CA1048616A - Electric cable with non-metallic means for relieving the tensile load - Google Patents
Electric cable with non-metallic means for relieving the tensile loadInfo
- Publication number
- CA1048616A CA1048616A CA75241125A CA241125A CA1048616A CA 1048616 A CA1048616 A CA 1048616A CA 75241125 A CA75241125 A CA 75241125A CA 241125 A CA241125 A CA 241125A CA 1048616 A CA1048616 A CA 1048616A
- Authority
- CA
- Canada
- Prior art keywords
- sheath
- plastic
- electrical cable
- cable according
- electrostatic screen
- 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
Links
Landscapes
- Insulated Conductors (AREA)
Abstract
Abstract of the Disclosure Disclosed is a screened electric cable resistant to tension and having a non-metallic load-relieving means made of glass fibres in which the satisfactory mechanical and electrical properties associated with unscreened designs are retained. The cable comprises one or more insulated conductors as the cable core and insulating foil wound thereover. A plastic internal sheath is extruded around the cable core and covered with an electrostatic shield of metal foil which, in turn, is surrounded by a plastic external sheath in which are embedded bundles of glass fibres arranged concentrically with the cable core, running parallel therewith, and spaced apart from each other. A ratio of about 1:3:1 is provided between the wall thickness of the insulating sheath of the conductors, the wall thickness of the internal sheath, and the distance between the screen and the glass fibre bundles.
Description
~8~16 . ' .
This invention relates to electric cables with non-metallic means for relieving the tensile load, especially for power or telecommunication, for example self-supporting aerial cables for overhead transmission lines.
The cables may be composed of at least one insulated conductor and a synthetic plastic sheath containing substantially continuous longitudinal elements for taking up the tensile load in the cable, for example when the latter is sus-pended between the poles or pylons of the overhead system, thereby relieving the conductor of the load. Such self-supporting aerial cables are used to carry power or are used for telecommunication purposes, and they may serve 10 for connecting remote users of telecommunication equipment.
Electric cables with non-metallic load-relieving means are already B knownJ ~ the said cables consisting of one or more insulated conductors wrapped with a protective layer of non- ~ -hygroscopic material, provided (covered) with an internal sheath of plastic material by extrusion, followed by an overlying external sheath of the same material in which are embedded "bundles" of glass fibres running in spaced î relationship with each other, concentric with the cable core and parallel therewith. The said bundles of glass fibres are preferably bundles of, for example, seven glass fibre yarns, each glass fibre yarn consisting, for in-20 stance, of 1850 glass fibres arranged parallel with each other.
As compared with cables having load-relieving means made of metal-lic materials, for example, steel-wire-netting, cables having load-relieving means made of glass fibre yarns have considerably better transmission proper-ties when used in the telecommunications field. They are satisfactorily flexible, have small outside diameters, and are noted for their favourable sagging properties when suspended between poles or pylons. Furthermore, the load-relieving means is not susceptible to corrosion. If, however, a cable of this kind has to be provided with a screen, in the form of metallic tape3 for example, this again has a detrimental effect upon the transmission properties.
3Q It îs the ~urpose of the present invention to provide a screened A
. . .
- . . . . . . ..
.-. . ~ - . . - ~ .
.- . .... . . . . . . ... .
1~)'}8~16 electric cable resistant to tension and having a non-metallic load-relieving means made of glass fibres, in which the satisfactory mechanical and electri-cal properties associated with unscreened designs are retained in full, and in which, above all, the characteristic value of the transmission properties, namely the mutual capacitance, does not exceed the limit of 42 nF/km generally specified for telecommunications cables for this fieid of application.
One way of achieving low mutual capacitance values in telecommuni-cations cables is to increase the wall thickness of the conductor insulation.
It has been found, however, that this fails to produce the desired effect if the screening tape is applied directly over the wrapped covering tape of the cable core.
Another known way of exerting a favourable effect upon mutual capacitance is to increase the distance between the screen and the cable core.
The invention applies this principle, to which end it takes advantage of the presence of an internal and an external sheath like those used in electrical cables of the same type. In this case the screen may be fitted between the said internal and external sheaths.
Since the wall thickness of the internal sheath has a considerable effect upon the flexibility of the cable, there is a danger that this increase in the wall thickness may so stiffen the cable as to make it completely un-suitable for practical application, and may also produce a detrimental in-crease in the overall diameter thereof. Moreover, any increase in outside ~ -diameter is in any case undesirable, since it makes it impossible to use the straining clamps normally used to run unscreened aerial cables between towers.
It must also be remembered that any increase in external dimensions results in a corresponding increase in weight in the event of icing.
One special purpose of the invention, therefore, is to keep the wall thickness of the inner sheath within limits which will ensure a screened cable with optimal transmission properties, satisfactory flexibility, and an outside diameter ~hich does not differ, or at least not appreciably, from that ., - - : : ' .~. , `~
` 1~48616 of an unscreened cable.
In achieving the above-mentioned purpose, the dimensions of the outer sheath must also be taken into consideration, since these cannot be reduced indiscriminately in the endeavour to keep the outside diameter of the ~ cable as small as possible. It is particularly important not to reduce the distance between the screen surrounding the inner sheath and the glass fibre bundles to less than a specific minimum, since otherwise the mechanical ~; interaction between the material of the outer sheath and the load-carrying bundles of glass fibres embedded therein, and which ensure a mechanically intereonneeted unitary struetural system between the bundles and the external sheath, may be greatly disturbed.
Thus, in aecordanee with the present invention, there is provided i an eleetrieal eable having a non-metallie means for relieving the tensile load and eomprising one or more eonduetors as the eable eore, eaeh conductor ' having an insulating sheath, an insulating foil wound thereover, a plastic internal sheath extruded therearound, surrounded by a plastic external sheath in which are embedded bundles of glass fibres arranged coneentrieally with the eable core, running parallel therewith, and spaeed ~part from eaeh other, eharaeterized in that an electrostatie screen made of metal foil is inserted between the internal sheath and the external sheath, and in that a speeifie numerieal ratio, namely about 1:3:1, exists between the wall thiek-ness of the insulating sheath of the eonduetors, the wall thickness of the internal sheath, and the distance between the sereen and the glass fibre bundles.
The objeetives of the invention relating to mutual capaeitanee values, flexibility, and outside diameter may be fully and optimally achieved when the foregoing combination of characteristies is maintained.
Aecording to a further advantageous development of the invention, the electrostatic sereen consists of plastic-laminated aluminum tapes of a ~ _3_ .
1~)4~3616 total thickness of about 40 microns, the metallic side of the said tapes being arranged to face the internal sheath.
Further exemplary embodiments, of the invention are characterized by the alternative use of bare or plastic laminated copper strips and of corrugated or combined metal foils as screens. The metal strips may be laminated on both sides with plastic, e.g. polyethylene on one side and polyterephthalate on the other.
The drawing illustrates an embodiment of the invention in the form of a diagrammatic cross-sectional view of a self-supporting aerial cable with ten conductor pairs.
The structure of the cable is as follows: Round about a central plastic core (heart of the cable) 10 of circular cross section are arranged five spiral quads 11 each consisting of two conductor pairs 12/12, each spiral quad consisting of four individual insulated conductors 12 twisted together to form one unit, with the insulated conductors 12 at the four corners of a square, diametrically opposite insulated conductors 12/12 being used to provide the circuits. The conductors 13 are insulated with polyethylene 14. The central core (heart) 10 and the five spiral quads 11 are in their entirety wrapped with a protective layer 15, for example a helical lapping of one or more plastic tapes. Over this cablc core an extruded internal sheath 16 of polyethylene is arranged.
A screen 17 of plastic laminated aluminum tapes is wound onto internal sheath 16, the said tapes being preferably about 40 microns in thickness.
Arranged over screen 17 is an external sheath 18 also consisting of polyethylene applied by extrusion. Embedded in this external sheath 18 are twenty four bundles 1~ of glass fibre yarn running parallel with the axis of the cable and arranged in a circle surrounding the cable core. Note that the "cable core" is considered to include those elements within sheath ~ ~ 4 - ~
..
: . , ". .
` 104~t~16 ~ 15, i.e. the quads (sub-cables) 11 and, if used, the central core 10. The v~ said bundles take up the tensile forces to which the cable is subjected .. .
when it is used as an aerial cable and also in other cases. A method for embedding bundles 19 in external sheath 18 is described in our United States x Patent 3,879,518 issued April 22, 1975.
,..:
:;:
~, . .
.;~, /
,, :
., ~' .
r. .
.",~ ~' ' .' ' ' :
-4a-- . ,~ .. .
` - -~48616 The ratio between wall thickness "a" of insulation 14 of conduc-tors 13, and wall thickness "b" of internal sheath 16, and distance "c" be-tween screen 17 and glass fibre bundles 19 is as 1:3:1, so that the outside diameter of the cables varies, depending upon the design thereof - the number of conductor pairs. The following table shows this by way of example:
Number of Wall thickness Wall thickness Distance "c" Outside Outside dia-conductor of insulating of internal between screen diameter meter of ~- pairs sheaths sheath and glass- unscreened - fiber bundles design a b ~mm) (mm) (mm) (mm) (mm) . ~ ,
This invention relates to electric cables with non-metallic means for relieving the tensile load, especially for power or telecommunication, for example self-supporting aerial cables for overhead transmission lines.
The cables may be composed of at least one insulated conductor and a synthetic plastic sheath containing substantially continuous longitudinal elements for taking up the tensile load in the cable, for example when the latter is sus-pended between the poles or pylons of the overhead system, thereby relieving the conductor of the load. Such self-supporting aerial cables are used to carry power or are used for telecommunication purposes, and they may serve 10 for connecting remote users of telecommunication equipment.
Electric cables with non-metallic load-relieving means are already B knownJ ~ the said cables consisting of one or more insulated conductors wrapped with a protective layer of non- ~ -hygroscopic material, provided (covered) with an internal sheath of plastic material by extrusion, followed by an overlying external sheath of the same material in which are embedded "bundles" of glass fibres running in spaced î relationship with each other, concentric with the cable core and parallel therewith. The said bundles of glass fibres are preferably bundles of, for example, seven glass fibre yarns, each glass fibre yarn consisting, for in-20 stance, of 1850 glass fibres arranged parallel with each other.
As compared with cables having load-relieving means made of metal-lic materials, for example, steel-wire-netting, cables having load-relieving means made of glass fibre yarns have considerably better transmission proper-ties when used in the telecommunications field. They are satisfactorily flexible, have small outside diameters, and are noted for their favourable sagging properties when suspended between poles or pylons. Furthermore, the load-relieving means is not susceptible to corrosion. If, however, a cable of this kind has to be provided with a screen, in the form of metallic tape3 for example, this again has a detrimental effect upon the transmission properties.
3Q It îs the ~urpose of the present invention to provide a screened A
. . .
- . . . . . . ..
.-. . ~ - . . - ~ .
.- . .... . . . . . . ... .
1~)'}8~16 electric cable resistant to tension and having a non-metallic load-relieving means made of glass fibres, in which the satisfactory mechanical and electri-cal properties associated with unscreened designs are retained in full, and in which, above all, the characteristic value of the transmission properties, namely the mutual capacitance, does not exceed the limit of 42 nF/km generally specified for telecommunications cables for this fieid of application.
One way of achieving low mutual capacitance values in telecommuni-cations cables is to increase the wall thickness of the conductor insulation.
It has been found, however, that this fails to produce the desired effect if the screening tape is applied directly over the wrapped covering tape of the cable core.
Another known way of exerting a favourable effect upon mutual capacitance is to increase the distance between the screen and the cable core.
The invention applies this principle, to which end it takes advantage of the presence of an internal and an external sheath like those used in electrical cables of the same type. In this case the screen may be fitted between the said internal and external sheaths.
Since the wall thickness of the internal sheath has a considerable effect upon the flexibility of the cable, there is a danger that this increase in the wall thickness may so stiffen the cable as to make it completely un-suitable for practical application, and may also produce a detrimental in-crease in the overall diameter thereof. Moreover, any increase in outside ~ -diameter is in any case undesirable, since it makes it impossible to use the straining clamps normally used to run unscreened aerial cables between towers.
It must also be remembered that any increase in external dimensions results in a corresponding increase in weight in the event of icing.
One special purpose of the invention, therefore, is to keep the wall thickness of the inner sheath within limits which will ensure a screened cable with optimal transmission properties, satisfactory flexibility, and an outside diameter ~hich does not differ, or at least not appreciably, from that ., - - : : ' .~. , `~
` 1~48616 of an unscreened cable.
In achieving the above-mentioned purpose, the dimensions of the outer sheath must also be taken into consideration, since these cannot be reduced indiscriminately in the endeavour to keep the outside diameter of the ~ cable as small as possible. It is particularly important not to reduce the distance between the screen surrounding the inner sheath and the glass fibre bundles to less than a specific minimum, since otherwise the mechanical ~; interaction between the material of the outer sheath and the load-carrying bundles of glass fibres embedded therein, and which ensure a mechanically intereonneeted unitary struetural system between the bundles and the external sheath, may be greatly disturbed.
Thus, in aecordanee with the present invention, there is provided i an eleetrieal eable having a non-metallie means for relieving the tensile load and eomprising one or more eonduetors as the eable eore, eaeh conductor ' having an insulating sheath, an insulating foil wound thereover, a plastic internal sheath extruded therearound, surrounded by a plastic external sheath in which are embedded bundles of glass fibres arranged coneentrieally with the eable core, running parallel therewith, and spaeed ~part from eaeh other, eharaeterized in that an electrostatie screen made of metal foil is inserted between the internal sheath and the external sheath, and in that a speeifie numerieal ratio, namely about 1:3:1, exists between the wall thiek-ness of the insulating sheath of the eonduetors, the wall thickness of the internal sheath, and the distance between the sereen and the glass fibre bundles.
The objeetives of the invention relating to mutual capaeitanee values, flexibility, and outside diameter may be fully and optimally achieved when the foregoing combination of characteristies is maintained.
Aecording to a further advantageous development of the invention, the electrostatic sereen consists of plastic-laminated aluminum tapes of a ~ _3_ .
1~)4~3616 total thickness of about 40 microns, the metallic side of the said tapes being arranged to face the internal sheath.
Further exemplary embodiments, of the invention are characterized by the alternative use of bare or plastic laminated copper strips and of corrugated or combined metal foils as screens. The metal strips may be laminated on both sides with plastic, e.g. polyethylene on one side and polyterephthalate on the other.
The drawing illustrates an embodiment of the invention in the form of a diagrammatic cross-sectional view of a self-supporting aerial cable with ten conductor pairs.
The structure of the cable is as follows: Round about a central plastic core (heart of the cable) 10 of circular cross section are arranged five spiral quads 11 each consisting of two conductor pairs 12/12, each spiral quad consisting of four individual insulated conductors 12 twisted together to form one unit, with the insulated conductors 12 at the four corners of a square, diametrically opposite insulated conductors 12/12 being used to provide the circuits. The conductors 13 are insulated with polyethylene 14. The central core (heart) 10 and the five spiral quads 11 are in their entirety wrapped with a protective layer 15, for example a helical lapping of one or more plastic tapes. Over this cablc core an extruded internal sheath 16 of polyethylene is arranged.
A screen 17 of plastic laminated aluminum tapes is wound onto internal sheath 16, the said tapes being preferably about 40 microns in thickness.
Arranged over screen 17 is an external sheath 18 also consisting of polyethylene applied by extrusion. Embedded in this external sheath 18 are twenty four bundles 1~ of glass fibre yarn running parallel with the axis of the cable and arranged in a circle surrounding the cable core. Note that the "cable core" is considered to include those elements within sheath ~ ~ 4 - ~
..
: . , ". .
` 104~t~16 ~ 15, i.e. the quads (sub-cables) 11 and, if used, the central core 10. The v~ said bundles take up the tensile forces to which the cable is subjected .. .
when it is used as an aerial cable and also in other cases. A method for embedding bundles 19 in external sheath 18 is described in our United States x Patent 3,879,518 issued April 22, 1975.
,..:
:;:
~, . .
.;~, /
,, :
., ~' .
r. .
.",~ ~' ' .' ' ' :
-4a-- . ,~ .. .
` - -~48616 The ratio between wall thickness "a" of insulation 14 of conduc-tors 13, and wall thickness "b" of internal sheath 16, and distance "c" be-tween screen 17 and glass fibre bundles 19 is as 1:3:1, so that the outside diameter of the cables varies, depending upon the design thereof - the number of conductor pairs. The following table shows this by way of example:
Number of Wall thickness Wall thickness Distance "c" Outside Outside dia-conductor of insulating of internal between screen diameter meter of ~- pairs sheaths sheath and glass- unscreened - fiber bundles design a b ~mm) (mm) (mm) (mm) (mm) . ~ ,
2 0.25 0.75 0.25 8.4 8.2 4 0.25 0.75 0.25 11.3 10.8 -6 0.25 0.75 0.25 11.7 11.6 -~
0.25 0.75 0.25 13.6 13.6 ~' ' Column 6 of this table also gives the outside diameters of con-ventional unscreened types of cable in practical use, for purposes of compari- -son with the outside diameters achieved with the design according to the invention. It should be noted that the main differences between screened and unscreened cables is the wall thickn~ss of insulating sheaths 14 (0.36 mm) in the latter and the greater distance (0.5 mm) between wrapping 15 and glass fibre bundles 19 in the former. As expected, this produces mutual-capacitance values which, in comparison with the design according to the invention, are still lower than the established limits.
In each case, the mutual capacitances in the designs according to the invention, as shown in the said table, are below the limit value of 42 nF/km.
.
' .
- :: , . : : , :
.
....
0.25 0.75 0.25 13.6 13.6 ~' ' Column 6 of this table also gives the outside diameters of con-ventional unscreened types of cable in practical use, for purposes of compari- -son with the outside diameters achieved with the design according to the invention. It should be noted that the main differences between screened and unscreened cables is the wall thickn~ss of insulating sheaths 14 (0.36 mm) in the latter and the greater distance (0.5 mm) between wrapping 15 and glass fibre bundles 19 in the former. As expected, this produces mutual-capacitance values which, in comparison with the design according to the invention, are still lower than the established limits.
In each case, the mutual capacitances in the designs according to the invention, as shown in the said table, are below the limit value of 42 nF/km.
.
' .
- :: , . : : , :
.
....
Claims (7)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. An electrical cable having a non-metallic means for relieving the tensile load and comprising one or more conductors as the cable core, each conductor having an insulating sheath, an insulating foil wound thereover, a plastic internal sheath extruded therearound, surrounded by a plastic external sheath in which are embedded bundles of glass fibres arranged concentrically with the cable core, running parallel therewith, and spaced apart from each other, characterized in that an electrostatic screen made of metal foil is inserted between the internal sheath and the external sheath, and in that a specific numerical ratio, namely about 1:3:1, exists between the wall thickness of the insulating sheath of the conductors, the wall thickness of the internal sheath, and the distance between the screen and the glass fibre bundles.
2. An electrical cable according to claim 1, characterized in that the electrostatic screen consists of plastic-laminated aluminum strips totalling about 40 microns in thickness, the metal side of which faces the internal sheath.
3. An electrical cable according to claim 1, characterized in that the electrostatic screen is made of bare copper strips.
4. An electrical cable according to claim 1, characterized in that the electrostatic screen consists of plastic-laminated copper strips, the metal side of which faces the internal sheath.
5. An electrical cable according to claim 1, characterized in that the electrostatic screen consists of corrugated metal foils.
6. An electrical cable according to claim 1, characterized in that the electrostatic screen consists of a metal strip laminated on both sides with a layer of plastic.
7. An electrical cable according to claim 6 wherein the metal strip is laminated on one side with polyethylene and on the other side with polyterephthalate.
Priority Applications (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA75241125A CA1048616A (en) | 1975-11-26 | 1975-11-26 | Electric cable with non-metallic means for relieving the tensile load |
| AT50176A AT345366B (en) | 1975-11-26 | 1976-01-26 | ELECTRIC CABLE WITH METAL-FREE STRAIN RELIEF DEVICE |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA75241125A CA1048616A (en) | 1975-11-26 | 1975-11-26 | Electric cable with non-metallic means for relieving the tensile load |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1048616A true CA1048616A (en) | 1979-02-13 |
Family
ID=4104674
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA75241125A Expired CA1048616A (en) | 1975-11-26 | 1975-11-26 | Electric cable with non-metallic means for relieving the tensile load |
Country Status (2)
| Country | Link |
|---|---|
| AT (1) | AT345366B (en) |
| CA (1) | CA1048616A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN104318997A (en) * | 2014-11-07 | 2015-01-28 | 成都冠禹科技有限公司 | Low-smoke zero-halogen damp-proof fire-resistant tensile-resistant industrial cable |
-
1975
- 1975-11-26 CA CA75241125A patent/CA1048616A/en not_active Expired
-
1976
- 1976-01-26 AT AT50176A patent/AT345366B/en not_active IP Right Cessation
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN104318997A (en) * | 2014-11-07 | 2015-01-28 | 成都冠禹科技有限公司 | Low-smoke zero-halogen damp-proof fire-resistant tensile-resistant industrial cable |
Also Published As
| Publication number | Publication date |
|---|---|
| AT345366B (en) | 1978-09-11 |
| ATA50176A (en) | 1978-01-15 |
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