Energy cable having a crosslinked electrically insulating layer, and method for extracting crosslinking by-products therefrom
An energy cable includes, at least one cable core including an electric conductor, a crosslinked electrically insulating layer, and zeolite particles placed in the cable core. The zeolite particles are able to extract and absorb, very efficiently and irreversibly, the by-products deriving from the cross-linking reaction, so as to avoid space charge accumulation in the insulating material during cable lifespan. A method for extracting crosslinking by-products from a cross-linked electrically insulating layer of an energy cable core, which includes manufacturing the energy cable core containing zeolite particles, heating the energy cable core up to a temperature causing migration of the crosslinking by-products from the crosslinked electrically insulating layer; and then placing a metal screen around the energy cable core.
1. An energy cable comprising at least one cable core comprising:
an electric conductor formed by a plurality of stranded electrically conducting filaments;
an extruded crosslinked electrically insulating layer;
a semiconducting layer; and
zeolite particles that are placed in the cable core, wherein the zeolite particles have (a) a SiO 2 /Al 2 O 3 molar ratio equal to or lower than 20; (b) a maximum diameter of a sphere that can diffuse along at least one axes direction equal to or greater than 3 Å; and (c) a sodium content, expressed as Na 2 O, equal to or lower than 0.3% by weight.
2. The energy cable according to claim 1 , wherein the zeolite particles are dispersed in/on a substrate, said substrate comprising filling material, hygroscopic yarn and/or hygroscopic tape.
3. The energy cable according to claim 1 , wherein the zeolite particles have a SiO 2 /Al 2 O 3 molar ratio equal to or lower than 15.
4. The energy cable according to claim 1 , wherein the zeolite particles are placed in the cable core: (i) within voids among said filaments; (ii) in contact with the semiconducting layer; or (iii) within voids among said filaments and in contact with the semiconducting layer.
5. The energy cable according to claim 4 , wherein when the zeolite particles are placed in contact with the semiconducting layer, the semiconducting layer is an outer semiconducting layer surrounding the electrically insulating layer.
6. The energy cable according to claim 1 , wherein the extruded crosslinked electrically insulating layer comprises at least one polyolefin crosslinked by reaction with at least one organic peroxide.
7. A method for extracting crosslinking by-products from a cross-linked electrically insulating layer of an energy cable core, comprising:
manufacturing an energy cable core comprising an electric conductor formed by a plurality of stranded electrically conducting filaments, an extruded crosslinked electrically insulating layer containing cross-linking by-products, and zeolite particles that are placed in the cable core, wherein the zeolite particles have (a) a SiO 2 /Al 2 O 3 molar ratio equal to or lower than 20; (b) a maximum diameter of a sphere that can diffuse along at least one axes direction equal to or greater than 3 Å; and (c) a sodium content, expressed as Na 2 O, equal to or lower than 0.3% by weight;
heating the energy cable core up to a temperature causing migration of the crosslinking by-products from the crosslinked electrically insulating layer to the zeolite particles, whereby the zeolite particles absorb the crosslinking by-products; and
then placing a metal screen around the energy cable core.
8. The method according to claim 7 , wherein heating the energy cable is carried out at a temperature of from 70° C. to 80° C., for 7 to 15 days.
9. The method according to claim 7 , wherein heating the energy cable causes at least one fraction of the crosslinking by-products to be irreversibly absorbed into the zeolite particles.
10. The method according to claim 7 , wherein the zeolite particles are placed in the cable core: (i) within voids among said filaments; (ii) in contact with the semiconducting layer; or (iii) within voids among said filaments and in contact with the semiconducting layer.
11. The method according to claim 7 , wherein the extruded crosslinked electrically insulating layer comprises at least one polyolefin crosslinked by reaction with at least one organic peroxide.