Abstract:
A wind turbine including a generator with a stator and a rotor, a cooling arrangement, a wind turbine brake including a brake disk and a caliper with brake pads is provided. An air duct with a filter is located near the brake pads of the caliper. During the operation of the cooling arrangement, a part of the air flow is guided via the brake pads. The brake dust produced by the brake pads during operation of the brake will be reduced by the filter of the air duct.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to European Application No. 15185338.9 having a filing date of Sep. 15, 2015 the entire contents of which are hereby incorporated by reference. 
       FIELD OF TECHNOLOGY 
       [0002]    The following relates to a wind turbine and a method to collect brake dust of a wind turbine brake. 
       BACKGROUND 
       [0003]    EP 2 182 619 A shows a wind turbine comprising a stator and a rotor and a cooling arrangement. The cooling arrangement comprises an air cooling and a liquid cooling device which are connected by an air-to-liquid heat exchanger, which is applied to transport heat out of the generator by the cooling liquid. 
         [0004]    EP 2 902 619 shows a cooling arrangement for a wind turbine with an outer rotor and an inner stator. A cooling arrangement is realized to guide an air flow over the outside rotor to transfer heat from the generator to the cooling air flow. 
         [0005]    EP 2 333 321 A shows a wind turbine with a brake system comprising brake disk in a flexible portion for compensating or absorbing an expansion of the brake system. 
         [0006]    A typical braking system of a wind turbine comprises a brake disk, a caliper with brake pads. During braking operation, the caliper presses the brake pads onto the surface of the rotor disk, thus reducing the rotor speed of the wind turbine and producing heat. Additionally, brake dust from the brake pads can be released within the generator. 
       SUMMARY 
       [0007]    An aspect relates to the amount of brake dust released. 
         [0008]    A wind turbine comprises a generator with a stator and a rotor for producing electrical power. The generator comprises a cooling arrangement generating a cooling air flow to cool at least parts of the generator during operation of the cooling arrangement. A wind turbine brake is installed to be able to reduce the speed of the wind turbine. The brake comprises a brake disc and at least one brake caliper with at least one brake pad, wherein the at least one brake pad being located within the stream of a part of the cooling air flow during operation of the cooling arrangement. An air duct is located with its inlet opening at the at least one brake pad so that the part of the cooling air flow streaming over the brake pad will flow through the air duct. The air duct comprises a filter which reduces significantly the amount of brake dust produced by the at least one brake pad during operation of the wind turbine brake and flowing within the stream of a part of the cooling air flow during operation of the cooling arrangement. 
         [0009]    Furthermore, the air duct comprises a valve which enables or disables the air flow through the air duct, wherein the valve is at least open during operation of the wind turbine brake. The valve is preferably closed in non-braking operation to provide more air flow outside the air duct and thus increase the cooling performance. 
         [0010]    Furthermore, the cooling arrangement comprises at least one fan which is located preferably at the stator is able to produce the cooling air flow. 
         [0011]    Furthermore, the cooling system comprises a heat exchanger resulting in a closed air flow circuit within the wind turbine 
         [0012]    Alternatively, the cooling arrangement comprises fans drawing the cooling air from the outside of the wind turbine via filters and dehumidifiers into the generator, wherein the cooling arrangement comprises fans drawing the cooling air warmed up by the generator to the outside of the wind turbine. 
         [0013]    Furthermore, the dust-collecting-capacity of the filter is at least as high as the volume of the brake-dust being produced/created during the lifetime of the at least one brake pad of the brake caliper. Thus, the filter can be cleaned/changed/replaced simultaneously with the standard maintenance service to replace the at least one brake pad or the brake pads of the respective caliper. 
         [0014]    Furthermore, the stream of a part of the cooling air flow is warmed-up by the generator before streaming around the brake pads. Thus, the stator windings are not in the direct airflow path which still may content some brake dust. 
         [0015]    Alternatively, the stream of a part of the cooling air flow is not yet warmed-up by the generator before streaming around the brake pads. 
         [0016]    Furthermore, the method to collect brake dust of a wind turbine brake comprises the following steps: 
         [0000]    The part of the cooling air flow comprising the brake dust created by the at least one brake pad will flow through the air duct and been filtered by the filter of the air duct during operation of the cooling system. 
         [0017]    Furthermore, the filter bag comprising the brake dust will be replaced or the filter containing the brake dust will be emptied or the brake dust will be sucked out of the filter by a vacuum cleaner at earliest when the at least one brake pad has to be replaced thus enabling a reduced number of service maintenance events. 
         [0018]    Furthermore, the power of the part of the cooling arrangement producing the flow of the part of the cooling air flow (AF, comprising the brake dust will be increased preferably to a maximum value during operation of the wind turbine brake. 
         [0019]    Generally, this brake dust “sucking/collecting” system does not require an additional motor or fan, but it makes use of the pressure differences in the generator air cooling system. The system is suitable for both the generators with
       “liquid link” with a heat exchanger and a “closed cooling system” or   for those with direct cooling with an “open” cooling system.       
 
         [0022]    The brake dust released during the braking operation will be prevented from entering the generator thus increasing the lifetime of parts of the wind turbine. 
         [0023]    The proposed solution makes use of the depression in the generator cavity to suck the dust particles released while braking. A tube or a system of tubes should be connected to the brake calipers (high pressure) at one end and to the stator cavity (low pressure) at the other end in order to suck in the dust. In the tube a valve and a filter should be installed. The valve should close the tube during normal turbine operation and it should open it during braking. Any type of filter could be used, and suitable types would be cyclone filter which would not require a filter change or a bag filter which could be sized to collect as much as the brake pads volume. 
         [0024]    It has to be 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 other notified, in addition to any combination of features belonging to one type of subject matter also any combination between features relating to different subject matters, in particular between features of the method type claims and features of the apparatus type claims is considered as to be disclosed with this document. 
         [0025]    The aspects defined above and further aspects of embodiments of the present invention are apparent from the examples of embodiment to be described hereinafter and are explained with reference to the examples of embodiment. The following will be described in more detail hereinafter with reference to examples of embodiment but to which embodiments of the invention is not limited. 
     
    
     
       BRIEF DESCRIPTION 
         [0026]    Some of the embodiments will be described in detail, with reference to the following figures, wherein like designations denote like members, wherein: 
           [0027]      FIG. 1  shows a simplified diagram of a direct-drive wind turbine; 
           [0028]      FIG. 2  shows a simplified wind turbine of  FIG. 1  with a different cooling airflow. 
       
    
    
     DETAILED DESCRIPTION 
       [0029]    The illustration in the drawing is schematic. It is noted that in different figures, identical elements or features are provided with the same reference signs. In order to avoid unnecessary repetitions elements or features which have already been elucidated with respect to a previously described embodiment are not elucidated again at a later position of the description. 
         [0030]      FIG. 1  is a simplified diagram of a direct-drive wind turbine  2 . A nacelle  6  is mounted on top of a tower  7 . A hub  8  with rotor blades  9  is mounted to a permanent-magnet generator  3 ,  4  comprising an outer rotor  4  and an inner stator  3  which are connected rotatable to each other by a bearing unit  61 . The rotor  4  comprises permanent magnets  5  facing the inner stator  3  circumferentially. In another embodiment (not shown), the magnetic fields of the magnets  5  can also be created electrically. 
         [0031]    During operation, the hub  8  with the blades  9  and the outer rotor  4  is caused to rotate about an axis of rotation R. Windings  30  on the inner stator  3  are cooled by guiding a cooling airflow AFx via the end windings  300  into an air-gap  20  between rotor  4  and stator  3  and then drawing the airflow AFx through the stator windings  30  and through radial cooling channels  34  of the stator  3 , and into an interior cavity  31  of the stator  3 . This interior cavity  31  extends about a main shaft  62  around the axis of rotation R. In this embodiment, the warmed air AF′ drawn into the interior cavity  31  is cooled by a number of heat exchangers  15  and then blown out of the interior cavity  31  by a number of fans  14  which direct a cooled airflow AF back into a cavity  200 R,  200 F at each end of the stator  3 . The diagram shows that a winding overhang  300 —also called stator end windings  300  which is part of the stator windings  30 —extends to some distance into the cavity  200 R between rotor housing  40  and brake-disc  41  at the non-drive end of the generator, and into the cavity  200 F between rotor housing  40  and a front face  32 F at the drive end. At the non-drive end, the cavity  200 R is bounded by the cylindrical rotor housing body  40  and a brake disc  41 , and is sealed off from the nacelle or canopy  44  by a suitable cover  45  or seal  45 . One or several brake callipers  42  are circumferentially distributed and fixed on the non-drive end of the main shaft  62 . A brake calliper  42  comprises two brake pads  43  facing each side the brake disc  41 . In braking operation, the calliper  42  or the callipers  42  presses the brake pads  43  against the opposing surfaces of the rotating brake disc  41  resulting in transforming rotational energy into heat, thus forming a wind turbine brake  41 ,  42 ,  43 . The brake disc  41  serves as a braking or stopping means of rotational movements of the rotor  4  when interacting with the respective brake calliper(s)  42  disposed with a structural component of the stator  3  or nacelle  6 . 
         [0032]    Additionally fine brake dust  49  from abrasion of the brake pads  43  will be distributed into the surrounding air during operation of the wind turbine brake  41 ,  42 ,  43 . 
         [0033]    To ensure that the cooling airflow AF does not simply flow around the barrier-like winding overhang  300 , the cooling arrangement  1  comprises an arrangement of bypass openings  10  and manifolds  11 . In this exemplary embodiment, the bypass openings  10  are formed on the stator front face  32 F and stator rear face  32 R. As a cooling airflow AF is directed from the stator interior  31  into the cavity  200 R,  200 F and in the direction of the air-gap  20 , an underpressure inside the stator interior  31  acts to draw a portion AFy of the cooling airflow AF through the narrow spaces in the winding overhang  300 . The manifold  11  is arranged to ensure that the warmed air then passes directly into the stator interior  31  through the bypass openings  10 . This portion AFy of the cooling airflow AF effectively “bypasses” the air-gap and enters the stator interior  31  by a shorter route. The underpressure in the stator interior cavity  31  can be relative, i.e. as long as the pressure inside the stator interior  31  is lower than the pressure in a cavity  200 R,  200 F, a portion of the cooling airflow AF will be encouraged to pass through the spaces in the winding overhang  300 , since the openings  10  offer a path into the stator interior  31 . The pressure differential can be achieved by driving a number of fans  14  to blow the cooled air AF into the cavity  200 R,  200 F. The relatively small space in the cavity  200 F,  200 R (reduced even further by the presence of the manifold  11 ) encourages such a pressure differential. 
         [0034]    Axial cooling channels  35  and radial channels  34  (shown schematically) provide a path for a portion AFx of the cooling airflow AF alongside the windings  30  and into the stator interior  31 . The cooling airflow portion AFx can enter the air-gap  20  at either end, and can travel along the axial cooling channels  35  and then through the radial channels  34  into the stator interior  31 . Temperature measurements for this type of generator are made to determine the location of any winding overhang hotspot  300  and the required number and positions of bypass openings  10 , and the dimensions and positions of the manifolds  11 . 
         [0035]    The calliper(s)  42  with the brake pads  43  are located in the flow path AFup, AFdown which as a part of the cooling air flow AF. In operation of the fan  14  or the fans  14 , the upstream air flow AFup streams from the cavity  200 R to the brake pads  43 . The downstream air flow AFdown streams away from the brake pads  43  to the air gap  20  and the stator  3  and comprises the fine brake dust  49  created by abrasion of the brake pads  43 . 
         [0036]    An air duct  48 ,  50  is positioned in the downstream path AFdown in order to collect the air comprising the fine brake dust  48 . A dust filter  46  is positioned within the air duct  48 ,  50  between the inlet part  48  of the air duct  48 ,  50  and the outlet part  50  of the air duct  48 ,  50 . The filter  46  can be any type of filter, e.g. a cyclone filter or a bag filter. 
         [0037]    The air cleaned by the filter  46  will leave the air duct  48 ,  50  by its outlet  50  and be further distributed to the air-gap  20  via the cooling airflow portion and to the winding over-hang  300  via the cooling airflow portion AFy. 
         [0038]    The air duct  48 ,  50  comprises a valve  47  which can enable or stop the air flow in the air duct  48 ,  50 . Preferably, the valve  47  is positioned in the inlet part  48  of the air duct  48 ,  50 . 
         [0039]    Preferably, the valve  47  is open in operation of the/wind turbine brake  41 ,  42 ,  43  in order to collect the abrased brake dust  46  in the dust filter  46  and closed in non-braking operation in order to prevent the reduction of the cooling airflow AF created by the downstream air-flow AFdown within the air duct  48 ,  50 . 
         [0040]    Preferably, the power of the fans  14  producing the flow of the part of the cooling air flow AFup, AFdown comprising the brake dust  49  will be increased preferably to a maximum value during operation of the wind turbine brake  41 ,  42 ,  43 . 
         [0041]    The valve  47  can be a passive flap valve  47  opening depending on the magnitude of the downstream airflow AFdown or an electrical switchable, active flap valve  47 . 
         [0042]    The collecting capacity of the filter  46 , i.e. volume of the brake dust  49  the filter  46  can collect, e.g. in the filter bag or the collecting unit of the filter cyclone, should be at least as large as the volume of the brake pads  43  of the brake calliper  42 . Preferably, the filter bag of the filter  46  will be replaced or the filter cyclone of the filter  46  will be emptied if the brake pads  43  are replaced. This can be done in one maintenance session. 
         [0043]    The air duct  48 ,  50  is positioned at least partly within the cooling air stream flow AF. 
         [0044]      FIG. 2  shows a simplified wind turbine of  FIG. 1  with a different air flow 
         [0045]    The permanent-magnet generator  3 ,  4  comprises an outer rotor  4  and an inner stator  3  which are connected rotatable to each other by a bearing unit  61 . The rotor  4  comprises permanent magnets  5  facing the inner stator  3  circumferentially. In another embodiment (not shown), the magnetic fields of the magnets  5  can also be created electrically. 
         [0046]    During operation, the outer rotor  4  is caused to rotate about an axis of rotation R. Windings  30  on the inner stator  3  are cooled by guiding a cooling airflow AF via the end windings  300  into an air-gap  20  between rotor  4  and stator  3  and through the stator windings  30 , and into an interior cavity  31  of the stator  3 . This interior cavity  31  extends about a main shaft  62  around the axis of rotation R. In this embodiment, the warmed air AF′ drawn into the interior cavity  31  is cooled by a number of heat exchangers  15  and then blown out of the interior cavity  31  by a number of fans  14  which direct a cooled airflow AF back into a cavity  200 L of the stator  3 . The diagram shows that a winding overhang  300 —also called stator end windings  300  which is part of the stator windings  30 —extends to some distance into the cavity  200 L between the rotor housing  40  and a front stator face  32  at the drive end. 
         [0047]    At the non-drive end, the cavity  200 R is bounded by the cylindrical rotor housing body  40  and a brake disc  41 , and is sealed off from the nacelle or canopy  44  by a suitable cover  45  or seal  45  (shown in  FIG. 1 ). One or several brake callipers  42  are circumferentially distributed and fixed on the non-drive end of the main shaft  62 . A brake calliper  42  comprises two brake pads  43  facing each side the brake disc  41 . In braking operation, the calliper  42  or the callipers  42  presses the brake pads  43  against the opposing surfaces of the rotating brake disc  41  resulting in transforming rotational energy into heat, thus forming a wind turbine brake  41 ,  42 ,  43 . 
         [0048]    The calliper(s)  42  with the brake pads  43  are located in the flow path AFup, AFdown as part of the warmed-up cooling air flow AF′. In operation of the fan  14  or the fans  14 , the upstream air flow AFup flows to the brake pads  43  from the air gap  20  and the stator  3 . The downstream air flow AFdown streams away from the brake pads  43  to the non-drive end cavity  200 R and the interior cavity  31  and comprises the fine brake dust  49  created by abrasion of the brake pads  43 . 
         [0049]    An air duct  48 ,  50  is positioned in the downstream path AFdown in order to collect the air comprising the fine brake dust  48 . A dust filter  46  is positioned within the air duct  48 , 50  between the inlet part  48  of the air duct  48 ,  50  and the outlet part  50  of the air duct  48 ,  50 . The filter  46  can be any type of filter, e.g. a cyclone filter or a bag filter. 
         [0050]    The air AFdown cleaned by the filter  46  will leave the air duct  48 ,  50  by its outlet  50  and be further distributed to the non-drive end cavity  200 R and interior cavity  31 . 
         [0051]    The air duct  48 ,  50  comprises a valve  47  which can enable or stop the air flow in the air duct  48 ,  50 . Preferably, the valve  47  is positioned in the inlet part  48  of the air duct  48 ,  50 . 
         [0052]    Preferably, the valve  47  is open in operation of the turbine brake  41 ,  42 ,  43  in order to collect the abraded brake dust  46  in the dust filter  46  and closed in non-braking operation in order to prevent the reduction of the cooling airflow AF created by the downstream air-flow AFdown within the air duct  48 ,  50 . 
         [0053]    Preferably, the power of the fans  14  producing the flow of the part of the cooling air flow AFup, AFdown comprising the brake dust  49  will be increased preferably to a maximum value during operation of the wind turbine brake  41 ,  42 ,  43 . 
         [0054]    The valve  47  can be a passive flap valve  47  opening depending on the magnitude of the downstream airflow AFdown or an electrical switchable, active flap valve  47 . 
         [0055]    The collecting capacity of the filter  46 , i.e. volume of the brake dust  49  the filter  46  can collect, e.g. in the filter bag or the collecting unit of the filter cyclone, should be at least as large as the volume of the brake pads  43  of the brake calliper  42 . Preferably, the filter bag of the filter  46  will be replaced or the filter cyclone of the filter  46  will be emptied if the brake pads  43  are replaced. Alternatively, the brake dust  49  will be sucked out of the filter  46  by a vacuum cleaner. This can be done in one maintenance session. 
         [0056]    As alternative, the cooling arrangement with fans can be an “open” system in which the cooling air flow is drawn by from the outside of the wind turbine via filters and dehumidifiers into the generator. The cooling air will be warmed up by the generator and then be drawn by fans to the outside of the wind turbine. 
         [0057]    Although the present invention has been described in detail with reference to the preferred embodiment, it is to be understood that the present invention is not limited by the disclosed examples, and that numerous additional modifications and variations could be made thereto by a person skilled in the art without departing from the scope of the invention. 
         [0058]    It should be noted that the use of “a” or “an” throughout this application does not exclude a plurality, and “comprising” does not exclude other steps or elements. Also elements described in association with different embodiments may be combined. It should also be noted that reference signs in the claims should not be construed as limiting the scope of the claims.