Patent Publication Number: US-2015076969-A1

Title: Electric machine stator with axial vents

Description:
BACKGROUND OF THE INVENTION 
     The subject matter disclosed herein relates to an electric machine and, more particularly, to an electric machine stator with axial vents shaped as annular sectors. 
     In electric machines, a stator is normally formed to define a bore in which a rotor is rotatably supported. Rotation of the rotor can generate current in conductive elements disposed to extend through the stator when the electric machine is run in a generator mode. By contrast, current applied to such conductive elements can cause the rotor to rotate in a motor mode. 
     During operation of the electric machine in either the generator or motor mode, a large amount of heat can be generated in the conductive elements. This heat can lead to damage to the conductive elements, insulation systems, the stator or the rotor if the heat is not removed or the heated elements are not otherwise cooled. One way to remove heat and to cool the various elements in an electric machine is to form cooling or ventilation paths through the stator by which coolant, such as ambient air, is directed through or across heated parts, such as the conductive elements or the stator back iron. 
     Often, the cooling or ventilations paths are formed by the removal of material from the stator at the desired locations of the cooling or ventilation paths. Doing so results in an increase in flux density around the area of the removed material. However, saturation exhibits a non-linear thresholding effect, where the sensitivity of a region to change is dependent on the flux density in that region. Moreover, the initial distribution of flux density is dependent on the pole count and bar and slot arrangements and geometries. 
     BRIEF DESCRIPTION OF THE INVENTION 
     According to one aspect of the invention, a stator of an electric machine is provided and includes laminations arranged to form a core packet. Each lamination is formed to define an annular array of teeth at an inner radial portion thereof and an annular array of annular sectors at an outer radial portion thereof. 
     According to another aspect of the invention, a stator of an electric machine is provided and includes a stator core defining a bore in which a rotor is rotatably supportable. The stator core includes laminations arranged to form a core packet and each lamination includes an annular array of teeth at an inner radial portion thereof, the annular array of teeth defining an annular array of slots and an annular array of spokes at an outer radial portion thereof, the annular array of spokes defining an annular array of annular sectors. 
     According to another aspect of the invention, an electric machine is provided and includes a rotor and a stator defining a bore in which the rotor is rotatably supportable and operable in a motor or generator mode. The stator includes laminations respectively affixed adjacent to at least one or two neighboring laminations to form a core packet and each lamination is formed to define an annular array of teeth at an inner radial portion thereof and an annular array of annular sectors at an outer radial portion thereof. 
     According to yet another aspect of the invention, a method of assembling an electric machine is provided such that the electric machine includes a stator core having axial vents with a substantially consistent width between neighboring vents as well as between vents and an outer diameter of the stator core to thereby allow flux density to be adjusted while ensuring that all dimensions are able to be manufactured. 
     The method further limits the protrusion of the vents into the area surrounding the slots, which prevents saturation and improves performance, and provides that a number of vents and a number of slots are the same such that there will always be a path for flux lines entering or leaving a circumferential track around the outer diameter of the stator core regardless of the orientation of the field. 
     These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The subject matter, which is regarded as the invention, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
         FIG. 1  is a radial view of an electric machine in accordance with embodiments; 
         FIG. 2  is an axial view of a portion of a lamination of  FIG. 1 ; 
         FIG. 3  is an enlarged view of a group of annular sectors of  FIG. 2 ; 
         FIG. 4  is an enlarged view of a corner of an annular sector in accordance with an alternative embodiment; 
         FIG. 5  is an enlarged view of a corner of an annular sector in accordance with an alternative embodiment; and 
         FIG. 6  is a radial view of an axial vent formed by the annular sectors of a plurality of adjacent laminations. 
     
    
    
     The detailed description explains embodiments of the invention, together with advantages and features, by way of example with reference to the drawings. 
     DETAILED DESCRIPTION OF THE INVENTION 
     An electric machine is provided and includes a stator core with axial vents having shapes and sizes that provide a consistent width between neighboring vents as well as between vents and the outer diameter (OD) of the stator core. This configuration allows flux density to be adjusted while ensuring that all dimensions are able to be manufactured. It also limits the protrusion of the vents into the area around the slots, which prevents saturation and improves performance. Additionally, since a number of vents and a number of slots are the same, there will always be a path for flux lines entering or leaving the circumferential track around the OD regardless of the orientation of the field. 
     With reference to  FIG. 1 , an electric machine  10  is provided and configured to operate in a generator mode or a motor mode. The electric machine  10  includes a rotor  11  and a stator  12 . The stator  12  is formed to define a bore  120  in which the rotor  11  is rotatably supportable. Rotation of the rotor  11  within the bore  120  can generate or induce flux that in turn induces a flow of current in conductive elements (to be described below), which are disposed to extend through the stator  12  in a predefined number of windings, when the electric machine  10  is operated in the generator mode. By contrast, current applied to the conductive elements can cause the rotor  11  to rotate when the electric machine  10  is operated in the motor mode. 
     The stator  12  is formed of a plurality of laminations  20  that are stacked between end plates  200 . The end plates  200  are used to compress the laminations  20  and to provide support to end turns of the conductive elements. Each lamination  20  is formed from a relatively thin piece of sheet metal that is punched, stamped or otherwise cut into shape and then affixed adjacent to at least one or two neighboring and substantially similarly shaped and sized laminations. The bonding is achieved by an application of heat and pressure in accordance with various known methods. 
     With enough laminations  20  affixed adjacent to one another, the laminations  20  may form at least a first core packet  30  and a second core packet  40 . The first and second core packets  30  and  40  may be separated from one another by a spacer  50  that is formed to define a radial vent  51 . 
     The laminations  20  may be formed from metals or para-magnetic materials such as electrical steel or the like. 
     With reference to  FIGS. 2 and 3 , each of the laminations  20  has an inner radial portion  60  and an outer radial portion  70 . At the inner radial portion  60 , the laminations  20  are each formed to define an annular array of teeth  61 . Each tooth  61  includes a pair of opposed radial sidewalls  610  that face an adjacent tooth  61  and a circumferential sidewall  611  that faces radial inwardly toward the bore  120 . The annular array of teeth  61  thus defines a corresponding annular array of conductive element regions or slots  62  in which a plurality of conductive elements  620  are operably disposable. 
     The plurality of conductive elements  620  may be formed of a plurality of copper strands or a plurality of strands of another similarly conductive material. The strands are arranged in one or more columns in the slots  62  and have a current carrying capacity in accordance with design parameters. A layer of electrical insulation may be provided to surround each individual strand to thereby electrically insulate that strand from adjacent strands in the column or in adjacent columns 
     The electrical insulation surrounding each of the strands may be formed of a high thermal conductivity composite including one or more of polymers/resins, high thermal conductivity fillers and structural reinforcement materials such as E, S or S2 glass fibers, polyester fibers, Kevlar fibers or a like reinforcement material. Fillers made of boron nitride having cubic or hexagonal crystal structure or silica may be used. In this manner, heat transfer from each of the strands through the insulation is improved resulting in reduction of localized hot spot temperatures within individual strands and increased heat removal through axial teeth formation and axial vents (to be described below). 
     The plurality of conductive elements  620  may be connected or otherwise coupled to an electrical grid for providing alternating current to the grid. That is, when the electric machine  10  is operating in the above-noted generator mode, the electric machine converts mechanical energy embodied as a rotation of the rotor  11  to electrical energy by means of electromagnetic induction. In addition, the rotor  11  may also be connected to a grid, for example, in case of a doubly fed generator. 
     In accordance with embodiments, the plurality of conductive elements  620  may be wired with one another and with an external circuit so as to provide the stator  12  with a wiring configuration of a predefined or desired number of poles. As an example, as shown in  FIG. 2 , the wiring configuration may be that of a 6-pole wiring configuration. 
     Each of the laminations  20  is formed to define an annular array of annular sectors  71  at the outer radial portion  70  and proximate to an outer diameter of the laminations  20 . Each annular sector  71  has an isosceles crowned-trapezoidal shape with a first circumferential arc-segment edge  710 , a second circumferential arc-segment edge  711 , which is parallel with and disposed radially outwardly from the first circumferential arc-segment edge  710  and first and second radial edges  712  and  713 . The first radial edge  712  is oriented along a radial dimension of the lamination  20  and connects complementary ends of the first and second circumferential arc-segment edges  710  and  711 . The second radial edge  713  is similarly oriented along the radial dimension of the lamination  20  and connects the opposite complementary ends of the first and second circumferential arc-segment edges  710  and  711 . The first and second radial edges  712  and  713  are angled with respect to each other at a predefined radial angle measured at a rotational axis of the rotor  11 . 
     With reference to  FIGS. 3 ,  4  and  5 , the first and second circumferential arc-segment edges  710  and  711  and the first and second radial edges  712  and  713  may be formed such that one or more of the annular sectors  71  has one or more angular corners  714  (see  FIG. 3 ) or one or more rounded corners  715  (see  FIG. 4 ). Alternatively or additionally, the first and second circumferential arc-segment edges  710  and  711  and the first and second radial edges  712  and  713  may be formed such that one or more of the annular sectors  71  has one or more chamfered corners  716  (see  FIG. 5 ). 
     In order to define the shape of the annular sectors  71 , the laminations  20  each include a rim portion  72  at a radially outermost portion of the outer radial portion  70 , a circumferential portion  73 , which is proximate to but displaced from the rim portion  72 , and radially oriented spokes  74 . In accordance with embodiments, the rim portion  72  and the circumferential portion  73  may each have a substantially uniform radial width. At each annular sector  71 , the rim portion  72  provides the second circumferential arc-segment edge  711  and the circumferential portion  73  provides the first circumferential arc-segment edge  710 . The radially oriented spokes  74  extend radially outwardly from the circumferential portion  73  to the rim portion  72  and provide the first and second radial edges  712  and  713  on opposite sides thereof. 
     With the configuration described above, the rim portion  72  is disposed radially outwardly from the annular sectors  71 , the circumferential portion  73  is disposed radially inwardly from the annular sections  71  and the spokes  74  are disposed circumferentially between adjacent pairs of annular sectors  71 . 
     In accordance with embodiments, each annular sector  71  may be circumferentially disposed between a pair of adjacent slots  62  and radially displaced from the pair of adjacent slots  62 . By a similar token, each annular sector  71  may be disposed in circumferential alignment with a corresponding tooth  61 . In this way, as noted above, there will always be a path for flux lines  80  (see  FIGS. 2 and 3 ). In addition, the teeth  61  may each have substantially similar shapes and sizes, the annular sectors  71  may also have substantially similar shapes and sizes and the spokes  74  may have substantially similar shapes and sizes. In other words, the circumferential displacements between adjacent slots  62  may be substantially uniform and the circumferential displacements between adjacent annular sectors  71  may be substantially uniform. 
     When the laminations  20  are affixed adjacent to one another to form the first and second core packets  30  and  40 , the teeth  61  and the annular sectors  71  of each of the laminations  20  circumferentially line up with one another. As such, the teeth  61  form axial teeth formations  90  (see  FIG. 1 ) around which the conductive elements may be wired and the annular sectors  61  form axial vents  91  (see  FIG. 1 ). These axial vents  91  fluidly communicate with an exterior of the stator  12  and/or the electric machine  10  and the radial vent  51  (see  FIG. 1 ) such that coolant, such as ambient air, can flow through the radial vent  51  and the axial vents  91 . 
     Although described above as ambient air, it is to be understood that the coolant may include other fluids as well. These other fluids may include, for example, ambient air, nitrogen gas and/or hydrogen gas. 
     In accordance with further embodiments of the application and, with reference to  FIG. 6 , it will be understood that the axial vents  91  can be formed to permit laminar fluid flow therein or turbulent fluid flow therein. In the latter case, for example, the axial vents  91  can include turbulators  910  or other aerodynamic features that cause fluid flow with the axial vents  91  to become turbulent or form vortices  911  leading to increased heat removal from the surrounding material. The turbulators  910  can be formed from the laminations  20  themselves or as inserts to be inserted into the axial vents  91  following the stacking of the laminations  20 . 
     In accordance with further aspects, a configuration or geometry of a cross-sectional shape of the annular sectors  71  may be determined by way of a finite element analysis (FEA) or another similar analytical algorithm. 
     In accordance with further embodiments, an amount of fluid flow through the axial vents  91  may be substantially similar to the amount of fluid flow through the radial vent  51 . In this way, continued fluid flow through the electric machine  10  as a whole may be achieved without the risk of backflows or other similar issues. Thus, a size of each of the axial vents  91  may be provided such that the total amount of cross-sectional area through all of the axial vents  91  permits the substantially similar amount of fluid flow between the axial vents  91  and the radial vent  51 . 
     While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.