Patent Grant
6924436
1. Field of the Invention
This invention relates to electrical cabling and, more particularly, to a partial discharge resistant electrical cable and a method for manufacturing the cable.
2. Description of Related Art
Generally, oilfield wireline operations concern the testing and measurement of geologic formations proximate a well periodically prior to completion or after the well has been fully drilled. Electrical power requirements for tools used to test and measure the geologic formations have increased over time as the capabilities of the tools have improved. Accordingly, cables used to deliver electrical power to the tools are required to handle greater amounts of power.
As the electrical voltage applied to a cable exceeds a critical value, generally known as the inception voltage, a partial discharge of an electrical field within the cable, produced by the electrical voltage across the cable's conductor, may occur. Referring to
Generally, conventional wireline cables include stranded copper conductors insulated with fluoropolymers or polyolefins. It is desirable for the insulating materials to be strong, wear resistant, and capable of withstanding high temperatures, so that they are able to tolerate environments typically encountered during manufacturing and use. Such polyolefin-type polymers can generally be easily compression extruded in small thicknesses onto stranded copper conductors at economically viable speeds, producing insulated conductors having substantially no air or other gases entrapped between the conductor and the insulation.
However, such fluoropolymers are generally very difficult to compression extrude through small die orifices to produce thin layers of insulation on conductors at economically viable speeds. Secondary bonding forces (such as Van der Waal's forces) within simple hydrocarbons, such as polyolefin-type polymers, may generally be about 40 KJoules/mole, while such forces within fluoropolymers may generally be about 4 KJoules/mole. Thus, fluoropolymers generally achieve their strength and toughness by having molecules with very high molecular weights that entangle with neighboring molecules to compensate for the low secondary bonding force. The high molecular weight of the fluoropolymers leads to considerably higher viscosities at their processing temperatures than other polymeric insulation materials. Further, many fluoropolymers may experience severe melt fracture, visible as excessive surface roughness, when compression extruded in small thicknesses due to their high molecular weights.
Accordingly, fluoropolymer insulation is typically extruded through large die orifices and the material is stretched, while in a melted state, to a desired thickness and shaped onto the conductor. While this process may produce cabling at economically viable speeds, air or other gases are often trapped between the conductor and the insulation.
The present invention is directed to overcoming, or at least reducing, the effects of one or more of the problems set forth above.
In one aspect of the present invention, an electrical cable is provided. The electrical cable includes a conductor comprising a plurality of strands defining interstices therebetween and a first insulating layer comprising a polymer that is disposed on the conductor such that the first insulating layer substantially fills the interstices.
In another aspect of the present invention, an electrical cable is provided. The electrical cable includes a conductor comprising a plurality of strands defining interstices therebetween, a first insulating layer comprising a polymer that is disposed on the conductor such that the first insulating layer substantially fills the interstices, and an adhesion layer comprising a polymer that is disposed on the first insulating layer. The electrical cable further comprises a second insulating layer comprising a polymer that is disposed on the adhesion layer, wherein the adhesion layer is miscible with the polymer of the first insulating layer and the polymer of the second insulating layer.
In yet another aspect of the present invention, an electrical cable is provided. The electrical cable includes a conductor comprising a plurality of strands defining interstices therebetween, a first insulating layer comprising a polymer that is disposed on the conductor such that the first insulating layer substantially fills the interstices, and a second insulating layer comprising a polymer that is disposed on the first insulating layer. The electrical cable further includes a lubricating layer comprising a low molecular weight polymer that is disposed on the second insulating layer.
In another aspect of the present invention, an electrical cable is provided. The electrical cable includes a conductor comprising a plurality of strands defining interstices therebetween, a first insulating layer comprising a polymer that is disposed on the conductor such that the first insulating layer substantially fills the interstices, and an adhesion layer comprising a polymer that is disposed on the first insulating layer. The electrical cable further includes a second insulating layer comprising a polymer that is disposed on the adhesion layer and a lubricating layer comprising a low molecular weight polymer that is disposed on the second insulating layer, wherein the adhesion layer is miscible with the polymer of the first insulating layer and the polymer of the second insulating layer.
The invention may be understood by reference to the following description taken in conjunction with the accompanying drawings, in which the leftmost significant digit(s) in the reference numerals denote(s) the first figure in which the respective reference numerals appear, and in which:
While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the scope of the invention as defined by the appended claims.
Illustrative embodiments of the invention are described below. In the interest of clarity, not all features of an actual implementation are described in this specification. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developer's specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure.
In this first illustrative embodiment, the first insulating layer 204 comprises a low molecular weight polymer having, for example, a melt index greater than about 15. Such low molecular weight polymers may include injection moldable grade polymers. The melt index of a polymer is, in general, inversely proportional to its molecular weight and is defined as the amount, in grams, of the polymer that can be forced through a 2.0955 mm diameter extrusion orifice when subjected to an extrusion force defined for the particular material by American Society for Testing Materials (ASTM) standards for ten minutes at a temperature also defined for the particular material by ASTM standards. Low molecular weight polymers typically have lower viscosities than higher molecular weight polymers, which have lower melt indices. Thus, the lower viscosity of the low molecular weight polymer allows the first insulating layer 204 to flow into and substantially fill the interstices 208 (corresponding to the voids 102 of
While the present invention encompasses any low molecular weight polymer deemed suitable for the first insulating layer 204, in one embodiment, the first insulating layer 204 comprises a low molecular weight fluoropolymer, e.g., MFA 940 AX (co-polymer of tetrafluoroethylene and perfluoromethyl vinyl ether with a melt index of 140 to 150) manufactured by Ausimont U.S.A. of Thorofare, N.J., U.S.A. Such fluoropolymers are generally capable of withstanding higher temperatures encountered when the cable 200 is used in an oilfield wireline operation. In one embodiment, the first insulating layer 204 has a thickness t1 within a range of about 0.002 mm to about 0.500 mm.
Low molecular weight polymers may generally lack the mechanical strength and wear resistance desired for electrical cables to be used in harsh environments, such as in oilfield wireline operations. Therefore, the second insulating layer 206 comprises a high molecular weight polymer that surrounds the first insulating layer 204 to provide a strong, wear resistant covering for the cable 200. Such high molecular weight polymers may include fluoropolymers having melt indices of about 15 or less. While the present invention encompasses any high molecular weight polymer deemed suitable for the second insulating layer 206, in one embodiment, the second insulating layer 206 comprises a high molecular weight fluoropolymer, e.g., MFA 620 (co-polymer of tetrafluoroethylene and perfluoromethyl vinyl ether with a melt index of 2 to 5) manufactured by Ausimont U.S.A. of Thorofare, N.J., U.S.A. Such fluoropolymers are generally capable of withstanding higher temperatures and harsh physical conditions encountered when the cable 200 is used in an oilfield wireline operation. In one embodiment, the second insulating layer 206 has a thickness t2 within a range of about 0.13 mm to about 1.30 mm.
While the present invention is not so limited, in one embodiment, the first insulating layer 204 and the second insulating layer 206 are made from different species of the same polymer having different molecular weights. For example, the first insulating layer 204 may be made from a low molecular weight fluoropolymer, while the second insulating layer 206 may be made from the same, but higher molecular weight, fluoropolymer.
As discussed above, reducing the likelihood of air or other gases becoming entrapped between the conductor 202 and the first insulating layer 204 generally decreases the likelihood that partial discharge of the electrical field will occur. In one embodiment, the first insulating layer 204 may have a higher permittivity than that of the second insulating layer 206, thus further decreasing the likelihood of partial discharge of the electrical field. Generally, materials having higher permittivity values can store more energy than materials having relatively lower permittivity values. Thus, higher permittivity materials are relatively more capable of allowing an opposing electrical field to exist therein when the cable 200 is in use. Such opposing electrical fields may counteract at least a portion of the electrical field produced by the voltage across the conductor 202.
Further, the combination of the first insulating layer 204 and the second insulating layer 206 may result in tangential electrical fields being produced within the insulating layers 204, 206 when the cable 200 is in use due to the higher permittivity, in a relative sense, of the first insulating layer 204 as compared to the second insulating layer 206. Such tangential electrical fields may also at least partially counteract the electrical field generated by the voltage across the conductor 202. In one embodiment, the polymer comprising the first insulating layer 204 has a permittivity within a range of about 2.8 to about 8.0, while the polymer comprising the second insulating layer 206 has a permittivity within a range of about 1.8 to about 2.7.
Each of the first insulating layer 204 and the second insulating layer 206 may be applied to the conductor 202 by any means known to the art. For example, the insulating layers 204, 206 may be applied to the conductor by compression, semi-compression, or tubing extrusion methods, as are generally known in the art. In one embodiment, depicted in
Alternatively, in the illustrative embodiment shown in
It may be desirable in certain situations to compression or semi-compression extrude the second insulating layer 206 onto the first insulating layer 204. However, as discussed above, the second insulating layer comprises a high molecular weight polymer. Such polymers include large molecules that result in the polymer having a greater viscosity than that of low molecular weight polymers. Generally, greater viscosity leads to greater shear stress between high molecular weight polymers and the extrusion die (not shown) when extruded than between low molecular weight polymers and the extrusion die. This can lead to severe melt fracture cracking of the surface of the polymer.
Thus, in a second illustrative embodiment, shown in
Still referring to
The cable 500 may be produced as illustrated in FIG. 6. The conductor 202 is fed into a three layer co-extruder head 602 in a direction indicated by arrow 604. Each of the first low molecular weight polymer and the high molecular weight polymer are compression or semi-compression extruded onto the conductor 202 by the three layer co-extruder head 602 to form each of the first insulating layer 204 and the second insulating layer 206, wherein a low molecular weight polymer is applied to the high molecular weight polymer just prior to extrusion to form the lubricating layer 502. Thus, the insulating layers 204, 206 and the lubricating layer 502 are co-extruded by the three layer co-extruder head 602.
Alternatively, as illustrated in
It may be generally desirable for the first insulating layer 204 and the second insulating layer 206, as illustrated in
For example, if the first insulating layer 204 comprises nylon and the second insulating layer 206 comprises ethylene tetrafluoroethylene (ETFE), such as regular Tefzel 2183 manufactured by E.I. du Pont de Nemours and Company (DuPont) of Wilmington, Del., U.S.A., it is unlikely that they will sufficiently bond together. In this example, the adhesion layer 802 may comprise modified Tefzel HT-2202, also manufactured by DuPont, which is miscible with both nylon and regular Tefzel. Thus, the insulating layers 204, 206 may be bonded together via the adhesion layer 802. In one embodiment, the adhesion layer 802 may have a thickness t4 within a range of about 1 to 2 mils.
The cable 800 may be produced as illustrated in FIG. 9. The conductor 202 is fed into a three layer co-extruder head 902 in a direction indicated by the arrow 904. The low molecular weight polymer and the adhesion layer polymer are extruded (e.g., by compression, semi-compression, or tubing extrusion methods) onto the conductor 202 to form the first insulating layer 204 and the adhesion layer 802, respectively. The high molecular weight polymer is then formed on the adhesion layer 802 by a tubing extrusion process performed by the three layer co-extruder head 902 to form the second insulating layer 206.
Alternatively, as shown in
The invention, however, is not so limited. Rather, as illustrated in
Each of the first insulation layer 204, the adhesion layer 802, and the second insulating layer 206 may be applied by separate extruder heads 1202, 1204, 1206, respectively, as illustrated in FIG. 12. In this illustrative embodiment, the conductor 202 is fed into the first extruder head 1202 in a direction indicated by arrow 1208, wherein the low molecular weight polymer is extruded (e.g., by compression, semi-compression, or tubing extrusion methods) onto the conductor 202 to form the first insulating layer 204. The conductor 202, with the first insulating layer 204 applied thereon, is then fed into the second extruder head 1204, wherein the adhesion layer polymer is extruded (e.g., by compression, semi-compression, or tubing extrusion methods) onto the first insulating layer 204 to form the adhesion layer 802. The conductor 202, with the first insulating layer 204 and the adhesion layer 802 applied thereon, is then fed into the third extruder head 1206, wherein the high molecular weight polymer is formed onto the adhesion layer 802 by a tubing extrusion process performed by the third extruder head 1206.
As indicated previously, it may be desirable in certain situations to compression or semi-compression extrude the second insulating layer 206, which comprises the high molecular weight polymer. In a fourth illustrative embodiment, shown in
The cable 1300 may be produced as illustrated in FIG. 14. The conductor 202 is fed into a four layer co-extruder head 1402 in a direction indicated by the arrow 1404. The first low molecular weight polymer and the adhesion layer polymer are co-extruded (e.g., by compression, semi-compression, or tubing extrusion methods) onto the conductor 202 to form the first insulating layer 204 and the adhesion layer 802, respectively. The high molecular weight polymer and the second low molecular weight polymer are also compression or semi-compression extruded onto the adhesion layer 802 by the four layer co-extruder head 1402 to form the second insulating layer 206 and the lubricating layer 502, respectively. Thus, the insulating layers 204, 206, the adhesion layer 802, and the lubricating layer 502 are co-extruded by the four layer co-extruder head 1402. It should be noted that cable 1300 may be manufactured on a three layer co-extruder head if the adhesion layer 802 is omitted.
Alternatively, as shown in
The invention, however, is not so limited. Rather, as illustrated in
Each of the first insulation layer 204, the adhesion layer 802, and the second insulating layer 206 may be applied by separate extruder heads 1702, 1704, 1706, respectively, as illustrated in FIG. 17. In this illustrative embodiment, the conductor 202 is fed into the first extruder head 1702 in a direction indicated by arrow 1708, wherein the first low molecular weight polymer is extruded (e.g., by compression, semi-compression, or tubing extrusion methods) onto the conductor 202 to form the first insulating layer 204. The conductor 202, with the first insulating layer 204 applied thereon, is then fed into the second extruder head 1704, wherein the adhesion layer polymer is extruded (e.g., by compression, semi-compression, or tubing extrusion methods) onto the first insulating layer 204 to form the adhesion layer 802. The conductor 202, with the first insulating layer 204 and the adhesion layer 802 applied thereon, is then fed into the two layer co-extruder 1706, wherein the high molecular weight polymer and the second low molecular weight polymer are compression or semi-compression extruded onto the adhesion layer 802 to form the second insulating layer 206 and the lubricating layer 502, respectively.
While extrusion has been presented herein as a means for applying the insulating layers 204, 206, the lubrication layer 502, and the adhesion layer 802 in various embodiments, the present invention is not so limited. Rather, any means known to the art may be used to apply the layers 204, 206, 502, 802. For example, a pultrusion process may be used to apply a high molecular weight polymer as the first insulating layer 204. Pultrusion, as it relates to electrical cable insulation, is generally defined as a process of pulling a conductor through a polymer, such that the polymer clings to the conductor. The coated conductor is then pulled through a heated shaping die where the polymer is softened and formed into an insulating layer.
In one illustrative embodiment shown in
As the conductor 202 is then fed through a container 1806 containing the particles (powder) of the first high molecular weight polymer, the polymer clings to the conductor 202, forming an unconsolidated coating 1808 of the high molecular weight polymer on the conductor 202. In one illustrative embodiment, the container 1806 contains a fluidized bed of the first high molecular weight polymer. The coated conductor 202 is heated to make the polymer particles melt before it is pulled through a heated pultrusion die 1810, which compresses and consolidates the coating 1808 to form the first insulating layer 204. The combination of the heat and compression provided by the pultrusion die 1810 forces the high molecular weight polymer into the interstices 208 (as shown in
In this illustrative embodiment, the conductor 202, with the first insulating layer 204 applied thereto, is fed into an extruder head 1812, wherein the second high molecular weight polymer is extruded onto the first insulating layer 204 to form the second insulating layer 206. While the illustrative embodiment shown in
The particular embodiments disclosed above are illustrative only, as the invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular embodiments disclosed above may be altered or modified and all such variations are considered within the scope of the invention. Accordingly, the protection sought herein is as set forth in the claims below.
This application claims priority from Provisional Application No. 60/366,328, filed Mar. 21, 2002, which is incorporated herein by reference.
| Number | Name | Date | Kind |
|---|---|---|---|
| 4734545 | Susuki et al. | Mar 1988 | A |
| 5220133 | Sutherland et al. | Jun 1993 | A |
| 5426264 | Livingston et al. | Jun 1995 | A |
| 5654095 | Yin et al. | Aug 1997 | A |
| 5718974 | Kmiec | Feb 1998 | A |
| 5782730 | Kawasaki et al. | Jul 1998 | A |
| 6060205 | Takeichi et al. | May 2000 | A |
| 6184473 | Reece et al. | Feb 2001 | B1 |
| 6359230 | Hildreth | Mar 2002 | B1 |
| 6534717 | Suzuki et al. | Mar 2003 | B2 |
| 6600108 | Mydur et al. | Jul 2003 | B1 |
| 20020062984 | Dlugas | May 2002 | A1 |
| Number | Date | Country |
|---|---|---|
| 0 365 152 | Sep 1989 | EP |
| 1 331 648 | Jul 2003 | EP |
| 07320560 | Dec 1995 | JP |
| 2001067944 | Mar 2001 | JP |
| 2003051214 | Feb 2003 | JP |
| 9831022 | Jul 1998 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 20030178223 A1 | Sep 2003 | US |
| Number | Date | Country | |
|---|---|---|---|
| 60366328 | Mar 2002 | US |
