Abstract:
A cap for disposition on a series loop of a bar wound armature of an electrical system and having openings in side walls thereof for providing ventilation flow to the solid series loop. The conductor bars of the series loop define gas flow passages internally of the cap to allow forced convective cooling of the conductors and, thus, the electrical winding. In an exemplary embodiment, lips are extended from the openings to capture cooling flow and to concurrently extend electrical creepage distances from loop to loop.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a cap for insulating series loop connections on bar wound armatures of electrical systems such as generators and, more particularly, to a cap assembly for providing series loop cooling and extended electrical creepage distances from loop to loop. 
     U.S. Pat. No. 5,633,543 and U.S. Pat. No. 5,652,469 describe ventilated cooling systems for rotating electrical machines, such as generators, which provide for end region cooling. 
     An exemplary reverse flow ventilation system of the type disclosed in U.S. Pat. No. 5,633,543, is illustrated by way of example in FIG.  1 . More specifically, FIG. 1 shows a cross-section of one-half of a generator  10  (see axial center-line  12  and longitudinal center-line  14 ) having a conventional reverse flow ventilated cooling system. A portion  16  of the flow of cooling gases is directed to the rotor  18 . The cooling gases are drawn through ventilation ducts  20  in the rotor by centrifugal forces created by the spinning rotor. As the gases flow through the rotor, heat in the rotor is transferred to the gases. The heated rotor gases exit the ducts  20  at the surface of the rotor into an air gap  22  between the rotor  18  and stator  24 . Spinning fans  26  mounted at the ends of the rotor draw the heated gas through the gap  22  between the stator and rotor. The heated gas is directed by an external duct  28  to a heat exchanger  30  that cools the gas. 
     The stator  24  is cooled by ventilation flow paths that are separate from the flow path in the rotor. Cold gas  32  cooled by the heat exchanger  30  enters a plenum chamber  34  surrounding the stator  24 . Because the end sections of the stator are closest to the rotor exhaust fans  26 , cooling gas tends naturally to flow in greater volume near the ends of the stator than through ducts at the center of the stator. This potential unbalance in the flow of cooling gas through the stator has traditionally been compensated for by baffle chambers  36  that extend around outer surface  38  of the stator. 
     The cooled gas  32  passes through the baffle chambers  36  (or directly to the stator near the center of the stator) and into cooling gas intake ducts  40  defined between packets  42  of stator core laminations. As the gas flows radially inward through the stator, heat from the stator coils  44 ,  46  is transferred to the gas. The fans  26  draw the warmed gas from the stator, into the air gap  22  and out to the external duct  28  to the heat exchanger  30 . 
     A portion of the cooled gas  32  from the heat exchanger  30  is exhausted from exhaust ports  48  in the ends of the plenum chamber  34  and flows around the stator to cool the stator end turns  50 . 
     U.S. Pat. No. 5,142,182 describes an adjustable width cap for insulating the series loop on wound armatures in electrical systems. The molded cap is formed from two identical cap sections which are assembled to define a loop cap enclosure that is adjustable in width for receiving different sized series loops. To mechanically lock the cap sections to one another, potting resin is disposed within the cap section. 
     The provision of molded end caps as disclosed in U.S. Pat. No. 5,142,182 precludes the direct gas cooling of the solid series loops  50 . Thus, heat generated thereby must be thermally conducted along a heat flow path from the electrical winding, through the molded cap to the cooling gas. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention is embodied in a modified cap assembly for providing ventilation to solid series loops, which concurrently extends electrical creepage distances from loop to loop. In an embodiment of the invention, the solid series loops are ventilated by providing ventilation openings in the side walls of the cap and a cooling gas flow path through the cap to allow forced convective cooling of the conductor and, thus, the electrical winding therewithin. More specifically, the invention is embodied in a cap for disposition on a series loop of a bar wound armature of an electrical system, that is formed by assembling a pair of cap sections. A cutout is defined in one or both side walls of one or both cap sections to provide at least one ventilation opening in each side wall of the assembled cap. In the presently preferred embodiment, the conductor bars of the series loop disposed within the cap are configured to define gas flow passage(s) between the ventilation openings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These, as well as other objects and advantages of this invention, will be more completely understood and appreciated by careful study of the following more detailed description of the presently preferred exemplary embodiments of the invention taken in conjunction with the accompanying drawings, in which: 
     FIG. 1 is a schematic cross-sectional diagram of a generator showing a reverse flow cooling system; 
     FIG. 2 is a perspective view of the region designated by detail A in FIG. 1, illustrating a cap applied to a series loop connection in an embodiment of the invention; 
     FIG. 3 is a perspective view similar to FIG. 1 with one cap section omitted to reveal the series loop configuration and interaction of the cap therewith; 
     FIG. 4 is a perspective view of a plurality of circumferentially adjacent series loops with end caps applied thereto; 
     FIG. 5 is an enlarged cross-sectional view of a series loop connection with cap applied thereto; 
     FIG. 6 is a cross-sectional view taken along line  6 — 6  of FIG. 5; 
     FIG. 7 is a side elevational view of a cap section, two of which cap sections form the caps illustrated in FIGS. 2 and 4; 
     FIG. 8 is an end elevational view of a cap section taken from the left in FIG. 7; and 
     FIG. 9 is an end elevational view of the cap formed by assembling the cap sections to define a cap. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIGS. 2-3 there is illustrated a series loop or end turn  50  with a single-shot brazed connection. As illustrated, the conductor bars  52 ,  54  are formed in such a manner to define a gas ventilation flow passages. In the illustrated embodiment, each bar  52 ,  54  is generally U-shaped in cross-section so as to define, with the cap  56  mounted thereto, gas flow channels or passages, respectively generally shown at  58 ,  62 . As an alternative to a U-shaped conductor bars, a simple bar conductor can be provided having one or more hollow passages defined longitudinally thereof for receiving and conducting cooling gas therethrough. 
     In the illustrated, presently preferred embodiment, cap  56  is formed of two identical or homomorphic cap sections assembled together to form essentially a five-sided enclosure having opposed side walls, an end wall, a pair of covers spaced one from the other and an opening opposite the end wall for receiving the series loop connection  50 . For case of description of the assembly of the cap section, the letter notations (a) and (b) are used as suffixes to denote the parts of the first and second cap sections, respectively, in assembly. However, the description of the cap sections in general will omit such suffixes. 
     Referring to FIG. 7, each cap section  64  includes a pair of spaced side walls, e.g., first and second side walls  66 ,  68 , an end wall  70 , and a cover  72  extending between side walls  66  and  68  and from end wall  70 , leaving free, as illustrated in FIGS. 3 and 7, the margins of the side and end walls along the side of the cap section opposite the cover  72 . 
     End wall  70  is comprised of a pair of end wall segments, e.g., first and second end wall segments  74  and  76 , respectively. End wall segments  74  and  76  extend generally parallel to one another but are offset in a longitudinal direction and in a radial direction one from the other. For purposes of this description, the longitudinal direction is in the direction of the arrow A in FIG. 3, whereas the radial direction extends in the direction of the arrow B, i.e., from one side wall to another. Longitudinally offset end wall segments  74  and  76  have radial end edges  78  and  80 , respectively, which extend from the free margins of the end wall segments inwardly toward the cover  72 . Edges  78  and  80  are also inclined toward one another to define an inset portion or opening  82  at least equal to about one-half of the transverse dimension of the end wall  70 , as illustrated in FIG.  8 . Thus, edges  78  and  80  lie longitudinally and radially offset one from the other. Additionally, edges  78  and  80  and inset portion  82  defined thereby lie substantially medially of the length of end wall  70 , for reasons which will become apparent from the ensuing description. It will be appreciated, however, that inset portions defined by inclined edges such as edges  78  and  80  may be located at spaced locations along end wall  70 , rather than medially as illustrated, provided such edges can intermesh one with the other when the cap sections  64   a ,  64   b  are assembled, as set forth hereinbelow. The opposite end of cap section  64 , the left end as shown in FIG. 7, is defined by the free end edges of side walls  66 ,  68  and the free end edge of cover  72 . 
     As best illustrated in FIGS. 7 and 8, a longitudinally extending tab  84  is disposed adjacent first side wall  66  in generally parallel relation therewith and extends from a location adjacent cutout  100  (discussed hereinbelow) to a location approaching the free end edge of the cap section  64 . Tab  84  thus defines a slot  86  with side wall portion  66  in juxtaposition therewith for receiving, in assembly, a portion of the opposite second side wall  68  of another cap section  64 , as detailed below. Tab  84  extends from the cover  72  and is preferably of the same depth as side wall  66 . Tab  84  may, however, be secured to side wall  68  adjacent cover  72  and does not necessarily require securement to cover  72 . Along the opposite side wall  68 , there is provided a rib  88 . Rib  88  is disposed at a longitudinal location along side wall  68  beyond the tab  84 . 
     To assist in securing cap sections  64   a  and  64   b  one to the other in assembly, an opening  90  is formed through tab  84 . A similar opening  92  is formed through the second side wall  68  adjacent its distal end. More particularly, to lock the cap section in assembled relation one with the other, a potting resin  94  may be disposed in the cap sections, and will flow into the openings  90  and  92 . When the resin is cured, the potting resin will thus form locking pins. 
     It will be appreciated that, with the foregoing construction of the cap sections, each cap section may be formed of a dielectric material, for example, a resin, formed in a single mold whereby an assembly of a pair of such homomorphic or identical cap sections may form the cap for receiving the series loop connection. 
     To assemble a pair of cap sections  64  to form cap  56 , the side walls and end wall segments are respectively intermeshed whereby the cap sections, in final assembly, are radially offset one from the other a distance corresponding substantially to the thickness of a side wall. The cap sections  64  are, however, longitudinally aligned one with the other. This radial offset can be seen in FIG. 2, wherein the first side wall  66   a  and a first end wall segment  74   a  of a first cap section  64   a  are illustrated, whereas the cover  72   b , the first end wall segment  74   b  and second side wall  68   b  of a second cap section  64   b  are illustrated. 
     Referring to FIG. 5, when identical cap sections  64  are intermeshed one with the other, side walls  66   a  and  68   a  of cap section  64   a  lie in generally parallel juxtaposition with the respective side walls  68   b  and  66   b , respectively, of the second cap section  64   b . First side wall  66   a  of the first cap section  64   a  lies outwardly of side wall  68   b  of second cap section  64   b . Likewise, the first side wall  66   b  of second cap section  64   b  lies outwardly of second wall  68   a  of first cap section  64   a . Note also that a portion of side wall  68   b  of second cap section  64   b  lies between tab  84   a  and side wall  66   a  of first cap section  64   a  and inwardly of rib  88   b  of second cap section  64   b . Similarly, a portion of side wall  68   a  of first cap section  64   a  lies between tab  84   b  and side wall  66   b  of second cap section  64   b  and inwardly of rib  88   b.    
     A review of FIGS. 2,  4 , and  5  also reveals that first and second end wall segments  74   a  and  76   a  of the first cap section  64   a  lie in side-by-side parallel relation with respective second and first end wall segments  76   b  and  74   b  of second cap section  64   b . It will also be appreciated from a review of FIG. 5 that the insert edges of the end wall segments  78   a  and  80   a  of the cap section  64   a  respectively intermesh with the inset edges of the end wall segments  78   b  and  80   b  of the cap section  64   b . Thus, the cap sections are radially offset one from the other, as illustrated in FIG. 5, but are longitudinally aligned one with the other. The inset edges  78  and  80  accommodate the longitudinal alignment and radial offset. It will also be appreciated from a review of FIGS. 4 and 9 that the cap sections may be assembled to a selected width (transverse dimension), depending upon the degree to which the sections are intermeshed. 
     Each cap section  64  further includes cutouts  100 ,  102  and part surrounding extended lips  104 ,  106  projecting generally radially from each side wall  66 ,  68  thereof so that when the cap sections  64   a  and  64   b  are assembled to define the cap, a ventilation or cooling flow opening  108  is defined by extended lips  104   a  and  106   b  and a ventilation or cooling flow opening  110  is defined by extended lips  104   b  and  106   a , on radially opposite sides of the cap  56 . As can be seen, the lips of the cutouts respectively defining of the ventilation openings have a complementary configuration so as to nest to define a substantially continuous peripheral lip of the respective ventilation opening. 
     As mentioned above, the conductor bars  52 ,  54  are formed in such a manner as to define a gas ventilation flow passages. In the illustrated embodiment, each bar  52 ,  54  is generally U-shaped in cross-section so as to define, with the cap  56  mounted thereto, air flow channels  58 ,  62 . As an alternative to U-shaped conductor bars, a simple bar conductor can be provided having one or more hollow passages defined therethrough for receiving and conducting cooling gas therethrough. Thus, as shown in FIG. 1, a portion of the cooling air flow directed towards the series loops, circumferentially disposed as shown in FIG. 4, can flow into radially outer ventilation opening  110  and into and through cooling passages  58 ,  62  to directly cool the conductors  52 ,  54 . The warmed gas can then exit through radially inner ventilation opening  108  to join the warmed gas flowing out from gap  22 . 
     The extended lips  104 ,  106  on the cap  56  provide two functions in the preferred embodiment of the invention. First, they increase the electrical creepage distance from series loop to series loop. This allows the series loops to be effectively insulated from each other while still providing a ventilation passage for cooling gas. Second, the lips may be angled so as to optimize the amount of cooling gas captured from the ventilation flow field. The angle is dependent upon the type and direction of cooling gas and the orientation of the series loop, and thus the end cap, with respect thereto. In the event the lips are to be angled in opposite directions at each radial side of the cap, for example, towards the plane of the end wall at the radially outer side and towards the open end of the cap at the radially inner side of the cap then the radially upper and radially lower halves of the caps will be non-symmetrical, so that each cap section is not identical. Where the extruded lips  104 ,  106  project symmetrically at each radial side of the cap, then the halves may be made from the same mold. 
     In the illustrated embodiment the extended cap lips are angled circumferentially inwardly, away from adjacent caps. This is to allow for the extension without decreasing the amount of circumferential space left in between adjacent series loop assemblies. 
     To preclude the possibility of the open conductors  52 ,  54  causing problems during operational malfunctions, the strap and bar assembly may be coated with a non-conducting paint. This will circumvent any possibility of the gas ionizing under extreme conditions and yet allow the forced convection cooling of the loops as aforesaid. 
     The gas ventilation flow paths  58 ,  62  defined by the bars  52 ,  54  and the cap sections  64   a  and  64   b  must be maintained patent. Thus, no cap filler may be allowed to intrude substantially into the gas passage. This may be accomplished either by adding ridges to the cap to compartmentalize and thus contain the applied filler or by clearing the gas passages immediately after assembly and filling with potting. 
     It will be appreciated that the cap sections  64  may be assembled directly onto the series loop connection  50 . Thus, the cap sections may be disposed on opposite sides of a series loop and pressed toward one another, with the side walls and the end wall segments intermeshing with one another, respectively, as previously described. Alternatively, the cap sections may be disposed about the end loop in a clamshell-type manner. Of course, additional securing means may be desirable and may comprise, e.g., banding tapes disposed about the cap sections when assembled. 
     While the invention has been described with reference to the preferred embodiment wherein the cap sections are identical or nearly identical such that a cutout, such as a hole or slot, is defined in each side wall of each cap section, to be aligned with one another to define the ventilation openings  108 ,  110  in the cap  56 , in the alternative, a cutout may be provided in each side wall of only one of the cap sections, a cutout may be provided in one side wall of each cap section (so as to be disposed on opposite sides of the assembled cap structure), or independent cutouts or openings may be provided in each cap section, particularly where sidewall overlap is limited. These and other alternatives will be readily understood by the skilled artisan. Thus, 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 embodiments, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.