GB2155656A

GB2155656A - Overhead flexible electric conductor comprising an optical fibre

Info

Publication number: GB2155656A
Application number: GB08505961A
Authority: GB
Inventors: Kenneth Albert Austin
Original assignee: BICC PLC
Current assignee: Balfour Beatty PLC
Priority date: 1984-03-08
Filing date: 1985-03-07
Publication date: 1985-09-25
Also published as: GB8505961D0; GB8406084D0

Abstract

An overhead flexible electric conductor comprises a circumferentially rigid metal alloy or metal e.g. aluminium central core 4 having an elongate compartment 3 within and extending throughout the length of the core, an optical guide comprising an optional plastics tube 2 which is loosely housed in the elongate compartment 3 and which has an optical fibre 1 loosely housed in the bore of the tube, and, surrounding the central core 4, at least one e.g three layers of helically wound bare metal e.g. steel wires 6. The external transverse dimension of the central core 4 and the internal transverse dimension of the innermost layer of helically wound steel wires 6 are such that the central core is loosely housed within the elongate space 5 bounded by the innermost layer of steel wires. <IMAGE>

Description

SPECIFICATION An improved overhead flexible electric conductor This invention relates to overhead flexible electric conductors for use in overhead electric transmission and distribution systems of the kind in which at least one overhead flexible electric conductor is suspended at spaced positions along its length from towers, pylons, poles or other upstanding supports.

In the Complete Specification of our British Patent No: 1 598438 there is described and claimed an overhead flexible electric conductor comprising a substantially circumferentially rigid central core of metal or metal alloy having an elongate compartment within and extending throughout the length of the core; at least one optical fibre loosely housed in the elongate compartment; and, surrounding the central core, at least one layer of helically wound bare elongate elements of metal or metal alloy.

It is an object of the present invention to provide an improved overhead flexible electric conductor incorporating at least one optical fibre which is of such a construction that any tendency for the conductor to vibrate when in service is substantially reduced.

According to the invention, the improved overhead flexible electric conductor comprises a substantially circumferentially rigid central core of metal or metal alloy having an elongate compartment within and extending throughout the length of the core; at least one optical fibre loosely housed in the elongate compartment; and at least one layer of helically wound bare elongate elements of metal or metal alloy surrounding the central core, wherein the external transverse dimension of the central core and the internal transverse dimension of the layer of helically wound bare elongate metal elements or of the inner or innermost layer of helically wound bare elongate metal elements are such that the central core is loosely housed within the elongate space bounded by the layer of helically wound bare elongate metal elements or by the inner or innermost layer of helically wound bare elongate metal elements.

The central core and the surrounding layer of layers of helically wound bare elongate metal elements may be tensioned separately when the conductor is in service, but satisfactory self-damping characteristics can be obtained with the central core and the surrounding layer or layers of helically wound bare elongate metal elements tensioned together, thereby eliminating the necessity to employ special installation techniques.

Each elongate metal element of the or each layer may be of substantially circular crosssection or, in some circumstances, each elongate metal element of the or each layer may have a cross-section approximating to a sector of an annulus. In the latter case, where two or more layers of helically wound bare elongate metal elements each of a cross-section approximating to a sector of an annulus surround the central core, each layer, except the outer or outermost layer, may be loosely housed within the bore of the outer layer immediately adjacent thereto by the provision of a small clearance between these adjacent layers, thereby permitting relative movement between the layers and increasing the amount of friction present. Overhead conductors of this particular construction show little tendency to vibrate or oscillate.

With a view to reducing further any tendency for the overhead conductor to vibrate or otherwise oscillate when in service, the outer or outermost layer of helically wound bare elongate metal elements may be of such a construction that alternate elements each has a radial dimension that is substantially greater than that of the element sandwiched therebetween, thereby providing in the outer surface of the conductor a plurality of helically extending grooves.

Preferably, the central core is of aluminium or an aluminium-based alloy and the elongate elements of the or each layer surrounding the central core are of steel.

The central core preferably is initially a single extrudate of substantially C-shaped transverse cross-section, one or each of the limbs of the C having been folded inwardly so that the gap between the free ends of the limbs is closed. Alternatively, the central core may be an extruded tube or a longitudinally applied, transversely folded tape of sufficient thickness to provide the required circumferen tial rigidity.

Those parts of the elongate compartment within the central core not occupied by the optical fibre or optical fibres may be substantially filled with water-impermeable medium of a grease-like nature which is of such a consistency that the or each optical fibre is free to move relative to the conductor when the conductor is installed and when any flexing of the conductor occurs while it is in service. The greasy water-impermeable medium may consist of, or may comprise as a major constituent, petroleum jelly.

The presence within the elongate compartment of the central core of optical fibres and greasy water-impermeable medium of lower density than the metal or metal alloy of the central core ensures that the central core will have a tension to mass ratio different from that of the surrounding elongate metal elements with the result that, even without separately tensioning the central core and the surrounding layer or layers of helically wound elongate metal elements, under vibrating conditions there will be a wave velocity difference between the central core and the surrounding layer or layers which will tend to improve further the anti-damping characteristics of the conductor.

The or each optical fibre of the improved overhead flexible electric conductor may be separate and unsupported, may be a component element of an optical bundle (by which is meant a group of optical fibres or a group of fibres including at least one optical fibre and at least one non-optical reinforcing fibre or other reinforcing elongate element), or may be supported by a flexible elongate carrier member which is itself loosely housed in the elongate compartment. In the latter case, the flexible elongate carrier member may be at least one tape on or within which the or each optical fibre is secured or it may be a flexible fibrous rope which is loosely housed in the elongate compartment and around which the or each optical fibre is helically wound.In an alternative embodiment, the flexible elongate carrier member may be a tube of plastics material in which the or each optical fibre is loosely housed, the plastics tube itself being loosely housed in the elongate compartment.

In a modification of this alternative embodiment, the plastics tube itself may be a component part of an optical cable which is loosely housed in the elongate compartment.

In all cases, preferably the or each optical fibre is of a length substantially greater than that of the elongate compartment within the central core.

The invention is further illustrated, by a description, by way of example of two preferred forms of self-damping overhead flexible electric conductor incorporating an optical fibre with reference to the accompanying drawing, in which: Figure 1 is a transverse cross-sectional view of the first preferred form of self-damping overhead flexible electric conductor, and Figure 2 is a transverse cross-sectional view of the second preferred form of self-damping overhead flexible electric conductor.

Referring to Fig. 1, the first preferred form of overhead flexible electric conductor comprises a circumferentially rigid central core 4 of aluminium formed from a single extrudate of C-shaped transverse cross-section whose limbs have been folded inwardly so that the gap between the free ends of the limbs is closed. Loosely housed in the elongate compartment 3 bounded by the central core 4 is a plastics tube 2 in the bore of which is loosely housed an optical fibre 1 of a length substantially greater than that of the elongate compartment within the central core. The central core 4 is surrounded by three layers of helically wound round steel wires 6, adjacent layers being of opposite hand.The external transverse dimension of the central core 4 and the internal transverse dimension of the innermost layer of helically wound steel wires 6 are such that the central core is loosely housed within the elongate space 5 bounded by the innermost layer of helically wound steel wires.

As a consequence, when the conductor is in service, any tendency for the conductor to vibrate is substantially reduced.

The second preferred form of overhead flexible electric conductor shown in Fig. 2 comprises four layers of helically wound bare elongate steel elements 16, each having a cross-section approximating to a sector of an annulus, adjacent layers being of opposite hand. Each layer, except the outermost layer, is loosely housed within the bore of the outer layer immediately adjacent thereto by the provision of a small clearance 1 7 between these adjacent layers. The four layers of helically wound steel elements 1 6 bound a space 1 5 in which is loosely housed a circumferentially rigid aluminium central core 14 formed from a single extrudate of C-shaped transverse cross-section whose limbs have been folded inwardly so that the gap between the free ends of the limbs is closed.An optical fibre 11 of a length greater than that of the elongate compartment 1 3 within the central core 14 is loosely housed in the elongate compartment. By virtue of the fact that the elongate core 14 is loosely housed in the space 1 5 bounded by the layers of helically wound steel wires, any tendency for the conductor to vibrate when it is in service is substantially reduced. To reduce further any tendency for the overhead conductor to vibrate or otherwise oscillate when in service, the outermost layer of helically wound steel elements is of such a construction that alternate elements 1 6 each has a radial dimension that is substantially greater than that of the elements 1 8 sandwiched between them, thereby providing in the outer surface of the conductor a plurality of helically extending grooves.

Claims

1. An overhead flexible electric conductor comprising a substantially circumferentially rigid central core of metal or metal alloy having an elongate compartment within and extending throughout the length of the core; at least one optical fibre loosely housed in the elongate compartment; and at least one layer of helically wound bare elongate elements of metal or metal alloy surrounding the central core, wherein the external transverse dimension of the central core and the internal transverse dimension of the layer of helically wound bare elongate metal elements or of the inner or innermost layer of helically wound bare elongate metal elements are such that the central core is loosely housed within the elongate space bounded by the layer of helically wound bare elongate metal elements or by the inner or innermost layer of helically wound bare elongate metal elements.

2. An overhead flexible electric conductor as claimed in Claim 1, wherein the central core and the surrounding layer or layers of helically wound bare elongate metal elements are tensioned together when the conductor is in service.

3. An overhead flexible electric conductor as claimed in Claim 1 or 2, wherein each elongate metal element of the or each layer is of substantially circular cross-section.

4. An overhead flexible electric conductor as claimed in Claim 1 or 2, wherein each elongate metal element of the or each layer has a cross-section approximating to a sector of an annulus.

5. An overhead flexible electric conductor as claimed in Claim 4, wherein two or more layers of helically wound bare elongate metal elements each of a cross-section approximating to a sector of an annulus surround the central core and each layer, except the outer or outermost layer, is loosely housed within the bore of the outer layer immediately adjacent thereto by the provision of a small clearance between these adjacent layers, thereby permitting relative movement between the layers and increasing the amount of friction present.

6. An overhead flexible electric conductor as claimed in any one of the preceding Claims, wherein the outer or outermost layer of helically wound bare elongate metal elements is of such a construction that alternate elements each has a radial dimension that is substantially greater than that of the elements sandwiched therebetween, thereby providing in the outer surface of the conductor a plurality of helically extending grooves.

7. An overhead flexible electric conductor as claimed in any one of the preceding Claims, wherein the central core is of aluminium or aluminium-based alloy and the elongate elements of the or each layer surrounding the central bore are of steel.

8. An overhead flexible electric conductor as claimed in any one of the preceding Claims, wherein the central core is initially a single extrudate of substantially C-shaped transverse cross-section, one or each of the limbs of the C having been folded inwardly so that the gap between the free ends of the limbs is closed.

9. An overhead flexible electric conductor as claimed in any one of Claims 1 to 7, wherein the central core is an extruded tube.

1 0. An overhead flexible electric conductor as claimed in any one of Claims 1 to 7, wherein the central core is a longitudinally applied, transversely folded tape of sufficient thickness to provide the required circumferential rigidity.

11. An overhead flexible electric conductor as claimed in any of the preceding Claims, wherein those parts of the elongate compartment within the central core not occupied by the optical fibre or optical fibres are substantially filled with water-impermeable medium of a grease-like nature that is of such a consistency that the or each optical fibre is free to move relative to the conductor when the conductor is installed and when any flexing of the conductor occurs while it is in service.

1 2. An overhead flexible electric conductor as claimed in Claim 11, wherein the greasy water-impermeable medium consists of, or comprises as a major constituent, petroleum jelly.

1 3. An overhead flexible electric conductor as claimed in any one of the preceding Claims, wherein the or each optical fibre is a component element of an optical bundle.

1 4. An overhead flexible electric conductor as claimed in any one of Claims 1 to 12, wherein the or each optical fibre is supported by a flexible elongate carrier member which is itself loosely housed in the elongate compartment.

1 5. An overhead flexible electric conductor as claimed in Claim 14, wherein the flexible elongate carrier member is at least one tape on or within which the or each optical fibre is secured.

1 6. An overhead flexible electric conductor as claimed in Claim 14, wherein the flexible elongate carrier member is a flexible fibrous rope which is loosely housed in the elongate compartment and around which the or each optical fibre is helically wound.

1 7. An overhead flexible electric conductor as claimed in Claim 14, wherein the flexible elongate carrier member is a tube of plastics material in which the or each optical fibre is loosely housed, the plastics tube itself being loosely housed in the elongate compartment.

1 8. An overhead flexible electric conductor as claimed in Claim 17, wherein the plastics tube itself is a component part of an optical cable which is loosely housed in the elongate compartment.

1 9. An overhead flexible electric conductor as claimed in any one of the preceding Claims, wherein the or each optical fibre is of a length substantially greater than that of the elongate compartment within the central core.

20. An overhead flexible electric conductor substantially as hereinbefore described with reference to and as shown in Fig. 1 of the accompanying drawing.

21. An overhead flexible electric conductor substantially as hereinbefore described with reference to and as shown in Fig. 2 of the accompanying drawing.