Abstract:
An enclosure for a rotor in a generator including the rotor, rotor windings and a stator, the enclosure comprising a plurality of composite rings located adjacent one another along a length dimension of the rotor so as to contain the rotor windings on the rotor, the rings each comprising at least two layers selected from the group consisting essentially of metals, glass fiber laminates and graphite fiber laminates.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present invention relates to generators and, more particularly, to an enclosure for a generator rotor.  
         [0002]     In a conventional generator having a rotor and a stator, the rotor is provided with field windings that excite the generator while receiving a current from an exciting current source. The stator is provided with armature windings from which electrical power is output. Typical rotor construction requires that a field winding be assembled, bar by bar, into radial slots milled into a rotor forging. Containment of the rotor field windings is typically achieved using rotor wedges, rotor teeth and retaining rings.  
         [0003]     In commonly owned U.S. Pat. No. 6,239,527, an enclosure for a rotor in a generator is described that is constructed of a non-magnetic, and preferably filament wound tube. The &#39;527 patent discloses that the enclosure may be formed as a continuous tube or as a plurality of rings, preferably slightly oval in shape.  
         [0004]     In commonly owned U.S. Pat. No. 6,291,919, a metal enclosure shield is disposed between the non-magnetic enclosure and the winding assemblies on the rotor. The enclosure shield is constructed of an electrically conductive material such as aluminum and is designed to provide adequate electromagnetic shielding for the rotor field winding, with good electrical contact with the magnetic core poles, while also providing axial stiffness to the winding structure. However, the insertion of a metallic shield radially between the composite enclosure and the field winding as described in the &#39;919 patent is not a satisfactory solution in light of, for example, structural and manufacturing issues relating to stress concentration.  
         [0005]     In commonly owned U.S. Pat. No. 6,495,942, the rotor enclosure is preferably constructed from a low density composite material such as a carbon fiber-glass fiber composite material.  
         [0006]     Graphite epoxy based composite laminates have significant specific strength (strength-to-density ratio) compared to metallic material. However, graphite laminates have low interlaminar shear strength and the inplane tensile strength of the composite is very sensitive to surface damage that severs fibers. Thus, the use of graphite laminates as structural components in a rotating stress field (such as a rotor structural enclosure) is technologically problematic.  
         [0007]     Moreover, when graphite (carbon fiber) composite interfaces with a conductive metallic component, such as an aluminum alloy, Galvanic interaction and resulting corrosion is likely to occur.  
       BRIEF DESCRIPTION OF THE INVENTION  
       [0008]     In an exemplary embodiment of this invention, the structural rotor enclosure, preferably in a multiple ring configuration, is constructed as a layered composite. Generally, the rings are comprised of two, three or more (as many as five) layers selected from graphite (carbon) fiber laminates, metallic layers and glass fiber layers. In the detailed description section hereinbelow, various combinations of layers are described that are within the scope of the invention.  
         [0009]     The length and arrangement of enclosure rings for particular applications may vary. For example, a plurality of relatively short rings may be located between a pair of longer rings or tube sections. In a variation of this arrangement, the rings in the center section may also vary in thickness and axial length.  
         [0010]     In another embodiment, the enclosure may be comprised of a plurality of uniformly or non-uniformly sized rings with different layering arrangements along the axial length of the enclosure.  
         [0011]     Different zones or layers can be made separately, then assembled or bonded together, but the rings can also be made co-wound with the core layers if they are filament/tow wound.  
         [0012]     Accordingly, in one exemplary embodiment, the invention relates to an enclosure for a rotor in a generator including the rotor, rotor windings and a stator, the enclosure comprising a plurality of composite rings located adjacent one another along a length dimension of the rotor so as to contain the rotor windings on the rotor, the rings each comprising at least two layers selected from the group consisting essentially of metals, glass fibers and graphite fiber laminates.  
         [0013]     In another aspect, the invention relates to an enclosure for a rotor in a generator including the rotor, rotor windings and a stator, the enclosure comprising a plurality of composite rings located adjacent one another along a length dimension of the rotor so as to contain the rotor windings on the rotor, the rings each comprising at least three layers selected from the group consisting essentially of metals, glass fibers and graphite fiber laminates; wherein the plurality of rings include a plurality of axially shorter rings located between a pair of axially longer rings; and further wherein the axially shorter rings vary in diameter in opposite directions toward a center ring of smallest diameter, and have different compositions than the axially longer rings.  
         [0014]     In still another aspect, the invention relates to an enclosure for a rotor in a generator including the rotor, rotor windings and a stator, the enclosure comprising a plurality of composite rings located adjacent one another along a length dimension of the rotor so as to contain the rotor windings on the rotor, the rings each comprising two layers including a radially inner metal layer and a radial outer layer of graphite fiber laminates; wherein the plurality of rings include a plurality of axially shorter rings located between a pair of axially longer rings, the axially shorter rings decreasing in diameter in opposite directions towards a center ring of smallest diameter.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]      FIG. 1  is an exploded perspective view of a winding assembly and generator rotor along with an enclosure formed by a plurality of uniform diameter enclosure rings;  
         [0016]      FIG. 2  is a partial cross-section taken along the line  2 - 2  of  FIG. 1 ;  
         [0017]      FIG. 3  is a partial cross-section through an enclosure formed by a plurality of non-uniform diameter and/or axial length rings with different compositions along the length of the enclosure in accordance with another exemplary embodiment of the invention;  
         [0018]      FIG. 4  is a partial cross-section through a plurality of enclosure rings in accordance with still another exemplary embodiment of the invention;  
         [0019]      FIG. 5  is a partial cross-section through a plurality of enclosure rings illustrating various other possible combination of layers of material for the enclosure rings; and  
         [0020]      FIG. 6  is similar to  FIG. 5  but illustrating still other possible layering arrangements for the enclosure rings. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0021]     With reference to  FIG. 1 , a generator rotor  10  includes a multi-pole magnetic core  12  (two-pole core shown) and a plurality of winding assemblies  14 , assembled over the respective poles  16 ,  18 . The construction of the magnetic core  12  and winding assemblies  14  is known, and details thereof need not be further provided.  
         [0022]     After the winding assemblies  14  are assembled over the parallel sided forging of the two-pole magnetic core  12 , an enclosure  20  is telescoped over the assembly.  
         [0023]     In the embodiment shown in  FIGS. 1 and 2 , the enclosure  20  is a tubular structure made up of a plurality of discrete rings. In the exemplary embodiment shown, rings of uniform diameter but of two different axial lengths are employed. Relatively longer rings  22  are arranged at opposite ends of the enclosure  20 , with a plurality of shorter rings  24  located axially between the rings  22 . Generally, the rings are multi-layered composites, with as few as two and as many as five discrete layers selected from a group including metals, glass fiber laminates and graphite (carbon) fiber laminates. The metal layer or layers may be composed of an electrically conductive metal such as aluminum. For purposes of this disclosure, the term intermediate layer or radially intermediate refers to any layer that is not a radially innermost or outermost layer.  
         [0024]      FIG. 2  illustrates the composition of the rings  22 ,  24 . Each of the rings in this exemplary embodiment is formed with five layers. More specifically, the radially innermost layer  26  is composed of a metal material. Adjacent the metal layer  26  is a glass fiber laminate layer  28 . The middle or core intermediate layer  30  is comprised of graphite (carbon) fiber laminates. The radially outer layers include a glass fiber laminate layer  32 , adjacent the middle layer, and a radially outermost metal layer  34 . Thus, the middle layer  30  serves as a core zone that insulates the outer layers  32 ,  34  from the inner layers  26 ,  28  and provides the majority of circumferential, or hoop, strength and stiffness. This same layered composition is utilized in each of the rings  22 ,  24  along the length of the enclosure  18 .  
         [0025]     In another exemplary embodiment illustrated in  FIG. 3 , the enclosure  36  is also comprised of a pair of axially longer rings  38  located on either side of a centrally located plurality of axially shorter rings  40 ,  42 ,  44  that decrease in diameter in uniform fashion toward the smallest diameter center ring  46 . In this arrangement, the rings are of two-layered construction where the radially outer layer  48  of each ring is comprised of the graphite (carbon) fiber laminates and the radially inner layer  50  is comprised of metal.  
         [0026]      FIG. 4  illustrates yet another enclosure  52  that is similar in outward appearance to that shown in  FIG. 3 , but here, the composition of the longer rings  54  at the respective opposite ends of the enclosure  52  differs from the composition of the shorter rings  56 ,  58 ,  60  and  62  in the center portion of the enclosure, respectively. More specifically, the two outer or end rings  54  are each comprised of a radially outer layer  64  of graphite (carbon) fiber laminates, an intermediate glass fiber laminate layer  66 , and a radially inner metal layer  68 . The shorter rings  56 - 62  in the center portion of the enclosure each include radially inner and outer glass fiber laminate layers  70 ,  72  sandwiched about an intermediate layer  74  of graphite (carbon) fiber laminates.  
         [0027]      FIG. 5  illustrates a plurality of enclosure rings of varying composition and diameter, and is merely intended to illustrate the wide variety of combinations of layers that may make up the individual, discrete rings of the enclosure, i.e.,  FIG. 6  does not show the rings of a single enclosure. Typically, the compositions and diameters would differ only between the end or outside rings and the rings in the center portion of the enclosure as shown in  FIGS. 2-4 . From left to right, in  FIG. 5 , the ring  76  is comprised of an intermediate layer  78  of graphite (carbon) fiber laminates while both the radially inner and outer layers  80  and  82  are metal layers.  
         [0028]     The ring  84  is a two layer construction including a radially inner layer  86  of graphite (carbon) fiber laminates and a radially outer metal layer  88 .  
         [0029]     Ring  90  is a three layer construction that includes a radially inner layer  92  of graphite (carbon) fiber laminates, an intermediate glass fiber laminate layer  94 , and a radially outer metal layer  96 .  
         [0030]     Ring  98  is a three layer construction that includes a radially inner glass fiber layer  100 , an intermediate layer  102  of graphite (carbon) fiber laminates, and an outer glass fiber laminate layer  104 .  
         [0031]     Ring  106  is a two layer construction that includes a radially inner glass fiber laminate layer  108  and a radially outer layer  110  of graphite (carbon) fiber laminates.  
         [0032]     Ring  108  is a two layer construction that includes a radially inner layer  110  of graphite (carbon) fiber laminates and a radially outer glass fiber laminate layer  112 .  
         [0033]     Still other possible ring compositions are shown in  FIG. 6 . Ring  114  is a four layer construction that includes a radially inner metal layer  116 , a glass fiber laminate layer  118 , a layer of graphite (carbon) fiber laminates  120 , and a radially outer glass fiber layer  122 .  
         [0034]     Ring  124  is a four layer construction similar to ring  114  with the exception that the radially outer glass fiber laminate layer  122  has been replaced by a metal layer  126 .  
         [0035]     Ring  128  is also of four layer construction with a radially inner glass fiber laminate layer  130 , a radially adjacent graphite (carbon) fiber laminate layer  132 , another glass fiber layer  134 , and a radially outer metal layer  136 .  
         [0036]     Ring  138  is a construction similar to ring  128  with the exception that the radially inner glass fiber laminate layer  130  has been replaced by a metal layer  140 .  
         [0037]     Ring  142  is a three layer construction including a radially inner glass fiber laminate layer  144 , an intermediate layer  146  of graphite (carbon) fiber laminates and a radially outer metal layer  148 .  
         [0038]     Ring  150  is also a three layer construction similar to ring  142  but wherein the radially inner and outer layers have been reversed so that ring  150  includes a radially inner metal layer  152 , an intermediate layer  154  of graphite (carbon) fiber laminates and a radially outer glass fiber laminate layer  156 .  
         [0039]     For most applications, the discrete ring compositions for a given enclosure will be uniform throughout but as already noted in connection with  FIG. 4 , the compositions of the shorter rings in the middle portion of the enclosure may differ from the longer rings at opposite ends of the enclosure. Nevertheless, there are many combinations of the three essential layer types that may be utilized as described above in connection with  FIGS. 5 and 6 .  
         [0040]     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.