Abstract:
A wedge for use in a generator rotor includes a wedge body having a generally triangular shape with flat surfaces, and such that when the wedge is placed in a generator rotor, the flat surfaces will define circumferential extents of the wedge body relative to a rotational axis of the rotor, and said flat surfaces extending to a radially outermost extent of the wedge body. A wedge and winding combination, a generator rotor, a generator and a method all using the wedges are disclosed and claimed.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    This application relates to a generator wedge for use in a generator rotor. 
         [0002]    Typically, a generator includes a rotor having a plurality of field coils, or windings. The rotor is driven to rotate by some source of rotation, such as a turbine rotor. The rotor rotates in proximity to a stator, and the rotation of the rotor generates current in stator windings. Generator wedges are used to support the windings under centrifugal load. 
         [0003]    The wedges are typically radially supported by a main field lamination stack. Given the significant centrifugal loading within a high speed generator, the stresses on the main field lamination often drive the selection of a lamination material, and result in a compromise as to magnetic properties as well as lamination geometry. 
         [0004]    There is a need for a generator rotor and wedge design reducing or eliminating the need for compromise in lamination magnetic properties and geometries due to rotor wedge retention considerations. 
       SUMMARY OF THE INVENTION 
       [0005]    A wedge for use in a generator rotor includes a wedge body having a generally triangular shape with flat surfaces, and such that when the wedge is placed in a generator rotor, the flat surfaces will define circumferential extents of the wedge body relative to a rotational axis of the rotor. The flat surfaces extend to a radially outermost extent of the wedge body. 
         [0006]    A wedge and winding combination for use in a generator rotor includes a wedge body having a generally triangular shape with flat surfaces, and such that when the wedge is placed in a generator rotor, the flat surfaces will define circumferential extents of the wedge body relative to a rotational axis of the rotor, and the flat surfaces extend to a radially outermost extent of the wedge body. The flat surfaces contact a mating flat surface on each of a pair of windings. 
         [0007]    A generator rotor includes a main lamination stack defining an axis. Pairs of circumferentially spaced windings have wedges placed circumferentially between each pair. The wedges include a wedge body having a generally triangular shape with flat surfaces. The flat surfaces define circumferential extents of the wedge body relative to the axis of the rotor, and extend to a radially outermost extent of the wedge body. The flat surfaces of said wedges sit radially outwardly of surfaces on the windings to provide support for the windings. The flat surfaces of the wedges also sit radially outwardly of mating surfaces on the main lamination stack. 
         [0008]    A generator includes a stator, and a rotor including a main lamination stack defining an axis. Pairs of circumferentially spaced windings have wedges placed circumferentially between each pair. The wedges include a wedge body having a generally triangular shape with flat surfaces. The flat surfaces define circumferential extents of the wedge body. The flat surfaces extend to a radially outermost extent of the wedge body. The flat surfaces of the wedges sit radially outwardly of surfaces on the windings to provide support for the windings. The flat surfaces of the wedges also sit radially outwardly of mating surfaces on the main lamination stack. 
         [0009]    A method of forming a generator rotor for an electrical generator includes the steps of defining a main lamination stack having openings spaced circumferentially about a central axis of the main lamination stack. Opposed pairs of circumferentially spaced windings are placed within the openings in the main lamination stack. Generally triangular wedge bodies are inserted circumferentially intermediate each winding in each pair of the windings. The wedges are designed to have surfaces which sit radially outwardly of the windings and surfaces of the main lamination stack which define the opening such that the wedges define a radial support surface for the main lamination stack, and the windings. A containment sleeve is force-fit around the wedges and the main lamination stack to provide radial support for the wedges. 
         [0010]    These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  shows a portion of a prior art generator. 
           [0012]      FIG. 2  is a portion of the inventive generator. 
           [0013]      FIG. 3  is an exploded view of a portion of a rotor. 
           [0014]      FIG. 4  is an exploded view showing a portion of a rotor with a containment sleeve. 
           [0015]      FIG. 5  shows the wedge of this invention. 
           [0016]      FIG. 6A  shows an end view of the inventive wedge. 
           [0017]      FIG. 6B  is a cross-sectional view along line  6 B- 6 B of  FIG. 6A . 
           [0018]      FIG. 6C  is a top view of the wedge. 
       
    
    
     DETAILED DESCRIPTION 
       [0019]    A portion of a known generator  10  is illustrated in  FIG. 1 , somewhat schematically. As known, a rotor  12  is driven to rotate, and rotates adjacent to a stator  14 , shown schematically. Windings  22  and main lamination stack  23  are driven to rotate with the rotor, and current is generated in the stator  14 . 
         [0020]    As known, wedges  16  provide a guide surface with circumferential ends  18  to support the windings  22 . In addition, radial support for the wedge  16  is provided by edges  20  of the lamination stack  23 , which contact ends  18  of the wedge  16  at a radially outer surface  19 . As mentioned above, since the lamination stack provides radial support for the wedges  16 , the material utilized for the lamination stack is sometimes compromised to provide mechanical properties for this support, rather than being selected for magnetic properties dictated by its main function. 
         [0021]      FIG. 2  shows one potential embodiment of the inventive generator  30  which eliminates reliance upon the main field lamination stack for wedge radial support. In the embodiment of  FIG. 2 , a rotor  31  rotates adjacent to a stator  14 . The wedge  32  has circumferential edge surfaces  34  that sit along a radially outer surface  36  of the lamination stack  37 . The terms radial and circumferential are defined relative to a rotational axis of the rotors. Generally flat side surfaces  39  extend to a radially outermost extent of the wedge  32  and sit along a flat surface  40  of the windings  38 , and a flat outer surface of the portion  36  of the lamination stack  37 . A containment sleeve  50  surrounds the lamination stack  37  and the wedges  32 . In the  FIG. 2  embodiment, the wedges provide radial support to the lamination stack  37 , and to the windings  38 . Thus, the problem discussed above of compromising the material of the lamination stuck such that it can provide support to the wedges is eliminated. 
         [0022]    As can be appreciated from  FIG. 3 , the assembled rotor  31  has plates  44  that sit on end surfaces  46  and  146  of the wedges  32 . An axial central portion  48  of the wedges  32  extends radially outwardly beyond the ends  46  and  146 . The plates  44  provide a reaction surface for radial forces on the wedges, and at the end surfaces  46  and  146 . 
         [0023]    As shown in  FIG. 4 , the containment sleeve  50  has ends  52  that will cover the plates  44  and the remainder of the rotor  31  when assembled. The containment sleeve  50  may be formed of a carbon fiber composite, or other suitable materials. The containment sleeve  50  is an interference fit on the wedges  32 , the plates  44 , and the lamination stack  37 . Thus, the containment sleeve provides the radial support for the wedges in this embodiment. 
         [0024]    The wedge  32  is shown in greater detail in  FIG. 5 . The wedge body is typically formed of an appropriate aluminum, and may be of a material similar to that which has been utilized in the past. In one embodiment, 2024-T851 aluminum is utilized, although other nonmagnetic materials may also be selected. End surfaces  46  and  146  are spread along a central axis of the rotor that will receive the wedge  32 . 
         [0025]    A ledge  54  connects the surfaces  46  and  48 . The cross-section of the wedge  32  extends between the circumferential edges  34 , and includes the generally flat surfaces  39 , and a flattened apex  58 . The apex  58  is at a tangent relative to a radius extending from the central axis of the rotor, while the outer surfaces  46  (and  146 ) and  48  are curved on a circular arc about that same axis. 
         [0026]    Grooves  56  are formed in the surface  48  and reduce eddy current losses to improve the generator efficiency. 
         [0027]    The cross-section of the wedge  32  may be extruded to have one or more hollow cavities (not shown). 
         [0028]    As shown in  FIG. 6A , the wedge  32  has a generally triangular shape, and is centered about a generating point C. The generating point C is the origin of a radius R 1 , which extends to the top surface  48 , and a radius R 2 , which extends to the surface  46  (and would also extend to the surface  146 ). The side surfaces  39  are defined by moving a distance d 1  and d 2  from a horizontal and vertical axis, and then defining a parallel line to the vertical and horizontal axes. In this manner, the shape of the wedge body is defined. In one embodiment, the distances d 1  and d 2  were both selected to be 1.325″ (33.6 mm), nominally. This was in a wedge wherein the radius R 1  was selected to be 2.625″ (66.7 mm), and the radius R 2  was selected to be 2.535″ (64.4 mm). In embodiments of this invention, a ratio of the d 1  (or d 2 ) to R 1  ranges between 0.45 and 0.55. 
         [0029]    Also, as can be seen, the end  58  of the wedge  32  is truncated. The truncated end  58  could be defined as being tangent to a radius from the generating point C. A line is drawn that is parallel to this tangent, and at a distance d 3  to this tangent d 3  was 1.98″ (50.3 mm) in one embodiment. The ratio of the distance d 3  to R 1  is between 0.65 and 0.75 in embodiments of this invention. The resulting wedge shape will have beneficial attributes, and will be of an adequate size to provide the support required for both the windings and lamination stack with this shape. 
         [0030]    As shown in  FIG. 6B , the grooves  58  and the intermediate surfaces  48  have respective lengths d 4  and d 5 ; d 5  is greater than d 4 . In one embodiment, d 4  was 0.060″ (1.52 mm) and d 5  was 0.128″ (3.25 mm). In embodiments, the ratio of d 4  to d 5  is selected to be between 0.4 and 0.5. 
         [0031]    As shown in  FIG. 6C , the end surfaces  46  and  146  are of different lengths. End surface  46  is of a length d 6 , while end surface  146  is of a length d 7 . The length of surface  46  is longer as there is a winding cross-over geometry which must be accommodated at that end. The windings must cross-over and return toward the other end, and additional space is necessary at this end. In one embodiment, the length d 6  was 0.499″ while the length d 7  was 0.420″ (10.7 mm). This was in a wedge having an overall length d 8  of 5.199″ (132 mm). In embodiments, the ratio of d 6  to d 7  is between 1.15 and 1.25. 
         [0032]    The wedge as disclosed in this application is able to provide robust radial support for the lamination stack and the windings. In this manner, the lamination stack can be designed primarily or solely for magnetic properties, and compromises due to the requirement of providing radial support for the wedge may be reduced or eliminated. 
         [0033]    In a sense, the lamination plates could be said to have openings formed by their side surfaces  36 , and for accommodating the windings  38 . The windings  38  and the wedges  32  are inserted into those openings. The wedge then provides radial support to the winding and the lamination stack. The sleeve is then force-fit around the assembly (after the plates  44  are mounted) and the sleeve provides radial support to the wedges  32 . 
         [0034]    Although an embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.