Abstract:
A method and apparatus for compressing the endplate of an electric generator to relieve the restraining force on a plurality of key blocks that restrain the endplate in compression. The method includes simultaneously applying independent compressive loads at each of the key block locations to the endplate to relieve pressures on the key blocks and removing the key blocks so the endplate can be removed.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention pertains generally to tools for servicing electric generators and more particularly to a tool for removing the endplate from a WESTAC electric generator. 
     2. Related Art 
     Commonly large electric generator stators are made up of a tandem array of iron laminations that are held in compression between endplates. Most generators of that type have through bolts holding the endplates and the laminated core together. The through bolts allow for easy removal and access to the core for field maintenance inspections and servicing. However, WESTAC electric generators, manufactured by Siemens Power Generation, Inc., do not have through bolts. This latter type of electric generators core is held together by 15 key bars or blocks that maintain an endplate in compression against the core laminations. In order to remove the endplate, which is a large Bellville washer, it is necessary to compress and flatten the endplate to relieve the pressure off of the key bars so that they may be removed. The current method of flattening the endplate is by the use of a single four inch by 93 inch diameter plate that weights over 7,000 pounds (3175.14 kg.).  FIG. 1  shows a planned view of a skeleton of an electric generator oriented in the vertical position normally used for stacking the laminations, with the prior art compression plate  12  in place. The compression plate  12  is held in position against the endplate  24  by a first end portion of all thread  14 . All thread  14  passes through the compression plate  12  and extends past the length of the core where it is captured at a second end by a leverage plate  15  that spans the opposite end of the generator frame. A hydraulic jack  20  fits over the all thread  14  and seats against the compression plate  12 . The hydraulic jack  20  is locked in position on the all thread  14  by a jack nut  16  and a thrust washer  18 . The hydraulic jack  20  exerts a compressive force on the endplate  24  through a cast iron spider  22  that extends between the back face of the compression plate  12  and the hydraulic jack  20 . This current system requires the use of a large overhead crane to position the 7000 lb. (3175.14 kg.) compression plate. In addition, it has only been used in the factory with the WESTAC frame in the vertical position. It could probably be adapted for use in the field with the generator frame in the horizontal position, but extensive modifications would be required to install and use this large compression tool for field applications. Cranes large enough to install the compression tool typically cost upwards of $1,000 (E822.45) per day, so it is important to minimize such auxiliary equipment costs. 
     Accordingly, an improved tool is desired that will enable compression of a WESTAC endplate without the use of an overhead crane. 
     Furthermore, a new tool is desired that is easier to use in the field than the methods currently being employed and that will reduce costs. 
     SUMMARY OF THE INVENTION 
     This invention provides an improved method of removing the endplate of an electric generator that is held in compression against a core of the generator at a first end by a plurality of key bars that are supported in place against the generator frame. Each key bar has a slot which captures a peripheral arc of the circumference of the endplate to hold the endplate in compression. The plurality of key bars are substantially evenly spaced around the circumference of the generator frame. The method of this invention is more amendable to field maintenance procedures and less costly to operate than the methods heretofore employed. The method comprises simultaneously leveraging a separate compression tool independently off of the generator frame adjacent each key bar to apply a compressive load upon an exposed surface of the endplate sufficient to loosen the endplate from the key bars. Once the endplate is sufficiently compressed the key bars and the endplate can be removed from the generator frame. Preferably, each compression tool is pivotally attached to an end portion of the generator frame adjacent the corresponding key bar that the compression tool is associated with. 
     In the preferred embodiment, the compression tool comprises a housing having a first end of a laterally extending arm pivotally attached proximate to one end of the housing. A second end of the laterally extending arm is attached to the end portion of the frame adjacent the corresponding key bar. Desirably, the laterally extending arm comprises two parallel plates that are attached proximate to the one end of the housing with a pivot pin. The end portion of the generator frame adjacent the key bar is captured between the two parallel plates of the second end of the laterally extending arm with a pivot pin that extends through aligned bores in each of the parallel plates and the end portion of the generator frame. An anchor rod extends through the interior of the generator and is anchored at a first end of the anchor rod against a second axial end of the generator and connected at a second end of the anchor rod proximate to a second end of the housing of the compression tool such that the second end of the housing can move axially along the anchor rod. A portion of the housing, intermediate the first and second ends of the housing, contacts the endplate. The endplate is compressed by moving the second end of the housing axially along the second end of the anchor rod in the direction of the interior of the generator. Means are provided for moving the second end of the housing along the second end of the anchor rod, comprising a hollow hydraulic cylinder that captures the anchor rod within its piston. Preferably, the portion of the housing intermediate the first and second ends of the housing that contacts the endplate is a stand-off or pedestal that protrudes from the housing and is rigidly attached thereto. Once the endplate has been removed the core laminations may be held in place with a plurality of anchor rods respectively positioned with wood slot filler in empty coil slots in the core laminations. 
     In another embodiment of the invention, where core laminations have been replaced, the separate compression tools may be used to compress intermediate stacks of the laminations together. In this embodiment, the separate compression tools are leveraged off of the generator frame at a plurality of locations around the circumference of the generator at the same time to apply a compressive load upon a face of an exposed lamination. To that end, the compression tool comprises a housing having a first end pivotally attached to the generator frame. An anchor rod that extends through the interior of the generator and is anchored at a first end of the anchor rod against a second axial end of the generator is connected at a second end of the anchor rod proximate to a second end of the housing of the compression tool such that the second end of the housing can move axially along the anchor rod. A push rod extends axially from and is supported by the housing intermediate the first and second ends of the housing. The push rod, at an extended end, contacts the face of the generator lamination and compresses the laminations when the housing is moved axially along the second end of the anchor rod in the direction of the laminations. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A further understanding of the invention can be gained from the following description of the preferred embodiments when read in conjunction with the accompanying drawings in which: 
         FIG. 1  is a planned view of the shell of a WESTAC electric generator in a vertical position with a prior art compression loading plate in place; 
         FIG. 2  is a perspective view of an end section of a WESTAC generator with a single compression tool of this invention connected between the end of the generator frame adjacent a key bar and an anchor rod; 
         FIG. 2A  is an enlarged view of the endplate-key bar-frame extension connection; 
         FIG. 3  is a perspective view of the compression tool of this invention; 
         FIG. 4  is a perspective view of the endplate of a WESTAC generator with a plurality of compression tools in place engaging the generator frame adjacent the key bars, and the anchor rods; 
         FIG. 5  is a planned view of a support structure and trolley system for moving the endplate of a WESTAC generator away from the core; and 
         FIG. 6  is a perspective view of a rear portion of a WESTAC generator with a portion of the core iron removed and the compression tool of this invention in place to compress the exposed laminations. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 2  shows a perspective view of a portion of the end of a WESTAC generator with the external housing and the internal rotor removed. The stator core  30  is made up of a large number of iron laminations that are stacked in tandem and held in compression by the endplate  24 , which is an extremely large Bellville washer under in excess of 1,160,000 pounds of compression. The stator core is restrained in the circumferential direction by the generator frame  28 . The endplate  24  is captured in position and maintained under compression by key blocks or bars  26  that capture the peripheral edge of the endplate  24  in a notched groove. The key bars  26  are wedged between the endplate  24  and the frame extensions  27 .  FIG. 2A  shows an enlarged view of the endplate-key bar-frame extension interface. The endplate  24  has a circumferential lip  25  that the key bar  26  is wedged against to retain the endplate in compression. The key bar  26 , in turn, is captured in position by a groove in the underside of the frame extension  27 . 
     The stator core laminations form a plurality of transverse slots  32  that extend axially the length of the core and are positioned around the entire internal circumference of the stator. The slots house the stator windings. 
       FIG. 2  shows a single compression tool  40  of this invention in position to compress the endplate  24 . The compression tool  40  has a housing  48  that is connected at a first end  50  through a laterally extending arm  44  to the generator frame extension  27  by means of a connecting pin  46  which extends through a hole in the laterally extending arm  44  that matches with a mating hole  42  in the frame extension  27 . The laterally extending arm  44  is pivotally connected to the first end  50  of the housing  48  through a pivot pin  54 . An anchor rod  34 , e.g., a 1.25 in. (3.18 cm) all thread, extends through a second end  52  of the housing  48  and fits in an empty coil winding slot and runs the length of the generator core. The all thread anchor rod  34  is reacted off the opposite end of the generator core by being bolted to plates which span adjacent to the generator finger plates  35 . A hollow hydraulic cylinder  36  is placed over the end of the anchor rod that passes through the second end  52  of the housing  48  and is captured by an anchor nut  34 . A pedestal or stand-off  56  extends outward from the housing  48  intermediate the first and second ends of the housing  50  and  52  in line with the endplate  24  and contacts the endplate. As the hydraulic cylinder  36  expands it will react off of the pin  54  and press inward on the endplate  24  transmitting a compressive load through the stand-off  56 . In producing the WESTAC generators, the specifications call for a final nominal press of the core of 580 tons (5.16 MN). This works out to approximately 77,333 pounds (343.99 KN) of force required at each key  26  to be able to flatten the endplate  24 . Through calculations, it is determined that approximately 2,800 psi (19.3 newtons/sq. mm.) at the location of the hydraulic cylinder is required to obtain the necessary force. A 30 ton (266.89 KN) hollow hydraulic cylinder, such as the Enerpac RCH  302  is sufficient for this purpose. The 2,800 psi (19.3 newtons/sq. mm.) was calculated for a hydraulic cylinder having a piston surface area equal to that of the RCH  302 . The pressure will have to be adjusted for different piston surface areas. The RCH  302  hollow hydraulic cylinder is available from Enerpac, a Division of Actuant Corp., Milwaukee, Wis. However, it should be appreciated that other mechanical, pneumatic, or electrive motive forces can be employed to move the second end  52  of the housing  48  along the anchor rod  34  to provide a compressive load to the endplate  24 . Wood slot filler and all thread is used in the empty winding slots  32  to hold the rest of the core together so that the endplate  24  can be removed after the keys  26  are taken out. 
       FIG. 3  provides a perspective view of the compression tool  40  of this invention showing a better view of the laterally extending arm  44  which is made up of two parallel plates  62  and  64  that capture the hole  42  within the generator frame extension  27  therebetween through insertion of the pin  46 . The anchor rod  34  passes through the slot  58  in the housing  48 . In addition, there is a bore  60  that extends completely through the housing  48  for supporting a push rod, not shown in  FIG. 3 , which will be described in more detail hereafter. 
     In a WESTAC generator there are 15 key bars that are equidistantly spaced around the circumference of the electric generator.  FIG. 4  illustrates that separate compression tools  40  are provided for each of the 15 key bars and operate simultaneously at their respective key bar locations to compress the endplate  24 . 
       FIG. 5  illustrates a trolley set-up that can be employed to move the endplate  24  away from the generator  10 . A trolley  70  rides on an I-beam  68  which is held in position by support columns  66 . Preferably the I-beam is constructed out of a high strength aluminum alloy. A hook  74  can support a strap  72  which is wrapped around the endplate  24 . Employing this arrangement the endplate  24  can be moved sufficiently away from the end of the generator  10  to permit access to the core for core iron replacement by standard techniques. 
     After the core has been worked on, it will be necessary to compress the stacked tandem laminations ten times to 400 tons (3.56 MN) for every 18 inches of new iron replaced. The compression tool  40  of this invention is able to adapt itself to perform these intermediate presses as well.  FIG. 6  illustrates a configuration of the tool  40  in position to perform a single intermediate press. A push rod  76  is supported by the housing  48  intermediate the first and second ends  50  and  52  and extends out parallel to the anchor rod  34  towards the core iron  30 . The distal end of the push rod  76  is connected to an end plate  78  which spreads the load on the exposed surface of the core iron  30 . The housing  48  is suspended and supported by the frame  28  at its first end  50 . A longitudinal frame strut  29  is captured by the first end  50  of the housing  48  by insertion of the pin  54 . The tool  40  functions in the same manner as previously explained for employing a compressive load to the end plate  24 . However, in the embodiment shown in  FIG. 6  the compressive load is imparted by the push rod  76  through the endplate  78 . The push rod  76  can be retracted through the housing  48  through the housing slot  60  as more laminations are added, to further compress the core. Though only one compressive tool  40  is shown, it should be appreciated that the 15 identical compressive tools  40 , as previously shown in  FIG. 4 , can function in this embodiment to provide compressive loads simultaneously around the circumference of the face of the exposed core iron. 
     After the core has been adequately compressed, the endplate can be restored employing the same method that was used for removing the endplate. The compression tools  40  will be used to flatten the endplate by simultaneously applying a compressive load around the circumference of the endplate so the keys may be replaced between the periphery of the endplate and the frame extensions  27 . Accordingly, an improved method and apparatus is provided that does not require an overhead crane. Each of the 15 assemblies weighs approximately 65-70 pounds (29.48-31.75 kg.) and can easily be maneuvered by two people. One complete assembly can be readily set up in under 10 minutes and the cost of materials is significantly less than that of the 7,000 lb. prior art compression plate. 
     While specific embodiments of the invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular embodiments disclosed are meant to be illustrative only and not limiting as to the scope of the invention, which is to be given the full breadth of the appended claims and any and all equivalents thereof.