System and method for extending the lifespan of power cables

Abstract

A system and corresponding method for extending the service life of a power cable (10) attached to an offshore structure (100). The system comprises a guide unit (102) for guiding a power cable (10) from a body of water to an offshore structure (100) so that the power cable (10) is in a position to be electrically connected to the offshore structure (100), wherein the power cable has a first length portion that is mainly vertically positioned along the offshore structure (100) and a second length portion that deviates outward from the offshore structure (100) and extends through a body of water. A transition area between the first and second length portions defines a primary fatigue area (104), and the guide unit (102) further comprises a portion that can engage with the transition area of ​​the power cable (10).

Description

Technical Field

[0001] The present disclosure generally relates to the field of offshore power generation structures and power cables. More specifically, the present invention describes systems and methods for extending the service life of power cables attached to offshore structures.

Background Art

[0002] Power cables, such as inter-array power cables, are used to transport energy generated at offshore structures. For example, wind turbines or windmills on offshore structures transmit power to land using power cables. Similar power cables can also be used at other renewable energy production sites, and further at offshore oil and gas structures. The power cable extends from the offshore structure into the sea. Waves, currents, wind, and the movement of the offshore structure cause relative movement between the power cable and the offshore structure. This relative movement wears out the power cable.

[0003] I-tubes and J-tubes are fixed to the offshore structure and are used to guide and protect the power cable as it extends from the offshore structure into the water area. During operation, an offshore structure equipped with both tubes and cables is subject to interference from wind, waves, and ocean currents during deployment at sea. These impose periodic mechanical stresses on the power cable, causing mechanical damage to the power cable. The weakest point of each power cable is the area near the connection at the floating vessel. This main fatigue area is where the cable receives the highest mechanical stress and is thus the most prone to damage.

[0004] The design challenge in providing the cable with the tube is how to address the fatigue caused by the interaction between the cable and the tube. Existing systems have drawbacks regarding the service life of such cables. Therefore, further contributions in this technical field are sought.

Summary of the Invention

[0005] The object of the present invention is to provide a system and method for extending the service life of power cables. This object can be achieved by the features defined in the independent claims. Further improvements are characterized by the dependent claims. The present invention is defined by the claims.

[0006] According to a first embodiment, a system is provided for extending the service life of a power cable attached to an offshore structure. The system comprises a guide unit for guiding the power cable from the water to the offshore structure so that the power cable is in a position to be electrically connected to the offshore structure. The power cable has a first length portion that is mainly vertically aligned along the offshore structure and a second length portion that deviates outward from the offshore structure and extends through the water. The transition area between the first and second length portions defines the primary fatigue region. The guide unit further comprises a portion that can engage with the transition area of ​​the power cable. The system further comprises means for providing relative motion between the guide unit and the power cable and locking means for locking the relative motion between the guide unit and the power cable, so that the portion of the guide unit that can engage with the transition area of ​​the power cable has a variable position along the longitudinal length of the power cable. The system may be configured such that the primary fatigue region is variable along the length of the power cable. This allows the fatigue zone of the power cable to be shifted relative to the guide unit of the offshore structure, thereby extending the service life of the power cable.

[0007] The relative motion provided and prevented by the system may be substantially vertical relative motion between the guide unit and the power cable. Alternatively, or in addition, such relative motion may be in a direction along the longitudinal length of the guide unit.

[0008] The system may further include a plurality of locking positions distributed along the longitudinal direction of the guide unit. Each locking position can engage with a locking mechanism to prevent relative movement. The plurality of locking positions may be predetermined along the longitudinal direction of the guide unit.

[0009] The means for providing relative motion may include an actuator and / or a hoisting device. The means may be further configured to move the power cable from a first locking position to a second locking position among a plurality of predetermined locking positions. The means may provide relative motion between the guide unit and the power cable. The hoisting device is located on an offshore structure and may further include a tensioning element that can be attached to the power cable. Thus, the hoisting device is capable of raising and lowering the power cable.

[0010] The system may further include a controller communicated with locking means and means for providing relative motion. The controller may be configured to monitor the state of the primary fatigue region and generate instructions for providing relative motion and / or locking the relative motion via the locking means based on the state of the primary fatigue region. Optionally, or in addition, the controller is communicated with a sensor. The sensor may be configured to monitor the state of the primary fatigue region and transmit that state to the controller. The controller may further be configured to generate instructions for activating the locking means when the power cable is moved from a first locked position to a second locked position. The controller may further be configured to deactivate the locking means and generate instructions for providing relative motion when the state exceeds a predetermined threshold. Optionally, the state includes the elapsed time since the last time relative motion was provided. The controller may further be configured to generate instructions for activating the locking means when the primary fatigue region has been displaced by a predetermined length. The predetermined length may be a predetermined clearance length.

[0011] The guide unit may be selected from the group consisting of I-tubes, J-tubes, telescopic tubes, short tube elements, bell mouths, and connector units. Optionally, a bend stiffener can be attached to the lower end of the guide unit. The offshore structure may be a floating offshore structure. Preferably, the floating offshore structure includes a wind turbine and / or a wave energy converter and / or a tidal turbine.

[0012] A second embodiment provides a method for extending the service life of a power cable attached to an offshore structure. The method includes providing a system according to a first aspect of the present invention, deactivating a locking mechanism and providing relative motion for moving the power cable relative to a guide unit, and activating the locking mechanism to lock the relative motion between the power cable and the guide unit. The step of providing relative motion between the power cable and the guide unit may further include pulling the power cable from a first locked position to a second locked position.

[0013] The method may further include detecting the state of the primary fatigue region via a controller. The step of deactivating the locking mechanism and providing relative motion may be performed when the state exceeds a predetermined threshold. In addition, or alternatively, the step of activating the locking mechanism may be performed when the primary fatigue region has been displaced by a predetermined clearance length.

[0014] At least one of the embodiments described above provides one or more solutions to problems and shortcomings in the background art. Other technical advantages of the disclosure will be readily apparent to those skilled in the art from the following description and claims. The various embodiments of the application obtain only some of the advantages described. None of the advantages are essential to the embodiments. Any claimed embodiment can be technically combined with one or more other claimed embodiments.

[0015] This disclosure will be further explained with reference to the examples shown in the accompanying drawings. [Brief explanation of the drawing]

[0016] [Figure 1] This is a schematic diagram of an offshore structure and conveying equipment. [Figure 2A] This is a schematic diagram of the guide unit held in the first locked position. [Figure 2B] This is a schematic diagram of the guide unit held in the second locked position. [Figure 3] This is a detailed diagram of a hoisting device located on an offshore structure. [Figure 4] This is a detailed diagram of an actuator positioned on an offshore structure. [Modes for carrying out the invention]

[0017] Embodiments of the present invention provide a system and method for extending the service life of power cables attached to offshore structures. This detailed description details at least one method of carrying out the claimed invention with reference to the drawings.

[0018] As shown in Figure 1, the system comprises a guide unit 102 and means 300, 400 for providing relative motion between the guide unit 102 and the power cable 10. The offshore structure 100 may have the guide unit 102, and the guide unit 102 may be movably attached to the offshore structure 100. As shown in Figure 1, the guide unit 102 is suitable for a power cable 10 that can be attached to the offshore structure 100. The power cable 10 has a first length portion that is positioned vertically along the offshore structure 10 and a second length portion that deviates outward from the offshore structure and extends into the water. The power cable 10 may ultimately be laid on the seabed 50. In other words, the power cable 10 may have a first length portion that extends from the upper end of the guide unit 102 to the lower end of the guide unit 102 and a second length portion that extends from the lower end of the guide unit 102 to below the sea surface 40.

[0019] The guide unit 102 guides the power cable 10 from the water to the offshore structure 100 and functions to ensure that the power cable 10 is in a position to be electrically connected to the offshore structure 100. Electrical connection to the offshore structure 100 may also include connection to one or more electrical components on the offshore structure. The offshore structure 100 may further include a wind turbine 30, thereby forming part of a power distribution system that facilitates power transmission from the wind turbine 30 to various components. In Figure 1, the offshore structure 100 is shown to include a wind turbine 30, but the offshore structure 100 may have any structure suitable for power generation.

[0020] The guide unit 102 may be movably mounted on the support column 101, and the guide unit 102 and the support column 101 each extend parallel to each other in a direction substantially perpendicular to the sea surface 40. As is best seen in Figures 2A and 2B, the guide unit may be slidably positioned on the support column 101, for example by wheels 108. This allows relative motion when a portion of the guide unit 102 engages with the transition area of ​​the power cable 10. A transport device may be provided for transporting the power cable 10 from a floating vessel (e.g., a ship) to the offshore structure 100.

[0021] The guide unit 102 may be a generally hollow body structured to guide the power cable 10. The guide unit 102 may interact with the primary fatigue region 104 of the power cable 10. The primary fatigue region 104 of the power cable 10 is the region near where the power cable 10 is connected to the offshore structure 100 via the guide unit 102. The primary fatigue region 104 may be further defined as being in the transition area between the first and second length portions of the power cable 10. A portion of the guide unit 102 may further interact with the power cable 10 in the transition area due to wind and current forces. The primary fatigue region 104 is the region of the power cable 10 most susceptible to failure by external forces. As can be seen from Figure 1, the lower end of the guide unit 102 interacts with the power cable 10 and as the two move relative to each other. The lower end of the guide unit 102 may be a portion that can engage with and interact with the transition area of ​​the power cable 10. This interaction may cause wear on the main fatigue region 104 of the power cable 10.

[0022] To protect the power cable 10, a bend stiffener 20 may be provided toward the lower end of the guide unit 102 to reduce the bending motion of the power cable 10. The bend stiffener 20 may be formed of an elongated sleeve defining a substantially cylindrical passage capable of accommodating at least a portion of the power cable 10. The bend stiffener 20 may include a bend stiffener connector that is detachably connected to the guide unit 102. In Figure 1, the guide unit 102 includes a J-tube with a flange that can be attached to the bend stiffener connector. However, different types of guide units 102, such as I-tubes, J-tubes, telescopic tubes, short tube elements, bell mouths, and connector units, may be used with or without the bend stiffener 20.

[0023] The system comprises locking means 110 for locking the relative movement between the guide unit 102 and the power cable 10, and means 300, 400 for providing relative movement between the guide unit 102 and the power cable 10. The locking means 110 locks the relative movement between the guide unit 102 and the power cable 10. The relative movement provided by the means 300, 400 is related to the substantially vertical relative movement between the guide unit 102 and the power cable 10. The relative movement may be in a direction along the longitudinal length of the guide unit 102. Additional horizontal relative movement may occur between the power cable 10 and the guide unit 102 due to forces by wind and / or current. The present invention can provide and / or prevent relative movement in the vertical direction or in the direction of the guide unit 102, but the power cable 10 is displaceable horizontally within the guide unit 102, whereby the main fatigue region 104 of the power cable 10 can engage with the guide unit 102.

[0024] The locking means 110 may include known devices suitable for selectively restricting the relative movement between the guide unit 102 and the power cable 10. For example, the power cable 10 may be held within the guide unit 102 by the locking means. For example, the power cable 10 may be held by the offshore structure 100, and the guide unit 10 may also be held by the offshore structure 100. The means 300, 400 and the locking means 110 are capable of moving the main fatigue region 104 along the longitudinal length of the power cable 10 and locking the power cable 10 in place when the main fatigue region 104 is moved. The main fatigue region 104 may be moved by moving the power cable 10 without moving the guide unit 102, or by moving the guide unit 102 without moving the power cable 10, or a combination of both. An example of moving the guide unit 102 is shown in Figures 2A and 2B, where the guide unit 102 is raised from a lower position (height) in Figure 2A to a higher position (height) in Figure 2B. Therefore, in Figure 2A, the guide unit 102 is closer to the seabed 50 than in Figure 2B. In this way, the main fatigue region 104 can be moved along the power cable 10. This provides the technical benefit of extending the service life of the power cable 10. The distance between the position in Figure 2A and the position in Figure 2B may be a predetermined length. The lower position may be a first locking position, and the higher position may be a second locking position. Figures 2A and 2B show two locking positions, but there may be more than two locking positions. The locking positions may be predetermined. The means for providing relative motion may include an actuator 300 or a hoisting device 400, which may be configured to move the power cable 10 from a first locking position to a second locking position among a plurality of locking positions.

[0025] With the system shown in the figure, it becomes possible to make the part of the guide unit 102 that interacts with the transition area in the main fatigue area of the power cable 10 variable over time. As a result, the service life of the power cable 10 is extended. The system may further include a storage space for storing the surplus cable length drawn towards the offshore structure 100, and means for guiding the surplus folding length of the power cable 10 to the storage space.

[0026] The controller 120 may be communicatively connected to a sensor configured to monitor the state of the main fatigue area 104, and may also be further communicatively connected to means for providing relative movement and locking means. Based on the state received from the sensor, the controller 120 can perform an operation of generating an instruction for activating / deactivating the locking means and / or the means for providing relative movement. The state of the guide unit 102 and / or the state of the power cable 10 may provide appropriate data for determining whether the power cable 10 in the main fatigue area 104 is damaged, such as, for example, the wall thickness of the power cable or the elapsed time since a part of the power cable in the main fatigue area was last moved. The controller 120 may use empirical data and / or statistical analysis to determine an appropriate period between activations of the means for providing relative movement. The period may be, for example, 6 months, 1 year, 3 years, or 5 years. The controller 120 may be manually operated to move the main fatigue area by the relative movement between the guide unit 102 and the power cable 10.

[0027] The end of the power cable 10 closest to the offshore structure 100 may have a plurality of predetermined locking positions distributed in the longitudinal direction of the guide unit 102. Each locking position can engage with the locking means 110 to prevent relative movement between the power cable 10 and the guide unit 102. The means for providing relative movement may be further configured to move the end of the power cable 10 from a first locking position to a second locking position among the plurality of predetermined locking positions.

[0028] The controller 120 may be programmed with predetermined thresholds related to minimum or maximum quantities, so that the controller 120 can be further configured to activate or deactivate the locking means 110 and the means providing relative motion when the state reaches the predetermined threshold. The predetermined threshold may be related to the minimum thickness of the layers of the power cable 10 in the main fatigue region 104. The sensor may also be operated to monitor the difference in elapsed time since the means providing relative motion was last activated. In such a configuration, the predetermined threshold may be the maximum elapsed time. Optionally, the controller 120 may be further configured to deactivate the means providing relative motion and generate an instruction to activate the locking means 110 when the main fatigue region 104 has been displaced by a predetermined length. The controller 120 may be configured to deactivate the means providing relative motion and generate an instruction to activate the locking means 110 when the power cable 10 has been moved from a first locking position to a second locking position.

[0029] Looking at Figure 3, the means for providing relative motion may include, for example, a hoisting device 400 positioned on the offshore structure 100. For clarity, part of the guide unit 102 is omitted from the illustration. The hoisting device 400 may include a frame 410 that is detachably attached to the offshore structure 100. A rotating drum 420 on which a wire 432 is wound may be positioned at the upper end 412 of the frame 410. The wire 432 hangs downward due to gravity and can extend into the guide unit 102 and along the entire length of the guide unit 102, with the wire end 434 terminating below the opening at the lower end of the guide unit 102. The wire end 434 can be attached to the end of the power cable 10. The hoisting device 400 can wind up the wire 432, thereby pulling the attached power cable 10 toward the frame 410. The hoisting device 400 may be remotely controllable by being connected to a controller, such as a controller 120. The rotating drum 420 may further include a motor configured to wind the wire end 434 toward or away from the upper end of the guide unit 102. The hoisting device 400 is capable of pulling the power cable 10 into the guide unit 102 and through the opening of the guide unit 102, thereby protecting the power cable 10 at least partially by the guide unit 102. The hoisting device 400 is also capable of lowering the power cable 10 again through the guide unit 102 until the wire 432 emerges from the opening at the lower end of the guide unit 102.

[0030] Looking at Figure 4, a detailed view of an example of the lower end of the guide unit 102 is shown. Means for providing relative motion may include, for example, an actuator 300 positioned on the offshore structure 100. On the side of the guide unit 102 adjacent to the support column 101, a bracket 310 may be provided, having a rack tooth profile 312 extending along the length of the guide unit 102. A motor-driven gear 320 may be rotatably mounted on the guide unit 102 and form an interlocking mesh with the corresponding teeth of the rack tooth profile 312. The bracket 310 may further be provided with a guide roller 330 extending from the bracket 310 and in contact with the support column 101. The gear 320 may be designed to rotate by power supplied from the motor and move the guide unit 102 relative to the support column 101. Alternatively, the bracket 310 may be provided on the support column 101 and the gear 320 on the guide unit 102.

[0031] Looking at the operation method of the system shown in the figure, the method may include the following steps in any order: A power cable 10 is supplied to the system, with a first length portion positioned vertically along the offshore structure 100, and a second length portion extending outward from the offshore structure 100 into the water and finally laid on the seabed. The power cable 10 may be held in place by a locking means 110 in the initial state. The locking means is deactivated, and a means for providing relative motion is activated, causing the power cable 10 to move relative to the guide unit 102. Due to the relative motion, different portions of the power cable 10 are positioned within the main fatigue region 104 and receive interaction from a portion of the guide unit 102 that can engage with the transition area of ​​the power cable 10. The means for providing relative motion is deactivated, and the locking means 110 is activated, locking the relative motion between the power cable 10 and the guide unit 102. As an alternative to manually operating or deactivating the locking means and / or the means providing relative motion, the process may be automated by using the controller 120 to provide relative motion when the state of the main fatigue area reaches a predetermined threshold. Optionally, the operation step of the means providing relative motion may further include pulling the power cable 10 from a first locked position to a second locked position.

[0032] The method may further include detecting the state of the primary fatigue region via the controller 120. For example, a sensor may detect the state of the power cable 10 in the primary fatigue region 104. Deactivation and provision of relative motion of the locking means 110 may be performed when the state exceeds a predetermined threshold. In addition, or alternatively, activation of the locking means 110 may be performed when the primary fatigue region 104 has been displaced by a predetermined length. For example, when the power cable 10 has moved by a predetermined length relative to the primary fatigue region 104 of the guide unit 102.

[0033] The above-described solution addresses the shortcomings of the prior art. As seen in previous disclosures, mechanical stress due to wind and / or tidal forces causes frequent interaction between the transition area of ​​the power cable 10 and the interaction portion of the protective tube. Such interaction exposes the primary fatigue region to frequent, cyclic stress, making it prone to failure. However, by selectively varying the location of the primary fatigue region along the length of the power cable 10, the service life of the power cable 10 is extended.

[0034] The power cable 10 may be a power cable. However, this disclosure is not limited to power cables. The power cable 10 may be any flexible connecting member used in underwater applications, such as a flexible pipeline, tension cable, attachment cable, communication cable, and / or chain.

[0035] Those skilled in the art will see that various modifications and changes are possible to the system and method for extending the service life of power cables 10 attached to an offshore structure 100. Other embodiments will also become apparent to those skilled in the art by examining the implementation of the system and method described in this specification and disclosure. This specification and examples should be considered illustrative only, and the true scope is intended to be indicated by the following claims and equivalents.

Claims

1. A system for extending the service life of a power cable (10) attached to an offshore structure (100), A guide unit (102) for guiding a power cable (10) from a body of water to the offshore structure (100) and ensuring that the power cable (10) is in a position to be electrically connected to the offshore structure (100), wherein the power cable comprises a first length portion that is mainly arranged vertically along the offshore structure (100) and a second length portion that deviates outward from the offshore structure (100) and extends through the body of water, The transition area between the first length portion and the second length portion defines the main fatigue region (104), The guide unit (102) further comprises a portion that can engage with the transition area of ​​the power cable (10), The system further comprises means for providing relative motion along a first length portion between the guide unit (102) and the power cable (10), and locking means (110) for locking the relative motion between the guide unit (102) and the power cable (10), wherein the portion of the guide unit (102) that can engage with the transition area of ​​the power cable (10) has a variable position along the longitudinal length of the power cable (10).

2. The system according to claim 1, further comprising a plurality of locking positions distributed in the longitudinal direction of the guide unit (102), each of which can engage with the locking means (110) to prevent the relative movement.

3. The system according to claim 2, wherein the means for providing the relative motion comprises an actuator (300) or a hoisting device (400) and is further configured to move the power cable (10) from a first locking position to a second locking position among the plurality of locking positions.

4. The system according to claim 3, wherein the hoisting device (400) is positioned on the offshore structure (100) and further comprises a tensioning element that can be attached to the power cable (10), and the hoisting device (400) is capable of raising and lowering the power cable (10).

5. The system further comprises a controller (120) that is in communication with the locking means (110) and the means for providing the relative motion, The system according to any one of claims 1 to 4, wherein the controller (120) is configured to monitor the state of the main fatigue region and generate instructions for providing the relative motion and / or instructions for locking the relative motion via the locking means based on the state of the main fatigue region.

6. The system according to claims 3 and 5, wherein the controller (120) is configured to generate an instruction to activate the locking means (110) when the power cable (10) is moved from the first locking position to the second locking position.

7. The controller (120) is further configured to deactivate the locking means (110) when the state exceeds a predetermined threshold, and to generate an instruction to provide the relative motion, and optionally, The system according to claim 5 or 6, wherein the state includes the elapsed time from the time when the relative motion was last provided.

8. The system according to any one of claims 5 to 7, wherein the controller (120) is further configured to generate an instruction to activate the locking means (110) when the main fatigue region is displaced by a predetermined length.

9. The system according to any one of claims 1 to 8, wherein the guide unit (102) is selected from the group consisting of an I-tube, a J-tube, a telescopic tube, a short tube element, a bell mouth, and a connector unit.

10. The system according to any one of claims 1 to 9, wherein a bend stiffener (20) can be attached to the lower end of the guide unit (102).

11. The system according to any one of claims 1 to 10, wherein the offshore structure (100) is a floating offshore structure, and optionally the floating offshore structure is equipped with a wind turbine (30).

12. A method for extending the service life of a power cable (10) attached to an offshore structure (100), To provide a system according to any one of claims 1 to 11, The locking means (110) is deactivated, and relative motion is provided to move the power cable (10) relative to the guide unit (102). The locking means (110) is activated to lock the relative motion between the power cable (10) and the guide unit (102). A method that includes this.

13. When providing the system described in claim 3, the step of providing the relative motion is: The method according to claim 12, further comprising pulling the power cable (10) from the first locking position to the second locking position.

14. When providing the system described in claim 7, The state of the main fatigue region (104) is detected via the controller (120), The step of deactivating the locking means (110) and providing the relative motion is performed when the state exceeds a predetermined threshold. The method according to claim 12, including the method described in claim 12.

15. When providing the system described in claim 8, The state of the main fatigue region (104) is detected via the controller (120), The step of activating the locking means (110) is performed when the main fatigue region (104) is displaced by a predetermined length. The method according to claim 12, including the method described in claim 12.

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