Patent Application
20120205137
The present invention relates to an integrated high power umbilical, including a number of high power cables for transfer of large amounts of electric power/energy, filler material in the form of stiff, elongate plastic elements/profile elements located at least partially around and between the high power cables, and that are collectively gathered into a twisted bundle by means of a laying and closing operation, and a protective sheath that encapsulates the high power cables and the filler material.
Initially, the basis for the present invention was to arrive at a mechanically protected power cable which was especially prepared as a DEH cable (Direct Electric Heating) and designed to be deployed into the sea. Such DEH cables are used to heat pipelines transporting produced hydrocarbons in order to prevent hydratization. The DEH cable can for example be strapped securely to the pipeline, a so-called “Piggyback” solution. The DEH cable constitutes one of the conductors and the pipeline itself constitutes the other conductor in the heating system. Such a heating system is disclosed and described in closer detail in NO 323516.
It is a well known matter that when alternating current (AC) is supplied in a conductor, capacitance between the metallic conductor and the environment (remote ground) will arise. The capacitive AC current that arises is called charging currents.
Traditionally, such high voltage power cables have been designed with cable armoring and cable mantles, or what is called a screen. The screen is present to take care and drain away the capacitive currents that arise when these high voltage cables are in operation and transfer large amounts of electric energy/power. This is now solved in a different way, and is developed in connection with existing high power umbilicals. The existing high power umbilicals inherently have the above mentioned mechanical protection, namely as a filler material in the form of stiff, elongate plastic elements/profile elements.
Why a need to solve the screening in a different way exists, is inter alia reasoned as follows. For a cable extending from the seabed and up to a floating vessel, the cable needs to pass through a dynamic zone, normally in the sea surface area. A cable that operates in the dynamic zone is imparted undesired movements (by waves, wind, currents, etc.) that over time give rise to fatigue, and particularly in the mentioned cable mantle which is designed to take care of the capacitive currents. When the cable is of heavy gauge, and the mantle is located far from the center line of the cable, the mantle in particular is subjected to fatigue damage and subsequent rupture in the dynamic zone. Thus, it has been greatly desired to find a replacement for this cable mantling, which normally has been a thick foil of copper or other suitable metallic material.
In some way or another, the capacitive currents that occur within the sea cables have to be drained off to the surrounding seawater in order to limit axial capacitive currents through the transverse cross section of the cable and the voltage built up along the outer sheath.
Surprisingly it has turned out that the described profile elements and the outer sheath of the umbilical can be made of a material that has good semiconducting properties and can be taken in use with the present power umbilical. Together with seawater in the cross section, they will together conduct current along the umbilical.
Transfer of current between the pipe and the seawater takes place via anodes and the current in the seawater flows in parallel with the pipe. The length of the transfer zone is given by physical laws and is normally 50 m for 60 Hz application. See
Thus, according to the present invention, an integrated high power umbilical of the introductory said kind is provided, which is distinguished in that at least one of the surrounding elements, i.e. the filler material or the sheath, is made of a semiconducting material, said semiconducting material being able to drain off, or dissipate, capacitive currents arising in the high power cable when the high power cable conducts large amounts of electric energy/power.
It is, however, to be mentioned that the power umbilical according to the present invention can be supplied in many variants and embodiments that are especially adapted to the specific field of use of the umbilical. The common denominator for them all is that they need to have good ability to dissipate or drain away capacitive currents without the use of a metallic screen, as traditionally done. This good ability to drain away capacitive currents takes place, inter alia, through the use of the extruded profile elements that both have the good capacity to create mechanical protection for a current transferring cable and simultaneously act as a semiconductor that contribute to drain off capacitive currents.
In addition, the integrated high power umbilical can be further processed in order to increase the dissipation of capacitive currents. This primarily takes place in that radially extending channels are provided through the outer sheath of the umbilical and the hollow, extruded profile elements so that the seawater present within the profile elements and the radially extending holes, or apertures, by themselves form communication routes for drainage, or dissipation, of capacitive currents.
As a further option, one may provide a fibre optics conductor to the high power umbilical for use to monitor the condition of the high power umbilical on a continuous basis. By too excessive heat development, the fibre optics conductor will receive a temperature increase and this, in turn, provides a signal to a monitoring station that takes measures in order to stop the current.
News and Advantageous Features of the Cables are:
With the New Cable the following are Achieved:
Thus this integrated high power umbilical includes high voltage power cables without the traditional armoring and screening. Umbilicals use cables with semiconductive outer jacket only. The capacitive currents are drained out through the outer jacket of the cable and conducted out to the sea. The capacitive currents are eliminated by contact with each other along their length. Lack of contact with seawater/ground will probably result in immediate consume of and melting of the semiconductive jacket. Further, semiconductive cables omit steel armoring or screen, but having stiff, elongate plastic elements for static and dynamic applications, have never been used previously. This solution is applicable for long static cables/umbilicals and short dynamic cables/umbilicals.
Preferably, the electric high power cables, the filler material and the at least one electric conductor can be SZ laid and closed, i.e. alternately laid and closed by continuously alternating direction, in the entire or part of the longitudinal, extension of the high power umbilical, combined with that the SZ laid and closed bundle is kept fixed substantially torsion stiff by the protective sheath. As an alternative, the integrated high power umbilical can be laid and closed in the traditional way into a helix having a relatively long laying length.
In one embodiment, both at least one of the stiff, elongate plastic elements and the protective outer sheath are made of a semiconducting material, for example carbon containing polyethylene (PE), polyvinylchloride (PVC), polypropylene (PP) and acrylonitrile butadiene styrene (ABS).
The stiff, elongate plastic elements can include longitudinally extending channels for receipt of seawater, and the protective outer sheath can include substantially radially extending channels that communicate with the longitudinally extending channels, said seawater forming a semiconductor to transport away, or dissipate, capacitive currents generated in the high power umbilical.
In one embodiment, at least one fibre optics conductor can be arranged in the high power umbilical, which fibre optics conductor is able to monitor the condition of the high power umbilical on a continuous basis, where a rupture will generate a warning signal.
The stiff, elongate plastic elements can have channels in the form of apertures, holes, slits or similar such that the seawater is able to transport away, or dissipate, the capacitive currents to the surrounding seawater.
In another embodiment, or supplementary, the electric high power cables can be three-phase cables, where the three-phase cables are arranged in a triangle within the transverse cross section thereof, that are either in contact with each other or with the semiconductive profiles.
In a more complex embodiment the high power umbilical can include electric wires and/or fibre optics conductors which also are laid and closed into a SZ configuration and are located internal of the outer sheath, alternatively laid and closed in the traditional way.
In addition, it may include at least one load carrying element that is predetermined located in the transverse cross section of the high power umbilical, where the element(s) also is(are) laid and closed in a SZ configuration, alternatively laid and closed in the traditional way.
The umbilical may also include an anti rotation band, or strength band, or a tape, which is helically winded about the bundle just internal of the protective sheath. Alternatively the strength band, or the tape, is helically winded around the bundle in two or more layers, laid and closed in opposite directions.
In possible embodiments, the load carrying elements can be light weight rods of composite material having embedded carbon fibres, so-called carbon fibre rods, and/or steel threads, steel wire, and/or fibre rope and/or polyester rope.
In particular cases, the power umbilical can include at least one fluid pipe in its transverse cross section, which pipe can be made metal and/or plastic material laid and closed in the same configuration as the other elements.
According to the present invention, also an integrated high power umbilical of the introductory said kind is provided, which is distinguished in that at least one of the surrounding elements, i.e. the filler material, or the sheath, is made of a semiconducting material, said semiconducting material being able to drain off, or dissipate, capacitive currents arising in the high power umbilical when the high power cable conducts large amounts of electric energy/power, and that at least one fibre optics conductor is arranged in the high power umbilical, which fibre optics conductor is able to monitor the condition of the high power umbilical on a continuous basis, wherein a temperature increase will generate a warning signal. An elongation in a fibre will provide a similar signal that the umbilical has been inflicted a curvature or damage.
The unique dynamic umbilical design of the applicant makes the use of this technology possible since the cables are carefully protected by the filler material in the form of profiled elongate channel elements. Without the use of surrounding elongate plastic elements/plastic profiles, the cables will be too weak regarding installation loads and operational strain and stress. The cables have a simplified design. Mechanical protection and structural strength are transferred to the umbilical structure or design. The axial strength is carried by external load carrying elements integrated in the transverse cross section. The design will therefore not require any additional water barrier. The semiconducting materials are new and the materials are tested with excellent results. The semiconductive materials are also waterproof up to 90° C. over 20 years. Longer operations are not tested. For normal power transfer applications a designed life time of 30 years is foreseen.
Thus it is to be understood, in accordance with what is described above, that the following alternatives have come up, which are reflected in the patent claims, to conduct or direct the capacitive currents out into the sea:
It is to be understood that it will be possible to combine one or more of the alternatives indicated above.
Other and further objects, features and advantages will appear from the following description of preferred embodiments of the invention, which is given for the purpose of description, and given in context with the appended drawings where:
In the shown embodiment according to
In addition, in one embodiment, the power umbilical K can include at least one metallic electric conductor, in
The laid and closed bundle can optionally be kept together and in place by a strength band. An outer sheath or jacket 1, for example of polyethylene PE, is extruded onto the bundle. Polyethylene with addition of carbon is considered as semiconductive. As mentioned the cross section can also include fluid pipes (not shown) in some embodiments or variants.
The inner and outer channel elements 2, 3 are laying at least partly around and between the electric cables 4 and are typically made as rigid, elongate, continuous elements of plastic material such as PVC. The electric cables 4, the possible wires/fibre optics conductors 5, the filler material 6 and the channel elements 2, 3 and the at least one load carrying element 7, are as mentioned alternating laid and closed, i.e. having steadily changing direction, in the entire or part of the longitudinal extension of the power umbilical, alternatively continuously helical. In addition, the laid and closed bundle is kept substantially torsional stiff by the protective sheath 1, optionally by the addition of a strength band that is helically wound around the bundle immediate inside the protective sheath 1.
As mentioned, the rigid elongate plastic elements 2, 3 can be made of semiconducting plastic material. Optionally, only the inner channel elements 2 or only the outer channel elements 3, or as mentioned only one single channel element 3B, can be semi conducting. As mentioned, also the protective jacket 1 can be made of semiconductive material.
The rigid elongate profile elements 2, 3 can include longitudinally extending channels 9 that communicate with radial extending holes, slits or similar in the profile elements 2, 3 and through the protective jacket 1 such that the water that fills the channels 9 and the holes are able to transport away the capacitive currents into the surrounding sea water.
The electric power cables 4 can in turn be three-phase cables which in the cross section thereof can be arranged in a triangle, which either are in contact with each other or with the semiconducting plastic profiles 2, 3.
As an illustrating example of the dimensions in question, without thereby being limiting, the cable can have a transversal cross section of 2000 mm2. Designed life time is 30 years. It is further to be understood that ordinary electric wires for control functions, can in addition possibly be included in all embodiments and variants, all according to actual needs.
In addition, the power umbilical K2 can include one or more low voltage electric wires 6′, which is arranged in the cross section and extends in the longitudinal direction of the power umbilical. The low voltage wires 6′ are placed separate from and external of the power cables 4′.
The bundle can optionally be kept together and in place by a strength band. An outer sheath or jacket 1′, for example of polyethylene (PE), is extruded onto the bundle.
The outer, intermediate and inner channel elements 2′, 2a′, 3′ are laying at least partly around and between the electric power cables 4′ and are typically made as rigid, elongate, continuous elements of plastic material. The power cables 4′, the possible wires/fibre optics conductors 5′, 6′, the channel elements 2′, 2a′, 3′ and the at least one load carrying element 7′, 7″, are as mentioned alternating laid and closed, i.e. having steadily changing direction, in the entire or part of the longitudinal extension of the power umbilical K2, alternatively continuously helical. In addition, the laid and closed bundle is kept substantially torsional stiff by the protective sheath 1′, optionally by the addition of a strength band that is helically winded around the bundle immediate inside the protective sheath 1′.
As mentioned, the rigid elongate plastic elements 2′, 2a′, 3′ can be made of semiconducting plastic material. Optionally, the inner channel elements 2′ only, the intermediate elements 2a′ only, the outer channel elements 3′ only, or, as mentioned, only one single channel element can be semiconducting. Also the protective jacket 1′ can be made of semiconductive material.
| Number | Date | Country | Kind |
|---|---|---|---|
| 20093260 | Oct 2009 | NO | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/NO2010/000395 | 11/1/2010 | WO | 00 | 4/27/2012 |
