HVDC Power Cable With Water-Blocking Capability

Abstract

A high voltage DC power cable designed for voltages of 320 kV or higher, including: a multi-wire conductor, an inner semiconducting layer arranged around the multi-wire conductor, the inner semiconducting layer forming a screen layer for the multi-wire conductor, a solid insulation system arranged around the inner semiconducting layer, and a water-blocking compound configured to restrict water migration into the high voltage DC power cable.

Claims

1-18. (canceled)

19. A high voltage DC power cable designed for voltages of 320 kV or higher, comprising: a multi-wire conductor, an inner semiconducting layer arranged around the multi-wire conductor, the inner semiconducting layer forming a screen layer for the multi-wire conductor, a solid insulation system arranged around the inner semiconducting layer, and a water-blocking compound configured to restrict water migration into the high voltage DC power cable, wherein the water-blocking compound is a liquid with a viscosity greater than 20 Pa.Math.s at a temperature of 20° C., wherein the water-blocking compound is electrically conducting, wherein the water-blocking compound includes a carbon-based component which provides the electric conductivity of the water-blocking compound, wherein the carbon-based component is graphite, wherein the water-blocking compound includes polybutadiene, and an antioxidant.

20. The high voltage DC power cable as claimed in claim 19, wherein the water-blocking compound is provided in interstices between the wires of the multi-wire conductor.

21. The high voltage DC power cable as claimed in claim 19, wherein the water-blocking compound is provided radially outwards of and around the solid insulation system.

22. The high voltage DC power cable as claimed in claim 19, wherein the water-blocking compound comprises a hydrocarbon-based component or a silica-based component.

23. The high voltage DC power cable as claimed in claim 19, wherein the solid insulation system is composed of an electrically insulating material which has an electrical conductivity of at most 1000 fS/m, at most 100 fS/m, or at most 10 fS/m measured at nominal voltage at a temperature of 20° C.

24. The high voltage DC power cable as claimed in claim 19, wherein the solid insulation system is composed of an electrically insulating material which has the inherent property that a non-heat treated 1 mm thick press-moulded plate made from the electrically insulating material has an electrical conductivity of at most 50 fS/m measured after 24 hours at 70° C. and an electric field of 30 kV/mm applied across the thickness dimension of the press-moulded plate.

25. The high voltage DC power cable as claimed in claim 19, comprising an electrically conducting or an electrically non-conducting tape wound around the multi-wire conductor and arranged between the multi-wire conductor and the inner semiconducting layer.

26. The high voltage DC power cable as claimed in claim 25, wherein the tape is in direct contact with the multi-wire conductor and/or the water-blocking compound and with the inner semiconducting layer.

27. The high voltage DC power cable as claimed in claim 19, wherein the multi-wire conductor is formed by a plurality of layers of wires, wherein the water-blocking compound is provided in interstices between each layer of wires.

28. The high voltage DC power cable as claimed in claim 19, wherein the water-blocking compound is provided on an outermost layer of wires of the multi-wire conductor.

29. The high voltage DC power cable as claimed in claim 19, wherein the solid insulation system is partially cross-linked so that it only passes a hot set test according to IEC 60811-507 up to 50% of the load specified by IEC 60811-507.

30. The high voltage DC power cable as claimed in claim 29, wherein the solid insulation system is partially cross-linked so that it only passes a hot set test according to IEC 60811-507 up to 40%, such as up to 30%, such as up to 25%, of the load specified by IEC 60811-507.

31. The high voltage DC power cable as claimed in claim 19, wherein the solid insulation system comprises a thermoplastic polypropylene-based material.

32. The high voltage DC power cable as claimed in claim 20, wherein the water-blocking compound comprises a hydrocarbon-based component or a silica-based component.

33. The high voltage DC power cable as claimed in claim 20, wherein the solid insulation system is composed of an electrically insulating material which has an electrical conductivity of at most 1000 fS/m, at most 100 fS/m, or at most 10 fS/m measured at nominal voltage at a temperature of 20° C.

34. The high voltage DC power cable as claimed in claim 20, comprising an electrically conducting or an electrically non-conducting tape wound around the multi-wire conductor and arranged between the multi-wire conductor and the inner semiconducting layer.

35. The high voltage DC power cable as claimed in claim 20, wherein the water-blocking compound is provided on an outermost layer of wires of the multi-wire conductor.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0053] The specific embodiments of the inventive concept will now be described, by way of example, with reference to the accompanying drawings, in which:

[0054] FIG. 1 schematically shows a cross-section of an example of a high voltage DC power cable;

[0055] FIG. 2 schematically shows a cross-section of another example of a high voltage DC power cable;

[0056] FIG. 3 schematically shows a cross-section of yet another example of a high voltage DC power cable; and

[0057] FIG. 4 is a flowchart of a method of manufacturing a high voltage DC power cable.

DETAILED DESCRIPTION

[0058] The inventive concept will now be described more fully hereinafter with reference to the accompanying drawings, in which exemplifying embodiments are shown. The inventive concept may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided by way of example so that this disclosure will be thorough and complete, and will fully convey the scope of the inventive concept to those skilled in the art. Like numbers refer to like elements throughout the description.

[0059] FIG. 1 schematically shows a cross-section of an example of a high voltage DC (HVDC) power cable 1-1. The exemplified HVDC power cable 1-1 is a land cable but could alternatively be a submarine power cable. In the latter case, the general structure of the HVDC power cable would be somewhat different, as it would be configured for underwater use and e.g., comprise a water-blocking sheath and optionally armouring. The HVDC power cable 1-1 is designed to have a voltage rating equal to or greater than 320 kV.

[0060] The HVDC power cable 1-1 comprises a multi-wire conductor 3. The multi-wire conductor 3 comprises a plurality of wires 3a. The wires 3a are arranged in a stranded configuration. The multi-wire conductor 3 has interstices between the wires 3a. The fill-factor of the multi-wire conductor 3 as provided by the wires may for example be in the range 92-96%. This means that the conductor material fills 92-96% of the cross-sectional area of the multi-wire conductor 3.

[0061] In the present example, the stranded wires 3a are rounded wires and the multi-wire conductor 3a is a stranded round conductor. The multi-wire conductor could alternatively for example be a keystone or profiled conductor, or a segmental or Milliken conductor.

[0062] The exemplified HVDC power cable 1-1 comprises an inner semiconducting layer 5. The inner semiconducting layer 5 is provided around the multi-wire conductor 3. The inner semiconducting layer 5 acts as a conductor screen. The inner semiconducting layer 5 hence forms a screen layer for the multi-wire conductor 3. The exemplified inner semiconducting layer 5 may be polymer-based and may comprise a conductive component such as carbon black.

[0063] The HVDC power cable 1-1 comprises a solid insulation system 7. The solid insulation system 7 is an electrical insulation system. The solid insulation system 7 is provided around the inner semiconducting layer 5. The solid insulation system 7 is hence arranged radially outwards of the inner semiconducting layer 5.

[0064] The solid insulation system 7 is composed of, or comprises, an electrically insulating material which has an electrical conductivity of for example at most 1000 femto Siemens (fS)/m, such as at most 100 fS/m, or at most 10 fS/m, measured at nominal voltage at a temperature of 20° C.

[0065] The solid insulation system 7 may be partially cross-linked so that it only passes a hot set test according to IEC 60811-507 up to 50% of the load specified by IEC 60811-507. The solid insulation system 7 thus fails the hot set test according to IEC 60811-507 when the load is larger than 50% of the load specified by IEC 60811-507.

[0066] The standard IEC 60811-507 referred to is Edition 1.0 of 2012-03.

[0067] The solid insulation system 7 may be partially cross-linked so that it only passes a hot set test according to IEC 60811-507 up to 40%, such as up to 30%, such as up to 25% of the load specified by IEC 60811-507.

[0068] An example of a compound with this property is LS4258DCE by Borealis.

[0069] The solid insulation system 7 may be polymer-based. The solid insulation system 7 may for example comprise cross-linked polyethylene, or polypropylene.

[0070] The HVDC power cable 1-1 comprises an outer semiconducting layer 9. The outer semiconducting layer 9 is provided around the solid insulation system 7. The outer semiconducting layer 9 is hence arranged radially outwards of the solid insulation system 7. The solid insulation system 7 is sandwiched between the inner semiconducting layer 5 and the outer semiconducting layer 9.

[0071] The outer semiconducting layer 9 acts as an insulation screen for the solid insulation system 7. The exemplified outer semiconducting layer 9 may be polymer-based and may comprise a conductive component such as carbon black.

[0072] The HVDC power cable 1-1 may comprise a metallic screen 11. The metallic screen 11 may be provided around the outer semiconducting layer 9. The metallic screen 11 may for example comprise copper. The metallic screen 11 may comprise a plurality of screen wires 11a. The screen wires 11a may be distributed along the perimeter of the outer semiconducting layer 9. The screen wires 11 a may be helically wound around the outer semiconducting layer 9. The screen wires 11 a may for example comprise copper.

[0073] The HVDC power cable 1-1 has an outer serving or sheath 13 covering the metallic screen 11. The outer serving or sheath 13 forms the outermost layer of the HVDC power cable 1-1. The outer serving or sheath 13 may for example comprise a polymeric material.

[0074] The HVDC power cable 1-1 comprises a water-blocking compound 15. The water-blocking compound 15 is arranged to restrict water migration into the HVDC power cable 1-1.

[0075] FIG. 1 shows one example of the configuration of the water-blocking compound 15 in the HVDC power cable 1-1. The water-blocking compound 15 is arranged between the interstices of the wires 3a. The wires 3a are arranged in layers, and the interstices in and between all layers may be filled with the water-blocking compound 15. All the interstices between the wires 3a of the multi-wire conductor 3 are hence filled with the water-blocking compound 15. The water-blocking compound 15 is arranged radially outside of the multi-wire conductor 3, on the outer surface of the outermost layer of the wires 3a. Water is hence prevented to migrate longitudinal in the interstices of the multi-wire conductor 3.

[0076] The water-blocking compound 15 may for example be a liquid. The water-blocking compound 15 may have a viscosity equal to or greater than 20 Pa*s. The water-blocking compound 15 may according to one example be a solid with a Shore D less than 65 at a temperature of 20° C.

[0077] The water-blocking compound 15 may be electrically conducting. The water-blocking compound 15 may for example comprise a carbon-based component which makes the water-blocking compound 15 electrically conducting. The carbon-based component may for example be graphite.

[0078] The water-blocking compound 15 may be hydrocarbon-based on silica-based. The water-blocking compound 15 may comprise a hydrocarbon-based component or a silica-based component. The water-blocking compound 15 may for example comprise polybutadiene, an antioxidant, and graphite.

[0079] The water-blocking compound 15 may be hydrophobic or hydrophilic. The water-blocking compound 15 may according to one example comprise a swelling agent.

[0080] FIG. 2 shows a cross-section of another example of an HVDC power cable 1-2. The general structure of the HVDC power cable 1-2 is similar to the HVDC power cable 1-1. The HVDC power cable 1-2 however comprises a tape 17. The tape 17 is wound around the multi-wire conductor 3. The tape 17 may be wound around the multi-wire conductor 3 along the entire length of the multi-wire conductor 3. The tape 17 may be electrically conducting or electrically non-conducting/electrically insulating. The tape 17 may for example comprise a polymer. The tape 17 is arranged between the multi-wire conductor 3 and the inner semiconducting layer 5. The tape 17 may be in direct contact with the inner surface of the inner semiconducting layer 5. The tap 17 may be in direct contact with the multi-wire conductor 3 and/or with the water-blocking compound 15.

[0081] FIG. 3 shows a cross-section of an example of an HVDC power cable 1-3. The structure of the HVDC power cable 1-3 is similar to the HVDC power cable 1-1. The HVDC power cable 1-2 has the water-blocking compound 15 provided in the interstices between the screen wires 11a. The water-blocking compound 15 is also provided on the outer surface of the screen wires 11a.

[0082] The water-blocking compound 15 may in this example optionally also be provided in the interstices between the wires 3a of the multi-wire conductor 3.

[0083] The water-blocking compound 15 could according to one variation be provided directly on the outer surface of the outer semiconducting layer 9 instead of around/between the interstices of the screen wires 11a.

[0084] The HVDC power cable 1-3 may according to one variation include a tape wound around the outer semiconducting layer. The tape may for example be wound around the screen wires 11a. The water-blocking compound may according to one example at least partly be in direct contact with the tape.

[0085] FIG. 4 shows a flowchart of a method of manufacturing an HVDC power cable such as HVDC power cable 1-1 to 1-3. The method in general comprises providing the water-blocking compound 15 internally in the HVDC power cable 1-1 to 1-3 to restrict water migration into the HVDC power cable 1-1 to 1-3.

[0086] For the HVDC power cables 1-1 and 1-2, the providing of the water-blocking compound 15 internally comprises a) stranding the plurality of wires 3a to form the multi-wire conductor 3. The stranding involves providing the water-blocking compound 15 between each layer of wires 3a. This may be achieved during the stranding process, as the stranding machine strands the wires 3a layer by layer. The stranding may furthermore involve providing the water-blocking compound 15 on the outermost layer, on the outer surface, of the wires 3a. The method may further comprise b) extruding the inner semiconducting layer 5 and the solid insulation system 7 onto the multi-wire conductor 3, which has had its interstices/spaces between the wires 3a provided with the water-blocking compound 15. The outer semiconducting layer 9 is extruded on the solid insulation system 7. The extrusion may be a triple-extrusion process, in which the inner semiconducting layer 5, the solid insulation system 7 and the outer semiconducting layer 9 are co-extruded.

[0087] For the HVDC cable 1-3, the providing of the water-blocking compound 15 involves providing it onto and in between the screen wires 11a.

[0088] All the HVDC power cables 1-1 to 1-3 disclosed herein may be free of water swelling tape.

[0089] The inventive concept has mainly been described above with reference to a few examples. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the inventive concept, as defined by the appended claims.