Patent Publication Number: US-2015068150-A1

Title: Flange assembly for a tower segment

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to EP 13168756.8 filed on May 22, 2013, the entire contents of which are hereby incorporated by reference. 
     FIELD OF TECHNOLOGY 
     The following concerns a flange assembly for a tower segment. It also concerns a method of construction of such a flange assembly. In particular, the tower segment is realized as a tower segment of a wind turbine tower. 
     BACKGROUND 
     Wind turbines comprise a tower and a nacelle placed on top of that tower, whereby the nacelle is equipped with a rotor which rotates due to the impact of wind. In the nacelle, the rotational movement of the rotor is used to generate electric power. 
     In order to increase power output of wind turbines, the nacelles of the wind turbines are positioned at ever increasing heights. This implies that rotors with longer rotor blades can be installed which then means a higher output of electric energy. Currently, heights of about 80 metres are quite usual, especially in offshore areas. Because of that, the towers which hold the nacelles need to be constructed stable enough to both carry the weights and to withstand the forces that increase substantially with the increase of height. Such forces are, for instance, vibration forces but also forces due to the movement of the tower in the wind. 
     Generally, there are two types of towers available today, namely concrete towers and metal tower, i.e. steel towers. Both constructions have in common that they are often not constructed in one piece but rather based on tubular tower sections which are placed on top of each other to build up the entire height of the tower. It is therefore necessary to interconnect these tower sections firmly, for instance, by bolting them together along inner or outer flanges at either tubular ends of the tower sections. Such flanges thus project perpendicularly to the axial extension of the tubular tower sections, either into the shape of the tube of the tower sections or out of that shape to the outside of the tube. 
     Such flanges, in particular in the case of steel towers, are often produced separately and then firmly connected to the tubular parts of the tower sections, for instance, by bolting them together. 
     With the ever-increasing heights of wind turbine towers, the construction of flanges has become a problem: Increasing heights also imply that the diameter of the tower sections, in particular of the lower tower sections, becomes larger and larger as well. For instance, diameters of up to 6.5 metres at the bottom tower section can currently be found. About the same diameters have to be realized for the flanges of such bottom tower sections. The enormous size of such flanges poses problems both during production—as only few facilities can produce such large flanges—and during transport and assembly on site. This leads to an increase in both effort and cost. 
     SUMMARY 
     An aspect relates to supplying flanges, in particular, large flanges, in an easier manner and/or with less consumption of resources. 
     According to embodiments of the invention, a flange assembly as mentioned in the introductory paragraph comprises a number of flange portions, each with a first interface to the tower segment and a second interface to connect to another flange portion. The flange assembly is used for the construction of a flange, be it an inner flange or an outer flange, of a tower segment, such as a wind turbine tower. The tower segment comprises a metal structure, such as steel, and the flange assembly comprises the same material as the tower segment. That means, if the tower segment primarily comprises metal, the flange assembly is also made of metal, and can be the same metal or metal alloy as the metal tower segment. Metal is used in exemplary embodiments of both the tower segment and the flange as the connection between the flange (portion) and the tower segment is easier to accomplish, and also because currently, concrete towers sections are often produced with the flange as an integral part. 
     The flange assembly may comprise a single flange portion. In such embodiment, at least one more flange portion is needed to establish a flange. The first interface of each flange portion serves to be connected to the tower segment. This can, for instance, be accomplished by welding and/or bolting (in the case of a metal tower segment and metal flange portion). 
     In essence, embodiments of the invention may be based on two principles, namely that of division and that of connection: In order to reduce the size of the produced and/or transported flange assembly overall, use is made of a flange that is divided into a plurality of flange portions. However, using several flange portions that are separately connected to a tower segment may not be enough; the construction might be too instable to withhold the forces and tensions inflicted on the tower, at least the tower of a wind turbine that has to endure even more forces than a tower which serves a less mechanical function, such as a lighthouse. 
     Therefore, a flange portion of the flange assembly is equipped with a second interface to interconnect with an adjacent flange portion along the (inner or outer) circumference of the tower. The second interface can be characterized as a contact region of the flange portion which is equipped to get into a firm and stable mechanical contact with the adjacent flange portion. Such equipment of the contact region can also be accomplished upon assembly of the flange portions to become a flange. For instance, the flange portions may be welded together and/or interconnected by a filling material. However, welding may not be essentially necessary, but rather only constitutes one possibility of connection of flange portions. 
     Embodiments of the second interface can be located at an end region of the flange portion along its principal extension. This principal extension describes a part of a circle along the inner or outer circumference of the tower section. In fact, each flange portion therefore has two such end regions that are both equipped with a second interface that may be the same shape and/or according to the same connection mechanism. This way, one flange portion can be connected at either end region to an adjacent flange portion. In the case where the assembly comprises a number of flange portions which are semi-circular, i.e. constitute exactly one half of a circle, a first flange portion can be connected to a second flange portion of the same size to make up a complete flange. That implies that the two flange portions are connected at both their end regions to each other. In case one single flange portion describes less than a half circle, more flange portions (given the flange portions all have the same sizes) are connected so that each flange portion is in contact with two different adjacent flange portions at either end regions. 
     In an exemplary embodiment, the second interface comprises some dedicated connection element such as a protruding element which fits into a receiving element of the second interface of an adjacent flange portion. 
     Although dividing a flange into several portions that are separately connected via their first interfaces to a tower section may result in a substantial reduction of strength at the junction between two tower sections, it is possible to overcome this weakening by interconnecting the flange portions so that they function together virtually like a flange made of one piece. Therefore, embodiments of the invention provide a solution to the problem of increasing sizes of flanges whilst maintaining sufficient stability at the same time. 
     The above-mentioned method of construction of a flange assembly for a tower segment—namely for connection to a corresponding flange assembly of another tower segment—comprises the step of providing a flange portion and equipping it with a first interface to the tower segment and with a second interface to connect to a further flange portion. 
     Further, embodiments of the invention also concern a flange for a tower segment comprising a flange assembly, the flange portions of which are interconnected. That means that each of the flange portion is at least connected to one other adjacent flange portion as indicated above. 
     Thus, embodiments of the invention also concern a method of construction of a flange for a tower segment comprising the steps of providing a flange assembly comprising a plurality of flange portions, each with a first interface to the tower segment and a second interface to connect to another flange portion, and interconnecting the flange portions via their second interfaces to form the flange. 
     Furthermore, embodiments of the invention concern a tower segment, in particular of a tower of a wind turbine, comprising a flange, and also a method of construction of a tower segment, in particular of a tower of a wind turbine, comprising the steps of providing a flange constructed using the method according to embodiments of the invention, and connecting the flange to the tower segment via the first interfaces. 
     Lastly, embodiments of the invention also concern a tower, in particular a tower of a wind turbine, comprising at least one tower segment, and a method of constructing a tower, in particular a tower of a wind turbine, whereby a number of tower segments are interconnected, at least one tower segment of which is produced according to a method according to embodiments of the invention. 
     Exemplary embodiments and features of the invention are given by the dependent claims, as revealed in the following description. Features of different claim categories may be combined as appropriate to give further embodiments not described herein. 
     As indicated above, a flange assembly may comprise a single flange portion of the above-described kind. In order to be able to produce a flange out of a flange assembly, the flange assembly may comprise a plurality of flange portions each interconnectable with at least another flange portion via their second interfaces. In an exemplary embodiment, the number of flange portions is chosen such that a complete flange can be produced by interconnecting them via their second interfaces. For instance, if each of the flange portions describes a third of a circle, three of the above-described flange portions are included in the package or set, i.e. are part of the flange assembly. 
     In an exemplary embodiment, as few flange portions are used as possible because interconnecting the flange portions is also time-consuming Thus, in one exemplary embodiment, two flange portions are in the flange assembly, i.e. the set of flange portions that make a flange when interconnected. In case tower segments become even bigger and/or if the transport facilities at hand are considerably small, it may however also be suitable to use smaller and thus more flange portions instead of only two, for instance, three or four flange portions to make a flange when interconnected. More flange portions than four may be used as necessary or suitable. 
     According to a first embodiment, complementary second interfaces of interconnectable flange portions are realized to interconnect by means of a form fit. That implies that the shape of one second interface of one flange portion fits to the shape of a second interface of an adjacent flange portion in such way that they engage. For that purpose, the contact regions of the second interfaces of the two adjacent flange portions comprise more than one single flat surface. Rather, both contact surfaces of the two second interfaces must be curved and/or comprise angles and be realized and located such that they correspond in shape to be fitted into/onto each other. The two contact surfaces are thus designed as complementary connection surfaces. 
     According to a second embodiment, which can be used as an alternative or as an add-on, the second interfaces of interconnectable flange portions are realized to interconnect by means of a force closure and/or by means of welding. 
     That second embodiment implies that not only a form fit can be used as a connection principle between two adjacent flange portions, but an even firmer connects in which forces and/or tensions are directly and reliably transferred from one flange portion into the adjacent next one. 
     Welding has the advantage that the two flange portions are permanently joined such that they form one integral element. However, welding may only be desired in special applications rather than as a rule. For example, welding may introduce additional stress into the flange. That means that welding is only an option, but not an overall necessity. 
     Force closure is a less permanent solution with a comparable effect concerning stability of the interconnection. Thereby, in an exemplary embodiment, a number of fasteners, such as bolts, are used for the connection. For that purpose, both adjacent flange portions comprise through-openings through which the fasteners can be led before tightening. These through-openings must be complementary in shape and position. Such an embodiment may be desired because through openings already exist in some flanges and can serve the purpose of interconnecting adjacent flanges of two adjacent tower sections. Thus, the through-openings of the flange portions in the region of the second interfaces can be used at the same time to connect flange portions. 
     In particular, a second interface of at least one flange portion comprises a protruding element which protrudes from an end of that flange portion with respect to a circumference of the tower segment. This means that the end of the flange portion is extended by the protruding element, at least partially. Such a protruding element can then be used to (at least partially) establish the second interface of the flange portion. This provides for a considerably easy form fit effect. This is particularly so with a first flange portion, the second interface of which comprising a first protruding element which protrudes from the end of the first flange portion at a first level and with the second interface of an adjacent flange portion comprising a second protruding element which protrudes from the end of that adjacent flange portion at a second level. Both can then be aligned and interconnected such that the first and second protruding elements are positioned one above the other when the two flange portions are connectedly aligned at a substantially same level along the circumference of the tower segment. In other words, one (e.g. upper) protruding element of one flange portion lies above another (e.g. lower) protruding element of an adjacent flange portion whilst the two flange portions are essentially aligned along the same level with respect to their designated position relative to the tower segment. 
     The second interface of a first flange portion comprises a tooth that corresponds in shape and position with an inlet opening of a second interface of an adjacent flange portion to interconnect with the inlet opening. Such tooth can thus be form fitted into the inlet opening. It is directed at an angle other than 0° or 180° to the principal extension of the flange portions. This way the connection between the tooth and the inlet opening can compensate and/or transfer forces or tensions directed from one flange portion towards the adjacent flange portion. 
     It is possible to realize embodiments of the invention using a number of differently sized and/or shaped or otherwise differently configured flange portions. That may for instance be useful in such cases in which the tower section which is to be equipped with a flange comprises an opening in its shell which opening opens towards an adjacent tower section. Then, it may be that not a complete circle can be realized as a flange. However, a plurality of flange portions, the complete amount of flange portions in some embodiments, of the flange assembly has the same shape and size. This means that one standard flange portion can be used for each flange so that production (and also transport) becomes easier, less time-consuming and thus also cheaper. 
     Although flanges have been described throughout this description as simply circular, it may be noted that other shapes of flanges along the circumference of a tower section may also be realized, this certainly depending on the respective shape of the tower section. Thus, in particular oval tower sections and flanges can be realized. Even tower sections (and thus flanges) may be used with angled cross sections. 
    
    
     
       BRIEF DESCRIPTION 
       Other objects and features of the present invention will become apparent from the following detailed descriptions considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for the purposes of illustration and not as a definition of the limits of the invention. They are not necessarily drawn to scale, wherein: 
         FIG. 1  shows a wind turbine according to the prior art; 
         FIG. 2  shows a prior art tower section connection; 
         FIG. 3  shows a top view of a first embodiment of a flange and a flange arrangement; 
         FIG. 4  shows a section view along a section line IV-IV of  FIG. 3 ; 
         FIG. 5  shows a section view along a section line B-B of  FIG. 3 ; 
         FIG. 6  shows a section view along a section line VI-VI of  FIG. 3  of a second embodiment of a flange and a flange arrangement; 
         FIG. 7  shows a section view along a section line B-B of  FIG. 3  of the second embodiment; and 
         FIG. 8  shows a schematic block diagram of the methods according to embodiments of the invention. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a wind turbine  4  of a usual construction. A nacelle  6  is supported by a tower  5 . The tower  5  is made by stacking tower sections  2  one on top of the other to reach the desired height. As the diagram indicates, the tower  5  is usually widest at the bottom and tapers gradually towards the nacelle  6 . The tower sections  2  are therefore also tapered accordingly. Adjacent tower sections  2  must be firmly secured to each other. To this end, a tower section  2  will have an interior and/or an exterior flange at its upper and/or lower edges (depending on its position in the tower), to match the flange(s) of one or two adjacent tower sections. 
       FIG. 2  shows a prior art connection arrangement for the sections  2  of a wind turbine tower  5 . Here, the problems with the prior art constructions are illustrated using two different flange realisations, although it is usual to use the same realisation for both tower sections  2 . 
     The upper part of the diagram shows an upper tower section  2  with a shell  20  welded to an upper flange  100 ′, leaving a raised weld seam  23 . The lower part of the diagram shows a lower tower section  2  with a shell  20  welded to a lower flange  100 ′, also, leaving a raised weld seam  23 . Both the upper and the lower flange  100 ′ are equipped with corresponding through-openings  10  one of which each is indicated in the diagram. These through-openings  10  are supplied all along the circumference of both tower sections  2 , in order to permit bolts  3  to be inserted through them. These bolts  3  are firmly tightened by nuts  30  at either side, with washers  31  adjacent to the nuts. In addition, between the upper washer  31  and the upper flange  100 ′, there is a strengthening element  70 , also equipped with a complementary through-opening to permit the bolt  3  to pass through it. By tightening the nuts  30  at both ends of the bolt  3 , the two flanges  100 ′ are firmly pressed together and connected by force closure. 
     According to the prior art, such flanges  100 ′ as shown in  FIG. 2  are made of one piece. According to embodiments of the invention, this is changed.  FIGS. 3 to 7  thus show two embodiments of a flange  100  and of a flange assembly  8 . Thereby,  FIG. 3 , although referring to the first embodiment, is used as a reference for  FIGS. 6 and 7  as well, although it becomes clear from these latter section views that the second embodiment is different with some respects—thus the different elements are marked by a “′” in the respective reference signs in  FIGS. 6 and 7 . Still, for the purpose of referring to the section points,  FIG. 3  fully suffices. 
     Referring to  FIG. 3 , the flange assembly  8  comprises two semi-circular flange portions  8   a,    8   b  which are interconnected at two interface regions  16 . In this interconnected state they thus form a flange  100 . It is also shown that the flange portions  8   a,    8   b  in the interface regions  16  comprise a number of through-openings  10  such as the ones shown in  FIG. 2 . As will be shown with reference to  FIGS. 4 to 7 , these through-openings  10  are part of the connection between the two flange portions  8   a,    8   b.    
       FIGS. 4 and 5  show two section views of this first embodiment of  FIG. 3 . Both flange portions  8   a,    8   b — FIG. 5  shows the first flange portion  8   a —comprise an essentially square (along the perpendicular extension to the main extension ME of the flange portions  8   a,    8   b ) main body  12  and an upper connection part  24 . The surface  14  of the upper connection part  24  facing away from the main body  12  serves as a first interface  14  for welding to a tower section—cf.  FIG. 2 . In the interface region  16  each of the flange portions  8   a,    8   b  comprises a second interface  16   a,    16   b.  These two second interfaces  16   a,    16   b  are complementary in shape and position: The second interface  16   a  of the first flange portion  8   a  comprises a protruding element  22   a  (protruding from the end surface  18   a  of the first flange portion  8   a  towards the end surface  18   c  of the second flange portion  8   b ) which fits exactly under a corresponding protruding element  22   b  (protruding from the end surface  18   c  of the second flange portion  8   b  towards the end surface  18   a  of the first flange portion  8   a ). Along an inner surface  18   b,  the two protruding elements  22   b,    22   a  are placed on top of each other. They are thus form fitted. To further enhance the connection of the two flange portions  8   a,    8   b  bolts  3  (not shown) are inserted into the through-openings  10  so that a bolt passing through both flange portions  8   a,    8   b  in the interface region  16  will automatically interconnect the two flange portions  8   a,    8   b  by additional force closure. Additionally, a filling material, in particular an adhesive and/or a sealing filling material can be introduced along the contact surfaces  18   a,    18   b,    18   c  of the interface region  16 . This can serve as a sealing material but also add more strength to the overall connection. 
       FIGS. 6 and 7  show a second embodiment of the invention in two section views. As most of the features in these figures are the same as in the preceding two figures, only the additional elements will be described: 
     A first flange portion  8   a ′ and a second flange portion  8   b ′ make up the flange assembly  8 ′ and indeed (cf.  FIG. 3 ) the complete flange  100 . The difference with the first embodiment lies in the geometric approach of the two second interfaces  16   a ′,  16   b ′. Namely, the protruding element  22   a ′ of the first flange portion  8   a ′ comprises a tooth  26  projecting from the connection surface  18   b  upwards. Correspondingly, the protruding element  22   b ′ comprises an inlet opening  28  into which the tooth  26  fits. This combination of tooth  26  and inlet opening  28  adds more strength to the overall connection of the two flange portions  8   a ′,  8   b′.    
     Referring now to  FIG. 8 , this shows schematic block diagrams of all mentioned methods Z, Y, X, R according to embodiments of the invention. 
     Firstly, method Z of construction of a flange assembly  8 ,  8 ′ according to embodiments of the invention will now be described. Embodiments of method Z comprises a first step W of providing a flange portion  8   a,    8   a ′ and a second step V of equipping that flange portion  8   a,    8   a ′ with a first interface  14  to a tower segment and with a second interface  16   a,    16   a ′ to connect to a further flange portion  8   b,    8   b′.    
     In order to further construct a flange  100  according to method Y, that method Y comprises a step U in which a plurality of such flange portions  8   a,    8   b,    8   a ′,  8   b ′ is provided and interconnected via their second interfaces  16   a,    16   b,    16   a ′,  16   b ′ to form the flange  100 . 
     A tower segment  2  is constructed according to the method X, which after the provision of the flange  100  by method Y, further comprises a step T of connecting the flange  100  to the tower segment  2  via the first interfaces  14 . 
     Lastly, a tower  5  can be constructed using method R, which further comprises step S, whereby a number of tower segments  2  are interconnected, at least one tower segment  2  of which has been produced according to the last-mentioned method X. 
     Although the present invention has been disclosed in the form of various exemplary embodiments and variations thereon, it will be understood that numerous additional modifications and variations could be made thereto without departing from the scope of the invention. 
     For the sake of clarity, it is to be understood that the use of ‘a’ or ‘an’ throughout this application does not exclude a plurality, and ‘comprising’ does not exclude other steps or elements.