Abstract:
The invention relates to a method for conducting service on a wind turbine after the wind turbine is erected and after the hub ( 1 ) of the wind turbine is mounted on the main shaft ( 3 ) of the wind turbine. The method comprises mounting of servicing equipment a crane ( 8 ) on the hub ( 1 ) of the wind turbine and lowering and hoisting wind turbine appliances from and to the hub. Thereby, it is possible to lower from and to lift to the hub, the appliances which is to be replaced or repaired without using the hatch constituting the escape way and without having to transfer the appliances through the nacelle and along the tower. The invention also relates to means ( 5, 6 ) for primarily securing the equipment to the hub of the wind turbine.

Description:
FIELD OF THE INVENTION 
     The invention relates to a method for conducting service on a wind turbine after the wind turbine is erected and after the hub of the wind turbine is mounted on the main shaft of the wind turbine. The invention also relates to equipment for conducting such service and furthermore the invention relates to a connecting piece and a crane constituting part of the equipment. Finally, the invention relates to a wind turbine, to a hub and to uses of a hub. 
     BACKGROUND OF THE INVENTION 
     Although much of the appliances installed in a wind turbine is intended for lasting a very long time, some of the appliances must be replaced or must be repaired during the service life of the wind turbine. Equipment installed in the nacelle or in the tower of the wind turbine may be removed from or lifted to the nacelle by means of cranes or other lifting means provided on or in connection with the nacelle. The tower and the machine frame of the nacelle are solid structures where even large cranes may be secured to and where even heavy appliances may be lowered from or lifted to without any difficulties. However, appliances installed in the hub, in connection with the wings or in connection with the hub may be more difficult to access and to handle for possible removal in order for the appliances to be replaced or be repaired at a more suited location than the service location of the appliances. Often, a hatch is provided in the top of the nacelle housing, enabling access from or to the outside of the hub and from or to the nacelle and further down or up through the tower. This manner, in which appliances at the more remote locations mentioned is handled, is a secure manner, but also quite time-consuming. Also, during handling through the hatch of the nacelle housing, the escape way from the remote locations is blocked, endangering the working conditions at these remote locations. 
     SUMMARY OF THE INVENTION 
     It may be an object of the present invention to provide a method and equipment to be used by the method, and which does not posses the above-mentioned disadvantages. 
     This object is obtained by a method comprising mounting of servicing equipment on the hub of the wind turbine and lowering and hoisting wind turbine appliances from and to the hub. Thereby, it is possible to lower from and to lift to the hub, the appliances which is to be replaced or repaired without using the hatch constituting the escape way and without having to transfer the appliances through the nacelle and along the tower. 
     In a preferred embodiment the servicing equipment is mounted to the outside surface of the hub, and where the equipment to be lowered from and hoisted to the hub is lowered and hoisted to the hub at a front of the hub. Even more preferred, the servicing equipment is mounted by means of already available holes, said holes formerly used for hoisting the hub to the main shaft of the wind turbine. In a preferred embodiment, a connecting piece, preferably a collar of a connecting piece is provided with means for releasing adherence by the cement-like structure of the connecting piece to the hub. 
     By securing the servicing equipment to the surface of the hub and by furthermore utilising already available holes, it is very easy and fast to erect the servicing equipment and possible to lower or to hoist any equipment from the hub, the blades or the spinner without having to access the interior of the hub, i.e. all the already limited space inside the hub will not be occupied by the servicing equipment according to the invention. 
     Accordingly, the object of the invention is also obtained by equipment being provided with means for primarily securing the equipment to the hub opposite from securing the equipment to the nacelle or other parts, different from the hub, of the wind turbine. 
     The previously mentioned advantages, which are obtained by the method according to the invention, are fulfilled by means of the equipment according to the invention. Securing the equipment primarily to the hub avoids obstructing the hatch in the top of the nacelle, and makes it possible easily to handle appliances to and from the hub, the blades and the hub. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the following the wind turbine will be described with reference to the drawing, where 
         FIG. 1  is a plane view of equipment according to the invention mounted onto the hub of a wind turbine, 
         FIG. 2  is a perspective view of a hub for a wind turbine and with coupling elements mounted on the hub, 
         FIG. 3  is one plane view of a hub for a wind turbine and with one coupling element mounted on the hub, 
         FIG. 4  is another plane view of a hub for a wind turbine and with one coupling element mounted on the hub, 
         FIG. 5  is a perspective view of part of a hub for a wind turbine and with one coupling element mounted on the hub, 
         FIG. 6  is a perspective view of a cross section of a hub for a wind turbine and with a cross section of one coupling element mounted on the hub, 
         FIG. 7  is a perspective view of part of equipment according to the invention to be mounted on a hub of a wind turbine, 
         FIG. 8  is one plane view of the part of equipment according to the invention to be mounted on a hub of a wind turbine, 
         FIG. 9  is another plane view of the part of equipment according to the invention to be mounted on a hub of a wind turbine, and 
         FIG. 10  is a third plane view of the part of equipment according to the invention to be mounted on a hub of a wind turbine. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows how equipment to be used, when conducting service on the wind turbine, is placed, when the equipment is mounted on a hub  1 . The hub  1  is mounted to the main shaft  2  of the wind turbine, and the main shaft  2  extends from the nacelle  3  of the wind turbine. The hub  1  is provided with an outer cap called the spinner  4 , which, for the sake of clarity, in the figure is partly cut away in order to show the mounting of the equipment on the hub. 
     The equipment comprises different main parts. Primarily, a first connecting piece  5  and a second connecting piece  6  is secured to the surface  7  of the hub  1 . The remaining parts of the equipment are secured to the connecting pieces so that all of the equipment via the two coupling elements is secured to the hub. The remaining parts of the equipment comprise a crane  8 , a gangway  9  with guard rails  10 , a ladder  11  leading from the nacelle  3  to the gangway  9  and a curb  12  mounted foremost on the hub  1  end being suspended from the crane  8 . The crane  8  is secured to the first connecting piece  5  such that an entirety of the crane  8  is positioned upwardly and/or outwardly relative to hub  1 , and the gangway  9  is secured to the crane  8  and to the second connecting piece  6 . 
     In the embodiment shown, the crane  8  is hoisting a hydraulic actuator  13  up to the hub  1  for replacement or for re-installation after formerly having been hoisted down for repair. Such hydraulic actuator  13  may weigh up to 250 kg. The entire torque from the equipment on the first connecting piece  5  must be absorbed by the securing of the first connecting piece  5  to the surface  7  of the hub  1 . This sets extremely high demands to the securing of the first connecting piece  5  to the hub  1 . That is why persons skilled in the art have come to the conclusions that it is not possible. 
       FIG. 2  is a perspective view of the first connecting piece  5  and the second connecting piece  6 , when secured to the surface  7  of the hub  1 . The first connecting piece  5  consists of a substantially cylindrical element, and the second connecting piece  6  consists of a plate-like element. In the embodiments shown, both the first connecting piece  5  and the second connecting piece  6  are secured to the surface  7  of the hub  1  in already existing and available mounting holes (not shown). The already existing and available holes are holes, which formerly have been used during erection and assembly of the wind turbine, when hoisting, by means of a mobile crane or raft-mounted crane, the hub from the ground to the main shaft and maintaining the hub in place during bolting of the hub to the main shaft. Thus, the holes for securing the first connecting piece and the second connecting piece to the surface of the hub are not initially provided for that purpose. 
       FIG. 3  and  FIG. 4  are plane drawings,  FIG. 5  is a perspective plane view and  FIG. 6  is a perspective cross sectional view, all showing the first connecting piece  5 , when being secured to the surface  7  of the hub  1 . As can be seen, the surface  7  of the hub  1  is curved in the plane of the figure. Thus, the first connecting piece  5  must be able to adapt to the curvature of the surface  7  of the hub  1  in order to obtain a proper securing of the first connecting piece  5  to the hub. Only by achieving a proper securing will the first connecting piece  5  be able to hold the crane  8 , even when the crane is lifting heavy appliances to the hub such as hydraulic actuators to be mounted inside the hub. 
     The first connecting piece  5  is provided with means for passing five bolts  14  through the connecting piece  5  from a top of the connecting piece  5  and to the threaded holes  15  already provided and available in the surface  7  of the hub  1 . The bolts  14  extend through guiding liners  16  inside the first connecting piece  5 , the guiding liners  16  extending from an upper internal disc-like structure  17  to a lower disc-like structure  18  and through the lower disc-like structure  18  into a bottom cavity  19  of the first connecting piece  5 . The bottom cavity  19  is delimited by the lower disc-like structure  18  and by a lower flange  20  of the first connecting piece  5 . 
     The bottom cavity  19  is intended for taking up of a cement-like substance (not shown) creating a physical connection between an under-side  21  of the lower disc-like structure  18  and the surface  7  of the hub  1 . The cement-like substance is intended for creating a completely homogeneous connection between the surface  7  of the hub  1  and the first connecting piece  5 . Because the surface  7  of the hub  1  is not worked more than absolutely necessary, when being manufactured, the surface  7  of the hub  1  is somewhat rough. If perhaps the first connecting piece had a concave surface being made of metal like the connecting piece itself and being congruent with the convex surface of the hub, the abutment between the concave surface of the first connecting piece and the convex surface of the hub would not be homogeneous, because of the rough surface of the hub. 
     However, introducing a cement-like substance into the cavity  19  made in the very bottom of the first connecting piece  5 , the cement-like substance will fill out any unevenness of the rough surface  7  of the hub  1  and will also fill out the entire cavity  19  in the bottom of the first connecting piece  5 . Thus, a complete congruent and homogenous abutment will be established between the underside  21  of the lower disc-like structure  18  and the surface  7  of the hub  1 . This complete congruent and homogenous abutment is necessary in order for the first connecting piece to be able to carry the loads lowered or hoisted by the crane, without the risk of the crane tilting and breaking loose from the surface of the hub together with the first connecting piece. Preferred cement-like substances are substances from the Danish company Densit A/S, said substances being very hard and durable, although being workable when yet not cured. 
     Fitting of the first connecting piece  5  to the surface  7  of the hub  1  takes place by initially inserting a threaded end of the bolts  14  into the already available holes  15  in the surface  7  of the hub  1 . The holes  15 , as mentioned, are previously being made, when manufacturing the hub, and is, until now, only intended for hoisting, by means of a large crane, the hub from the ground to the mounting flange of the main shaft. 
     Subsequently to the insertion of the bolts  14  into the already available holes  15 , the bolts  14  are fastened or nuts  22 , as shown, at threaded other ends of the bolts  14  are fitted and fastened. Because the number of bolts  14  are limited to the number of already available holes  15 , and because the holes  15 , and thus the bolts  14 , are situated quite close, the bolts  14  or the nuts  22  must be fastened quite much in order for the crane  8  to be able to hoist the sometimes heavy appliances to the hub  1 . Eventually, the bolts  14  or nuts  22  are fastened up to 50% of the yield point of the bolts. Depending on the size of the already available holes  15 , the bolts  14  may have different sizes, however a typical size being M30 bolts, i.e. having a diameter of 30 mm. 
     Alternatively to providing a congruent and homogeneous abutment between the often rather rough surface of the hub and the first connecting piece, the surface of the hub, onto which the first connecting piece is to be mounted, may be worked so that a smoother surface is established. This may establish the possibility of a bottom surface of the first connecting piece being a machined surface, being concave and being the abutment surface towards the surface of the hub in stead of a cement-like substance. 
     A flange  23  on the outer circumference of the first connecting piece  5  is provided with threaded holes  24  for securing by bolts (not shown) of the crane  8  to the first connecting piece  5 . Therefore, a corresponding flange is provided on the crane (see  FIG. 7 ). 
     The bottom flange  20  assisting in the establishment of the cavity  19  for the cement-like substance is provided with small bolts  25  extending through threaded holes (not shown) in the bottom flange  20 . Because the bottom flange  20  is inclined an angle α, as shown, the bolts  25  are also inclined as shown, i.e. with the end of the blots extending into the cavity  19  and directed towards the bottom of the first connecting piece and towards the surface  7  of the hub  1 . 
     The bolts  25  are not intended for further securing of the first connecting piece  5  to the surface  7  of the hub  1 . The bolts  25  are intended for being tightened and thus being urged into the cavity  19 . Because the end of the bolts extending into the cavity are inclined towards the bottom of the first connecting piece and towards the surface  7  of the hub  1 , then, when tightening the bolts, the end of the bolts at one time during the tightening will meet the surface  7  of the hub  1 . Further tightening of the bolts  25  will cause the first connecting piece  5  to raise itself from the surface  7  of the hub  1  and free the first connecting piece  5  from the hub  1 , if the bolts  14  initially are loosened. This technique is used, when the first connecting piece  5  has been used for supporting the crane  8  and no longer is to be used, but has to be freed from the surface  7  of the hub  1  so that the wind turbine can come into operation again. 
       FIG. 7  is a perspective view and  FIG. 8 ,  FIG. 9  and  FIG. 10  are plane views of a crane  8  according to the invention. The crane  8  has a mast  30  and a jib  31 , the jib  31  being connected to the mast  30  by a hinged connection  32 . The mast  30  has a flange  33  intended for being secured to the flange  23  of the first connecting piece  5 . A plurality of bolts  34  is provided for securing the crane  8  to the first connecting piece  5 . 
     Above the flange  33  along the mast  30 , four studs  35  extend outwards from the mast  30  on opposite sides of the mast  30 . The studs  35  are intended for carrying the front-most part of the gangway (see  FIG. 1 ). Preferably, the studs  35  are made of a material lighter than steel such as an aluminium alloy in order to reduce the overall weight of the crane  8 . A preferred alloy is Alumec from Uddeholm Tooling having a module of elasticity being about ⅓ that of steel, but has rigidity being about the same as for steel. The studs  35  are mounted in bushings  36  provided in the mast  30 . Thus, in the embodiment shown, the studs  35  consist of four studs in total extending trough the bushings  36  in the mast  30  and projecting on each side of the mast  30 . 
     An upper link  37  and a lower link  38  are provided between the mast  30  and the hinged connection  32 . Thus, the hinged connection  32  is provided at an outmost end of the links  37 , 38 . The links  37 .  38  are made from a material being very light in order to reduce the overall weight of the crane  8 . The links  37 , 38  have a shape, resulting in the links  37 . 38  converging from a greater dimension at the mast  30  of the crane  8  to a smaller dimension at the hinged connection  32 . In a preferred embodiment, the links are also made of a material being lighter than steel such as an aluminium alloy, preferably Alumec from Uddeholm Tooling having, as mentioned, a module of elasticity being about ⅓ that of steel, but having rigidity being equal to that of steel. Thus, the strength of the links is not compromised. 
     The jib  31  is made of a material being rigid enough to carry the load to be hoisted, but still being as light-weighted as possible in order to reduce the overall weight of the crane  8  and especially the weight contributing much to the torque applied to the first connecting piece. In a preferred embodiment the jib  31  is made of Alumec from Uddeholm Tooling. Between the lower link  38  and the jib  31  a hydraulic actuator  39  is provided. The hydraulic actuator  39  is intended for swivelling the jib  31  around the hinged connection  32  in relation to the links  37 , 38  and in relation to the mast  30  and the hub  1 , onto which the crane  8  is mounted. 
     From an upper part of the hinged connection  32  and obliquely downward to an out-most end, although not outer-most end, of the jib  31 , a brace  40  is inserted. The jib  31  is a so-called IPE-profile, and the lowering and hoisting means consists of a trolley  41  with a wire  42 . The trolley  41  preferably has a set of two or more wheels  43  on each side of the jib  31 . Thereby, the trolley  41  has the advantage of distributing the load along the length of the jib  31 . Thereby, the jib  31  may be made using as little material as possible in relation to the weight to be lowered and hoisted by the wire  42  and thus in consideration of the total weight of the jib  31  and the crane  8 . In the embodiment shown, the outer-most point of the jib is situated in a distance from the crane mast centre of about 2.5 m.