Patent SE-1600146-A1 (SE)
Inventor: HEDLUND JOHAN
IPC: H02G9/00
Filed: 2016-04-26
Abstract: BEND RESTRICTOR FOR A SUBMARINE POWER CABLE. The present disclosure relates to a bend restrictor () for a submarine power cable (). The bend restrictor () comprises a plurality of bend restrictor members (a-n), each bend restrictor member (a-n) being arranged to be mounted around the submarine power cable (), wherein the bend restrictor members (a-n) are configured to be assembled with each other one after the other, wherein the bend restrictor members (an) are configured to restrict relative rotation between them, and wherein one of the bend restrictor members (n) is configured to restrict rotation of the submarine power cable () relative to the bend restrictor ().(Fig. 1). The present disclosure generally relates to submarine power cables. In particular it relates to a bend restrictor for submarine power cables.BACKGROUND. A submarine power cable that is to be installed on the seabed is laid by special vessels that transport the submarine power cable. The submarine power cable may be wound on a large drum or carousel on the vessel during transport. During installation the submarine power cable is wound off the drum, and fed through tensioners that provide control of axial movement of the submarine power cable. From this position the submarine power cable is lowered into the sea via a substantially horizontal chute. The submarine power cable is thereby subjected to bending forces while changing orientation from essentially horizontal to vertical.Submarine power cables may be jointed at sea on a cable laying vessel by means of a rigid joint. A rigid joint comprises a large rigid steel structure, or rigid cover, inside which the joint is made. In order to fixate the submarine power cable to the steel structure, the armour wires of the submarine power cable can for example be welded to a flange inside the steel structure. Bend restrictors are provided around the power cable ends entering the rigid cover. The bend restrictors are attached to the two external end faces of the rigid joint to limit the bending of the cable in the transition area between the power cable and the rigid cover.A stiff transition is obtained between the torsionally stiff structure of the rigid joint and the power cable due to the fixation of the armour wires inside the rigid cover. Therefore, in case the submarine power cables to be jointed are of a type that only have a single layer armouring, a second armour layer is normally provided around the end portions of the two power cables that are to be jointed, during the jointing procedure. The second armouring layer is laid helically in an opposite direction in relation to the first armouring layer. In this manner, both armouring layers are welded to the steel structure. This procedure is however time-consuming.In view of the above, an object of the present disclosure is to provide a bending restrictor which solves or at least mitigates existing problems of the prior art.Hence, according to a first aspect of the present disclosure there is provided a bend restrictor for a submarine power cable, wherein the bend restrictor comprises: a plurality of bend restrictor members, each bend restrictor member being arranged to be mounted around the submarine power cable, wherein the bend restrictor members are configured to be assembled with each other one after the other, wherein the bend restrictor members are configured to restrict relative rotation between them, and wherein one of the bend restrictor members is configured to restrict rotation of the submarine power cable.Hence, relative rotation between the bend restrictor members is restricted. Since the bend restrictor is configured to be mounted to a rigid structure such as a rigid cover of a rigid joint, torsional forces between the submarine power cable and the rigid structure may be reduced or even eliminated for submarine power cable having only a single armour layer, without having to provide the power cable with a second armour layer in the vicinity of the rigid cover.According to one embodiment a majority of the bend restrictor members have a flange portion having an inner surface provided with a plurality of radial teeth distributed in the circumferential direction.According to one embodiment a majority of the bend restrictor members have a circumferential groove provided with a plurality of recesses distributed in the circumferential direction and configured to engage with the plurality of teeth of another bend restrictor member.One embodiment comprises a metal insert having radially outwards extending protrusions, wherein one of the bend restrictor members has an inner surface comprising a plurality of axial grooves, wherein each axial groove is configured to receive a radially outwards extending protrusion, and wherein the metal insert is configured to be welded to armour wires of the submarine power cable, thereby restricting rotation of the submarine power cable relative to the bend restrictor. This bend restrictor member hence enables axial displacement between the bend restrictor and the submarine power cable, but restricts relative rotation between the submarine power cable and the bend restrictor.According to one embodiment one of the bend restrictor members is an interface member configured to be mounted to a rigid steel structure.According to one embodiment the interface member comprises a metal material.According to one embodiment the bend restrictor members comprise a plastic material.Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to "a/an/the element, apparatus, component, means, etc. are to be interpreted openly as referring to at least one instance of the element, apparatus, component, means, etc., unless explicitly stated otherwise.The specific embodiments of the inventive concept will now be described, by way of example, with reference to the accompanying drawings, in which: Fig. l schematically shows an example of a longitudinal section of a bend restrictor comprising a plurality of bend restrictor members;Fig.schematically shows a longitudinal section of one of the bend restrictor members in Fig.;Fig.a shows a cross-section along line A-A in Fig.;Fig.b schematically shows a cross-section along line B-B in Fig.;Fig.a schematically shows a longitudinal section of a distal bend restrictor member;Fig.b schematically shows a cross-section along line C-C in Fig.a;Fig.c schematically shows a cross-section of a metal insert; andFig.schematically shows a side view of a rigid joint including two bend restrictors of the type shown in Fig..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.Fig.shows an example of bend restrictorcomprising a plurality of bend restrictor membersa-n arranged to be assembled with each other one after the other. Each bend restrictor membera-n may for example comprise two halves that can be placed around a submarine power cable from two sides thereof, which halves can be fixed to each other.Bend restrictor membera forms a proximal end of the bend restrictor. With proximal is here meant location with respect to rigid structure, such as a rigid steel structure, to which the bend restrictoris to be mounted. Bend restrictor membera is hence an interface member configured to be mounted to a rigid structure. To this end, bend restrictor membera may have a flange surfaceprovided with a plurality of axial openings for bolting the bend restrictora to a corresponding flange surface of the rigid structure. A proximal flange, including flange surface, may be made of a metal material, while the remainder of the bend restrictora may be made of a plastic material. Bend restrictor membera may hence be made of two distinct components; one metal component and one plastic component. Bend restrictora could alternatively be composed of only one material, e.g. only metal.Bend restrictorfurthermore has a bend restrictor membern that forms a distal end of the bend restrictor. According to the present example, this bend restrictor membern is configured to be slidably mounted to the armour wires of a submarine power cable. Bend restrictor membersb ton-are intermediate bend restrictor members, i.e. in an assembled state they are arranged between bend restrictor membera and bend restrictor membern. These intermediate bend restrictor members are generally identical except that they may have successively reduced outer diameters in the distal direction, i.e. the axial direction towards bend restrictorn.The bend restrictor membersa-n are configured to receive a submarine power cable. Each bend restrictor membera-n hence has a through-openingextending in the longitudinal direction, i.e. along the central axis of the bend restrictor.Turning now to Fig.one of the intermediate bend restrictors is shown. Bend restrictorb has a body formed by a proximal flange portion, a distal flange portion, and a circumferential groovearranged between the proximal flange portionand the distal flange portion. Through-openingextends longitudinally through the body.The proximal flange portionhas an inner surfacea provided with a plurality of radial teethb, as shown in Fig.a. In a corresponding manner the circumferential grooveis provided with a plurality of recessesa, as shown in Fig.b. It should be noted that the cross-sections shown in Figsa andb are not to scale with regards to the longitudinal section shown in Fig.. The radial teethb of one bend restrictor memberb-n is configured to engage with the recessesa of another bend restrictor memberb-n. In particular, adjacent bend restrictor membersb-n are configured to engage with each other in this manner. In Fig., for example, bend restrictor memberc has teeth engaging with recesses of bend restrictor memberb, and bend restrictor memberd has teeth engaging with recesses of bend restrictor memberc. Bend restrictor membera also has recesses configured to engage with teeth of another bend restrictor, in this case bend restrictor memberb.The teethb and the recessesa may be configured to provide essentially a friction fit or press-fit therebetween thereby not only restricting but preventing relative rotation. Alternatively, the teeth and recesses may be designed with a play therebetween to allow some rotation, however restricting the amount of rotation possible.Fig.a shows a longitudinal section of bend restrictor membern, and Fig.b shows a cross-section of bend restrictor membern along line C-C. The main body of bend restrictor membern has an inner surfaceforming a through-opening of the bend restrictor membern, and having a plurality of axial grooves. The axial groovesare distributedalong the circumference of the inner surface. According to the example in Fig.b, the inner surfaceis provided with four axial grooves, but fewer or more than four axial grooves could alternatively be provided.Bend restrictorfurthermore has a metal insertprovided with radial protrusionsa, also shown in Fig.c, each being configured to be received in a respective axial groove, preferably with a friction fit or press-fit. The metal insertis hence configured to be arranged in the through-opening defined by inner surface. The metal insertis hence locked rotationally to the bend restrictor membern, but allowed to slide along the axial groovesThe metal insertis hollow, having a longitudinal through-openingc arranged coaxial with the through-openingof the bend restrictor membern. Through-openingmay therefore have a slightly larger diameter than the diameters of the through-openingsof the remaining bend restrictor membersa ton-i, i.e. to accommodate the metal insert.The metal inserthas a longitudinal extension that may correspond e.g. to the length of through-openingof bend restrictor membern.The metal inserthas an inner surfaceb to which the armour wires of a submarine power cable may be welded. When armour wires have been welded to the metal insert, it becomes rotationally locked relative to the submarine power cable. The submarine power cable is thereby rotationally locked, or at least restricted to rotate, relative to the bend restrictor membern.The bend restrictor membersa-n disclosed herein may for example be made of a plastic material. Bend restrictor membera may also comprise a metal material, in particular the flange forming the flange surface.Fig.shows a rigid jointof a submarine power cable. The rigid jointhas a rigid steel structure or rigid coverprovided with two bend restrictors, one at each end of the rigid cover.The bend restrictor presented herein may for example be utilised in subsea applications such as subsea power transmission or subsea power distribution.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.