Abstract:
A wind generator includes: a nacelle; a hub carried by the nacelle and including at least a pair of wind turbine blades; and an electricity producing generator including a stator and a rotor carried by the nacelle. The rotor is connected to the hub and rotatable in response to wind acting on the blades to rotate the rotor relative to the stator to generate electricity. A cooling system is carried by the nacelle and includes at least one ambient air inlet port opening through a surface of the nacelle downstream of the hub and blades, and a duct for flowing air from the inlet port in a generally upstream direction toward the hub and in cooling relation to the stator.

Description:
This invention was made with Government support under Subcontract ZAM-4-31235-05 awarded by NREL and under Prime contract DE-AC36-99-G010337 awarded by U.S. Department of Energy. The government has certain rights in the invention. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to wind assisted cooling for wind turbine generators and particularly relates to a cooling system which utilizes flow induced pressure and suction to receive cooling air from the ambient environment and routes the cooling air to the wind generator parts susceptible to thermal related degradation. 
     Wind turbine generators typically stand on pylons hundreds of feet in the air. The generators include a hub mounting two or typically three airfoil blades which drive the generator. Within the nacelle mounting the hub, a rotor is rotated by the airfoil blades and hub. Rotation of the rotor either through a direct drive system or a gearbox causes relative rotation between magnetic poles and coils to generate electricity. In the direct drive generator, the rotor rotates at the same speed as the blades rotate and consequently a large radius is required to obtain the tangential velocity required to produce electricity. A gearbox of course, increases the rotational speed to a high value, e.g., 1000 RPM which itself causes problems. 
     As with any generator, heat is generated and it is necessary to cool the various parts of the generator. The cooling of a wind generator must be done efficiently to minimize losses and it will be appreciated that space restrictions prevent the use of elaborate cooling pipes, blowers, filters, heat exchangers and the like to facilitate cooling. Traditional generator cooling apparatus has been bulky, expensive and difficult to maintain. Because of the nature of wind turbine generators and the need to locate the generators hundreds of feet above ground while at the same time providing cooling for the generator, there is an established need to provide an improved cooling system for wind turbine generators e.g., to utilize wind flow around the nacelle to assist airflow ingestion into and exhaustion of heated air from the nacelle for purposes of cooling the generator. 
     BRIEF DESCRIPTION OF THE INVENTION 
     In one exemplary but non-limiting embodiment of the invention, there is provided a wind generator comprising a nacelle; a hub rotatably carried by the nacelle and including at least a pair of wind turbine blades; an electricity producing generator including a stator and a rotor, the rotor being connected to the hub and rotatable in response to wind acting on the blades to rotate the rotor relative to the stator to generate electricity; and a cooling system carried by the nacelle including at least one ambient air inlet port opening through a surface of the nacelle downstream of the hub and blades, and a duct for flowing air from the inlet port in a generally upstream direction toward the hub and in cooling relation to the stator. 
     In another exemplary but non-limiting embodiment, there is provided a method of cooling the stator of a wind turbine generator having a nacelle carrying the stator and a rotor connected to a hub mounting wind turbine blades, comprising the steps of (a) suctioning ambient cooling air through a forward-facing inlet port along a surface of the hub or nacelle; (b) flowing the cooling air through the generator stator to cool the stator; and (c) exhausting the cooling air from the stator at a location downstream of the hub and blades. 
     In a further exemplary but non-limiting embodiment, the inlet port is in the nacelle at a location downstream of the hub and blades. 
     The invention will now be described in detail in connection with the drawings identified below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic representation of a wind assisted cooling system for a wind turbine generator; 
         FIG. 2  is a perspective view illustrating portions of the cooling system for the wind turbine generator; 
         FIG. 3  is an enlarged fragmentary cross-sectional view of a portion of the stator and rotary components of the generator illustrating a portion of the cooling circuit; 
         FIG. 4  is an enlarged endwise schematic representation of the double-sided generator employed in the cooling system hereof; 
         FIG. 5  is a fragmentary perspective view illustrating the various components of the wind assisted cooling system for the wind turbine generator hereof; 
         FIG. 6  is a schematic representation of a further exemplary embodiment of a wind assisted cooling system for a wind turbine generator; 
         FIG. 7  is a partial perspective view of a hub and nacelle with cooling air inlet configuration in accordance with another exemplary embodiment; 
         FIG. 8  is a perspective view of a cooling air inlet arrangement in the hub in accordance with still another exemplary embodiment; 
         FIG. 9  is a fragmentary cross-section of the hub shown in  FIG. 8 ; and 
         FIG. 10  is a partial perspective view of a cooling air inlet in a hub in accordance with yet another embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIG. 1 , there is schematically illustrated a wind turbine generator, generally designated  10 , and including a rotating hub  12  mounting two or more airfoil shaped blades  14 , a fixed nacelle  16  and a pylon  18  for structurally supporting the wind turbine generator hundreds of feet above ground level G. 
     Referring to  FIGS. 3-5 , the nacelle  16  mounts a plurality of coils, or windings  22  forming part of the stator and a plurality of magnets or poles  24  about the rotor adjacent a forward part of the rotor near the hub  12 . The illustrated present embodiment includes a double-sided generator having, as part of the stator, inner stator coils  22  and outer stator coils  26  and, as part of the rotor, outer magnets or poles  24  and inner magnets or poles  28 . Thus the wind driven blades  14  drive the hub  12  which, in turn, rotates the outer and inner magnets  24  and  28  relative to the outer and inner stator coils  26  and  22  to generate electricity. It will be appreciated that the inner and outer stator coils  22  and  26  respectively constitute generally elliptically or oval shaped coils spaced circumferentially one from the other about the generator stator. The stator coils are also mounted on a yolk  30  fixed to the nacelle  16 . It will be appreciated from a review of  FIGS. 3 and 4 , that there are gaps  32  between the individual coils in both the inner and outer coils  22 ,  26 . There are also axial gaps  34  between the outer portion of the rotor and the outer coils  26  as well as between the inner portion of the rotor  40  of the inner coils  22 , which provide flow paths for flowing a cooling fluid, in this instance air. 
     Referring to  FIGS. 1-3 , the cooling system includes a plurality of air intakes  44 , three being shown in  FIG. 2 . The intakes  44  constitute pipes for transmitting air received in an inlet  46  ( FIG. 1 ) opening along the surface of the nacelle  16 . Thus, three inlets  46  are circumferentially spaced one from the other about the nacelle, for example about 120 degrees apart for receiving air passing over the nacelle  16 . Because of the shape of the nacelle  16  and the aerodynamic boundary layer flow along the surface of the nacelle, the inlets suction a part of the boundary layer flow forward of the inlets for transmission along the pipes  44  to an inlet manifold  50  ( FIG. 3 ). Manifold  50  comprises an annulus of similar diameter as the stator coils and is spaced behind the inner and outer stator coils  22  and  26 . The manifold  50  may be continuous or segregated into compartments of equal circumferential lengths for providing cooling air to an associated segment of the stator coils axially forwardly of the inlet manifold  50 . Since the flow of inlet air per se is not sufficient to maintain the generator in a cooled condition, the inlet air flow is augmented by blowers  52  ( FIG. 2 ) disposed in the pipes  44  in advance of the inlet manifold  50 . Various filters  54  are also placed in the inlet pipes  44 . 
     On the axially forward side of the generator, there are provided a plurality of circumferentially spaced outlets  55  each including an exhaust pipe  56  and an exhaust collar, collectively called an exhaust can  58 . An annular generally C-shaped channel  60  overlies the exhaust can  58  on the outlet side of the cans  58 . The base of the channel  60  is spaced from and overlies the exhaust outlets of the exhaust pipe  56 . Channel  60  also has free side edges spaced axially from the forward face of the rotating component providing generally radially extending heated cooling air exhaust passages  59 . Thus the heated cooling air exits the exhaust pipe  56  and turns 180 degrees for flow axially back towards the stator and then turns 90 degrees for radial egress into the atmosphere. Consequently, the exhaust flow of cooling air is essentially annular about the surface of nacelle. 
     It will be appreciated that the cooling system illustrated in  FIGS. 1-5  may be characterized as a front exit system. Such system has various advantages. For example, the components of the system are enclosed within the nacelle and are thus protected from outside elements. The generator elements, e.g., the rotor coils  22 ,  26  can be easily replaced. The C-shaped channel also not only protects the individual exhaust pipes and collars but diverts the exiting flow back towards the nacelle. An annular flow director  58  is illustrated in  FIG. 1  to facilitate airflow over the step in the rotor between the hub and the magnetic poles. Thus the air exiting the C-shaped channel is essentially sucked from the channel to join the boundary layer flow along the outer surface of the nacelle. 
     Referring to the embodiment illustrated in  FIG. 6 , there is disclosed a rear exit cooling system for a wind turbine. In this configuration, cooling air enters through entry ports  68  along the front face of the annular compartment  70  housing the stator coils to cool the stator coils substantially by air flow in the reverse direction than the direction of air flow in the previous embodiment. The heated air from the cooling flow about the stator coils  22 ,  26  constitutes a rear exit approach using the pressure head due to the wind at the entry ports  68 . In this embodiment, one or more of a blower, internal vented laminations and an encased external fan may be used to assist the cooling air flow. For example, blowers  72  may augment the passage of air from the front entry ports to the rear exit port  75 . 
     Variations of the above described cooling inlet configurations are disclosed in  FIGS. 7-10 . In  FIG. 7 , blade root and nacelle ducts are employed to ingest wind air for nacelle and hub cooling. More specifically, the blade roots  74 , where the blades are attached to the hub  76 , are each provided with a duct  78  (one shown) with an inlet opening  80  facing forward (upstream of the nacelle  82 ). The duct  78  feeds ingested wind air into a hub duct  84  that, in turn feeds cooling air to the annular manifold or plenum  70  as described in connection with  FIG. 6 . 
     Additional cooling wind air may be ingested via nacelle scoops  86  that also open in a forward direction. The number of scoops  86  may be varied about the periphery of the nacelle, but with preferably in a symmetrical array. The array in  FIG. 7  includes four such scoops (three shown). Scoops  86  feed the cooling air through cooling air intake holes  88  in the nacelle wall to join the cooling air entering the blade root ducts flowing to the manifold or plenum  70 . 
       FIGS. 8 and 9  illustrate a hub  90  formed with three hub ducts  92  (two shown), located circumferentially between the blade roots  93 . Each hub duct has a forwardly facing inlet opening  94 . Each duct maybe provided with a filter  96  at the inlet opening, as well as a plurality of internal baffles  98  arranged to form a serpentine flow path for the cooling air. The ninety degree bends in the flow path helps remove moisture from the air prior to entering the annular chamber  70 . After passing through the generator, the cooling air will exit the nacelle  100  via rear exit vents  102  (one shown in phantom). 
       FIG. 10  illustrates a hub  104  provided with a single forwardly-facing air intake  106  in the center of the hub. The cooling air flows through internal openings  108  between the blade root holes  110  and into the nacelle and the annular chamber  70 . 
     While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.