CA1158327A - Moisture-proofing of electrical cable with an outer layer electrochemically similar to the core - Google Patents
Moisture-proofing of electrical cable with an outer layer electrochemically similar to the coreInfo
- Publication number
- CA1158327A CA1158327A CA000363058A CA363058A CA1158327A CA 1158327 A CA1158327 A CA 1158327A CA 000363058 A CA000363058 A CA 000363058A CA 363058 A CA363058 A CA 363058A CA 1158327 A CA1158327 A CA 1158327A
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- CA
- Canada
- Prior art keywords
- conductors
- wires
- tube
- metal
- core
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
- H01B7/00—Insulated conductors or cables characterised by their form
- H01B7/17—Protection against damage caused by external factors, e.g. sheaths or armouring
- H01B7/18—Protection against damage caused by wear, mechanical force or pressure; Sheaths; Armouring
- H01B7/20—Metal tubes, e.g. lead sheaths
- H01B7/202—Longitudinal lapped metal tubes
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
- H01B7/00—Insulated conductors or cables characterised by their form
- H01B7/17—Protection against damage caused by external factors, e.g. sheaths or armouring
- H01B7/28—Protection against damage caused by moisture, corrosion, chemical attack or weather
- H01B7/2813—Protection against damage caused by electrical, chemical or water tree deterioration
Landscapes
- Insulated Conductors (AREA)
- Manufacturing Of Electric Cables (AREA)
Abstract
D-6939(Kab) MOISTURE-PROOFING OF ELECTRICAL CABLE
ABSTRACT OF THE DISCLOSURE
The synthetic insulation jacket of a cable is pro-tected against water-treeing from the interior in that the bundle of conductors are sealingly enveloped in a tube of preferably the same material so that moisture, lodged in the voids between the conductors, cannot penetrate the insulation.
ABSTRACT OF THE DISCLOSURE
The synthetic insulation jacket of a cable is pro-tected against water-treeing from the interior in that the bundle of conductors are sealingly enveloped in a tube of preferably the same material so that moisture, lodged in the voids between the conductors, cannot penetrate the insulation.
Description
11~832~ 1 ¦~ D-6939(Kab) , 1 ~ BACKC,~OUND OF THE INVEN~'IOl~
2 ~ __ _ _ _ _ _ ___
3 The present invention relates to a moisture-proof,
4 electrical cable for hiyh voltages.
6 Cables of the type to which the invention pertains 7 include plural conductors, preferably in a stranded configu-8 ration and being enveloped by and in an insulating, synthetic 9 material. For many years, damages -to such a type of cable have been observed which can be traced to the ingress 11 and accumulation of water. The water causes formation of 12 so-called water trees in -the insulation. Recently, great 13 effort has been devoted to discover details about these 14 water trees and to provide Eor adequate remedies. Many publications exist describing the growth of these water trees, 16 and many suggestions have been made concerning their avoidance 17 to, thereby, increase the life of such type of cable.
~8 19 All approaches to solving the problem begin with the point that the mois-ture, to do any damage, must first 21 enter into and penetrate -the insulation. Emphasis here is 22 placed on the point of preventing moisture penetration after 23 the cable has been installed, e.g., in wet soil, or the like.
24 It has -to be observed, however, -that moisture may diffuse alreaa into the insulation during cable manufacture. For example, 26 if the insulation is cured (cross-linking, vulcanization) in ~8 -2-,.
~' .
~ ~58327 I D- 6939(Kab) 1 ~ steam, water is indeed directly applied. Some water rnay readily 2 I be trapped, particularly if subsequen-tly a me-tal jacke-t is 3 I formed around the insulation. Moreover, such a jac]~et may a I be damaged and water or water vapor may pene-trate direc-tly
6 Cables of the type to which the invention pertains 7 include plural conductors, preferably in a stranded configu-8 ration and being enveloped by and in an insulating, synthetic 9 material. For many years, damages -to such a type of cable have been observed which can be traced to the ingress 11 and accumulation of water. The water causes formation of 12 so-called water trees in -the insulation. Recently, great 13 effort has been devoted to discover details about these 14 water trees and to provide Eor adequate remedies. Many publications exist describing the growth of these water trees, 16 and many suggestions have been made concerning their avoidance 17 to, thereby, increase the life of such type of cable.
~8 19 All approaches to solving the problem begin with the point that the mois-ture, to do any damage, must first 21 enter into and penetrate -the insulation. Emphasis here is 22 placed on the point of preventing moisture penetration after 23 the cable has been installed, e.g., in wet soil, or the like.
24 It has -to be observed, however, -that moisture may diffuse alreaa into the insulation during cable manufacture. For example, 26 if the insulation is cured (cross-linking, vulcanization) in ~8 -2-,.
~' .
~ ~58327 I D- 6939(Kab) 1 ~ steam, water is indeed directly applied. Some water rnay readily 2 I be trapped, particularly if subsequen-tly a me-tal jacke-t is 3 I formed around the insulation. Moreover, such a jac]~et may a I be damaged and water or water vapor may pene-trate direc-tly
5 I the otherwise undamaged insulation.
7 The water trees themselves are believed to be formed 8 I when the insulation is subjected to an electric field sur-I rounding the conductor. The water trees grow until they cause an electric breakthrough, which, in turn, destroys the cable 11 locally. The cable des-truction can be fur-thered by water 12 in the conductor core which corrodes. A]so, water in the 13 ~ interface between the conduc-tors proper and a smoo-thing la~er 14 I surrounding the conductor bundle may tend -to form an electro-voltaic cell resulting in electrocorrosion. Particularly 16 I prone to this kind of damage are aluminum conductors sur-17 rounded by a carbon-black-containing layer.
19 Numerous attempts have been made to avoid water damages 20 ¦ as described. These attempts follow a common approach; the 21 ingress of water is to be stopped. For example, United States 22 Patent 4,145,567 suggests winding a metal ribbon around the 23 insulation; German Printed Patent Applica-tion 27 54 336 pro-2~ poses the generation of a diffusion gradient, directed in radial outward direction; Germany Printed Paten-t Applica-26 tion 27 37 108 proposes the use of a water-absorbing, outer D-6939~Kab~ , ' ~
1 i coating. All of these approaches may have merit and impede, 2 I or even prevent, the diffusion of water into the insulation 3 ¦ from the outside of the cable. They do not, however, prevent 4 I the migration of water inside the conductor bundle.
7 The water trees themselves are believed to be formed 8 I when the insulation is subjected to an electric field sur-I rounding the conductor. The water trees grow until they cause an electric breakthrough, which, in turn, destroys the cable 11 locally. The cable des-truction can be fur-thered by water 12 in the conductor core which corrodes. A]so, water in the 13 ~ interface between the conduc-tors proper and a smoo-thing la~er 14 I surrounding the conductor bundle may tend -to form an electro-voltaic cell resulting in electrocorrosion. Particularly 16 I prone to this kind of damage are aluminum conductors sur-17 rounded by a carbon-black-containing layer.
19 Numerous attempts have been made to avoid water damages 20 ¦ as described. These attempts follow a common approach; the 21 ingress of water is to be stopped. For example, United States 22 Patent 4,145,567 suggests winding a metal ribbon around the 23 insulation; German Printed Patent Applica-tion 27 54 336 pro-2~ poses the generation of a diffusion gradient, directed in radial outward direction; Germany Printed Paten-t Applica-26 tion 27 37 108 proposes the use of a water-absorbing, outer D-6939~Kab~ , ' ~
1 i coating. All of these approaches may have merit and impede, 2 I or even prevent, the diffusion of water into the insulation 3 ¦ from the outside of the cable. They do not, however, prevent 4 I the migration of water inside the conductor bundle.
6 The migration of water in the conductor bundle is actually a kind of conduction of water through the voids and 8 gaps between and alongside the conductors of the bundle. One 9 has stopped this conduction by applying a technique which resembles bùlkheads. This approach has been used in particular 11 I for communication cables, but has also been applied to power 12 ¦ cables. German Printed Patent Application 21 54 749 discloses 13 I metallic, transverse walls, placed at regular intervals in 14 the cable core. German Printed Patent Application 28 08 438 discloses such "bulkheads" consisting of cured rubber-elastic 16 material. These plug-like elements are r axially, short~as 17 compared with the distance from bulkhead to bulkhead. Indeed, 18 these bulkhead-like plugs prevent axial migration of moisture 19 through the conductor bundle or core.
2~
21 However, we have discovered that water, which has 22 remained in the'cable since its production, such as conden- ¦
sated water, will remain, e.g., inbetween two plugs. ~his 24 water can penetrate the synthetic, semiconductlve smoothing layer and will reach the insulation. After a high voltage 26 has been applied and is being applied to the cable, water trees , ' ~ ~58327 will grow, quite rapidly so in the immediate vicinity of the conductors because the electric field streng~h is quite high.
According to the present invention there is provided a moisture-proof, electrical cable, comprising a core composed of a plurality of stranded-together wires or conductors, there being inherently voids between the conductors or wires, and a metal tube made of a longitudinally folded and welded strip, made of the same material as the wires or conductors and being waterproof and directly disposed around the wires or conductors in metal-to-metal contact with outer ones of the wires or conductors so as to serve additionally as an outermost conduct-ive layer; and an insulation of synthetic material, being prone to exhibit watertreeing and being disposed around the metal tube of the core, the metal tube sealing the insulation from the interior of the core containing the stranded-together wires or conductors.
~ :L5~3~"t Application of the invention in this instance is of particular significance ~ecause such a smoothing layer is usually made of an e~truded, electrically conductive synthetic (polymer with carbon black as an additive~. These types of layers are particularly sensitive to moisture and have to be most prominently protected to ensure trouble-free cable use.
Aside from waterproofing the insulation, this tube has the added advantage of preventing the stranded conductors or wires from untwisting during production. The insulation can be protected against ingress of water from the outside in any conventional manner; but see also Canadian Application Serial No, 359,36~ filed August 31, 1980 of common assignee.
However, internal, bulkhead like protection may not be needed.
The primary function of the tube as formed about the conductor or wlre bundle is to prevent moisture which is lodged or flows through the voids between the conductors from penetrating the insulation to, thereby, avoid the formation of water trees. In order to avoid the formation of electrovoltaic cells as between wires and tubes, they should be made of electrochemically similar material; i.e., they should have a substantially similar position in the electrovoltaic series. For practical reasons, the same kind of metal should be used; a copper tube for copper wires, and an aluminum tube for aluminum wires (or aluminum alloy), these being the most ~ ~83~7 I ~-6939(Kab) .
1 , commonly used metals. In the case of copper-plated aluminum 2 I wires (low weight), the tube should also be made of copper.
3 I The tightly fitting and drawn tube has also a mechanically 4 ~ stabilizing effect on -the cable, while kinking of the tube is prevented due to its tight fit on the conductor bundle 6 serving physically as internal tube support. The -tube,
2~
21 However, we have discovered that water, which has 22 remained in the'cable since its production, such as conden- ¦
sated water, will remain, e.g., inbetween two plugs. ~his 24 water can penetrate the synthetic, semiconductlve smoothing layer and will reach the insulation. After a high voltage 26 has been applied and is being applied to the cable, water trees , ' ~ ~58327 will grow, quite rapidly so in the immediate vicinity of the conductors because the electric field streng~h is quite high.
According to the present invention there is provided a moisture-proof, electrical cable, comprising a core composed of a plurality of stranded-together wires or conductors, there being inherently voids between the conductors or wires, and a metal tube made of a longitudinally folded and welded strip, made of the same material as the wires or conductors and being waterproof and directly disposed around the wires or conductors in metal-to-metal contact with outer ones of the wires or conductors so as to serve additionally as an outermost conduct-ive layer; and an insulation of synthetic material, being prone to exhibit watertreeing and being disposed around the metal tube of the core, the metal tube sealing the insulation from the interior of the core containing the stranded-together wires or conductors.
~ :L5~3~"t Application of the invention in this instance is of particular significance ~ecause such a smoothing layer is usually made of an e~truded, electrically conductive synthetic (polymer with carbon black as an additive~. These types of layers are particularly sensitive to moisture and have to be most prominently protected to ensure trouble-free cable use.
Aside from waterproofing the insulation, this tube has the added advantage of preventing the stranded conductors or wires from untwisting during production. The insulation can be protected against ingress of water from the outside in any conventional manner; but see also Canadian Application Serial No, 359,36~ filed August 31, 1980 of common assignee.
However, internal, bulkhead like protection may not be needed.
The primary function of the tube as formed about the conductor or wlre bundle is to prevent moisture which is lodged or flows through the voids between the conductors from penetrating the insulation to, thereby, avoid the formation of water trees. In order to avoid the formation of electrovoltaic cells as between wires and tubes, they should be made of electrochemically similar material; i.e., they should have a substantially similar position in the electrovoltaic series. For practical reasons, the same kind of metal should be used; a copper tube for copper wires, and an aluminum tube for aluminum wires (or aluminum alloy), these being the most ~ ~83~7 I ~-6939(Kab) .
1 , commonly used metals. In the case of copper-plated aluminum 2 I wires (low weight), the tube should also be made of copper.
3 I The tightly fitting and drawn tube has also a mechanically 4 ~ stabilizing effect on -the cable, while kinking of the tube is prevented due to its tight fit on the conductor bundle 6 serving physically as internal tube support. The -tube,
7 particularly when made of the same metal as the conductor,
8 becomes an integral part of the conducting assembly. This, g in turn, leads to an overall reduction in cross section and diameter of the cable which, in turn, enhances its flexibility. ¦
11 ¦ The overall layer configuration conduc-tor-insulation-shield-12 jacket remains the same. The tube, moreover, functions already 13 to some extent as a smoothing layer, and the electric field 14 of the conductor assembly becomes more uniform as compared to just a wire bundle. In some cases, an additional conduc-tive 1~ smoothing layer may not be needed. The invention can be 17 applied to all those cables in which the cable core is com-1~ posed of a multitude of wires, filaments, and conductors, 19 even those with special profiles (circle segments), in which 2Cl moisture can propagate lengthwise.
22 It should be mentioned that encasing of wire bundles of 23 uninsulated cables is known per se (British Patent 757,745), 2~ but that aspect has no bearing upon the problem of water -trees.
5~33~7 ; D-6939(Kab) l DESCRIPTION OF 'I'l~E DRAW_NGS
2 ~
3 I While the specification concludes with claims, parti-4 ¦ cularly pointing out and distinctly claiming the subject 5 ¦ matter which is regarded as the invention, it is believed 6 ~ that the invention, the objects and features of the inven-tion, and fur-ther objects, features and advantages thereof, 8 will be bet-ter understood from the following descri.pt.ion taken in connection with the accompanying drawings, in which:
11 ~ Figure 1 is a cross section through a cable improved 12 in accordance with the preEerred errlbodiment of t:he inven-tion;
13 and 1~
Figures 2 and 3 are respectively cross sections through 16 differentt types of cable, also i.mproved in accordance with 1~ ¦ the preferred embodiment.
19 Proceeding now to the detailed description of the drawings, the conductor core 1 in Figure 1 is comprised of a bundle 21 of stranded wires 2, e.g~, copper wires. This bundle of 22 conduc-tors 2 is jacketed in a copper -tube or sleeve 3. This 23 sleeve or tube has been made :Erom a copper strip which is 2~ folded longitudinally around the s-tranded bundle of wires or conductors. Next, the edges of the strip have been seam-26 welded to form a water--tight, well-sealed enclosure around 3 ~ 7 D-6939(Kab) 1 the wires. Thereafter, the tube is drawn onto the wires 2 11 or conductors, into intimate metal-to~metal con-tact with 3 I the outer layer of conductors or wires of the stranded bundle.
The tube may also be sized to have a circular outer periphery and contour so tha-t the effective outer contour of the con-6 ductor assembly 2, 3 is already quite smooth, and the elec-7 ` tric field developed by this assembly is quite uniform.
11 ¦ The overall layer configuration conduc-tor-insulation-shield-12 jacket remains the same. The tube, moreover, functions already 13 to some extent as a smoothing layer, and the electric field 14 of the conductor assembly becomes more uniform as compared to just a wire bundle. In some cases, an additional conduc-tive 1~ smoothing layer may not be needed. The invention can be 17 applied to all those cables in which the cable core is com-1~ posed of a multitude of wires, filaments, and conductors, 19 even those with special profiles (circle segments), in which 2Cl moisture can propagate lengthwise.
22 It should be mentioned that encasing of wire bundles of 23 uninsulated cables is known per se (British Patent 757,745), 2~ but that aspect has no bearing upon the problem of water -trees.
5~33~7 ; D-6939(Kab) l DESCRIPTION OF 'I'l~E DRAW_NGS
2 ~
3 I While the specification concludes with claims, parti-4 ¦ cularly pointing out and distinctly claiming the subject 5 ¦ matter which is regarded as the invention, it is believed 6 ~ that the invention, the objects and features of the inven-tion, and fur-ther objects, features and advantages thereof, 8 will be bet-ter understood from the following descri.pt.ion taken in connection with the accompanying drawings, in which:
11 ~ Figure 1 is a cross section through a cable improved 12 in accordance with the preEerred errlbodiment of t:he inven-tion;
13 and 1~
Figures 2 and 3 are respectively cross sections through 16 differentt types of cable, also i.mproved in accordance with 1~ ¦ the preferred embodiment.
19 Proceeding now to the detailed description of the drawings, the conductor core 1 in Figure 1 is comprised of a bundle 21 of stranded wires 2, e.g~, copper wires. This bundle of 22 conduc-tors 2 is jacketed in a copper -tube or sleeve 3. This 23 sleeve or tube has been made :Erom a copper strip which is 2~ folded longitudinally around the s-tranded bundle of wires or conductors. Next, the edges of the strip have been seam-26 welded to form a water--tight, well-sealed enclosure around 3 ~ 7 D-6939(Kab) 1 the wires. Thereafter, the tube is drawn onto the wires 2 11 or conductors, into intimate metal-to~metal con-tact with 3 I the outer layer of conductors or wires of the stranded bundle.
The tube may also be sized to have a circular outer periphery and contour so tha-t the effective outer contour of the con-6 ductor assembly 2, 3 is already quite smooth, and the elec-7 ` tric field developed by this assembly is quite uniform.
9 The tube or sleeve 3 is, thus, actually made part of
10 I the conductoI core. The strip of which the sleeve is made
11 should, for this reason, be of the same kind of metal as the
12 conductor so that, upon sitting tightly on the bundle, a
13 uniformly conductive assembly is established therewith~
14 Sleeve or tube 3 is covered by a conductive layer 4 which serves as a supplemental smoothing layer. This is particularly 16 needed i~ the tube, as drawn, tends to match to some extent 17 the uneven outer contour of the wire bundle underneath.
18 Moreover, the layer (any layer) extruded onto tube 3 will 19 adhere better when the surface of tube ~ is not quite even.
Indents or bosses may even intentionally be provided in order 21 to enhance adhesion of any layer that is extruded thereon;
22 for this reason, a first layer should be a conductive layer 23 (e.g., layer ~) being extruded onto the tube. The water-proof 2~ and water-proofing tube 3 serves already as a protection against ingress of water from the interior of the bundle 26 into the sensitive layer 4.
I 1~5~327 I D-6939(Kab) 11 ~
1 I The conductor assembly is insulated by a suitable 2 ¦ layer 5, e.g., of polyethylene or the like. The tube 3 3 serves as a moisture barrier to preven-t any water that may 4 reside in the voids between the condllctors 2 of the b~lndle from penetrating the insulation from the inside.
7 Insulation 5 is conventionally covered by an outer, con-ductive layer 6 which, in turn, carries a shield 7 (e.g., 9 plural wires, and so forth). The cable is protected by an outer jac~et 8, such as a polyvinylchloride or rubber jacket, 11 possibly including flame-retarding additives.
13 The conductors and tubes do no-t have to be made of 1~ copper; one may use copper-plated aluminum wires wi-th a copper -tube for reasons of weight, or one may use an all~
16 aluminum assembly. For reasons of uniform conduction 17 the metals should be the same; at least to the extent that 18 they contact each other. As far as the specific purpose 19 of the invention is concerned, the metals should be at least electrochemically similar so that they will not undergo 21 electro--corrosion if moisture migrates through the interior 22 of the core.
2~ As far as the conduc-tor assembly is concerned, the ratio of diameter d of the s-trandecl core or wire bundle 26 to -thic~ness s of tube 3 is rather cri-tical.
. I
~ 15~27 ¦ D-6939(Kab) l I ear1ier, the conductive tube 3 becomes a part of -the con-2 I ductive core proper, particularly so when made of -the same 3 I material as the stranded wires 2. From tha-t point of view, I
it appears -to make li.ttle difEerence how many wires may actually be replaced by the tube for a given total of solid 6 ¦ material and conductive cross section and cross sectional 7 ¦ area F. However, there are other points to be considered.
8 ¦ The larger the ratio d/s, the more likely it becomes that tube 3 will kink when the cable is bent during conventional installation. On the other hand, when the tube's wall is too 11 -thick, the cab].e will loose its flexibility and become quite 12 stiff.
1~ The total effec~ive cross section for this assembly is the sum of the cross section of all conductors in the bundle 16 to which the cross section of tube 3 is added. Thus, one 17 does not diminish the conductive performance of the cable 18 by choosing the thickness s of tube 3 sufficiently thick 19 and by choosing a smaller bundle. In the case of copper, it was found that d/s = 25, which is an optimized or nearly 21 optimized ratio. It was found, moreover, that for this relation, 22 -the tube's thickness s equals one-twentieth of the square root 23 of the total desired solid material (metal) cross sectional 24 area F available for conduction. In the case of aluminum, the ratio should be d/s = 18, and the wall's thickness s 26 can be calculated to be equal to 17 ~F.
28 -11- ~
29 .
,3L1~3~7 I D-6939(Kab) Followillg these rules will resul-t in a -tube that is, 2 11 even after being drawn onto -the conductor bundle, quite 3l~ smooth,obviating thereby the need for a smoothing layer.
~¦l If, however, the insulation would not adequately adhere to 5 ¦ such a metal tube, intentional unevennesses should be provided 6 ¦ on tube 3; and that, in turn, renders advisable -the use of 7 ¦ a smoothing layer of conductive synthetics. The insula-81~ tion (5) will adhere better to such a layer, even when 9 1! having a smoo-th surface. The larger the ratio d/s, -the more likely it becomes that tube 3 will kink when the cable is 11 bent during conven-tional installation. On the other hand, 12 when the tube's wall is too thick, the cable will loose its 13 flexibility and become quite stiffo 1~
Figure 2 i]lustrates a modified conductor core. The 16 core is comprised here of a plurality of (four) sections or 17 segmented conductors 9 which are stranded together. Other 18 numbers, such as three or six, could be used. Each conduc- ¦
19 tox 9 may be solid or consist by itself of stranded wires.
~f the conductors 9 are made of aluminum, an aluminum tube 10 21 has been formed about the conductors, in the manner described 22 above (longitudinally folded, welded strip). This -tube 10 23 is also watertight and avoids migra-tion of water from the 24 voids between the conduc-tors 9 into an insulation layer on 26 -the outside.
1,' D-693g(Kab~
Il I
1 ll Fiyure 3 illustrates an example in which the conduc-2 j tor core includes wires 11 stranded onto and around a support 3 I tube 12 whose in-terior is hollow. Tube 13 is provided as a moisture barrier and wires 11 as well as -tube 13 are made of the same material, e.g., aluminurn or copper. This 6 type of an assembly will be chosen if the skin effect causes 7 the interior of a conductor to not contribute -to -the con- ¦
8 duction. I
g 10 I It should be mentioned that the invention may actually 1 render -the plugs, alluded to earlier, unnecessary, which 12 would facilitate installa-tion.
14 The inven-tion is no-t limited -to the embodiments described above; but all changes and modifications thereof, 16 not constituting departures from the spirit and scope of 17 the invention, are intended to be included.
1~ ll 2g
18 Moreover, the layer (any layer) extruded onto tube 3 will 19 adhere better when the surface of tube ~ is not quite even.
Indents or bosses may even intentionally be provided in order 21 to enhance adhesion of any layer that is extruded thereon;
22 for this reason, a first layer should be a conductive layer 23 (e.g., layer ~) being extruded onto the tube. The water-proof 2~ and water-proofing tube 3 serves already as a protection against ingress of water from the interior of the bundle 26 into the sensitive layer 4.
I 1~5~327 I D-6939(Kab) 11 ~
1 I The conductor assembly is insulated by a suitable 2 ¦ layer 5, e.g., of polyethylene or the like. The tube 3 3 serves as a moisture barrier to preven-t any water that may 4 reside in the voids between the condllctors 2 of the b~lndle from penetrating the insulation from the inside.
7 Insulation 5 is conventionally covered by an outer, con-ductive layer 6 which, in turn, carries a shield 7 (e.g., 9 plural wires, and so forth). The cable is protected by an outer jac~et 8, such as a polyvinylchloride or rubber jacket, 11 possibly including flame-retarding additives.
13 The conductors and tubes do no-t have to be made of 1~ copper; one may use copper-plated aluminum wires wi-th a copper -tube for reasons of weight, or one may use an all~
16 aluminum assembly. For reasons of uniform conduction 17 the metals should be the same; at least to the extent that 18 they contact each other. As far as the specific purpose 19 of the invention is concerned, the metals should be at least electrochemically similar so that they will not undergo 21 electro--corrosion if moisture migrates through the interior 22 of the core.
2~ As far as the conduc-tor assembly is concerned, the ratio of diameter d of the s-trandecl core or wire bundle 26 to -thic~ness s of tube 3 is rather cri-tical.
. I
~ 15~27 ¦ D-6939(Kab) l I ear1ier, the conductive tube 3 becomes a part of -the con-2 I ductive core proper, particularly so when made of -the same 3 I material as the stranded wires 2. From tha-t point of view, I
it appears -to make li.ttle difEerence how many wires may actually be replaced by the tube for a given total of solid 6 ¦ material and conductive cross section and cross sectional 7 ¦ area F. However, there are other points to be considered.
8 ¦ The larger the ratio d/s, the more likely it becomes that tube 3 will kink when the cable is bent during conventional installation. On the other hand, when the tube's wall is too 11 -thick, the cab].e will loose its flexibility and become quite 12 stiff.
1~ The total effec~ive cross section for this assembly is the sum of the cross section of all conductors in the bundle 16 to which the cross section of tube 3 is added. Thus, one 17 does not diminish the conductive performance of the cable 18 by choosing the thickness s of tube 3 sufficiently thick 19 and by choosing a smaller bundle. In the case of copper, it was found that d/s = 25, which is an optimized or nearly 21 optimized ratio. It was found, moreover, that for this relation, 22 -the tube's thickness s equals one-twentieth of the square root 23 of the total desired solid material (metal) cross sectional 24 area F available for conduction. In the case of aluminum, the ratio should be d/s = 18, and the wall's thickness s 26 can be calculated to be equal to 17 ~F.
28 -11- ~
29 .
,3L1~3~7 I D-6939(Kab) Followillg these rules will resul-t in a -tube that is, 2 11 even after being drawn onto -the conductor bundle, quite 3l~ smooth,obviating thereby the need for a smoothing layer.
~¦l If, however, the insulation would not adequately adhere to 5 ¦ such a metal tube, intentional unevennesses should be provided 6 ¦ on tube 3; and that, in turn, renders advisable -the use of 7 ¦ a smoothing layer of conductive synthetics. The insula-81~ tion (5) will adhere better to such a layer, even when 9 1! having a smoo-th surface. The larger the ratio d/s, -the more likely it becomes that tube 3 will kink when the cable is 11 bent during conven-tional installation. On the other hand, 12 when the tube's wall is too thick, the cable will loose its 13 flexibility and become quite stiffo 1~
Figure 2 i]lustrates a modified conductor core. The 16 core is comprised here of a plurality of (four) sections or 17 segmented conductors 9 which are stranded together. Other 18 numbers, such as three or six, could be used. Each conduc- ¦
19 tox 9 may be solid or consist by itself of stranded wires.
~f the conductors 9 are made of aluminum, an aluminum tube 10 21 has been formed about the conductors, in the manner described 22 above (longitudinally folded, welded strip). This -tube 10 23 is also watertight and avoids migra-tion of water from the 24 voids between the conduc-tors 9 into an insulation layer on 26 -the outside.
1,' D-693g(Kab~
Il I
1 ll Fiyure 3 illustrates an example in which the conduc-2 j tor core includes wires 11 stranded onto and around a support 3 I tube 12 whose in-terior is hollow. Tube 13 is provided as a moisture barrier and wires 11 as well as -tube 13 are made of the same material, e.g., aluminurn or copper. This 6 type of an assembly will be chosen if the skin effect causes 7 the interior of a conductor to not contribute -to -the con- ¦
8 duction. I
g 10 I It should be mentioned that the invention may actually 1 render -the plugs, alluded to earlier, unnecessary, which 12 would facilitate installa-tion.
14 The inven-tion is no-t limited -to the embodiments described above; but all changes and modifications thereof, 16 not constituting departures from the spirit and scope of 17 the invention, are intended to be included.
1~ ll 2g
Claims (6)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A moisture-proof, electrical cable, comprising a core composed of (i) a plurality of stranded-together wires or conductors, there being inherently voids between the conductors or wires, and (ii) a metal tube made of a longitudinally folded and welded strip, made of the same material as the wires or conductors and being waterproof and directly disposed around the wires or conductors in metal-to-metal contact with outer ones of the wires or conductors so as to serve additionally as an outermost conductive layer; and an insulation of synthetic material, being prone to exhibit watertreeing and being disposed around the metal tube of the core, the metal tube sealing the insulation from the interior of the core containing said stranded-together wires or conductors.
2. A moisture-proof, electrical cable, comprising a core compound of (i) a plurality of stranded-together wires or conductors, there being inherently voids between the conductors or wires, and (ii) a metal tube made of a longitudinally folded and welded strip, being waterproof and directly disposed around the wires and conductors in metal-to-metal contact so as to serve additionally as an outermost conductive layer, the wires or conductors being made of metal similar to the metal of which the tube is made in the sense of a close position in the electrovoltaic series; and an insulation of synthetic material being prone to exhibit watertreeing and being disposed around the metal tube of the core, the metal tube sealing the insulation from the interior of the core.
3. A cable as in Claim 1 or Claim 2, the metal being of copper, the tube having a wall thickness which is approximately 1/20 ? F, wherein F is the total effective cross section of the conductors or wires and of the tube.
4. A cable as in Claim 1 or Claim 2, the metal being of aluminum, the tube having a wall thickness which is approximately 1/17/ ? F, wherein F is the total effective cross section of the conductors or wires and of the tube.
A cable core as in Claim 1 or 2, said metal tube having a surface roughness to enhance adhesion to the insulation.
6. A cable as in Claim 1 or 2, said insulation being polyethylene.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DEP2942925.2 | 1979-10-24 | ||
| DE19792942925 DE2942925A1 (en) | 1979-10-24 | 1979-10-24 | HUMIDITY PROTECTED ELECTRIC CABLE |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1158327A true CA1158327A (en) | 1983-12-06 |
Family
ID=6084242
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000363058A Expired CA1158327A (en) | 1979-10-24 | 1980-10-23 | Moisture-proofing of electrical cable with an outer layer electrochemically similar to the core |
Country Status (16)
| Country | Link |
|---|---|
| JP (1) | JPS5682508A (en) |
| AU (1) | AU6346780A (en) |
| BE (1) | BE885846A (en) |
| CA (1) | CA1158327A (en) |
| CH (1) | CH652524A5 (en) |
| DE (1) | DE2942925A1 (en) |
| DK (1) | DK446380A (en) |
| FI (1) | FI72618C (en) |
| FR (1) | FR2468189A1 (en) |
| GB (1) | GB2061597B (en) |
| IN (1) | IN151783B (en) |
| IT (1) | IT1146140B (en) |
| NL (1) | NL181466C (en) |
| NO (1) | NO156468C (en) |
| SE (1) | SE8007430L (en) |
| SG (1) | SG59483G (en) |
Families Citing this family (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5043538A (en) * | 1989-07-03 | 1991-08-27 | Southwire Company | Water resistant cable construction |
| US5408279A (en) * | 1993-10-27 | 1995-04-18 | Chiou; Ching-Hae | Eye glasses designed to facilitate carrying |
| DE19522628C2 (en) * | 1995-06-22 | 1997-12-18 | Alcatel Kabel Ag | Process for manufacturing a sector conductor for electrical power cables |
| DE19549406C2 (en) * | 1995-06-22 | 1997-12-11 | Alcatel Kabel Ag | Process for manufacturing a sector conductor for electrical power cables |
| EP3036747B1 (en) * | 2014-11-07 | 2019-06-19 | NKT Cables Group A/S | Grounding conductor, electrical power system and use of grounding conductor |
| CN105529073A (en) * | 2016-01-22 | 2016-04-27 | 安徽慧艺线缆集团有限公司 | Anti-interference and anti-stretching cable for mobile communication |
| CN105551626A (en) * | 2016-01-27 | 2016-05-04 | 安徽猎塔电缆集团有限公司 | Industrial stretch-proof shield cable |
Family Cites Families (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB757745A (en) * | 1954-02-23 | 1956-09-26 | Pirelli General Cable Works | Improvements in or relating to overhead line conductors and methods of manufacturing such conductors |
| JPS527640Y2 (en) * | 1971-05-29 | 1977-02-17 | ||
| DE2508928A1 (en) * | 1975-03-01 | 1976-09-09 | Felten & Guilleaume Carlswerk | Water-resistant high voltage cable - having conductor enclosed within electrically-conducting sheath between conductor plastic cable insulation |
| GB1569454A (en) * | 1976-08-18 | 1980-06-18 | Electric Power Res Inst | Electric cables |
-
1979
- 1979-10-24 DE DE19792942925 patent/DE2942925A1/en not_active Ceased
-
1980
- 1980-09-24 FR FR8020522A patent/FR2468189A1/en active Granted
- 1980-10-07 CH CH7472/80A patent/CH652524A5/en not_active IP Right Cessation
- 1980-10-07 GB GB8032240A patent/GB2061597B/en not_active Expired
- 1980-10-09 IN IN1146/CAL/80A patent/IN151783B/en unknown
- 1980-10-14 NL NLAANVRAGE8005670,A patent/NL181466C/en not_active IP Right Cessation
- 1980-10-16 JP JP14377580A patent/JPS5682508A/en active Pending
- 1980-10-17 AU AU63467/80A patent/AU6346780A/en not_active Abandoned
- 1980-10-21 FI FI803307A patent/FI72618C/en not_active IP Right Cessation
- 1980-10-21 IT IT49960/80A patent/IT1146140B/en active
- 1980-10-22 DK DK446380A patent/DK446380A/en not_active Application Discontinuation
- 1980-10-23 NO NO803156A patent/NO156468C/en unknown
- 1980-10-23 CA CA000363058A patent/CA1158327A/en not_active Expired
- 1980-10-23 SE SE8007430A patent/SE8007430L/en not_active Application Discontinuation
- 1980-10-23 BE BE0/202572A patent/BE885846A/en not_active IP Right Cessation
-
1983
- 1983-09-29 SG SG594/83A patent/SG59483G/en unknown
Also Published As
| Publication number | Publication date |
|---|---|
| DE2942925A1 (en) | 1981-05-07 |
| IT1146140B (en) | 1986-11-12 |
| SE8007430L (en) | 1981-04-25 |
| FI72618B (en) | 1987-02-27 |
| SG59483G (en) | 1984-07-27 |
| NL181466C (en) | 1987-08-17 |
| JPS5682508A (en) | 1981-07-06 |
| GB2061597B (en) | 1983-07-13 |
| NO156468C (en) | 1987-09-23 |
| NO156468B (en) | 1987-06-15 |
| IN151783B (en) | 1983-07-30 |
| FR2468189B1 (en) | 1984-01-20 |
| FI803307L (en) | 1981-04-25 |
| IT8049960A0 (en) | 1980-10-21 |
| GB2061597A (en) | 1981-05-13 |
| DK446380A (en) | 1981-04-25 |
| NO803156L (en) | 1981-04-27 |
| AU6346780A (en) | 1981-04-30 |
| BE885846A (en) | 1981-04-23 |
| CH652524A5 (en) | 1985-11-15 |
| FR2468189A1 (en) | 1981-04-30 |
| NL8005670A (en) | 1981-04-28 |
| FI72618C (en) | 1987-06-08 |
| NL181466B (en) | 1987-03-16 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |