Abstract:
A method and system is provided for calculating a number of wedges for a slot in a dynamoelectric machine. The method includes the steps of providing a computer that is programmed to perform a method for calculating, which includes the steps of acquiring a length of the slot, acquiring a length of one or more wedges, and calculating a number of wedges required for the slot. The number of wedges required for the slot is displayed on a display device.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates generally to dynamoelectric machines and more particularly, to a method and system for determining the number of wedges required for a slot in the dynamoelectric machine. 
     Armature windings, also known as stator bar or rotor windings, are routinely inspected in at least some known electrical power generators, to verify their operation. In some known generators, a stator yoke in the generator surrounds an armature core and partially encloses the armature windings. The stator windings are formed from a plurality of copper conductors that are wound in the armature to form loops. The armature windings may be arranged within a stator slot in such a manner that desired voltage and current characteristics may be maintained by the generator during operation. 
     At least one known generator includes a wedge system to induce a radial retaining force (RRF) to the stator from wedges to facilitate reducing movement of the stator bar windings within the stator slot. However, if the wedge system itself becomes loose, the amount of RRF is reduced such that the stator bar windings may move during operation. Over time, the relative motion of the stator bar windings cause damage to insulation surrounding the stator bar wedges, and/or a potential stator bar winding failure through electrical shorts to ground. Accordingly, within known generators, the wedge system is periodically inspected to determine if any stator bar winding movement within the stator slots exceeds predetermined tolerances. Some machines may need a rewind operation where the windings and wedge system are replaced. 
     Currently, several known methods of determining the number of wedges per slot are employed. One known method involves hand calculations resulting in many different lengths of wedges. Another known method involves manually selecting wedges of various lengths and installing them until the slot is filled. All the previously known methods result in a high degree of slot-to-slot variation on the number and length of wedges used. 
     BRIEF DESCRIPTION OF THE INVENTION 
     In one aspect of the invention, a method is provided for calculating a number of wedges for a slot in a dynamoelectric machine. The method includes the steps of providing a computer that is programmed to perform a method for calculating, which includes the steps of acquiring a length of the slot, acquiring a length of one or more wedges, and calculating a number of wedges required for the slot. The number of wedges required for the slot is displayed on a display device. 
     In another aspect of the invention, a system is provided for calculating a number of wedges for a slot in a dynamoelectric machine. The system includes a computer programmed to perform the steps of, acquiring a length of the slot, acquiring a length of one or more wedges, and calculating a number of wedges required for the slot. A display device can be used for displaying the number of wedges required for the slot. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective end illustration of an exemplary electric generator; 
         FIG. 2  is a partial perspective illustration of a portion of the stator core in the electric generator stator shown in  FIG. 1 ; 
         FIG. 3  is an enlarged partial perspective illustration of a portion of the stator core shown in  FIG. 2 ; 
         FIG. 4  is a simplified, top illustration of a stator slot filled with body wedges and end wedges; 
         FIG. 5  is a simplified, top illustration of a stator slot filled with body wedges and end wedges; 
         FIG. 6  is a block diagram of a wedge calculating system according to aspects of the present invention; 
         FIG. 7  is a flowchart illustrating some of the process steps to determine the number of mechanical-style wedges required for a slot in a dynamoelectric machine, according to aspects of the present invention; 
         FIG. 8  is a flowchart illustrating some of the process steps to determine the number of non-mechanical style wedges required for a slot in a dynamoelectric machine, according to aspects of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A dynamoelectric machine is defined as any apparatus that converts electrical energy between the electrical and the mechanical state by means of an electromagnetic effect. Windings are employed in the armature and field of a dynamoelectric machine, and may be held in place by a retaining system incorporating various components (e.g., wedges, ripple springs, etc.). 
       FIG. 1  is a perspective end view of an exemplary electric generator  100 . A rotor  102  is transparently represented by dashed lines. A plurality of stator bar windings  104  are positioned in slots  106  defined around an inner circumference of a stator core  108 . In the exemplary embodiment, stator bar windings  104  are formed from a plurality of flat bar conductors or stator bars that are coupled together to form a pre-determined winding path through winding  104 . In one embodiment, the stator bars are fabricated from copper. 
       FIG. 2  illustrates a partial, perspective illustration of a stator core  108 . The stator core  108  has a plurality of slots  106 , generally extending in an axial direction, which contain the windings  210 . As one example, two windings  210  may be contained within each slot  106 . The windings  210  are housed in the lower portion of the slots  106 . Various filler strips  220 , slides  230  and wedges  240  may be installed above the windings  210 . 
       FIG. 3  is an enlarged, partial perspective illustration of a stator core, and shows the interrelation between the slots  106 , slides  230  and wedges  240 . The dovetail shaped wedge  240  engages a dovetail groove  315  and a slide  230  is normally driven under the wedge  240 . The stator core  108  may be comprised of many laminations of magnetic steel or iron material. The laminations form groups, and these groups are separated by spacers. The spacers define cooling vent slots  350 , which are generally orthogonal to the slots  106 . The cooling vents  350  between the groups of laminations allow for ventilation and cooling of the stator core. Typically, the vent gaps  242  in the wedges  240  are aligned with the cooling vents  350 . 
       FIG. 4  illustrates a simplified, top plan view of one slot  106  filled with body wedges  440 , and end wedges  450 . The total length of the slot L S , is the distance from one end of the slot to the other in an axial direction. The length of the body wedges and the end wedges are L BW  and L EW , respectively. In this example, it can be seen that there are eight body wedges  440  of length L BW , and two end wedges  450  of length L EW . The various dimensions vary by specific application, but as one example, the core length or slot length could be L S =67.5″. The body wedge length might be L BW =6.75″, and the end wedges could also be L EW =6.75″. However, it is common for the end wedges  450  to have a different length than the body wedges  440 , and each opposing end wedge may have a different length as well. 
       FIG. 5  illustrates a simplified, top plan view of one slot  106  filled with body wedges  540 , end wedges  550  and a center wedge  560 . A second wedge  570  may also be utilized. However, in some applications the second wedge  570  may be replaced with a body wedge  540 . The total length of the slot L S , is the distance from one end of the slot to the other in the axial direction. The length of the body wedges, end wedges and the center wedge are L BW , L EW  and L CW , respectively. The middle spacing distance L MS , is the distance from the end of the slot to the midpoint. In this example, it can be seen that there are eight body wedges  540  of length L BW , two end wedges  550  of length L EW  and one center wedge of length L CW . The center wedge  550  can be used for alignment of the vent gaps  242  in body wedges  540 ,  240  to the cooling vents  350  (see  FIG. 3 ). 
     The system for determining the number of wedges for a slot in a dynamoelectric machine, according to aspects of the present invention, can be implemented in software (e.g., firmware), hardware, or a combination thereof. In the currently contemplated best mode, the system is implemented in software, as an executable program, and is executed by a special or general purpose digital computer, such as a personal computer (PC; IBM-compatible, Apple-compatible, or otherwise), workstation, minicomputer, or mainframe computer. An example of a general purpose computer that can implement the system of the present invention is shown in  FIG. 6 . In  FIG. 6 , the wedge calculating system is denoted by reference numeral  600 . 
     Generally, in terms of hardware architecture, as shown in  FIG. 6 , the computer  611  includes a processor  612 , memory  614 , and one or more input and/or output (I/O) devices  616  (or peripherals) that are communicatively coupled via a local interface  618 . The local interface  618  can be, for example but not limited to, one or more buses or other wired or wireless connections, as is known in the art. The local interface  618  may have additional elements, which are omitted for simplicity, such as controllers, buffers (caches), drivers, repeaters, and receivers, to enable communications. Further, the local interface may include address, control, and/or data connections to enable appropriate communications among the aforementioned components. 
     The processor  612  is a hardware device for executing software, particularly that stored in memory  614 . The processor  612  can be any custom made or commercially available processor, a central processing unit (CPU), an auxiliary processor among several processors associated with the computer  611 , a semiconductor based microprocessor (in the form of a microchip or chip set), a macroprocessor, or generally any device for executing software instructions. Examples of some suitable commercially available microprocessors are as follows: a PA-RISC series microprocessor from Hewlett-Packard Company, an 80×86 or Pentium series microprocessor from Intel Corporation, a PowerPC microprocessor from IBM, a Sparc microprocessor from Sun Microsystems, Inc, or a 68xxx series microprocessor from Motorola Corporation. 
     The memory  614  can include any one or combination of volatile memory elements (e.g., random access memory (RAM, such as DRAM, SRAM, SDRAM, etc.)) and nonvolatile memory elements (e.g., ROM, hard drive, tape, CDROM, etc.). Moreover, the memory  614  may incorporate electronic, magnetic, optical, and/or other types of storage media. Note that the memory  614  can have a distributed architecture, where various components are situated remote from one another, but can be accessed by the processor  612 . 
     The software in memory  614  may include one or more separate programs, each of which comprises an ordered listing of executable instructions for implementing logical functions. In the example of  FIG. 6 , the software in the memory  614  includes the wedge calculating system  600  in accordance with the present invention and a suitable operating system (O/S)  622 . A nonexhaustive list of examples of suitable commercially available operating systems  622  is as follows: (a) a Windows operating system available from Microsoft Corporation; (b) a Netware operating system available from Novell, Inc.; (c) a Macintosh operating system available from Apple Computer, Inc.; (e) a UNIX operating system, which is available for purchase from many vendors, such as the Hewlett-Packard Company, Sun Microsystems, Inc., and AT&amp;T Corporation; (d) a LINUX operating system, which is freeware that is readily available on the Internet; (e) a run time Vxworks operating system from WindRiver Systems, Inc.; or (f) an appliance-based operating system, such as that implemented in handheld computers or personal data assistants (PDAs) (e.g., PalmOS available from Palm Computing, Inc., and Windows CE available from Microsoft Corporation). The operating system  622  essentially controls the execution of other computer programs, such as the wedge calculating system  600 , and provides scheduling, input-output control, file and data management, memory management, and communication control and related services. 
     The wedge calculating system  600  is a source program, executable program (object code), script, or any other entity comprising a set of instructions to be performed. When a source program, then the program needs to be translated via a compiler, assembler, interpreter, or the like, which may or may not be included within the memory  614 , so as to operate properly in connection with the O/S  622 . Furthermore, the wedge calculating system  600  can be written as (a) an object oriented programming language, which has classes of data and methods, or (b) a procedure programming language, which has routines, subroutines, and/or functions, for example but not limited to, C, C++, Pascal, Basic, Fortran, Cobol, Pert, Java, and Ada, or (c) configured as a spreadsheet having multiple inputs and multiple outputs; the outputs calculated by predetermined mathematical operations. In the currently contemplated best mode of practicing the invention, the wedge calculating system  600  is configured as a spreadsheet having multiple inputs and multiple outputs; the outputs calculated by predetermined mathematical operations. 
     The I/O devices  616  may include input devices, for example but not limited to, a keyboard, mouse, scanner, microphone, etc. Furthermore, the I/O devices  616  may also include output devices, for example but not limited to, a printer, display, etc. Finally, the I/O devices  616  may further include devices that communicate both inputs and outputs, for instance but not limited to, a modulator/demodulator (modem; for accessing another device, system, or network), a radio frequency (RF) or other transceiver, a telephonic interface, a bridge, a router, etc. 
     If the computer  611  is a PC, workstation, or the like, the software in the memory  614  may further include a basic input output system (BIOS) (omitted for simplicity). The BIOS is a set of essential software routines that initialize and test hardware at startup, start the O/S  622 , and support the transfer of data among the hardware devices. The BIOS is stored in ROM so that the BIOS can be executed when the computer  611  is activated. 
     When the computer  611  is in operation, the processor  612  is configured to execute software stored within the memory  614 , to communicate data to and from the memory  614 , and to generally control operations of the computer  611  pursuant to the software. The wedge calculating system  600  and the O/S  622 , in whole or in part, but typically the latter, are read by the processor  612 , perhaps buffered within the processor  612 , and then executed. 
     When the wedge calculating system  600  is implemented in software, as is shown in  FIG. 6 , it should be noted that the wedge calculating system  600  can be stored on any computer readable medium for use by or in connection with any computer related system or method. In the context of this document, a computer readable medium is an electronic, magnetic, optical, or other physical device or means that can contain or store a computer program for use by or in connection with a computer related system or method. The wedge calculating system  600  can be embodied in any computer-readable medium for use by or in connection with an instruction execution system, apparatus, or device, such as a computer-based system, processor-containing system, or other system that can fetch the instructions from the instruction execution system, apparatus, or device and execute the instructions. In the context of this document, a “computer-readable medium” can be any means that can store, communicate, propagate, or transport the program for use by or in connection with the instruction execution system, apparatus, or device. The computer readable medium can be, for example but not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, device, or propagation medium. More specific examples (a nonexhaustive list) of the computer-readable medium would include the following: an electrical connection (electronic) having one or more wires, a portable computer diskette (magnetic), a random access memory (RAM) (electronic), a read-only memory (ROM) (electronic), an erasable programmable read-only memory (EPROM, EEPROM, or Flash memory) (electronic), an optical fiber (optical), and a portable compact disc read-only memory (CDROM) (optical). Note that the computer-readable medium could even be paper or another suitable medium upon which the program is printed or stored, as the program can be electronically captured, via for instance optical scanning of the paper or other medium, then compiled, interpreted or otherwise processed in a suitable manner if necessary, and then stored in a computer memory. 
     In an alternative embodiment, where the wedge calculating system  600  is implemented in hardware, the wedge calculating system can be implemented with any or a combination of the following technologies, which are each well known in the art: a discrete logic circuit(s) having logic gates for implementing logic functions upon data signals, an application specific integrated circuit (ASIC) having appropriate combinational logic gates, a programmable gate array(s) (PGA), a field programmable gate array (FPGA), etc. 
     The number of wedges, and their respective lengths, required to fill slot  106  can be determined by the method and system according to aspects of the present invention. The method described below, utilizes a series of nested statements to optimize the wedge design by selecting the longest possible wedge (or by using the size wedge available) that will fit evenly in slot  106 . If the only possible solution is a body wedge length of one vent spacing, a center wedge may be added to reduce the quantity of body wedges. 
     Table 1 lists the various inputs and outputs of the equations used to calculate the length and quantity of wedges required. For core inputs, N CV  is the number of cooling vents  350  present in one slot  106 . The core length, L S , is the length of one slot  106 . The middle spacing, L MS , is the combined length of a punching packet and cooling vent in the center section of the core. The end packet length is L EP  and the cooling vent length is L CV . For wedge inputs, E BW  is the maximum available body wedge length, and the locking or end wedge length is E LW . Wedges can come in multiple lengths, and there may be multiple sizes available for installation. The outputs of the method yield the maximum body wedge length L BW , end wedge lengths L EW1  and L EW2 , total number of body wedges N BW  for one slot, and the second wedge lengths, L 2W1  and L 2W2 , if desired. In addition, the various inputs below can be obtained manually or by measuring using physical or electronic devices, and the results may be stored in a medium which can be accessed by the method and system herein described. 
     
       
         
               
               
             
               
               
               
               
             
               
               
             
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 INPUTS 
                 OUTPUTS 
               
               
                   
               
             
             
               
                 CORE 
                 WEDGE 
               
             
          
           
               
                 Number of Cooling 
                 N CV   
                 Body wedge length 
                 L BW   
               
               
                 Vents 
               
               
                 Core Length 
                 L S   
                 End Wedge length 
                 L EW1 /L EW2   
               
               
                 End Spacing 
                 L ES   
                 Number of body 
                 N BW   
               
               
                   
                   
                 wedges 
               
               
                 Middle Spacing 
                 L MS   
                 Locking Wedge 
                 L EW   
               
               
                   
                   
                 Length 
               
               
                 End Packet Length 
                 L EP   
                 Second Wedge 
                 L 2W1 /L 2W2   
               
               
                   
                   
                 Length 
               
               
                 Cooling Vent Length 
                 L CV   
               
             
          
           
               
                 WEDGE 
                   
               
             
          
           
               
                 Body Wedge Length 
                 E BW   
               
               
                 (max) 
               
               
                 Locking Wedge 
                 E LW   
               
               
                 Length 
               
               
                   
               
             
          
         
       
     
     The first step in the method, according to aspects of the present invention, is to calculate the end spacing, L ES . The end spacing is defined as the axial length of the last packet of core laminations plus one half the length of the cooling vent. The end packet length is defined as the axial length of the outboardmost core laminations up to the first cooling vent. The end spacing can be calculated with the following equation:
 
 L   ES   =L   EP   +L   CV /2  (Equation 1)
 
     The next step is to calculate the middle spacing, L MS . The middle spacing is defined as the axial length of any one of the packets of core laminations in the middle section of the core plus the length of one cooling vent. The middle spacing can be calculated by the following equation:
 
 L   MS =(( L   S −(2 *L   ES ))/( N   CV −1))  (Equation 2)
 
     Alternatively, the middle spacing could be manually measured using physical or electronic devices. For example, a tape measure could be used to measure the middle spacing. The length of the slot, L S , can also be manually measured using physical or electronic devices. 
     After the middle spacing is determined, the end or locking wedge length and maximum body wedge length can be determined by using equations 3 and 4, respectively.
 
 L   EW =Rounddown(( E   LW   −L   ES )/ L   MS )* L   MS   +L   ES   (Equation 3)
 
 L   BW =Rounddown( E   BW   /L   MS )* L   MS   (Equation 4)
 
     Two types of locking wedges can be accounted for in the method, according to aspects of the present invention. One type of wedge is a mechanical locking wedge, which uses some form of mechanical tab inserted into the core cooling vent to lock the wedge. Another type of wedge is a non-mechanical locking wedge, which relies on an adhesive or other retention means, other than physical insertion of a projection into the cooling vent, to lock the wedge. The optimization process or method for each style wedge is illustrated in  FIGS. 7 and 8 . 
       FIG. 7  illustrates a process  700  to calculate and optimize the number of mechanical-style locking wedges. In step  710 , the end wedge length, L EW1  and L EW2 , can be set equal to the end spacing distance, L ES , plus the middle spacing distance, L MS . In step  720 , the second wedge lengths, L 2W1  and L 2W2 , are set equal to the maximum body wedge length, E BW . In step  730 , it is decided if the estimated number of body wedges is an integer value. If the answer is yes, then the process is finished. If the answer is no, then the process continues to step  740 . In step  740 , the second wedge length, L 2W1 , is set equal to the second wedge length, L 2W1 , minus the middle spacing distance, L MS . In step  750 , it is decided if the estimated number of body wedges is an integer value. If the answer is yes, then the process is finished. If the answer is no, then the process continues to step  760 . In step  760 , the second wedge length, L 2W2 . is set equal to the second wedge length, L 2W2 , minus the middle spacing distance, L MS . In step  770 , it is decided if the estimated number of body wedges is an integer value. If the answer is yes, then the process is finished. If the answer is no, then the process loops back to step  740  and repeats. 
       FIG. 8  illustrates a process  800  to calculate and optimize the number of non-mechanical-style locking wedges. In step  810 , the end wedge lengths, L EW1  and L EW2 , are set equal to the end spacing distance, L ES . In step  820 , it is decided if the estimated number of body wedges is an integer value. If the answer is yes, then the process is finished. If the answer is no, then the process continues to step  830 . In step  830 , the end wedge length, L EW1 , is set equal to the end wedge length, L EW1 , plus the middle spacing distance, L MS . In step  840 , it is decided if the estimated number of body wedges is an integer value. If the answer is yes, then the process is finished. If the answer is no, then the process continues to step  850 . In step  850 , end wedge length, L EW2 , is set equal to the end wedge length, L EW2 , plus the middle spacing distance, L MS . In step  860 , it is decided if the estimated number of body wedges is an integer value. If the answer is yes, then the process is finished. If the answer is no, then the process loops back to step  830  and repeats. 
     The number of body wedges can now be determined by using equation 5. 
     
       
         
           
             
               
                 
                   
                     N 
                     BW 
                   
                   = 
                   
                     ( 
                     
                       
                         
                           L 
                           S 
                         
                         - 
                         
                           L 
                           
                             EW 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             1 
                           
                         
                         - 
                         
                           L 
                           
                             EW 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             2 
                           
                         
                         - 
                         
                           L 
                           
                             2 
                             ⁢ 
                             W 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             1 
                           
                         
                         - 
                         
                           L 
                           
                             2 
                             ⁢ 
                             W 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             2` 
                           
                         
                       
                       
                         L 
                         BW 
                       
                     
                     ) 
                   
                 
               
               
                 
                   ( 
                   
                     Equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     5 
                   
                   ) 
                 
               
             
           
         
       
     
     In equation 5, N BW  is the total number of body wedges required for one slot, L s  is the length of the slot, L EW1  and L EW2  are the lengths of the two end wedges, L 2W1  and L 2W2  are the length of the two second wedges, if required. L BW  is the maximum calculated acceptable body wedge length. For non-mechanical style wedges, the values of the two second wedges, L 2W1  and L 2W2 , can be set equal to zero. 
     The above equations illustrate one of many variations of calculating the number and length of body and end wedges required to fill a slot in a dynamoelectric machine. Any suitable equation may be substituted, or the order of the calculations may be varied as desired in the specific application. 
     While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.