Offshore system comprising dynamic submarine power cable
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- NKT HV CABLES AB
- Filing Date
- 2023-06-20
- Publication Date
- 2026-06-17
AI Technical Summary
Bending stiffeners in dynamic submarine power cables create hotspots due to low thermal conductivity, limiting the maximum current capacity of the cables.
Incorporating a bending reinforcement with a central channel and an offshore structural tube that allows water cooling through radial openings or forced convection to manage heat distribution along the cable.
The cooling mechanism reduces the temperature of the cable, enabling higher current capacity and lower conductor cross-section requirements, thus enhancing the cable's performance and efficiency.
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Abstract
Description
[Technical field]
[0001] The present disclosure relates generally to offshore systems comprising dynamic submarine power cables. [Background technology]
[0002] Power generating floating offshore structures, such as floating wind turbines, are connected to dynamic subsea power cables to deliver the power generated by the floating wind turbines to the power grid. Other types of floating offshore structures, such as floating oil platforms, can be connected to dynamic subsea power cables for power consumption purposes.
[0003] The floating offshore structure is subjected to wave motions, therefore the dynamic subsea power cable is connected to the floating offshore structure via bending stiffeners to control the bending radius of the cable. Summary of the Invention
[0004] Power cables are designed to be able to operate at a maximum operating temperature which may be 90°C according to international standards such as IEC 60287-1-1.
[0005] It has been found that the bending stiffener, due to its low thermal conductivity, creates a cable hot spot along the cable path between the seabed and the floating offshore structure. This hot spot is the hottest area of the dynamic submarine power cable. The maximum current allowed in the dynamic submarine power cable is therefore determined by the temperature within the power cable as it extends through the bending stiffener.
[0006] A general object of the present disclosure is to provide an offshore system that overcomes, or at least mitigates, problems in the prior art.
[0007] Thus, an offshore system is provided comprising: a dynamic submarine power cable; a bend stiffener having a lower end and an upper end, the bend stiffener having a central channel extending from the lower end to the upper end, the central channel receiving the dynamic submarine power cable with a radial spacing between an inner surface of the central channel and an outer surface of the dynamic submarine power cable along a length of the dynamic submarine power cable disposed within the bend stiffener, the radial spacing forming a longitudinal channel between the bend stiffener and the dynamic submarine power cable; and an offshore structural tube connected to the bend stiffener, wherein A) the offshore structural tube has an inner tube channel in fluid communication with the longitudinal channel. A) the offshore structural tube has a through opening extending from the inner tube channel through a wall of the offshore structural tube to allow water flowing through the bend stiffener from the lower end to exit the offshore structural tube through the through opening to provide water cooling of the dynamic submarine power cable within the bend stiffener; or B) the bend stiffener has a radial through opening located within ¼ of the entire axial length of the bend stiffener from the upper end and defined by the distance between the lower end and the upper end to allow water flowing through the bend stiffener from the lower end to exit the bend stiffener through the radial through opening to provide water cooling of the dynamic submarine power cable within the bend stiffener.
[0008] Thus, hotspot regions of the dynamic submarine power cable are cooled by water, as a result of which higher currents can be supplied through the dynamic submarine power cable and / or the cross section of the conductor(s) of the dynamic submarine power cable can be reduced during the design stage as a result of a cooler dynamic submarine power cable in the bending stiffeners.
[0009] The radial through openings may be located within ⅕ or 1 / 10 of the total axial length of the bending stiffener from the top end of the bending stiffener, according to some examples.
[0010] The hottest point of a dynamic submarine power cable in an uncooled bend stiffener is typically about 2 / 3 of the total length of the bend stiffener measured from the bottom end. By locating the radial through openings within 1 / 4, 1 / 5, or 1 / 10 of the total axial length of the bend stiffener measured from the top end, the hottest point is cooled and the heat distribution curve shifts towards the top end of the bend stiffener. Even the uncooled top section of the dynamic submarine power cable in the bend stiffener has a substantially lower temperature than if the dynamic submarine power cable were completely uncooled.
[0011] The water cooling may be by natural convection, according to one example, which makes the cooling robust since no pumps or similar devices are required for water cooling.
[0012] According to one example, the offshore system may include a pump configured to pump water through the longitudinal channel and through the through openings in the offshore structural tubes. Thus, forced water cooling may be achieved.
[0013] The pump may, for example, be located outside the offshore structure pipe.
[0014] As an example, the applicant has taken a 3 x 1000 mm conductor having a maximum allowable conductor temperature of 90°C. 2 The improvement provided by natural convection was analyzed for a 230 kV nominal voltage AC dynamic submarine power cable. In the simulation, a current of 1050 A was fed through the dynamic submarine power cable. This resulted in a maximum conductor temperature of the cable inside the bending stiffeners of about 140 °C in the absence of natural convection. When natural convection through the bending stiffeners was included in the simulation, the maximum conductor temperature only reached 70 °C, i.e. the temperature was reduced by about 50%.
[0015] According to one embodiment, the offshore structure pipe is an I-pipe.
[0016] According to one embodiment, the flexural stiffener is a submerged flexural stiffener. Thus, the flexural stiffener may be placed underwater.
[0017] According to one embodiment, the through openings or the radial through openings are arranged in the water, so that the through openings or the radial through openings are submerged in the water.
[0018] According to one embodiment, the dynamic submarine power cable is a high voltage power cable with a rated voltage of at least 33 kV.
[0019] The dynamic submarine power cable may have a rated voltage of at least 132 kV, such as at least 220 kV, according to some examples.
[0020] According to one embodiment, the offshore structural tube is positioned vertically above the bending reinforcement.
[0021] According to one embodiment, the dynamic subsea power cable extends inside an inner pipe channel of the offshore structure pipe.
[0022] One embodiment includes an offshore floating structure, the offshore structure tube forming part of the offshore floating structure.
[0023] According to one embodiment, the offshore floating structure is one of a floating wind turbine, a floating electrical substation, a floating hydrocarbon platform, or a floating hydrocarbon vessel.
[0024] According to a second aspect, there is provided a method of cooling a dynamic submarine power cable in an offshore system, the offshore system including: a dynamic submarine power cable; a bend stiffener having a lower end and an upper end, the bend stiffener having a central channel extending from the lower end to the upper end, the central channel receiving the dynamic submarine power cable with a radial spacing between an inner surface of the central channel and an outer surface of the dynamic submarine power cable along a length of the dynamic submarine power cable disposed within the bend stiffener, the radial spacing forming a longitudinal channel between the bend stiffener and the dynamic submarine power cable; and an offshore structural tube connected to the bend stiffener, the offshore structural tube having an inner tube channel in fluid communication with the longitudinal channel, the offshore structural tube having an inner tube channel in fluid communication with the longitudinal channel, the inner tube channel being in fluid communication with the longitudinal channel, the outer ... The method includes providing a bend stiffener such that its lower end is submerged in seawater to allow seawater to enter the longitudinal channel, the method comprising providing a bend stiffener having a through opening extending from the side pipe channel through a wall of the offshore structure pipe to allow water flowing through the bend stiffener from a lower end to exit the offshore structure pipe through the through opening to provide water cooling of a dynamic submarine power cable within the bend stiffener, or the bend stiffener having a radial through opening located within ¼, ⅕, or ⅙ of the total axial length of the bend stiffener from the upper end and defined by a distance between the lower end and the upper end to allow water flowing through the bend stiffener from a lower end to exit the bend stiffener through the radial through opening to provide water cooling of a dynamic submarine power cable within the bend stiffener, the method comprising providing a bend stiffener such that its lower end is submerged in seawater to allow seawater to enter the longitudinal channel.
[0025] According to one embodiment, seawater flows along the longitudinal channels and exits through the through openings or the radial through openings by natural convection.
[0026] According to one embodiment, the through openings or the radial through openings are arranged under water.
[0027] In general, all terms used in the claims should be interpreted according to their ordinary meaning in the art unless otherwise expressly defined herein. All references to "a / an / the element, apparatus, component, means, etc." should be interpreted non-limitingly as referring to at least one example of the element, apparatus, component, means, etc., unless otherwise specified. Specific embodiments of the inventive concept will now be described, by way of example, with reference to the accompanying drawings, in which: [Brief description of the drawings]
[0028] [Figure 1] 1 shows a schematic of an offshore system. [Diagram 2] 2 shows a schematic enlarged cross-sectional view of a portion of one implementation of the offshore system of FIG. 1; [Diagram 3] 2 shows a schematic enlarged cross-sectional view of a portion of another implementation of the offshore system of FIG. 1; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0029] The inventive concept will now be more fully described below with reference to the accompanying drawings, in which exemplary embodiments are shown. However, the inventive concept may be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. Rather, these embodiments are provided as examples 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 reference numerals refer to like elements throughout the description.
[0030] 1 shows an example of an offshore system 1. The offshore system 1 includes an offshore floating structure 3.
[0031] The offshore system 1 is deployed in water 5 such as seawater. Specifically, the offshore floating structure 3 is deployed in water 5 and floats on the water surface.
[0032] In this embodiment, the offshore floating structure 3 is a floating wind turbine, but may alternatively be, for example, a floating electrical substation, a floating hydrocarbon platform, a floating hydrocarbon vessel, a semi-submersible platform, or any other offshore floating structure that generates or consumes electricity.
[0033] The offshore floating structure 3 comprises an offshore structure pipe 7. The offshore structure pipe 7 may be made of a metal, such as steel. The offshore structure pipe 7 extends vertically or essentially vertically downwards in a direction towards the seabed.
[0034] The offshore structure pipe 7 may be an I-pipe.
[0035] The offshore system 1 includes a bending stiffener 9. The bending stiffener 9 has an upper end 9a and a lower end 9b. The bending stiffener 9 tapers in a direction from the upper end 9a to the lower end 9b.
[0036] The flexural stiffener 9 has a central channel extending from an upper end 9a to a lower end 9b along a longitudinal axis of the flexural stiffener 9.
[0037] The bending reinforcement 9 is connected to the offshore structure pipe 7. The upper end 9a of the bending reinforcement 9 is connected to the lower part of the offshore structure pipe 7. The offshore structure pipe 7 is disposed vertically or essentially vertically above the bending reinforcement 9.
[0038] The offshore system 1 comprises a dynamic submarine power cable 11 .
[0039] The dynamic submarine power cable 11 may be a single or multi-phase AC power cable or a single or multi-pole DC power cable.
[0040] The dynamic submarine power cable 11 may be a high voltage AC or DC power cable.
[0041] The dynamic submarine power cable 11 comprises a conductor and an insulation system disposed around the conductor. The insulation system comprises an inner semiconducting layer, an insulating layer disposed outside the inner semiconducting layer, and an outer semiconducting layer disposed outside the insulating layer.
[0042] The dynamic submarine power cable 11 comprises a metallic water barrier arranged concentrically with the conductors outside the insulation system. The metallic water barrier may be corrugated or smooth. The metallic water barrier may comprise lead or may be lead-free. If lead-free, the metallic water barrier may comprise, for example, copper, aluminum, or stainless steel. Alternatively, the dynamic submarine power cable 11 may have a wet design, i.e. may not have a metallic water barrier.
[0043] The dynamic submarine power cable 11 comprises a polymer sheath disposed on the outside of a metallic water barrier.
[0044] The dynamic submarine power cable 11 may comprise one or more armor layers disposed about the polymer sheath. The armor layer(s) may include metal wires or ropes, for example made of galvanized steel or austenitic stainless steel, synthetic wires such as jacketed aramid fibers, or a combination of both.
[0045] The dynamic submarine power cable 11 may have an outer serving disposed outside the one or more armor layers.
[0046] When the dynamic submarine power cable 11 includes multiple electrical phases or poles, the dynamic submarine power cable 11 includes multiple conductors, each conductor having the corresponding structures described above disposed therearound, i.e., insulation system, metallic water barrier, and polymer sheath. Each such structure forms a power core. Armor layer(s) are disposed around all of the power cores.
[0047] The dynamic submarine power cable 11 passes through the entire bending stiffener 9 in a central channel of the bending stiffener 9 .
[0048] A dynamic submarine power cable 11 extends from the offshore floating structure 3 to the seabed.
[0049] The dynamic submarine power cable 11 passes through the offshore structure pipe 7 and is fixed to the offshore floating structure 3. The dynamic submarine power cable 11 can be fixed to the offshore floating structure 3 by a hang-off device.
[0050] The dynamic submarine power cable 11 terminates on the offshore floating structure 3 .
[0051] The dynamic submarine power cable 11 may be cooled by natural convection of water inside the bending stiffeners 9 or by forced cooling, as described in more detail below.
[0052] FIG. 2 shows an enlarged view of one realization of the offshore system 1 in the area of the bending stiffener 9 which is immersed in water.
[0053] The central channel 9c of the bending stiffener has an inner surface that is radially spaced from the outer surface of the dynamic submarine power cable 11 along the entire length of the dynamic submarine power cable 11 that passes through the bending stiffener 9. Thus, there is a radial spacing between the dynamic submarine power cable 11 and the central channel 9c. The inner surface of the central channel 9c may comprise radially inwardly extending structures, such as, for example, ribs that extend along the length of the bending stiffener 9. The radially inwardly extending structures are in contact with the dynamic submarine power cable 11. The inner surface may include a plurality of grooves, the grooves being provided between adjacent pairs of the radially inwardly extending structures. For example, the radial spacing may be formed by grooves between the radially inwardly extending structures.
[0054] The radial spacing forms a longitudinal channel between the bending stiffener 9 and the dynamic submarine power cable 11. The longitudinal channel extends from the upper end 9a to the lower end 9b of the bending stiffener 9 along the entire length of the dynamic submarine power cable 11 disposed within the bending stiffener 9.
[0055] The offshore structure tube 7 has an inner tube channel 7a in fluid communication with the longitudinal passage of the bending stiffener 9. The longitudinal passage opens vertically upwards into the inner tube channel 7a.
[0056] The offshore structure pipe 7 has one or more through openings 7b extending from the inner pipe channel 7a through a wall 7c of the offshore structure pipe 7. The inner pipe channel 7a is thus in fluid communication with the exterior of the offshore structure pipe 7.
[0057] As shown in FIG. 2, in use water 13 enters the longitudinal channel between the bending stiffener 9 and the dynamic submarine power cable 11 at the lower end 9b of the bending stiffener 9.
[0058] The water 13 is heated by the dynamic submarine power cable 11 due to the current flowing through the dynamic submarine power cable 11. This causes the water 13 to rise inside the bending reinforcement 9 along the longitudinal channel.
[0059] The water 13 flows through the entire bend stiffener 9 and, upon exiting the bend stiffener 9, rises further into the inner pipe channel 7a of the offshore structure pipe 7. When the water 13 reaches one or more through openings 7b, the water 13 passes through the one or more through openings 7b and exits the offshore structure pipe 7. Thus, the water 13 circulates back to the water body outside the bend stiffener 9 and the offshore structure pipe 7, which are submerged in water. This process is repeated continuously, and thus the dynamic submarine power cable 11 is water-cooled by natural convection or, alternatively, by forced cooling.
[0060] FIG. 3 shows an enlarged view of another realization of the offshore system 1 in the region of the bending stiffener 9' which is immersed in water.
[0061] The bending stiffener 9' is similar to the bending stiffener 9. However, the bending stiffener 9' has one or more radial through opening(s) 9d extending from the central channel 9c to the outer surface of the bending stiffener 9'. Each such radial through opening 9d is located in the upper region of the bending stiffener 9'. The bending stiffener 9' has a total axial length L, which is the length of the bending stiffener 9' measured between the upper end 9a and the lower end 9b, i.e. the distance between the upper end 9a and the lower end 9b. The one or more radial through openings 9d are located at a distance d from the upper end 9a, which distance d is at most 1 / 4, 1 / 5, or 1 / 10 of the total axial length L. Thus, d≦1 / 4L, or d≦1 / 5L, or d≦1 / 10L, measured from the upper end 9a.
[0062] The water 13 flows through the bending stiffener 9' to the radial through-opening 9d. When the water 13 reaches the radial through-opening 9d, it passes through the radial through-opening 9d and exits the bending stiffener 9'. Thus, the water 13 circulates back to the water body outside the bending stiffener 9' where it is immersed in water. This process is repeated continuously, thus the dynamic submarine power cable 11 is water-cooled by natural convection or, alternatively, by forced cooling.
[0063] The inventive concept has been described above primarily with reference to certain examples, however, as will be readily appreciated by those skilled in the art, other embodiments than those disclosed above are equally possible within the scope of the inventive concept, as defined by the appended claims.
Claims
1. Offshore system (1), Dynamic submarine power cable (11) and A bending reinforcement member (9, 9') having a lower end (9b) and an upper end (9a), wherein the bending reinforcement member (9, 9') has a central channel (9c) extending from the lower end (9b) to the upper end (9a), and the central channel (9c) receives the dynamic submarine power cable (11) along the length of the dynamic submarine power cable (11) disposed within the bending reinforcement member (9, 9') with a radial gap between the inner surface of the central channel (9c) and the outer surface of the dynamic submarine power cable (11), and the radial gap forms a longitudinal channel between the bending reinforcement member (9, 9') and the dynamic submarine power cable (11), and The system comprises an offshore structural pipe (7) connected to the aforementioned bending reinforcement members (9, 9'), A) The offshore structural pipe (7) has an inner pipe channel (7a) that is in fluid communication with the longitudinal waterway, and the offshore structural pipe (7) has a through-opening (7b) that extends from the inner pipe channel (7a) through the wall (7c) of the offshore structural pipe (7), so that water (13) flowing from the lower end (9b) through the bending reinforcement (9) can exit the offshore structural pipe (7) through the through-opening (7b) in order to provide water cooling for the dynamic submarine power cable (11) within the bending reinforcement (9), or B) An offshore system (1) wherein the bending reinforcement (9') has a radial through-opening (9d) located within 1 / 4 of the axial total length (L) defined by the distance between the lower end (9b) and the upper end (9a) of the bending reinforcement (9), from the upper end (9a), allowing water (13) flowing from the lower end (9b) through the bending reinforcement (9) to exit the bending reinforcement (9') through the radial through-opening (9d) to provide water cooling for the dynamic submarine power cable (11) within the bending reinforcement (9').
2. The offshore system (1) according to claim 1, wherein the offshore structural pipe (7) is an I-pipe.
3. The offshore system (1) according to claim 1 or 2, wherein the bending reinforcement member (9) is an underwater bending reinforcement member.
4. The offshore system (1) according to claim 1 or 2, wherein the through-opening (7b) or the radial through-opening (9d) is located underwater.
5. The offshore system (1) according to claim 1 or 2, wherein the dynamic submarine power cable (11) is a high-voltage power cable with a rated voltage of at least 33 kV.
6. The offshore system (1) according to claim 1 or 2, wherein the dynamic submarine power cable (11) extends inside the inner pipe channel (7a) of the offshore structural pipe (7).
7. The offshore system (1) according to claim 1 or 2, comprising an offshore floating structure (3), wherein the offshore structural pipe (7) forms a part of the offshore floating structure (3).
8. The offshore system (1) according to claim 7, wherein the offshore floating structure (3) is one of a floating wind turbine, a floating substation, a floating hydrocarbon platform, or a floating hydrocarbon vessel.
9. A method for cooling a dynamic submarine power cable (11) of an offshore system (1), wherein the offshore system (1) comprises the dynamic submarine power cable (11), a bending reinforcement member (9) having a lower end (9b) and an upper end (9a), the bending reinforcement member (9) having a central channel (9c) extending from the lower end (9b) to the upper end (9a), the central channel (9c) receiving the dynamic submarine power cable (11) having a radial gap between the inner surface of the central channel (9c) and the outer surface of the dynamic submarine power cable (11) along the length of the dynamic submarine power cable (11) positioned within the bending reinforcement member (9), the radial gap forming a longitudinal channel between the bending reinforcement member (9) and the dynamic submarine power cable (11), and an offshore structural pipe (7) connected to the bending reinforcement member (9), The offshore structural pipe (7) has an inner pipe channel (7a) that is in fluid communication with the longitudinal waterway, and the offshore structural pipe (7) has a through opening (7b) that extends from the inner pipe channel (7a) through the wall (7c) of the offshore structural pipe (7), so that water (13) flowing from the lower end (9b) through the bending reinforcement (9) can exit the offshore structural pipe (7) through the through opening (7b) in order to provide water cooling for the dynamic submarine power cable (11) within the bending reinforcement (9), or the bending reinforcement The material (9') has a radial through-opening (9d) located within 1 / 4, 1 / 5, or 1 / 10 of the axial total length (L) of the bending reinforcement (9), defined by the distance between the lower end (9b) and the upper end (9a), from the upper end (9a), allowing water (13) flowing from the lower end (9b) through the bending reinforcement (9) to exit the bending reinforcement (9') through the radial through-opening (9d) in order to provide water cooling for the dynamic submarine power cable (11) within the bending reinforcement (9'). The method described above is A method comprising providing the bending reinforcement member (9) such that the lower end (9b) is submerged in seawater and allows seawater to enter the longitudinal channel.
10. The method according to claim 9, wherein the seawater flows along the longitudinal channel and exits through the through-opening (7b) or the radial through-opening (9d) by natural convection.
11. The method according to claim 9 or 10, wherein the through-opening (7b) or the radial through-opening (9d) is located in water.