Silicone multilayer insulation for electric cable

Abstract

A cable has at least one elongated electric conductor and a multilayer insulation surrounding the electric conductor. The multilayer insulation has a first semiconducting layer and an electrically insulating layer. The two layers are made from a silicone rubber based composition. A method for making this cable includes co-extruding the first semiconducting layer and the electrically insulating layer.

Claims

1. Process for manufacturing an electric cable, the electric cable has at least one elongated electric conductor; and a multilayer insulation surrounding said electric conductor, wherein said multilayer insulation having a first semiconducting layer and an electrically insulating layer, said two layers being made from a silicone rubber based composition, said method comprising the step of; co-extruding the first semiconducting layer and the electrically insulating layer, wherein the composition used to obtain the first semi-conducting layer further comprises carbon rovings as conductive filler.

2. Process according to claim 1, wherein the multilayer insulation has a second semiconducting layer made from a silicone rubber based composition, to form a 3-layer insulation, so that the first semiconducting layer, the electrically insulating layer and the second semiconducting layer are co-extruded layers.

3. Process according to claim 2, wherein the first semiconducting layer is surrounded by the electrically insulating layer, and the electrically insulating layer is surrounded by the second semiconducting layer.

4. Process according to claim 1, wherein at least one of the layers of said multilayer insulation is a crosslinked layer.

5. Process according to claim 1, wherein the multilayer insulation is surrounded by a metal shield.

6. Process according to claim 1, wherein the electric cable is a power cable supporting a voltage level of at least 5 kV.

7. Process according to claim 1, wherein the layers of the multilayer insulation are extruded simultaneously.

8. Process according to claim 1, wherein the co-extrusion is done with the same extrusion head.

9. Process according to claim 4, wherein the layers of said multilayer insulation are crosslinked layers.

10. Process for manufacturing an electric cable, the electric cable has at least one elongated electric conductor; and a multilayer insulation surrounding said electric conductor, wherein said multilayer insulation having a first semiconducting layer and an electrically insulating layer, said two layers being made from a silicone rubber based composition, said method comprising the step of; co-extruding the first semiconducting layer and the electrically insulating layer, so that the presence of gas and/or the presence of space between the extruded layers are substantially removed, wherein the composition used to obtain the first semi-conducting layer further comprises carbon rovings as conductive filler.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) Other characteristics and advantages of the present invention will emerge in the light of the description of non-limiting examples, given with reference to figures according to the invention, wherein:

(2) FIG. 1 shows a schematic view in perspective and in cross section of an electric cable according to the invention, and

(3) FIG. 2 shows an extrusion head to co-extrude a multilayer insulation to form an electric cable according to the invention.

DETAILED DESCRIPTION

(4) For reasons of clarity, only the elements that are essential for understanding the invention have been schematically represented, and without being drawn to scale.

(5) The power cable 1, illustrated in FIG. 1, comprises an elongated central conducting element 2, especially made of copper or aluminum. Successively and coaxially around this conducting element 2, the power cable 1 also comprises a first semiconducting layer 3 known as the inner semiconducting layer, an electrically insulating layer 4, a second semiconducting layer 5 known as the outer semiconducting layer, a metal shield 6, and an outer protective sheath 7, the three layers 3, 4 and 5 being co-extruded layers according to the invention. The presence of the metal shield 6 is preferential. The presence of the protective outer sheath 7 is preferential, but not essential.

(6) The co-extrusion process of the layers 3, 4 and 5 of FIG. 1 is illustrated in FIG. 2.

(7) FIG. 2 shows the co-extrusion process of: a first silicone rubber semiconducting composition 30, commercialized by the company MESGO under the reference MG1414N60P, said first silicone rubber semiconducting composition comprising around 40-50% by weight of carbon black as conductive filler; a silicone rubber electrically insulation composition 40, commercialized by the company RADO under the reference Silopren 2270H; and a second silicone rubber semiconducting composition 50, commercialized by the company MESGO under the reference MG1414N60P, said second silicone rubber semiconducting composition comprising around 40-50% by weight of carbon black as conductive filler.

(8) Said three compositions 30, 40 and 50 flow respectively from three different extruders (not represented) to the inside of an extrusion head 10.

(9) The three different extruders may be extruders well-known in the art.

(10) The extruder head 10 is commercialized by the company under ITAL under the reference TECA/35, used for three-layer extrusion.

(11) In said extruder head 10, said three compositions 30, 40 and 50 go through the same extrusion head extremity 20.

(12) In said extrusion head extremity 20, the compositions 30, 40 and 50 are applied simultaneously around the elongated central conducting element 2, to form respectively the coextruded layers 3, 4 and 5 around said elongated central conducting element.

(13) Hence, there is substantially no air bubble between the interface of the layers 3 and 4, and between the interface of the layers 4 and 5, so that said 3-layer insulation allows advantageously to decrease partial discharges in the electric cable, while guaranteeing good flexibility properties.