Abstract:
A generator for a power plant and a method for cooling the generator, where the generator includes a stator and a rotor, the stator carrying conductors. The conductors for a winding overhang at least at one end of the stator and the generator has a fan for cooling the winding overhang. The fan produces a cooling air flow directed onto the winding overhang and has an axial component and a radial component.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is the US National Stage of International Application No. PCT/EP2015/069606 filed Aug. 27, 2015, and claims the benefit thereof. The International Application claims the benefit of European Application No. EP14183928 filed Sep. 8, 2014. All of the applications are incorporated by reference herein in their entirety. 
     
    
     FIELD OF INVENTION 
       [0002]    The present invention relates to a generator for a power plant, and to a method for cooling the generator. 
       BACKGROUND OF INVENTION 
       [0003]    In turbo generators, the individual bars of the stator are connected by means of a so-called end winding. In the end winding, the bars are guided in both the tangential and the radial directions such that at the end of the end winding the bars that are to be connected lie next to one another. These bars must be electrically connected to one another, it being possible to effect the connection in various ways. One option is to connect the individual subconductors of one bar to the subconductors of a second bar, which is termed subconductor interconnection. Another option is to gather the subconductors of one bar into bundles, and to connect these bundles to the respective bundles of the opposite bar, which is termed bundle connection. A third variant involves fully soldering the subconductors of one bar to one another, and effecting the connection to the opposite bar in solid fashion using a bracket. All connection types share the fact that the connections must be established manually and insulation must be applied thereafter. The use of brackets gives rise to additional resistance losses, which lead to heating of the end winding. The increased temperatures further increase the electrical resistance and thus further reduce the efficiency of the generator. 
         [0004]    In many turbo generators, the bracket connection at the end winding is the performance-limiting component. This limiting effect is due to the brackets heating up because of the electrical resistance. 
         [0005]    Hitherto, the bracket connection was effected with a minimum insulation thickness in order to provide good indirect external cooling. However, thin insulation is possible only in the case of adjacent brackets with a low voltage difference. At phase transition points, thick insulation is applied. 
         [0006]    In addition, the stator end winding, inter alia, is cooled by a ventilator on the rotor. In that context, the ventilator blades are arranged radially with respect to a central axis of the rotor and generate an axial air stream which cools the stator end winding among other things. 
         [0007]    EP 0 643 465 A1 describes an air-cooled rotating electrical machine. JP S53 115304 U describes a machine having an end winding. JP S58 145066 U describes a machine having an end winding. 
       SUMMARY OF INVENTION 
       [0008]    The invention has an objective of providing a generator having improved cooling and higher efficiency associated therewith. 
         [0009]    The generator according to the invention has the advantage, over the generators known from the prior art, that the fan generates a cooling air stream which reduces the thermal load on the bracket connections or on the stator end winding, in that the heat is removed more efficiently by means of a cooling air stream with a radial and an axial component. By virtue of the improved cooling of the end winding, generators of the same size can be more efficient and/or more powerful. 
         [0010]    Advantageous refinements of and improvements to the generator indicated in the independent claim are made possible by the measures set out in the dependent claims. 
         [0011]    According to the invention, the fan has a first region, which generates a cooling air stream oriented axially with respect to a central axis of the rotor, and has a second region, which generates a cooling air stream oriented radially or diagonally with respect to the central axis of the rotor. By virtue of this solution, the cooling air stream in the axial direction is retained and is complemented by an additional cooling air stream in the radial and/or diagonal direction, thus making it possible to achieve an optimized flow onto the end winding and an associated improved removal of heat. 
         [0012]    In that context, it is particularly advantageous if the first region is designed concentrically about the central axis of the rotor, and the second region encloses the first region at least in certain sections, advantageously concentrically. By virtue of this solution, it is possible to achieve broader subdivision of the cooling air stream without additional guide vanes, thus enabling a structurally simple and cost-effective embodiment of the generator. 
         [0013]    One embodiment variant has a fan with at least one fan blade, wherein this fan blade has a first section which runs radially with respect to a central axis of the rotor, and has a second section which runs at an angle of 10° to 90° with respect to the central axis of the rotor. A fan blade of this type generates, in its first section, an axial cooling air stream and, in its second section, a cooling air stream which is formed radially or diagonally with respect to the axial cooling air stream. It is particularly expedient if the second section is formed at an angle of 30° to 75° with respect to the central axis of the rotor, since in this manner the second region generates an expedient cooling air stream running diagonally with respect to the central axis. 
         [0014]    In that context, it is especially advantageous if the second section adjoins, in the radial direction from the central axis of the rotor, the outside of the first section of the fan blade. Thus, the first region generates an essentially axial cooling air stream on the inside, while the second region generates a diagonal cooling air stream. It is thus possible, using one fan or one fan blade, to generate a cooling air stream with a radial and/or diagonal component and an axial component. 
         [0015]    One advantageous refinement is that the fan blade is of L-shaped design. This produces a radially oriented cooling air flow at that end of the fan blade that is remote from the central axis, while an axial flow is formed at that end of the cooling air blade which is oriented toward the central axis. 
         [0016]    One advantageous refinement is that the fan blade tapers in the direction from the central axis of the rotor to its end region oriented away from the rotor. This makes it possible to keep the moved masses low and to save material on the fan blade. 
         [0017]    Alternatively, there is provided an embodiment in which the fan has a first impeller for generating an air stream axially with respect to a central axis of the rotor, and a second impeller for generating an air stream radially or diagonally with respect to the central axis of the rotor. A fan having an axial ventilator and a radial ventilator also makes it possible, in a simple and cost-effective manner, to generate a cooling air stream which, in addition to an axial component, also has a radial and/or diagonal component. 
         [0018]    In that context, it is particularly advantageous if the second impeller is of annular design, wherein the first impeller and the second impeller are arranged concentrically with respect to one another. This makes it possible to achieve simple positioning and securing of the impellers with respect to one another, wherein the first impeller is arranged inside the annular second impeller. 
         [0019]    In that context, it is particularly advantageous if there is formed, on the fan, a ring which outwardly bounds the first, inner impeller and inwardly bounds the second impeller. It is thus possible for the first impeller and the second impeller to be easily mounted in a common housing or prefabricated as a subassembly, which reduces installation expenditure. 
         [0020]    In this application, the terms radial and diagonal are to be understood not only as angles of 90° or, respectively, 45° with respect to the central axis of the rotor, but as an angular range from 5° to approximately 100°, and serve to delimit a flow axially with respect to the central axis of the rotor, which is formed essentially at an angle of approximately 0°, that is to say parallel to the central axis. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]    An exemplary embodiment of the generator according to the invention will be explained below with reference to the appended drawings. In that context, identical components or components having identical functions are labeled with identical reference signs. 
           [0022]      FIG. 1  shows a section through a generator according to the invention. 
           [0023]      FIG. 2  shows a detail from the generator, illustrating a rotor with a fan blade and a baffle. 
           [0024]      FIG. 3  shows a fan blade of a generator according to the invention. 
           [0025]      FIG. 4  is a 3-D view of the drive shaft of the rotor with fan blades according to the invention. 
           [0026]      FIG. 5  is a front view of a combined radial/axial ventilator of a generator according to the invention. 
           [0027]      FIG. 6  is a side view of the combined radial/axial ventilator. 
       
    
    
     DETAILED DESCRIPTION OF INVENTION 
       [0028]      FIG. 1  shows a generator  10  for a power plant. The generator has a stator  20  in which there is arranged a rotor  30 . The rotor  30  has a drive shaft  31  which is rotatably mounted at two bearings  35 ,  36 . A central axis  32  runs through the drive shaft  31  of the rotor  30 . The stator  20  is shielded on both sides by dividers  25 . The stator  20  has a stator body  21  from which current conductors  22  exit at the ends  27  and form an end winding  24 . In order to connect the current conductors  22 , brackets  23  are provided at the ends and connect two adjacent current conductors  22  to one another in the end winding  24 . 
         [0029]    A fan  40  is attached to the rotor  30  and has, in the simple embodiment shown, fan blades  45  which are attached to the drive shaft  31  of the rotor, as shown in  FIG. 2 . The fan blades  45  are distributed evenly over the circumference of the drive shaft  31  and run in a plane with the divider  25  which laterally bounds the stator  20  and separates a suction side  28  of the fan  40  from a pressure side  29  of the fan  40 . The fan blade  45  has a blade root  52  which can be secured in a slot  51  of the drive shaft  31 . To that end, a clamping element  53  is provided on the drive shaft  31  and can be secured to the drive shaft  31  by means of a screw  54 , and thus securely fixes the blade root  52  of the fan blade  45 . The fan blade  45  has a first region  42  which runs radially or perpendicular with respect to the central axis  32  of the rotor  30  or of the drive shaft  31 . The first region  42  is designed to generate a cooling air flow which runs axially with respect to the central axis  32  of the rotor  30 . Adjoining this in the radially outward direction is a second region  44  which concentrically encloses the first region  42 . The second region  44  is designed to create a cooling air flow at an angle of 5° to approximately 100° with respect to the central axis of the rotor, which flow is hereinafter termed radial or diagonal cooling air flow. 
         [0030]      FIG. 3  shows the fan blade  45 . The fan blade  45  has a first section  47  which runs radially with respect to the central axis  32  of the rotor  30 , a second section  48  adjoining this in the radially outward direction and running at an angle α of approximately 30° with respect to the central axis  32  of the rotor  30 . Alternatively, other angles a between approximately 5° and approximately 85°, advantageously between 30° and 60°, are also conceivable. As the drive shaft  31  of the rotor  30  rotates, the first section  47  generates the first, axially oriented region  42  of the cooling air flow, while the second section  48  of the fan blade  45  generates the second, diagonal or radial region  44  of the cooling air flow. 
         [0031]    The fan blade  45  has, at an end  49  oriented away from the drive spindle  31 , a taper  46  in order to reduce pressure fluctuations at the end  49  of the fan blade  45 , and in order to concentrate the moved masses as close as possible to the rotor  31 .  FIG. 4  again shows the combination of drive shaft and fan, in a perspective view. 
         [0032]      FIG. 5  shows an alternative embodiment of the fan  40 . A first impeller  50  is arranged on the drive shaft  31  of the rotor  30  in order to generate a cooling air stream in the axial direction, parallel to the central axis  32  of the rotor  30 . The first impeller  50  is outwardly bounded by a ring  70 , the ring  70  simultaneously forming an outer diameter of the first impeller  50  and an inner diameter of a second impeller  60 , which is formed in annular fashion around the first impeller  50  and establishes a cooling air stream radially or diagonally with respect to the central axis  32  of the rotor  30 . In so doing, the ring  70  separates the axial cooling air stream of the first impeller  50 , which is designed as an axial ventilator, from the cooling air stream of the second impeller  60 , which is designed as a radial ventilator.  FIG. 6  additionally shows the ventilator from  FIG. 5  in a side view. 
         [0033]    When the generator  10  is in operation, the drive shaft  31  of the rotor  30  rotates. In the process, air is drawn in by the fan  40  on the suction side  28  of the divider  25  and is delivered to the pressure side  29 . In that context, the air flow is indicated by the small arrows in  FIG. 1 . The air flows in the axial direction through openings in the end  27  of the stator  20  into the generator  10  or between the drive shaft  31  of the rotor  30  and the stator body  21 , and flows back again on the outer side of the stator  20 . The solution according to the invention achieves a markedly better, direct flow of cooling air onto the end windings  24 , and therefore realizes better cooling of the end winding  24 . 
         [0034]    In the case of a closed cooling system, another coolant can also be used instead of air.