Abstract:
A steam turbine with at least one magnetic bearing for the shaft is provided, a metal paneling being attached in the area of a magnetic bearing. The metal paneling consists of metal rings insulated from one another. Further, cooling air ducts are provided in the area of the magnetic bearing.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority of European Patent Office Application No. 08016914.7 EP filed Sep. 25, 2009, which is incorporated by reference herein in its entirety. 
       FIELD OF INVENTION 
       [0002]    The present invention relates to a steam turbine with at least one magnetic bearing for the shaft, with steel paneling being attached in the area of a magnetic bearing. 
       SUMMARY OF INVENTION 
       [0003]    A magnetic bearing represents an alternate option to the support methods used to date. The outstanding attribute of the magnetic bearing is the lack of contact between supported part and bearing. The bearing forces needed are generated by an appropriate magnetic field which is established between the fixed part and the part to be supported. This means that the magnetic bearing is friction-free and needs no lubricant. 
         [0004]    If a magnetic bearing is used to support the shaft of a steam turbine, then the high temperatures occurring during the operation of the steam turbine are a problem for the magnetic bearing. 
         [0005]    Metal paneling is attached in the area of the magnetic bearing to minimize the eddy current losses in the bearing. This metal paneling normally consists of a number of metal rings insulated from one another by a suitable coating. The high temperatures in the shaft of a steam turbine can lead to the coating melting and thereby to the metal paneling being destroyed. 
         [0006]    An object of the present invention is thus to specify a steam turbine with at least one magnetic bearing for the shaft with which overheating of the magnetic bearing and thus destruction of the metal paneling is prevented. 
         [0007]    This object is achieved for the steam turbine given above by air ducts running in the area of the magnetic bearing in a longitudinal direction of the shaft being embodied for a supply of cooling air, with the air ducts being connected on the side of the magnetic bearing facing the blading to a cooling air supply device featuring a cooling air supply running radially and ending at the free end of the shaft end in the bearing housing. 
         [0008]    The explicit cooling of the magnetic bearing, specifically of a magnetic bearing arranged at the hot end of a steam turbine, prevents overheating of the insulating layers of the metal paneling and thereby destruction of the magnetic bearing. 
         [0009]    Further expedient embodiments of the inventive steam turbine emerge from the dependent claims and from the subsequent description of various exemplary embodiments of a steam turbine as claimed in the present invention which refer to the enclosed drawing. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    The figures show: 
           [0011]      FIG. 1  part of a longitudinal section through a steam turbine according to the present invention, 
           [0012]      FIG. 2  the detailed view D from  FIG. 1 , 
           [0013]      FIG. 3  part of a longitudinal section through a magnetic bearing at a shaft end with the inventively provided cooling air duct, and 
           [0014]      FIG. 4  part of a sectional perspective view of a shaft end with inventively provided cooling air ducts. 
           [0015]      FIG. 5  part of a sectional perspective view of a shaft end with further inventively provided cooling air ducts. 
       
    
    
     DETAILED DESCRIPTION OF INVENTION 
       [0016]      FIG. 1  shows the modules of an inventive steam turbine needed to understand the invention. The steam turbine essentially consists of the front bearing housing  1 , the rear bearing housing  2  which is located at the hot end of the steam turbine, and the center area  3  with the blading. 
         [0017]    The shaft of the steam turbine is supported in the front bearing housing  1  by a front screwed-on shaft end  4  and in the rear bearing housing  2  by a rear screwed-on shaft end  5 . 
         [0018]      FIG. 2  shows the section D through  FIG. 1 , i.e.  FIG. 2  shows the rear bearing housing  2  in detail. The magnetic bearing  6  with the metal paneling  7  is located in the rear bearing housing  2 . Arranged below the lamination are cooling air ducts  9 . The cooling air is supplied via a cooling air supply duct  8  to these cooling air ducts  9  which are arranged in a helical structure underneath the magnetic bearing  6 . 
         [0019]    The individual cooling air ducts  9  end at the free end of the shaft end in the rear bearing housing  2 . 
         [0020]      FIG. 3  shows part of a longitudinal section through the rear bearing housing  2  with the rear screwed-on shaft end  5 . This figure shows two cooling air guides. One is the cooling air guide through the cooling air ducts  9  which are arranged under the metal paneling  7  and end at the free end of the rear screwed-on shaft end  5 . 
         [0021]    At the same time, in accordance with a development of the present invention, there is a further cooling air guide which is routed to the actual shaft  13  and is routed back from there through a central axial hole into the rear bearing housing  2 . This cooling air guide is to be described in greater detail below. The precise attachment of the shaft end  5  to the shaft  13  is not to be described in any greater detail here. The figure merely shows an insulation bearing housing disk  14  between the actual shaft  13  and the screwed on shaft end  5 . This insulating disk  14  serves to interrupt the heat flow from the shaft  13  to the rear screwed-on shaft end  5 . 
         [0022]    The cooling air supply  8  supplies both the cooling air ducts  9  and also the cooling air supply in the direction of the shaft  13 . To this end radial blind holes  16  are provided at predetermined intervals in the area of the cooling air supply  8  embodied in the shape of a ring. Starting from the end of the rear screwed-on shaft end  5  lying opposite the actual shaft  13 , a number of axial holes  18  are provided in the periphery of the shaft end, which meet the radial blind hole  16 . In the vicinity of the end of the screwed-on shaft end  5  adjacent to the actual shaft further radial blind holes  17  are provided, which meet the peripheral axial holes  18 . 
         [0023]    The axial holes  18  are each closed off at their start with a closure piece  20 . Furthermore a central axial hole  19  exists which leads through the entire screwed-on shaft end  5 . In this way a further cooling air supply is produced which leads, starting from the cooling air supply  8 , through the radial blind holes  16 , the peripheral axial holes  18 , the radial blind holes  17 , through a free space between a part of the peripheral surface of the screwed-on shaft end  5  and a part of the inner peripheral surface of the shaft  13 , a chamber between shaft  13  and screwed-on shaft end  5  and through the central axial hole  19 . 
         [0024]    This significantly reduces the heat transfer from the shaft  13  to the rear screwed-on shaft end  5 . 
         [0025]    The cooling air guides for the rear screwed-on shaft end are described here. Naturally identical cooling air guides are possible for the front screwed-on shaft end. 
         [0026]    Also with the two shaft ends, when the circumstances allow, the second cooling air guide can be dispensed with. 
         [0027]      FIG. 4  shows part of a perspective cross sectional view of a shaft end with cooling air ducts  9  provided in accordance with the invention. The cooling air ducts  9  are led radially outwards by means of a ring  12  consisting of  2  parts in order to have cooling air applied to them by means of the cooling air supply  8 . The cooling air ducts  9  are formed by corresponding grooves in the shaft end as well as by the metal paneling  7  of the magnetic bearing. 
         [0028]      FIG. 5  shows part of a cross-sectional perspective view of a shaft end with further cooling air ducts  25  and  26  provided in accordance with the invention. These air ducts are formed either by grooves  25  on the inner side of the collar  22  carrying the metal paneling  23  or by axial holes  26  in the collar  22 . The cooling air ducts are led radially outwards by means of a ring  24 .