Abstract:
A method for handling a stator bar at a braze station including lifting the stator bar from a platform, wherein the stator bar is in a substantially horizontal orientation on the platform; turning the stator bar from the horizontal orientation to an orientation at least 45 degrees off horizontal; aligning an upper end of the bar with a brazing station and positioning a lower end of the bar in a pit; turning the bar to reverse positions of the ends of the bar, and returning the stator bar to a horizontal orientation.

Description:
RELATED APPLICATIONS 
       [0001]    This application is a divisional of application Ser. No. 11/159,334 (now U.S. Pat. No. 7,735,211), filed Jun. 23, 2005 and claims the benefit of U.S. Provisional Application Ser. No. 60/628,931, filed Nov. 19, 2004, which applications are incorporated in their entirety by reference herein. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates to large stator bars that are used in power and industrial generators, handling these bars before they are installed in a stator, and fitting header clips to the bars during assembly. 
         [0003]    Stator bars are typically large, long and heavy, e.g., 35 feet long and hundreds of pounds (lbs.). The bars are generally straight and extend the length of a stator. When seated in a stator, the straight sections of the stator bars form a cylindrical array around a rotor. The ends of the stator bars extend axially from opposite ends of the stator. The end portion of the stator bars extend from the ends of the stator and are curved to form end turns. The ends of stator bars are connected through copper or stainless steel fittings and water-cooled connections to form continuous hydraulic winding circuits. 
         [0004]    The ends of the bars are each connected to a hydraulic header clip. The hydraulic header clip serves as an electrical and a cooling flow connection for the armature winding bar. The hydraulic header clip is a hollow connector that includes an enclosed chamber for ingress or egress of a cooling liquid, typically deionized water. At one open end, the clip encloses the ends of the copper strands of the armature winding bar. 
         [0005]    A braze alloy bonds the end sections of the strands to each other and to the hydraulic header clip. A hydraulic header clip fitted to the end of the stator bar is brazed to the bar. The bar is preferably held vertically during the braze operation. 
         [0006]    To hold the bar vertically there is a need for a braze station that can accommodate a long stator bar in a vertical position. There is also a need for supports that can position a stator bar vertically in a braze station and rotate the stator bar from a horizontal position to a vertical position. In the past, stator bars have been positioned vertically while the clip is brazed. Buildings with very high roofs and brazing workstations elevated above the vertical end of a stator bar have been required for brazing vertical stator bars. These high roof buildings and elevated workstations are expensive to construct. There is long-felt need for facilities for brazing stator bars that are advantageous, e.g., less expensive to construct, then prior facilities. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0007]    A stator bar facility is disclosed including: a stator bar workstation; an in-ground pit below the workstation; a stator bar elevator extending from the workstation pit, and a coupling mechanism attached to the elevator, wherein the coupling mechanism further comprises a rotational mount to receive at least one stator bar, wherein the rotational mount enables the received stator bar to be turned from a substantially horizontal position to a substantially vertical position. 
         [0008]    In another embodiment, the stator bar brazing facility includes: an in-ground pit below the workstation; an elevated bridge spanning the in-ground pit; a stator bar braze station and coupled to the bridge; a stator bar elevator extending from the workstation pit, wherein said elevator further comprises an extendible arm, and a coupling mechanism attached to the arm of the elevator, wherein the coupling mechanism further comprises a rotational mount to receive at least one stator bar and is adapted to rotate the stator bar in a substantially vertical plane. 
         [0009]    A method for handling a stator bar at a braze station is also disclosed, where method comprises: lifting the stator bar from a platform, wherein the stator bar is in a substantially horizontal orientation on the platform; rotating the stator bar from the horizontal orientation to a substantially vertical orientation; positioning a upper end of the bar in alignment with a brazing station and a lower end of the bar in a pit; rotating the bar to reverse positions of the ends of the bar; and returning the stator bar to a horizontal orientation. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a schematic illustration of a liquid-cooled stator winding arrangement illustrating the stator, stator bars and hydraulic header clips coupled to inlet and outlet coolant headers. 
           [0011]      FIG. 2  is a perspective view of the end of an armature winding bar showing the tiered rows of hollow and solid strands, and interleaving sheets of braze material. 
           [0012]      FIG. 3  is a perspective exploded view of the end of an armature winding bar inserted into a hydraulic header clip, with braze material and a clip cover shown to the side of the clip. 
           [0013]      FIGS. 4 ,  5  and  6  are side, end and top views, respectively of a braze station for attaching end clips to winding bars. Line  4 - 4  in  FIG. 6  indicates the view shown in  FIG. 4 . Line  5 - 5  in  FIG. 6  indicates the view shown in  FIG. 5 . 
           [0014]      FIG. 7  is a top view of a braze station illustrating the loading of stator bars on the stator bar transport in the workstation pit. 
           [0015]      FIG. 8  is a side view of the braze station showing the stator bar transport extended to receive a stator bar from a loading station. 
           [0016]      FIG. 9  is a top view of the braze station showing the transport moving the stator bar over the pit. 
           [0017]      FIG. 10  is an end view of a braze station showing the stator bar turned to vertical position and being moved into position for brazing. 
           [0018]      FIG. 11  is an end perspective view of a cradle for holding stator bars in the braze station. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0019]      FIG. 1  illustrates a liquid-cooled stator bar arrangement for a stator in a typical liquid-cooled generator. A stator core  10  has stator core flanges  12  and core ribs  14 . Stator bars  16  (also referred to as armature winding bars) pass through radially extending slots in the stator core and are capped at opposite ends by hydraulic header clips  18  fitted to the ends of the bars. Inlet hoses  22  connect an inlet clip  18  to an inlet coolant header  24 . Outlet hoses  26  connect an outlet clip  18  to an outlet coolant header  28 . Each stator bar forms a half an armature coil. A pair of stator bars linked at their opposite ends form a complete armature coil. Copper or stainless steel fittings  20  connect adjacent ends of the stator bar pairs to form the complete armature coil. 
         [0020]      FIG. 2  is a perspective end view of an stator bar  16  without a hydraulic header clip. The bar is a rectangular array of solid  34  and hollow  36  copper strands.  FIG. 3  is a perspective view of the end of an armature winding bar  16  inserted in a clip  18  with braze strips  30  and a braze sheet  50 . A clip cover  32  is shown to the side of the clip  18 . In  FIG. 2 , the braze strips  30  are interleaved between tiered rows of solid the copper strands  34  and rows of hollow strands  36  of the bar  16 . Just prior to brazing and at the end of the stator bar, braze strips are inserted between the strands  34 ,  36 . In addition, the braze sheets  50  and clip  32  are assembled in the clip  18 . 
         [0021]    The hydraulic header clip  18  (also referred to as a stator bar clip) is formed of an electrically conductive material, such as copper. The clip  18  is hollow and includes a rectangular collar  38  that slides over the outer side surfaces of the end of the armature winding bar  16 . A rectangular slot  39  in the collar receives the end of the armature winding bar and interleaved strips  30  of the braze alloy. The clip cover  32  fits into the matching rectangular slot  39  in the side of the collar  38 . At the other end of the clip  18  is a cylindrical coupling end  40  that is configured to connect to the coolant circuit. 
         [0022]    The pre-braze positioned braze alloy strips extend beyond the ends of the short solid strands. The height of the alloy pre-positioned before brazing is selected so that the braze alloy will entirely melt during the braze process and not flow into the open ends of the extended hollow strands. 
         [0023]    During brazing, the stator bar is held in a vertical position and the end of the bar is horizontal. Melted braze alloy forms a pool over the solid strand ends of the stator bar. After brazing, the braze alloy forms a braze alloy isolation coating over the end of the armature bar (but not the end of the hollow strands). The isolation layer shields the solid strand ends and the joints from the coolant passage in the clip. The braze alloy also bonds the clip to the strands and the strand ends to each other. 
         [0024]      FIGS. 4 ,  5  and  6  are side, end and top views, respectively, of a braze station  90  for vertically brazing stator bars. The braze station  90  includes a pit  91 , a bridge  92  over the pit and a stator bar elevator  94  extending form the bottom of the pit  91  to the bridge. The in-ground pit  91  provides a large volume within which to reposition stator bars, e.g., to rotate the bar in a vertical plane while the center of the bar is at the level of the bridge  92 . The in-ground pit may have a depth of twelve (12) feet, a length of forty (40) feet and a width of thirty-two (32) feet (which is about the length of a stator bar). The dimensions disclosed herein are exemplary and a braze station may be designed with different dimension for a particular application of stator bars. The dimensions of the in-ground pit may be sufficient to allow a stator bar to be rotated about its center, where the bar center is at the elevation of the bridge and is generally aligned with the mid-point of the bridge length. 
         [0025]    Within the in-ground pit  91  is a deep pit  96  that is vertically aligned generally with the braze workstation  95  and the mid-point of the bridge  92 . The deep pit  96  may be cylindrical. The deep pit allows the stator bars to be lowered vertically until the upper end of the bar is level with the workstation. For example, the deep pit  96  may have a bottom that is below the bridge a distance equal to the length of a stator bar e.g., thirty-one and one-half feet, and the depth below ground level of twenty-three and one-half feet. The expense of excavation of the in-ground pit  91  and deep pit  96  is minimized by limiting the horizontal cross section of the deep pit  96  to an area sufficient to raise and lower a vertical stator bar and limiting the in-ground pit  91  to a depth sufficient to allow the stator bar to rotate about the upper limit of the distance traversed by the elevator  94 . 
         [0026]    The vertical braze station  90  may be in a factory bay with a roof that has sufficient less clearance, e.g., twenty-five feet, for handling of stator bars, such as to allow for a crane ceiling height. The bridge  92  in the station may be elevated to reduce the needed excavation depths of the pits  91 ,  96 . The bridge  92  has workstations  95  to allow technicians to braze the ends of the stator bars which are held vertically within the pit. Associated with the bridge are brazing hoods and other equipment (not shown) needed to braze the hydraulic clips to the end of the stator bars. The stator bars are stored horizontally on storage platforms  98  on either or both sides of the pit  91 . The platforms are substantially horizontal, but may be on a slight incline such as up to 10 degrees from horizontal. The bars may be mounted on cradles  110  ( FIG. 13 ) at the platforms. 
         [0027]    An elevator  94  in the pit and adjacent the bridge holds the stator bars while they are in the pit. Instead of an elevator, a crane or other stator bar handling mechanism may be used to move the stator bar from a platform  98  to the pit, and to rotate the bar so that it may be aligned with a workstation. The stator bars are supported by a cradle  110  that is latched to the elevator  94 . One cradle may hold a pair of stator bars. The elevator  94  moves the stator bars with respect to the workstations  95  and storage platforms  98 . The elevator moves the stator bars and cradle between the storage platforms  98  and the workstations, and turns the stator bars between horizontal and vertical positions. The elevator may comprise a pair of vertical rails  99  in a frame that is mounted over the deep pit  96  and sits on the floor of the shallower pit  91 . An electric motor  101  drives the elevator  94  up and down the rails  99  and thereby raises and lowers the cradle  110  and stator bars. In addition, the motor  101  may rotate the cradle in a vertical plane. 
         [0028]      FIG. 7  is a schematic top view showing the loading of a stator bar  100  and cradle  110  from the loading platform  98  to the elevator  94 . A dash line through the bridge shows the elevator  94  underneath the bridge. A workman  102  stands at the workstation  95  that moves up and down. As shown in  FIG. 7 , the workman  102  may be at the same level as are other work persons  103  on the bridge. In contrast,  FIG. 10  shows that the workstation  95  may move vertically to better position the workman and the braze hood  106  with respect to the end of the stator bar. 
         [0029]    As shown in  FIG. 8 , the elevator  94  extends its arm  104 , e.g., telescoping arm, outward to grasp a cradle  110  with one or more stator bars from the loading platform  98 . The arm has on a distal end a coupling and latching mechanism  105 , which may be a pair of fingers that grasp a connection on a cradle holding the stator bars. The latching mechanism further comprises a rotational attachment that enables the stator bar and its cradle to be rotated in a vertical plane about the distal end of the elevator arm  104 . 
         [0030]    The stator bars  100  are in a horizontal position as they are moved from the storage platform  98  to the pit  91 . The elevator  94  raises the cradle and its stator bars and turns the cradle and bars to a vertical orientation. Raising the stator bars allows the cradle and stator bars to be lifted off the platform. The vertical stator bars are lowered so that their upper ends are within reach of the workstation  95 . The workstation  95  may be raised or lowered and moved to the left or right (parallel to the bridge) to be properly positioned with respect to the stator bar ends. In addition, the elevator arm  104  may retract or extend the bars  100  (in a direction perpendicular to the bridge) to assist in positioning the bars with respect to the workstation. The braze station may provide six degrees of motion to position the ends of the stator bars in the braze hood. The six degrees are: up-down of bars and workstation, forward-back of bars, left-right of workstation. 
         [0031]    The workstation may include a braze housing  106  that is used to heat and braze the end of the stator bar to the clip. At the workstation  95 , the upper ends of the stator bars are mounted in the brazing hood  106  where the clip is brazed to the stator bar. The workstation  95  may be raised or lowered (compare  FIGS. 8 and 10 ) to orient the workstation to the best position with respect to the end of the stator bar. Once the clips have been brazed to the stator bars, the elevator arm  104  extents the stator bars and rotates them 180° (see circular arcs in  FIG. 4 ) to bring the opposite ends of the stator bars up to the workstation  95 , as is shown in  FIGS. 9 and 10 . When both ends of the stator bars have been brazed with hydraulic clips, the elevator  94  turns the stator bars to a horizontal position and the arm  104  extends to move the stator bars and cradle back to the loading platform  98 . 
         [0032]      FIG. 11  is a perspective end view of a stator bar cradle  110  and with two stator bars  100  mounted thereon. The cradle  110  is a rectangular frame having longitudinal beams and crossbeams that provide a rigid support for the stator bars. The stator bars may be loaded on the cradle at the platform  98  adjacent the braze station  90 . 
         [0033]    A stator bar holding cradle  110  secures a stator bar as the hydraulic header end clips are attached to the bar. The cradle is a protective device to avoid direct handling of the bars and avoid damage to the bars. In addition, the cradle serves as an interface to the elevator  94  to ensure an engagement for multi-positional handling by the elevator. The stator bar holding cradle  110  provides multi-positional handling of the stator bar. The cradle has at least three and preferably six degrees of freedom restraints on the bar for vertical position operation. 
         [0034]    The restraint system for the cradle  110  comprises angle adjustable two side-clamping grippers  112  arranged in an array along the length of the cradle. There may be for example six stator bar grippers  112  spaced evenly along the length of the cradle to grasp the straight section of a stator bar. These grippers are arranged lengthwise along the stator bar sled and are pivotably attached to the sled. The pivoting movement allows the grippers to adjust for slight bowing and other variations in the stator bar. The clamp grippers  112  grasp the straight section of a stator bar  100 . At each end turn section of the bar are two adjustable arms with end-turn clamp grippers  114  to grasp the end turns. The end adjustable grippers  114  have hydraulic expandable arms  116  that are adjusted to fit different bar arm lengths. The cradle  110  has a 90-degree (perpendicular) dual pin coupling system  118  to securely engage with a cradle connector, e.g., a pair of fingers, on the elevator  94 . 
         [0035]    The dual pin handling engagement and locking mechanism  188  may be at the center of the cradle. The dual pin mechanism may be a bracket of a pair of rectangular tubes that receive fingers from the elevator. The fingers engage the rectangular tubs and are locked to the tubes so that the cradle is securely attached to the elevator  94 . 
         [0036]    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.