Apparatus and system

Abstract

A weight bearing cable protection connector suitable for connecting a cable (figure 2, 102) to an offshore platform. The cable protection connector comprises an elongate tubular portion 106 having a c

Description

The present invention relates to cable protection devices and more particularly, to weight bearing cable protection devices for releasably securing a cable to an offshore installation. Offshore wind is set to make a significant contribution to the renewable energy transition, with most current wind turbines constructed close to shore in shallow waters. However, for offshore wind to achieve its full potential, wind turbines must be built far offshore, where winds are both stronger and more consistent. This poses a number of technical challenges, with one of the most important being that the water far offshore is generally much deeper and subject to stronger currents adding significant time, cost and risk associated with cable installation and maintenance, with the cables being subject to stronger forces. Installation is conventionally done by attaching a pulling head to the cable and by drawing the pulling head and cable attached to it through a conduit called an "l-tube", which is a downwardly projecting tube secured to the wind turbine platform. Once the pulling head has been pulled through the l-tube, it can be secured in position, thereby securing the cable to the wind turbine platform. To protect the cable from bending moments and shear stresses, it is known to secure a conventional cable protection device to the lower end of the l-tube, which provides the desired bend stiffening performance. However, in order to secure the protection device to the l-tube, it is necessary to pass securing bolts projecting from the end of the device through apertures into a securing flange at the lower end of the l-tube and to secure the two together by means of securing nuts. This securing operation would normally take place in a hostile environment outside of the wind turbine, increasing the risk to personnel and the installation time, with the consequential increase in associated costs. Therefore, there is a need to eliminate the requirement for the cable protection device to be secured to the lower end of the l-tube. The present invention seeks to provide a solution in which both pull-in and cable decoupling operations can be performed quickly, with any required manual input from personnel being performed from within the safety of the wind turbine structure. According to a first aspect of the present invention, there is provided a weight bearing cable protection connector for connecting a cable to an offshore platform, the cable protection connector comprises: an elongate tubular portion having a coupling at a proximal end for releasably securing the connector to an offshore platform; and a securing portion connected to a distal end of the elongate tubular portion for connection to a cable protection device, wherein the cable protection connector comprises an elongate through passageway for receipt of the cable. Traditionally, the axial load mounting of the string assembly is at the point of connection of the cable protection device to the conduit. The cable protection connector of the present invention is capable of bearing the weight of the string assembly and moves the axial load mounting further up the string assembly to the top of the cable protection system. By transferring the axial load mounting of a cable string assembly to the top of the cable protection system (i.e. an end of the cable that is coupled to the offshore platform), any manual input required in the course of a pull-in or disconnection operation may be limited to a single mounting and can be performed from within the wind turbine structure. This may allow for the use of simpler and cheaper cable protection devices, that are not required to be securely fastened in the opening of the I tube. This in turn means that both pull-in and disconnection operations may be performed without having to connect or disconnect a cable protection device from outside the wind turbine structure, resulting in a much quicker and safer operation. Moving the axial load mounting also may allow for the use of simpler, and consequently cheaper cable protection devices (i.e., those that are not required to connect to and provide an axial load mounting to a cable protection device, e.g., a bend restrictor). Optionally, the elongate tubular portion may comprise at least one elongate tubular member. Optionally, the elongate tubular portion may comprise a plurality of identical elongate tubular members. Optionally, the elongate tubular members may be connected to each other end-to-end by a tubular connection piece. Optionally, the tubular connection piece may prevent rotational and longitudinal movement of the elongate tubular member relative to an adjacent elongate tubular member. Optionally, the securing portion may comprise an upper portion having a first diameter and a lower portion having a second diameter different to the first diameter. Optionally, the first diameter may be chosen to be less than an inner diameter of a conduit. Optionally, the second diameter may be chosen to be more than the inner diameter of the conduit. Optionally, the coupling for releasably securing the proximal end of the elongate tubular portion comprises a circumferential recessed portion for receiving a split flange mechanism. According to a second aspect of the present invention, there is provided a system for connecting a cable protection device to an offshore platform comprising the weight bearing cable protection connector of the first aspect of the present invention and further comprising a cable protection device connected to a distal end of the securing portion. Optionally, the system further may comprise a hang-off connector mounted to an upper end of the elongate tubular portion. Optionally, the conduit may comprise an l-tube. One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Fig. 1 is a front perspective view of a cable string assembly comprising a cable protection tube in accordance with one or more embodiments of the present invention; Fig. 2 is a vertical through cross-section of the cable protection tube of Fig. 1 connected to a wind turbine structure; Fig. 3 is an exploded view of the connection point of the cable protection tube in Fig. 2 during a pull-in operation to a wind turbine structure; and Figs. 4a - 4b are vertical through cross-section views of the cable protection tube shown during a disconnection operation from a wind turbine structure. Fig. 1 illustrates an embodiment of a string assembly 100 for connecting an electrical cable 102 (not shown in Fig. 1 - see Fig. 2) to an offshore wind turbine. The electrical cable 102 is intended to be connected to the electrical circuitry of a wind turbine and the string assembly 100 encloses the electrical cable 102. The string assembly 100 illustrated in Fig. 1 comprises pull-head connector 104, which is releasably secured to an upper end of a cable protection tube 106. A lower end of the cable protection tube 106 is secured to an upper end of a protection device 108. The protection device 108 is conventional and comprises a tubular flexible member formed from a high-density polyurethane. In the embodiment described and shown, the protection device 108 is formed as a bend stiffener, which is tapered toward an end remote from the pull-head connector 104 and is designed to allow a predetermined degree of flexibility, but to prevent bending to such an extent that would result in damage to the electrical cable 102 passing through it. In the above paragraph, and hereinafter, the terms “upper” and “lower” are intended to refer to proximal and distal ends of the cable protection tube 106. The proximal end of the cable protection tube 106 is an end located at the offshore platform (e.g., the wind turbine platform). The distal end of the cable protection tube 106 is an end opposite to the proximal end. The term “upper” is also used hereinafter in connection with other features of the present invention to denote ends of those features that are proximal the offshore platform. Similarly, the term “lower” is also used hereinafter in connection with other features of the present invention to denote ends of those features that are distal the offshore platform It should be noted that further protection devices may be attached downstream of the protection device 108, to protect the enclosed electrical cable 102 along its length. However, the protection device 108 does not form part of the present invention and will not be described further. As shown in Fig. 1, the cable protection tube 106 comprises a mounting head 110 at its upper end and a reaction arm 112 at its lower end. A lower end of the mounting head 110 and an upper end of the reaction arm 112 Is secured to a respective end of a series of identical elongate tubular members 114. The mounting head 110, tubular members 114 and reaction arm 112 each comprise an internal passageway and, when they are located together to form the cable protection tube 106, these internal passageways combine to form a contiguous internal elongate passageway through the string assembly 100 for passage of the electrical cable 102 therethrough. As best seen in Figs. 2 and 3, the mounting head 110 comprises a generally tubular body 116 in which the pull-head connector 104 is mounted at its front end. The tubular body 116 is provided with an upper recessed waisted portion 118 and a lower recessed waisted portion 120, both of which extend around the entire outer circumference of the tubular body 116. The lower recessed waisted portion 120 forms a radial projection 122 at the lower end of the tubular body 116. The radial projection 122 is provided with a number of equiangularly spaced through apertures for receipt of correspondingly aligned securing bolts 124 projecting from an end face of a first tubular member 114. The securing bolts 124 are threadedly received by a nut in the lower recessed waisted portion 120 for securing the mounting head 110 to the first tubular member 114 in a series of tubular members. Each tubular member 114 is formed from a high-density polyurethane, which varies in thickness along its length, narrowing from either end towards a central waist portion 126. Any number of tubular members 114 can be comprised within the series and are secured to one another by way of a tubular connection piece 128. Each tubular member 114 is locked on to an adjacent tubular member 114 via the connection piece 128 and therefore cannot rotate relative thereto, nor move longitudinally relative thereto. As best seen in Figs. 1 and 2, the reaction arm 112 has a tubular body having an upper end portion 130, which is secured to a lower end of an adjacent tubular member 114 (i.e. the lowest tubular member in the series of tubular members), and a lower end portion 132, which is secured to the cable protection device 108. The upper end portion 130 of the reaction arm 112 comprises a frusto-conical shoulder that is contiguous with the adjacent tubular member 114. The frusto-conical shoulder terminates in an upper tubular portion that has an outer diameter that is complimentary to the inner diameter of a conduit through which the reaction arm 112 is received. In the illustrated example in Figure 2, the conduit is an T tube 134 provided at an entry point 136 in the wind turbine structure. The T tube 134 is formed as an elongate reinforcing tube 138 with a bell-mouth 140 formed at its lower end and which guides the string assembly 100 from the seabed into the T tube 134. The complimentary sized diameter of the upper tubular portion allows the upper end portion 130 of the reaction arm 112 to slide up into the elongate reinforcing tube 138 of the Ttube 134, forming a close or clearance fit. Similarly, the lower end portion 132 of the reaction arm 112 has a frusto-conical shoulder that is contiguous with the upper end portion 130. However, the frusto-conical shoulder of the lower end portion 132 terminates in a lower tubular portion that has a diameter that is greater than the inner diameter of the elongate reinforcing tube 138 of the T tube 134, thereby preventing the lower end portion 132 of the reaction arm 112 from travelling through the T tube 134. The diameter of the lower tubular portion may be sized to provide an interference fit with the bell-mouth 140 of the T tube 134 to provide sealing and corrosion protection to the interior of the T tube 134, just behind entry of the bell-mouth 140. It will be readily apparent that the number of tubular members 114 in the series can be adjusted to correspond to the length of the Ttube 134. The mounting head 110, tubular members 114 and reaction arm 112 of the cable protection tube 106 together provide a contiguous structural connection that can withstand and transfer high axial loads along the length of the cable protection tube 106. Referring now to Figure 3, an upper end of the T tube 134 is shown, in which the upper end projects through and is fixedly secured to a platform 142 in the wind turbine structure. The upper end of the T tube 134 is provided with a split flange 144 which is of conventional design having a top plate 146 and a bottom plate 148 and may comprise rubber gaskets (not shown) to provide a seal connection. The bottom plate 148 is integrally formed at the upper end of the T tube 134 from a radially extending shoulder portion which extends around the entire outer peripheral circumference ofthe Ttube 134. The top plate 146 comprises first and second halves, which together align vertically with the bottom plate 148, but which extend radially inwardly for receipt by the upper recessed waisted portion 118 ofthe mounting head 110. The top 146 and bottom 148 plates are provided with a series of vertically aligned apertures through which a securing bolt 150 is threadedly received by a corresponding nut 152. When assembled, the split flange 144 releasably secures the mounting head 110, which bears the axial load ofthe string assembly 100, to the platform 142 ofthe wind turbine structure. A pull-in operation and connection ofthe electrical cable 102 to the wind turbine structure will now be described with reference to Figs. 1-3. In use, the string assembly 100 is loaded onto a cable-laying vessel and is fitted to the electrical cable 102. The string assembly 100 is then discharged over the side of the vessel and into the water towards the wind turbine structure. This is achieved in a conventional manner by means of a winch wire (not shown) extending from the wind turbine structure, passing through the T tube 134 and which is secured to a clevis bolt 154 provided at the head ofthe pull-head connector 104. The winch wire is retracted, pulling the string assembly 100 up into the Ttube 134 until the mounting head 110 is level with the upper end ofthe Ttube 134, at which point the split flange 144 is assembled, securing the mounting head 110 of the cable protection tube 106 to the platform 142 ofthe wind turbine structure, supporting the axial load ofthe string assembly 100. The pull-head connector 104 is releasably secured to the mounting head 110 via one or more bolts (not shown) so that when the mounting head 110 is secured in the split flange 144 and bears the weight of the string assembly 100, the one or more bolts are released and the pull-head connector 104 is disconnected from the mounting head 110. Further retraction of the winch wire continues to pull the pull head connector 104 and the electrical cable 102 through the string assembly 100. As seen in Figure 2, once pulled through the string assembly 100, the electrical cable 102 is mounted to the wind turbine structure via a hang-off assembly 156. The hang-off assembly 156 is of conventional design and is assembled around the electrical cable 102, bolted to and sealed against the mounting head 110. The individual power cores 158 within the electrical cable 102 are then exposed and subsequently connected to corresponding power cores of the electrical circuitry of the wind turbine via respective cable connectors (not shown). Under normal operating conditions, the electrical cable 102 is supported by and secured to the wind turbine via the hang-off assembly 156, and no significant tension is placed on the electrical cable 102, such that the power cores 158 remain connected to their respective cable connectors and electrical power is able to be transferred between the electrical circuitry of the wind turbine and an offshore electrical network. However, excessive tension can be induced in the electrical cable 102 by extreme weather conditions, for example in the event of a severe storm. As a result, a high load can be induced in the electrical cable 102 leading to a potentially hazardous situation. This can lead to downwards tension in the electrical cable 102 with the highest stress occurring at the cable connection points (i.e., the point of connection to the electrical circuitry of the wind turbine, the hang-off assembly 156, and any fixed subsea assets). Damage at these points can result in considerable down-time of the offshore electrical network and considerable cost to repair. A disconnection operation will now be described with reference to Figs. 4a - 4c. In the event that the electrical cable 102 requires decoupling from the wind turbine structure, for example, to mitigate the effects of a storm event, or in the event of routine maintenance, the individual power cores 158 are disconnected from their respective cable connectors. Once disconnected, the power cores 158 are encased with a protective shroud 160, which is bolted to and seals against an upper end 162 of the hang-off assembly 156. The protective shroud 160 seals and protects the exposed power cores 158 from the elements and is provided with a clevis bolt 164 at its upper end for attachment to a winch wire. Once attached, the split flange 144 is manually disassembled and the axial load of the string assembly 100 is taken by the winch wire. The string assembly 100 is then lowered in a controlled manner either on to the deck of a vessel or to the sea floor for later retrieval and possible reconnection to the wind turbine structure. The cable protection tube 106 is capable of bearing the weight of the string assembly 100 and therefore, only a single connection to the wind turbine structure is required. By transferring the axial load mounting of the string assembly 100 to the connection point at the mounting head 110 at the top (i.e. upper end) of the cable protection tube 106, any manual input required in the course of a pull-in or disconnection operation can be performed from within the wind turbine structure. The weight of any cable protection devices 108 included on the string assembly 100 is borne by the cable protection tube, allowing for the use of simpler and cheaper protection devices, that are not required to be securely fastened in the opening of the T tube 134. This in turn means that both pull-in and disconnection operations are performed without having to connect or disconnect a cable protection device from outside the wind turbine structure, resulting in a much quicker and safer operation. The present description is for illustrative purposes only and should not be construed to narrow the breadth of the present disclosure in anyway. Thus, those skilled in the art will appreciate that various modifications might be made to the presently disclosed embodiment without departing from the full and fair scope of the present disclosure. For example, while the system has been described with reference to multiple tubular members 114 connected in series, only a single tubular member 114 may be required. Similarly, while the conduit in the described embodiment is an T tube 134, it is envisioned that the present invention can be used in connection with other conduits including, but not limited to, ‘J’tubes. The pull-head connector 104 has been described as being releasably secured to the mounting head 110 by way of one or more bolts. However, it is envisioned that the pull-head connector 104 could instead be releasably secured to the mounting head 110 by way of a weak link, designed to break on application of a predetermined tension, so that when the mounting head 110 is secured in the split flange 144, further pulling of the winch wire causes the weak link to fracture, disconnecting the pullhead connector 104 from the mounting head 110. In addition, the reaction arm 112 may be provided with a polyurethane coating. Similarly, the connection piece 128 may be formed from a reactive metal such as zinc or aluminium to provide sacrificial anode protection to the string assembly 100. While the electrical cable has been described as being used for the transfer of electrical power, it is envisioned that the cable can also be used to facilitate data transmission. Although described as a bend stiffener, it is also envisaged that the protection device 108 can be a bend restrictor that prevents over-bending at the interface between the electrical cable and the conduit. It is also envisioned that the function of the tubular member in displacing the axial load mounting further up the string assembly could be achieved with a bend restrictor. In addition, while the tubular member 114 has been described as having a varied thickness along its length towards a waisted portion, it is envisioned that the tubular member 114 could have a constant thickness along its length. Other aspects, features and advantages will be apparent upon examination of the attached drawings and appended claims.

Claims

1. A weight bearing cable protection connector for connecting a cable to an offshore platform, the cable protection connector comprising:an elongate tubular portion having a coupling at a proximal end for releasably securing the connector to an offshore platform; anda securing portion connected to a distal end of the elongate tubular portion for connection to a cable protection device, wherein the cable protection connector comprises an elongate through passageway for receipt of a cable.

2. The cable protection connector of claim 1, wherein the elongate tubular portion comprises at least one elongate tubular member.

3. The cable protection connector of claim 1, wherein the elongate tubular portion comprises a plurality of identical elongate tubular members.

4. The cable protection connector of claim 3, wherein the elongate tubular members are connected to each other end-to-end by a tubular connection piece.

5. The cable protection connector of claim 4, wherein the tubular connection piece prevents rotational and longitudinal movement of the elongate tubular member relative to an adjacent elongate tubular member.

6. The cable protection connector of any preceding claim, wherein the securing portion comprises an upper portion having a first diameter and a lower portion having a second diameter different to the first diameter.

7. The cable protection connector of claim 6, wherein the first diameter is chosen to be less than an inner diameter of a conduit.

8. The cable protection connector of claim 6, wherein the second diameter is chosen to be more than the inner diameter of the conduit.

9. The cable protection connector of claim 7, wherein the upper portion has a clearance fit with the conduit.

10. The cable protection connector of claim 8, wherein the lower portion has an interference fit with a bell-mouth of the conduit.

11. The cable protection connector of any preceding claim, wherein the coupling for releasably securing the proximal end of the elongate tubular portion comprises a circumferential recessed portion for receiving a split flange mechanism.

12. A system for connecting a cable protection device to an offshore platform comprising the weight bearing cable protection connectorof any of claims 1 to 11, further comprising a cable protection device connected to a distal end of the securing portion.

13. The system of claim 12, further comprising:a pull head connector releasably secured at a front end of the elongate tubular portion.

14. The system of claims 12, further comprising a hang-off connector mounted to an upper end of the elongate tubular portion.

15. The system of any of claims 12 to 14 when dependent on any of claims 6 to 10, wherein the conduit is an l-tube.

Images