AU2013200032A1

AU2013200032A1 - Power and or Telecommunications Cable Capable of Preventing the Propagation of a Fire

Info

Publication number: AU2013200032A1
Application number: AU2013200032A
Authority: AU
Inventors: Chantal Barioz; Roland Carriere; Alain Clertant; Christele Kensicher; Renee Loriol; Thierry Seux
Original assignee: Nexans SA
Current assignee: Nexans SA
Priority date: 2012-01-05
Filing date: 2013-01-04
Publication date: 2013-07-18
Also published as: CN103198891A; CN103198891B; FR2985596A1; EP2613326A1; EP2613326B1; FR2985596B1; CA2801931A1

Abstract

The present invention relates to a power and or telecommunications cable (1) comprising: - at least one elongated electrically conductive element (2), and - a thermally protective first layer (3) coaxially surrounding said electrically conductive element (2), characterized in that the thermally protective first layer (3) comprises glass fibres, with a mass per unit volume of at least 0.5 g/cm 3. Figure to be published: Figure 1 Fig.1 - 2

Description

1 Power and or telecommunications cable capable of preventing the propagation of a fire Field of the invention [001] The present invention relates to an aluminium-based cable that is capable of withstanding extreme thermal conditions, and that is more particularly capable of preventing the propagation of a fire. [002] The invention finds a particularly advantageous, but not exclusive, application in the field of power and or telecommunications cables, which are intended to remain operational for a defined period of time when they are subjected to high temperatures and or directly to flames. Background of the invention [003] One issue in the cable industry is that of improving the behaviour and performance of cables under extreme thermal conditions, especially those encountered during a fire. Specifically, for essentially safety reasons, it is essential to maximize the cable's capacities for retarding the propagation of flames, on the one hand, and for withstanding fire, on the other hand. A significant retardation of the progress of flames affords a proportionate amount of extra time for evacuating the premises and or for using appropriate extinction means. Better fire resistance offers the cable the possibility of functioning for longer, since its degradation is less rapid. [004] Whether it is electric or optical, intended for power transport or data transmission, a cable consists generally of at least one conductive element extending within at least one insulating element. It should be noted that at least one of the insulating elements may also act as a protective means and or that the cable may also comprise at least one specific protective element, forming a sheath. [005] In particular, a cable with an aluminium conductive element which is installed close to a flammable material must be able to withstand fire temperatures that may range from 750cC to 9000C so as not to propagate the fire. However, these fire temperatures are above the melting point of aluminium, which is about 6580C. [006] Now, it is known that among the best insulating and or protective materials used in cabling, many of them are also unfortunately excellent flammable materials. This is especially the case for polyolefins and copolymers thereof, for instance 2 polyethylene, polypropylene, copolymers of ethylene and vinyl acetate, and copolymers of ethylene and propylene. In any case, in practice, this excessive flammability proves to be entirely incompatible with the fire resistance imperatives mentioned previously. [007] In the field of cabling, many methods exist for improving the fire behaviour of the polymers used as insulating and or sheathing materials. [008] The most widespread solution used to date consisted in employing halogenated compounds, in the form of a halogenated by-product dispersed in a polymer matrix, or directly in the form of a halogenated polymer, for instance in the case of a polyvinyl chloride (PVC). However, the current regulations are now tending towards banning the use of substances of this type essentially on account of their potential toxicity and corrosiveness, whether at the time of manufacture of the material, or during its fire decomposition. This is all the more true since the decomposition in question may arise accidentally during a fire, but also deliberately during incineration. In any case, the recycling of halogenated materials still remains particularly problematic. [009] This is why recourse is increasingly being made to non-halogenated flame-retardant fillers, and especially to metal hydroxides such as aluminium hydroxide or magnesium hydroxide. However, technical solutions of this type have the drawback of requiring large amounts of fillers to achieve a satisfactory level of efficacy, whether in terms of capacity for retarding the propagation of flames, or of fire resistance. By way of example, the content of metal hydroxides may typically be up to 150% to 200% by weight relative to the total amount of resin. Now, any massive incorporation of fillers induces a considerable increase in the viscosity of the material, and, consequently, an appreciable reduction in the rate of extrusion, resulting in a large decrease in productivity. The addition of excessive amounts of flame-retardant additives is also the cause of significant deterioration of the mechanical and electrical properties of the cable. [010] Document GB 2 035 666 describes, in its prior art, a cable that is capable of functioning at high temperatures, comprising at least one aluminium or copper conductor, longitudinally or helically coated with a mineral insulating layer based on glass fibres. It is indicated that this material is difficult to handle and that the manufacturing process is thus long and cumbersome. Moreover, it is indicated in said document that the layer of glass fibres shows instability of its behaviour at temperatures 3 of about 4000C -5000C and that, at about 7000C -8000C, the glass fibre has a viscous phase, which makes it less insulating. [011] Any reference herein to known prior art does not, unless the contrary indication appears, constitute an admission that such prior art is commonly known by those skilled in the art to which the invention relates, at the priority date of this application. Summary of the invention [012] Thus, the aim of the present invention is to overcome, or at least ameliorate in part, the drawbacks of the prior art by proposing a fire-resistant power and or telecommunications cable, said cable also making it possible to prevent or minimise the problems of the prior art by especially affording substantially improved mechanical properties, while at the same time having operating functionality during a fire. [013] The present invention thus provides a power and or telecommunications cable comprising: - at least one elongated electrically conductive element, and - a first thermally protective layer coaxially surrounding the electrically conductive element, characterized in that the thermally protective first layer comprises glass fibres, in a mass per unit volume of at least 0.5 g/ cm 3 . [014] It has been demonstrated that such a layer of glass fibres makes it possible to make the cable fire-resistant by limiting the propagation of a fire by the cable to surrounding objects (curtains, etc.), while at the same time ensuring operating functionality. Specifically, the thermally protective first layer prevents the electrically conductive element from melting, especially when this element is made of aluminium. Thus, the thermal barrier formed by the layer of glass fibre prevents the melting of the electrically conductive element and, consequently, also prevents surrounding materials from being ignited, which may result from drops of molten aluminium, while at the same time enabling the cable to function despite the fire. [015] The glass fibre first layer thus affords better fire resistance than the glass fibre layer described in document GB 2 035 666.

4 [016] In one preferred embodiment, the first layer can comprise at least one tape of glass fibres. The tape especially helically surrounds the electrically conductive element. [017] The tape of glass fibres can cover the electrically conductive element with a degree of overlap of about 15%-20%. [018] The first layer of the invention can have a mass per unit volume of at least 0.8 g/cm 3 and preferably of at least 1 g/cm 3 . [019] The first layer can have a mass per unit volume of not more than 2 g/cm 3 and preferably not more than 1.5 g/ cm 3 . [020] Particularly preferably, the first layer can have a mass per unit volume ranging from 1.0 to 1.5 g/ cm 3 . [021] The first layer of the invention can be advantageously used as a thermal barrier, especially a flame barrier. It makes it possible to maintain the integrity of the electrically conductive element for a temperature of at least 8000C and preferably of at least 1000 C. It thus prevents the electrically conductive element from melting during a fire. Advantageously, the first layer of the invention can have a thermal conductivity of at most 0.25 W/m C (watts per meter degree Celsius). [022] Preferentially, the thickness of the first layer ranges from 0.10 mm to 0.40 mm. For example, if the first layer comprises only one tape of glass fibre, the thickness will be about 0.10 mm, and if it comprises two, the thickness will be about 0.40 mm. [023] Preferably, the first layer (made of glass fibre) has a mass per unit area that can range from 120 g/m 2 to 160 g/m 2 . [024] The electrically conductive element of the invention can be a material chosen from aluminium (AI) or an aluminium alloy. The aluminium alloy can be chosen from copper aluminium, nickel aluminium and nickel-copper aluminium, or a combination thereof. [025] The electrically conductive element can be, for example, of the single strand or multi-strand type. [026] Advantageously, the cable of the invention can comprise a second layer surrounding the first layer. This second layer can be formed by extrusion or by taping 5 according to techniques known to those skilled in the art so as to be composed of only one or of several sub-layers, preferably such as two. [027] Preferably, the second layer is electrically insulating and can be made of a material chosen from a synthetic rubber, for instance silicone rubber, and a polyolefin, for instance ethylene copolymers of the ethylene-vinyl acetate (EVA) type, or a combination thereof. [028] Advantageously, the thickness of the second layer ranges from 0.5 mm to 3.0 mm. [029] When the cable of the invention comprises the second layer, the first layer can be directly in physical contact with the electrically conductive element, and the second layer can be directly in physical contact with the first layer. The cable can also comprise a protective sheath surrounding the second layer. [030] In one particularly preferred embodiment, the power and or telecommunications cable is an insulated electrical conductor in which the elongated electrically conductive element is a central element. [031] A subject of the present invention is also the use of a cable as described above for limiting the propagation of a fire. Brief description of the drawings [032] For better understanding of the invention, the description will make reference to an attached drawing, which is given purely for illustrative purposes and without any implied limitation. [033] In this drawing: - figure 1 illustrates a perspective view in partial cutaway of a power and or cable according to one preferred embodiment of the invention. Detailed description of the embodiment or embodiments [034] Implementation examples: [035] Example 1: Example of the composition of a cable according to the invention (figure 1) [036] For reasons of clarity, only the elements that are essential for the understanding of the invention have been represented schematically in figure 1, and are not drawn to scale.

6 [037] The power cable 1, shown in figure 1, is an insulated electrical conductor comprising a central conductive element 2, especially made of aluminium, of multi strand type, and, successively and coaxially around this element, a first layer 3 formed from a strip (tape) of glass fibre sold by the company Stevtiss or Tisstech, or a glass fibre tape sold by the company Scapa under the reference SFR1 0/103. [038] This tape covers the conductive element with a degree of overlap of about 15%-20% so as to ensure that all of the surface of the conductive element is protected from flames. Over this glass fibre tape is placed a second layer 4 consisting of two sub layers of an extruded material based on silicone rubber: a layer of white material referenced El 111 made of a polysiloxane polymer, and a layer of black material referenced EM107 made of an ethylene copolymer in the European standard for rolling materials EN 50382-1. This second layer 4 is an optional layer. [039] In this example, the thickness of the tape (i.e. first layer 3) is 0.12 mm and its mass per unit volume is 1.16 g/cm 3 . The thickness of the second layer 4 is about 2.7 mm. [040] Example 2: Process for preparing a cable according to the invention [041] The multi-strand aluminium electrical conductor 4 is surrounded by a first layer of glass fibre tape as mentioned in Example 1. This glass fibre tape is then coated by extrusion of the two abovementioned layers of silicone rubber and of polyolefin. [042] Taping and extrusion techniques are well known to those skilled in the art and will not be explained in further detail in the present patent application. [043] Experimental test [044] The cable as described in Example 1 was subjected to a fire test. A blow torch projecting an 8500C flame was positioned close to the cable according to the invention for 1 hour such that the flame touches part of the cable. A sheet of paper was also placed close to the cable, about 30 cm away, while remaining distant from the blowtorch flame. [045] It was found after one hour that the second layer made of silicone rubber and of polyolefin ignited and was completely burnt in the zone in contact with the flame, but that the multi-strand aluminium conductor remained intact by virtue of the glass fibre tape. Moreover, this tape also remained intact. Furthermore, the sheet of paper placed 7 30 cm from the cable did not ignite, thus showing that the cable according to the invention is not a fire propagator. [046] Although the invention has been described in association with a particular embodiment, it is obvious that it is in no way limited thereto and that it comprises all the equivalent techniques of the means described and also combinations thereof if they fall within the context of the invention. [047] Where ever it is used, the word "comprising" is to be understood in its "open" sense, that is, in the sense of "including", and thus not limited to its "closed" sense, that is the sense of "consisting only of". A corresponding meaning is to be attributed to the corresponding words "comprise", "comprised" and "comprises" where they appear. [048] It will be understood that the invention disclosed and defined herein extends to all alternative combinations of two or more of the individual features mentioned or evident from the text. All of these different combinations constitute various alternative aspects of the invention. [049] While particular embodiments of this invention have been described, it will be evident to those skilled in the art that the present invention may be embodied in other specific forms without departing from the essential characteristics thereof. The present embodiments and examples are therefore to be considered in all respects as illustrative and not restrictive, and all modifications which would be obvious to those skilled in the art are therefore intended to be embraced therein.

Claims

1. Power and or telecommunications cable (1) comprising: - at least one elongated electrically conductive element (2), and - a thermally protective first layer (3) coaxially surrounding said electrically conductive element (2), characterized in that the thermally protective first layer (3) comprises glass fibres, with a mass per unit volume of at least 0.5 g/cm 3 .

2. Cable (1) according to claim 1, characterized in that the first layer comprises at least one tape of glass fibres.

3. Cable (1) according to claim 1 or 2, characterized in that the first layer has a mass per unit volume of at least 0.8 g/cm 3 and preferably of at least 1 g/cm 3 .

4. Cable (1) according to one of the preceding claims, characterized in that the first layer has a mass per unit volume of not more than 2 g/cm 3 and preferably not more than 1.5 g/cm 3 .

5. Cable (1) according to one of the preceding claims, characterized in that the first layer (3) has a mass per unit area of about 120 to 160 g/m 2 .

6. Cable (1) according to one of the preceding claims, characterized in that the thickness of the first layer (3) is about 0.10 mm to 0.40 mm.

7. Cable (1) according to one of the preceding claims, in which the electrically conductive element (2) is made of a material chosen from aluminium (Al) and an aluminium alloy.

8. Cable (1) according to one of the preceding claims, characterized in that it comprises a second layer surrounding said first layer.

9. Cable (1) according to claim 8, characterized in that the second layer is made of a material chosen from a synthetic rubber and a polyolefin, or a combination thereof.

10. Cable (1) according to one of the preceding claims, characterized in that the first layer (3) is directly in physical contact with the electrically conductive element (2).

11. Cable (1) according to one of the preceding claims, characterized in that it is an insulated electrical conductor in which the electrically conductive element (2) is a central element. 9

12. A power and or telecommunications cable, being substantially as herein before described with reference to the accompanying drawing and illustrative examples.