprising a plurality of optical fibres embedded side by side with their axes lying in a substantially common plane in a plastics material, the arrangement being such that, at any transverse cross-section of the conductor, the optical fibres of the helically wound optical fibre ribbon structure lie on an imaginary circle substantially concentric with the outer periphery of the conductor.

Preferably, the optical fibre ribbon structure has a lay length lying in the range 10d to 40d, where d is the overall diameter of the overhead conductor and, preferably also, the direction of lay of the optical fibre ribbon structure is opposite to that of the outermost layer of metal elements of the overhead electric conductor.

The plastics material of the optical fibre ribbon structure in which the optical fibres are embedded side by side preferably is a plastics insulating material having high quality antitracking properties, and/or the ribbon structure has an outer sheath of a plastics insulating material having high quality anti-tracking properties. Preferred plastics insulating materials having high quality anti-tracking properties that may be employed as the plastics material in which the optical fibres are embedded and/or as the outer sheath include cycloaliphatic epoxy resins, cycloaliphatic polyurethane resins, butyl rubber, silicone rubber, polytetrafluoroethylene and EPDM.

In some circumstances, however, with a view to reducing electric stress effects, especially at points of support of the conductor, the plastics material of the optical fibre ribbon structure may be semi-conductive and/or the ribbon structure may have an outer sheath of a semi-conductive plastics material.

The optical fibre ribbon structure may include at least one flexible elongate reinforcing element embedded side by side with the plurality of optical fibres in the plastics material with its axis and the axes of the optical fibres lying in said substantially common plane and, in this case, preferably at least two flexible elongate reinforcing elements are uniformly spaced across the width of the optical fibre ribbon structure. In a preferred embodiment, the plurality of optical fibres are positioned between two flexible elongate reinforcing elements.

The or each flexible elongate reinforcing element of the optical fibre ribbon structure is preferably made of a non-metal, such as polyethylene terephthalate. The or each flexible reinforcing element may have an overall diameter subtantially equal to that of each of the optical fibres but, preferably, the or each reinforcing element has a diameter substantially shorter than that of each of the optical fibres.

The optical fibre ribbon structure preferably is manufactured by the method described and claimed in the specification of our co-pending British Patent No: 2127578B.

In some circumstances, at least one binding tape or string of electrically insulating material may be helically lapped around the helically lapped optical fibre ribbon structure, in a di rection of lay opposite to that of the optical fibre ribbon structure, to assist in maintaining the optical fibre ribbon structure tightly around the conductor.

The optical fibre ribbon structure of the improved overhead electric conductor is preferably helically wrapped under a predetermined constant tension around the conductor when the conductor is in situ, i.e. when the conductor is suspended between two towers or other upstanding supports, but it is to be understood that the invention does not exclude the optical fibre ribbon structure being helically wound around an electric conductor before it is suspended between two towers or other upstanding supports.

Where the improved overhead electric conductor is a phase conductor supported at the towers or other upstanding supports on insulators, with a view to reducing the possible risk of damage to the optical fibre structure arising from flashover at a support insulator due to lightning or switch surges, additional electrical insulation may be applied over the optical fibre ribbon structure in the vicinity of the support insulator and/or an electrically conductive shield, e.g. a metal tape or sleeve bonded to the conductor, may envelop the optical fibre ribbon structure in the vicinity of the support insulator.

The improved overhead electric conductor or the present invention has the very important advantage that it can mechanically support a large number of optical fibres with negligible localised in overall diameter of the overhead conductor. Furthermore, since the optical fibre ribbon structure does not effect a subtantial localised increase in the overall diameter of the overall conductor, there is a negligible increase in risk of galloping of the overhead conductor when the conductor is in service. A further advantage arises from the fact that jointing and terminating of the optical fibres of the optical fibre ribbon structure can be simply effected independently of the overhead conductor.

The invention is further illustrated by a description, by way of example, of a preferred overhead electric conductor mechanically supporting a plurality of optical fibres with reference to the accompanying drawing which shows an enlarged diagrammatic transverse cross-sectional view of the conductor; for the purposes of clarity, the drawing is not to scale.

Referring to the drawing, the overhead electric conductor 1 comprises a central core 2 of seven steel wires 3, twelve aluminium wires 4 helically lapped around the steel core 2 and, helically wound around the conductor under a substantially constant tension, an optical fibre ribbon structure 5. The direction of lay of the optical fibre ribbon structure 5 is opposite to that of the aluminium wires 4 and the optical fibre ribbon structure has a lay length of approximately 25d, where d is the overall diameter of the conductor 1. The optical fibre ribbon structure 5 comprises four optical fibres 6 positioned between two flexible elongate reinforcing elements 7 of polyethylene teraphthalate, the optical fibres and reinforcing elements being embedded side by side with their axes lying in a substantially common plane in a plastics insulating material 8 having high quality anti-tracking properties.

If desired, to assist in maintaining the optical fibre ribbon structure 5 tightly around the conductor 1, at least one binding tape or string (not shown) of electrically insulating material may be helically lapped around the helically lapped optical fibre ribbon structure in a direction of lay opposite to that of the optical fibre ribbon structure.

Claims

1. An overhead electric transmission or distribution system, wherein at least one of the overhead electric conductors of the system comprises at least one layer of helically wound bare elongate elements of metal or metal alloy and has helically wrapped around the conductor, an optical fibre ribbon structure comprising a plurality of optical fibres embedded side by side with their axes lying in a substantially common plane in a plastics material, the arrangement being such that, at any transverse cross-section of the conductor, the optical fibres of the helically wound optical fibre ribbon structure lie on an imaginary circle substantially concentric with the outer periphery of the conductor.

2. An overhead electric transmission or distribution system as claimed in Claim 1, wherein the optical fibre ribbon structure has a lay length lying in the range 10d to 40d, where d is the overall diameter of the overhead conductor.

3. An overhead electric transmission or distribution system as claimed in Claim 1 or 2, wherein the direction of lay of the optical fibre ribbon structure is opposite to that of the uppermost layer of metal elements of the overhead electric conductor.

4. An overhead electric transmission or distribution system, as claimed in any one of the preceding Claims, wherein at least one binding tape or string of electrically insulating material is helically lapped around the helically wrapped optical fibre ribbon structure, in a direction of lay opposite to that of the optical fibre ribbon structure, to assist in maintaining the optical fibre ribbon structure tightly around the conductor.

5. An overhead electric transmission or distribution system as claimed in any one of the preceding Claims, wherein the optical fibre ribbon structure is helically wrapped around the conductor under a predetermined constant tension.

6. An overhead electric transmission or distribution system as claimed in any one of the preceding Claims in which the electric conductor is a phase conductor supported at the towers or other upstanding supports of the system on insulators, wherein additional electric insulation is applied over the optical fibre ribbon structure in the vicinity of the support insulator and/or an electrically conductive shield envelops the optical fibre ribbon structure in the vicinity of the support insulator.

7. An overhead electric transmission or distribution system as claimed in any one of the preceding Claims, wherein the optical fibre ribbon structure includes at least one flexible elongate reinforcing element embedded side by side with the plurality of optical fibres in the plastics material with its axis and the axes of the optical fibres lying in substantially common plane.

8. An overhead electric transmission or distribution system as claimed in Claim 7, wherein the plurality of optical fibres of the optical fibre ribbon structure are positioned between two flexible elongate reinforcing elements embedded in the plastics material.

9. An overhead electric transmission or distribution system as claimed in Claim 7 or 8, wherein the or each flexible elongate reinforcing element of the optical fibre ribbon structure is made of a non-metal.

10. An overhead electric transmission or distribution system as claimed in any one of the preceding Claims, wherein the plastics material of the optical fibre ribbon structure in which the optical fibres are embedded side by side is a plastics insulating material having high quality anti-tracking properties, and/or the ribbon structure has an outer sheath of a plastics insulating material having high quality antitracking properties.

11. An overhead electric transmission or distribution system as claimed in any one of Claims 1 to 9, wherein the plastics material of the optical fibre ribbon structure is semi-conductive and/or the ribbon structure has an outer sheath of a semi-conductive plastics material.

12. For use in an overhead electric transmission or distribution system, an overhead electric conductor comprising at least one layer of helically wound bare elongate elements of metal or metal and, helically wrapped around the conductor, an optical fibre ribbon structure comprising a plurality of optical fibres embedded side by side with their axes lying in a substantially common plane in a plastics material, the arrangement being such that, at any transverse cross-section of the overhead conductor, the optical fibres of the helically wrapped optical fibre ribbon structure lie on an imaginary circle substantially concentric with the outer periphery of the conductor.

13. An overhead electric conductor as claimed in Claim 12, wherein the direction of lay of the optical fibre ribbon structure is opposite to that of the outermost layer of metal elongate elements of the overhead electric conductor.

14. An overhead electric conductor as claimed in Claim 12 or 13, wherein at least one binding tape or string of electrically insulating material is helically lapped around the helically wrapped optical fibre ribbon structure, in a direction of lay opposite to that of the optical fibre ribbon structure, to assist in maintaining the optical fibre ribbon structure tightly around the conductor.

15. For use in an overhead electric transmission or distribution system, an overhead electric conductor substantially as hereinbefore described with reference to and as shown in the accompanying drawing.

16. An overhead electric transmission or distribution system, wherein at least one of the overhead electric conductors of the system is substantially as hereinbefore described with reference to and as shown in the accompanying drawing.