Abstract:
A winding assembly for a rotor is disclosed comprising a plurality of rotor field windings and a field support holding said plurality of windings in said winding assembly, wherein the winding assembly is mountable on said rotor.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to rotors in synchronous machines. In particular, the invention relates to supports for a rotor field winding in generators.  
           [0002]    Conventional generators have rotors that support field windings. These rotors typically have rotor cores with axial slots that receive each turn of the field windings. These rotor slots restrain the windings against the centrifugal forces that arise as the rotor spins. During assembly, the winding is installed turn by turn in the slots of the rotor core. The winding is assembled as it is installed in the slots of the rotor core. Assembling the winding as it is installed in the rotor core is inefficient, time consuming and requires highly-skilled technicians. There is a need for an improved method of installing a field winding in the rotor core of a generator.  
         BRIEF SUMMARY OF THE INVENTION  
         [0003]    A modular field winding support system has been developed. This system allows for pre-formed winding turns to be installed in a rotor core. The modular support system includes a series of winding spacers that hold each of the winding turns. These spacers are laterally spaced along the long side of the windings. Each spacer holds a plurality of windings. A group of spacers collectively hold a nested assembly of windings. The winding spacers and hence the windings are secured to a rotor core by a locking mechanism. A rotor core may support a pair of opposite assemblies of windings.  
           [0004]    The winding spacers are fitted to the pre-fabricated windings prior to their assembly with the rotor core. The winding spacers have some flexibility to adjust to variances in the winding turns and the rotor core. The pre-fabricated winding turns and winding spacer assembly is mounted on the rotor core. A locking mechanism secures the winding support and the winding turns to the rotor core.  
           [0005]    In a first embodiment, the invention is a winding assembly for a rotor comprising: a plurality of rotor field windings, and a winding support holding said winding in a slot of the support, wherein the winding assembly is mountable on said rotor.  
           [0006]    In another embodiment, the invention is a winding assembly for a rotor core comprising: an array of field windings arranged in an array, each of said windings having a pair of opposite long sides, and a pair of opposite end sections and a plurality of winding spacers supporting the long sides of said field windings, said winding spacers each having a first edge and a second edge, wherein each of said first edges slidably engage a respective spacer slot on a first surface of the rotor core, and each of said second edges engage a respective spacer slot on a second surface of the rotor core.  
           [0007]    In a further embodiment, the invention is a method for assembling a plurality of field windings and securing the windings on a rotor core comprising the steps of: arranging a plurality of field windings in a winding assembly using a plurality of spacers to hold the windings in the assembly, wherein each spacer has a plurality of slots and each slot receives one of said plurality of rotor windings; mounting the winding assembly on the rotor core by inserting edges of the plurality of spacers into slots on the rotor core, and securing the edges of the plurality of spacers to the rotor core. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    [0008]FIG. 1 is a cross-sectional diagram of a generator having a rotor and stator.  
         [0009]    [0009]FIG. 2 is a perspective view of the rotor from the generator, wherein the rotor lacks field winding assemblies.  
         [0010]    [0010]FIG. 3 is an assembly drawing showing a rotor assembly incorporating the field winding and spacer assembly.  
         [0011]    [0011]FIG. 4 is a perspective view of a field winding and spacer assembly.  
         [0012]    [0012]FIG. 5 is a perspective view of a spacer.  
         [0013]    [0013]FIG. 6 is a cross-sectional diagram of the rotor with a pair of field winding and spacer assemblies.  
         [0014]    [0014]FIG. 7 is an enlarged cross-sectional diagram showing a quarter-section of the rotor with a field winding and spacer assembly. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0015]    [0015]FIG. 1 is a cross-sectional diagram of an exemplary generator  1  having a stator  3  and a rotor  4 . The rotor is supported on bearings  5  in a generator housing  6 . The stator includes an annular array of armature windings (stator coils)  7  that form a cavity for the rotor.  
         [0016]    [0016]FIG. 2 is a diagram of a rotor  4  having a generally rectangular rotor core  10  with opposite pole surfaces  22  arranged along a Q-axis. The rotor core includes fins  14  arranged along the D-axis of the core. The rotor core  10  is supported by rotor end shafts  8  that are axially (along the center-axis  11 ) aligned with the rotor core. The end shafts are supported by bearings  5 . The end shafts may connect to a drive coupling to a power turbine and to an electrical collector.  
         [0017]    The rotor core  10  may be formed of an iron forging. The rotor fins  14  of the rotor core may be formed in any suitable manner, including being integral with the rotor core forging by being machined or forged from the rotor forging, cast with the rotor forging, or welded to the rotor forging. Alternatively, the fins  14  may be mechanically secured to the rotor core forging using dovetails or the like.  
         [0018]    The rotor core is semi-rectangular in cross section and has a pair of opposite flat surfaces  20  and a pair of opposite arc-shaped surfaces  22 . The fins  14  extend upright from the longitudinal center of the flat surfaces of the rotor core. The flat surfaces each have a series of spacer slots  24  (see FIG. 3) that are orthogonal to the center axis  11 . These spacer slots are open at the edge of the flat surface adjacent the arc surfaces  22  so that the edges of winding spacers  26  may slide into these slots.  
         [0019]    In addition, the rotor flat surfaces  20  each include a locking slot  28  parallel to the center axis  11 . The locking slot intersects the spacer slots  24  on the rotor flat surface. The locking slot slidably receives a locking bar  30  that secures the spacers to the rotor core. The spacer bar is positioned in the locking slot such that notches  36  on the bar are aligned with the slots on the rotor flat side. Once the spacers have been inserted into the spacer bar, the bar is moved laterally in the locking slot to engage and secure with locking notches  38  in the edges of the spacers. The fins  14  of the rotor also have spacer slots  32  to receive an opposite end of the spacers  26 . The spacer slots  32  in the fins may have closed ends  34 . As the edges of the spacers are inserted into the fin slots, the opposite edges of the spacer slide into the open-ended slots on the flat side of the rotor core.  
         [0020]    The arc-shaped surfaces  22  of the rotor core have apertures  88  to receive connections for a shield  62  (FIG. 1). At least a portion of the arc surfaces  22  extend to the surface of the cylindrical envelope  40  formed by the rotation of the rotor core. This envelope is nearly the same diameter as the rotor cavity formed in the stator. An annular air gap  44  is formed between the rotor cylindrical envelope  40  and the rotor cavity surface in the stator. The outer edge  48  of the fins, need not extend to the enclosure, but may be slightly short of the envelope to facilitate mounting a rotor enclosure onto the rotor core. The outer peripheral surfaces  49  of the windings, and the arc surfaces  22  of the rotor core extend to the cylindrical envelope surface.  
         [0021]    [0021]FIG. 3 is a perspective view of a field winding assembly  13  being mounted on the rotor core  10 . The winding assembly is prefabricated with spacers before being mounted on the rotor core. The winding assembly  13  is aligned with the rotor core such that the center open area  78  of the windings is above the semi-rectangular rotor core and coaxial with the Q-axis of the core. The edges of the spacers  26  in the winding assembly are aligned with the slots  24  on the flat surfaces  20  of the rotor core. A hoist or other mechanical lifting device may be used to move the winding assembly over the rotor core.  
         [0022]    As the winding assembly is lowered onto the rotor core, edges  72  of the spacers slide into the core slots  24 . The spacers are arranged on both sides  59  of the windings. The spacers on each winding side slide into respective core slots  24  on both sides of the core surfaces  20 . The locking bars  30  on both of the opposite core surfaces  20  are positioned in the locking slots  28  such that the notches  80  on the locking bar are aligned with the slots  24  on the flat surfaces  20 . The edges  72  of the spacer slide into the rotor slots  24 , past the locking bar and seat in the rotor core slots  24 . The locking bar aligns the spacers with respect to the rotor slots  24 .  
         [0023]    As the edges  72  of the spacer near the bottom of the rotor core slots, the opposite edges  76  of the spacer are inserted vertically into the spacer slots  32  on the fins. The upper end  34  of the fin slots  32  are expanded to allow an adjustment tool to facilitate the insertion of the spacer edge  76  into the fin slot. The spacers are flexible and may be slightly deformed to fit into the slots of the fin and/or the rotor core. Once the edges  72 ,  76  of all of the spacers have been fully seated in their respective slots in the rotor core or fin, the locking bar is moved laterally slightly in the locking slot so as to secure the spacers and hence the field winding assembly to the rotor core.  
         [0024]    A winding assembly  86  that is fully seated on the rotor core is shown on the lower half of the FIG. 3. During assembly, once the winding assembly is seated and secured to the rotor, the rotor may be turned halfway around so that a second winding assembly can be lowered vertically onto the rotor core. While a two-winding assembly arrangement is shown here, other embodiments of the winding/rotor assembly may have one or three or more winding assemblies mounted on the rotor.  
         [0025]    [0025]FIG. 4 is a perspective view of a field winding assembly  13 . The winding spacers  26  for each assembly  13  hold the individual rotor field windings  56  in an array having a generally half-cylindrical shape. The windings are nested one winding within another winding in the winding assembly  13 . The nested array of field windings  56  are held to the rotor by the spacers  26  arranged on opposite sides  58  of the windings.  
         [0026]    The winding assembly  13  may be pre-formed before being mounted on the rotor core  10 . The field windings  56  may be formed of copper or other highly-conductive material. Each winding may  56  have a racetrack shape, but other winding shapes may be employed such as a saddle shape. The racetrack windings  56  each have a pair of straight long sides  58 , and a semi-circular end section  60 . The long sides  58  of the windings are supported by a, the spacers  26  on the rotor core. The spacers are distributed along the length of each side  58  of the winding array.  
         [0027]    The end sections  60  of the windings extend laterally beyond the rotor core and over a portion of the end shaft sections (see FIG. 1). The end winding sections  60  may be contained by an cylindrical composite enclosure shield  62  (FIG. 1) that fits over the outer surface of the rotor core and extends laterally beyond each end of the rotor core to cover the end sections  60  of the field windings.  
         [0028]    [0028]FIG. 5 is a perspective view of a spacer  26  that has a quarter-disk shape  66  with teeth  68  and slots  70  between the teeth. The spacers may be formed of a metallic material or a non-metallic material, such as a composite material. The slots  70  formed between the teeth of the spacers each receive a winding. The depth of each slot in the spacer is selected so as to receive the assigned winding  56  for the slot, and to position the outer periphery  49  of the winding at the edge of the cylindrical envelope  40  of the rotor. As the windings are inserted into the slots of each spacer, the slots  70  in the spacer may slightly pinch together (due to the presence of adjacent windings) and secure the windings in the slots of the spacer.  
         [0029]    The spacers are distributed along the long sides  58  of the windings so as to be aligned with the slots  24  on the rotor core and the spacer slots  32  on the fins of the rotor core. In this regard, the spacers may slide laterally along the field windings so as to align with the slots in the rotor. In addition, the spacers may be ductile so as to flex to accommodate variations in field windings, and in the slots in the rotor core and fins.  
         [0030]    The inside edge surfaces of the spacers  26  conform to the surfaces of the flat surface  20  of the rotor core and the fin  14  surface. The spacer edge  72  that abuts the flat surface  20  of the rotor is generally a straight edge to fit into the slot  24  on the rotor core. This edge slides into the slot on the rotor core as the winding assembly is inserted onto the rotor core. A notch  74  on the edge  72  of the spacer aligns with the locking slot  28  on the rotor core. This notch engages the locking bar  30  to secure the spacer and hence winding assembly  13  to the rotor core. The other edge  76  of the spacer fits into the spacer slot  32  on the fins. This edge may have a ledge  77  that engages the end of the spacer slot in the fin. This other edge  76  is inserted into the fin spacer slot  32  perpendicular to the slot (as the opposite edge of the spacer slides in parallel to the slot  24  on the rotor flat surface).  
         [0031]    [0031]FIG. 6 shows in cross section a rotor core  12  and winding assembly. The cross-section is through the rotor core at a slot  63  in the arc-shaped pole face  22  of the core. The two winding assemblies  13  (one winding assembly in the upper half of the figure, and a second winding assembly in the lower half of the figure) are supported on the rotor core so as to form a circular array of rotor field windings. The rotor core  12  supports the field winding and spacer assemblies  13  in an annular array of two winding assemblies  13  around the central axis  11  of the rotor. The outer periphery  49  of the windings extends to the end of the cylindrical envelope  40  formed by the rotor core.  
         [0032]    [0032]FIG. 7 is an enlarged cross section of a quarter-section of rotor core and a single winding assembly  13 . The locking bar  30  secures each spacer  26  to the rotor core, and the ledge  77  on the other edge of the spacer engaging the spacer slot  32  on the fin. Each winding  56  is seated in a spacer slot  79  such that the upper edge of the winding extends to the cylindrical envelope  40  of the rotor. A composite enclosure shield  62  (FIG. 1) may wrap around the rotor core and winding assembly. The spacers have threaded bolt holes  88  to receive bolts that hold the shield to the winding assembly. Similarly, the arc-shaped portion of the rotor core may have bolt holes for bolts that hold the shield to the rotor core.  
         [0033]    The spacers  26  are one embodiment of a winding support that holds a rotor field winding that may be assembled with the winding, before the support and winding are mounted on the rotor core. The winding support is not an integral part of the forging. Once mounted on the rotor core, the winding support could be permanently attached to the forging (e.g., welding) or detachably connected to the forging, such as via the locking mechanisms disclosed here. The support could be separate spacers or an integrated assembly.  
         [0034]    While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiments, it is to be understood that the invention is not to be limited to the disclosed embodiments, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.