Abstract:
The present disclosure relates to a ring for a rotor of an electric machine as a support for a retaining ring and for cooling coils of the rotor. It is an object of the invention to provide measures for cooling coils of a rotor of an electric machine. Disclosed is a ring for an electric machine, the ring is connected between a retaining ring and coils wound around a rotor, whereas the ring is fabricated from a non-conductive material.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to European Patent Application No. 15177903.0 filed Jul. 22, 2015, the contents of which are hereby incorporated in its entirety. 
       TECHNICAL FIELD 
       [0002]    The present disclosure relates to a ring for a rotor of an electric machine as a support for a retaining ring and for cooling coils of the rotor. 
         [0003]    The electric machine is in particular a rotating electric machine such as a synchronous generator to be connected to a gas or steam turbine (turbogenerator) or a synchronous generator to be connected to a hydro turbine (hydro generator) or an asynchronous generator or a synchronous or asynchronous electric motor or also other types of electric machines. 
       BACKGROUND 
       [0004]    Such high power electric machines, as turbogenerators are cooled due to high heat generation in operation. In the following the concept of gaseous cooling of the rotor of the electric machine is disclosed, as an example cooling by medium air. In particular, the coils comprising windings wound around the rotor to induce a magnetic field in the rotor core are to be cooled or ventilated. To this end cooling paths are designed at the end of the coils along which the cooling gas flows. It may be advantageous to specify these coolings paths and enhance the cooling efficiency. 
       SUMMARY 
       [0005]    It is an object of the invention to provide measures for cooling coils of a rotor of an electric machine. 
         [0006]    This object is solved with the features of claim  1  and claim  7  according to the independent claims. The invention provides an efficient cooling to the coils of a rotor. The design of the ring with the material of glass fibre reduces the risk for cracks in the ring among others. This material further reduces the risk of relative movement between the ring and adjacent parts. Moreover, an earth fault is reduced when building the ring with non-conductive material, for example glass fibre. The slots have the shape of wedges regarding the radial cross-section of the ring having a deeper cavity at the outer end than at the inner end. These wedge shapes regulate the pressure of the gaseous cooling means along the slots 
         [0007]    Further examples of the invention are disclosed in the dependent claims. 
         [0008]    Advantageously, slots are formed in the outer face of the ring in the axial direction of the rotor. These slots further define the cooling paths for the gaseous cooling means. The specific shapes of the slots reduce the risk of blockage of the ventilation. The ring becomes less sensitive to dirt and less sensitive to copper movement. 
         [0009]    In a further example of the invention the slots have a rectangular shape and the slots are equidistant to each other. These measures ensure an equal flow of gaseous cooling means to the coils. 
         [0010]    In another example of the invention ventilation holes are designed in the slots to transport a cooling medium from the outside of the ring to the inside of the ring to the coils or from the inside of the ring from the coils to the outside of the ring. 
         [0011]    In a further example of the invention sheet layers are arranged between the ring and the coils for electrical insulation. These sheet layers have the main function of providing electrical insulation. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    Further characteristics and advantages will be more apparent from the description of a preferred but non-exclusive example of the ring, illustrated by way of non-limiting example in the accompanying drawings, in which: 
           [0013]      FIG. 1  shows a perspective view of a rotor of an electric machine with a shaft and coils wound around the rotor core, whereby a ring according to an example of the invention is arranged between the end of the coils and a retaining ring, for sake of illustration the retaining ring is transparent; 
           [0014]      FIG. 2  shows a cut perspective view of a ring according to an example of the invention assembled at the shaft of a rotor and attached to the coil of the rotor and a retaining ring, with slots formed in the outer face of the ring in the axial direction of the rotor, and ventilation holes designed in the slots to transport a cooling medium from the outside of the ring to the inside of the ring to the coils; 
           [0015]      FIG. 3  shows a schematic cut side view of a ring according to an example of the invention below a retaining ring, with ventilation holes designed in the ring and arrows illustrating the direction of the cooling flow. 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    With reference to the figures, these show different views of examples of the ring  1 , wherein like reference numerals designate identical or corresponding parts throughout the several views. 
         [0017]      FIG. 1  shows a perspective view of a rotor  2  of an electric machine with a rotor shaft  20  or shaft  20 , which is commonly driven by a coupled turbine (not shown) which drives the rotor  2  with a velocity of some thousand rounds per minute. Around main parts of the shaft  20  a compact rotor core  22  is built from solid magnetic forging. Within notches or slots  11  of the rotor core  22  coils  6  from copper are housed around the rotor core  22 . These coils  6  or windings magnetize the rotor core  22  in operation. At each end section of the rotor  2  a retaining ring  4  is fixed which is shown here for sake of illustration as transparent. It is clear that the retaining ring  4  is commonly not transparent but built commonly from metal. Between the retaining ring  4  and the coils  6  the ring  1  is arranged which is fixed both to the retaining ring  4  and to the coils  6 . The ring  1  is fabricated from a non-conductive material. The non-conductive material can be a material used as insulator in electric machines with proper mechanical properties for use in the rotor  2  exhibiting high rotation speeds of some thousand rounds per minute. The material of the ring  1  is chosen for minimum expansion with thermal heating of the rotor  2 . This is one reason why the ring  1  is made from a non-conducting material. The ring  1  is designed at its surface with slots  11  projecting in the axial direction of the shaft  20 . The slots  11  have an even distance between each other and have a rectangular shape regarded in the axial direction in this example. The slots  11  project from the outer end  13  in the direction to the inner end  14  in the direction of the centre of the shaft  20 . The slots  11  do not project along the whole length of the ring  1  in this example. The slots  11  further contain ventilation holes  10  which project through the whole width of the ring  1  in the radial direction of the shaft  20 . The ventilation holes  10  thus form ducts or passages in the ring  1  for a cooling medium to pass the ring  1 , in particular gaseous means. The gaseous means passing the ventilation holes  10  mainly serves for cooling the coils  6  underneath the ring  1 . 
         [0018]      FIG. 2  shows a cut perspective view of the ring  1  according to an example of the invention for an illustration in more detail. The cut perspective view shows a detail of  FIG. 1 , especially the surface of the ring  1 . The ring  1  is assembled at the shaft  20  of the rotor  2  and attached to the coils  6  of the rotor  2  and the retaining ring  4 . In  FIG. 2  the shape of the slots  11  formed in the outer face of the ring  1  in the axial direction of the rotor  2  can be seen. The slots  11  have the shape of wedges regarding the tangential cross-section of the ring  1 . With other words the slots  11  have a deeper cavity  12  at the outer end  13  than the cavity  12  at the inner end  14  of the slots  11 . This means the cross-section of the ring  1  in the area of the slots  11  is smaller at the outer end  13 . Also, the ventilation holes  10  designed in the slots  11  to transport air from the outside of the ring  1  to the inside of the ring  1  to the coils  6  or vice versa are shown. 
         [0019]      FIG. 3  shows a schematic cut side view of the ring  1  according to an example of the invention cut in the area of one of the slots  11 . Above, a cut view of the retaining ring  4  is shown. Under the retaining ring  4  a cavity  12  is designed which has the shape of a wedge enlarging in the direction to the right which is the outer end  13 . The cavity  12  illustrates one of the wedge shaped slots  11  as described under  FIG. 2  above. Under the cavity  12  formed by one of the slots  11  the ring  1  is shown. At the left the rotor core  22  is connected to the ring  1 . Further shown are the ventilation holes  10  designed through the ring  1  in a vertical direction through the whole breadth of the ring  1 . The ventilation holes  10  have cylindric shapes in this example and are evenly distributed along the length of the ring  1 . The arrows in  FIG. 3  illustrate the direction of the cooling medium flow along the ring  1  and especially along the coils  6  to be cooled arranged at the rotor core  22 . 
         [0020]    While the invention has been described in detail with reference to exemplary embodiments thereof, it will be apparent to one skilled in the art that various changes can be made, and equivalents employed, without departing from the scope of the invention. The foregoing description of the preferred embodiments of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and modifications and variations are possible in light of the above teachings or may be acquired from practice of the invention. The embodiments were chosen and described in order to explain the principles of the invention and its practical application to enable one skilled in the art to utilize the invention in various embodiments as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto, and their equivalents.