Patent Publication Number: US-2022224185-A1

Title: Electric Machine

Description:
TECHNICAL FIELD 
     The present invention relates to an electric machine. 
     BACKGROUND 
     An electric machine may be provided with a rotor, a stator surrounding the rotor, and a frame surrounding the stator. 
     The shaft of the electric machine may be rotatably supported on the frame with bearings at the drive end and at the non-drive end of the electric machine. The bearings may be sleeve bearings, whereby one of the sleeve bearings of the electric machine may be an axially locating sleeve bearing and the other sleeve bearing of the electric machine may be a normal sleeve bearing without any axial locating capacity. The axially locating sleeve bearing may be provided at the drive end of the electric machine. 
     There are also actual axial bearings comprising a disc attached to the shaft and support elements acting on opposite surfaces of the disc radially outside the outer surface of the shaft. The support elements may be supported in a bearing frame. An actual axial bearing is, however, an expensive component and therefore used only in critical applications. 
     An earthquake causes ground acceleration which stresses the electric machines. The biggest problem in earthquakes is to hold the rotor in its position when the earthquake happens. 
     SUMMARY 
     An object of the present invention is to achieve an improved electric machine. 
     The electric machine according to the invention is defined in the claims. 
     The electric machine comprises
         a shaft,   a rotor being supported on the shaft,   a stator surrounding the rotor,   a frame surrounding the stator,   a bearing at a drive end and a bearing at a non-drive end of the electric machine for supporting the shaft rotatably on the frame, both bearings being sleeve bearings.       

     The electric machine is characterized in that
         both bearings are axially locating sleeve bearings, the axial play limiting the axial movement of the shaft being greater in one of the two axially locating sleeve bearings compared to the axial play in the other of the two axially locating sleeve bearings so that an axial movement of the shaft is limited only by the bearing with the smaller axial play during normal operational circumstances and by both bearings during exceptional events such as during seismic events, the bearing with the greater axial play reducing the axial load of the first bearing in such exceptional events.       

     The invention provides an effective way of dealing with the problem of keeping the rotor in a predetermined axial position during a seismic event. The bearing with the greater axial play does not take part in the limiting of the axial movement of the rotor during normal operational conditions. The bearing with the greater axial play limits the axial movement of the rotor only during exceptional seismic events, e.g. during earthquakes. The bearing with the greater axial play may take 50% of the total axial shock load during an earthquake after an initial threshold force has been reached. 
     This may be achieved by arranging an axially locating sleeve bearing at each end of the electric machine. The axial play of one of the axially locating sleeve bearings may be greater than the axial play of the other axially locating sleeve bearing. The larger axial play may be dimensioned so that expected thermal expansions do not activate the axial positioning of the axially locating sleeve bearing with the greater play i.e., they are handled by the axial positioning of the axially locating sleeve bearing with the smaller axial play. The shock load during an earthquake may be estimated to be in the order of 800 kN. The axial deformations in the axially locating sleeve bearing with the smaller axial play may be several millimetres during an earthquake. 
     The axially locating sleeve bearing is an axial load carrying bearing. 
     The electric machine may be an electric motor or an electric generator. 
     The electric machine may be a large electric machine. The shaft height of the electric machine may be in the range of 1120 to 2000 mm. The electric machine may be a high voltage electric machine. The electric machine may be a rib cooled electric machine. The output power of the electric machine may be in the range of 1 to 25 MW. The voltage of the electric machine may be up to 11.5 kV. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the following the invention will be described in greater detail by means of preferred embodiments with reference to the attached drawings, in which 
         FIG. 1A  shows an axial cross section of an electric machine according to prior art, 
         FIG. 1B  shows an axial cross-section of an electric machine according to an embodiment of the present invention, 
         FIG. 2  shows an axially locating sleeve bearing according to an embodiment of the present invention, 
         FIG. 3A  shows a normal sleeve bearing with no axial locating according to prior art, 
         FIG. 3B  shows an axially locating sleeve bearing on the non-drive side according to an embodiment of the present invention, 
         FIG. 4  shows a pedestal mounted sleeve bearing of an electric machine according to an embodiment of the present invention, 
         FIG. 5  shows a flange mounted sleeve bearing of an electric machine according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1A  shows an axial cross section of an electric machine according to prior art. 
     The electric machine may comprise a shaft  10 , a rotor  100 , a stator  200 , and a frame  300 . 
     The shaft  10  may be rotatably supported with bearings  20 ,  30 A at a drive end D and at a non-drive end N of the electric machine. The bearings  20 ,  30 A may be positioned in bearing housings  40 ,  50 A arranged outside the end plates  320 ,  330  of the frame  300 . A first one  320  of the two end plates  320 ,  330  may be attached to a first axial end of the frame  300  at the drive end D of the electric machine. A second one  330  of the two end plates  320 ,  330  may be attached to a second axial end of the frame  300  at the non-drive end N of the electric machine. The first axial end of the frame  300  is opposite to the second axial end of the frame  300 . The shaft  10  may rotate around an axis X-X of rotation. The drive end D of the electric machine is to the left in the figure and the non-drive end N of the electric machine is to the right in the figure. 
     The rotor  100  may be fitted on a cylindrical middle portion  11  supported on the shaft  10  so that the rotor  100  rotates in synchronism with the shaft  10 . The rotor  100  may comprise a rotor winding  110 . 
     The stator  200  may surround the rotor  100 . The stator  200  may be attached to the frame  300 . The frame  300  may surround the stator  200 . The stator  200  and the frame  300  are both stationary. 
     The stator  200  may comprise a stator core  210  and a stator winding  220 . The stator winding  220  may be positioned in axial grooves arranged on an inner surface of the stator core  210 . The stator winding  220  may further comprise end portions  220 A,  220 B extending outwards from opposite axial ends of the stator core  210 . 
     The exciter  60  of the electric machine is positioned on the shaft  10  within the frame  300  of the electric machine. 
     There is an air gap G between the inner perimeter of the stator core  210  and the outer perimeter of the rotor  100 . 
     The frame  300  may comprise a cover  310  covering the electric machine from the top of the electric machine. The bearings  20 ,  30 A are pedestal mounted in this embodiment. The bearing housings  40 ,  50 A are supported on support blocks  340 ,  350 . The support blocks  340 ,  350  may be supported on the floor on the site. 
     First axial air passages may be formed between the outer perimeter of the rotor  100  and the inner perimeter of the stator  200 . Second axial air channels may be formed between the outer perimeter of the stator core  210  and the frame  300 . The stator core  210  and the rotor  100  may have a laminated structure formed of a pack of sheets. 
     The first bearing  20  on the drive side of the electric machine may be an axially locating sleeve bearing. The second bearing  30 A on the non-drive side of the electric machine may be a normal sleeve bearing. This is a normal prior art way of dealing with the axial forces in electric machines. Only one of the bearings, normally the drive end bearing  20 , is an axially locating sleeve bearing being able to withstand axial forces for keeping the shaft  10  axially in a correct position during normal operational conditions. 
       FIG. 1B  shows an axial cross section of an electric machine according to an embodiment of the present invention. 
     The electric machine may comprise a shaft  10 , a rotor  100 , a stator  200 , and a frame  300 . 
     The shaft  10  may be rotatably supported with bearings  20 ,  30 B at a drive end D and at a non-drive end N of the electric machine. The bearings  20 ,  30 B may be positioned in bearing housings  40 ,  50 B arranged outside the end plates  320 ,  330  of the frame  300 . A first one  320  of the two end plates  320 ,  330  may be attached to a first axial end of the frame  300  at the drive end D of the electric machine. A second one  330  of the two end plates  320 ,  330  may be attached to a second axial end of the frame  300  at the non-drive end N of the electric machine. The first axial end of the frame  300  is opposite to the second axial end of the frame  300 . The shaft  10  may rotate around an axis X-X of rotation. The drive end D of the electric machine is to the left in the figure and the non-drive end N of the electric machine is to the right in the figure. 
     The rotor  100  may be fitted on a cylindrical middle portion  11  supported on the shaft  10  so that the rotor  100  rotates in synchronism with the shaft  10 . The rotor  100  may comprise a rotor winding  110 . 
     The stator  200  may surround the rotor  100 . The stator  200  may be attached to the frame  300 . The frame  300  may surround the stator  200 . The stator  200  and the frame  300  are both stationary. 
     The stator  200  may comprise a stator core  210  and a stator winding  220 . The stator winding  220  may be positioned in axial grooves arranged on an inner surface of the stator core  210 . The stator winding  220  may further comprise end portions  220 A,  220 B extending outwards from opposite axial ends of the stator core  210 . 
     The exciter  60  of the electric machine is positioned on the shaft  10  within the frame  300  of the electric machine. 
     There is an air gap G between the inner perimeter of the stator core  210  and the outer perimeter of the rotor  100 . 
     The frame  300  may comprise a cover  310  covering the electric machine from the top of the electric machine. The bearings  20 ,  30 B are pedestal mounted in this embodiment. The bearing housings  40 ,  50 B are supported on support blocks  340 ,  350 . The support blocks  340 ,  350  may be supported on the floor on the site. 
     First axial air passages may be formed between the outer perimeter of the rotor  100  and the inner perimeter of the stator  200 . Second axial air channels may be formed between the outer perimeter of the stator core  210  and the frame  300 . The stator core  210  and the rotor  100  may have a laminated structure formed of a pack of sheets. 
     In an embodiment of the present invention both the first bearing  20  on the drive side of the electric machine and the second bearing  30 B on the non-drive side of the electric machine are axially locating sleeve bearings. 
     In an embodiment of the present invention both the first bearing  20  and the second bearing  30 B are axially locating sleeve bearings, the axial play limiting the axial movement of the shaft  10  being greater in one  30 B of the two axially locating sleeve bearings  20 ,  30 B compared to the axial play in the other  20  of the two axially locating sleeve bearings  20 ,  30 B so that an axial movement of the shaft  10  is limited only by the first bearing  20  with the smaller axial play during normal operational circumstances and by both bearings  20 ,  30 B during exceptional events, the second bearing  30 B with the greater axial play reducing the axial load of the first bearing  20  in such exceptional events. 
     When referring to the term “exceptional events”, in this application, it is meant to refer to any exceptional event taking place near the electric machine installation not foreseen or not considered as typical for the electric machine installation, such as earthquakes, seismic events, military explosions, rock blasting, pile-driving or other similar exceptional events effective to the electric machine installation. 
     When referring to the term “normal operational circumstances”, in this application, it is meant to refer to any normal operational circumstances that are not considered to fall under the term “exceptional events”. 
     In the present application the two axially locating sleeve bearings  20 ,  30 B are dimensioned so that in “normal operational circumstances” the first bearing  20  with the smaller axial play limits the axial movement of the shaft  10  as an axially locating sleeve bearing  20  and only when an initial threshold force of an “exceptional event” is reached both of the two axially locating sleeve bearings  20 ,  30 B limit the axial movement of the shaft  10 . 
       FIG. 2  shows an axially locating sleeve bearing according to an embodiment of the present invention. 
     The bearing on the drive side in the electric machine in  FIG. 1B  is an axially locating sleeve bearing  20 . A vertical centre line Y-Y of the bearing is shown in the figure. 
     The shaft  10  comprises collars  12 ,  13  extending radially outwards from the outer surface of the shaft  10 . The collars  12 ,  13  rotate with the shaft  10 . The shaft  10  comprises further a portion  15  with a smaller diameter between the two collars  12 ,  13 . The bearing  20  comprises a bearing frame  22 . A spherical seat  21  is positioned in the bearing frame  22  between the collars  12 ,  13 . A sleeve  25  surrounding the shaft  10  and forming the bearing surface between the shaft  10  and the bearing  20  is supported in the seat  21 . Each collar  12 ,  13  comprises an outer and an inner radial surface. The bearing frame  22  comprises first bearing supports  23  seating against the inner radial surfaces of the collars  12 ,  13 . The bearing frame  22  comprises further second bearing supports  24  seating against the outer radial surfaces of the collars  12 ,  13 . The bearing frame  22  is supported in the bearing housing  40  which is not shown in the figure. The shaft  10  becomes thus supported in the axial direction between the bearing supports  23 ,  24  in the bearing frame  22 . The shaft  10  is further rotatably supported in the radial direction by the sleeve  25 . 
     There is an axial play between the rotating radial surfaces of the collars  12 ,  13  of the shaft  10  and the corresponding opposite stationary radial surfaces in the bearing  20 . The play allows thus a small movement of the shaft  10  in the axial direction. The maximum axial play of the rotor  100  may be ±8 mm. The axial movement of the shaft  10  should thus in all events be limited to a range being smaller than this maximum play±8 mm. 
       FIG. 3A  shows a normal sleeve bearing with no axial locating according to prior art. 
     The bearing on the non-drive side in the electric machine in  FIG. 1A  is a normal sleeve bearing  30 A. A vertical centre line Y-Y of the bearing is shown in the figure. 
     There are no collars on the shaft  10  in a normal sleeve bearing. The outer surface of the shaft  10  is straight i.e., has a uniform diameter in the area of the sleeve bearing  30 A. The bearing  30 A comprises a bearing frame  32 A. A spherical seat  31 A is positioned in the bearing frame  32 A. A sleeve  35 A surrounding the shaft  10  and forming the bearing surface between the shaft  10  and the bearing  30 A is supported in the seat  31 A. The bearing frame  32 A comprises first bearing supports  33 A forming the outermost portions of the bearing frame  32 A. The bearing frame  32 A is supported in the bearing housing  50 A which is not shown in the figure. The shaft  10  is thus rotatably supported only in the radial direction through the sleeve  35 A. 
       FIG. 3B  shows an axially locating sleeve bearing on the non-drive side according to an embodiment of the present invention. 
     The bearing on the non-drive side in the electric machine in  FIG. 1B  is an axially locating sleeve bearing  30 B. A vertical centre line Y-Y of the bearing is shown in the figure. 
     The shaft  10  comprises collars  16 ,  17  extending radially outwards from the outer surface of the shaft  10 . The collars  16 ,  17  rotate with the shaft  10 . The shaft  10  comprises further a portion  18  with a smaller diameter between the two collars  16 ,  17 . The bearing  30 B comprises a bearing frame  32 B. A spherical seat  31 B is positioned in the bearing frame  32 B between the collars  16 ,  17 . A sleeve  35 B surrounding the shaft  10  and forming the bearing surface between the shaft  10  and the bearing  30 B is supported in the seat  31 B. Each collar  16 ,  17  comprises an outer and an inner radial surface. The bearing frame  32 B comprises first bearing supports  33 B seating against the inner radial surfaces of the collars  16 ,  17 . The bearing frame  32 B comprises further second bearing support  34 B seating against the outer radial surface of the collar  16 . The bearing frame  32 B is supported in the bearing housing  50 B which is not shown in the figure. The shaft  10  becomes thus supported in the axial direction between the bearing supports  33 B,  34 B in the bearing frame  22 . The shaft  10  is further rotatably supported in the radial direction by the sleeve  35 B. 
       FIG. 4  shows a pedestal mounted sleeve bearing of an electric machine according to an embodiment of the present invention. 
     The bearing  20  comprises an axial centre line X-X and a vertical centre line Y-Y. 
     The spherical seat  21  seats in the bearing frame  22 . The sleeve  25  is supported in the spherical seat  21 . The spherical seat  21  and the sleeve  25  may be provided with oil passages  29 A,  29 B for supplying oil from an oil chamber  26  to the bearing surface. The bearing  20  comprises further two seals  27 A,  27 B positioned at an axial distance from each other on opposite axial sides of the sleeve  25 . Each seal  27 A,  27 B acts against an outer surface of the shaft  10 . The seals  27 A,  27 B prevent penetration of the bearing lubricant along the shaft  10  outside the bearing  20 . 
       FIG. 5  shows a flange mounted sleeve bearing of an electric machine according to an embodiment of the present invention. 
     The bearing  20  comprises an axial centre line X-X and a vertical centre line Y-Y. 
     The frame  22  of the bearing  20  is attached to a flange  70  in this embodiment. The spherical seat  21  seats in the bearing frame  22 . The sleeve  25  is supported in the spherical seat  21 . The spherical seat  21  and the sleeve  25  may be provided with an oil passage  29 A for supplying oil from an oil chamber  26  to the bearing surface. The bearing  20  comprises further two seals  27 A,  27 B positioned at an axial distance from each other on opposite axial sides of the sleeve  25 . Each seal  27 A,  27 B acts against an outer surface of the shaft  10 . The seals  27 A,  27 B prevent penetration of the bearing lubricant along the shaft  10  outside the bearing  20 . There is a further a machine seal  28  preventing air circulating within the electric machine from acting on the actual seals  27 A,  27 B. 
     The rotor core and the stator core may have a laminated structure being made of electrical steel sheets. 
     The invention is not limited to the examples described above but may vary within the scope of the claims.