Patent Publication Number: US-2003222530-A1

Title: Horizontal-axis electrical machine

Description:
[0001] The present invention relates to the field of electrical machines. It concerns a horizontal-axis electrical machine according to the preamble of claim 1.  
       [0002] Such a machine is known, for example, from the applicant&#39;s EP-A2-0 633 643.  
       [0003] In the case of gas-cooled electrical machines, such as turbogenerators for example, the operationally related heating causes great axial and radial expansions to occur in the laminated stator core, in particular in relatively high output ranges, and these expansions have to be transferred as uniformly as possible to the casing surrounding the laminated stator core. It has already been proposed in this respect in U.S. Pat. No. 4,663,553 to wedge the laminated stator core in a multiplicity of bearing rings which are perpendicular to the longitudinal axis of the machine, spaced apart from one another and securely welded on opposite sides to the bottom casing section by means of vertical fastening plates and horizontal pieces of tube. This type of fastening allows simple assembly and easy accessibility of the structural parts to be welded and, furthermore, ensures good quality of the welds.  
       [0004] However, it has been found that, in the case of large machines, vibrational isolation between the laminated stator core and the casing would be desirable in order to reduce noise emissions and reliably avoid excessive mechanical stresses of the connecting points between the laminated stator core and the bottom casing section. Such isolation is achieved according to the initially cited EP-A2-0 633 643 in a simple and cost-effective way by the fastening plates arranged between the bearing rings and the bottom casing section being connected to the bearing rings and the bottom casing section in such a way that they act as leaf springs. Such a resilient suspension of the laminated stator core in the casing is reproduced in FIG. 1. FIG. 1 shows in a simplified half-side cross section a horizontal-axis electrical machine  10 , which comprises concentrically in relation to a longitudinal axis  36  of the machine a rotor  12  and a laminated stator core  11  surrounding the rotor  12 . The rotor  12  and the laminated stator core  11  are accommodated in a casing  14 , which is subdivided along a horizontal center plane  23  into a bottom casing section  15  and a top casing section  16 . The top casing section  16  can be removed from the bottom casing section  15  for assembly and/or maintenance purposes.  
       [0005] The laminated stator core  11  is—as already described in U.S. Pat. No. 4,663,553 or in EP-A2-0 633 643—fastened in a wedged manner in a multiplicity of bearing rings  13  ( 13 ,  13 ′,  13 ″ in FIG. 2) arranged one behind the other in the longitudinal axis  36  of the machine. The bearing rings  13  have widenings  22 , which protrude laterally on opposite sides and at which they are resiliently connected to the bottom casing section  15 . For this purpose, at the upper and lower ends of each widening  22  there are respectively welded on laterally projecting fastening blocks  20 ,  21 , at which for their part a fastening plate  19  acting as a leaf spring is externally welded onto the ends. The fastening plate  19  is welded in its middle region via a plurality of pieces of tube  18 , arranged one above the other, to a vertical, planar casing portion  17  of the bottom casing section  15 . This type of fastening is represented in FIG. 2 in longitudinal section along the plane A-A from FIG. 1.  
       [0006] Since the laminated stator core  11  has in comparison with the casing  14  a comparatively large mass, considerable acceleration forces can occur between the laminated stator core  11  and the casing  14  during transportation of the machine  10  from its place of production to the place of use, subjecting the resilient fastening and, in particular, the welds provided there to high mechanical stresses. To avoid stresses of this kind during transportation, or at least reduce them to a harmless level, so-called transport arresting screwed joints  28 ,  29  are used—as shown in FIG. 2. These transport arresting screwed joints are essentially adjustable supporting elements which support the bearing rings  13 ′,  13 ″ against neighboring casing ribs  24 ,  25  and  26 ,  27 , respectively, of the bottom casing section  15  during transportation. For this purpose, threaded sleeves, into which corresponding screws are screwed at the free end, are welded on parallel to the principal axis  36  of the machine on both sides of the bearing ring. When the laminated stator core  11  is inserted into the bottom casing section  15  during pre-assembly at the factory, the screws are initially screwed into the threaded sleeves sufficiently far not to be in the way. Once the bearing rings  13 ,  13 ′ and  13 ″ have been welded to the bottom casing section  15 , the screws of the transport arresting screwed joints  28 ,  29  are unscrewed until they butt with the upper side of the screw head against the neighboring casing rib, as represented in FIG. 2. The laminated stator core  11  is then securely braced in the bottom casing section  15 . When there is an axial acceleration of the laminated stator core  11  in relation to the casing  14  during transportation, the acceleration forces occurring can thus be introduced reliably into the casing ribs  24 , . . . ,  27 , without exerting any load on the resilient suspension.  
       [0007] However, it is disadvantageous here that, after the machine  10  has been set up and before it is put into operation, the transport arresting screwed joints have to be unscrewed or loosened, so that a clearance of, for example, 20 mm is created between the screws and the casing ribs  24 , . . . ,  27  in order that the laminated stator core  11  can freely expand in relation to the housing when the operationally related heating occurs. This is of no consequence if the machine is sent to the place where it is to be set up without a top casing section  16  and with a special transport cover, because unscrewing of the transport arresting screwed joints before fitting of the top casing section  16  is possible without any great additional effort. If, on the other hand, the machine  10  is sent in the complete casing  14  without a transport cover, the top casing section  16  first has to be disassembled at the place of use in the plant in order to loosen the transport arresting screwed joints. This is followed by re-fitting of the top casing section. This procedure is cost-intensive and time-consuming.  
       [0008] It is therefore the object of the invention to provide a machine of the type stated at the beginning in which secure transportation is ensured with regard to the acceleration forces and their effects on the resilient mounting of the laminated stator core, without any transport securing means having to be unscrewed at the place where the machine is set up.  
       [0009] The object is achieved by the overall combination of features of claim 1. The essence of the invention is to limit the relative movement between the laminated stator core and the bottom casing section by suitable means in such a way that, on the one hand, excessive movements or acceleration forces are absorbed during transportation and, on the other hand, the operationally related thermal expansions of the laminated stator core are not hindered.  
       [0010] A first preferred embodiment of the machine according to the invention is characterized in that the casing ribs run parallel to the bearing rings, in that the securing means are respectively arranged between a bearing ring and a neighboring casing rib, and in that the securing means are designed as spacers which extend between the respective bearing ring and the neighboring casing rib, and which are connected by one end securely to the bearing ring or the neighboring casing rib and have a clearance between the other end and the neighboring casing rib or the bearing ring. A suitably chosen clearance can allow the movement during transportation to be effectively limited, without hindering the thermal expansion during later operation.  
       [0011] It is particularly simple if the spacers are designed such that they are adjustable in their length, because then the spacers can be adapted flexibly to the various applications during their fitting. The spacers preferably comprise in each case a threaded sleeve and a screw screwed into the threaded sleeve.  
       [0012] Allowance can be made for the thermal expansion during operation, increasing toward the outer ends of the laminated stator core, by providing that—if the laminated stator core extends on both sides of a vertical center plane oriented perpendicular to the longitudinal axis of the machine—the spacers for the bearing rings further away from the vertical center plane are respectively arranged only between the bearing ring and the neighboring casing rib lying closer to the vertical center plane, while the spacers for the bearing rings lying closer to the vertical center plane are respectively arranged between the bearing ring and the two neighboring casing ribs.  
       [0013] Further embodiments emerge from the dependent claims. 
     
    
    
     [0014] The invention is to be explained in more detail below on the basis of exemplary embodiments in conjunction with the drawing, in which:  
     [0015]FIG. 1 shows in a simplified half-side cross section a horizontal-axis electrical machine with resilient fastening of the laminated stator core in the casing, as to be considered for the implementation of the invention;  
     [0016]FIG. 2 shows in a simplified longitudinal section in the plane A-A from FIG. 1 the machine according to FIG. 1 with a transport arresting screwed joint used until now; and  
     [0017]FIG. 3 shows a representation comparable with FIG. 2, with transport securing means according to a preferred exemplary embodiment of the invention.  
    
    
     [0018] The invention, as represented in FIG. 3 by way of example, now uses instead of the previous transport arresting screwed joints, which have to be tightened for transportation and subsequently laboriously loosened again, fixedly adjusted spacers  31  . . . ,  33 . Although the spacers  31 , . . . ,  33  are of a structurally identical design to the transport arresting screwed joints  28 ,  29  of FIG. 2, they differ significantly with respect to arrangement and function. The spacers  31 , . . . ,  33  in each case comprise threaded sleeves  34 , which are welded at one end to one of the bearing rings  13 ,  13 ′ and  13 ″, and screws  35 , which are screwed into the free end of the threaded sleeves  34  and then fixed.  
     [0019] The spacers  31 , . . . ,  33  are respectively attached to the edge of the horizontal widening  22  of the bearing rings  13 , . . . ,  13 ″ such that they lie in the horizontal center plane  23 . The screws  35  are all screwed into the threaded sleeves  34  to the extent that there is a clearance SP of just a few millimeters between the upper sides of the screw heads and the adjacent casing rib  30  or  25 , . . . ,  27 . This clearance SP remains unchanged during and after the transportation of the machine  10  and only changes when the laminated stator core thermally expands during operation.  
     [0020] Since, during the operationally related thermal expansion of the laminated stator core  11 , the relative movement between the laminated stator core  11  and the bottom casing section  15  is all the greater the further the location on the laminated stator core  11  is away from the vertical center plane  37 , and in the vertical center plane  37  itself tends toward zero, the design and arrangement of the spacers  31 , . . . ,  33  change with the distance from the vertical center plane  37  of the laminated stator core  11 . For the bearing rings  13 ,  13 ′ further away from the vertical center plane  37 , the spacers  31 ,  32  are respectively arranged only on one side between the bearing ring and the neighboring casing rib  30  or  25  lying closer to the vertical center plane  37 . On the right-hand side (not represented in FIG. 3) of the vertical center plane  37 , the arrangement is correspondingly mirror-inverted.  
     [0021] In this way, the transportationally related relative movement, which is uniform for the entire laminated stator core  11 , can be reliably limited in both possible axial directions. If the laminated stator core  11  moves to the left in FIG. 3, the outer spacers to the right of the center plane  37  limit the movement. If, on the other hand, the laminated stator core  11  moves to the right, the outer spacers  31 ,  32  to the left of the center plane  37  limit the movement. The operationally related thermal relative movement, which is directed outward in opposite directions on both sides of the center plane  37 , on the other hand, is not hindered by the outer spacers  31 ,  32 , because their clearance increases. For the bearing rings  13 ″ lying closer to the vertical center plane  37 , for which the thermally related relative movement is likely to be small, the spacers  33  may be respectively arranged in opposite directions between the bearing ring and the two neighboring casing ribs  26 ,  27 . During operation, the clearance SP between the spacer  33  and the casing ribs  26 ,  27  then increases on the right-hand side of the bearing ring  13 ″, while it decreases on the left-hand side, without however becoming zero.  
     [0022] Altogether, acceleration forces of up to 1 g can be reliably absorbed and dissipated in this way without changing the spacers  31 , . . . ,  33  during transportation of the machine  10 , while during later operation the laminated stator core  11 , being warmer than the casing  14 , can freely expand.  
     [0023] List of Designations  
     [0024] 10  electrical machine (horizontal-axis)  
     [0025] 11  laminated stator core  
     [0026] 12  rotor  
     [0027] 13 ,  13 ′,  13 ″ bearing ring  
     [0028] 14  casing  
     [0029] 15  bottom casing section  
     [0030] 16  top casing section  
     [0031] 17  casing portion (vertical, planar)  
     [0032] 18  piece of tube  
     [0033] 19  fastening plate  
     [0034] 20 ,  21  fastening block  
     [0035] 22  widening (horizontal)  
     [0036] 23  center plane (horizontal)  
     [0037] 24 , . . . ,  27 ,  30  casing rib  
     [0038] 28 ,  29  transport arresting screwed joints  
     [0039] 31 , . . . ,  33  spacers  
     [0040] 34  threaded sleeve  
     [0041] 35  screw  
     [0042] 36  longitudinal axis of machine  
     [0043] 37  center plane (vertical)  
     [0044] SP clearance