GB2029043A

GB2029043A - Overhead power cables

Info

Publication number: GB2029043A
Application number: GB7835574A
Authority: GB
Original assignee: Standard Telephone and Cables PLC
Current assignee: STC PLC
Priority date: 1978-09-05
Filing date: 1978-09-05
Publication date: 1980-03-12
Also published as: GB2029043B; DE2934684C2; ES483880A1; DE2934684A1; IT1207236B; FR2435786B1; FR2435786A1; IT7925489A0

Abstract

An overhead power cable construction which can be used as an earth conductor and which includes one or more optical fibres (10) for communications purposes arranged in an aluminium tube (11) formed from a C-sectioned element subsequently deformed into a tube. The aluminium tube is surrounded by strength members (13), which may in turn be surrounded by an aluminium or copper members (14). <IMAGE>

Description

SPECIFICATION Overhead power cables This invention relates to power cables and earth conductors for use with overhead power cables.

Power cables may be suspended in an insulating manner from the arms of pylons or other supports spaced apart over the cable route. In order to provide protection from lightening strikes an earth conductor may be arranged to run above the power cables between the pylons so that lightening strikes the earth conductor rather than the power cables. The earth conductor is not insulated from the pylon, but rather it is in electrical contact with all the dead metal of the pylon or support and connects it to earth. The earth conductor is therefore an uninsulated cable. Conventional designs for such earth conductors employ strands of aluminium wire for electrical conductivity purposes and galvanised steel for tensional strength. The conductors may consist of seven or more aluminium and galvanised steel wires built up in concentric layers.The centre wire or wires are of galvanised steel wires built up in concentric layers. The centre wire or wires are of galvanised steel and the outer layer or layers of aluminium. Such conductors are described in British Standard Specification 215: Part 2: 1970 and may be used both for power transmission and earch conductor purposes.

The present invention aims to provide alternative constructions of overhead power cables and earth conductors.

According to one aspect of the present invention there is provided an overhead power cable or an overhead earth conductor cable, the cable comprising one or more optical fibres arranged within an electrically-conductive tube, a longitudinal strength member around the electrically-conductive tube, and a further electrical conductor of tubular configuration in contact with the strength member.

According to another aspect of the present invention there is provided a method of manufacturing an overhead power cable or an overhead earth conductor cable, including arranging one or more optical fibres in the channel of an element of electrically conductive material having a C-shaped cross-section, closing the element to form a tube around the optical fibres, providing a longitudinal strength member around the electricaily-conductive tube, and arranging a further electrical conductor of tubular configuration in contact with the strength member.

According to a further aspect of the present invention there is provided an electricity distribution system including a plurality of pylons supporting one or more overhead power cables and an overhead earth conductor cable, at least one of the cables comprising one or more optical fibres arranged within an electrically-conductive tube, a longitudinal strength member around the electrically-conductive tube, and a further electrical conductor of tubular configuration in contact with the strength member.

Embodiments of the invention will now be described with reference to the accompanying drawings, in which Fig. 1 shows a section through a known overhead power cable which can be used as an earth conductor; Fig. 2 shows a section through a first embodiment according to the present invention; Fig. 3 shows a section through a-second emodiment according to the present invention; Fig. 4 shows a section through a third embodiment according to the present invention, and Fig. 5 shows a section through a fourth embodiment according to the present invention.

Cables including optical fibres are disclosed in our co-pending Application No. 51773/77 1,550,588 (C. S. Parfree-P. Worthington 8-5) and the constructions shown therein have been modified in the embodiments of the present invention in order to make them suitable for use as overhead power cables or earth conductors.

Referring firstly to Fig. 1 which shows a known steel-reinforced aluminium conductor 1 which can be used as an overhead power cable or an earth conductor. The conductor 1 includes seven galvanised steel wires 2 forming a core, around which two layers of aluminium wires 3 are laid. The inner layer has twelve wires 3, and the outer layer has eighteen wires. For the so-called "Lynx" version of the conductor 1 (275 KV), the diameter of both the steel and aluminium wires is 2.79 mm. The overall diameter, the tensile strength, the weight and the d.c. resistance of the "Lynx" conductor are given in Table I (see below). The nominal aluminium area is 1 75mm2. Different sizes of power and earth cables are used for different voltages.

The present invention aims to provide alternative constructions to the known ones but which have comparable equivalent nominal aluminium area, diameter, tensile strength, weight and d.c. resistance values, and which also include optical fibres for communications purposes. The four embodiments of the invention are alternatives to the "Lynx" construction outlined above, but obviously alternatives to other known constructions eg. different diameters can be correspondingly designed using the basic arrangement of the present invention.

The four embodiments shown in Figs. 2 to 5 have as the common feature a group of, for example, five individually clad optical fibres 10 arranged loosely in an electrically conductive tube 11 comprising for example a closed aluminium C-section. Such a construction is shown in our co-pending Application No. 51773/77 (C. S. Parfree-P. Worthington 8-5). The optical fibres are arranged in the channel of an open aluminium C-section which is then passed through a die to effect closure thereof. The seam 1 2 can be welded or soldered to hermetically seal the tube 1 or alternatively it may be held closed by arranging a layer of wires thereon.

The embodiment of Fig. 2 has a longitudinal strength member comprising a layer of twenty-two 1.6 mm diameter high tensile steel wires 13 arranged around and surrounding the aluminium tube 11, and this is surrounded by a further electrical conductor of tubular configuration comprising a layer of eighteen 2.79 mm. diameter aluminium wires 14. The approximate parameter of this embodiment and the embodiments of Figs. 3, 4 and 5 are given in table I.

The embodiment of Fig. 3 has a layer of fourteen 2.11 mm. diameter high tensile steel wires 15 arranged on the aluminium tube 11, and this is surrounded by a 1.57 mm. thick copper tape 1 6 which is applied longitudinally to the steel wire covered tube and the longitudinal edges 17 welded together.

The embodiment of Fig. 4 has a layer of fourteen 2.11 mm. diameter high tensile steel wires 18 arranged on the aluminium tube 11, and this is surrounded by a layer of eleven 4.06 mm. diameter aluminium wires 19.

The embodiment of Fig. 5 has a layer of ten 3.05 mm. diameter aluminium alloy (e.g. that known by the Trade Mark SILMALEC (BS 2898)) wires 20 arranged on the aluminium tube 10, and this is surrounded by a layer of sixteen 3.05 mm. diameter aluminium alloy wires 21.

The layers of wires may be applied using conventional armouring or laying-up machines.

In the embodiments of Figs. 2, 3 and 4 the strength member comprises a layer of high tensile steel wires, whereas in the embodiment of Fig. 5 two layers of an aluminium alloy are used which perform both the electrical conduction and the tensile strength functions.

Lynx (Fig. 1) Fig.2 Fig.3 Fig.4 Fig.

Overall diameter (mm) 19.53 19.53 14.7 19.71 19.6 Tensile strength (KN) 79.80 85.8 76.8 76.8 57.8 Weight (Kg/m) 0.842 0.78 0.75 0.79 0.59 D.C. Resistance (Q/Km) 0.157 0.16 0.19 0.15 0.15 Closed Aluminium 'C' Section Outer diameter (mm) 10.8 10.8 7.37 7.37 7.37 Inner diameter(mm) 5.4 5.4 4.10 4.10 4.10 The embodiments of Figs. 2 to 5 and the "Lynx" construction are designed to have the same equivalent aluminium area i.e. 1 75mm2, so as to provide the required low d.c. resistance. It is important that 12R is kept low to prevent heat damage during a lightening strike.

As can be ascertained from the figures quoted in table I, the optical fibres are incorporated into the power cable or earth conductor such that neither the tensile strength or d.c. resistance is substantially impaired relative to the parameters of the present construction of Fig. 1, and with benefits such as increased tensile strength, or weight reduction or overall diameter reduction in certain embodiments.

The arrangement of the optical fibres for communications purposes and control information and data transmission within the earth conductor or power cable structure provides a low cost alternative to the use of existing telephone networks.

Embodiments employing more or less optical fibres than described can be envisaged, together with alternative strength member and aluminium wire or alloy arrangements which provide similar parameters to the described "Lynx" or other known constructions of power cables or earth conductors, with suitable design modifications. The arrangement of the optical fibres within the aluminium tube protects the fibres, whilst the aluminium tube itself provides part of the current carrying capacity of the earth conductor. The tube could alternatively be made of other electrically conducting materials, which can be formed to the initial C-section, and which will give the required low d:c. resistance together with high tensile strength.

Claims

1. An overhead power cable or an overhead earth conductor cable, the cable comprising one or more optical fibres arranged with an electrically-conductive tube, a longitudinal strength member around the electrically-conductive tube, and a further electrical conductor of tubular configuration in contact with the strength member.

2. A cable construction as claimed in claim 1, wherein the electrically-conductive tube is of aluminium and the tubular strength member comprises a layer of high tensile steel wires applied over the electricallyconductive tube.

3. A cable construction as claimed in claim 1, wherein the electrically-conductive tube is of aluminium and the tubular strength member comprises two concentric layers of an aluminium alloy wire applied over the electrically-conductive tube.

4. A cable construction as claimed in claim 2, wherein the layer of high tensile steel wires is surrounded by a layer of aluminium wires.

5. A cable construction as claimed in claim 2, wherein the layer of high tensile steel wires is surrounded by a copper tube.

6. A method of manufacturing an overhead power cable or an overhead earth conductor cable, including arranging one or more optical fibres in the channel of an element of electrically conductive material having a C-shaped cross-section, closing the element to form a tube around the optical fibres, providing a longitudinal strength member around the eiectrically-conductive tube, and arranging a further electrical conductor of tubular configuration in contact with the strength member.

7. A method as claimed in claim 6, wherein the element is of aluminium and wherein the seam of the tube is welded or soldered.

8. A method as claimed in claim 6 or 7, wherein arranging the tubular strength member comprises arranging a layer of wires around the electrically-conductive tube.

9. A method as claimed in claim 8, wherein the strength member wires are of high tensile steel.

10. A method as claimed in claim 8, wherein the strength member wires are of an aluminium alloy.

11. A method as claimed in claim 9, further including applying a layer of aluminium wires over the strength member wires.

12. A method as claimed in claim 9, further including forming a tube with a longitudinal seam from copper tape over the strength member wires, and welding the longitudinal edges of the copper tape together.

13. A method of manufacturing an overhead power cable or an earth conductor substantially as herein described with reference to Figs. 2, 3, 4 or 5 of the accompanying drawings.

14. An overhead power cable or an earth conductor manufactured by a method as claimed in any one of claims 6 to 13.

1 5. An overhead power cable or an earth conductor substantially as herein described with reference to Figs. 2, 3, 4 or 5 of the accompanying drawings.

1 6. An electricity distribution system including a plurality of pylons supporting one or more overhead power cables and an overhead earth conductor cable, at least one of the cables comprising one or more optical fibres arranged within an electrically-conductive tube, a longitudinal strength member around the electrically-conductive tube, and a further electrical conductor of tubular configuration in contact with the strength member.