Fire Resistant Electric Cable

Abstract

A cable includes a conductor and a first semiconductive layer arranged in a radially outer position with respect to the conductor. An insulating layer is arranged in a radially outer position with respect to the first semiconductive layer. A second semiconductive layer is arranged in a radially outer position with respect to the insulating. A conductive screen is arranged in a radially outer position with respect to the second semiconductive layer. A heat block layer is arranged in a radially outer position with respect to the conductive screen. The heat block layer includes a layer made of a fire resistant or a flame retardant halogen-free material. A rubberized glass fiber tape is arranged in a radially outer position with respect to the heat block layer. An outer sheath is arranged in a radially outer position with respect to the rubberized glass fiber tape.

Claims

1-9. (canceled)

10. A cable, comprising: a conductor; a first semiconductive layer arranged in a radially outer position with respect to the conductor; an insulating layer arranged in a radially outer position with respect to the first semiconductive layer and directly contacting the first semiconductive layer; a second semiconductive layer arranged in a radially outer position with respect to the insulating layer and directly contacting the insulating layer; a conductive screen arranged in a radially outer position with respect to the second semiconductive layer; a heat block layer arranged in a radially outer position with respect to the conductive screen, the heat block layer comprising a layer made of a fire resistant or a flame retardant halogen-free material; a rubberized glass fiber tape arranged in a radially outer position with respect to the heat block layer and having a rubberized surface outward facing; and an outer sheath arranged in a radially outer position with respect to the rubberized glass fiber tape and directly contacting the rubberized surface of the rubberized glass fiber tape.

11. The cable according to claim 10, wherein the rubberized glass fiber tape is bonded to the outer sheath.

12. The cable according to claim 10, further comprising a first glass fiber tape radially interposed between the conductive screen and the rubberized glass fiber tape.

13. The cable according to claim 12, further comprising a second glass fiber tape radially interposed between the conductive screen and the rubberized glass fiber tape.

14. The cable according to claim 10, further comprising a glass fiber tape radially interposed between the conductive screen and the heat block layer.

15. The cable according to claim 10, further comprising a glass fiber tape radially interposed between the heat block layer and the rubberized glass fiber tape.

16. The cable according to claim 10, further comprising: a first glass fiber tape radially interposed between the conductive screen and the heat block layer; and a second glass fiber tape radially interposed between the heat block layer and the rubberized glass fiber tape.

17. The cable according to claim 10, comprising a metallic armor radially interposed between the heat block layer and the rubberized glass fiber tape.

18. The cable according to claim 17, further comprising a first glass fiber tape arranged in a radially outer position with respect to the heat block layer, wherein the metallic armor is radially interposed between the first glass fiber tape and the rubberized glass fiber tape.

19. The cable according to claim 10, wherein the outer sheath is made of a flame retardant halogen-free material.

20. The cable according to claim 10, wherein the outer sheath is made of a mud and/or oil resistant material.

21. A cable, comprising: a conductor; a first semiconductive layer arranged in a radially outer position with respect to the conductor; an insulating layer arranged in a radially outer position with respect to the first semiconductive layer; a second semiconductive layer arranged in a radially outer position with respect to the insulating layer; a conductive screen arranged in a radially outer position with respect to the second semiconductive layer; a first glass fiber tape arranged in a radially outer position with respect to the conductive screen; a heat block layer arranged in a radially outer position with respect to the first glass fiber tape, the heat block layer comprising a layer made of a fire resistant or a flame retardant halogen-free material; a second glass fiber tape arranged in a radially outer position with respect to the heat block layer; a metallic armor arranged in a radially outer position with respect to the second glass fiber tape; a rubberized glass fiber tape arranged in a radially outer position with respect to the metallic armor and having a rubberized surface outward facing; and an outer sheath arranged in a radially outer position with respect to the rubberized glass fiber tape.

22. The cable according to claim 21, wherein the insulating layer directly contacts the first semiconductive layer.

23. The cable according to claim 21, wherein the second semiconductive layer directly contacts the insulating layer.

24. The cable according to claim 21, wherein the outer sheath directly contacts the rubberized surface of the rubberized glass fiber tape.

25. The cable according to claim 24, wherein the rubberized glass fiber tape is bonded to the outer sheath.

26. The cable according to claim 21, wherein the outer sheath is made of a flame retardant halogen-free material.

27. The cable according to claim 21, wherein the outer sheath is made of a mud and/or oil resistant material.

28. A cable, comprising: a conductor; a first semiconductive layer arranged in a radially outer position with respect to the conductor; an insulating layer arranged in a radially outer position with respect to the first semiconductive layer and directly contacting the first semiconductive layer; a second semiconductive layer arranged in a radially outer position with respect to the insulating layer and directly contacting the insulating layer; a conductive screen arranged in a radially outer position with respect to the second semiconductive layer; a first glass fiber tape arranged in a radially outer position with respect to the conductive screen; a heat block layer arranged in a radially outer position with respect to the first glass fiber tape, the heat block layer comprising a layer made of a fire resistant or a flame retardant halogen-free material; a second glass fiber tape arranged in a radially outer position with respect to the heat block layer; a metallic armor arranged in a radially outer position with respect to the second glass fiber tape; a rubberized glass fiber tape arranged in a radially outer position with respect to the metallic armor and having a rubberized surface outward facing; and an outer sheath arranged in a radially outer position with respect to the rubberized glass fiber tape and directly contacting the rubberized surface of the rubberized glass fiber tape.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0038] 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 sole FIGURE, which shows a schematic cross-section view of a fire resistant medium and high voltage electric cable according to an exemplary embodiment of the present invention.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0039] Referring to the FIGURE, a cable is indicated with numeral reference 100. Cable 100 is designed to be used, for example, in off-shore installations.

[0040] Cable 100 comprises, in the radially innermost portion thereof, a core 105 and, in the radially outer portion thereof, an outer sheath 200.

[0041] The core 105 includes at least one conductor 110, an insulating system 115 arranged in a radially outer position with respect to the conductor 110 and a conductive screen 150 arranged in a radially outer position with respect to the insulating system 115.

[0042] The insulating system 115 comprises a first semiconductive layer 120 arranged in a radially outer position with respect to the conductor 110 and in direct contact with the conductor 110, an insulating layer 130 arranged in a radially outer position with respect to the first semiconductive layer 120 and in direct contact with the first semiconductive layer 120 and a second semiconductive layer 140 arranged in a radially outer position with respect to the insulating layer 130 and in direct contact with the insulating layer 130.

[0043] While a single core 105 is shown in the FIGURE and described below, the following description applies to multicore cables as well.

[0044] The first semiconductive layer 120 mitigates concentration of electric field inside the cable 100 by uniformly distributing charges on the surface of the conductor 110. Furthermore, the first semiconductive layer 120 minimizes degradation of the insulating layer 130, which is caused by ionization, by filling the gaps formed between the conductor 110 and the insulating layer 130.

[0045] The insulating layer 130 insulates the conductor 110 from outside by covering and protecting the conductor 110 so that current may not flow outside of the cable 100.

[0046] The second semiconductive layer 140 uniformly distributes electrical stress inside the insulation system 115.

[0047] The conductor 110 can be made of a rod or of stranded wires made of an electrically conductive metal, such as copper or aluminum. For example, the conductor 110 comprises tinned stranded and compressed copper wires.

[0048] The layers 120, 130 and 140 of the cable insulating system 115 can be made of extruded polymeric material. Examples of suitable polymeric materials are polyethylene homopolymers or copolymers, such as cross-linked polyethylene (XLPE), or elastomeric ethylene/propylene (EPR) or ethylene/propylene/diene (EPDM) copolymers, also cross-linked, or thermoplastic materials, for example propylene-based materials as disclosed in WO 02/03398, WO 04/066317, WO 04/066318, WO 07/048422, WO11/092533 and WO 08/058572. The semiconducting layers material further comprises a suitable amount of conductive filler, for example carbon black.

[0049] Layers 120, 130 and 140 forming the insulating system 115 are preferably coextruded.

[0050] The conductive screen 150 can be made of a metallic tape or a metallic braid of copper, aluminum, a copper alloy, an aluminum alloy or a combination thereof.

[0051] For example, the conductive screen 150 is made of a tinned annealed copper wire braid. The conductive screen 150 can connect the cable 100 with the ground.

[0052] A semiconducting tape (not illustrated) made, for example, of the same material of the second semiconductive layer 140 can be interposed between the conductive screen 150 and the second semiconductive layer 140.

[0053] A second glass fiber tape 160 is arranged in a radially outer position with respect to the conductive screen 150.

[0054] A polymeric tape (not illustrated) made, for example, of polyethylene terephthalate (PET) can be interposed between the second glass fiber tape 160 and the conductive screen 150. The protecting tape allows easing the stripping of the radially outer layer/s during installation.

[0055] The second glass fiber tape 160 includes glass fibers. The glass fiber tape can comprise a layer made of polymeric material, for example ethylene-propylene diene monomer (EPDM), ethylene-vinyl acetate (EVA), linear low density polyethylene (LLDPE) and mixture thereof, avoiding damaging the edges of the tape. Self-supporting (not supported by a further layer) woven glass fiber tape are also suitable.

[0056] A heat block layer 165 is arranged in a radially outer position with respect to the second glass fiber tape 160.

[0057] The heat block layer 165 is made of an extruded polymeric material which can be fire resistant or halogen-free flame retardant (LSoH). Examples of fire resistant materials are ceramifying silicone or polymer materials containing ceramifying charges. Examples of halogen-free flame retardant materials are optionally cross-linked ethylene homopolymer or copolymer or mixture thereof charged with a flame retardant filler, such as aluminum or magnesium hydroxide. Preferably, the halogen-free flame retardant material for the heat block layer of the invention is a mixture comprising ethylene vinyl acetate (EVA) and linear low density polyethylene (LLDPE) comprising from 30 wt % to 70 wt % of aluminum or magnesium hydroxide with respect to the total weight of the mixture.

[0058] A first glass fiber tape 170 is arranged in a radially outer position with respect to the heat block layer 165. The first glass fiber tape 170 is made substantially as the above in connection with the second glass fiber tape 160

[0059] When the first glass fiber tape 170 and/or the second glass fiber tape 160 comprise a layer made of polymeric material, the positioning of the layer (whether in contact with the heat block barrier 165 or not) is inconsequential.

[0060] In a preferred embodiment, both the first and the second glass fiber tapes 170, 160 are provided in radially inner and outer position with respect to the heat block layer 165 so as their support tapes are in direct contact with the heat block layer 165.

[0061] In case of fire, the second glass fiber tape 160 and the first glass fiber tape 170 firmly keep in position the heat block layer 165, so that the glass fiber tape 160, the heat block layer 165 and the glass fiber tape 170 define an assembly 175 which allows delaying both propagation of the fire within the core 105 and heat build-up in the insulation system 115.

[0062] A metallic armor 180 is arranged in a radial outer position with respect to the first glass fiber tape 170.

[0063] The metallic armor 180 can be made of a metallic tape or a metallic braid of galvanized steel, copper, aluminum, a copper alloy, an aluminum alloy or a combination thereof. The metallic armor can also perform as electric screen.

[0064] For example, the metallic armor 180 is made of a tinned annealed copper wire braid.

[0065] In certain cables applications, the metallic armor 180 can be missing.

[0066] A rubberized glass fiber tape 190 is arranged in a radially outer position with respect to the metallic armor 180.

[0067] The rubberized glass fiber tape 190 includes glass fibers, preferably in woven form, arranged on a support tape made of an elastomeric material selected, for example, from the group comprising ethylene-propylene diene monomer (EPDM), ethylene-vinyl acetate (EVA), linear low density polyethylene (LLDPE) and mixture thereof.

[0068] The elastomeric material of the rubberized glass fiber tape has the function of bonding the tape to the outer sheath during extrusion and, optionally, curing of the latter, to hold the sheath in place when burning, and of supporting the glass fibers during production to avoid damages while winding.

[0069] An outer sheath 200 is arranged in a radially outer position with respect to the rubberized glass fiber tape 190, in direct contact with the elastomeric support thereof.

[0070] The outer sheath 200 is preferably made of a halogen free, flame retardant material analogous to that used for the heat block layer. More preferably, the outer sheath 200 is made of a halogen free, flame retardant and mud and/or oil resistant polymeric material. Examples of halogen free, flame retardant and mud and/or oil resistant polymeric (preferably thermosetting) materials are alkylene/alkyl acrylate copolymer or a mixture of alkylene/alkyl acrylate copolymers, preferably having an average content of alkyl acrylate comonomer of at least 40 wt % by weight with respect to the weight of the copolymer/s, these materials being charged with a flame retardant filler, such as aluminum or magnesium hydroxide. For example, the alkylene comonomer of copolymer is an ethylene co-monomer. For example, the alkyl acrylate comonomer is selected from methyl acrylate and butyl acrylate.

[0071] The combination of rubberized glass fiber tape 190 and outer sheath 200 provide a barrier to the propagation of the fire towards the innermost layers of the cable 100.

[0072] In case of multicore cables, two or more cores are stranded, a filling material is provided into the gaps between the cores and the heat block layer or, if present, the second glass fiber tape is provided to enclose the cores and the filling material. The structure of the multicore cable in the radial outer portion with respect to the heat block layer or, if present, the second glass fiber tape is identical to the one discussed above with respect to the cable 100 of the FIGURE.

[0073] A sample of a cable having the construction of cable 100 and having the construction as from Table 1 has been subjected to fire tests according to IEC 60331-21 at 750? C.

TABLE-US-00001 TABLE 1 Conductor Tinned stranded and compressed copper (STCC), IEC 60228, 2004-11, class 2 First semiconductive ethylene-propylene rubber layer Insulating layer ethylene-propylene rubber, IEC 60092-360, 2014-04 Second ethylene-propylene rubber semiconductive layer Conductive screen Tinned annealed copper wire braid Protecting tape PET tape Second glass fiber tape Rubberized glass fiber tape Heat block layer EVA/LLDPE 85:15 + aluminium hydroxide (180 phr) First glass fiber tape Rubberized glass fiber tape Armor Tinned annealed copper wire braid Polymeric glass fiber Rubberized glass fiber tape tape Outer sheath ethylene vinyl acetate SHF 2 (IEC 60092-360, 2014-04)

[0074] The cable repeatedly resisted for about 2 hours before short circuit between the conductor and the conductive screen being detected.