Patent Application
20140174785
This application claims priority to Norwegian Patent Application No. 2012 1547, filed on Dec. 21, 2012, the entirety of which is incorporated by reference.
1. Field of the Invention
The invention relates to an ROV cable with improved electrical durability compared to prior art.
2. Description of Related Art
Conventional ROV cables used today have functioned relatively well, however with a constrained electrical lifetime, due to dimensional constraints that make it difficult and even impossible to apply any safety margins in the cable design. Such cables are typically used in conjunction with Remote Operated Vehicles (ROVs) being deployed from Tether Management Systems (TMSs), or directly from the surface.
Electrical failure of ROV cables may cause downtime for the operator, re-termination and in worst case abortion of the mission and sail to harbour for a replacement umbilical. Operational downtime is a key parameter for ROV operators, due to its effect on total operational cost.
The cable core consisting of multiple insulated electrical copper conductors are conventionally screened by interstitial drain wires electrical short-circuited by a collective metallic tape encapsulating the cable core. Screening is important to prevent hazard to equipment and personnel and to avoid corrosion of the steel wire armouring. The tape conventionally used is a two component tape with one metallic layer (typically Copper or Aluminium) and one polymeric side. The problem with such metallic tapes is that they tend to crack, due to the extensive amount of bend cycles such a cable experiences in operation. By cracking, the tape may lose its function of connecting the drain wires electrically, and in addition introduce metallic islands (isolated metallic tape sections not connected to ground potential).
U.S. Pat. No. 5,132,491 describes a coaxial cable having an insulated centre conductor and drain wires helically wrapped with two layers of a polymer tape, which has on one side a metal coat and on the other side a semiconductive adhesive polymer film layer. The polymer tape may be any polymer tape material known to be useful for wrapping around insulated signal conductors of coaxial signal cables. It is usually a thermoplastic polymer, but may be PTFE, and is preferably a polyester tape. The tape may be metal-coated in any customary way with an electrically conductive metal, aluminium being preferred. On the reverse side of tape is affixed a semiconductive polymer film, usually a conductive carbon-filled polyester adhesive tape. Other materials could be used to achieve a thinner more flexible coating. The object of the invention is to provide a ROV cable which improves the electrical durability of prior art cables.
The object of the invention is achieved by means of the features of the patent claims.
In one embodiment, a ROV cable according to the invention comprises insulated electric conductors, drain wires, collective screen tape, and protection, wherein the screen tape comprises a polymeric semi-conductive tape.
The insulated electrical conductors are the conductive elements of the cable, and will transfer electric power or signals. Power conductors can be of varying sizes with voltage rating up to 6.6 kV. The power conductor cores have a dual polymer insulation design, the inner part is semi-conductive and the outer part is an insulator.
The drain wires are electrical conductors (e.g. Cu) which are sheathed with semi-conductive polymer. The collective screen tape short-circuits all drain wires, so that any fault current are equally distributed among the drain wires. The screen tape also confines the dielectrical field within the cable.
The term semi-conductive will in this context mean a volume resistivity<1000Ωm. The polymeric semiconductive tape is made of a material that is more elastic and fatigue resistive than metal and less prone to fatigue failure during bending. In one embodiment, the polymeric semiconductive tape is a semiconductive nylon tape.
In other embodiments, the polymeric semi-conductive tape is made of polyamide, or polyamide and an adhesive. In the latter case, the adhesive may provide the desired conductivity to achieve the semi-conducting properties.
The screen tape wrapping/outer protection may comprise one or several layers.
The invention will now be described in more detail, by means of an example and with reference to the accompanying drawings.
In
An outer protection comprises in this embodiment a cable core sheathing 24 with high durability, for example made of thermoplastic polyester and a torque balanced steel wire armouring comprising contra-helical layers for protection. Experiments have shown that the use of semiconductive polymeric screen tape, in conjunction with Nexans already developed dual polypropylene insulation system, will heighten the onset level of partial discharge activity and heighten the breakdown voltage of the conductors, and thereby prolong the electrical lifetime. A semiconductive polymer tape (e.g. nylon) has the following advantages in comparison with a two-component metallic tape:
| Number | Date | Country | Kind |
|---|---|---|---|
| NO 20121547 | Dec 2012 | NO | national |
