the process according to the invention has been employed for the manufacture of the layer making up the intermediate electrical insulator the process can be employed for the manufacture of one or both of the semiconducting shields a composition of the material of the semiconducting shields once the crosslinking stage is complete comprises for example by weight substantially 63 5 of a polyolefin such as a polar polymer of ethylene acrylate or ethylene vinyl acetate type charged with 35 of carbon black 0 5 of peroxide and 1 of cocrosslinking agent of course this example is not limiting here again the liquid solution is thus chosen so that said material comprises after the extrusion stage a lower percentage by weight of peroxide with respect to the polyolefin than the percentage by weight of the cocrosslinking agent with respect to the polyolefin in the case of the semiconducting shields the process comprises the successive stages of mixing the different components of the composition comprising at least one polyolefin via a continuous mixer injecting the liquid solution comprising at least one peroxide and one cocrosslinking agent into the composition extruding the mixture formed of the composition and of the liquid solution crosslinking said extruded mixture the different aspects of the invention described in connection with the intermediate electrical insulator apply of course to the two semiconducting shields apart from the fact that the liquid solution is not injected at the same time into the composition in addition the process according to the invention can be employed for the manufacture both of the.