AU2010258513A1 - Electric cable adapted for ensuring the continuity of power distribution in the event of fire - Google Patents

Abstract

The present invention relates to an electric cable that includes one or more insulated electric conductors, each of the insulated electric conductors comprising an electric conductor surrounded by an insulation layer, the insulation layer including a first polymer layer (2a) surrounding the electric conductor, the first layer (2a) being obtained from a first composition including a matrix polymer formed from a thermoplastic polymer, and at least one ceramic-forming feedstock, characterized in that the insulation layer further includes a second cross-linked polymer layer (2b) surrounding said first layer, the second layer (2b) being obtained from a second position including a matrix polymer containing polyolefins and substantially free from any ceramic-forming feedstock or halogen compound.

Description

WO 2010/142917 1 PCT/FR2010/051154 Electric cable adapted for ensuring the continuity of power distribution in the event of fire The present invention relates to a power cable 5 capable of ensuring continuity of power distribution in the event of a fire, said cable comprising one or more insulated electrical conductors. The invention applies typically, but not exclusively, to the field of fire-resistant, and 10 especially halogen-free, security cables that are capable of operating for a given period of time under fire conditions, without in any way either propagating a fire or generating substantial smoke. These security cables are particularly power transport cables or low-frequency 15 transmission cables, such as control or signaling cables. One of the major challenges in the cable industry is to improve the behavior and the performance of cables under extreme thermal conditions, especially those encountered during a fire. For essentially security 20 reasons, it is in fact essential to maximize the capability of the cable to withstand a fire so as to ensure continuity of operation, especially of emergency evacuation assistance equipment. In the event of a fire, the cable must be able to 25 withstand the fire so as to operate as long as possible and to limit its degradation. A security cable also must not be hazardous for its environment, that is to say it must not propagate the fire and must not give off toxic and/or opaque smoke when it is exposed to extreme thermal 30 conditions. Document EP 0 942 439 teaches a halogen-free fire resistant security cable comprising an assembly of insulated electrical conductors, said assembly being surrounded by an external jacket. Each insulated 35 electrical conductor is formed by an electrical conductor WO 2010/142917 2 PCT/FR2010/051154 surrounded by a polymeric insulating monolayer obtained from a composition comprising a polymer material -and at least one ceramic-forming filler, said polymer insulating layer thus being able to be converted, at least on the 5 surface, to the ceramic state at high temperatures corresponding to fire conditions. The polymeric material of this single insulating layer is chosen from a polysiloxane (polyorganosiloxane) and an ethylene copolymer, or a blend thereof. 10 Other halogen-free fire-resistant security cables are known that have electrical conductors surrounded by a bilayer polymeric insulation. For example, document EP 1 347 464 describes a bilayer insulation capable of being converted, at least on the surface, into the 15 ceramic state at high temperatures corresponding to fire conditions. Each of the layers of the bilayer insulation comprises an ethylene/octene copolymer and a ceramic forming filler. However, it has been found that these security 20 cables of the prior art, even though they do have good fire resistance properties, are mechanically brittle. More particularly, the insulated electrical conductors are sensitive to the various mechanical stresses typically undergone by these cables when they are being 25 manufactured, being transported, being handled, being installed or being connected. Furthermore, their electrical resistance at high temperature in a wet environment, especially according to the IEC 60502-1 Standard, is insufficient because of- the presence of the 30 ceramic-forming fillers. The object of the present invention is to alleviate the drawbacks of the prior art techniques, in particular by providing a power cable that can be easily handled, limiting the risk of mechanically degrading the insulated 35 electrical conductors of which it is composed, while WO 2010/142917 3 PCT/FR2010/051154 still maintaining excellent fire resistance properties meeting the IEC 60331-21 Standard and improved electrical resistance meeting the IEC 60502-1 Standard. The subject of the present invention is a power 5 cable comprising one or more insulated electrical conductors, each of said insulated electrical conductors comprising an electrical conductor surrounded by an insulating layer, preferably an electrically insulating layer, the insulating layer comprising a first polymeric 10 layer surrounding the electrical conductor, the first layer being obtained from a first composition comprising a polymer matrix based on a thermoplastic polymer and at least one ceramic-forming filler, characterized in that the insulating layer further includes a crosslinked 15 second polymeric layer surrounding said first layer, the second layer being obtained from a second composition comprising a polyolefin-based polymer matrix containing substantially neither a ceramic-forming filler nor a halogenated compound. 20 In what follows: - the term "first composition comprising a polymer matrix based on a thermoplastic polymer" means that the polymer or polymers used in the first composition are predominantly (in % by weight in the matrix) one or more 25 thermoplastic polymers; and - the term "second composition comprising a polyolefin-based polymer matrix" means that the polymer or polymers used in the second composition are predominantly (in % by weight in the matrix) one or more 30 polyolefins. Furthermore, the term "halogenated compounds" is understood to mean a compound of any kind that contains at least one halogen element, such as for example fluoropolymers or chlorinated polymers, such as polyvinyl 35 chloride (PVC), halogenated plasticizers, halogenated- WO 2010/142917 4 PCT/FR2010/051154 containing mineral fillers, etc. By virtue of the invention, the crosslinked polyolefin-based second polymeric layer (external layer) mechanically protects the thermoplastic-polymer-based 5 first polymeric layer (internal layer). This property makes it possible in the insulating layer of each insulated electrical conductor to improve the mechanical properties of the cable, especially the hardness, abrasion resistance and tear resistance of the insulated 10 electrical conductors of which it is composed, to facilitate the installation of said cable and to make the cable more robust during its manufacture, while still guaranteeing very good adhesion between the first and second layers of the insulating layer. 15 More particularly, the insulating layer of the power cable of the invention has excellent mechanical temperature resistance (or hot creep) meeting the EN 60811-2-1 Standard. In addition, the power cable comprising the 20 insulating layer according to the invention meets the IEC 60331-21 Standard with excellent fire resistance properties. The electrical conductors are thus protected from fire or, in other words, the power cable makes it possible to ensure high quality fire behavior in terms of 25 at least cohesion of the electrically insulating ash. Another advantage of the insulating layer of the power cable of the invention relates to its electrical resistance. Owing to the absence of ceramic-forming filler in the external layer of the insulating layer of 30 the invention, the electrical resistance properties of the cable at high temperature according to the IEC 60502 1 Standard are significantly improved. Another advantage of the insulating layer of the power cable of the invention lies in the fact that it 35 significantly limits the evolution of toxic smoke when it WO 2010/142917 5 PCT/FR2010/051154 is subjected to extreme thermal conditions. Finally, the invention as thus defined has the advantage of being inexpensive since it makes it possible for the use of polyorganosiloxane in the insulating layer 5 of the insulated electrical conductors to be significantly limited, or even to be completely avoided, while still having very good fire resistance properties. First polymeric layer (or internal layer) 10 According to the present invention, the thermoplastic polymer of the first composition may be advantageously chosen from olefin polymers, acrylate or methacrylate polymers, vinyl polymers such as, for example, polyvinyl chloride, and fluoropolymers, or a 15 blend thereof. As preferred examples, the olefin polymers are chosen from: ethylene homopolymers; ethylene/octene (PEO) copolymers; ethylene/vinyl acetate (EVA) copolymers; ethylene/butyl acrylate (EBA) copolymers; ethylene/methyl 20 acrylate (EMA) copolymers; ethylene/ethyl acrylate (EEA) copolymers; ethylene/butyl acrylate (EBA) copolymers; ethylene/ethyl acrylate (EEA) copolymers; ethylene/propylene rubber (EPR) copolymers; ethylene/propylene/diene monomer (EPDM) copolymers; or a 25 blend thereof. In a preferred embodiment, the polymer matrix of the first composition comprises at least 95% by weight of thermoplastic polymer, preferably said polymer matrix comprising only one or more thermoplastic polymers. 30 In another preferred embodiment, the first composition comprises no more than 5% polyorganosiloxane by weight, preferably no more than 2% polyorganosiloxane by weight and even more preferably the first composition comprises no polyorganosiloxane. 35 The ceramic-forming filler used in the first WO 2010/142917 6 PCT/FR2010/051154 composition enabl-es the first layer to be converted, at least on the surface, into the ceramic state at high temperatures, corresponding to fire conditions, and thus to form what is called a "ceramicizing" first layer. This 5 ceramicizing layer therefore provides sufficient insulation when the second (external) layer has disappeared as a result of combustion phenomena. The ceramic-forming filler according to the invention may be chosen from a meltable ceramic filler 10 and a refractory filler, or a mixture thereof. The ceramic-forming filler preferably comprises at least one meltable ceramic filler and at least one refractory filler. More particularly, the meltable ceramic filler has 15 a melting point below a high temperature T and the refractory filler has a melting point above said temperature T. This temperature T is advantageously at least 7500C and possibly up to 11000C. The meltable ceramic filler may be at least one 20 mineral filler chosen from boron oxides (e.g. B 2 0 3 ), anhydrous zinc borates (e.g. 2ZnO.3B 2 0 3 ) or hydrated zinc borates (e.g. 4ZnOB 2

O

3

-H

2 0 or 2ZnO3B 2 03-3.5H 2 0), anhydrous boron phosphates (e.g. BPO 4 ) or hydrated phosphates, or one of their precursors. To give an example, calcium 25 borosilicates may be mentioned as boron oxide precursor. This meltable ceramic filler typically has a melting point below 5000C and gives rise to an amorphous phase (e.g. a glass) when the temperature exceeds 500 0 C. The refractory filler may be at least one mineral 30 filler chosen from magnesium oxides (e.g. MgO), calcium oxides (e.g. CaO), silicon oxides (e.g. SiO 2 or quartz), aluminum oxides (e.g. A1 2 0 3 ), chromium oxides (e.g. Cr 2 0 3 ), zirconium oxides (e.g. Zr0 2 ) and phyllosilicates such as, for example, montmorillonites, sepiolites, illites, 35 attapulgites, talcs, kaolins or micas (e.g. muscovite WO 2010/142917 7 PCT/FR2010/051154 mica 6SiO 2 3Al 2 0 3

K

2 0-2H 2 0), or one of their mixtures. Preferably, the ceramic-forming filler is -composed of two refractory fillers such as, for example, muscovite mica and calcium oxide CaO or one of its precursors (e.g. 5 calcium carbonate CaCO 3 ) and a meltable ceramic filler such as, for example, a boron oxide precursor. The amount of ceramic-forming fillers may be defined in that the first composition comprises at least 90 parts by weight of said fillers per 100 parts by 10 weight of polymers, preferably at most 250 parts by weight of said fillers per 100 parts by weight of polymers so as to limit the rheological problems in the composition. More particularly, the amount of meltable ceramic 15 filler may range from 5 to 100 parts by weight, preferably 20 to 80 parts by weight, and the amount of refractory filler may range from 50 to 200 parts by weight, preferably 70 to 120 parts by weight, per 100 parts by weight of polymers in the first composition. 20 In a preferred embodiment, the first composition is not crosslinked, or in other words the first layer formed around the electrical conductor is not crosslinked. Moreover, and in one particular embodiment, the first (or internal) polymer layer contains no halogenated 25 compound. Crosslinked second (or external) polymeric layer The crosslinked second polymeric layer is different from the first polymer layer as it is "non-ceramicizing" 30 since it contains substantially no ceramic-forming filler. The term "substantially" means that the second composition may furthermore include a ceramic-forming filler, but only as an additive. Consequently, the second layer may not have the properties of being able to be 35 converted, at least on the surface, to the ceramic state WO 2010/142917 8 PCT/FR2010/051154 at high temperatures corresponding to fire conditions, especially for example when the second composition comprises less than 50 parts by weight of ceramic-forming filler. 5 The polyolefin of the second composition may be advantageously chosen from ethylene homopolymers and copolymers, or a blend thereof. A preferred example of ethylene homopolymers, mention may be made of low-density polyethylene (LDPE). 10 As for ethylene copolymers, these may be advantageously chosen from: ethylene/octene (PEO) copolymers; ethylene/vinyl acetate (EVA) copolymers; ethylene/butyl acrylate (EBA) copolymers; ethylene/methyl acrylate (EMA) copolymers; ethylene/ethyl acrylate (EEA) 15 copolymers; ethylene/propylene rubber (EPR) copolymers; and ethylene/propylene/diene monomer (EPDM) copolymers; or a blend thereof. Ethylene/vinyl acetate (EVA) copolymers may be mentioned as preferred ethylene copolymer. 20 Preferably, the polymer matrix of the second composition differs from the polymer matrix of the first composition. In a preferred embodiment, the polymer matrix of the second composition comprises at least 95% by weight 25 of polyolefin, and preferably said polymer matrix comprises only one or more polyolefins. In another preferred embodiment, the second composition comprises no more than 5% polyorganosiloxane by weight, preferably no more than 2% polyorganosiloxane 30 by weight, and even more preferably the second composition comprises no polyorganosiloxane. According to a first variant, the second composition may further include at least one mineral filler different from a ceramic-forming filler. 35 The mineral filler may be a hydrated fire-retarding WO 2010/142917 9 PCT/FR2010/051154 mineral filler chosen especially from metal hydroxides such as, for example, magnesium dihydroxide (MDH) or aluminum trihydroxide (ATH) . The fire-retarding mineral fillers employed mainly act by a physical route by 5 decomposing endothermically, this having the consequence of lowering the temperature of the insulating layer and of limiting flame propagation along the cable. The mineral filler may also be a carbonate, such as calcium carbonate. 10 The amount of mineral fillers may be defined in that the second composition comprises at least 90 parts by weight of said fillers per 100 parts by weight of polymers, preferably at most 200 parts by weight of said fillers per 100 parts by weight of polymers, so as to 15 limit the rheological problems in the composition. The crosslinked second polymeric layer of this first variant is most particularly advantageous when it is combined with a non-crosslinked first polymeric layer comprising, as ceramic-forming filler, only one or more 20 refractory fillers. According to a second variant, the second layer is what is called "unfilled", or in other words the second layer, in addition to not containing a ceramic-forming filler, does not contain a hydrated fire-retarding 25 mineral filler and more particularly no mineral filler. The crosslinking of the second composition, to obtain the crosslinked second layer, may be carried out by conventional crosslinking techniques well known to those skilled in the art, such as for example silane 30 crosslinking in the presence of a crosslinking agent, peroxide crosslinking through the action of heat or crosslinking by photochemical means, such as irradiation by beta-radiation or irradiation by ultraviolet radiation in the presence of a photoinitiator. Silane crosslinking 35 in the presence of a crosslinking agent in the second WO 2010/142917 10 PCT/FR2010/051154 composition is preferred since it avoids the use of specific additional equipment such as radiation lamps or chambers for radiation crosslinking or salt-bath lines or steam tubes for peroxide crosslinking. 5 In one particularly preferred embodiment, the second composition contains only the polymer matrix and, if necessary, the components intended for crosslinking said second composition such as, for example, a crosslinking agent, and thus to form the crosslinked 10 second layer. The latter is therefore an unfilled crosslinked layer. The layers, whether the first polymeric layer and/or the second polymeric layer of the invention, may contain additives well known to those skilled in the art 15 such as, for example, surface treatment agents, antioxidants, waxes, etc. Process for manufacturing the insulating layer The process for manufacturing the electrically 20 insulating layer, and more generally the power cable, is well known to those skilled in the art. The preferred technique for forming the first and second compositions is extrusion using an extruder. The first and second compositions may be extruded 25 in two successive steps or concomitantly. In the latter case, the technique is referred to as coextrusion. The second layer is typically crosslinked after the second composition has been formed by extrusion. If the first layer is also crosslinked, the 30 crosslinking step typically takes place either directly after the step of forming the first composition by extrusion, or after the step of forming the second composition by extrusion. The first and second layers of the invention are 35 preferably in direct contact with each other, or in other WO 2010/142917 11 PCT/FR2010/051154 words the insulating layer comprises no interlayer between the first and second layers. The insulating layer may therefore be defined as a "bilayer". 5 Outer jacket The power cable of the invention may additionally comprise an outer jacket surrounding the insulated electrical conductor or conductors. This outer jacket is well known to those skilled in the art. It may burn 10 completely in places and be converted to residual ash through the effect of the high temperatures of a fire without in any way propagating the fire. The material of which the outer jacket is composed may for example be a polyolefin-based polymer matrix and 15 at least one hydrated fire-retarding mineral filler chosen especially from metal hydroxide such as, for example, magnesium dihydroxide and aluminum trihydroxide. The outer jacket may be a tubular jacket or else what is called a "filling" jacket, both types of jacket 20 being well known to those skilled in the art. A tubular jacket is preferred so as to ensure that the cross section of the cable has a circular shape, whereas a filling jacket is preferred when the insulated electrical conductors are arranged in parallel, one beside another 25 in the same plane. In both cases, the outer jacket is conventionally obtained by extrusion. Power cable According to a first variant, when the power cable 30 comprises an outer jacket as defined above, the power cable may furthermore include empty spaces provided between the outer jacket on the one hand and the insulated electrical conductor or conductors on the other. In this case, and to ensure that the cable has a 35 cylindrical shape over its entire length, the outer WO 2010/142917 12 PCT/FR2010/051154 jacket is preferably tubular. According to a second variant, when the power cable comprises an outer jacket as defined above, the power cable may further include a filling material between the 5 outer jacket on the one hand, and the insulated electrical conductor or conductors on the other. This filling material is well known to those skilled in the art and the purpose thereof is to ensure that the cable has a cylindrical shape over its entire 10 length. It is typically extruded around the insulated electrical conductor or conductors. The filling is composed for example of a polyolefin-based polymer matrix to which mineral fillers have been added such as, for 15 example, calcium carbonate and, particularly preferably, hydrated fire-retarding fillers such as those described above. For achieving greater adhesion of the ash on the filling material, it is preferred to use hydrated fire retarding mineral fillers combined with phyllosilicate 20 type mineral fillers. According to a third variant, when the power cable comprises an outer jacket as defined above, the outer jacket may be a filling jacket, especially when the power cable contains neither empty spaces nor a filling 25 material. According to another feature of the invention, and to guarantee an HFFR (halogen-free. flame retardant) cable, power cable, or in other words the elements of which said power cable is composed, preferably does/do 30 not contain halogenated compounds. More particularly, the first (or internal) polymeric layer and the crosslinked second (or external) polymeric layer contain no halogenated compound. 35 Process for manufacturing the insulating layer WO 2010/142917 13 PCT/FR2010/051154 Another subject of the invention is a process for manufacturing a power cable as described above in accordance with the invention, characterized in that it comprises the steps consisting in: 5 i. forming the insulating layer as described above around an electrical conductor; ii. optionally, assembling at least two insulated electrical conductors as obtained in step i; iii. optionally, extruding a filling material as 10 defined above around the insulated electrical conductor or conductors of step i or ii; and iv. optionally, extruding an outer jacket as defined above around the insulated electrical conductor or conductors of step i, ii or iii. 15 In one particular embodiment according to the invention, the thickness of the first (internal) layer ranges from 0.10 mm to 1.50 mm while the thickness of the second (external) layer ranges from 0.05 mm to 1.50 mm, especially when the cross section of the electrical 20 conductor ranges from 1.5 mm 2 to 4 mm 2 According to a first variant of this embodiment, when the cross section of the electrical conductor is 1.5 mm 2 , the thickness of the first layer preferably ranges from 0.30 mm to 0.80 mm, and more particularly to 25 0.60 mm. In this case, the thickness of the second layer preferably ranges from 0.10 mm to 0.50 mm. According to a second variant of this embodiment, when the cross section of the electrical conductor is 2.5 mm 2 , the thickness of the first layer preferably 30 ranges from 0.30 mm to 0.90 mm. In this case, the thickness of the second layer is preferably from 0.10 mm to 0.60 mm. According to a third variant of this embodiment, when the cross section of the electrical conductor is 35 4 mm 2 , the thickness of the first layer preferably ranges WO 2010/142917 14 PCT/FR2010/051154 from 0.35 mm to 1 mm. In this case, the thickness of the second layer preferably ranges from 0.10 mm to 0.70 mm. Other features and advantages of the present invention will become apparent in the light of the 5 following examples and the herein-appended figures, said examples and figures being given by way of illustration and in no way being limiting. Figure 1 shows a schematic cross-sectional view of a power cable in a first embodiment according to the 10 invention. Figure 2 shows a schematic cross-sectional view of a power cable in a second embodiment according to the invention. Figure 3 shows a schematic cross-sectional view of 15 a power cable in a third embodiment according to the invention. For the sake of clarity, the same elements have been denoted by identical references in these figures. Likewise, only the elements essential for understanding 20 the invention have been shown schematically, and have not been drawn to scale. The power cable shown in Figure 1 comprises three insulated electrical conductors, 1, 2a, 2b and an outer jacket 3 surrounding all three insulated electrical 25 conductors, which in particular are twisted together, the insulated electrical conductors having a substantially circular cross section. Each of the three insulated conductors is made up of an electrical conductor 1 surrounded by a first 30 insulating layer 2a (internal layer) and by a second insulating layer 2b (external layer) directly in contact with said first insulating layer 2a. The first and second insulating layers 2a, 2b are as defined in the present invention. 35 The outer jacket 3 leaves empty spaces 4 between it WO 2010/142917 15 PCT/FR2010/051154 and the set of insulated electrical conductors that it surrounds. This outer jacket 3 is tubular since it has an annular shape in cross section. The outer jacket 3 is produced from a fire 5 retarding composition comprising a polyolefin-based polymer matrix. The power cable shown in Figure 2 comprises five insulated electrical conductors 1, 2a, 2b or 1, 2b and an outer jacket 3 surrounding all five insulated electrical 10 conductors, the insulated electrical conductors having a substantially circular cross section. Four of the five insulated electrical conductors 1, 2a, 2b are respectively surrounded by a first insulating layer 2a (internal layer) and by a second insulating 15 layer 2b (external layer) directly in contact with said first insulating layer 2a. The first and second insulating layers 2a, 2b are as defined in the present invention. The remaining insulated electrical conductor 1, 2c 20 is typically connected to ground. It comprises an electrical conductor surrounded by a polymeric insulating layer 2c. This layer may be a monolayer or a bilayer, for example of the same nature as the first layer 2a and/or as the second layer 2b of the invention. 25 The five insulated conductors are assembled, and especially twisted, around a strength member 5. A filling material 6 surrounds all five insulated electrical conductors. Finally, an outer jacket 3 is extruded around all 30 five insulated electrical conductors and the filling material. The cylindrical shape, or in other words the circular cross section, of the power cable of the invention as shown in Figures 1 and 2 is in no way 35 limiting.

WO 2010/142917 16 PCT/FR2010/051154 The power cable may also have what is called a "flat" cross section as illustrated in Figure 3. Figure 3 shows a power cable according to the invention in which the insulated electrical conductors 1, 2a, 2b, which are 5 four in number in this embodiment, are arranged in parallel alongside one another in the same longitudinal mid-plane P of the power cable. The set of insulated electrical conductors arranged in this way forms a strip of insulated electrical conductors, this strip being 10 covered with an outer jacket 3 so as to keep the insulated electrical conductors 1, 2a, 2b in the longitudinal mid-plane P. Examples 15 Power cables were produced with electrical conductors surrounded by various types of insulating layer according to the prior art and according to the invention. The structure and the nature of these cables are detailed in Table 1 below, divided into two Tables la 20 and lb. Each of the power cables comprises N insulated electrical conductors, one electrical conductor of which is connected to ground. The N-1 electrical conductors are detailed in Table la, whereas said insulated electrical conductor connected to ground is detailed in Table 1b. 25 The power cable structure as such, which may be taken into account for understanding Tables la and 1b, is as shown in Figure 2.

N4- CN I r) .~ U) a)E0 Q >I >1 '-4 a)) I I (00-H i-I I LA -I o0 ) a) 0 >1 00 0)0 >H 0 H a)) H J I in v_ _ _ _ _ _ _d_0 ) _ _ _ 0.) >i H 4N a) -1 0 0 rHii Q) 4-0 Q 4 . Nq U)H -4 H W( >I -H1 4-4 4-44-4 0 ~ 4-4 ) a) a o~~~~ .- r-Ua 4J Q)~4 J i-I~ ~ U !) ~ - 0).- 4-4 H!) ( J (0 1-1 eq~- LW~4 a) ~ a) ~ ~ oi Z (o .11 a) m4J~ a~4) w ) .4 -I 0(0 U W- .0 (0 1 4-0 E UU !J 44 E-- O A U -H -4 Co o> C 0 0 C0 OD 01 nC U) In LA LA n 0 -4 0 z -4 0 0 o~ 0-04 z 4-4 C 0> 0 0 0 0) LA CA 0 4H -) 0 0 4) 00 00 00 ) 01 0 44 0 H (Ni (N 0 (N a) 0 (N m 0 Ch o; 0 ) 0 H 0 a) Q (1 a) a) (z>1 Q) -- s 0 M 0 (a 0 -+ 1o 0 r44 O QJ) 0 ) Ho H1 H- 44 U (n U o 02)- 02 H 13 02H 02A V) 0 ro 02 Id It a0 0 ) w O~ - J0 H Q H 0 )0 0 o .r Iti H4H 2.4J- ~ *H44-4 Zn '-I '-I in -1 0u C.)H 2 0 4 t30) .3.N4E 0)W w01 00 C~ ~ 4 4 U) 00a) 0 o 0 ~~ ~ >1- '0 *r 'd0) _~ 4-4 4 a)4 U 4 z0 -~ r4 .1.10) .)0).1 4 r-) 0)0 0) z u> 0 . 4- 44 4-O 1 - ) 0 0)I -L 1-0) (1 H) (40 W(0z 0 > 4> '-4r4 o wo w 0 4U 0 4 1 > '-a4-lE l 4- 0( 0- - 4 ri4 - i o i o (0 -Z444 04 ( - or '-I '-4 U.) 0 U In) Ln 0 nO *H Co 0 0r4 CD 0) uU G)) *r 0C)O 0 E1 if A a)Lf4J4 Co a) a m > w w0) 0r O0 i 0 r-I +, 9 0 r 00W (0 0 er-i 9f- f-- 0 ) -1 ) 1 U) r ~ U) 0) H U H (10 H 4 .3) - d .- -. H C4 H > - ri - -r J U *H .

>, 4- j u -r - A- ) 00H.a o 0 C'4 0 -I -I) a)LI OD r 0 a 0 Q 0 -I r-H In N) NOOH o1 u 0 0 00 E-1~~ 0 4~ 0o-: 4-4 (o ' .- 'i W OO0 a 04 4J I- H C) 1 ;2; -HO 10 HH 0 0 : Ql OQ) u 0 H 4 H J -4 H 4-4 1 C 41 -4 () m a ) z1 HH H ) 00 4 1H -4 ) H4J Hi NZ W- HOU -' > 0 u 0 a0 H4 H1 H1 H4- 4 0 *H WOO1 : (1)0 r-I 00 a) U) 0 0 41 a) 10 04C

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0 100 4 4 4-4 -H 14 4-4 44-l ' 0 0 ) 0 ) U : v Z 4-4 444 In '-I in 0 0 -1 (1(1 0~ 0 ) uJ r 00 4-J o 4-4 ) -1 4 ~ 0 0>1 )( 4-) 1 -m 0 4J4 4 U) U Q) . 000 J-) a)) >1A U) J 0% 0 H d 0 0)00 *0)i H- I 4 I) _0 1 a) Z a )O M ,W0 >1 >1 1 r- E-4 4 ) 4-) r- z Q) ( 0 0 1 ) a) Q) -l 0I0)r 0) 0Jl4Jf -'-I 0 U4 -H 4 -H -X '-Z4 ' N 0 2c WO 2010/142917 23 PCT/FR2010/051154 In Table 1: - The term "Ceramicizing thermoplastic layer 1" refers to a layer obtained from an uncrosslinked EVA material containing 100 to 200 parts by weight of a 5 mixture of two refractory fillers, such as muscovite mica (50 to 150 parts by weight) and CaO (5 to 50 parts by weight), and 5 to 50 parts by weight of zinc borate, the parts by weight being expressed with respect to 100 parts by weight of EVA; 10 - the term "Ceramicizing thermoplastic layer 2" refers to a layer obtained from an uncrosslinked PEO material containing 100 to 200 parts by weight of magnesium oxide and 5 to 50 parts by weight of zinc borate, the parts by weight being expressed with respect 15 to 100 parts by weight of PEO; - the term "Ceramicizing thermoplastic layer 3" refers to a layer obtained from an uncrosslinked PEO material containing 100 to 200 parts by weight of muscovite mica and 5 to 50 parts by weight of zinc 20 borate, the parts by weight being expressed with respect to 100 parts by weight of PEO; - the term "Ceramicizing thermoplastic layer 4" refers to a layer obtained from an uncrosslinked PEO material containing 100 to 200 parts by weight of 25 magnesium oxide (MgO), the parts by weight being expressed with respect to 100 parts by weight -of PEO; - the term "Silicone layer" refers to a layer obtained from a crosslinked polyorganosiloxane material sold by Wacker under the reference R502/75; 30 - the term "Unfilled XLPE" refers to a crosslinked unfilled polyethylene material sold by BOREALIS under the reference Visico 4423; - the term "Filled XEVA" refers to a crosslinked EVA material containing fire-retarding fillers, sold by 35 Padanaplast under the reference Cogegum GFR 360; WO 2010/142917 24 PCT/FR2010/051154 - the term "Filled XLPE" refers to a crosslinked polyethylene material containing fire-retarding fillers, which is sold by Padanaplast under the reference Cogegum GFR 325; 5 - the term "cohesion 1" refers to an HFFR filling material (or filling) sold by CONDOR under the reference CC420; - the term "cohesion 2" refers to an HFFR filling material (or filling) sold by CONDOR under the reference 10 Confill D-F0704; - the term "Filling thickness" refers to the thickness of the filling between the internal periphery of the outer jacket and the external periphery of the insulating layer of the insulated electrical- conductor; 15 and - the term "HFFR jacket" refers to an uncrosslinked HFFR polyolefin material sold by Polyone under the reference ECCOH 5860. 20 Fire resistance tests Each of the cables referenced 1 to 7 in Table 1 underwent fire resistance tests. The fire resistance tests were carried out according to the following two standards: IEC 60331-21 and DIN 4102-12. 25 The IEC 60331-21 Standard consists in. subjecting a power cable to its nominal voltage when it is suspended horizontally above a flame having a temperature of at least 750 0 C for a specified period of time, but with no mechanical stress. Over this period, it is checked 30 whether there is a short circuit or a rupture of the electrical conductors. The test is passed when there is neither a short circuit nor rupture of the electrical conductors during the test and the following 15 minutes. A power cable having passed the test for 30 minutes is 35 then classified as FE30. When it passes the test for WO 2010/142917 25 PCT/FR2010/051154 90 minutes or for 180 minutes, it is then classified as FE90 to FE180 respectively. The DIN 4102-12 Standard consists in subjecting a power cable together with its fasteners in a furnace at 5 least 3 meters in length for a specified period of time according to a standardized (ISO 834) temperature curve. In addition, the power cable and its fasteners are subjected to the maximum admissible weight and to the prescribed loads. Since the electrical conductors - are 10 under their service voltage, they must neither break nor create short circuits, otherwise the test would be considered a failure. A power cable having passed the test for 30 minutes at 8420C is then classified as E30. When it passes the test for 60 minutes at 9450C or for 15 90 minutes at 10600C, it is then classified as E60 or E90 respectively. This type of test, close to the reality of a fire, relates not only to the power cable but also to the systems for fastening said cable. Table 2 below shows the very satisfactory results 20 of the fire resistance tests carried out on the power cables according to the present invention (cables referenced 1 to 5 and 9 to 11) in accordance with the IEC 60331-21 Standard. Remarkably, it may also be noted that the cable referenced 3 according to the present 25 invention, even with no filling, meets this standard. Furthermore, when a filling is present (cables referenced 1, 2, 4, 5, 10 and 11), the DIN 4102-12 Standard is met more easily. Moreover, 'very satisfactory results are observed 30 with the cables referenced 9 to 11, the respective internal layers of which contain, as ceramic-forming filler, only a refractory filler. In view of the results for the cables referenced 10 and 11, it should also be noted that the combination, on 35 the one hand, of an internal layer containing, as WO 2010/142917 26 PCT/FR2010/051154 ceramic-forming filler, only a refractory filler and, on the other hand, of a crosslinked external layer based on a filled ethylene polymer, especially one containing a fire-retarding filler, particularly surprisingly enables 5 the DIN 4102-12 Standard to be met. Finally, the cables referenced 1 to 5 and 9 to 11 have fire resistance properties at least equivalent, if not better, than the cable referenced 6, the manufacturing cost of which is much higher (because of 10 the presence of polyorganosiloxane in the insulating layers of the electrical conductors). Table 2 Cable 1 2 3 4 5 6 reference IEC FE180 FE180 FE180 FE180 FE180 FE180 60331-21 (> 180 (> 180 (> 180 (> 180 (> 180 (> 180 min) min) min) min) min) min) DIN E30 E30 Failure E30 E30 Failure 4102-12 (> 30 (> 30 (> 30 (> 30 min) min) min) min) 15 WO 2010/142917 27 PCT/FR2010/051154 Table 2 (continued) Cable 7 8 9 10 11 reference IEC FE90 FE90 FE180 FE180 FE180 60331-21 (> 90 (> 90 min) (> 180 (> 180 (> 180 min) (FE180 min) min) min) (does not test not pass carried FE180) out) DIN Failure Failure Failure E30 (> 30 E30 (> 4102-12 min) min) 5 Electrical resistance test The cables referenced 2, 4 and 8 in Table 1 underwent electrical resistance tests, the outer jackets of said cables being removed beforehand. The electrical resistance tests were carried out according to the 10 IEC 60502-1 (paragraph 17.2) Standard. The IEC 60502-1 Standard consists in immersing a ring of insulated electrical conductors having a minimum length of 5 meters in water at the maximum temperature for the electrical conductors in normal service (e.g. 15 90 0 C) for at least one hour before the test. A DC voltage of between 80 V and 500 V is then applied between the ring of insulated electrical conductors and the water for a sufficient time (between 1 and 5 minutes). Finally, the transverse resistivity is calculated 20 from the insulation resistance according to the following formula: p = 270RL/ln (D/d) in which: 25 p is the transverse resistivity in ohms.m; WO 2010/142917 28 PCT/FR2010/051154 R = insulation resistance in ohms; L = length of the insulated conductor in m; D = outside diameter of the insulating jacket in mm; and 5 d = inside diameter of the insulating jacket in mm. Table 3 below shows the very satisfactory results of the electrical resistance tests carried out on the power cables according to the present invention (cables referenced 2, 4 and 10) in contrast to the cable 10 referenced 8 according to the prior art. Table 3 Cable reference 2 4 8 10 p (ohms.m) at 90 0 C > 1 x 108 2 x 1012 6 x 106 > 1 x 10 15 Hot creep test The NF EN 60811-2-1 Standard describes the measurement of the hot creep of a material under load. The corresponding test is also commonly referred to as hot set test. 20 Specifically, it consists in testing one end of a specimen of material with a weight corresponding to application of a stress equivalent to 0.2 MPa and in placing the assembly in a heated oven at 200(±l)OC for a period of 15 minutes. After this time, the hot elongation 25 under load of the specimen, expressed in %, is recorded. The suspended weight is then removed and the specimen is left in the oven for a further 5 minutes. The remaining permanent elongation, also called the set, is then measured, before being expressed in %. 30 It should be recalled that the more crosslinked a material, the lower the elongation and set values. It should also be pointed out that if a specimen were to break during the test, under the combined action of the WO 2010/142917 29 PCT/FR2010/051154 mechanical stress and the temperature, the result of the test would then logically be considered as a failure. This test was carried out on the insulating layer of the N-1 electrical conductors of the cables referenced 5 1 to 11. The results are given in Table 4 below. Table 4 Cable 1 2 3 4 5 6 reference Hot creep Passes Passes Passes Passes Passes Passes test 10 Table 4 (continued) Cable 7 8 9 10 11 reference Hot creep Fails Fails Passes Passes Passes test 15 It should be noted that the insulating layers according to the invention (cables referenced 1 to 5 and 9 to 11) successively pass the NF EN 60811-2-1 Standard 20 in that the elongation under load and the set are less than 175% and 25% respectively. Even though the bilayer insulation of the cable referenced 6 also satisfactorily passes this standard, it is well to recall that it has fire resistance properties inferior to those of the 25 cables according to the invention while being economical since it contains polyorganosiloxanes.

Claims (10)

1. Power cable comprising one or more insulated electrical conductors, each of said insulated electrical 5 conductors comprising an electrical conductor surrounded by an insulating layer, the insulating layer comprising a first polymeric layer (2a) surrounding the electrical conductor, the first layer (2a) being obtained from a first composition comprising a polymer matrix based on a 10 thermoplastic polymer and at least one ceramic-forming filler, characterized in that the insulating layer further includes a crosslinked second polymeric layer (2b) surrounding said first layer, the second layer (2b) being obtained from a second composition comprising a 15 polyolefin-based polymer matrix containing substantially neither a ceramic-forming filler nor a halogenated compound.

2. Cable according to claim 1, characterized in that the thermoplastic polymer of the first composition 20 is chosen from olefin polymers, acrylate or methacrylate polymers, vinyl polymers and fluoropolymers, or a blend thereof.

3. Cable according to claim 1 or 2, characterized in that the ceramic-forming filler is chosen from a 25 meltable ceramic filler and a refractory filler, or a mixture thereof.

4. Cable according to any one of the preceding claims, characterized in that the first layer (2a) is not crosslinked. 30

5. Cable according to any one of the preceding claims, characterized in that the polyolefin of the second composition is chosen from ethylene homopolymers and copolymers, or a blend thereof.

6. Cable according to any one of the preceding 35 claims, characterized in that the first composition WO 2010/142917 31 PCT/FR2010/051154 and/or the second composition comprise no more than 5% polyorganosiloxane by weight.

7. Cable according to any one of the preceding claims, characterized in that the crosslinking of the 5 second composition, to obtain the crosslinked second layer (2b), is silane crosslinking in the presence of a crosslinking agent in the second composition.

8. Cable according to any one of claims 1 to 7, characterized in that it further includes an outer jacket 10 (3) surrounding the insulated electrical conductor or conductors.

9. Cable according to claim 8, characterized in that it further includes a filling material (6) between the outer jacket (3) on the one hand, and the insulated 15 electrical conductor or conductors on the other.

10. Cable according to any one of the preceding claims, characterized in that it contains no halogenated compounds.