Patent Publication Number: US-6218926-B1

Title: Reactor and transformer core assembly

Description:
FIELD OF THE INVENTION 
     The present invention relates to reactor and transformer cores and specifically to assembly of the laminated core. 
     BACKGROUND OF THE INVENTION 
     The construction of large reactor and transformer cores has been a time and labor intensive task due to the clamp fixturing, lamination alignment, temporary assembly, clamp welding and final assembly which has been required in the assembly process when assembling larger transformers in the 100 KVA to 5,000 KVA power range. The weight of the cores of these transformers ranges from 1000 pounds to more than 15,000 pounds and therefore requires an extremely strong clamp. The core laminations are supported and held in position by clamps, one on each side of the core. It has been the practice to make the clamp from sections of structural steel channel or a combination of structural steel channels and structural steel angles. Structural channels and angles are commercially available in standard sizes. The sizes of structural channels and angles selected for making the clamps are generally those with dimensions closest to the width of the core laminations. Therefore, the clamps provide little if any protection to the edges of the core laminations. The core assembly process starts by fixturing each channel section of the first clamp in proper position with respect to the other channel or angle sections of the clamp. The fixturing must be strong enough to maintain the respective positions of each channel or angle section of the clamp during the laying up of the core laminations. The flanges of channel sections are placed down in the fixture such that the core laminations can be laid on the flat surface of the clamp. Angle sections can be positioned such that flanges are either up or down. When channel and angles are used together, tie straps, which provide a means for alignment and attachment, are welded to each end of the channels. This is done as a subassembly process before core assembly is started. Alignment pins are placed in holes provided in the channels or angles for threaded fasteners used during final assembly of the core. The alignment pins are smooth and slightly smaller in diameter than the threaded fasteners used for final assembly. Each of the many lamination layers of the core consist of thin (5-15 mills thick) segments of magnetizable metal, each individually slidably placed on the alignment pins. Each lamination segment has mitered ends which must be positioned with respect to the adjacent mitered end of the other lamination segments of that layer and with respect to the position of the mitered ends of the previously laid lamination layer segments. After the final core laminations are placed on the stack, the channel and angle sections making up the second clamp are positioned on top of the core stack. A final alignment of the core laminations and clamps is completed and the core assembly is temporarily secured by strapping or banding placed around each leg of the core. Lifting eyes are attached to the clamps and the core assembly is lifted to the upright position. The alignment pins are removed and threaded fasteners installed and tightened. The core assembly is then moved to a welding station where the channel and/or angle sections forming each of the first and second clamps are welded together. After welding, the core assembly is moved to a final assembly area where the coil and various electrical connectors and brackets are installed. Assembling a reactor or transformer core by this method is extremely time consuming and labor intensive. Therefore, it would be desirable to eliminate many of these steps to reduce time and labor cost. 
     SUMMARY OF THE INVENTION 
     The present invention provides a solution to the extensive clamp fixturing, lamination alignment, temporary assembly, clamp welding and final assembly steps that have been required in assembling large reactor and transformer cores. The present invention provides a single piece flanged clamp for each side of the laminated core. The flanged clamps are made from sheet or plate steel and can be easily manufactured by conventional sheet metal tooling methods or by computer numeric controlled (CNC) machines and industrial robots. The manufacturing process includes the steps of punching the coil window, the hardware assembly holes, lifting holes, coil bracket mounting holes and flange notches, forming the flanges and welding the corners of adjacent flanges. Manufacturing the flanged clamp from one piece of sheet or plate steel permits the width of the side legs, top leg, bottom leg and the depth of the flanges to be selectively controlled. This permits the side, top and bottom legs to extend out past the edges of the core laminations for better protection. Extending the flanges of the bottom legs provides a more stable platform for the core assembly and can include holes for permanent mounting of the core assembly. Since each flanged clamp is of one piece construction, no assembly fixturing is required. Using a one piece flanged clamp on each side of the core assembly improves the alignment of core laminations, which in turn results in better performance and reduced noise. Core construction is accomplished by placing the first flanged clamp on a generally flat surface such that the edges of the outwardly facing flanges are in contact with the generally flat surface. In this position, the generally flat surface of the flanged clamp forms a horizontal plane on which the core laminations are stacked. Alignment pins are then placed in the holes provided for final assembly fasteners, thus allowing the flanged clamp to serve as a fixture for laying up the core laminations. Each segment of the core lamination is slidably positioned on the alignment pins. After the desired number of laminations have been stacked on the first flanged clamp, the second flanged clamp is positioned on top of the core and the alignment pins are removed. Final assembly fasteners are then placed in the holes previously occupied by the alignment pins and tightened such that the two flanged clamps and the intermediate core laminations are tightly secured together. The core is then completely assembled and can be moved to the upright position for inserting the coil and making final wiring connections. The one piece flanged clamp and construction method of the present invention, as described above, can also be used in the construction of large liquid filled, wound core transformers. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 a front view of a typical core assembly of the prior art. 
     FIG. 2 a side view of a typical core assembly of the prior art. 
     FIG. 3 is an exploded view of the core assembly of FIGS. 1 and 2. 
     FIG. 4 is a front view of a core assembly constructed in accordance with the present invention. 
     FIG. 5 is a side view of a core assembly constructed in accordance with the present invention. 
     FIG. 6 is an exploded view of the core assembly of FIGS. 4 and 5. Before one embodiment of the invention is explained in detail, it is to be understood that the invention is not limited in its application to the details of construction in the description or as illustrated in the drawings. The invention is capable of other embodiments and of being practiced or being carried out in various other ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. 
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
     FIG. 1 illustrates a core assembly generally indicated by reference numeral  10  of the prior art as used in larger transformers of the 100 KVA to 5,000 KVA power range. These core assemblies  10  range in weight from 1000 pounds to more than 15,000 pounds. Two clamp assemblies  14 , constructed of a combination of structural channels  18  and structural angles  22  provide structural support and protection for the core assembly  10  and a coil (not shown) to be installed within a coil window  26  defined by the clamp assemblies  14 . One clamp assembly  14  is placed on each side of the core assembly  10  during construction. The channels  18  form the generally vertical side legs  28  of each clamp assembly  14  and the angles  22  form the generally horizontal top  30  and bottom  34  of each clamp assembly  14 . A tie strap  38  is welded to each end of each channel  18 . Each tie strap  38  includes a hole  42  for receiving assembly hardware  46  such as a threaded rod and nuts, which are used during final assembly to secure the core assembly  10 . Other assembly hardware holes  50  are provided in each channel  18  and each angle  22  for receiving assembly hardware  46  during final assembly. 
     Referring now to FIG. 2, it can be seen that a number of core laminations  54  are sandwiched between the two clamp assemblies  14 . These core laminations  54  are supported and held in position by the two clamp assemblies  14 . In this construction of the core assembly  10 , flanges  58  of the angles  22  are turned inward over the core laminations  54 , and flanges  62  of the angles  22  are generally parallel with the core laminations  54 . This provides some protection for the core laminations but also makes for an unstable core assembly  10 , since the ratio of the width of the core assembly  10  to the height of the core assembly  10  is small. Therefore, the core assembly  10  is susceptible to being tipped over. To prevent this from occurring and to provide a mounting bracket for the core assembly, one or more mounting feet  66  are provided. Each mounting foot  66  is welded to the bottom  34  of the two clamp assemblies  14  during final assembly. Z-shaped coil mounting brackets  70  and lifting pads  74  (best seen in FIG. 1) are welded to the top  30  of each clamp assembly  14  at final assembly or during a prior sub assembly operation. 
     Referring now to FIG. 3, the steps of assembling the core assembly  10  will be discussed in greater detail. The assembly process starts by securely fixturing each channel  18  and each the angle  22  of one of the two clamp assemblies  14  in its proper position with respect the other channel  18  and angle  22  of that clamp assembly  14 . The fixturing means (not shown) must be strong enough to support the weight of the core assembly  10  and maintain the respective positions of each channel  18  and angle  22  of the clamp assembly  14  during the laying up of the core laminations  54 . The channels  18  are placed in the fixture such that their generally flat surfaces  78  face upward. In this example the angles  22  are positioned such that normally horizontal flanges  58  extend upward and the normally vertical flanges  62  are generally parallel with the flat surfaces  78  of the channels  18 . The holes  42  in the tie straps  38  are aligned with holes  82  in the angles  22  for general position alignment between the channels  18  and angles  22 . After fixturing of the channels  18  and angles  22  has been completed, alignment pins  86  are placed in at least one of the assembly hardware holes  50  of each channel  18  and angle  22 . The alignment pins  86  are smooth and slightly smaller in diameter than the threaded fasteners  46  used for final assembly. The core lamination  54  is made up of the many lamination layers  90  each having four thin (5-15 mills thick) lamination segments  94  of magnetizable metal. The first layer  90  of core laminations  54  is laid on the flat surfaces  78  of the channels  18  and the flanges  62  of the angles  22 , one segment  94  at a time. Each lamination segment  94  has mitered ends  98  which must be positioned with respect to the adjacent mitered end  98  of the other lamination segments  94  of that layer  90  and with respect to the position of the mitered ends  98  of the previously laid lamination layer  90 . After the final core lamination layer  90  is placed on the core lamination  54 , the channel  18  and angle  22  making up the other of the two clamps  14  are positioned on top of the core lamination  54 . After a final alignment of the core laminations  54  and clamps  14  is completed, the core assembly  10  is temporarily secured by strapping or banding placed around each leg of the core assembly  10 . Lifting eyes  102  are attached to the clamps  14  and the core assembly  10  is lifted to the upright position. The alignment pins  86  are removed and threaded fasteners  46  installed and tightened. The core assembly  10  is then moved to a welding station where the channels  18  and angles  22  forming each of the two clamps  14  are welded together. After welding, the core assembly  10  is moved to a final assembly area where a coil and various electrical connectors and brackets such as the Z-shaped coil mounting brackets  70  and lifting pads  74  are installed. 
     Referring now to FIG. 4, the core assembly of the present invention is shown and generally indicated by reference numeral  106 . A one piece flanged clamp  110  forms each side of the core assembly  106 . The flanged clamps  110  are manufactured prior to starting the assembly of the core assembly  106 . The flanged clamps  110  are manufactured from one sheet or plate of steel (unitized) and can be easily manufactured by conventional sheet metal tooling methods or by computer numeric controlled (CNC) machines and industrial robots. The manufacturing process for each flanged clamp  110  requires the steps of punching the coil window  114 , hardware assembly holes  118 , lifting holes  122  (see FIG. 5) and coil bracket mounting holes  126  (see FIG.  6 ); forming the peripheral flanges  130 ; and welding the comers of the adjacent flanges  130 . Manufacturing the flanged clamp  110  from one piece of sheet or plate steel permits the width of the side legs  134 , top leg  138  and bottom leg  142 , and the depth of the flanges  130  to be selectively controlled. As can be observed when comparing the core assembly  106  of the present invention with the core assembly  10  of FIGS. 1-3, the wider side, top and bottom legs,  134 ,  138  and  142  respectively, provide better protection for the core laminations  144 , shown in dotted lines in FIG.  4 . 
     Referring now to FIG. 5, an end view of the core assembly  106  is shown. Punching the lifting holes  122  in the flanges of the side legs  134  eliminates the need for a welding operation to add lifting eyes  102  of the prior art (see FIG.  1 ). 
     Referring now to FIG. 6, an exploded view of the core assembly  106  is shown. The manufacturing process of a core assembly  106  in accordance with the present invention will be described with respect to FIG.  6 . Core assembly  106  construction is accomplished by placing one of the two flanged clamps  110  on a generally flat surface (an assembly platform, the floor, etc. not shown) such that the edges  146  of the outwardly facing flanges  130  are in contact with the generally flat surface. In this position, the generally flat surfaces  150  of the flanged clamp  110  forms a horizontal plane on which the core laminations  144  are stacked. Alignment pins  154  are then placed in the hardware assembly holes  118  provided for final assembly fasteners  158 , thus allowing the flanged clamp  110  to serve as a fixture for laying up the core laminations  144 . Each segment  162  of the core lamination  144  is slidably positioned on the alignment pins  154 . After the desired number of laminations  144  have been stacked on the flanged clamp  110 , the other of the two flanged clamps  110  is positioned on last core lamination  144  and the alignment pins  154  are removed. Final assembly fasteners  158  are then placed in the hardware assembly holes  118  previously occupied by the alignment pins  154  and tightened such that the two flanged clamps  110  and the intermediate core laminations  144  are tightly secured together. The core assembly  106  is then completely assembled and can be moved to the upright position for inserting a coil and making final wiring connections. 
     It is to be understood that magnetic core construction in accordance with the present invention can be used for both single and three phase cores. It is also within the scope of the invention to use the final assembly hardware  158  in place of the alignment pins  154  during assembly. Further, in some applications, alignment pins  154  are not required to maintain alignment of the core lamination segments  162  during assembly.