Abstract:
A contact arrangement is provided, e.g. of the type that functions as a wiping contact for a moving contact such as a pivotally mounted switch blade in an electrical power distribution switch. The contact arrangement in an illustrative embodiment includes spaced apart contact members that are biased toward each other to define predetermined contact pressure/force characteristics with respect to the interposed moving contact. The contact members in a preferred embodiment include predetermined contact areas and predetermined structural features to minimize deformation due to magnetic forces experienced in the presence of high currents. The structural features are also arranged to define current paths that increase the contact pressure. In a particular embodiment the contact areas are formed on the contact members so as to minimize the size of the moving contact.

Description:
[0001]    This application claims the benefit of U.S. Provisional Application No. 60/190,652 filed on Mar. 20, 2000. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates generally to electrical switch contact arrangements and power distribution switches and more particularly to an improved wiping contact arrangement for use with a pivotally mounted switch blade.  
           [0004]    2. Description of Related Art  
           [0005]    Various switches and operating mechanisms are shown in the following U.S. Pat. Nos.: 2,918,556, 3,563,102; 3,676,629; 3,845,433; 4,169,973; 4,293,834; 4,398,072, 4,484,046; 5,140,117; 5,224,590; 5,504,293 and 5,772,009. For example, these patents disclose various stationary and wiping contact arrangements. While these contact arrangements may be generally suitable for their intended use, it is always desirable to provide simplified structures with improved operating characteristics.  
         SUMMARY OF THE INVENTION  
         [0006]    Accordingly, it is a principal object of the present invention to provide an improved contact arrangement for electrical switches having improved operating characteristics.  
           [0007]    It is another object of the present invention to provide a wiping contact arrangement for a moving contact with improved contact pressure during high currents.  
           [0008]    These and other objects of the present invention are achieved by a contact arrangement, e.g. of the type that functions as a wiping contact for a moving contact such as a pivotally mounted switch blade in an electrical power distribution switch. The contact arrangement in an illustrative embodiment includes spaced apart contact members that are biased toward each other to define predetermined contact pressure/force characteristics with respect to the interposed moving contact. The contact members in a preferred embodiment include predetermined contact areas and predetermined structural features to minimize deformation due to magnetic forces experienced in the presence of high currents. The structural features are also arranged to define current paths that increase the contact pressure. In a particular embodiment the contact areas are formed on the contact members so as to minimize the size of the moving contact. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0009]    The invention, both as to its organization and method of operation, together with further objects and advantages thereof, will best be understood by reference to the specification taken in conjunction with the accompanying drawing in which:  
         [0010]    [0010]FIG. 1 is a front elevational view of a switch utilizing a contact arrangement in accordance with the principles of the present invention;  
         [0011]    [0011]FIG. 2 is a view, partly in section, taken generally along the line  2 - 2  of FIG. 1;  
         [0012]    [0012]FIG. 3 is a perspective view of the contact arrangement of FIGS. 1 and 2;  
         [0013]    [0013]FIG. 4 is a front elevational view of the contact arrangement of FIG. 3;  
         [0014]    [0014]FIG. 5 is a front elevational view of a contact member of the contact arrangement of FIGS. 3 and 4;  
         [0015]    [0015]FIG. 6 is right-side elevational view of the contact member of FIG. 5;  
         [0016]    [0016]FIG. 7 is a top plan view of the contact member of FIG. 5; and  
         [0017]    [0017]FIG. 8 is an enlarged partial view of the contact member of FIG. 6. 
     
    
     DETAILED DESCRIPTION  
       [0018]    Referring now to FIGS. 1 and 2, the contact arrangement of the present invention will be described in conjunction with a power distribution switch  10  that includes multiple switch poles, e.g. three switch-pole assemblies  12 ,  14  and  16  as illustrated in the specific embodiment of FIG. 1. In this specific illustrative embodiment, the three switch-pole assemblies  12 ,  14  and  16  are operable between open and closed positions via pivotally mounted switch blades  18 ,  20  and  22  respectively, the closed position being shown in FIGS. 1 and 2, the open position shown in phantom in FIG. 2 at  18 ′. The switch blades  18 ,  20  and  22  are carried by an operating member  30  that is mounted for pivotal movement about an axis  32  that is substantially horizontal in the illustrative arrangement. Each of the switch-pole assemblies  12 ,  14  and  16  includes a stationary contact assembly  36  having arc-extinguishing capabilities in the specific embodiment where the switch  10  is a load-interrupting switch. The stationary contact assemblies  36  are each supported by an insulator  38  affixed to a frame  40  of the switch  10 . The switch blades  18 ,  20  and  22  are each electrically connected to a respective lower contact terminal  42  via a sliding contact arrangement provided by lower contact assemblies  43  (FIG. 2) carried by the lower contact terminal  42 . The sliding contact feature is also commonly referred to as a wiping contact. The lower contact terminals  42  are supported with respect to the frame  40  at planar portions  45  (FIG. 2) via insulators  44 , for example, lower contact terminals  42   a, b  and  c  supported by respective insulators  44   a, b  and  c.    
         [0019]    The operating member  30  is rotated via a linkage  50  that connects an operating shaft  52  of the operating member  30  to be driven by an operating mechanism  54 . The operating mechanism  54  is a stored energy device that is operated by a handle  56 . The operating member  30  is rotatably mounted at a first end by the operating shaft  52  within a bearing  58 . The opposite end of the operating member  30  includes a cylindrical bearing surface  64  that is pivotally supported at  60  via a support bracket  62  that is affixed to the support insulator  44 . In a specific embodiment, the support bracket  62  is conductive. Thus, in operation, the support bracket  62  is energized at the same potential as the lower contact terminal  42 .  
         [0020]    It has been found desirable to mount the contact assemblies  43  so as to be aligned along the path between the center  32  of the operating member  30  and the base of the support insulators  44 . In that way any movement of the insulators that may be caused by extreme loading results in movement of the contact assemblies  43  more nearly along the circumferential surface contact of the switch blades  18 ,  20  and  22 . For example, different mounting orientations result in movement of the contact assemblies in a direction that tends to separate the contact assemblies from the switch blades  18 ,  20  and  22 .  
         [0021]    In accordance with additional aspects of the present invention, the insulators  44  supporting the operating member  30  are oriented such that their longitudinal axes, e.g.  80 , are aligned with respect to the radial axis  82  of the operating member  30  as seen in FIG. 2 but not directly below the operating member  30 . This orientation provides for preservation of space in the cable termination area, generally referred to at  84  beneath and to the rear of the lower contact terminals  42 , while also simplifying the mounting of the lower contact terminals  42  and the lower contact assemblies  43  to the support insulators  44 . Specifically, this permits mounting of the planar portions  45  of the lower contact terminals  42  and the lower contact assemblies  43  directly to an upper planar surface  86  of the support insulators  44  which simplifies the shape and fabrication of the lower contact terminals  42  and the lower contact assemblies  43  and avoids the need for additional parts to mount these components. As seen in FIG. 2, a lower mounting member  88  of the frame  40 , to which the lower planar surfaces  90  of the insulators  44  are mounted, is tilted or inclined with respect to the generally planar configuration of the switch  10  and the frame  40  and an upper mounting member  92  of the frame  40  to which the upper support insulators  38  are mounted. The generally planar configuration of the switch  10  and the frame  40  are typically arranged vertically for application in metal-enclosed gear.  
         [0022]    Referring now additionally to FIGS.  3 - 8 , the lower contact assemblies  43  include spaced apart contact members  66 ,  68  that define one or more contact gaps, e.g. two contact gaps  75 ,  77  in an illustrative embodiment, via the provision of formed structural protusions  70 ,  72 ,  74  and  76  that are partial, generally spherical convexities in a specific embodiment, the formed structural protusions  70 ,  72 ,  74  and  76  also defining and being referred to as generally circular contact areas. In the illustrative embodiment, the contact members  66 ,  68  are bifurcated at  67  such that the contacts within the contact gaps  75 ,  77  are each independent of the other. The contact members  66 ,  68  are biased toward one another by a biasing arrangement, e.g. a spring member  71 ,  73  in a specific embodiment assembled to each bias a respective contact member  66 ,  68 . For example, in a specific arrangement, the lower contact assembly  43  is assembled via a fastening pin  81 , e.g. a rivet, and a washer  83  being retained under the widened end  85  of the pin  81 . In an illustrative embodiment, each of the spring members  71 ,  73  includes biasing finger members  87 ,  89  that are arranged to respectively bias the contact protusions  70 ,  72 ,  74  and  76 . When assembled, the spring members  71 ,  73  bias the contact members  66 ,  68  so as to provide a predetermined contact force or pressure on the switch blade  18 , e.g. in the range of 20-30 pounds at a contact gap of ⅛ of an inch in a specific embodiment for a medium voltage switch (e.g. rated at 15 or 25 kV, and continuous current of 600 amperes and 20,00 to 40,000 amperes fault closing). This contact arrangement relies on magnetic effects to increase the contact forces or pressures during high current faults. It will be understood to those skilled in the art that not maintaining adequate contact pressure can result in deterioration or destruction of the contact surfaces.  
         [0023]    In accordance with important aspects of the present invention, the contact members  66 ,  68  include structural provisions (described in more detail hereinafter) that strengthen the contact members  66 ,  68  so as to resist deformation due to magnetic forces experienced during high currents. At high currents, magnetic effects increase the contact pressure. However, the forces exerted by the magnetic effects is limited by the strength of the contact members  66 ,  68 . If the contact members are not of sufficient strength, the contact members  66 ,  68  merely bend instead of increasing the force of the contact pressure. On the other hand, if the contact members  66 ,  68  are of sufficient strength, the increased forces are applied uniformly along each contact member  66 ,  68  such that the maximum forces can be applied at the contact gaps  75 ,  77  to increase the contact pressure. Accordingly, bending of the contact members  66 ,  68  is undesirable since it reduces the maximum contact pressure; in extreme cases, the contact members  66 ,  68  being sufficiently deformed to the extent of coming in contact with each other. In a preferred embodiment, these structural provisions also aid in defining the current paths through the contact members  66 ,  68  to the lower contact terminal  42  so as to increase the contact pressure. In a specific illustrative embodiment, the structural provisions include formed structural elements  78 ,  79  that define shapes that depart from the plane of the contact members  66 ,  68  so as to strengthen the contact members  66 ,  68  from bending and the like. It has also been found that these structural elements  78 ,  79  and their placement on the contact members  66 ,  68  increase contact pressure in the contact gaps at  75 ,  77  due to the parallel current paths in the contact members  66 ,  68  in the vicinity of the structural elements  78 ,  79  being closer together (i.e. compared to the absence of the structural elements  78 ,  79  in the directions formed). In accordance with additional aspects of the present invention, the contact protusions  70 ,  72   74  and  76  are formed in a shape that defines the contact surface along the leading or top edge of the contact members  66 ,  68  such that there is minimal space from the center  91  of the contact areas  70 ,  72 ,  74  and  76  to the edge  93  of the contact members  66 ,  68 , this arrangement also being characterized as truncating or cutting back of the generally circular contact areas  70 ,  72 ,  74  and  76 . With this arrangement, the radius of the switch blade  18  may be minimized in that the truncated shape of the contact areas  70 ,  72 ,  74  and  76  permits the contact to be made nearer the center of the switch blade  18  and the operating member  30 , e.g. the axis  32 .  
         [0024]    While there have been illustrated and described various embodiments of the present invention, it will be apparent that various changes and modifications will occur to those skilled in the art. Accordingly, it is intended in the appended claims to cover all such changes and modifications that fall within the true spirit and scope of the present invention.