Abstract:
A reaction turbine stator vane segment comprising an integral grouping of plural vanes, an arcuate tip shroud connected between radially inner tips of the vanes, and an arcuate mounting portion extending across radially outer tips of the vanes, the arcuate tip shroud formed with plural seal components extending radially inwardly from the tip shroud.

Description:
[0001]     This application is a continuation of application Ser. No. 10/968,959, filed Oct. 21, 2004, the entire content of which is hereby incorporated by reference in this application. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     This invention relates to steam turbines having seals between rotating and non-rotating components, and more particularly, to seal configurations incorporated into integral tip shrouds of grouped stator vanes in a reaction turbine.  
         [0003]     Each stage of a reaction steam turbine includes a plurality of circumferentially spaced buckets mounted on a drum rotor surrounded by a plurality of stationary reaction stator vanes. The buckets and nozzles form one stage of the turbine, and define the main steam flow path. By way of contrast, in an impulse turbine, the buckets are mounted on the periphery of rotor wheels and the nozzle partitions are supported in surrounding diaphragms. It is highly desirable in any case to minimize or eliminate as many steam leakage paths as possible that stem from the main steam flow path.  
         [0004]     One source of leakage in a reaction turbine is a radial gap between grouped sets of reaction stator vanes provided with integral tip shrouds, and opposed radially outer portions of the rotor. One known technique for sealing this radial gap involves the utilization of insertable strip seals on the rotor that oppose seal lands on the reaction stator tip shrouds that have been sprayed with an abradable coating. Another prior technique involves the incorporation of radially projecting labyrinth teeth at the inner free ends of the nozzle or stator vanes that form labyrinth seals with radially opposed component parts of the turbine rotor. See, for example, commonly owned U.S. Pat. No. 6,786,699. The combination of labyrinth seal teeth with brush seals has also been utilized at the interface between diaphragm inner webs at the radially inner ends of nozzle partitions and rotor lands in impulse turbines. See, for example, commonly owned U.S. Pat. No. 6,669,443 and commonly owned U.S. Pat. No. 6,290,232.  
         [0005]     There remains a need, however, for effective seal configurations for use with grouped reaction turbine stator vanes having integral tip shrouds that will effectively reduce the radial gap between the tip shrouds and the opposed rotor lands.  
       BRIEF DESCRIPTION OF THE INVENTION  
       [0006]     The present invention is directed toward novel seal configurations for grouped reaction stator vane segments with integral tip shrouds. The exemplary embodiments relate to integrated one-piece stator vane segments incorporating multiple vanes and seal configurations that may include a combination of strip seals, brush seals or integral seal teeth that oppose rotor seal lands in the assembled steam turbine.  
         [0007]     For purposes of this invention, the term “grouped reaction stator vanes with integral tip shrouds” refers to a plurality (2 or more, and up to about 50) of reaction turbine stator vanes with integral cover shrouds that have been grouped together by machining as a one-piece or unitary group, where two or more groups make up a 360° ring; or by welding or brazing individual vanes to form a group, where two or more groups also make up a 360° ring.  
         [0008]     In a first configuration, a machined one-piece stator vane segment includes a plurality of vanes, integral tip shroud and integral dovetail (or other mounting configuration). The stator tip shroud extends over the plurality of vanes, connecting the tips thereof, and is provided with a generally centered insert. The insert includes a brush seal, and the insert is flanked by conventional caulked strip seals upstream and downstream of the brush seal. In a second exemplary configuration, the integral stator tip shroud is provided with a generally axially centered (i.e., in a flow direction) insert having a brush seal with integral machined labyrinth seal teeth located upstream and downstream of the insert. In a third configuration, the stator tip shroud is machined to include a dovetail slot into which a seal strip assembly may be inserted. The insertable seal strip assembly is provided with an axially centered brush seal with integral labyrinth seal teeth upstream and downstream of the brush seal.  
         [0009]     For all of the configurations, the opposed rotor surface may be machined to include a high-low-high land configuration or, a low-high-low land configuration to match a similar seal arrangement in the tip shrouds. In addition, the specific number of seals, opposed seal lands, and choice of specific seals and/or combination of seals may vary based upon specific application.  
         [0010]     Accordingly, the present invention in its broader aspects relates to a reaction turbine stator vane segment comprising an integral grouping of plural vanes, an arcuate tip shroud connected between radially inner tips of the vanes, and an arcuate mounting portion extending across radially outer tips of the vanes, the arcuate tip shroud formed with plural seal components extending radially inwardly from the tip shroud.  
         [0011]     In another aspect, the invention relates to reaction turbine stator vane segment comprising a unitary machined grouping of plural vanes, an arcuate tip shroud connected between radially inner tips of the vanes, and an arcuate mounting portion extending across radially outer tips of the vanes, the arcuate tip shroud formed with plural seal components extending radially inwardly from the tip shroud, wherein the plural seal components include a brush seal insert received in a groove in the tip shroud, with additional seal components on opposite sides of the brush seal.  
         [0012]     The invention will now be described in detail in connection with the drawings identified below. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]      FIG. 1  is a perspective view of a grouped reaction stator vane segment;  
         [0014]      FIG. 2  is a partial end elevation of a grouped reaction stator vane segment incorporating a seal configuration in accordance with a first exemplary embodiment of the invention;  
         [0015]      FIG. 3  is a partial end elevation of a grouped reaction stator vane segment incorporating a seal configuration in accordance with a second exemplary embodiment of the invention; and  
         [0016]      FIG. 4  is a partial end elevation of a grouped reaction stator vane segment incorporating a seal configuration in accordance with a third exemplary embodiment of the invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0017]     With reference to  FIG. 1 , a grouped reaction stator vane segment  10  includes a plurality of reaction vanes  12 , an integral, arcuate tip shroud  14  at the radially inner ends of the vanes, and a dovetail or other mounting configuration  15  at the radially outer ends of the vanes. While the figure shows a group of four vanes  12 , it is to be understood that the segment may include other numbers of vanes, for example, 6, 8, 12, up to as many as 50 vanes or more, the latter forming a 180° segment. Together, two or more such segments form a closed 360° ring of reaction vanes.  
         [0018]     In the preferred arrangement, the segment  10  is machined from a single block of metal material, preferably a stainless steel alloy, but individual vanes may also be grouped by welding, brazing or other suitable means to form a segment.  
         [0019]     Turning now to  FIG. 2 , the segment  10  and, specifically, the tip shroud  14  is provided with a combined strip and brush seal arrangement. Specifically, a brush seal insert  16  is slidably received within a groove  18  formed in a radially inner face  19  of the tip shroud  14 . The insert incorporates brush seal elements  20  that extend radially inward to a location closely adjacent a land  22  on the turbine rotor  24 . A pair of strip seals  26 ,  28  are seated in respective grooves  30 ,  32  in the face  19  of the tip shroud on opposite sides of the brush seal insert, and secured by, for example, peening. These strip seals extend inwardly with the tips closely adjacent respective lands  34 ,  36  of the rotor  24 . Note that the strip seals  26 ,  28  lie, respectively, upstream and downstream of the generally axially centered brush seal  16  (relative to the direction of steam flow), in a high-low-high arrangement vis-à-vis the turbine lands. It will be understood that the turbine land configuration could be reversed, with appropriate relocation of seal tips in a low-high-low configuration.  
         [0020]      FIG. 3  illustrates an alternative arrangement in connection with a reaction stator vane segment  38 . In this embodiment, the tip shroud  40  is fitted with a generally axially centered brush seal insert  42 , seated in a groove  43  formed in the radially inner face  44  of the tip shroud, with brush seal elements  45  similar to the insert  16  in  FIG. 2 . Labyrinth seal teeth  46 ,  48 , respectively, are formed integrally with the tip shroud  40  and lie upstream and downstream of the brush seal insert  42 , interacting with lands  50  and  52  on the rotor  54 . The brush seal elements  44  extend inwardly to a turbine land  56 . Here again, a high-low-high land configuration is illustrated but, as in the case of  FIG. 2 , that configuration may be reversed to a low-high-low arrangement.  
         [0021]      FIG. 4  illustrates yet another embodiment of the invention where the reaction vane segment  58  includes an integrated tip shroud  60 , the radially inner face  61  of which is formed with a dovetail-like groove  62  that receives an arcuate seal strip assembly insert  64 . The insert  64  is provided with a generally axially centered brush seal  66  having brush seal elements  68  that extend inwardly to a location closely adjacent the turbine land  70 . The insert  64  is also formed with integrated upstream and downstream labyrinth seal teeth  72 ,  74  which extend radially inwardly to a location closely adjacent respective lands  76 ,  78  of the rotor  80 . As in the prior embodiments, the high-low-high land configuration may be reversed to a low-high-low configuration, with suitable modification of the sealing elements. It will be appreciated that the labyrinth seal teeth  72 ,  74  could be replaced with strip seals similar to those in  FIG. 2 .  
         [0022]     The above-described seal configurations reduce the radial gap between the rotor and the reaction stator vane tip shrouds, and at the same time reduce assembly time for the rotor and eliminate the need for an abradable coating on the reaction stator&#39;s integral tip shroud. It will be appreciated that the tip shrouds may incorporate seals and/or seal inserts with any combination of strip seals, brush seals, or labyrinth seal teeth.  
         [0023]     While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.