ENERGY CABLE HAVING A CROSSLINKED ELECTRICALLY INSULATING LAYER, AND METHOD FOR EXTRACTING CROSSLINKING BY-PRODUCTS THEREFROM

Abstract

The present invention relates to an energy cable comprising a cable core comprising an electric conductor and a crosslinked electrically insulating layer, wherein the cable core further comprises a microporous material having a bimodal pore volume distribution with a first peak of the distribution having a maximum at a pore diameter value within the range 5.5-6.5 and a second peak of the distribution having a maximum at a pore diameter value within the range 7.5-8.5 , the maximum values of the first and the second peak corresponding to an incremental pore volume of at least 410.sup.3 cm.sup.3/g. The present invention also relates to a method for extracting methane crosslinking by-products from a crosslinked electrically insulating layer of an energy cable.

Claims

1. An energy cable comprising a cable core comprising an electric conductor and a crosslinked electrically insulating layer, wherein the cable core further comprises a microporous material having a bimodal pore volume distribution with a first peak of the distribution having a maximum at a pore diameter value within the range 5.5-6.5 and a second peak of the distribution having a maximum at a pore diameter value within the range 7.5-8.5 , the maximum values of the first and the second peak corresponding to an incremental pore volume of at least 410.sup.3 cm.sup.3/g.

2. The energy cable according to claim 1, wherein the second peak has a maximum value higher than the maximum value of the first peak.

3. The energy cable according to claim 1, wherein the cumulative pore volume of the pores having a diameter up to 10 of the microporous material is equal to or higher than 50.10.sup.1 cm.sup.3/g.

4. The energy cable according to claim 1, wherein the microporous material is selected from: hyper-crosslinked polymers; activated carbons; alumino-silicates; metal-organic frameworks (MOFs); porous aromatic frameworks (PAFs); covalent organic frameworks (COFs) and mixture thereof.

5. The energy cable according to claim 4, wherein the hyper-crosslinked polymer comprises dichloroxylene (DCX) and 4,4-bis(chloromethyl)-1,1-biphenyl (BCMBP) as constitutional repeating units.

6. The energy cable according to claim 1, wherein the electric conductor comprises a plurality of stranded electrically conducting filaments and the microporous material is within voids among said filaments.

7. The energy cable according to claim 1, wherein the cable core comprises at least one semiconducting layer and the microporous material is into or in contact with at least one semiconducting layer.

8. The energy cable according to claim 7, wherein the cable core comprises an inner and an outer semiconducting layer and the microporous material is into or in contact with the inner semiconducting layer.

9. The energy cable according to claim 1, wherein the electric conductor comprises a plurality of stranded electrically conducting filaments and the microporous material is within voids among said filaments, and wherein the cable core comprises at least one semiconducting layer and the microporous material is into or in contact with at least one semiconducting layer.

10. The energy cable according to claim 9, wherein the cable core comprises an inner and an outer semiconducting layer and the microporous material is into or in contact with the inner semiconducting layer.

11. The energy cable according to claim 1, wherein the microporous material is in form of particles.

12. The energy cable according to claim 9, wherein the particles are dispersed in/on a substrate, such substrate including any of filling material, hygroscopic yarn or hygroscopic tape.

13. A method for extracting methane from a crosslinked electrically insulating layer of an energy cable, said method comprising the following sequential stages: manufacturing an energy cable core comprising an electric conductor, a crosslinked electrically insulating layer containing methane as crosslinking by-product, and a microporous material having a bimodal pore volume distribution with a first peak having a maximum at a pore diameter value within the range 5.5-6.5 and a second peak having a maximum at a pore diameter value within the range 7.5-8.5 , the maximum values of the first and the second peaks corresponding to an incremental pore volume of at least 410.sup.3 cm.sup.3/g; and leaving the energy cable core to stand for a period of from 0.5 to 7 days to allow the methane crosslinking by-product migrating from the crosslinked electrically insulating layer to the microporous material and being adsorbed.

14. The method according to claim 13, comprising a heating stage carried out during the stage of leaving the energy cable core to stand.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0070] Further characteristics will be apparent from the detailed description given hereinafter with reference to the accompanying drawings, in which:

[0071] FIG. 1 is a transversal cross section of a first embodiment of an energy cable, particularly suitable for medium or high voltage, according to the present disclosure;

[0072] FIG. 2 is a transversal cross section of a second embodiment of an energy cable, particularly suitable for medium or high voltage, according to the present disclosure;

[0073] FIGS. 3a, 3b, 4a, 4b, 5a, 5b, 6a and 6b show characterizations of microporous material according to the disclosure and of comparative ones.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0074] In FIG. 1, a transversal section of a first preferred embodiment of a cable (1) according to the present disclosure is schematically represented, which comprises an electric conductor (2), an inner semiconducting layer (3), an electrically insulating layer (4), an outer semiconducting layer (5), a metal screen (6) and a sheath (7). Electric conductor (2), inner semiconducting layer (3), electrically insulating layer (4) and outer semiconducting layer (5) constitute the core of cable (1). Cable (1) is particularly intended for the transport of medium or high voltage current.

[0075] The conductor (2) consists of metal filaments (2a), preferably of copper or aluminium or both, stranded together by conventional methods. The electrically insulating layer (4), the inner and outer semiconducting layers (3), (5) are made by extruding polymeric materials according to known techniques. Around the outer semiconducting layer (5), a metal screen layer (6) is usually positioned, made of electrically conducting wires or strips helically wound around the cable core or of an electrically conducting tape longitudinally wrapped and overlapped (preferably glued) onto the underlying layer. The electrically conducting material of said wires, strips or tape is usually copper or aluminium or both. The screen layer (6) may be covered by a sheath (7), generally made from a polyolefin, usually polyethylene, in particular high density polyethylene. In accordance with an embodiment of the present disclosure, the microporous adsorbent material, in form of particles or powder dispersed in a filling material, is within voids (2b) among said filaments (2a).

[0076] In FIG. 2, a transversal section of another embodiment of the cable (1) according to the present disclosure is schematically represented, which comprises the same elements as described in FIG. 1, with the addition of a hygroscopic tape (3a), wound onto the electric conductor (2), carrying particles of the microporous adsorbent material dispersed thereupon.

[0077] In a further embodiment, particles of the microporous material may be dispersed in a filling material within voids (2b) among the metal filaments (2a) forming the electric conductor (2), analogously to what described in FIG. 1.

[0078] In another further embodiment, the inner semiconducting layer (3) of the cable (1) is in the form of a semiconductive tape wound around the electric conductor (2), such semiconductive tape carrying particles of the microporous adsorbent material.

[0079] FIGS. 1 and 2 show two embodiments of the present disclosure. Suitable modifications can be made to these embodiments according to specific technical needs and application requirements without departing from the scope of the disclosure.

[0080] The following examples are provided to further illustrate the content of the disclosure.

Example 1 (HCP 1)

[0081] A HCP microporous material according to the invention was prepared as follows.

[0082] In a round-bottom flask (equipped with magnetic stirrer, reflux condenser and thermometer), under nitrogen atmosphere, 1 mol of -dichloroxylene (DCX) and 2.7 mol of 4,4-bis(chloromethyl)-1,1-diphenyl (BCMBP) were dissolved in 119 mol of dichloroethane (DCE), at room temperature (25 C.). 3.7 mol of FeCl.sub.3 were then added to the reaction mixture, which was then heated at 80 C. for 48 h under nitrogen flow. After 48 h, a solid formed in the flask and HCl release ended. The solid product was left to cool, recovered from the flask and grounded, then sequentially washed with water, methanol and diethyl ether in a Soxhlet extractor (24 hours for each solvent). Finally, the product was dried in an oven at 60 C. for 24 hours.

Example 2 (HCP 2)

[0083] A comparative HCP microporous material was prepared as follows.

[0084] In a round-bottom flask (equipped with magnetic stirrer, reflux condenser and thermometer), under nitrogen atmosphere, 1 mol of -dichloroxylene (DCX) and 3.19 mol of 4,4-bis(chloromethyl)-1,1-diphenyl (BCMBP) were placed. Separately, 4.16 mol of FeCl.sub.3 were dissolved in 125 moles of dichloroethane. The resulting solution was added to the flask which was then heated at 80 C. for 18 h under nitrogen flow. Thereafter, a solid formed in the flask. The solid product was left to cool, recovered from the flask and washed, on a filter paper, with water and methanol up to discolouring, then with ethyl ether. Finally, the product was dried in an oven at 60 C. for 24 hours.

Examples 3 (Activated Carbon 1)

[0085] An activated carbon (Maxsorb MSC-30, commercially available by Kansai Coke & Carbon) and having a pore volume distribution according to the present disclosure was used as adsorbent material.

Examples 4 (Activated Carbon 2)Comparative

[0086] An activated carbon (Centaur, commercially available by Chemviron) and having a pore volume distribution that does not fall within the present disclosure was used as adsorbent material for comparative purposes.

[0087] Characterization of the Materials of Examples 1-4

[0088] Samples of the materials of Examples 1 to 4 were characterized by using a for TriStar II Plus+MicroActive surface area and porosity analyzer (by Micromeritics) by determining the adsorption isotherms of N.sub.2 at about 196 C., from 0.1 to 1 bar.

[0089] The results are shown in the attached FIG. 3a, 3b (material of Example 1), 4a, 4b (material of Example 2), 5a, 5b (material of Example 3), 6a and 6b (material of Example 4).

[0090] The graphs of FIGS. 3a, 4a, 5a and 6a reports the cumulative pore volume (cm3/g, in ordinate) versus pore diameter (A, in abscissa) of each material tested. The graphs of FIGS. 3b, 4b, 5b and 6b reports the incremental pore volume (cm3/g, in ordinate) versus pore diameter (A, in abscissa) of each material tested.

[0091] The materials of all of the Examples have a bimodal distribution, but that of Example 4 (FIG. 6b) has a first peak at about 5 , out of the range set forth by the present disclosure. In addition, none of its peaks has an incremental pore volume of at least 410.sup.3 cm.sup.3/g. The material of Example 2 (FIG. 4b), though having both the first and second peaks at a diameter value according to the present disclosure, has one of these peaks (the first) with an incremental pore volume of lower than 410.sup.3 cm.sup.3/g (at about 3.110.sup.3 cm.sup.3/g). The materials of Examples 2 and 4 are comparative materials.

[0092] The materials of Examples 1 and 3 are according to the present disclosure in that they have a first peak at about 5.8 and a second peak at, respectively nearly 8.4 and about 8.2 . All of the first and second peaks of the materials of Examples 1 and 3 have an incremental pore volume of at least 410.sup.3 cm.sup.3/g.

[0093] Only the materials of Examples 1 and 3 have a cumulative pore volume of the pores having a diameter up to 10 (1 nm) higher than 50.10.sup.1 cm.sup.3/g (as from FIGS. 3a and 5a).

[0094] Methane Adsorption of the Materials of Examples 1-4 [0095] methane adsorption isotherms were determined at 1 bar and room temperature.

[0096] The results are reported in Table 1.

TABLE-US-00001 TABLE 1 Methane uptake as mmol/g Example (and cm.sup.3/g) at 1 bar/25 C. 1 0.7 (17.12) 2* 0.2 (4.89) 3 1.1 (24.46) 4* 0.1 (2.45) The examples marked with an asterisk (*) are comparative.

[0097] The microporous materials of Examples 1 and 3 according to the present disclosure are suitable for irreversibly adsorbing methane in an amount allowing the elimination or at least the reduction of the crosslinked insulating layer degassing process. No methane desorption was detected. The microporous materials of Examples 1 and 3 have such methane adsorbing capacity at pressure and/or temperature suitable for treating an energy cable before putting it into operation.