Abstract:
A distribution transformer having a slot-and-tab core frame assembly. The core frame ( 17 ) encloses a transformer core ( 11 ) having at least one phase and provides compression on the core yokes and end members of the transformer to bind the assembly together. First and second clamps ( 10, 24 ) of the core frame contain receiving slots ( 34 ) for the tabbed ( 18, 28 ), longitudinal side supports ( 20 ), creating an interlock when connected. For larger transformers, the tabbed side supports may be alternatively comprised of a subassembly of end plates, cams, and tabbed locking plates, encompassing a sturdy locking mechanism.

Description:
FIELD OF INVENTION 
       [0001]    The present application is directed to transformers and, more particularly, to supports for cores of transformers. 
       BACKGROUND 
       [0002]    A frame for a core of a distribution transformer serves the purpose of clamping and compressing top and bottom yokes of the core, thereby holding the core together. The construction of a conventional transformer core frame typically involves bolting, welding, or dowel pinning to achieve mechanical interlocking of component members of the core frame. The production of such core frames is costly and labor intensive. Accordingly, there is a need for a new type of core frame that is simpler and easier to produce. The present invention is directed to such an improved core frame. 
       SUMMARY 
       [0003]    The present invention is directed to a distribution transformer with a slot-and-tab interlocking core frame. The core frame encloses a ferromagnetic core having one or more core limbs. The core frame is formed of first and second clamps and side supports. The first clamp of the core frame has two plates positioned parallel to one another and compresses a first yoke of the core. The second clamp of the core frame has two plates positioned parallel to one another and compresses a second yoke of the core. Each of the plates in the first and second clamps has a slot formed in each opposing end portion. 
         [0004]    The side supports of the core frame each have a first and second end portion having tabs extending outwardly from the sides. The core frame is assembled by positioning the tabs of the second end portion of each side support into the receiving slots of the second clamp. The coil assemblies are placed over each core limb and when more than one core limb is present, the outer core limbs and side supports together receive a coil assembly. The tabs of the first end portion of each side support are placed into the receiving slots of the first clamp and an interlock is created between the clamps and side supports, holding the core frame together. 
         [0005]    For larger transformers, the side supports should be capable of holding more weight. The side supports in heavier transformers may be assembled using locking plates, cams and main plates to strengthen the core frame. The locking plates have holes formed near the center. The main plate has holes formed near each opposing end. Each side support has two locking plates fastened to a main plate using four cams. Each cam has two circular ends with different circumferences. The cam ends having a larger circumference are placed into the main plate openings. The cam ends having a smaller circumference are placed into the locking plate openings. The cams fasten the locking plates to the main plate to form an assembled side support. 
         [0006]    Once assembled, the side supports of the strengthened core frame have two tabs extending outwardly from each opposing edge and therefore, the first and second plates each have two corresponding slots on each opposing end to receive the tabs. The core frame is assembled by positioning the tabs of the second ends of the side supports into the corresponding receiving slots of the plates of the second clamp. The coil assemblies are placed over each core limb and when more than one core limb is present, the outer core limbs and side supports together receive a coil assembly. The tabs of the first ends of the side supports are placed into the corresponding receiving slots of the plates of the first clamp, and an interlock is formed, binding the core frame together. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    In the accompanying drawings, structural embodiments are illustrated that, together with the detailed description provided below, describe exemplary embodiments of a distribution transformer having a slot-and-tab interlocking core frame. One of ordinary skill in the art will appreciate that a component may be designed as multiple components or that multiple components may be designed as a single component. 
           [0008]    Further, in the accompanying drawings and description that follow, like parts are indicated throughout the drawings and written description with the same reference numerals, respectively. The figures may not be drawn to scale and the proportions of certain parts may have been exaggerated for convenience of illustration. 
           [0009]      FIG. 1  is a front perspective view of a first distribution transformer having a first core frame constructed in accordance with a first embodiment of the present invention; 
           [0010]      FIG. 2  shows a front view of the first distribution transformer, with the coil windings removed and a portion of the core in phantom; 
           [0011]      FIG. 3  is a side view of one of the side supports of the first core frame; 
           [0012]      FIG. 4  is a side view of the first distribution transformer of  FIG. 2  showing the connection between the tabs of one of the side supports and clamps of the first core frame; 
           [0013]      FIG. 5  is a front perspective view of a second distribution transformer having a second core frame constructed in accordance with a second embodiment of the present invention; 
           [0014]      FIG. 6  is a front view of the second distribution transformer, having the coil windings removed and a portion of the core in phantom; and 
           [0015]      FIG. 7  is a side view of the second distribution transformer of  FIG. 6 , showing an assembled side support of the core frame, the side support comprising a main plate, cams and locking plates. 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    In the present invention, slot-and-tab interlocking replaces the labor-intensive aspects of bolting or welding and results in less production time required for core frame assembly. The present invention also reduces the number of pieces required in the assembly. The slot-and-tab interlocking mechanism is useful in smaller, lower weight transformers, whereas an embodiment of the slot-and-tab transformer core frame utilizing a support member subassembly having main plates, cams, and locking plates is preferred in larger, heavier transformers. Lower cost and less labor in frame assembly are the major objectives of this invention. 
         [0017]    The present invention is directed to a distribution transformer  15 ,  50  having a core  11  supported by an improved core frame  17  of the present invention. The distribution transformer  15 ,  50  may be single phase or poly-phase (e.g. three phases). In addition, the distribution transformer  15 ,  50  may be dry or fluid-filled. If the distribution transformer  15 ,  50  is fluid-filled, the distribution transformer includes a tank filled with a dielectric fluid in which the core and the core frame are disposed. The core  11  of the distribution transformer  15 ,  50  is comprised of thin, stacked laminations of magnetically permeable material, such as grain-oriented silicon steel or amorphous metal. The laminations are typically arranged in stacks such that the core has one or more legs or limbs disposed vertically between a pair of yokes disposed horizontally. In a three-phase transformer, the core limbs and yokes typically connect to form a pair of core windows. A coil assembly  32  is disposed around each core limb, and comprises primary and secondary coil windings. The primary and secondary coil windings are often arranged concentrically along the length of the core limbs. Alternatively, the primary and secondary windings may be mounted one above the other along the length of each core limb. The windings  32  fill the core window as completely as possible without allowing the contact of adjacent windings. The transformer core is enclosed within the core frame. 
         [0018]    Referring now to  FIG. 1 , there is shown a first distribution transformer  15  constructed in accordance with a first embodiment of the present invention. The first distribution transformer  15  has a first core frame  17  that is comprised of first and second clamps  10 ,  24  and first and second side supports  20 ,  26 . The first and second clamps  10 ,  24  and the first and second side supports  20 ,  26  may be constructed from a different material than the core  11 . For example, the first and second clamps  10 ,  24  and the first and second side supports  20 ,  26  may be comprised of regular, non-electrical grade carbon steel, which has different magnetic properties than grain-oriented silicon steel or amorphous metal. The first clamp  10  of the first core frame comprises a pair of first plates  12 , each of which has opposing end portions. A receiving slot  34  is formed in each of the end portions. The first plates  12  are positioned parallel to one another, one on each side of a first yoke  16  of the core  11 . The first clamp  10  contacts and compresses the first yoke  16  of the core, as shown in  FIG. 1 . 
         [0019]    The second clamp  24  of the first core frame  17  comprises a pair of second plates  14 , each of which has opposing end portions. A receiving slot  34  is formed in each of the end portions. The second plates  14  are positioned parallel to one another, one on each side of a second yoke  30  of the core  11 . The second clamp  24  contacts and compresses the second yoke  30  of the core. 
         [0020]    Referring now to  FIG. 2 , a front view of the first core frame  17  is shown with the coil windings  32  removed and a portion of the core  11  in phantom. The first and second plates  12 ,  14  have receiving slots on each opposing end and surround the first and second yokes  16 ,  30 , respectively. The core limbs  38 ,  40 ,  42  are disposed between the yokes  16 ,  30 . In order to maintain the compression of the first and second clamps  10 ,  24  on the core  11 , the first and second plates  12 ,  14  have holes  44  to receive bolts, dowel pins or welded pieces. 
         [0021]    The first core frame has a first side support  20  and a second side support  26  as previously described. Referring now to  FIG. 3 , a side support  20  or  26  is shown in detail having first tabs  18  and second tabs  28 . Each side support has opposing side edges and opposing first and second end portions. The first end portion of each side support has first tabs  18  extending outwardly from the side edges. The second end portion of each side support has second tabs  28  extending outwardly from the side edges. 
         [0022]    The first core frame is assembled by placing the second tabs  28  of the first and second side supports  20 ,  26  into the receiving slots  34  of the second plates of the second clamp, compressing the second yoke  30  of the core. The coil assemblies  32 , comprised of primary and secondary windings, are placed over the core limbs  38 ,  40 ,  42 . As shown in  FIG. 1 , the outer core limbs  38 ,  42  and side supports  20 ,  26  make contact and together receive coil assemblies. The first tabs  18  of the first and second side supports are placed into the receiving slots  34  of the first plates  12  of the first clamp, compressing the first yoke  16  of the core. Referring now to  FIG. 4 , a side view of the connection between the tabs  18 ,  28  of a side support and the slots  34  of the clamps is shown. 
         [0023]    Referring now to  FIG. 5 , there is shown a second distribution transformer  50  constructed in accordance with a second embodiment of the present invention. The second distribution transformer has a second core frame  55  that is comprised of first and second clamps  54 ,  62  and first second side supports  51 ,  53 . The first and second clamps  54 ,  62  and the first and second side supports  51 ,  53  may be constructed from a different material than the core  11 , in the same manner as described in the first distribution transformer  15 . The first clamp  54  of the second core frame  55  comprises a pair of first plates  52 , each of which has opposing end portions. Two receiving slots  64  are formed in each of the end portions. The first plates  52  are positioned parallel to one another, one on each side of the first yoke  16 . The first clamp  54  contacts and compresses the first yoke  16  of the core  11 , as shown in  FIG. 5 . 
         [0024]    The second clamp  62  of the second core frame  55  comprises a pair of second plates  58 , each of which has opposing end portions. Two receiving slots  64  are formed in each of the end portions. The second plates  58  are positioned parallel to one another, one on each side of the second yoke  30 . The second clamp  62  contacts and compresses the second yoke  30  of the core  11 . 
         [0025]    The second core frame  55  has two side supports, a first side support  51  and a second side support  53  as shown in  FIG. 5 . The side supports  51 ,  53  of the second core frame  55  are each comprised of first and second locking plates  59 ,  60  connected to a main plate  66 . The side supports  51 ,  53  are assembled by connecting the main plate  66  to the first and second locking plates  59 ,  60  using cams  56 , each having circular ends of different circumferences. A first end of each cam  56  has a larger circumference than a second end. The main plate  66  has opposing end portions wherein at least two openings  70  are formed in each end portion for receiving the first end of the cams  56 . Each of the locking plates  59 ,  60  has at least two openings  68  formed near the center for receiving the second end of the cams  56 . The cams  56  fasten the locking plates  59 ,  60  and main plate  66  together to form a side support. After assembly, the side supports  51 ,  53  of the second core frame have two opposing end portions with two tabs extending from each side edge, resulting in a first end portion having four first tabs  72  and a second end portion having four second tabs  74 . 
         [0026]    Referring now to  FIG. 7 , a side view of a side support  51  or  53  is shown, having first and second locking plates  59 ,  60  fastened to a main plate  66  using four cams  56 . As the weight of the transformer increases, it may be necessary to increase the number of cams on each end of the first and second side supports to three or four. The increased contact surface area provided by adding additional cams may result in a sturdier interlock for the core frame. In the same manner, the number of tabs  72 ,  74  on each side edge of the first and second ends of the side supports  51 ,  53  and the corresponding number of slots  64  formed in each opposing end of the first and second plates  52 ,  58 , may be increased as the weight of the transformer increases. 
         [0027]    The second core frame  55  is assembled by placing the four second tabs  74  of the first and second side supports  51 ,  53  into the receiving slots  64  of the second plates  58  of the second clamp  62 , compressing the second yoke  30  of the core  11 . The coil assemblies  32 , comprised of primary and secondary windings are placed over the core limbs  38 ,  40 ,  42 . As shown in  FIG. 5 , the outer core limbs  38 ,  42  and side supports  51 ,  53  make contact and together receive the coil assemblies  32 . The four first tabs  72  of the assembled first and second side supports  51 ,  53  are placed into the receiving slots  64  of the first plates  52  of the first clamp  54 , compressing the first yoke  16  of the core  11 . 
         [0028]    While the present application illustrates various embodiments of a distribution transformer having a slot-and-tab interlocking core frame, and while these embodiments have been described in some detail, it is not the intention of the applicant to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. Therefore, the invention, in its broader aspects, is not limited to the specific details, the representative embodiments, and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the spirit or scope of the applicant&#39;s general inventive concept.