AU597179B2

AU597179B2 - Underwater cables

Info

Publication number: AU597179B2
Application number: AU18189/88A
Authority: AU
Inventors: Derek William Hatton
Original assignee: Pacific Dunlop Ltd
Current assignee: Australian Cables Pty Ltd
Priority date: 1987-06-23
Filing date: 1988-06-21
Publication date: 1990-05-24
Anticipated expiration: 2008-06-21
Also published as: AU1818988A

Description

I

AUSTRLIA

Form PATENTS ACT 1952 COMPLETE SPECIFICATION

(ORIGINAL)

FOR OFFICE USE 5971 Short Title: Int. Cl: ::ation Number: 0 Lodged; te Specification-Lodged: Accepted: Lapsed: Vta: Published: IThis document contah~s amendments 4 41o"L! uuuj' 9 Se~tio.a 44=4 tby tuje Sille vishig Examiner oa I I *1 'A es Art: Applicant: 3s of Applicant: TO BE COMPLETED BY APPLICANT PACIFIC DUNLOP LCMITED and THE OVERSEAS TELECOMMU'.ICATIONS COMMISSION (AUSTRALIA) 23RD FLOOR, 500 BOURKE STREET, MELBOURNE, VIC. 3000, and 32-36 MARTIN PLACE, SYDNEY, N.S.W. 2000, respectively Actual Inventor: DEREK WILLIAM HATTON Addru.ss for Service: Comnplete Specification CLEMhENT HACK CO., 601 St. Kilda Road, Melbourne, Victoria 31004, Australia.

for the invention entitled:, "UNDERWATER CABLES" The following statement is a full description of this invention, including the best method of performing it known to me:- PF/CPIF/2/80 -2u I 1 r t

S

St t UNDERWATER CABLES 4 5 This invention relates to underwater cables and in particular relates to underwater cables for use with optical fibres.

K IIn recent years there has been considerable increase in the use of optical fibre cables. These cables are often submerged on the sea bed for use between adjacent land masses.

To ope:rate satisfactorily on the sea bed the cables must possess a number of qualities including appropriate tensile strength, adequate protection of the fibres from water, p;:essure and hydrogen and the provision of a conductor path for the electrical power requirements of repeaters that are conventionally used with such cables.

3 The cables are traditionally of composite structure with the various components performing more than one function.

A typic-, cable has the optical fibre unit or bundle of optical fibres aligned with the central axis of the cable and surrounded by a combination of stranded steel wires forming the strength member and a tubular copper conductor providing the conductive path for power to the repeaters. This structure is then surrounded by a layer of polyethylene or similar material to provide insulation. In one design the conductor is positioned near the centre of the cable surrounding the optical fibre unit whilst in other designs the *o copper conductor is drawn over the stranded steel strength member which surrounds the optical fibres.

In designs where the insulation is directly over the copper conductor, the smooth interface between the copper conductor and the insulation ensures uniformity of the electric field at the interface. However, in this example the mechanical forces required to lay the cable or to recover it from the sea bed tend to be transferred from the cable ship to !0 the strength member of the cable though the interface of the insulation and the copper conductor. The smoothness of the Fitt exterior of the copper conductor reduces the bond between the insulation and the copper and the mechanical forces have a tendency of causing separation. It has been proposed to 0 "25 enhance the bond between the polyethylene and the copper by using copolymer blends such as polyethylene containing acrylic acid or vinyl acetate.

In another example the insulation is applied directly over the stranded steel strength member. In this example the bond between the strength member and the insulation is greatly improved by the mechanical interference created by the penetration oz the polyethylene into the outer interstices of the outer wires. However, the electric field at the interface is no longer uniform and there is con)cern that the long term effects of uneven electric field distribution may lead to reduced service life.

c I I^ I--L -~--r---rrri~4x 4 It is the above problems that have brought about the present invention.

According to the present invention there is provided an underwater cable comprising a longitudinally extending bundle if optical fibres surrounded by a copper or copper alloy conductor tube, at least one layer of high tensile strength material wound onto the conductor tube, a semi-conductive layer of polymeric material extruded over the high tensile material, and a layer of insulating material [0 bonded onto the semi-conductive layer.

In the preferreO ,irbodiment the high tensile S strength material comprises a layer of aluminium and a layer of steel wolind onto the copper or copper alloy tube.

S Preferably the layers of steel and aluminium comprise wires wound one onto the other in opposite directions to produce a torque balanced configuration.

Preferably the interstices of stranded wires are filled with a suitable water blocking material such as silicon greases and rubbers, or polyurethane rubbers or similar 2L materials. The semi-conductive polymeric material is preferably semi-conductive polyethylene, ethyl vinyl acetate or other senti-conductive thermoplastic materials. In a preferred embodiment the insulating layer is polyethylene.

One embodiment of the present invention will now be described by way of example only, with reference to the Saccompanying drawing which is a cross-sectional view of an underwater cable.

The cable as shown in the accompanying drawing comprises a central core 10 of longitudinally extending optical fibres. This core 10 may for example comprise strands or bundles of fibres encapsulated in rubber, plastics or a suitable gel compound. The optical fibre core 10 is surrounded by a copper or copper alloy hermetically sealed tube 11 having a diameter that is at least four times the wall thickness. The thickness is determined from the tensile strength of the copper or copper alloy and the pressure that it is to be subjected to corresponding to the operating depth of the cable. It is desirable that the copper or copper alloy tube 11 should be in the highest temper possible so that the range in which stress and strain are linearly related is close to the maximum. It is in this range where deformation of the tube is elastic that the material will fully recover its original dimensions after the stress is removed.

'The copper tube 11, in addition to providing part of the electrical conductivity and acting as a water and water pressure barrier, also prevents any hydrogen emitted or generated by the cable components outside the tube 11 from l penetrating the fibres. It is known that hy':ogen can diffuse into the glass fibres and render them opaque to infrared light thus increasing the atteniation. Copper and copper alloys are 'itt..

amongst the most impermeable materials to hydrogen.

The copper or copper alloy tube 11 is surrounded by a composite stranded strength member 14 that comprises an inner layer of stranded high tensile steel wires 12 surrounded b' an outer layer of stranded hard drawn aluminium alloy wires 13. The number, size, and lay angle of the two layers of wires are selected to provide the desired strength and torque balance. The two layers 12 and 13 combine with the copper or I copper alloy tube 11 to form the electrical conductor.

Inner interstices 15 of the stranded wires are filled with a suitable water blocking material to prevent 4 S 25 water ingress and movement along the cable in the event of cable damage. Suitable materials for water blocking are silicone greases and rubbers, or polyurethane rubbers or similar materials.

The composite stranded strength member 14 is then surrounded by a layer 16 of semi-conductive polyethylene or ethyl vinyl acetate or similar semi-conductive thermoplastic material. The semi-conductive compound is extruded over the composite strength member 14 and fills the outer interstices 17 of the stranded strength member 14 thus giving, by mechanical interference, a good bond between the strength member 14 and the semi-conductive layer 16. The cable is then coated with a suitable layer 18 of insulating polyethylene 6 that surrounds the semi-conductive layer 16 and forms a strong smooth bond at the interface 19. The good mechanical bond between the semi-conductive layer 16 and the strength member 14 provides the desired resistance against separation due to the transfer of mechanical forces and the smooth interface 19 between the semi-conductive layer 16 and the insulating layer 18 ensures a uniform electric field and avoids the occurrence of regions of high electrical field which tend to arise where insulation is placed directly over an irregular shaped layer such as a strength member of stranded wire.

Example The tube is made from copper/copper alloy for example a tube made with Alloy C638 as made by Olin Corp.

Illinois, which is an alloy of 95% copper with addition of .j t 15 aluminium, silicon and cobalt.

Strength Members The following example provides a torque balanced construction.

ist Layer 0 Material: High tensile steel with a breaking stress of 2250 MPa ,s ENumber and size of wires: 12/1.24 mm ,2nd Layer i 25 Material: Aluminium alloy 1120 Number and size cf wires: 12/2.08 mm

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7 Semi-conductive Layer Extruded semi-conductive polyethylene.

The use of aluminium wires in the strength memberprovides the necessary tensile strength whilst at the same time reduces the weight of the cable. The provision of the semi-conductive layer between the strength member and the insulation ensures a good bond and reduces the chances of separation due to mechanical forces. Furthermore, the .;rniooth interface between the semi-conductive layer and the insulation 10 ensures against breakdown caused by pockets of high strength f« electric field at the interface.

The present invention in its broadest aspect relates to all types of underwater optical fibre cables and is not restricted to the precise details of the optical fibre 15 construction as illustrated in the preferred embodiment. It is further understood that the cable may incorporate ot1er compounds and layers for various mechanical, electrical and other desired characteristics without departing from the broad spirit of the invention.

o tr S 4

Claims

1. An underwater cable comprising a longitudinally extending bundle of optical fibres surrounded by a copper copper alloy conductor tube, at least one layer of high tensile strength material wound onto the conductor tube, a semi-conductive layer of polymeric material extruded over the hic'h tensile material, and a layer of insulating material bonded onto the exterior of the semi-conductive layer.

2. Thu underwater cable according to Claim i, t wherein the high tensile strength material comprises a Slayer of aluminium and a layer of steel wound onto the copper or copper alloy tube. 4 44

3. The underwater cable according to Claim 2, wherein the layers of steel and aluminium comprise wires wound one onto the other in opposite directions to produce a torque balanced configuration.

4. The underw ter cable according to Claim 3, wherein the stranded wires form interstices that are filled ,04604 with a suitable water blocking material.

The underwater cable according to any one of the o preceding claims, wherein the copper or copper alloy tube has a diameter that is at least four times the wall thickness.

6. The underwater cable according to any one of the preceding claims, wherein the polymeric material is either polyethylene or ethyl vinyl acetate.

7. An underwater cable according to any one of the I I 9 preceding claims and substantially as described in the example.

8. An underwater cable substantially as described herein with reference to and as illustrated in the accompanying drawings. Dated this 6th day of March, 1990 PACIFIC DUNLOP LIMITED and THE OVERSEAS TELECOMMUNTCATIONS COMMISSION (AUSTRALIAI By Their Patent Attorneys: GRIFFITH HACK CO. Fellows Institute of Patent Attorneys of Australia. S t So 1 |0 4 o o