NO20181604A1 - Cable with metallic fabric layer - Google Patents

Description

Cable with metallic fabric layer

The present invention relates to cables, in particular to offshore, winch operated cables.

Offshore cables are used in a number of challenging environments that expose the cables to high physical stress. One such application is winch operated offshore cables, such as those used to supply power and communication signals to ROVs offshore. Such cables are deployed over sheaves at high tension.

There are numerous designs for prior art ROV cables, however a common arrangement comprises a plurality of insulated power conductors arranged at the core of the cable. Between, and in common contact with adjacent power conductors are arranged interstitial drain wires. Such drain wires are typically Cu conductors having a semiconductive outer layer or skin. An individual drain wire, having a semiconductive skin, creates a ground connection to its adjacent conductors with which it is in contact. Drain wires could also possibly be arranged without an outer layer.

In one prior art arrangement, a metallic tape is wrapped around the power conductors and interstitial drain wires, between the core and an outer insulation layer and/or armor layer. The metallic tape has a number of functions, primary among them being to create an electrical contact between all of the interstitial drain wires, thus creating a common ground connection having an effectively larger cross section.

Metallic tape may however become brittle and may crack and pulverize under the stress and tension experienced by winch operated cables. In such an occurrence the metallic tape loses its ability to create a common connection between the drain wires of the cable, which can result in degradation or failure of the cable.

It is an object of the present invention to provide a cable, for example an offshore, winch operated ROV cable, having a layer around the conductor core of the cable that provides a common electrical connection between interstitial drain wires, but which is not subject to cracking and pulverization under high physical stress and tension.

The present invention is defined in the following claims. According to one embodiment, the cable comprises a plurality of conductors, a plurality of interstitial drain wires arranged between and in electrical contact with adjacent conductors, and a layer wrapped about the conductors and drain wires, the layer being made of an electrically conductive fabric material and being in common electrical contact with the plurality of drain wires.

In one embodiment, the electrically conductive fabric material replaces the interstitial drain wires, with the fabric itself functioning as the common ground between the conductors.

In one embodiment, the electrically conductive fabric is arranged between the conductors/drain wires and an outer insulating layer of the cable. In one embodiment the cable further comprises an armor layer.

In one embodiment, the cable comprises one or more central cores of conductors, with an outer layer of conductors arranged about the one or more central cores. The central cores may have their own sets of interstitial drain wires arranged between the conductors of the central core or cores. About the conductors/drain wires of the central core or cores may be a layer of a conductive material in electrical contact with the conductors or drain wires functioning as a ground connection. The central cores in certain applications will be less subject to physical stress than the outer layer of conductors. Therefore the electrically conductive material wrapped about the conductors/drain wires of the core may be a metallic tape (for example if such metallic tape in the core is less subject to degradation) or may also be an electrically conductive fabric material if physical stress of the core is also a concern.

In one embodiment, the electrically conductive fabric comprises plastic fibers woven into a fabric material, the plastic fibers being coated with an electrically conductive material. In one embodiment, the electrically conductive material is a metal. In one embodiment, the electrically conductive material in a metallic alloy. In one embodiment, the alloy is a Cu/Ni alloy. In one embodiment, the plastic fibers are polyester or nylon. In a preferred embodiment, the electrically conductive material is a Cu/Ni coated, polyester taffeta, of a type commercially available from Laird ™ Performance Materials under the commercial name Flectron®.

Metallic fabrics such as the Flectron® product are known, but they are typically available in small rolls and used in different applications than the present invention, such as for example as a wrap at terminal connections of cables or as shielding against electromagnetic interference or radio frequency interference. It is not believed that such metallic fabrics have ever been employed as a layer material in the manufacture of cables. For example, the Flectron ® product is the subject of US patent no. 8968861 entitled “Flame retardant, electrically conductive adhesive material and related methods”, indicating its intended use for purposes not related to the present invention.

The invention will be described in detail with reference to the accompanying figures, wherein:

Fig 1 is a perspective view of an embodiment of a cable according to the invention.

Fig 2 is a perspective view of an alternative embodiment of the invention.

As shown in figure 1, the cable of the present invention comprises a plurality of insulated power conductors 10. Arranged between and in electrical contact with adjacent conductors 10 are a plurality of interstitial drain wires 12. Drain wires 12 may be covered in an semiconductive outer skin (13) such as polyethylene (PE). Drain wires 12 function, inter alia, as a ground connection for conductors 10 in the event of current leakage.

Arranged about the conductors 10 and the drain wires 12 is a layer of an electrically conductive fabric material 14. The fabric material 14 is characterized by its structure as a woven material with flexibility and physical clothlike properties, in particular the property of being non-brittle and being resistant to cracking or pulverization under physical stress. The electrically conductive fabric material 14 is in common electrical contact with drain wires 12, thus, inter alia, creating a common ground connection having an effectively larger cross section than the individual drain wires. It is to be understood that an embodiment of the invention contemplates the layer of fabric material replacing the drain wires 12 entirely as the ground connection, as shown in Fig 2.

The cable may optionally comprise one or more central cores 17 comprising central core conductors 11 having their own central core drain wires 19. The central core may itself have a layer of central core conductive material 15 wrapped about central core conductors 11/central core drain wires 19. Central core conductive material 15 may in alternate embodiments be a metallic tape as shown in Fig 1 or an electrically conductive fabric material 14’ similar to layer 14, as shown in Fig 2 (in the embodiment without drain wires).

According to one embodiment, the electrically conductive fabric material 14 is made of woven fibers of plastic, polyester or nylon. The fibers are coated with an electrically conductive material. In one embodiment, the electrically conductive material is a metal. In one embodiment the metal is Cu. In one embodiment the metal is Aluminum. In one embodiment, the electrically conductive material in a metallic alloy. In one embodiment, the alloy is a Cu/Ni alloy. In a preferred embodiment, the electrically conductive material is a Cu/Ni coated, polyester taffeta, of a type similar to a commercially available product from Laird ™ Performance Materials, marketed under the commercial name Flectron®.

As further shown in figure 1, the cable according to one embodiment of the invention further comprises an insulation layer 16, for example a thermoplastic insulating sheath and an optional layer of steel wire armor 18. The insulating layer 16 and optional armor layer 18 are made and arranged as known in the art.

Claims (14)

1. A cable comprising a plurality of conductors (10) and an insulating layer (16) characterized in that the cable further comprises a layer of an electrically conductive fabric material (14) wrapped about the conductors intermediate the conductors and the insulating layer, the fabric material being in common electrical contact with the conductors.

2. A cable according to claim 1 wherein the cable comprises a plurality of interstitial drain wires (12) arranged between and in electrical contact with adjacent conductors (10), and wherein the fabric material (14) is in common electrical contact with the drain wires.

3. A cable according to claim 2, wherein the drain wires (12) have a semiconductive skin (13).

4. A cable according to one of the preceding claims, wherein the electrically conductive fabric material (14) is made of woven fibers of plastic, polyester or nylon.

5. A cable according to claim 3, wherein the fibers are coated with an electrically conductive material.

6. A cable according to claim 4, wherein electrically conductive material is a metal.

7. A cable according to claim 4, wherein electrically conductive material is Cu.

8. A cable according to claim 4, wherein electrically conductive material is aluminum.

9. A cable according to claim 4, wherein electrically conductive material is an alloy.

10. A cable according to claim 4, wherein electrically conductive material is a Cu/Ni alloy.

11. A cable according to one of the preceding claims, further comprising an armor layer (18) of steel armor wires.

12. A cable according to one of the preceding claims, further comprising one or more central cores (17) comprising central core conductors (11), wherein a layer of central core conductive material (14’/15) is wrapped about central core conductors (11).

13. A cable according to claim 12, further comprising central cores interstitial drain wires (19) arranged between central core conductors (11).

14. A cable according to claim 12 or 13 wherein central core conductive material is an electrically conductive fabric material (14’) according to one of claims 4-10.