Electrical Device Comprising a Cross-linked Layer

Abstract

The present invention relates to an electrical device (1, 20, 30) comprising a cross-linked layer (3, 4, 5) obtained on the basis of a cross-linkable polymer composition comprising a polymer material and particles with polyhedric structure, characterized in that the particles have a melting point of at most 200° C.

Claims

1. An electrical device (1, 20, 30) comprising a crosslinked layer (3, 4, 5) obtained from a crosslinkable polymer composition comprising a polymer material and particles having a polyhedral structure, characterized in that the particles have a melting point of at most 200° C.

2. The device as claimed in claim 1, characterized in that the particles comprise Si—O groups.

3. The device as claimed in claim 1 or 2, characterized in that the particles are POSSs (polyhedric oligomeric silsesquioxanes).

4. The device as claimed in any one of the preceding claims, characterized in that the particles comprise at least one vinyl (CH═CH.sub.2) functional group.

5. The device as claimed in any one of the preceding claims, characterized in that the particles are nanoparticles.

6. The device as claimed in any one of the preceding claims, characterized in that the crosslinkable polymer composition comprises at most 20.0% by weight of particles having a polyhedral structure and preferably at most 10.0% by weight of particles having a polyhedral structure, with respect to the total weight of the crosslinkable polymer composition.

7. The device as claimed in any one of the preceding claims, characterized in that the crosslinkable polymer composition comprises a crosslinking agent.

8. The device as claimed in claim 7, characterized in that the crosslinking agent is an organic peroxide.

9. The device as claimed in claim 8, characterized in that the crosslinkable polymer composition comprises less than 1.0% by weight of organic peroxide, with respect to the total weight of the crosslinkable polymer composition.

10. The device as claimed in any one of the preceding claims, characterized in that the polymer material comprises one or more olefin polymers.

11. The device as claimed in claim 10, characterized in that the olefin polymer is an ethylene/propylene/diene monomer terpolymer (EPDM).

12. The device as claimed in any one of the preceding claims, characterized in that it is an electric cable (1) comprising an elongated electrically conducting component surrounded by said crosslinked layer.

13. The device as claimed in claim 12, characterized in that the elongated conducting component (2) is surrounded by a first semiconducting layer (3), an electrically insulating layer (4) surrounding the first semiconducting layer, and a second semiconducting layer (5) surrounding the electrically insulating layer, the crosslinked layer being at least one of these three layers, and the crosslinked layer preferably being the electrically insulating layer (4).

14. The device as claimed in any one of claims 1 to 12, characterized in that it is an electric cable accessory (20, 30), said accessory comprising the crosslinked layer.

15. The device as claimed in claim 14, characterized in that the accessory is an electric cable joint or termination.

Description

[0138] Other characteristics and advantages of the present invention will become apparent in the light of the description of nonlimiting examples of an electric cable according to the invention and electric cable accessory according to the invention, made with reference to the figures.

[0139] FIG. 1 represents a diagrammatic view of an electric cable according to a preferred embodiment in accordance with the invention.

[0140] FIG. 2 represents a diagrammatic view of an electrical device according to the invention comprising a joint in longitudinal section, this joint surrounding the ends of two electric cables.

[0141] FIG. 3 represents a diagrammatic view of an electrical device according to a first alternative form of the invention comprising a termination in longitudinal section, this termination surrounding the end of a single electric cable.

[0142] FIG. 4 represents histograms relating to the crosslinking density for crosslinked layers according to the invention and according to comparative compositions.

[0143] FIG. 5 represents the conductivity at 90° C. as a function of the frequency (Hz) for crosslinked layers according to the invention and according to comparative compositions.

[0144] FIG. 6 represents the tangent delta (tan(δ)) at 90° C. as a function of the frequency (Hz) for crosslinked layers according to the invention and according to comparative compositions.

[0145] For reasons of clarity, only the components essential for the understanding of the invention have been represented diagrammatically, this being done without observing a scale.

[0146] The medium- or high-voltage power cable 1, illustrated in FIG. 1, comprises an elongated central conducting component 2, in particular made of copper or of aluminum. The power cable 1 additionally comprises several layers positioned successively and coaxially around this conducting component 2, namely: a first semiconducting layer 3 referred to as “inner semiconducting layer”, an electrically insulating layer 4, a second semiconducting layer 5 referred to as “outer semiconducting layer”, an earthing and/or protective metal shield 6 and an external protective sheath 7.

[0147] The electrically insulating layer 4 is an extruded and crosslinked layer obtained from the crosslinkable polymer composition according to the invention.

[0148] The semiconducting layers are also extruded and crosslinked layers which can be obtained from the crosslinkable polymer composition according to the invention.

[0149] The presence of the metal shield 6 and of the external protective sheath 7 is preferential but not essential, this cable structure being as such well known to a person skilled in the art.

[0150] FIG. 2 represents a device 101 comprising a joint 20 surrounding, in part, two electric cables 10a and 10b.

[0151] More particularly, the electric cables 10a and 10b respectively comprise an end 10′a and 10′b which are intended to be surrounded by the joint 20.

[0152] The body of the joint 20 comprises a first semiconducting component 21 and a second semiconducting component 22 separated by an electrically insulating component 23, said semiconducting components 21, 22 and said electrically insulating component 23 surrounding the ends 10′a and 10′b respectively of the electric cables 10a and 10b.

[0153] This joint 20 makes it possible to electrically connect the first cable 10a to the second cable 10b, in particular by virtue of an electrical connector 24 positioned at the center of the joint 20.

[0154] At least one of the components chosen from the first semiconducting component 21, the second semiconducting component 22 and said electrically insulating component 23 can be a crosslinked layer as described in the invention.

[0155] The first electric cable 10a comprises an electrical conductor 2a surrounded by a first semiconducting layer 3a, an electrically insulating layer 4a surrounding the first semiconducting layer 3a, and a second semiconducting layer 5a surrounding the electrically insulating layer 4a.

[0156] The second electric cable 10b comprises an electrical conductor 2b surrounded by at least one first semiconducting layer 3b, an electrically insulating layer 4b surrounding the first semiconducting layer 3b, and a second semiconducting layer 5b surrounding the electrically insulating layer 4b.

[0157] These electric cables 10a and 10b can be those described in the present invention.

[0158] At said end 10′a, 10′b of each electric cable 10a, 10b, the second semiconducting layer 5a, 5b is at least partially denuded in order for the electrically insulating layer 4a, 4b to be at least partially positioned inside the joint 20, without being covered with the second semiconducting layer 5a, 5b of the cable.

[0159] Inside the joint 20, the electrically insulating layers 4a, 4b are directly in physical contact with the electrically insulating component 23 and the first semiconducting component 21 of the joint 20. The second semiconducting layers 5a, 5b are directly in physical contact with the second semiconducting component 22 of the joint 20.

[0160] FIG. 3 represents a device 102 comprising a termination 30 surrounding a single electric cable 10c.

[0161] More particularly, the electric cable 10c comprises an end 10′c intended to be surrounded by the termination 30.

[0162] The body of the termination 30 comprises a semiconducting component 31 and an electrically insulating component 32, said semiconducting component 31 and said electrically insulating component 32 surrounding the end 10′c of the electric cable 10c.

[0163] At least one of the components chosen from the semiconducting component 31 and the electrically insulating component 32 can be a crosslinked layer as described in the invention.

[0164] The electric cable 10c comprises an electrical conductor 2c surrounded by a first semiconducting layer 3c, an electrically insulating layer 4c surrounding the first semiconducting layer 3c, and a second semiconducting layer 5c surrounding the electrically insulating layer 4c.

[0165] This electric cable 10c can be that described in the present invention.

[0166] At said end 10′c of the electric cable 10c, the second semiconducting layer 5c is at least partially denuded in order for the electrically insulating layer 4c to be at least partially positioned inside the termination 30, without being covered with the second semiconducting layer 5c of the cable.

[0167] Inside the termination 30, the electrically insulating layer 4c is directly in physical contact with the electrically insulating component 32 of the termination 30. The second semiconducting layer 5c is directly in physical contact with the semiconducting component 31 of the joint 30.

EXAMPLES

[0168] 1. Electrically Insulating Crosslinkable Polymer Compositions

[0169] Crosslinkable polymer compositions, the amounts of the compounds of which are expressed as percentages by weight with respect to the total weight of the polymer composition, are collated in table 1 below.

[0170] The polymer material in table 1 is composed solely of EPDM.

[0171] The compositions C1 to C3 are comparative tests and the compositions I1 to I3 are in accordance with the invention.

TABLE-US-00001 TABLE 1 Crosslinkable polymer compositions C1 C2 C3 I1 I2 I3 Polymer 99.5 99.0 88.0 99.0 98.5 88.0 material Particles I 0 0 0 0.5 0.5 10.0 Particles C 0 0 10.0 0 0 0 Crosslinking 0.5 1.0 2.0 0.5 1.0 2.0 agent

[0172] The origins of the compounds of table 1 are as follows: [0173] Polymer material is EPDM sold by ExxonMobil under the reference Vistalon 1703P; [0174] Particles I are particles of the POSS type, sold by Hybrid Plastics under the reference OL1170 (Octavinyl POSS), the melting point of which is 177° C.; [0175] Particles C are particles of the POSS type, sold by Hybrid Plastics under the reference OL1118 (allylisobutyl POSS), the melting point of which is 246° C.; [0176] Crosslinking agent is an organic peroxide of the dicumyl peroxide (DCP) type, sold by Arkema under the reference Luperox DCP, the half-life of which is 1 minute at 175° C.

[0177] 2. Preparation of the Crosslinking Layers

[0178] The combinations calculated in table 1 are processed as follows.

[0179] The polymer is introduced onto an open mill at a temperature of 120° C. The particles and also the crosslinking agent are added on a roller at the same temperature, the mixing conditions (temperature and duration) being such that the crosslinking agent does not decompose during this mixing stage. Preforms are thus obtained.

[0180] The peroxide crosslinking is subsequently carried out during the manufacture of the molded plaques from these preforms. For this, the preforms are molded under a pressure of 200 bar at 180° C. for approximately 8 minutes, the molding temperature then making it possible for the crosslinking agent to decompose. The plaques obtained are thus crosslinked and have a thickness of approximately 1 mm.

[0181] 3. Characterization of the Crosslinked Layers

[0182] The crosslinking density (v), the conductivity at 90° C. and the tangent delta (tan δ) at 90° C. were measured starting from the plaques formed above, according to the following methods.

[0183] 3.1. The Crosslinking Density (v)

[0184] The crosslinking density was measured by DMA (Dynamic Mechanical Analysis) using test specimens with a thickness of approximately 1 mm stressed under tension from 30 to 150° C. with a temperature rise gradient of 3° C. min.sup.−1.

[0185] The stressing frequency was set at 1 Hz and the strain at 0.1%.

[0186] The crosslinking density is obtained via the measurement of the storage modulus at 120° C. according to the well-established formula of rubber elasticity:

[00001]$v=\frac{\rho }{\mathrm{Mc}}.Math..Math.\mathrm{and}.Math..Math.\mathrm{Mc}.Math.\frac{3.Math.\rho .Math..Math.\mathrm{RT}}{E_r^{\prime }}$

[0187] with R being the ideal gas constant, T the temperature at which the modulus E′ is taken, E′ the value of the rubber modulus (in this instance at 120° C.) and p the density of the polymer at this temperature.

[0188] 3.2. The Conductivity and the Tangent Delta (Tan δ), at 90° C.

[0189] The conductivity and the tangent delta (or loss factor) were measured by dielectric spectroscopy.

[0190] The tests were carried out on samples with a thickness of approximately 1 mm, over a range of frequencies at 10.sup.−1 to 10.sup.6 Hz, with a voltage of 1 V. The temperature at 90° C. was applied during the test.

[0191] 4. Results

[0192] The results obtained are calculated in FIGS. 4, 5 and 6.

[0193] FIG. 4 represents histograms related to the crosslinking density for crosslinked layers according to the invention and according to comparative compositions.

[0194] The composition I1 clearly shows a crosslinking density substantially identical to that of the composition C2, it being known that the composition I1, with particles according to the invention, comprises half as much organic peroxide as the composition C2.

[0195] In addition, it is also noticed that the composition I2 exhibits a markedly greater crosslinking density than that of the composition C2, it being known that the composition I2, with particles according to the invention, comprises an identical amount of organic peroxide to the composition C2.

[0196] Consequently, the crosslinkable polymer compositions according to the invention exhibit better levels of crosslinking and thus a better mechanical strength.

[0197] The crosslinkable polymer compositions according to the invention in addition make it possible to advantageously reduce the amounts of organic peroxide used for equivalent thermomechanical properties: risks of electrical breakdown due to the crosslinking byproducts (formed during the decomposition of these same peroxides) are de facto significantly limited, indeed even prevented.

[0198] FIGS. 5 and 6 respectively represent the conductivity at 90° C. as a function of the frequency (Hz) and the tangent delta (tan(δ)) (or tangent of the loss angle) at 90° C. as a function of the frequency (Hz), for crosslinked layers according to the invention and according to comparative compositions.

[0199] It is clearly noticed that the compositions I2 and I3 according to the invention exhibit a much lower loss at 0.1 Hz than the comparative composition C3.

[0200] Specifically, the results at 0.1 Hz are calculated in the following table 2:

TABLE-US-00002 TABLE 2 Crosslinkable compositions I2 I3 C3 Conductivity at 90° C. 2.51 × 10.sup.−16 2.70 × 10.sup.−16 4.77 × 10.sup.−15 Tangent delta at 90° C. 1.98 × 10.sup.−3 2.10 × 10.sup.−3 3.77 × 10.sup.−2

[0201] Consequently, the crosslinkable polymer compositions according to the invention exhibit better dielectric properties (i.e., better electrical insulation).