JOINT FOR HIGH VOLTAGE DIRECT CURRENT CABLES

Abstract

The present invention relates to a joint (100) for high voltage direct current cables (200, 300) extending 5 along a longitudinal axis (X) between two opposite end portions (110, 120), the joint (100) comprising: a central semiconducting electrode (140); two semiconducting deflectors (150, 160); a field grading layer (170) longitudinally extending 10 between each one of the deflectors (150, 160) and the central electrode (140) and in electric contact therewith; a joint insulating layer (180) surrounding the central electrode (140), the two deflectors (150, 160) 15 and the field grading layer (170); and a joint outer semiconductive layer (190) surrounding and in direct contact with the insulating layer (180).

Claims

1. A joint for connecting high voltage direct current cables along a longitudinal axis, the joint comprising: a central semiconducting electrode; two semiconducting deflectors; a field grading layer longitudinally extending between each one of the deflectors and the central electrode and in electric contact therewith; a joint insulating layer surrounding the central electrode, the two semiconducting deflectors and the field grading layer; and a joint outer semiconductive layer surrounding and in direct contact with the insulating layer.

2. The joint according to claim 1 wherein the two semiconducting deflectors are positioned and dimensioned so as to each longitudinally protrude beyond respective end portions of the joint insulating layer.

3. The joint according to claim 1 wherein the two semiconducting deflectors are positioned and dimensioned so to each longitudinally end at respective end portions of the joint.

4. The joint according to claim 1 wherein the field grading layer is at least partially superposed over and partially embeds the semiconducting deflectors, and is at least partially superposed over and partially embeds the central electrode.

5. The joint according to claim 1 wherein the field grading layer includes two portions each being laterally positioned between a respective one of the two semiconducting deflectors and the central electrode along the longitudinal axis.

6. The joint according to claim 1 wherein the joint insulating layer and the joint outer semiconductive layer have rectangular cross sections in a longitudinal direction and have substantially a same length.

7. The joint according to claim 1 wherein the joint outer semiconductive layer has a substantially conical shape at its longitudinal ends and envelopes the joint insulating layer, the field grading layer and each of the semiconducting deflectors.

8. A cable assembly, comprising: a first cable having a first cable end, the first cable end including a first conducting core, a first insulating layer and a first semiconductive outer layer, the first conducting core being exposed from the first insulating layer, and the first insulating layer being exposed from the first semiconductive outer layer; a second cable having a second cable end substantially aligned with the first cable end in a first direction, the second cable end including a second conducting core, a second insulating layer and a second semiconductive outer layer, the second conducting core being exposed from the second insulating layer, and the second insulating layer being exposed from the second semiconductive outer layer; a metal connector positioned adjacent to both the first conducting core and the second conducting core and between the first insulating layer and the second insulating layer in the first direction; and a joint having a central semiconducting electrode, a first semiconducting deflector and a second semiconducting deflector, the first semiconducting deflector being separated from the second semiconducting deflector by the central semiconducting electrode in the first direction, the central semiconducting electrode being positioned adjacent to the metal connector, the first semiconducting deflector being positioned adjacent to the first insulating layer, and the second semiconducting deflector being positioned adjacent to the second insulating layer.

9. The cable assembly of claim 8, wherein the first semiconducting deflector is also adjacent to the first semiconductive outer layer, and the second semiconducting deflector is also adjacent to the second semiconductive outer layer.

10. The cable assembly of claim 8, wherein the joint further includes a field grading layer that is positioned between the central semiconducting electrode and each of the first semiconducting deflector or the second semiconducting deflector in the first direction.

11. The cable assembly of claim 10, wherein the field grading layer overlaps one or more of the first semiconducting deflector, the second semiconducting deflector or the central semiconducting electrode in a second direction that is orthogonal to the first direction.

12. The cable assembly of claim 10, wherein the field grading layer includes a first part and a second part that are separated from the first part by the central semiconducting electrode, the first part being positioned between the first semiconducting deflector and the central semiconducting electrode in the first direction, The second part being positioned between the second semiconducting deflector and the central semiconducting electrode in the first direction.

13. The cable assembly of claim 8, wherein the joint further includes a joint insulating layer, the joint insulating layer being separated from the first insulating layer by the first semiconducting deflector and being separated from the second insulating layer by the second semiconducting deflector.

14. The cable assembly of claim 13, wherein the joint insulating layer overlaps one or more of the first semiconductive outer layer or the second semiconductive outer layer in a second direction that is orthogonal to the first direction.

15. The cable assembly of claim 13, wherein one or more of the first semiconducting deflector or the second semiconducting deflector extends beyond the joint insulting layer.

16. The cable assembly of claim 8, wherein the joint further includes a joint semiconductive outer layer surrounding the joint insulating layer.

17. The cable assembly of claim 16, wherein the joint semiconductive outer layer covers one or more of the first semiconducting deflector or the second semiconducting deflector from the first direction.

18. The cable assembly of claim 16, wherein the joint semiconductive outer layer directly overlaps one or more of the first semiconductive outer layer of the first cable end or the second semiconductive outer layer of the second cable end in a second direction that is orthogonal to the first direction.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Further characteristics will be apparent from the detailed description given hereinafter with reference to the accompanying drawings, in which:

[0040] FIG. 1 is a schematic cross-sectional side view of the joint according to the present invention in an assembled configuration with two connected cables.

[0041] FIG. 2 is a schematic cross-sectional perspective view of a joint for HVDC cables according to the present invention;

[0042] FIG. 3 is a schematic cross-sectional side view of the joint of FIG. 2;

[0043] FIG. 4 is a schematic cross-sectional side view of another joint according to the present invention;

[0044] FIG. 5 is a schematic cross-sectional side view of another embodiment of the joint of the invention in assembled configuration with two connected cables;

[0045] FIG. 6 is a schematic cross-sectional side view of a further joint according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0046] A joint 100 for the connection of two HVDC cables 200, 300 according to the present invention is shown in FIGS. 1 to 6.

[0047] In particular, FIGS. 1 and 5 show a joint 100 according to the invention assembled on two joined HVDC cables 200, 300 each comprising respective conducting core 20, 30 and a cable insulation system surrounding the respective conducting core 20, 30. Each cable insulation system comprises a cable inner semiconductive layer (not illustrated) surrounding and in contact with the respective conducting core 20, 30, a cable insulating layer 22, 32, surrounding and in contact with the respective inner semiconductive layer, and a cable outer semiconductive layer 24, 34, surrounding and in contact with the respective insulating layer 22, 32. Around to the outer semiconductive layer 24, 34 a metal screen 28, 38 is provided.

[0048] During junction operation, the end portion of each HVDC cable 200, 300 to be connected is peeled so as to expose a tract of conducting core 20, 30 and a tract of cable insulating layer 22, 32. In particular, each metal screen 28, 38 and each cable outer semiconductive layer 24, 34 is cut and removed leaving exposed a tract of the respective cable insulating layer 22, 32. A boundary 26, 36 is formed between each cable outer semiconductive layer 24, 34 and the respective insulating layer 22, 32.

[0049] As shown in FIGS. 1 and 5, the junction between two HVDC cables 200, 300 is performed by connecting the respective conducting cores 20, 30, e.g. by soldering or clamping. Once the electrical connection between the abovementioned conductors has been performed, the space corresponding to the removed sections of insulating material is filled with a metal connector 10.

[0050] In an assembled configuration, the joint 100 is fitted on the connected HVDC cables 200, 300.

[0051] As from FIGS. 1-6, the joint 100 extends along a longitudinal direction X between two opposite end portions 110, 120 and that is suitable to be fit over the conducting core connection in the assembled configuration.

[0052] The joint 100 comprises a central electrode 140, made of semiconductive material and two deflectors 150, 160, made of semiconductive material.

[0053] The central electrode 140 is positioned in an intermediate position with respect to the end portion 110, 120 of the joint 100 and, as shown in FIGS. 1 and 5, is arranged to surround the metal connector 10 around the connected conducting cores 20, 30.

[0054] The two deflectors 150, 160 are positioned at the end portions 110, 120 of the joint 100 and, in the assembled configuration, are arranged to surround the boundaries 26, 36 and neighbouring portions of the respective cable outer semiconductive layer 24, 34 and insulating layer 22, 32.

[0055] The joint 100 also comprises a field grading layer 170 which, in the embodiment of FIGS. 1-3 and 5, longitudinally extends to partially cover and partially embed the two deflectors 150, 160 and to totally cover and partially embed the central electrode 140.

[0056] In particular, the field grading layer 170 overlaps the radially external surface and the longitudinal ends of the central electrode 140, and partially overlaps the radially external surface of the two deflectors 150, 160 and embeds their longitudinal end facing the central electrode 140. The field grading layer 170, transversally extends so as to be interposed between each one of the deflectors 150, 160 and the central electrode 140.

[0057] The joint 100 further comprises a joint insulating layer 180 that overlaps the field grading layer 170 so as to be positioned radially external thereto, and a joint outer semiconductive layer 190 overlapping the insulating layer 180 so as to be positioned radially external to such an insulating layer 180. In the embodiment of the FIGS. 1-5, the field grading layer 170 longitudinally extends so as to be interposed between the insulating layer 180 and the electrodes 140, 150, 160.

[0058] Alternatively, as shown in FIG. 6, the field grading layer 170 is divided into two portions each in side-by-side relationship with one deflector 150, 160 and the central electrode 140 along the longitudinal axis X. In this case, the material of the field grading layer 170 is not superposed to deflector 150, 160 and central electrode 140. The field grading layer 170 longitudinally extends just between each one of the deflectors 150, 160 and the central electrode 140. In this alternative embodiment, the insulating layer 180 overlaps the field grading layer 170 and the electrodes 140, 150,160.

[0059] In the embodiments of FIGS. 1-4 and 6, the field grading layer 170, the joint insulating layer 180 and the joint outer semiconductive layer 190 have substantially the same longitudinal dimension.

[0060] In the embodiment of FIGS. 2 and 3, the two deflectors 150, 160 are positioned and dimensioned so as to protrude beyond the end portions of the field grading layer 170 of the joint insulating layer 180 and of the joint outer semiconductive layer 190.

[0061] In the embodiment of FIG. 4, the two deflectors 150, 160 are positioned and dimensioned so to end at the the end portions 110, 120 of the joint 100.

[0062] As it can be observed in FIGS. 3 and 4, the extremities 152, 162 of the two deflectors 150, 160 facing towards the central electrode 140 are chamfered without tips in order to reduce the risk of charge accumulation. Also, both the ends of the central electrode 140 are chamfered without tips in order to reduce the risk of charge accumulation. In the embodiment where the field grading layer 170 partially embeds the two deflectors 150, 160 and the central electrode 140, as shown in FIGS. 1-5, the material of the field grading layer 170 intrudes around their chamfered ends

[0063] In the embodiments of FIGS. 1-4 and 6, the joint insulating layer 180 and the joint outer semiconductive layer 190 have a substantially rectangular longitudinal cross-section. In this case, which is preferred according to the invention, the joint outer semiconductive layer 190 is electrically connected to the deflectors 150, 160, the cable outer semiconductive layer 24, 34 and the cable screens 28-38, for example by a copper mesh.

[0064] In the embodiment of FIG. 5, the joint outer semiconductive layer 190 has ends extending over the ends of the joint insulating layer 180 and of the field grading layer 170 so as to reach two deflectors 150, 160 and, in the assembled configuration, the cable outer semiconductive layers 24, 34 and the cables screens 28, 38. In this case, no further electrical connection is needed to join the joint outer semiconductive layer 190, the deflectors 150,160, the cable outer semiconductive layers 24, 34 and the cable screens 28, 38.

[0065] The thickness of the layers of the joint of the present invention can be selected in view of the voltage of the cables to be connected and of the specific materials used for the joint itself, according to the skilled person experience. For example, the joint for cables designed to transport 500 kV can have deflectors from 6 to 12 mm thick, field grading layer from 9 to 16 mm thick and a joint insulating layer from 30 to 60 mm thick.