Patent Application
20110120745
The invention relates to a cable having a core to which are attached a plurality of elongate conducting elements. In particular four conducting elements are used to form a quad cable.
Quad cables are known in the art, for example U.S. Pat. No. 5,521,333 (Kobayawshi et al.) assigned to Sumitomo Electric Industries, Ltd., teaches a transmission cable including four insulated electric wires with a low dielectric central interposition member or elongate core. In the quad cable of this patent the elongate core is preferably made of polyethylene. The insulation of the insulated electric wires are also preferably made from polyethylene. A jacket of polyvinylchloride is disposed about the insulated wires. The insulated electric wires of this patent are held in place about the elongate core by means of polyester tape wound about the wires.
Quad cables incorporating an elongate core or filler made from expanded polytetrafluoroethylene are known from U.S. Pat. No. 5,574,250 (Hardie et al.) assigned to W.L.Gore & Associates. In this patent, the four insulated electric wires are held in position by a spacer layer.
A further quad cable is known from DE-A-31 04 429 (Fröscher) assigned to Siemens in which two signal conductors and two earth wires are disposed about a central core made of a dielectric material. This application does not disclose the means by which the signal conductors or earth wires are held in place about the core.
The use of electrical cables in marine environments is known to be problematic since there is a risk that water may penetrate into the cable in the event of a cut or breach in the outer jacket. The most common method of protecting the cable in the art involves the use of flooding materials to fill the interstices of the cable. Such flooding materials include synthetic polymers and petroleum greases. One known disadvantage of the use of these materials is that the dielectric constant of the cable is changed by the addition of these materials in the cable. Furthermore, as the conductors move within the cable, the relative position of the interstices move which affects the electrical properties of the cable. It has been particularly difficult in the past to provide water blocking quad cables since additional handling and processing steps are required which are both messy and inefficient.
U.S. Pat. No. 5,949,018 (Esker) assigned to CommScope, Inc., teaches a water blocked cable construction which provides one way of solving this problem. In this patent, a water swellable flooding material is taught which is placed between two metal braided shields. The material used is a hydrogel polymer which is solid when dry but swells up and becomes gel-like on immersion in water.
U.S. Pat. No. 5,734,126 (Siekierka et al.) assigned to Belden Wire & Cable Company teaches a twisted pair cable which is suitable for high frequency signal transmission. The cable has two solid, stranded or hollow conductor wires which are surrounded respectively by a cylindrical dielectric insulation layer. Each of the conductors is disposed centrally within and thus substantially concentric with the corresponding insulation. The insulated conductors are joined or bonded together along their entire length by an appropriate adhesive. Alternatively, the adjacent dielectric insulation layers can be bonded together by causing material contact while the dielectrics are at elevated temperature and then cooling to provide a joined cable having no adhesive.
Similarly U.S. Pat. No. 5,382,390 (Hubis et al.) assigned to W.L.Gore & Associates, Inc., teaches a twisted pair in which the dielectric insulators of the insulated conductors are bonded together by heating. Neither the Siekerka nor the Hubis patent make reference, however, to quad cables. Indeed their teachings are not applicable since it is necessary in a quad cable to maintain a fixed spatial relationship between the individual conductors, e.g. by use of a central spacing member or core, and this is not possible to implement using the teachings of these two patents.
It is the object of the invention to provide an improved quad cable.
It is furthermore an object of the invention to ensure that the individual conductors of a quad cable maintain a substantially fixed spatial relationship to each other throughout the length of the cable.
It is furthermore an object of the invention to improve the flexibility of the cable whilst maintaining its electrical properties.
It is yet a further object of the invention to provide a multi-conductor cable for use in a fluid environment such as a marine environment or in oil fields.
These and other objects of the invention are solved by providing a cable comprising an elongate core made of a first dielectric material with a core outer surface. Four or more (a plurality of) elongate conducting elements are disposed about the elongate core. Each of the elongate conducting elements has an inner conductor which is surrounded by an insulating layer made of a second dielectric material. The outer surface of the insulating layer of the elongate conducting elements is divided into a first outer surface area and a second outer surface area. The first outer surface area of the elongate conducting elements is attached to the core outer surface.
The use of the core in the cable provides a spacer in the centre of the cable about which the elongate conducting elements can be arranged. In the case of the quad cable four elongate conducting elements are provided. The outer surface of the insulators of the elongate conducting elements are attached to the outer surface of the core so that they elongate elements remain in a fixed position even when the cable is flexed. Thus the electrical properties of the cable, e.g. attenuation or characteristic impedance, remain substantially unchanged during flexing since the distance between the inner conductors of each of the elongate conducting elements remains substantially unchanged.
In one advantageous body of the invention, the second outer surface area of each of the elongate conducting elements is exposed to the environment, i.e. the cable is not provided with an outer jacket about the elongate conducting elements. Such a construction is particularly advantageous in environments in which a fluid, such as sea water or oil, could leak underneath the jacket and thus between the jacket and the elongate conducting elements, The fluid will locally alter the dielectric constant of the cable and thus affect the electrical properties of the cable.
Both the first and second dielectric materials are advantageously selected from the group of polymers consisting of polyethylene, polyester, perfluoralkoxy, fluoroethylene-propylene, polypropylene, polymethylpentene, full density polytetrafluoroethylene or expanded polytetrafluoroethylene. Most preferably expanded polytetrafluoroethylene is used for both dielectric materials since this material has a low dielectric constant and can be bonded to each other by sintering.
In one embodiment of the cable the insulating layer comprises a plurality of insulating layers with different dielectric constants, for example an inner one of the plurality of insulating layers is made of expanded PTFE and an outer one of the plurality of insulating layers is made of full density PTFE. This has the advantage that the effective dielectric constant of the elongate conducting elements and thus of the cable can be tailored to the required value.
The invention also provides for a method for the construction of a cable comprising the following steps:
In this method the step of attaching the plurality of elongate conducting elements to the elongate core is carried out by heat treatment and preferably by sintering since this provides, with the correct choice of materials, an extremely strong bond between the plurality of elongate conducting elements and the elongate core.
The sintering can be carried out in a salt bath or in an oven at a temperature between 320° C. and 420° C. and preferably of approximately 390° C.
The cable of the invention can be incorporated in a streamer for use in seismic surveys. Such streamers need to be flushable, i.e. the oil within the streamer can be flushed out of the interior of the streamer if required. Since—as explained above—there are no interstices between the conducting elements in which the oil remains trapped and thus locally affects the dielectric constant, the electrical properties of the signal carrying cable are greatly improved.
A quad cable 10 comprising found elongate conducting elements 30 disposed about an elongate core 20 is shown in
The elongate elements 30 are made of an inner conductor 40 of AWG size, for example, 20 or 22 surrounded by an insulating layer 50. The inner conductor 40 can be made from any conducting material such as copper, nickel-plated copper, tin-plated copper, silver-plated copper, tin-plated alloys, silver-plated alloys or copper alloys. Alternatively the inner conductor could be an optical fibre surrounded by a cladding layer. The insulating layer 50 is made of a dielectric material such as polyethylene, polyester, perfluoralkoxy, fluoroethylene-propylene, polypropylene, polymethylpentene, full density polytetrafluoroethylene or expanded polytetrafluoroethylene. Preferably expanded polytetrafluoroethylene such as that described in U.S. Pat. No. 3,953,556, U.S. Pat. No. 4,187,390 or U.S. Pat. No. 4,443,657 is used. The elongate elements 30 have an outer surface area which is divided into a first outer surface area 60 and a second outer surface area 70.
The materials from which the insulating layer 50 and the elongate core 20 are made are chosen such that the two elongate core 20 and the insulating layer 50 can be attached to each other by adhesive or direct bonding. Preferably the attachment is made by direct bonding and most preferably by sintering as will be explained below. The insulating layer 50 and the elongate core 20 are preferably made from the same material. The attachment between the insulating layer 50 and the elongate core is made at the first outer surface area 60.
The embodiment of the invention in
The embodiment of the invention of
A further embodiment of the invention is depicted in
Manufacture of the cable 10 for the preferred embodiment of the invention is carried out as shown diagrammatically in
The cable 10 is then passed through an extruder 110 if a jacket 80 is to be extruded onto the cable 10.
The cable 10 can find one application in so-called streamers. These are used by oil exploration companies to carry out seismographic surveys of the ocean bottom sub surface to search for hydrocarbons.
This cable 10 has the construction as shown in
Each of the four elongate elements 30 is made of an inner conductor 40 of silver plate copper of size AWG 2019 surrounded by an insulating layer 50 which comprises three layers 50a, 50b, 50c of tapes wrapped about the inner conductor 40. The first tape 50a is made of ePTFE and has a thickness of 101.6 μm. The second tape 50b is wound over the first tape 50a and the third tape 50c is wound over the second tape 50b. The second tape 50b and the third tape 50c are both made of full density PTFE and have a thickness of 101.6 μm and 76.2 μm respectively. The elongate elements 30 have a lay length of 38 mm. Prior to sintering the elongate elements 30 have a nominal outside diameter of 2.23 mm.
The elongate core 20 with the elongate elements 30 is passed at a maximum speed of 1.0 m per minute through the sintering oven 100 at 395° C. which results in a dwell time in the oven of around 3 minutes. Subsequent to sintering the elongate elements 30 had a nominal outside diameter of 1.88 mm. The cable 10 has a maximum diameter of 4.6 mm.
This has the same construction and is made in the same way as the cable 10 of Example 1. The elongate elements 30 are made of an inner conductor 40 of size AWG 2219 about which is wrapped a single tape of ePTFE of 0.9 mm thickness. The elongate core 30 is made of ePTFE and has a nominal outside diameter prior to sintering of 0.9 mm.
The construction of Example 3 is shown in
This was made in the same manner as Example 1 except that the lay length was 19 mm. The cable was passed through a 3 m oven at a rate of 1 m/min and thus had a dwell time of around 3 minutes in the oven.
This was made in the same manner as Example 1 except that the lay length was 19 mm. The cable was passed through a 3 m oven at a rate of 1.3 m/min and thus had a dwell time of around 2.3 minutes in the oven. The four elongate elements 30 were poorly bonded to the elongate core 20.
This was made in the same manner as Example 1 except that the lay length was 19 mm. The cable was passed through a 3 m oven at a rate of 1.5 m/min and thus had a dwell time of around 2 minutes in the oven. The four elongate elements 30 were substantially not bonded to the elongate core 20.
Measurements of the differential impedance, attenuation and weight were made of the cables manufactured in Examples 1-3 and are given in the table below.
The attenuation measurements were made in air at a frequency of 20 MHz for Examples 1 and 2 and at 10 MHz for Example 3. The impedance measurements were also made in air by a Tectronics network analyser CSA 803.
Measurements on Example 2 were also made in 5% NaCl solution (equating to sea water). In this case the impedance was 111±5Ω and the attenuation was less than 54 dB/km. The same measurements were made using streamer fluid and the impedance was then 132±5Ω whilst the attenuation was less than 47 dB/km.
Approximately 1 m length of the cables 10 of Examples 4 to 6 were wrapped about an 11 mm outside diameter plastic mandrel and the impedance of a pair of the elongate elements 30 were measured before wrapping (as a straight cable) and after wrapping. The results are given in the table below. The impedance measurements in ohms along the 1 m length of the cable were made using the Tectronics network analyser CSA 803.
As can be seen from the table, the impedance variation along one of the pairs of the elongate elements 30 of Example 4 before and after wrapping is small as the elongate elements 30 remain bound to the elongate core 20. In Examples 5 and 6, however, there is poorer bonding or no bonding at all respectively. Thus the elongate elements 30 on wrapping about the plastic mandrel separate at least partly from the elongate core 20 which leads to a higher impedance and a greater variability in impedance. This experiment simulates the flexing of the cable 10 in real life which leads to bending of the cable and thus—if the elongate elements 30 are not sufficiently bonded—to separation from the elongate core 20.
| Number | Date | Country | Kind |
|---|---|---|---|
| 00102079.1 | Feb 2000 | EP | regional |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP01/01142 | 2/2/2001 | WO | 00 | 2/5/2007 |
