Fire-resistant cable

Abstract

The present invention relates to a fire-resistant cable comprising at least one electrically insulating composite layer based on at least one cementitious material and at least one starch, and the process for manufacturing same.

Claims

1. Power and/or telecommunications cable comprising: at least one elongated conductive element; and at least one electrically insulating composite layer surrounding said elongated conductive element, wherein the electrically insulating composite layer comprises at least one starch, at least one plasticizer for starch and at least one cementitious material, and wherein the cementitious material represents from 10 to 50% by weight relative to the total weight of said electrically insulating composite layer.

2. Cable according to claim 1, wherein the cementitious material comprises silicon (Si), aluminium (Al) or magnesium (Mg), oxygen (O), and at least one element selected from potassium (K), sodium (Na), lithium (Li), caesium (Cs) and calcium (Ca).

3. Cable according to claim 1, wherein the cementitious material is a geopolymer cement or is derived from a mixture consisting of a conventional anhydrous cement and water or a mixture consisting of a magnesium silicate, an alkali metal silicate, an alkaline base and water.

4. Cable according claim 1, wherein the electrically insulating composite layer has a thickness ranging from 0.5 to 5 mm.

5. Cable according to claim 1, wherein the starch is a native starch or a modified starch.

6. Cable according to claim 1, wherein the plasticizer for starch is a metal stearate, a polyethylene glycol, an ethylene glycol, a polyol, a sucrose, a plasticizer containing amide groups, any type of plasticizer based on modified polysaccharide(s) or a mixture thereof.

7. Cable according to claim 1, wherein the starch and the plasticizer for starch represent from 50 to 90% by weight relative to the total weight of said electrically insulating composite layer.

8. Cable according to claim 1, wherein the electrically insulating composite layer is an inner layer of the cable.

9. Cable according to claim 1, wherein said cable also comprises an outer protective sheath surrounding the composite layer(s).

10. Process for manufacturing the cable as defined in claim 1, wherein said process comprises at least the following steps: i) a step of preparing a composite composition comprising the cementitious material, the starch and the plasticizer for starch, ii) a step of applying the composite composition obtained in step i) around the elongated conductive element, iii) a step of hardening the composite composition in order to form the electrically insulating composite layer.

11. Process according to claim 10, wherein the cementitious material of step i) comprises water, silicon (Si), aluminium (Al) or magnesium (Mg), oxygen (O), and at least one element selected from potassium (K), sodium (Na), lithium (Li), caesium (Cs) and calcium (Ca).

12. Process according to claim 10, wherein the cementitious material is a geopolymer composition, a mixture consisting of a conventional anhydrous cement and water or a mixture consisting of a magnesium silicate, an alkali metal silicate, an alkaline base and water.

13. Process according to claim 10, wherein step i) is carried out by separately preparing the starch according to a step i-1) and the cementitious material according to a step i-2) then by mixing the starch and cementitious material according to a step i-3) in order to form the composite composition.

14. Process according to claim 10, wherein step ii) is carried out by hot extrusion of said composite composition.

15. Power and/or telecommunications cable comprising at least one elongated conductive element; and at least one electrically insulating composite layer surrounding said elongated conductive element, and wherein the electrically insulating composite layer comprises at least one starch, at least one plasticizer for starch and at least one cementitious material, and wherein the starch and the plasticizer for starch represent from 50 to 90% by weight relative to the total weight of said electrically insulating composite layer.

16. Power and/or telecommunications cable comprising at least one elongated conductive element; and at least one electrically insulating composite layer surrounding said elongated conductive element, wherein the electrically insulating composite layer comprises at least one starch, at least one plasticizer for starch and at least one cementitious material, and wherein the cementitious material comprises silicon (Si), aluminium (Al) or magnesium (Mg), oxygen (O), and at least one element selected from potassium (K), sodium (Na), lithium (Li), caesium (Cs) and calcium (Ca).

Description

(1) In these figures:

(2) FIG. 1 is a schematic sectional view of an electric cable of the prior art, not in accordance with the invention;

(3) FIG. 2 is a schematic sectional view of an electric cable according to an embodiment of the present invention.

(4) For the sake of clarity, only those elements essential to the understanding of the invention have been represented schematically in these figures, without respecting a scale.

DETAILED DESCRIPTION

(5) The electric cable 10 illustrated in FIG. 1 corresponds to a fire-resistant medium-voltage electric cable of SHXCHX type, for marine-type applications.

(6) This electric cable 10 comprises: a central elongated electrically conductive element 1 and, successively and coaxially around this central conductive element 1, an inner semiconducting shield 1.1, an electrically insulating layer 2 (e.g. made of ethylene elastomer and crosslinked propylene, EPR), an outer semiconducting shield 2.1, a semiconducting tape layer 3, a metal braid 4 (e.g. consisting of tin-plated copper threads with a circular section), an inner sheath comprising a polyester tape 5 and tin-plated copper threads 6, a polyester tape 7 and an outer sheath 8 (e.g. made of elastomer).

(7) The electric cable 11 illustrated in FIG. 2 corresponds to an electric cable with a similar structure to the cable of FIG. 1, but into which two electrically insulating composite layers as defined in the invention have been incorporated.

(8) This electric cable 11 comprises: a central elongated electrically conductive element 1 and, successively and coaxially around this central conductive element 1, an inner semiconducting shield 1.1, an electrically insulating layer 2 (e.g. made of ethylene elastomer and crosslinked propylene, EPR), an outer semiconducting shield 2.1, a semiconducting tape layer 3, a metal braid 4 (e.g. consisting of tin-plated copper threads with a circular section), an electrically insulating composite layer 9 as defined in the invention, an inner sheath comprising a polyester tape 5 and tin-plated copper threads 6, a polyester tape 7, an electrically insulating composite layer 9 as defined in the invention, and an outer sheath 8 (e.g. made of elastomer).

(9) The following examples make it possible to illustrate the present invention. They do not have any limiting effect on the overall scope of the invention as presented in the claims. The ratios between the oxides are mole ratios, and the percentages indicated are percentages by weight.

EXAMPLES

(10) The starting materials used in the examples are listed below: aqueous sodium silicate solution at approximately 50% by weight, of waterglass type from Simalco, of formula Na.sub.2O.2SiO.sub.2 and with a SiO.sub.2/Na.sub.2O mole ratio of approximately 2, starch, Roquette, Tackidex 1-735, plasticizer, Roquette, Neosorb 70/70, mains water, sodium hydroxide, Sigma Aldrich, of purity >85%, aluminosilicate, PoleStar 450R, Imerys, with an Al.sub.2O.sub.3/SiO.sub.2 mole ratio of 41/55 (i.e. of approximately 0.745).

(11) Unless indicated otherwise, all these starting materials were used as received from the manufacturers.

Example 1: Preparation of a Fire-Resistant Cable in Accordance with the Invention

(12) A starch composition was prepared by mixing 400 g of starch, 400 g of plasticizer and 160 g of water at ambient temperature.

(13) An aluminosilicate geopolymer composition as cementitious composition was prepared in the following manner: an alkali metal silicate solution was prepared by mixing 360 g of an aqueous sodium silicate solution, 200 g of water and 60 g of sodium hydroxide. 300 g of aluminosilicate were then mixed with the alkali metal silicate solution.

(14) Said aluminosilicate geopolymer composition comprised approximately 40% by weight of solids relative to the total weight of said composition.

(15) The aluminosilicate geopolymer composition had the following molar composition of formula (I):
0.54SiO.sub.2: 0.16Al.sub.2O.sub.3: 0.1Na.sub.2O: 2.3H.sub.2O(I)

(16) The geopolymer composition was mixed with the starch composition as described above, to form a composite composition.

(17) The composite composition was hot-extruded around an elongated electrically conductive element made of copper with a 50 mm.sup.2 cross section, using an extruder sold under the trade name FAIREX. The temperature within the extruder ranged approximately from 40 C. to 95 C.

(18) Said cable obtained comprised an elongated electrically conductive element surrounded by an electrically insulating composite layer comprising 65% by weight of starch and of plasticizer for starch and 35% by weight of an aluminosilicate geopolymer cement as cementitious material.

(19) The composite layer had a thickness of approximately 2.5 mm.

(20) The composite layer of the cable in accordance with the invention was evaluated in terms of fire-resistance performance according to standards IEC 60331-11 and IEC 60331-21. The cable as obtained in example 1, and by way of comparison a cable not in accordance with the invention not comprising a composite layer of the invention (i.e. elongated electrically conductive element alone), were subjected to a voltage of 10 kV for 120 minutes at 85 C.

(21) The results of this test are presented in table 1 below:

(22) TABLE-US-00001 TABLE 1 Time before breakdown Cable Voltage applied (in min) Cable in accordance with the 10 kV >120 invention of example 1 Cable not in accordance with 10 kV 13 the invention

(23) The results presented in table 1 confirm the fire resistance of the cable of the invention. Breakdown of the cable not in accordance with the invention is observed after 13 min, whereas the cable of the invention has not broken down after 120 min. Moreover, the cable of the invention can withstand a voltage of approximately 30 kV for at least 20 minutes.

(24) Moreover, breakdown of a cable not in accordance comprising an electrically insulating layer without starch, obtained solely from the aluminosilicate geopolymer composition as described above, was observed after 37 or 47 min.