Patent Publication Number: US-2022220944-A1

Title: Blade for a wind turbine and method for manufacturing a blade

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to EP Application No. 21382007.9, having a filing date of Jan. 12, 2021, the entire contents of which are hereby incorporated by reference. 
     FIELD OF TECHNOLOGY 
     The following relates to a blade for a wind turbine and method for manufacturing a blade, in particular, to blades comprising an ice formation prevention system and a lightning protection system. 
     BACKGROUND 
     Blades for a wind turbine with ice formation prevention system and a lightning protection system are known in the art. Taking into account that wind turbines and in particular, the blades of these turbines have high probabilities to being struck by a lightning, it is necessary to equipped the blade with a lightning protection system for minimizing the effect of the lightning in the blade, in particular in the electrical elements comprised in the blade and/or in the wind turbine. 
     On the other hand, the blades including conductive metal sheets in external laminate of the blade, in particular in the area of the leading edge, are known for preventing the formation of ice which adversely affects the efficiency of the wind turbine. 
     The presence of ice formation prevention systems in a blade could affect the efficiency of the lightning protection system also. For avoiding such a problem, EP 2857678 A1 describes a protection system that enables to disable the heating mode and enable the lightning protection mode whenever a lightning strike is detected. The protection system includes at least one surge protection device directly connecting the electrodes connected to the conductive sheets of the ice formation prevention system to a lightning down cable of the lightning protection system. 
     WO 2018/095649 A1 describes a blade comprising a lightning protection system with a down cable for conducting the lightning current received by a receptor to a grounding terminal, and electrically conductive layer arranged on an outer surface of a blade shell, the down cable and the conductive layer being electrically connected by a connecting surge device such that their potential is equalized. 
     SUMMARY 
     An aspect relates to a blade for a wind turbine comprising an ice formation prevention system, a lighting protection system, and surge protection devices that connect the ice formation prevention system with the lightning protection system ensuring the equipotentiality of both systems. The ice formation prevention system comprises heating means connected to power supply cables, the lightning protection system including at least one lightning down conductor and configured to conduct the lightning striking the blade to the ground through the lightning down conductor. 
     The heating means comprise at least one first radiant element and at least one second radiant element arranged faced to each other around a leading edge of the blade, with the first radiant element being connected to the power supply cables through respective electrical connectors at respective connection points. The lightning conductor is connected to each power supply cable at the connection points through the respective surge protection device, with the second radiant element being electrically connected to the first radiant element so that the second radiant element is electrically supplied only through the first radiant element. This way, the ice formation prevention system and the lightning protection system is electrically equipontentialized by the electrical connection between the first radiant element and the second radiant element. Once the first radiant element and the second radiant element are electrically connected not only the second radiant element is electrically powered but also the whole lightning protection system of the blade remains connected and equipontentialized with respect the ice prevention system. 
     A blade with two independent electrical circuits is obtained, the electrical circuits including the lighting protection system and the ice formation prevention system. Each shell includes one independent electrical circuit, both circuits being connected by connecting the second radiant element to the first radiant element. This way the electrical connections are minimized and optimized. 
     Another aspect of embodiments of the invention relates to a method for manufacturing the blade of the features described previously. The method comprises the following steps:
         depositing in a first mold a plurality of layers or sheets of fabric which will form the bottom shell of the blade, at least one first radiant element in a leading edge zone of the first mold, and at least a connecting element in contact with a cavity of the first mold and with one electrical terminal of the first radiant element, the connecting element being configured to define a contacting surface in the bottom shell over the first radiant element, in particular over the electrical terminal of the first radiant element,   molding the bottom shell,   connecting the first electrical terminal of the first radiant element to the first power supply cable, the second electrical terminal of the first radiant element to the second power supply cable, and the lightning down conductor to each power supply cable through the respective surge protection device,   depositing in a second mold a plurality of layers or sheets of fabric which will form the upper shell of the blade, including at least one second radiant element in a leading edge area of the second mold, and at least a connecting element in contact with the cavity of the second mold and with a terminal of the second radiant element, the connecting element being configured to define a contacting surface in the upper shell over the second radiant element, in particular over the electrical terminal of the second radiant element,   closing both molds against each other, with the connecting element of the first mold and the connecting element of the second mold facing each other, and sealing the upper shell and the bottom shell to each other,   removing the blade from the molds and   fixing connecting means to the contacting surface of the bottom shell and to the contacting surface of the upper shell, so that the second radiant element is electrically connected to the first radiant element so that the second radiant element is supplied electrically only through the first radiant element.       

     The method according to embodiments of the invention is more optimized as it allows to integrate the radiant elements during the manufacturing process and to integrate both the lightning protection system and the ice formation preventing system in a simple way during the manufacturing of the blade. A cost reduced method is thus obtained. 
    
    
     
       BRIEF DESCRIPTION 
       Some of the embodiments will be described in detail, with reference to the following figures, wherein like designations denote like members, wherein: 
         FIG. 1  shows a longitudinal section of a first embodiment of a blade according to embodiments of the invention; 
         FIG. 2  shows a detail of a first radiant element of the blade shown in  FIG. 1 ; 
         FIG. 3  shows a detail of a second radiant element of the blade shown in  FIG. 1 . 
         FIG. 4  shows a cross section of the blade shown in  FIG. 1  along line I-I; 
         FIG. 5  shows a cross section of a second embodiment of the blade according to embodiments of the invention; 
         FIG. 6  shows a cross section of a third embodiment of the blade according to embodiments of the invention; 
         FIG. 7  shows a detail of the blade shown in  FIG. 1 ; 
         FIG. 8  shows a section of a first mold with a bottom shell of the blade according to embodiments of the invention; and 
         FIG. 9  shows a section of a second mold with a top shell of the blade according to embodiments of the invention. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a blade  1  for a wind turbine according to embodiments of the invention comprising an ice formation prevention system  20  and a lightning protection system  30 . The ice formation prevention system  20  comprises heating means  21  connected to power supply cables  40  and  41 . The heating means  21  comprise at least a first radiant element  22  and at least a second radiant element  26  arranged adjacent to each other around a leading edge  7  of the blade  1  as shown in the figures, with the first radiant element  22  connected to power supply cables  40  and  41  through corresponding electrical connectors  34   a  and  34   b  at corresponding connection points C 1  and C 2 . In particular, the first radiant element  22  is connected to the first power supply cable  40  through the first electrical connector  34   a  at the first connection point C 1  and to the second power supply cable  41  through the second electrical connector  34   b  at the second connection point C 2 . Each power supply cable  40  and  41  runs lengthwise along the blade  1  inside a bottom shell  4  of the blade  1 . 
     The lightning protection system  30  includes at least one lightning down conductor  31  being configured to conduct to earth lightning strikes to the blade through a hub of the wind turbine (not shown in the figures). The lightning down conductor  31  extends longitudinally to the blade  1  from one end of the blade  1 . The lightning down conductor  31  is connected to each of the power supply cables  40  and  41  at the connection points C 1  and C 2 . The lightning protection system  30  also includes a lightning receiver  32  at the tip  9  of the blade  1 . This lightning receiver  32  is connected to the lightning down conductor  31 . 
     The blade  1  further comprises surge protection devices  33  (also known as SPD) that connect the ice formation prevention system  20  with the lightning protection system  30 , ensuring the equipotentiality of both systems  30  and  20  and avoiding electric arcs. The lightning down conductor  31  is arranged connected to each power supply cable  40  and  41  at the respective connection points C 1  and C 2  through the respective surge protection device  33 . In particular, one surge protector device  33  is connected to the first power supply cable  40  at the first connection point C 1  and to the lightning down conductor  31  at a third connection point C 3  and other surge protection device  33 ′ is connected to the second power supply cable  41  at the second connection point C 2  and to the lightning conductor  31  at a fourth connection point C 4  as is shown in  FIG. 2 . 
     The second radiant element  26  is not connected to any power supply cables  40  and  41 . The second radiant element  26  is electrically connected to the first radiant element  22  in such a way that the second radiant element  26  is only electrically supplied through the first radiant element  22 . 
     The blade  1  comprises a body  2  including an upper shell  3  and a bottom shell  4 , and a beam  5 . Each radiant element  22  and  26  is arranged in the body  2  around the leading edge  7  in particular the first radiant element  22  is arranged in bottom shell  4  and the second radiant element  26  is arranged in the upper shell  3  so that both radiant elements  22  and  26  are facing each other around the leading edge  7  of the blade  1  but are not in direct contact. The radiant elements  22  and  26  are arranged respectively on the bottom shell  4  and on the upper shell  3 . In particular, the radiant elements  22  and  26  are embedded in the corresponding shell  3  and  4 , being protected from the outside by an outer coating layer  11  preventing the outer coating layer  11  any short circuit that may occur between both radiant elements  22  and  26  being arranged closed to each other. The power supply cables  40  and  41  are arranged inside the bottom shell  4 . 
     Each radiant element  22  and  26  of the heating means  21  comprises a resistive element  23  and  27  and an electrical terminal  24   a ,  24   b ,  28   a  and  28   b  at each end of each resistive element  23  and  27 . Each electrical terminal  24   a ,  24   b ,  28   a  and  28   b  is connected to a corresponding metallic block  25  and  29  that ease the electrical connections between the electrical terminals and the corresponding surge protection device  33  or the corresponding electrical connector  34   a  and  34   b . In an embodiment, each metallic block  25  and  29  is embedded in the corresponding shell  3  and  4 . In other embodiments, each metallic block  25  and  29  is fixed to the inner surface of the corresponding shell  3  and  4 . 
     The blade  1  comprises conducting means  35  through which the second radiant element  26  is electrically connected to the first radiant element  22 . In particular, at least the first terminal  24   a  of the first radiant element  22  and the first terminal  28   a  of the second radiant element  26  are arranged connected to each other through the conducting means  35 . In an embodiment of the invention, the second terminal  24   b  of the first radiant element  22  and the second terminal  28   b  of the second radiant element  26  are arranged also connected to each other through the conducting means  35 . The conducting means  35  are not embedded in the blade  1 , they are fixed to the radiant elements  22  and  26  in contacting areas  12  and  13  in the upper shell  3  and the bottom shell  4 , the radiant elements  22  and  26  not being covered by the outer coating layer  11  in the contacting areas  12  and  13 . 
     In an embodiment of the invention, the conducting means  35  comprise a flat conductor directly connected to the terminals  24   a ,  24   b ,  28   a  and  28   b  of the radiant elements  22  and  26  respectively. The flat conductor is adhered to contacting areas  12  and  13  of the upper shell  3  and the bottom shell  4 . 
     In another embodiment of the invention, the conducting means  35  comprise a metal mesh directly attached to the terminals  24   a ,  24   b ,  28   a  and  28   b  of the radiant elements  22  and  26  respectively. The flat conductor is to contacting areas  12  and  13  of the upper shell  3  and the bottom shell  4 . 
     In an embodiment, the blade  1  comprises an additional surge protector device  33 ′ which connects the lightning down conductor  31  with the second power supply cable  41  so that one end of the additional surge protector device  33 ′ is connected to the third connection point C 3  and another additional surge protector device  33 ′ which connects the lightning down conductor  31  with the first power supply cable  40  so that one end of the additional surge protector device  33 ′ is connected to the fourth connection point C 4 . 
     Each surge protection device  33  and  33 ′, known as SPD, works as a switch that closes during the short time of the surge, i.e., it works as an open switch preventing the passage of current when a certain voltage is not exceeded and it works as a closed switch when a certain voltage is exceeded. When the specified voltage is exceeded, the overvoltage currents can flow to the ground via lightning down conductor  31  or to the supply network via the corresponding power supply cable  40  and  41 . This type of short circuit only lasts for the duration of the surge, normally a few microseconds. The surge protection device  33  can be based on a spark gap technology. In other embodiments the surge protection device is based on varistor technology and/or gas discharge tube or other. 
     In an embodiment, the radiant elements  22  and  26  are resistive elements. In an embodiment, radiant elements  22  and  26  comprise biaxial carbon fabrics. 
     In an embodiment, the electrical terminals  24   a ,  24   b ,  28   a  and  28   b  of the radiant elements  22  and  26  are wire meshes, made of copper, attached to the resistive elements  23  and  27 . 
     In an embodiment, the blade  1  is made of carbon fibers, the blade  1  comprising carbon spars  8  which extend longitudinally over the web  5 . In these blades  1  made of carbon fibers, one end of the surge protection device  33  is connected to the corresponding carbon spar  8 . Similarly, one of the ends of the auxiliary surge protection device  33 ′ is connected to the corresponding carbon spar  8 . 
     In the embodiment shown in  FIGS. 4, 5, 8 and 9 , the blade  1  is made of carbon fibers as indicated above. The lightning down conductor  31  and the power supply cables  40  and  41  extend along the core  5 , in particular they are arranged in the bottom shell  4 . The blade  1  includes in the bottom shell  4  one surge protection device  33  connected at one end to the first power supply cable  40  at the first connection point C 1  and at the other end to the lightning down conductor  31  at the third connection point C 3  and to the carbon spar  8  included in the bottom shell  4 . 
     The blade  1  comprises in the bottom shell  4  another surge protection device  33  connected at one end to the second power supply cable  41  at the second connection point C 2  and at the other end to the lightning down conductor  31  at the fourth connection point C 4  and to the carbon spar  8  included in the bottom shell  4 . In addition, the blade  1  includes an auxiliary surge protection device  33 ′ which is located in the bottom shell  4  and is connected at one end to the second supply cable  41  and at the other end, to the carbon spar  8  and the lightning down conductor  31  located in the bottom shell  4 . The blade  1  further comprises metallic blocks  25  and  29  each one fixed in the corresponding inner surface of the bottom shell  4  and of the upper shell  3 , the electrical connectors  34   a  and  34   b  of the radiant elements  22  and  26  being fixed to the metallic blocks  25  and  29 . The first power supply cable  40  is connected to the corresponding metallic block  25  in the bottom shell  4  and the surge protection device  33  is connected to the corresponding metallic block  29  in the upper shell  3 . 
     Finally, the blade  1  comprises in the upper shell  3  a surge protection device  33  connected at one end to the second radiant element  26  and at the other end, to the carbon spar  8 . 
     In another embodiment of the invention shown in  FIG. 5 , the blade  1  is also made of carbon fiber but includes a lightning down conductor  31  in each shell  3  and  4  of the body  2 , i.e., it includes a lightning down conductor  31  in the bottom shell  4  and another lightning down conductor  31  in the upper shell  3 . The lightning down conductor  31  in the upper shell  3  being connected to the second radiant element  26  through another surge protection device  33 , the lightning protection system  30  being equipontentialized in both shells  3  and  4  through the electrical connection between the first radiant element  22  and the second radiant element  26 . In an embodiment, both lightning down conductors  31  are embedded in the corresponding shells  3  and  4 . 
     The electrical connections between the first radiant element  22 , the supply cables  40  and  41 , the lightning down conductor  31  housed in the bottom shell  4  are analogous to the ones described for the previous embodiment shown in  FIG. 4 . 
     In the upper shell  3 , one end of the surge protection device  33  is connected to the lightning down conductor  31 , the lightning down conductor  31  being also connected to the cap spar  8 . 
     In another embodiment, shown in  FIG. 6 , the blade  1  is made of glass fibers and does not include carbon sparks. The blade  1  comprises one lightning down conductor  31  and one surge protection device  33  in the bottom shell  4 , the surge protection device  33  being connected at one end to the first supply cable  40  at the first connection point C 1  and at the other end to the lightning down conductor  31 . The blade  1  further comprises an auxiliary surge protection device  33 ′ which is housed in the bottom shell  4 , the auxiliary surge protection device  33 ′ being connected at one end to the second supply cable  41  and at the other end to the lightning down conductor  31 . 
     Finally, the heating elements  21  can comprise a plurality of first radiant elements  22  in the bottom shell  4  and a plurality of second radiant elements  26  in the upper shell  3 , arranged both radiant elements  22  and  26  along the leading edge  7  of the blade  1  and facing each other. In the embodiments shown in figures, the heating means  21  comprise three first radiant elements  22  and three second radiant elements  26  arranged opposite each other. 
     Another aspect of embodiments of the invention is a method for manufacturing the blade of the features described previously. The method comprises the following steps;
         depositing in a first mold  50  a plurality of layers or sheets of fabric  10  which will form the bottom shell  4  of the blade  1 , at least one first radiant element  22  in a leading edge zone  53  of the first mold  50 , and at least a connecting element  55  in contact with a cavity  51  of the first mold  50  and with one electrical terminal  24   a  y  24   b  of the first radiant element  22 , the connecting element  55  being configured to define a contacting surface  12  in the bottom shell  4  over the first radiant element  22 , in particular over the electrical terminal  24   a  and  24   b  of the first radiant element  22 ,   molding the bottom shell  4 ,   connecting the first electrical terminal  24   a  of the first radiant element  22  to the first power supply cable  40 , the second electrical terminal  24   b  of the first radiant element  22  to the second power supply cable  41 , and the lightning down conductor  31  to each power supply cable  40 , and  41  through the respective surge protection device  33 ,   depositing in a second mold  60  a plurality of layers or sheets of fabric  10  which will form the upper shell  3  of the blade  1 , including at least one second radiant element  26  in a leading edge area  63  of the second mold  60 , and at least a connecting element  65  in contact with the cavity  61  of the second mold  60  and with a terminal  28   a  and  28   b  of the second radiant element  26 , the connecting element  65  being configured to define a contacting surface  64  in the upper shell  3  over the second radiant element  26 , in particular over the electrical terminal  28   a  and  28   b  of the second radiant element  26 ,   closing both molds  50  and  60  against each other, with the connecting element  12  of the first mold  50  and the connecting element  13  of the second mold  60  facing each other, and sealing the upper shell  3  and the bottom shell  4  to each other,   removing the blade  1  from the molds  50  and  60 , and   fixing the conducting means  35  to the contacting surface  55  of the bottom shell  4  and to the contacting surface  65  of the upper shell  3 , so that the second radiant element  26  is electrically connected to the first radiant element  22  so that the second radiant element  26  is supplied electrically only through the first radiant element  22 .       

     The leading-edge zone  53  and  63  of the first mold  50  and of the second mold  60  form the leading edge  7  of the blade  1 . 
     Each connecting element  55  and  65  is arranged in a specific area of the corresponding leading-edge zone  53  and  63 , generating respective contacting surfaces  12  and  13  on the blade  1 . The contacting surfaces  12  and  13  face each other. In each mold  50  and  60 , the connecting elements  55  and  65  are arranged in contact with the cavity delimiting surface  52  and  62  of the corresponding cavity  51  and  61  and with the radiant elements  22  and  26 . 
     In the contacting surfaces  12  and  13  the first radiant element  22  and the second radiant element  26  are not covered by the outer coating layer  11  or by any other fibers or fabrics, i.e., they are exposed and visible. In particular, these contact areas  12  and  13  are formed at least on the first terminal  24   a  of the first radiant element  22  and on the first terminal  28   a  of the second radiant element  26 . 
     The bottom shell  4  and the upper shell  3  are molded by a vacuum infusion process. Once the plurality of layers or sheets of fabric  10 , the first radiant element  22 , and the corresponding connecting element  55  are deposited in the cavity  51  and  61 , vacuum is applied and resin is infused into the corresponding mold cavity  51  and  61 . After curing, the bottom shell  4  and the upper shell  3  are respectively obtained. 
     In one embodiment, the metallic block  25  and  29  is fixed to the corresponding shell  3  and  4 , after the curing, the corresponding radiant element  22  and  26  being connected to the metallic block  25  and  29 . In another embodiment, each metallic block  25  and  29  is arranged between the plurality of layers  10 , being embedded between them. 
     In the embodiment shown in  FIG. 5 , one lightning down conductor  31  is arranged in each mold  50  and  60 . The second radiant element  26  is connected to another lightning conductor  31  through another surge protection device  33  housed in the upper shell  3 , the lightning protection system  30  being equipontentiallized in both shells  3  and  4  through the conducting means  35 . In this embodiment, both lightning down conductors  31  are embedded in the corresponding shell  3  and  4 . The corresponding lightning down conductor  31  is connected with the corresponding spar cap  8  before applying vacuum. 
     Once the bottom shell  4  is molded, the beam  5  is fixed to the bottom shell  4 . Subsequently, the power supply cables  40  and  41  are arranged guided along the core  5 . The first radiant element  22  is connected to the respective metallic block  25 . After that, the electric connections between the corresponding electrical connectors  34   a  and  34   b , the first power cable  40 , the second power cable  41 , the surge protection devices  33  and  33 ′ and the lightning down conductor  31  are done as have been described previously along the description. 
     Before closing both molds  50  and  60 , the corresponding electrical connections between the first radiant element  22 , the power supply cables  40  and  41 , the lightning down conductor  31  and the corresponding surge protection devices  33  and  33 ′ are carried out in the first mold  50  as defined before. The electrical connections of the elements housed/included in the upper shell  3  and the ones housed/included in the bottom shell  4  being connected independently one from the other. 
     Once the blade  1  is demolded, the respective connecting elements  55  and  65  are removed from the corresponding contacting surfaces  12  and  13 , being the conducting means  35  fixed on the contacting surfaces  12  and  13 . 
     In an embodiment, each connecting element  55  and  65  has a rectangular geometry, thus generating substantially rectangular contacting surfaces  12  and  13 . 
     In a preferred embodiment, the conducting means  35  are adhered to the contacting surface  12  of the bottom shell  4  and to the contacting surface  13  of the upper housing  3 . After the blade  1  is demolded, the conducting means  35  are fixed to the contacting surfaces  12  and  13  by a curing adhesive. In particular, each connecting element  55  and  65  is an adhesive strip, preferably plastic, which placed in each mold  50  and  60  for defining the contacting surfaces  12  and  13 , being removed once the blade  1  is removed from the molds  50  and  60 . Once the adhesive strip is removed the conducting means  35  are then adhered to the adhesive-impregnated contacting surfaces  12  and  13 . In both cases, pressure may be applied on the conducting means  35  for enhancing the fixing process. 
     In other embodiments, the conducting means  35  can be fixed to the contacting surfaces  12  and  13  by any other known means. 
     In an embodiment, the layers  10  can be carbon layers or sheets, the first and second molds  50  and  60  housing carbon spars  8  so that the carbon spars  8  are embedded in the blade  1 . The carbon spars  8  included in the first mold  50  and second molds  60  are electrically connected to the corresponding surge protection devices  33  and  33 ′ and/or to the lightning down conductor  31  as has been described previously along the description. 
     In other embodiments in which the blade  1  comprises a plurality of first radiant elements  22  and a plurality of second radiant elements  26 , each mold  50  and  60  will include at least one connecting element  55  and  65  for each first radiant element  22  and for each second radiant element  26 , being the connecting elements  55  and  65  arranged faced to each other. 
     Although the present invention has been disclosed in the form of preferred 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.