Abstract:
A method of servicing a stator frame of a power generator. The method includes removing a first stator core from a main housing of the stator frame, removing a plurality of first dove-tail shaped keybars that extend axially within and are coupled to a main support structure forming part of the main housing, and installing a plurality of second keybars in the main support structure in place of the first dove-tail shaped keybars. The second keybars are adapted to support a second stator core. Each of the second keybars has a generally rounded engagement surface and the second stator core includes recesses with shapes corresponding to the generally rounded engagement surfaces of the second keybars such that the second stator core can be securely supported in the main support structure by the second keybars.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 12/352,732, filed Jan. 13, 2009, and entitled “METHOD OF SERVICING A POWER GENERATOR,” which claims the benefit of U.S. Provisional Application Ser. No. 61/037,887, entitled “CORE TO FRAME ATTACHMENT IN A UNIT WITHOUT BUILDING BOLTS,” filed Mar. 19, 2008, the entire disclosures of each of which are incorporated by reference herein. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to power generators, and more particularly, to a method of servicing stator frames in power generators. 
     BACKGROUND OF THE INVENTION 
     U.S. Pat. No. 5,875,540, the entire disclosure of which is incorporated by reference herein, discloses a process for forming a stator core in a stator frame. The process involves forming a plurality of core modules or donuts, each of which comprises a plurality of stator core rings laminated together. The stator frame is placed in an upright position. A predefined number of the core modules are then lowered into the upright stator frame. For a power generator which has been in operation for some time and is in need of a new stator core, turning its stator frame upright to receive a new stator core can be very difficult. 
     U.S. Pat. Nos. 7,302,754; 7,353,586; and 7,395,594, the entire disclosures of which are incorporated by reference herein, are directed at installing stator cores into stator frames without placing the stator frame in an upright position. U.S. Pat. No. 7,202,587, the entire disclosure of which is also incorporated by reference herein, discloses mounting stator core donuts having enlarged grooves in a stator frame using wedges that disperse forces to the donuts in a circumferential manner. The enlarged grooves make installing the donuts less difficult, while the wedges ensure a tight fit of the laminations within the stator frame. 
       FIG. 1  illustrates a known stator frame  10  for a power generator. The stator frame  10  comprises a main housing  11  for supporting a stator core, not shown in  FIG. 1 . The main housing  11  comprises an outer structure  13  and a main support structure  15  coupled to the outer structure  13 . The main support structure  15  comprising a plurality of stator bore or support rings  18  coupled to the outer structure  13  and a plurality of frame beams  16  coupled to the stator bore rings  18 . The main housing  11  further comprises a plurality of dove-tail shaped building bolts or keybars  12  coupled to the frame beams  16 . The stator core, not shown in  FIG. 1 , is supported in the stator frame  10  via the keybars  12 . 
       FIG. 2  illustrates a stator core lamination or donut  14  comprising a plurality of stator core rings (also referred to as laminations) laminated or otherwise coupled together and configured to be supported on the keybars  12  illustrated in  FIG. 1 . It is noted that a plurality of the stator core donuts  14  are stacked together within the stator frame  10  to form the stator core. Referring now to  FIG. 2 , each stator core donut  14  includes a plurality of slots or grooves  20  (see  FIG. 3 ) along its outer periphery to receive the keybars  12 . The grooves  20  have a dove-tail shape corresponding to the shape of the keybars  12  to ensure a secure and tight fit within the stator frame  10 , as more clearly shown in  FIG. 3 . It is noted that small radial gaps  21  are formed between the periphery of each stator core donut  14  and the inner diameter of the support rings  18 , as shown in  FIG. 2 . It is also noted that one or more mounting assist structures  23 A,  23 B,  23 C may be disposed in each groove  20  between the stator core donut  14  and the corresponding keybar  12 . The mounting assist structures  23 A,  23 B,  23 C assist in securing a tight fit between the stator core donut  14  and the keybars  12 . 
     SUMMARY OF THE INVENTION 
     In accordance with a first aspect of the present invention, a method of servicing a stator frame of a power generator is provided. The method comprises removing a first stator core from a main housing of the stator frame, removing a plurality of first dove-tail shaped keybars that extend axially within and are coupled to a main support structure forming part of the main housing, and replacing the first dove-tail shaped keybars from the stator frame with a plurality of second keybars by installing the second keybars in the main support structure where the first dove-tail shaped keybars were previously located. The second keybars are adapted to support a second stator core. Each of the second keybars has a generally rounded engagement surface and the second stator core includes recesses with shapes corresponding to the generally rounded engagement surfaces of the second keybars such that the second stator core can be securely supported by the main support structure via the second keybars. 
     The main support structure may comprise a plurality of stator bore rings and a plurality of frame beams, wherein the second keybars are coupled to the frame beams. 
     Installing a plurality of second keybars in the main support structure may comprise bolting the second keybars to the frame beams. 
     Bolting the second keybars to the frame beams may comprise installing bolts into counter-bored holes until end portions of the bolts are inserted past a radially inner surface of the second keybars. 
     The method may further comprise installing the second stator core onto the second keybars. 
     The method may further comprise servicing the frame beams such that the second stator core can be more easily axially slid onto the second keybars without the second stator core contacting the frame beams. 
     Servicing the frame beams may comprise removing radially inner corner edges of the frame beams to create a radial clearance for a radial outer edge of the second stator core. 
     A portable milling machine may be utilized to remove the radially inner corner edges of the frame beams. 
     In accordance with a second aspect of the present invention, a kit for servicing a stator frame of a power generator is provided, wherein the stator frame includes dove-tail keybars installed therein supporting a first stator core within a main support structure of a main housing. The kit comprises a plurality of second keybars and fasteners to couple the second keybars to the main support structure of the main housing. Each of the second keybars has a generally rounded engagement surface and is adapted to replace the dove-tail shaped keybars once the dove-tail keybars are removed from the main support structure of the stator frame. The second keybars are adapted to support a second stator core in the main support structure. The second stator core includes recesses with shapes corresponding to the generally rounded engagement surfaces of the second keybars. 
     The main support structure may comprise a plurality of stator bore rings and a plurality of frame beams, wherein the second keybars are coupled to the frame beams with the fasteners. 
     The fasteners may comprise bolts, which may be installed through counter-bored holes in the second keybars. 
     End portions of the second keybars may extend further radially inwardly than a radial end of the bolts. 
     The kit may further comprise a portable milling machine for removing radially inner corner edges of the frame beams to create a radial clearance for a radial outer edge of the second stator core. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       While the specification concludes with claims particularly pointing out and distinctly claiming the present invention, it is believed that the present invention will be better understood from the following description in conjunction with the accompanying Drawing Figures, in which like reference numerals identify like elements, and wherein: 
         FIG. 1  is a cut-away perspective view of a prior art generator frame including an annular array of dove-tail shaped keybars; 
         FIG. 2  is a cross sectional view of an inner portion of the prior art generator frame illustrated in  FIG. 1  and further including a prior art stator core donut; 
         FIG. 3  is an enlarged cross sectional view of a portion of the prior art generator frame and a portion of the stator core donut illustrated in  FIG. 2 ; 
         FIG. 4  is a cross sectional view of a portion of a generator frame including a replacement donut after the generator frame has been serviced according to embodiments of the invention; 
         FIG. 5  is an enlarged cross sectional view of a portion of the replacement donut illustrated in  FIG. 4  and a replacement keybar installed in the generator frame illustrated in  FIG. 4  during the servicing thereof; and 
         FIG. 6  is an exploded perspective view of a portion of the replacement keybar illustrated in  FIG. 5 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In the following detailed description of the preferred embodiments, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration, and not by way of limitation, specific preferred embodiments in which the invention may be practiced. It is to be understood that other embodiments may be utilized and that changes may be made without departing from the spirit and scope of the present invention. 
     After periods of electrical power generator use, it may become necessary to replace a stator core within a stator core frame of the power generator. As mentioned above, U.S. Pat. Nos. 7,302,754; 7,353,586; and 7,395,594 are directed at installing stator cores into stator frames without placing the stator frame in an upright position. Typically, the systems, structures, and methods disclosed by these patents are utilized with keybars having rounded engagement surfaces, i.e., the keybars are generally rounded in shape. This is because replacement of a stator core onto rounded keybars using a horizontal replacement process is believed to be easier and more efficient as compared to replacement of a stator core onto dove-tail shaped keybars. 
     As shown in  FIG. 1 , a power generator stator frame  10  may comprise a main housing  11  for supporting a stator core, not shown in  FIG. 1 . The main housing  11  comprises an outer structure  13  and a main support structure  15  coupled to the outer structure  13 . The main support structure  15  comprising a plurality of stator bore rings  18  fixedly coupled to the outer structure  13  and a plurality of frame beams  16  fixedly coupled to the stator bore rings  18 . The main housing  11  further comprises a plurality of building bolts or keybars  12 , which are dove-tail shaped in  FIG. 1 , and coupled to the frame beams  16 . The stator core, not shown in  FIG. 1 , is supported in the stator frame  10  via the keybars  12 . 
     In accordance with the present invention, after a stator core mounted to dove-tail shaped keybars  12  of a stator frame  10  is removed, the dove-tail shaped keybars  12  are then removed and replaced with generally rounded or cylindrical-shaped keybars followed by the installation of a new stator core onto the rounded keybars. By replacing the dove-tail shaped keybars  12  with rounded keybars, it is believed that installation of the new stator core within the stator core frame having rounded keybars will be accomplished in a more efficient manner. 
     Donuts  14  mounted on dove-tail shaped keybars  12 , see  FIGS. 1-3 , and defining a stator core to be replaced, are removed according to any traditional method(s) for removing such a stator core from a corresponding stator frame. For example, the stator core donuts  14  may be individually removed one by one by axially sliding the stator core donuts  14  along the dove-tail shaped keybars  12  until all stator core donuts  14  are removed from the stator frame  10 . It is noted that donuts  14  comprise two or more stator core rings laminated together. Instead of using donuts  14  in the present invention, individual stator core rings or laminations may be used instead. 
     Once the stator core donuts  14  are removed from the stator frame  10 , the dove-tail shaped keybars  12  are removed from the frame beams  16  by removing fasteners  22 , such as bolts, extending through counter-bored holes  24  (see  FIG. 3 ) formed in the keybars  12  and through corresponding holes  25  formed in the frame beams  16 . Removing the fasteners  22  frees each keybar  12  from its respective frame beam  16 . 
     In order for a replacement donut  30  (see  FIG. 4 ) to be more easily installed in the stator frame  10  and in accordance with the present invention, one or more of the frame beams  16  are serviced by removing radially inner corner edges  16 A 1 ,  16 B 1  (see  FIG. 3 ) of the frame beams  16 , such that the modified frame beams  16 ′ comprise beveled radially inner corner edges  16 A 2 ,  16 B 2  (see  FIG. 5 ). The beveled radially inner corner edges  16 A 2 ,  16 B 2  provide an amount of radial clearance between the frame beams  16 ′ and a radial outer edge  30 A of each of the replacement donuts  30 . The beveled radially inner corner edges  16 A 2 ,  16 B 2  may be formed in the frame beams  16 ′, for example, by grinding the radially inner corner edges  16 A 1 ,  16 B 1  using a portable milling machine (not shown), such as, for example, a TKF1500-0 model adjustable angle beveller manufactured by Trumpf Inc. of Farmington, Conn. 
     Replacement building bolts or keybars  32  are then installed on the frame beams  16 ′ in generally the same locations as the previously removed keybars  12 . As shown in  FIG. 5 , the replacement keybars  32  are generally rounded in shape and comprise a generally rounded engagement surface  34  instead of the dove-tail shape of the removed keybars  12 . 
     The replacement keybars  32  include counter-bored holes  36  formed therein, as shown in  FIGS. 5 and 6 , which counter-bored holes  36  may be substantially aligned with the holes  25  formed in the frame beams  16 ′, although it is understood that new holes (not shown) may be formed in the frame beams  16 ′ and aligned with the counter-bored holes  36  in the replacement keybars  32  if desired. Fasteners  38 , depicted in  FIGS. 5 and 6  as bolts, are then inserted into the counter-bored holes  36  in the replacement keybars  32  and threaded into the corresponding holes  25  in the frame beams  16 ′ to secure the replacement keybars  32  to the frame beams  16 ′. The fasteners  38  may be inserted into the counter-bored holes  36  until a radially inner surface  32 A of the corresponding replacement keybar  32  extends further radially inwardly than an end portion  38 A of each of the fasteners  38 , i.e., until the fasteners  38  are not extending out past the radially inner surfaces  32 A of the replacement keybars  32 . Thus, the replacement donuts  30  can be axially slid on the replacement keybars  32  without contacting the fasteners  38 . 
     As shown in  FIG. 5 , the replacement donuts  30  include grooves  50 . Each replacement donut  30  is positioned relative to the stator frame  10  such that each groove  50  is aligned with a corresponding replacement keybar  32 . Thereafter, the replacement donut  30  is horizontal moved into the stator frame such that the replacement keybars  32  are received in a corresponding one of the grooves  50  in the replacement donut  30 . The replacement donuts  30  may be installed into the stator frame using the structures and methods set out in U.S. Pat. Nos. 7,302,754, 7,353,586, and 7,395,594. Alternatively, any other suitable structures and methods can be used to install the replacement donuts  30  into the stator frame  10 . A plurality of donuts  30  are installed in this fashion until a predetermined number have been installed so as to define a replacement stator core. 
     In the illustrated embodiment, the grooves  50  are slightly oversized to allow for easier installation of the donuts  30  onto the replacement keybars  32 . So as to create a tight fit between each donut  30  and the replacement keybars  32 , first and second wedge structure assemblies  54  and  56  are provided in each groove  50  between the donut  30  and the corresponding keybar  32 , see  FIG. 5 . Each of the first and second wedge structure assemblies  54 ,  56  in the embodiment shown comprises a filler member  54 A,  56 A, and first and second wedges  54 B,  54 C and  56 B,  56 C. In the illustrated embodiment, six donuts  30 , each having a width of about six inches, are set in position. Thereafter, the first and second wedges  54 B,  54 C and  56 B,  56 C and filler members  54 A,  56 A, each about 36 inches long, are installed. The first and second wedge structure assemblies  54  and  56  are utilized to aid in mounting the replacement donuts  30  on the replacement keybars  32  and to secure a tight fit between the replacement donuts  30  and the replacement keybars  32 . It is understood that other types of mounting assist structures may be used as desired. 
     As noted above, the replacement of a stator core onto rounded keybars using a horizontal replacement process is believed to be easier and more efficient as compared to replacement of a stator core onto dove-tail shaped keybars. Hence, replacing the dove-tail shaped keybars  12  with the replacement keybars  32  facilitates an easier replacement of a stator core within the stator frame  10 . In particular, since tooling, methods, and structure have been developed to replace stator cores within stator frames using horizontal processes and cylindrical-shaped keybars, these developed tooling, methods, and structure can be utilized in the stator frames  10  once the replacement keybars  32  are installed. For example, the use of the replacement donuts  30  and the first and second wedge structure assemblies  54 ,  56  with the replacement cylindrical-shaped keybars  32  avoids developing new tooling, methods, and structure that would be required to use a horizontal process to replace a stator core in a stator frame that includes dove-tail shaped keybars. 
     While particular embodiments of the present invention have been illustrated and described, it would be obvious to those skilled in the art that various other changes and modifications can be made without departing from the spirit and scope of the invention. It is therefore intended to cover in the appended claims all such changes and modifications that are within the scope of this invention.