Abstract:
A bus bar assembly includes a first main conductor, a second main conductor, and an insulator member provided between the main conductors. The insulator member includes: (i) an insulator component, (ii) a first conductor layer provided on the top surface of the insulator component, and (iii) a second conductor layer provided on the bottom surface of the insulator component, wherein the first conductor layer includes an outer edge around a perimeter thereof, wherein the outer edge is located at least a certain distance from the outer edge around the perimeter of the insulator component, wherein the second conductor layer includes an outer edge around a perimeter thereof, wherein the outer edge is located at least the same certain distance from the outer edge of the insulator component, and wherein the certain distance is sufficient to cause the bus bar assembly to satisfy the creepage requirement of the assembly.

Description:
GOVERNMENT CONTRACT 
       [0001]    This invention was made with government support under U.S. Navy Contract (NAVSEA) N00024-07. The United States government may have certain rights in the invention. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to bus bar devices, and in particular, to a bus bar assembly that includes a conductive cladding provided on the insulator layer to increase the partial discharge inception voltage. 
       BACKGROUND OF THE INVENTION 
       [0003]    A bus bar is a multilayer device that is commonly used for power and/or signal distribution in electronic systems and power conversion equipment. Bus bars generally include at least two conductors (usually in the form of elongated strips or bars of a metal conductor such as copper) separated by an insulating layer made of, for example, a dielectric material. The conductors typically have a number of distribution pins extending therefrom which enable electrical connections to be made between the conductors and the remainder of the circuit components. 
         [0004]      FIG. 1  is a cross-sectional view of a portion of a prior art bus bar assembly  2 . Bus bar assembly  2  includes a first main conductor  4  made of, for example copper, a second main conductor  6  also made of, for example copper, and an insulator layer  8  made of, for example, a dielectric material, provided between the first main conductor  4  and the second main conductor  6 . Typically, air  10  is trapped in small air voids that exist between first main conductor  4  and insulator layer  8  and between second main conductor  6  and insulator layer  8 . Air  10  in the air voids frequently leads to a plasma creation in the air voids known as partial discharge. The Partial discharge is problematic as it slowly breaks down the material of insulator layer  10 . The partial discharge effect is caused by the high field strength that is used in a dielectric insulator, and is exacerbated by the relative dielectric constant of insulator layer  8  as compared to the dielectric constant of air  10 , which causes the field to concentrate in the small air voids. While this does not lead to an arc, it does lead to the plasma creation known as partial discharge. 
         [0005]    There is thus a need for a bus bar assembly that decreases the likelihood of the occurrence of partial discharge in the bus bar assembly. 
       SUMMARY OF THE INVENTION 
       [0006]    In one embodiment, a bus bar assembly for use in an application having a creepage distance requirement is provided that includes a first main conductor, a second main conductor, and an insulator member provided between the first main conductor and the second main conductor. The insulator member includes: (i) an insulator component having a top surface, a bottom surface, and a first outer edge around a perimeter thereof, (ii) a first conductor layer provided on the top surface of the insulator component, and (iii) a second conductor layer provided on the bottom surface of the insulator component, wherein the first conductor layer includes a second outer edge around a perimeter thereof, wherein the second outer edge is located at least a certain distance from the first outer edge around the perimeter of the insulator component, wherein the second conductor layer includes a third outer edge around a perimeter thereof, wherein the third outer edge is located at least the certain distance from the first outer edge around the perimeter of the insulator component, and wherein the certain distance is sufficient to cause the bus bar assembly to satisfy the creepage requirement. 
         [0007]    In another embodiment, a method of making a bus bar assembly is provided that includes determining a creepage distance requirement for the bus bar assembly, forming an insulator member as just described, and affixing the insulator member between a first main conductor and second main conductor. 
         [0008]    Therefore, it should now be apparent that the invention substantially achieves all the above aspects and advantages. Additional aspects and advantages of the invention will be set forth in the description that follows, and in part will be obvious from the description, or may be learned by practice of the invention. Moreover, the aspects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    The accompanying drawings illustrate presently preferred embodiments of the invention, and together with the general description given above and the detailed description given below, serve to explain the principles of the invention. As shown throughout the drawings, like reference numerals designate like or corresponding parts. 
           [0010]      FIG. 1  is a cross-sectional view of a portion of a prior art bus bar assembly; 
           [0011]      FIG. 2A  is an exploded view and  FIG. 2B  is an isometric view of a portion of a bus bar assembly according to one exemplary embodiment of the present invention; 
           [0012]      FIG. 3  is a cross-sectional view of the bus bar assembly of  FIG. 2  taken along lines  3 - 3  in  FIG. 2 ; and 
           [0013]      FIG. 4  is a cross-sectional view of a portion of a bus bar assembly according to an alternative exemplary embodiment of the present invention. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0014]    Directional phrases used herein, such as, for example and without limitation, top, bottom, left, right, upper, lower, front, back, and derivatives thereof, relate to the orientation of the elements shown in the drawings and are not limiting upon the claims unless expressly recited therein. 
         [0015]    As employed, herein, the statement that two or more parts or components are “coupled” together shall mean that the parts are joined or operate together either directly or through one or more intermediate parts or components. 
         [0016]    As employed herein, the term “number” shall mean one or an integer greater than one (i.e., a plurality). 
         [0017]      FIG. 2A  is an exploded view and  FIG. 2B  is an isometric view of a portion of a bus bar assembly  12  according to one exemplary embodiment of the present invention.  FIG. 3  is a cross-sectional view of bus bar assembly  12  taken along lines  3 - 3  in  FIG. 2A . Bus bar assembly  12  includes a first main conductor  14  having distribution prongs or fingers  15  and a second main conductor  16  having distribution prongs or fingers  17 . In the exemplary embodiment, first main conductor  14  and second main conductor  16  are made of copper, although other suitable conductive materials, such as other metals, may also be used. A plated insulator member  18  is provided in between first main conductor  14  and second main conductor  16 . 
         [0018]    As seen in  FIGS. 2A ,  2 B and  3 , plated insulator member  18  includes insulator element  20  having a conductor layer  22 A provided on a top surface thereof and a conductor layer  22 B provided on a bottom surface thereof In the exemplary embodiment, insulator element  20  is sheet of dielectric material such as, without limitation, FR-4, GPO-2 or GPO-3, or ceramic dielectric material. Also in the exemplary, non-limiting embodiment, plated insulator member  18  is made by plating conductor layer  22 A on the top surface of insulator element  20  and plating conductor layer  22 B on the bottom surface of insulator element  20  is made by plating conductor layers  22 A,  22 B onto insulator element  20  using any suitable metal plating technique, such as any of a number of known plating techniques used in printed circuit board manufacture to lay metallization onto a dielectric substrate such as FR-4. The deposition of conductor layers  22 A,  22 B onto insulator element  20  as just described will shift the charge point to the surface of each of conductor layers  22 A,  22 B. In the exemplary embodiment, the plating process will ensure that no air is trapped between conductor layer  22 A and the top surface of insulator element  20  or between conductor layer  22 B and the bottom surface of insulator element  20  (i.e., the possibility of entrained air or voids is eliminated). Alternatively, conductor layers  22 A,  22 B may be deposited on the respective surfaces of insulator element  20  using other suitable deposition methods, such as, without limitation, vapor deposition or sputtering, wherein no air is trapped between conductor layer  22 A and the top surface of insulator element  20  or between conductor layer  22 B and the bottom surface of insulator element  20 . 
         [0019]    The metallization deposited on both the top and bottom surfaces of insulator element  20  is then etched back from each of the outer edges  24  of insulator element  20  by an amount/distance that will make the creepage distance for bus bar assembly  12 , when finally assembled as described herein, appropriate for the given application, thereby forming plated insulator member  18 . In the exemplary, non-limiting embodiment shown in  FIGS. 2A ,  2 B and  3 , the plating on both the top and bottom surfaces of insulator element  20  is etched back an amount/distance at each outer edge location  24  that will result in conductor layer  22 A being aligned with the adjacent outer edge portion  26  (not including prongs  15 ) of first main conductor  14  and conductor layer  22 B being aligned with the adjacent outer edge portion  28  (not including prongs  17 ) of second main conductor  16  when bus bar assembly  12  is assembled as described below. In the exemplary, non-limiting embodiment, the remaining plating comprising conductor layers  22 A,  22 B are then tinned or plated to prevent corrosion. 
         [0020]    In an alternative embodiment, rather than the metallization being etched back as just described, the metallization is selectively deposited on both the top and bottom surfaces of insulator element  20  in a manner wherein conductor layer  22 A is aligned with the adjacent outer edge portion  26  (not including prongs  15 ) of first main conductor  14  and conductor layer  22 B is aligned with the adjacent outer edge portion  28  (not including prongs  17 ) of second main conductor  16  when the bus bar assembly  12  is assembled. 
         [0021]    After plated insulator member  18  is formed as just described, first main conductor  14  is coupled to the top surface of plated insulator member  18  on top of conductor layer  22 A in a manner wherein first main conductor  14  is electrically coupled to conductor layer  22 A and second main conductor  16  is coupled to the bottom surface of plated insulator member  18  on top of conductor layer  22 B in a manner wherein second main conductor  16  is electrically coupled to conductor layer  22 B. In the exemplary embodiment, this is accomplished by sandwiching plated insulator member  18  between first and second main conductors  14 ,  16  using, for example, a non-conductive clamp or bracket, although other suitable affixation methods (e.g., an adhesive) may also be employed. As can be seen in  FIG. 3 , due to the etching back of the metallization to form conductor layers  22 A,  22 B, bus bar assembly  12  will include an overhanging insulator portion  30  that extends beyond both first and second main conductors  14 ,  16  and the conductor layers  22 A,  22 B around the outer perimeter of bus bar assembly  12 . As noted above, overhanging insulator portion  30  will increase the surface path distance between first and second main conductors  14 ,  16  and, depending on the amount of etching selectively performed, enable bus bar assembly  12  to satisfy the creepage distance requirements of the application for which it is being made. In any particular application, the required creepage distance is determined by the voltage that will be applied to the two conductors (first and second main conductors  14 ,  16 ) and whatever standard is appropriate (e.g., IEC or UL). More fundamentally, the required creepage distance is determined to prevent arcing between the two conductors under reasonable cases of contamination and air quality. Typically, this is anywhere from 0.5 inches for low voltages (&lt;1 kV), several inches for medium voltages (e.g., 1-30 kV), and several feet for high voltages (&gt;30 kV). In addition, the required creepage distance is typically greater than the required air gap between two conductors because an arc may travel across moisture or other contaminates deposited on the surface. 
         [0022]    Moreover, by including plated insulator member  18  as just described, the inception voltage of partial discharge for bus bar assembly  12  will be increased significantly, thereby reducing the likelihood that detrimental partial discharge will occur. Furthermore, if air is trapped between first main conductor  14  and conductor layer  22 A and/or between second main conductor  16  and conductor layer  22 B, partial discharge there between will be prevented because both surfaces will be at the same potential. 
         [0023]      FIG. 4  is a cross-sectional view of a portion of a bus bar assembly  12 ′ according to an alternative exemplary embodiment of the present invention. Bus bar assembly  12 ′ includes a number of the same components as bus bar assembly  12 , and like components are labeled with like reference numerals in  FIG. 4 . As seen in  FIG. 4 , bus bar assembly  12 ′ a first main conductor  14  and a second main conductor  16  which, in the exemplary embodiment, are made of copper, although other suitable conductive materials, such as other metals, may also be used. In Addition, a plurality of plated insulator members  18  as described elsewhere herein are provided in between first main conductor  14  and second main conductor  16 . In the illustrated embodiment, four plated insulator members  18 A,  18 B,  18 C and  18 D are provided in between first main conductor  14  and second main conductor  16 , although more or less plated insulator members  18  may also be used within the scope of the present invention. As described elsewhere herein, the conductor layers  22  on each plated insulator member  18  are formed by depositing a conductive material on the respective surface of the plated insulator member  18  and etching that conductive material back from the edge of the associated insulator element  20  so that overhanging insulator portion  32  comprising a plurality of overhanging insulator portions  30  will be formed when bus bar assembly  12 ′ is assembled. In the exemplary embodiment, bus bar assembly  12 ′ is assembled by sandwiching plated insulator members  18 A,  18 B,  18 C,  18 D between first and second main conductors  14 ,  16  using, for example, a non-conductive clamp or bracket, although other suitable affixation methods (e.g., an adhesive) may also be employed. Overhanging insulator portion  32  comprising the plurality of overhanging insulator portions  30  will increase the surface path distance between first and second main conductors  14 ,  16  and, depending on the amount of etching selectively performed, enable bus bar assembly  12 ′ to satisfy the creepage distance requirements of the application for which it is being made. 
         [0024]    While preferred embodiments of the invention have been described and illustrated above, it should be understood that these are exemplary of the invention and are not to be considered as limiting. Additions, deletions, substitutions, and other modifications can be made without departing from the spirit or scope of the present invention. Accordingly, the invention is not to be considered as limited by the foregoing description but is only limited by the scope of the appended claims.