Abstract:
A rotating electrical machine includes a rotor configured to rotate about an axis. The rotor includes a rotor lamination stack having a plurality of sheets pressed into a composite assembly in an axial direction and being radially divided into an inner mechanical part and an outer electrical part. A rotor winding is disposed in the electrical part of the rotor lamination stack. A stator is concentrically surrounding the rotor. A plurality of shear bolts is disposed in the mechanical part and configured to reach through the rotor lamination stack. A plurality of further bolts is disposed in the electrical part, the plurality of shear bolts and a plurality of further bolts being configured to press the plurality of sheets in the axial direction.

Description:
CROSS REFERENCE TO PRIOR APPLICATIONS 
     This application is a continuation of International Patent Application No. PCT/EP2010/055153, filed on Apr. 20, 2010, which claims priority to German Patent Application Nos. DE 10 2009 018 549.6, filed on Apr. 24, 2009, and DE 10 2009 037 991.6, filed on Aug. 20, 2009. The entire disclosure of the applications is incorporated by reference herein. 
    
    
     FIELD 
     The present invention relates to the field of electrical power generation and to a rotating electrical machine. 
     BACKGROUND 
     Double-fed asynchronous machines in the power range from 20 MVA to over 500 MVA can be used for variable-speed energy production. These machines are distinguished by a distributed three-phase winding on the rotor. The rotor winding consists of individual bars which are embedded in slots in the rotor laminations. The individual bars are connected in the winding head to form a winding. The currents are fed in by at least three collector rings which are fixed to the shaft at the end of the machine. A section of such an asynchronous machine is reproduced in highly simplified form in  FIG. 1 . The asynchronous machine  10  shown in  FIG. 1  has a machine axis  13 . Rotatably about this axis  13  is a central body  11  with a shaft, on which the collector rings  12  are arranged. The rotor lamination stack  14 , to which an auxiliary rim  20  is connected below a winding head  16  of the rotor winding, is arranged around the central body  11 . The rotor lamination stack  14  is encompassed concentrically by a stator lamination stack  15  in which is mounted a stator winding, a stator winding head  17  of which projects outwards at the end of the body. The rotor lamination stack  14  is shown enlarged in section in  FIG. 2 . 
     As the rotors of double-fed asynchronous machines carry a rotor winding  18 , said winding must be safeguarded against the centrifugal forces which occur. On the one hand, the rotor lamination stack serves to absorb these forces and at the same time defines the path for the magnetic flux. The auxiliary rim  20  serves to absorb the centrifugal forces which act on the rotor winding head  16 . The auxiliary rim  20 , like the rotor lamination stack  14 , consists of laminated sheets which are pressed in the axial direction to form a composite assembly. In doing so, a pressing plate  19  which distributes the compression force applied by the bolts  21 ,  22  to the sheets of the rotor lamination stack can be used (see, for example, DE-A1-195 13 457 or DE-A1-10 2007 000 668). 
     Different requirements are imposed on the rotor lamination stack  14 . The principle of a subdivision into an electrical part  14   a  and a mechanical part  14   b  is shown in  FIG. 2 . On the one hand, there must be sufficient axial force between the layers of sheets in the teeth to guarantee the uniformity of the body. In order to avoid vibrations, the layers must not come loose, as relative movements between the teeth and the rotor winding  18  could damage the insulation. On the other hand, the pressure must not be too high in order to avoid damage to the insulation layers between the individual sheets, as such damage would lead to increased losses. The axial force must be higher in the mechanical part  14   b  of the rim than in the electrical part  14   a  in order to obtain a certain frictional force between the sheets. 
     SUMMARY OF THE INVENTION 
     In an embodiment, the present invention provides a rotating electrical machine including a rotor configured to rotate about an axis. The rotor includes a rotor lamination stack having a plurality of sheets pressed into a composite assembly in an axial direction and being radially divided into an inner mechanical part and an outer electrical part. A rotor winding is disposed in the electrical part of the rotor lamination stack. A stator is concentrically surrounding the rotor. A plurality of shear bolts is disposed in the mechanical part and configured to reach through the rotor lamination stack. A plurality of further bolts is disposed in the electrical part, the plurality of shear bolts and a plurality of further bolts being configured to press the plurality of sheets in the axial direction. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will be described in even greater detail below based on the exemplary figures. The invention is not limited to the exemplary embodiments. Other features and advantages of various embodiments of the present invention will become apparent by reading the following detailed description with reference to the attached drawings which illustrate the following: 
         FIG. 1  shows in a simplified representation a section of an asynchronous machine such as is suitable for the application of the invention; 
         FIG. 2  shows in an enlarged section the construction of the rotor lamination stack of the machine from  FIG. 1  including a pressing plate which is used for clamping the rotor lamination stack with different bolts according to an exemplary embodiment of the invention; 
         FIG. 3  shows in two part  FIGS. 3(   a ) and  3 ( b ) two different types of bolt for the electrical part of the rotor lamination stack; 
         FIG. 4  shows the principle construction of a multi-part shear bolt; 
         FIG. 5  shows in different part  FIGS. 5(   a ) to  5 ( d ) different types of connecting means for the concentric alignment of the subsections of a shear bolt with subdivided tube; and 
         FIG. 6  shows in plan view in the axial direction a sector of a pressing plate for clamping the rotor lamination stack according to a further exemplary embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     In am embodiment, the present invention relates to a double-fed asynchronous machine in the power range between 20 MVA and above 500 MVA. 
     In an embodiment, an electrical machine of the kind mentioned in the introduction is provided such that the different requirements on the clamping of the rotor lamination stack in the different regions can be considerably better fulfilled. 
     In an embodiment, the rotor lamination stack ( 14 ) is pressed in the mechanical part by means of shear bolts axially reaching through said rotor lamination stack, and in the electrical part by means of further bolts. 
     According to an embodiment of the invention, the further bolts can be designed as tensioning bolts passing through the rotor lamination stack in the axial direction. 
     Another embodiment of the invention is distinguished in that a pressing plate is provided at each end of the body in order to distribute the axial compression force on the rotor lamination stack, and that the further bolts are designed as forcing bolts which press against the pressing plates from the outside. 
     In an embodiment, when an auxiliary rim for supporting the rotor winding head is arranged particularly outside the pressing plates, the forcing bolts can with advantage be accommodated in the auxiliary rim. 
     A further embodiment of the invention is characterized in that at least some of the shear bolts are designed as solid bolts. 
     However, it is also conceivable and, with regard to the use of different materials, of advantage, when at least some of the shear bolts are designed as multi-part bolts which comprise an outer tube and a central tensioning bolt running through the tube. 
     In particular, in this case, the outer tube can be subdivided in the axial direction into a plurality of subsections in order to be able to better comply with the required tolerances and to simplify the erection and assembly process of the machine. 
     In doing so, it is of advantage when the subsections are equipped at each end with matching means for concentric alignment of the subsections with one another. 
     Another embodiment of the invention is distinguished in that the pressing plate is subdivided radially into a separate inner pressing plate and a separate outer pressing plate corresponding to the radial subdivision of the rotor lamination stack, and that the inner and outer pressing plates are releasably connected to one another. 
     An improvement of this embodiment is characterized in that the outer pressing plate is subdivided along the circumference into individual similar circumferential sections, that the circumferential sections of the outer pressing plate each abut the inner pressing plate with a straight tilting edge, and that the circumferential sections of the outer pressing plate are each suspended in the inner pressing plate by means of hammer claws. 
     According to  FIG. 2 , different types of bolt, namely shear bolts  22  and tensioning bolts  21 , are used for axially clamping the rotor lamination stack  14 . 
     The shear and tensioning bolts  22  and  21  respectively are used to build up the required pressure in the rotor lamination stack  14 . Two basic principles can be used to build up the pressure in the tooth region or electrical part  14   a:    
     Tensioning Bolts: 
     The tensioning bolts ( 21  in  FIG. 2  and  FIG. 3(   a )) run over the whole axial length of the rotor lamination stack  14 . As the tensioning bolts  21  are located in the magnetically active part (high magnetic induction) of the lamination stack, they must be electrically insulated. However, in order to prevent mechanical stressing of the insulation, these bolts must not be subjected to shear. The pressure on the pressing plate  19  and therefore the pressure in the teeth (see  29  in  FIG. 6)  can be “adjusted” by means of the tension in the tensioning bolts  21 . 
     Forcing Bolts in the Auxiliary Rim  20 : 
     Forcing bolts  23  in the auxiliary rim  20  can be used instead of the penetrating tensioning bolts  21  (see  FIG. 3  ( b )). If a forcing bolt  23  in the auxiliary rim  20  is used, the pressure is transmitted onto the tooth region of the rotor lamination stack via a bolt which is located in the auxiliary rim  20 . Here, a forcing plate  25  and a nut  24  are situated between forcing bolt  23  and pressing plate  19 . The pressure on the pressing plate  19  and therefore on the teeth can be “adjusted” by the depth to which the forcing bolt  23  is screwed into the nut  24 . 
     On the other hand, the shear bolts  22  undertake two tasks: Firstly, they serve to apply the axial force in the mechanical part  14   b  of the rotor lamination stack  14 . Secondly, they must absorb the shear forces which occur between the sheets of the rotor lamination stack  14 . For this reason, the shear bolts  22  cannot be insulated and are consequently located at the inner edge in the magnetically weakly used section of the mechanical part  14   b.    
     The shear forces to be transmitted define the material properties and the (outer) bolt diameter of the shear bolts  22 . The axial force in the rotor lamination stack  14  is adjusted by the extension of the bolts. In order to be able to guarantee sufficient residual pressure in the rotor lamination stack  14  in spite of setting phenomena of the rotor lamination stack  14 , a certain minimum extension is required in the initial state. This can lead to very high pressures in the case of large bolt diameters. 
     It is therefore advantageous, according to  FIG. 4 , to use thick-walled tubes  27  together with central tensioning bolts  26  which run in the bore of the tubes  27  instead of solid bolts. The shear forces to be transmitted define the material properties and the tube diameters. At the same time, the shear forces are absorbed by the tubes  27 . The pressure to be achieved on the rotor lamination stack is adjusted by the extension of the central tensioning bolts  26 . As the diameter of these rods is smaller than in the case of solid bolts, sufficiently large pressures can be achieved for the same extension. 
     A certain disadvantage of the solution with tubes  27  and central tensioning bolts  26  consists in the high demand on the accuracy of the bores in the tubes  27 . Particularly in the case of longer machines, it is very laborious to achieve the tight tolerances required. However, the same idea can also be realized with axially divided tubes  27 . Here, the tubes  27  are divided into a plurality of subsections ( 27   a  in  FIG. 5 ) which can be manufactured with the required tolerances considerably more easily. Furthermore, this embodiment simplifies the erection and assembly process of the machine. To enable the individual subsections  27   a  to be concentrically aligned with one another in a simple manner, according to  FIG. 5 , the ends can be provided with threads ( FIG. 5(   d ), designed with an offset ( FIG. 5(   c )) or chamfered ( FIG. 5(   b ), or conically tapering ( FIG. 5(   a )), wherein a combination of these solutions is also possible. 
     In addition to the design of the bolts, the conflicting demands on the electrical and mechanical part  14   a  and  14   b  of the stator lamination stack  14  can be even better achieved by a radially divided pressing plate  19 .  FIG. 6  shows a schematic representation of an exemplary embodiment of the pressing plate  19  in plan view in the axial direction. The pressing plate  19  is subdivided in both the radial direction and partially in the circumferential direction into a separate inner pressing plate  19   a  and a separate outer pressing plate  19   b.  For its part, the outer pressing plate  19   b  is subdivided in the circumferential direction into individual circumferential sections. As a result of the subdivision of the pressing plate  19  into an inner and a plurality of outer parts  19   a  and  19   b  following the division of the rotor lamination stack  14  into a mechanical part  14   b  and an electrical part  14   a,  the type of axial clamping for the different regions of the rotor lamination stack  14  can be optimized separately. 
     In order to be able to achieve a specific tilting of the outer pressing plate  19   b,  the division between the outer and inner pressing plate  19   a  and  19   b  respectively must have a tilting edge  28  which is straight in sections. As a result of the radial division of the pressing plate  19 , it is possible to achieve different pressures in the electrical and mechanical part  14   a  and  14   b  respectively of the rotor lamination stack  14 . 
     While the invention has been described with reference to particular embodiments thereof, it will be understood by those having ordinary skill the art that various changes may be made therein without departing from the scope and spirit of the invention. Further, the present invention is not limited to the embodiments described herein; reference should be had to the appended claims. 
     List Of Reference Numerals 
       10  asynchronous machine 
       11  central body (with shaft) 
       12  slip ring 
       13  axis 
       14  rotor lamination stack 
       14   a  electrical part 
       14   b  mechanical part 
       15  stator lamination stack 
       16  rotor winding head 
       17  stator winding head 
       18  rotor winding 
       19  pressing plate 
       19   a  inner pressing plate 
       19   b  outer pressing plate 
       20  auxiliary rim 
       21  tensioning bolt 
       22  shear bolt 
       23  forcing bolt 
       24  nut 
       25  forcing plate 
       26  central tensioning bolt 
       27  tube 
       27   a  subsection 
       28  tilting edge 
       29  tooth