Patent Publication Number: US-2018038351-A1

Title: Wind turbine with improved cooling

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to European Application No. EP 16182958.5, German Application No. DE 102016214543.6, and U.S. Application No. 62/371,388, all having a filing date of Aug. 5, 2016, the entire contents of all of which are hereby incorporated by reference. 
    
    
     FIELD OF TECHNOLOGY 
     The following relates to the field of wind turbines, in particular to wind turbines comprising a cooling system for cooling the wind turbine generator during operation. 
     BACKGROUND 
     It is known to cool wind turbine generators by feeding cooling air from the nacelle into the generator where it is circulated to cool the coils or windings of the generator. 
     EP2615299B1 discloses a cooling system of a wind turbine axially transporting cooling air from non-drive-end to drive-end side of the generator-stator via air-ducts running axially through the generator-stator room. Unfortunately, the cooling air arriving at the drive-end sided end windings of the stator is warmer than at the non-drive end sided end windings due to the heated air in the generator-stator room warming up the air in the said air-ducts. 
     To prevent corrosion in the generator, it is important that the cooling air is sufficiently dry. In order to lower the humidity of the cooling air, a part of the heated return air may be blended with the cooling air from the nacelle as disclosed in EP2806542A. 
     Therefore, there may be a need for an improved cooling of a wind turbine generator. 
     SUMMARY 
     This need may be met by the subject matter according to the independent claims. Advantageous embodiments are described by the dependent claims. 
     According to a first aspect of embodiments of the invention which provide a wind turbine comprising (a) a nacelle supported by a tower, (b) a generator, (c) a rotatable front assembly arranged on a side of the generator facing away from the nacelle, and (d) a cooling system for cooling the generator by feeding cooling air from the rotatable front assembly to the generator. 
     This aspect of embodiments of the invention are based on the idea that cooling air is fed from the rotatable front assembly and into the drive end of the generator, i.e. the part of the generator that is farthest away from the nacelle. Thereby, an efficient cooling of the generator, in particular of the drive end part of the generator, can be obtained. 
     The nacelle is supported by the tower which is fastened to the ground or sea bottom at its lower end. The nacelle constitutes the rear part of the wind turbine while the rotatable front assembly constitutes the front part (relative to the wind direction). The generator is arranged essentially between the nacelle and the rotatable front assembly in the sense that one side of the generator (the non-drive end) faces or is located within the nacelle while the opposite side of the generator (the drive end) faces the rotatable front assembly. In case of a direct drive (gearless) wind turbine, the generator is usually located between the nacelle and the rotatable front assembly and does not extend into the nacelle. In case of a geared wind turbine, the generator may, at least in part, extend into the nacelle. The rotatable front assembly comprises a number of components which interact to convert wind energy into rotational (mechanical) energy which in turn is converted into electrical energy by the generator. 
     According to an embodiment of the invention, the rotatable front assembly comprises a front assembly air intake and the cooling air comprises air taken in through the front assembly air intake. 
     In other words, the cooling air, which the cooling system feeds from the rotatable front assembly to the generator, comprises ambient air taken in through a front assembly air intake. 
     According to a further embodiment of the invention, the rotatable front assembly comprises a hub, at least one rotor blade mounted on the hub, and a spinner covering the hub. 
     The at least one rotor blade causes the hub to rotate around an axis (and thereby drive the generator) when incoming wind hits the rotor blade(s). The spinner is a housing or shield that covers the hub in order to protect it from the environment. 
     According to a further embodiment of the invention, the front assembly air intake is at least partially coincident with an opening in the spinner through which the at least one rotor blade extends. 
     In other words, ambient air may enter the rotatable front assembly through an opening in the spinner which allows the blade to extend from the hub. 
     According to a further embodiment of the invention, the front assembly air intake comprises a ring-shaped opening surrounding the at least one rotor blade. 
     The width of the ring-shaped opening, i.e. the difference between the outer diameter and inner diameter of the ring-shaped opening, is sufficiently large to take in a substantial amount of air and on the same time small enough to assure that larger objects and significant amounts of water (rain) cannot enter the rotatable front assembly. The sum of all air intake openings, i.e. the ring-shaped openings around the blades and the optional ring-shaped opening between stator and hub, may preferably have a total area between 0.4 m 2  and 1 m 2 , in particular around 0.6 m 2 . 
     Any water entering the rotatable front assembly is preferably guided through the rotor blades and ejected through openings at the blade tips as a result of the centrifugal force. 
     According to a further embodiment of the invention, the front assembly air intake comprises an air guide arranged on an outer surface of the spinner. 
     In other words, ambient air may be guided into the rotatable front assembly through an air guide, such as a duct, arranged on the outer surface of the spinner. 
     The opening of the air guide is sufficiently large to take in a substantial amount of air and on the same time small enough to assure that larger objects and significant amounts of water (rain) cannot enter the rotatable front assembly. The opening of the air guide may preferably have a total cross-sectional area between 0.1 m 2  and 0.3 m 2 , in particular around 0.2 m 2 . 
     According to a further embodiment of the invention, the front assembly air intake comprises an intake filter and/or an intake fan. 
     The intake filter may for example be a moisture filter, a dirt filter, a salt filter or a combination of such filters. 
     According to a further embodiment of the invention, the tower comprises a tower air intake located at a base portion of the tower and power cables for transmitting power from the generator to the base portion, wherein the cooling system comprises means for guiding air from the tower air intake to the rotatable front assembly such that the air is heated by the power cables, whereby the cooling air comprises air taken in through the tower air intake. Typically, the electrical losses of the cables are typically in the range between 300 Watt and 500 Watt per meter. 
     The power cables, in particular power cables transmitting power from the generator down through the tower to transformers and other electrical installations located at the base portion of the tower, will heat the ambient air taken in through the tower air intake as the air is guided upwards through the tower by the guiding means. This heating of the air is mainly produced by the electrical losses of the cables and causes a reduction in the relative humidity of the air. Thus, once the tower air reaches the rotatable front assembly, it will be drier (in the sense that its relative humidity is smaller) than the air surrounding the wind turbine. 
     Accordingly, the air taken in through the tower air intake and guided upwards by the guiding means will be relatively dry and thus well suited for cooling the generator by itself or for blending with possibly more humid cooling air from other sources. 
     Furthermore, the tower air may advantageously be mixed with air in the rotatable front assembly origination from one or more different air intakes, such as air intakes corresponding to the above-described front assembly air intakes. In this case, the dry tower air will reduce the relative humidity of the cooling air resulting from the mixing. Accordingly, the tower air may advantageously be used to adjust the relative humidity of the cooling air, thereby reducing the risk of causing corrosion in the stator windings  131 . 
     According to a further embodiment of the invention, the cooling system further comprises a tower fan arranged within the tower. 
     The tower fan may cause a larger amount of ambient air to be drawn in through the tower air intake. 
     In some embodiments, more than one tower fan may be arranged at various positions within the tower, e.g. in the vicinity of the tower air intake, close to the upper end of the tower, etc. 
     According to a further embodiment of the invention, the rotatable front assembly comprises one or more openings facing the generator, the openings being adapted to feed the cooling air to the generator. 
     The openings may in particular be formed in a rotor front plate between the hub and the generator. 
     According to a further embodiment of the invention, a filter is arranged in the vicinity of each of the one or more openings, i.e. in such a way that the cooling air passing through the respective opening is filtered before entering the generator. 
     According to a further embodiment of the invention, the filter arranged in each of the one or more openings is selected from the group consisting of a moisture filter, a dirt filter, and a salt filter. 
     According to a further embodiment of the invention, the cooling system further comprises one or more front fans arranged in the vicinity of at least one of the one or more openings. 
     More specifically, a front fan may be arranged in the vicinity of each opening, i.e. on the generator side of the opening, on the hub side of the opening, or within the opening itself. Preferably, each opening is equipped with at least one fan, such that the cooling air from the rotatable front assembly is drawn through the openings and into the generator. 
     According to a further embodiment of the invention, the cooling system further comprises a rear fan (main fan) arranged at a side of the generator facing away from the rotatable front assembly, the rear fan being adapted to draw the cooling air from the rotatable front assembly through the generator and towards the nacelle. 
     The rear fan may preferably be arranged within the nacelle at a position close to the generator to draw the cooling air from the rotatable front assembly through the generator and into an exhaust duct extending within the nacelle. 
     According to a further embodiment of the invention, the cooling system is further adapted to feed additional cooling air from the nacelle to the generator. 
     In this embodiment, cooling air is drawn into the generator from both sides, i.e. from the side facing the nacelle and from the side facing the rotatable front assembly. Thereby, a uniform cooling of the generator may be obtained. 
     According to a second aspect of embodiments of the invention which provide a method of cooling a generator of a wind turbine, the wind turbine comprising a nacelle supported by a tower, the generator, and a rotatable front assembly arranged on a side of the generator facing away from the nacelle. The method comprises (a) feeding cooling air from the rotatable front assembly to the generator. 
     This aspect of embodiments of the invention are based on the same idea as the first aspect discussed above. 
     According to a further embodiment of the invention, the cooling air comprises air taken in through a front assembly air intake and/or air taken in through a tower air intake. 
     In other words, the cooling air may consist of air taken in through the front assembly air intake, of air taken in through the tower air intake, or of a blend of air taken in through the front assembly air intake and air taken in through the tower air intake. 
     According to a further embodiment of the invention, the cooling air comprises a mixture of air taken in through a front assembly air intake and tower air taken in through a tower air intake located at a base portion of the tower, wherein the tower air is guided up through the tower and heated by power cables extending within the tower such that the relative humidity of the tower air is lower than the relative humidity of the air taken in through the front assembly air intake. 
     It is noted that embodiments of the invention have been described with reference to different subject matters. In particular, some embodiments have been described with reference to method type claims whereas other embodiments have been described with reference to apparatus type claims. However, a person skilled in the art will gather from the above and the following description that, unless otherwise indicated, in addition to any combination of features belonging to one type of subject matter also any combination of features relating to different subject matters, in particular to combinations of features of the method type claims and features of the apparatus type claims, is part of the disclosure of this document. 
     The aspects defined above and further aspects of embodiments of the present invention are apparent from the examples of embodiments to be described hereinafter and are explained with reference to the examples of embodiments. The invention will be described in more detail hereinafter with reference to examples of embodiments. However, it is explicitly noted that the invention is not limited to the described exemplary embodiments. 
    
    
     
       BRIEF DESCRIPTION 
         FIG. 1  shows a wind turbine; 
         FIG. 2  shows a wind turbine; 
         FIG. 3  shows a wind turbine; 
         FIG. 4  shows a first partial view of a rotatable front assembly of a wind turbine; 
         FIG. 5  shows a further partial view of the rotatable front assembly shown in  FIG. 4 ; 
         FIG. 6  shows a rotor front plate of a wind turbine; 
         FIG. 7  shows a further partial view of the rotatable front assembly shown in  FIGS. 4 and 5 ; 
         FIG. 8  shows a tower of a wind turbine; 
         FIG. 9  shows an overview of a rotatable front assembly of a wind turbine; 
         FIG. 10  shows a detailed view of a part of the rotatable front assembly shown in  FIG. 9 . 
     
    
    
     DETAILED 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 wind turbine according to an embodiment of the invention. The wind turbine comprises a nacelle  110  mounted on top of a tower  120 , a generator comprising a rotor  130  with magnets arranged to rotate around generator windings  131  mounted on a stator  132  (shown in  FIG. 5 ), and a rotatable front assembly  140  arranged on the side of the generator  130 ,  131 ,  132  that is opposite to (i.e. facing away from) the nacelle  110 . The rotatable front assembly  140  comprises at least one rotor blade  140   a , preferably three rotor blades  140   a . It is noted that the wind turbine shown in  FIG. 1  is a direct drive wind turbine. However, embodiments of the present invention are equally applicable to other types of wind turbines, such as gear drive wind turbines. 
     The wind turbine further comprises a cooling system for cooling the generator  130 ,  131 ,  132 , in particular the generator windings  131 ,  132 , by feeding cooling air  144  from the rotatable front assembly  140  into the generator  130 ,  131 ,  132 . The cooling air  144  is obtained through front assembly air intake  141 , or as tower air  122  which is guided from the tower  120  through tower air guiding means  152 , such as a pipe. The cooling air may also be a blend of air taken in through the front assembly air intake  141  and tower air  122 . In the latter case, the tower air  122  may in particular be useful for reducing the humidity of the cooling air  144 , as will be described in more detail below in conjunction with  FIG. 8 . 
     An inlet filter  142 , such as a moisture filter, dirt filter, salt filter or a combination thereof, is arranged in the air intake  141  to filter the ambient air that is taken into the front assembly  140 . Optionally, an inlet fan  143  may also be arranged in the vicinity of the air intake  141 . 
     The cooling air  144  is guided into the generator  130 ,  131 ,  132  through suitable openings connecting the rotatable front assembly  140  and the generator  130 ,  131 ,  132 . As will be discussed in more detail further below in conjunction with  FIG. 6 , the openings may in particular be formed in a rotor front plate. A rear fan  151  arranged in the vicinity of an interface between the generator  130 ,  131 ,  132  and the nacelle  110  draws the cooling air  144  through the generator  130 ,  131 ,  132 . After being circulated within the generator  130 ,  131 ,  132 , in particular in the vicinity of the generator windings  131 , the cooling air  144  leaves the generator  130 ,  131 ,  132  and passes through an exhaust guide  114  in the nacelle  110  before it leaves the nacelle  110  as exhaust air  115 . 
     In an optional modification of the embodiment, cooling air  113  may also be supplied from the nacelle  110  into the generator  130 ,  131 ,  132 . For this purpose, ambient air is taken into the nacelle through filer  111  with support from fans  112  and guided into the generator  130 ,  131 ,  132  as shown in  FIG. 1 . The humidity of the nacelle cooling air  113  may be reduced by means of exhaust air bypass  116  which bypasses a part of the exhaust air  115  into the nacelle where it is mixed with the air taken in through filter  111 . 
     It is explicitly noted that although  FIG. 1  only shows one front assembly air intake  141 , the front assembly  140  may comprise any number of air intakes  141 , in particular two, three, four or even more air intakes  141 . 
       FIG. 2  shows a wind turbine according to a further embodiment of the invention. More specifically, the embodiment shown in  FIG. 2  only differs from the embodiment shown in  FIG. 1  and discussed in detail above in that the intake filter  141  is replaced by filters  145  arranged in the vicinity of the openings or connections between the rotatable front assembly  140  and the generator  130 ,  131 ,  132 . Accordingly, in this embodiment the filtering of the air takes place where the cooling air  144  enters the generator  130 ,  131 ,  132  instead of where ambient air enters the rotatable front assembly  140 . In a modification of the embodiment shown in  FIG. 2 , both an inlet filter  142  as the one shown in  FIG. 1  and the filters  145  shown in  FIG. 2  may be used. 
     With regard to the remaining structure of the wind turbine shown in  FIG. 2 , reference is made to the corresponding description in relation to  FIG. 1  above. 
       FIG. 3  shows a wind turbine according to a further embodiment of the invention. More specifically, the embodiment shown in  FIG. 3  is a modification of the embodiment shown in  FIG. 2  and discussed above. In addition to the elements shown in  FIG. 2 , the front assembly  140  in  FIG. 3  is shown as including a hub  146  for supporting the rotor blade(s) of the wind turbine (not shown). Here, the filters  145  are arranged between the outer surface of the hub and close to the outer wall or cover (also referred to as the spinner) of the front assembly  140 . The tower air  122  is guided through the hub  146  to blend with the ambient air taken in through air intake(s)  141 . 
       FIG. 4  shows a first partial view of a rotatable front assembly of a wind turbine in accordance with an embodiment of the invention. More specifically,  FIG. 4  shows the rotatable front assembly  140  comprising spinner (or cover)  147  and hub  146 . The spinner  147  comprises an opening  148  for letting a rotor blade (not shown) through. The hub  146  comprises an opening or mounting portion  149  in which the rotor blade is to be mounted. The filter  145  is arranged between the spinner  147  and the hub  146  close to an opening into the generator  130 ,  131 ,  132 . Thereby, ambient air may be taken in through the blade opening  148  and pass through the filter  145  and into the generator  130 . 
       FIG. 5  shows a further partial view of the rotatable front assembly  140  shown in  FIG. 4 . In particular,  FIG. 5  shows an air guide  153  arranged on the side of the filter  145  facing the generator  130 ,  131 ,  132  for guiding the filtered cooling air into the generator  130 ,  131 ,  132  in order to cool the generator windings  131 . 
     With regard to  FIGS. 4 and 5 , it is noted that the spinner  147  and hub  146  may be designed to receive and hold more than one rotor blade, in particular three rotor blades. Furthermore, a plurality of filters  145  may be arranged around the perimeter of the generator rotor  130 . 
     In a modification of the embodiment shown in  FIG. 5 , a front assembly air intake may be formed in the gap between the front assembly  140  and the generator  130 , e.g. above the air guide  153 . In this case, ducts or pipes will additionally be formed between the gap and the spinner  147  or the spinner-sided air-intake of the filter(s)  145  in order to transport the air taken in towards the front of the front assembly  140  (i.e. towards the left side (i.e. air-intake side) of filter  145  in  FIG. 5 ), such that the air can be sent through the filter  145 , into the air guide  153  and further into the generator  130  as discussed above. 
       FIG. 6  shows a rotor front plate  160  of a wind turbine in accordance with an embodiment of the invention. The front rotor plate  160  designed to be arranged at the drive end of the generator  130 , i.e. facing the rotatable front assembly  140 , on the rotor of the generator  130  which rotates around the windings  131  to induce electrical currents therein. As shown, the front rotor plate  160  comprises three pairs of holes or openings  161   a ,  161   b ,  162   a ,  162   b ,  163   a ,  163   b  arranged close to the perimeter of the front rotor plate  160 . Each opening  161   a ,  161   b ,  162   a ,  162   b ,  163   a ,  163   b  may be connected with a corresponding filter  145  and a corresponding air guide  153  in the way shown in  FIG. 5 . 
     It is noted that  FIG. 6  also shows a cut-out formed between the openings  161   a  and  161   b . The cut-out is shaped to interact with a lifting tool during assembly of the wind turbine. Due to the large forces and stress that may occur during assembly, it may be advantageous to leave out the pair of openings  161   a  and  161   b  (which may otherwise be deformed during assembly) and instead increase the size of the other openings  162   a ,  162   b ,  163   a ,  163   b.    
       FIG. 7  shows a further partial view of the rotatable front assembly shown in  FIGS. 4 and 5 . In particular, the view of  FIG. 7  shows that the hub  146  comprises three blade mounting portions  149  and that the spinner  147  comprises three corresponding blade openings  148 . Although only a single filter unit  145  is shown (for reasons of clarity), a total of six filter units  145  may be implemented and arranged as discussed in connection with  FIG. 6  above. 
       FIG. 8  shows the tower  120  of a wind turbine according to an embodiment of the invention, in particular according to any of the embodiments described above or below. As shown, the tower  120  comprises a tower fan  121  arranged at an upper portion of the tower for drawing tower air  122  upwards (towards the nacelle) within the tower  120 . The tower air  122  is taken into the tower  120  in the area of tower entrance  124 . The air intake may be supported by lower fans  123 . The air entering the tower is filtered by filters  125  and passed by electrical installations  126 . On its way towards the fan  121  at the top of the tower, the air is heated by heat emitted by power cables  127 . The power cables  127  transmit electrical power generated by the generator to the electrical installations  126 , such as transformer, converter etc. Accordingly, once the tower air  122  reaches the top of the tower  120 , it is warmer and relatively dry, i.e. it has a lower relative humidity than the surrounding air. Accordingly, the tower air  122  will be highly suitable for cooling and/or dehumidifying the cooling air  144  supplied to the generator from the rotatable front assembly as described above. Simultaneously, the temperature of the cooling air  144  supplied to the generator will be increased to some extent. The humidity and the temperature of the cooling air  144  arriving at the generator can thus be controlled by the amount of tower air  122  provided by the fan  121  and/or fan  125  at the bottom or the top of the tower  120 . 
       FIG. 9  shows an overview of a rotatable front assembly  140 ′ of a wind turbine in accordance with an alternative embodiment of the invention. The rotatable front assembly  140 ′ of this embodiment differs from the rotatable front assembly  140  described in conjunction with the previous embodiments in that ambient air is not taken in through the blade opening  148  but instead through an air guide  154  arranged on the outer surface of the spinner  147 . The air guide  154  is formed as a rectangular, relatively flat conduit extending over the surface of the spinner  147  in such a way that the opening faces the incoming wind. Thereby, ambient air can easily be drawn into the rotatable front assembly  140 ′ and fed into the generator  130  to cool the generator windings  131 . 
       FIG. 10  shows a detailed view of a part of the rotatable front assembly  140 ′ shown in  FIG. 9 . As shown, ambient air is taken in through the air guide  154  and guided through the filter  145  and into the generator  130  by the air guide  153  extending through the front rotor plate  160 . 
     It is noted that the term “comprising” does not exclude other elements or steps and the use of the articles “a” or “an” does not exclude a plurality. Also elements described in association with different embodiments may be combined. It is further noted that reference signs in the claims are not to be construed as limiting the scope of the claims.