SELF-SUPPORTING OVERHEAD TELECOMMUNICATION/POWER CABLE

Abstract

A self-supporting overhead telecommunication/power cable includes a supporting portion and a transmission portion mutually arranged according to a figure-8 configuration. The transmission portion includes at a central position thereof, an optical fibre conductor and, at a radially outer position with respect to the optical fibre conductor, electrical conductors stranded around the optical fibre conductor. Preferably, the electrical conductors are grouped into sub-units which are stranded around the optical fibre conductor to provide a mechanical protection thereto.

Claims

1-10. (canceled)

11. A self-supporting overhead telecommunication/power cable comprising a supporting portion and a transmission portion mutually arranged according to a figure-8 configuration, wherein the transmission portion comprises, at a central position thereof, an optical fibre conductor and, at a radially outer position with respect to the optical fibre conductor, electrical conductors stranded around said at least one optical fibre conductor.

12. The self-supporting overhead telecommunication/power cable according to claim 11, wherein said at least one optical fibre conductor comprises a plurality of optical fibres housed in a buffer tube.

13. The self-supporting overhead telecommunication/power cable according to claim 11, wherein at least three electrical conductors are arranged and stranded around the optical fibre conductor.

14. The self-supporting overhead telecommunication/power cable according to claim 11, wherein the electrical conductors are selected from individual electrical conductors, copper pairs and a combination thereof.

15. The self-supporting overhead telecommunication/power cable according to claim 11, wherein the electrical conductors are grouped into sub-units which are stranded around the optical fibre conductor.

16. The self-supporting overhead telecommunication/power cable according to claim 15, wherein said sub-units are SZ stranded.

17. The self-supporting overhead telecommunication/power cable according to claim 15, wherein each sub-unit comprises a tape made of polymeric material.

18. The self-supporting overhead telecommunication/power cable according to claim 11, wherein said transmission portion comprises a water blocking filling material.

19. The self-supporting overhead telecommunication/power cable according to claim 11, comprising a figure-8 shaped outer sheath enclosing said supporting portion and said transmission portion.

20. The self-supporting overhead telecommunication/power cable according to claim 19, wherein the transmission portion comprises an outer tape wrapping the electrical conductors and the optical fibre conductor and arranged in a radial internal position with respect to the outer sheath.

Description

[0046] Further features and advantages of the present invention will appear more clearly from the following detailed description of preferred embodiments thereof, such description being provided merely by way of non-limiting example and being made with reference to the annexed drawings. In such drawings:

[0047] FIG. 1 is a schematic cross-section view of a self-supporting overhead telecommunication/power cable according to an exemplary embodiment of the present invention;

[0048] FIG. 2 is a schematic perspective view of a part of the cable of FIG. 1;

[0049] FIG. 3 is a schematic cross-section view of another self-supporting overhead telecommunication/power cable according to an exemplary embodiment of the present invention; and

[0050] FIG. 4 is a schematic cross-section view of a further self-supporting overhead telecommunication/power cable according to an exemplary embodiment of the present invention.

[0051] In FIG. 1, an embodiment of a self-supporting overhead telecommunication/power cable according to the present invention is indicated with numeral reference 100.

[0052] The cable 100 comprises a supporting portion 20 and a transmission portion 30 mutually arranged according to a figure-8 configuration.

[0053] The supporting portion 20 and the transmission portion 30 are defined in distinct portions of a figure-8 outer sheath 40 made of polymeric material, preferably high density polyethylene (HDPE). The sheath 40 includes an intermediate portion 50 mutually connecting the supporting portion 20 and the transmission portion 30.

[0054] Both the supporting portion 20 and the transmission portion 30 have a substantially circular cross-section.

[0055] The supporting portion 20 comprises a messenger wire 21, possibly made of glass-reinforced polymer or, preferably, of steel, intended to be attached to poles (not shown) during installation of the cable 100.

[0056] The transmission portion 30 comprises, at the central position thereof, an optical fibre conductor 31 comprising a buffer tube 32 housing a plurality of optical fibres 32a.

[0057] The buffer tube 32 is coaxially arranged within the transmission portion 30.

[0058] The number of optical fibres 32a within the buffer tube 32 can vary depending on the transmission requirements. This number can vary, for example, from 1 to 12.

[0059] Each optical fibre 32a comprises a glass core and, at a radially outer position with respect to the glass core, one or two coatings made of a polymeric material, for example acrylate.

[0060] The buffer tube 32 is made of polymeric material, for example polybutylene terephthalate.

[0061] The transmission portion 30 further comprises, at a radially outer position with respect to the optical fibre conductor 31, three sub-units 35a, 35b, 35c each including nine copper pairs 36. For the sake of clarity of illustration, the reference number 36 is associated to just one of the abovementioned copper pairs.

[0062] The copper pairs 36 are stranded together and wrapped by a tape 37 made of polymeric material, for example polypropylene.

[0063] The number of sub-units 35a, 35b, 35c can be greater than three as well as the number of copper pairs 36 inside each sub-unit 35a, 35b, 35c can be lower or greater than nine (for example from two to one hundred), depending on the transmission requirements. In the present case, the copper pairs 36 are equally divided into the sub-units 35a, 35b, 35c.

[0064] Preferably, the sub-units 35a, 35b, 35c are substantially equally spaced apart from each other around the optical fibre conductor 31. Thus, in the embodiment shown in FIG. 1, the three sub-units 35a, 35b, 35c are angularly arranged at 120° from each other around the optical fibre conductor 31.

[0065] As shown in FIG. 2, the sub-units 35a, 35b, 35c of the cable of FIG. 1 are stranded around the optical fibre conductor 31.

[0066] FIG. 2 shows the transmission portion 30 of the cable 100 without the outer tape 38 mentioned below.

[0067] The sub-units or, in the case, the individual electrical conductors, are capable to provide the transmission portion with a suitable structural strength and protect the optical fibre conductor against external loads which the cable can be subjected to in installation and/or operation. No additional protective and/or strengthening elements are thus required, so as not to avoid an increase of the size and weight of the cable and a reduction of the cable flexibility.

[0068] Preferably, the sub-units 35a, 35b, 35c are SZ stranded around the optical fibre conductor 31.

[0069] As shown in FIG. 1, each copper pair 36 comprises a twisted pair of telecommunication conductors 36a, each comprising a copper wire covered by an electrical insulation layer made of polymeric material, for example polyethylene. For the sake of clarity of illustration, the reference number 36a is associated to just one telecommunication conductor in each sub-unit 35a, 35b, 35c.

[0070] An outer tape 38 is provided in the transmission portion 30 to wrap the sub-units 35a, 35b, 35c around the optical fibre conductor 31. The tape 38 is preferably made of a polymeric material, for example polyester. The tape 38 can be longitudinally or helically applied onto the sub-units 35a, 35b, 35c.

[0071] A water-blocking filling material 39 is provided to embed the sub-units 35a, 35b, 35c and the optical fibre conductor 31 in order to prevent any water flow within the transmission portion 30. The water-blocking filling material 39 is also provided inside the buffer tube 32 to embed the optical fibers 32a.

[0072] At least one rip cord (not shown) can be provided in the transmission portion 30 and possibly in the supporting portion 20 as well.

[0073] FIG. 3 shows another embodiment of a self-supporting overhead telecommunication/power cable according to the present invention, which is indicated with numeral reference 200.

[0074] Unless specified, all of the reference numbers of FIG. 3 indicate the same cable elements as from the description of FIG. 1.

[0075] Cable 200 has a transmission portion 30 comprising, at a radially outer position with respect to the optical fibre conductor 31, four sub-units 35a, 35b, 35c, 35d each including five copper pairs 36, stranded together and wrapped by a tape 37.

[0076] A single copper pair 36bis is also stranded around the optical fibre conductor 31 together with the sub-units 35a, 35b, 35c, 35d.

[0077] In cable 200 a water-blocking filling material 39 is provided to embed the sub-units 35a, 35b, 35c, 35d, the copper pair 36bis and the optical fibre conductor 31. The water-blocking filling material 39 is not provided into the buffer tube 32.

[0078] FIG. 4 shows a further embodiment of a self-supporting overhead telecommunication/power cable according to the present invention, which is indicated with numeral reference 300.

[0079] Unless specified, all of the reference numbers of FIG. 4 indicate the same cable elements as from the description of FIG. 1.

[0080] Cable 300 has a transmission portion 30 comprising, at a radially outer position with respect to the optical fibre conductor 31, four sub-units 35a, 35b, 35c, 35d each including five copper pairs 36, stranded together and wrapped by a tape 37.

[0081] An individual electric conductor 36ter (comprising a conductive core 42 surrounded by an electrically insulating layer 41) is also stranded around the optical fibre conductor 31 together with the sub-units 35a, 35b, 35c, 35d.

[0082] In cable 300 a water-blocking filling material 39 is provided to embed the sub-units 35a, 35b, 35c, 35d, the individual electric conductor 36ter and the optical fibre conductor 31. The water-blocking filling material 39 is not provided into the buffer tube 32.

Tests

[0083] The Applicant has made a number of tests on cables 100 according to the invention.

[0084] The tested cables included a buffer tube housing up to twelve optical fibres of the type E (G657A1).

[0085] Each optical fibre had an inner diameter (core diameter) of 1.8±0.1 mm and an outer diameter (cladding diameter) of 3.0±0.1 mm.

[0086] Each copper pair included two annealed solid copper wires having each a nominal diameter of 0.5 mm and each surrounded by an insulation layer made of polyethylene and having a nominal diameter of 1.3 mm.

[0087] Tree sub-units each comprised nine telecommunication copper pairs SZ-stranded around the buffer tube.

[0088] The copper pairs of each sub-unit were wrapped with a layer of polyester material having a thickness and a width of 2.8±0.4 mm.

[0089] The transmission portion was filled with a water-blocking jelly.

[0090] The transmission portion had an outer tape of polyester material with a thickness of 0.05 mm.

[0091] The supporting portion included a steel messenger wire having a diameter of 2.65 mm.

[0092] The outer sheath of the cables, made of HDPE, had a thickness of 1.3 mm both in the supporting portion and the transmission portion.

[0093] The cables had a weight of about 400 Kg/km and a diameter of 18×27 mm. The cable maximum diameter was 23×32 mm.

[0094] The cables were subjected to quality tests for both the optical conductors and the electrical conductors. In particular, the optical fibres were subjected to attenuation tests according to IEC 60794-1-2 and the electrical conductors were subjected to electrical performance tests according to IEC 60708.

[0095] The mechanical and transmission properties of the tested cables are listed in tables 1-5 below.

TABLE-US-00001 TABLE 1 Electrical property at 20° C. Requirement Result Conductor resistance Max. average 91 85.8 (/km) Max. for 99% 96 86.3 Mutual Capacitance Max. average 56 41.87 (nF/km) Max. for 99% 64 43.1 Insulation Resistance Min. (M .Math. km) 1500 >1500 @ 500 V DC Voltage test core/core 1000 V DC, no passed 60 s breakdown

TABLE-US-00002 TABLE 2 Attenuation at 20° C. Attenuation (dB/Km) Buffer tube Optical fibre 1310 nm 1550 nm No. Colour No. Colour max 0.36 max 0.22 1 blue 1 red 0.314 0.183 2 green 0.315 0.184 3 blue 0.315 0.175 4 yellow 0.317 0.185 5 white 0.317 0.190 6 grey 0.314 0.186 7 brown 0.310 0.186 8 violet 0.318 0.193 9 turquoise 0.318 0.200 10 black 0.317 0.177 11 orange 0.310 0.177 12 pink 0.314 0.185

[0096] The cable water tightness was evaluated on 3 m-long cables in 1 m-high water for 24 hours. No water was found at the open cable end.

TABLE-US-00003 TABLE 3 Attenuation at −20° C. Attenuation (dB/Km) Buffer tube Optical fibre 1310 nm 1550 nm No. Colour No. Colour max 0.36 max 0.22 1 blue 1 red 0.322 0.176 2 green 0.312 0.171 3 blue 0.307 0.179 4 yellow 0.301 0.187 5 white 0.301 0.170 6 grey 0.309 0.188 7 brown 0.308 0.192 8 violet 0.302 0.176 9 turquoise 0.300 0.171 10 black 0.309 0.178 11 orange 0.319 0.187 12 pink 0.313 0.178

TABLE-US-00004 TABLE 4 Attenuation at +60° C. Attenuation (dB/Km) Buffer tube Optical fibre 1310 nm 1550 nm No. Colour No. Colour max 0.36 max 0.22 1 blue 1 red 0.322 0.214 2 green 0.334 0.205 3 blue 0.330 0.194 4 yellow 0.310 0.214 5 white 0.317 0.190 6 grey 0.321 0.188 7 brown 0.310 0.209 8 violet 0.313 0.183 9 turquoise 0.310 0.180 10 black 0.332 0.187 11 orange 0.325 0.182 12 pink 0.328 0.193

[0097] All of the cables tested passed each test, thus confirming that the cable according to the invention is capable of being effectively used in aerial installation for communication/data transfer without suffering of attenuation and performance problems.