Abstract:
A load coupling device for a power train including: a rotatable shaft; a first flange on a first end of the shaft, wherein the first flange is adapted to couple to a first rotating shaft of at a torque producing turbine or a torque driven electrical generator; a second flange on an opposite end of the shaft, wherein the shaft is adapted to couple to a second rotating shaft of the other of the turbine and the generator, and an annular ring extending radially outward from the first flange, wherein the mass of the annular ring is selected to shift a torsional natural frequency of the power train away from an operational condition of the power train. Trim masses may be added to make fine adjustments to the torsional natural frequency of the power train.

Description:
RELATED APPLICATION 
       [0001]    This application is a divisional of U.S. patent application Ser. No. 13/236,975 filed Sep. 20, 2011, the entirety of which application is incorporated by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The invention relates generally to compensating for torsional frequency in a power train or other systems including rotating bodies. 
         [0003]    Power trains are typically mechanical and electrical systems that generate and deliver power. An example of a power train is a turbine and generator coupled by a load coupling. The turbine applies torque to the load coupling which drives the generator that produces electrical power. 
         [0004]    Vibrations in the power train are induced by cyclical variations in the torque or other forces applied to or by the power train. If the frequencies of these cyclical variations coincide with the natural frequencies of the power train, the cyclical variations may cause excessive torsional vibrations in the power train. 
         [0005]    Power trains are often designed to operate away from their torsional natural frequencies. Despite well intentioned designs, power trains may experience cyclical variations in torque at frequencies at or near the natural frequencies. Under these cyclical variations, the power train may excessively vibrate and be damaged. There is a long felt need for devices and methods to adjust the inertia and natural torsional frequencies of a power train and other rotating bodies. 
         [0006]    The turbine and generator in an industrial power train are typically large and heavy devices. A turbine may be an industrial gas turbine or steam turbine which are large and heavy power generation units. Similarly, the generators may be large generators used by utilities to produce electrical power. Due to their large size and mass, it is difficult to modify the turbines and generators after they have been installed sufficiently to shift the natural frequencies at which they vibrate. There is a long felt need to adjust the inertia and natural torsional frequencies of industrial power trains that does not require substantial changes to the turbines or generators. 
       SUMMARY OF INVENTION 
       [0007]    A device and method has been developed to modify the torsional natural frequency of a power train. The device allows for modification of the moment of inertia of the power train. The moment of inertia may be adjusted by arranging masses positioned in an annular array around a flange of the load coupling. By removing, adding or changing the masses, the moment of inertia of the load coupling is changed. A change in the moment of inertia moves the torsional natural frequencies for the load coupling and power train. By proper selection and positioning of the masses around the load coupling, the torsional natural frequencies of the power train may be adjusted to provide adequate torsional frequency margins for the power train during expected operational conditions. 
         [0008]    A load coupling device for a power train has been conceived which includes: a rotatable shaft; a first flange on a first end of the shaft, wherein the first flange is adapted to couple to a first rotating shaft of a torque producing power supply or a torque driven power load; a second flange on an opposite end of the shaft, wherein the shaft is adapted to couple to a second rotating shaft of the other of the torque power supply and the torque driven power load, and an additional mass added to the first flange, wherein the additional mass is selected to shift a torsional natural frequency of the power train away from an operational condition of the power train. 
         [0009]    The additional mass may be an annular ring extending radially outward from a coupling region of the first flange, wherein the coupling region of the first flange receives fasteners to secure the first flange to a flange of the first rotating shaft. The annular ring may be integral with the first flange, wherein the load coupling is adapted to be substituted for an existing load coupling in the power train. The annular ring may be fitted to an outer circumference of the first flange. 
         [0010]    The load coupling device may further include trim masses adapted to be sequentially added to the additional mass. The trim masses may be plugs arranged in an annular array, rings or plates arranged in an annular array. The plugs may be removable trim mass plugs arranged in a circular array in the annular ring. 
         [0011]    A load coupling device has been conceived for a power train comprising: a rotatable shaft; a first flange on a first end of the shaft, wherein the first flange is adapted to couple to a first rotating shaft of a torque producing turbine or a torque driven electrical generator; a second flange on an opposite end of the shaft, wherein the shaft is adapted to couple to a second rotating shaft of the other of the turbine and the generator, and an annular ring extending radially outward from the first flange, wherein the mass of the annular ring is selected to shift a torsional natural frequency of the power train away from an operational condition of the power train. 
         [0012]    A power train has been conceived comprising: a torque producing power source including a rotating connecting flange; a torque driven power load including a rotating connecting flange; a load coupling having a first flange adapted to couple to the connecting flange of one of the torque producing power source and the torque driven power load; a second flange on load coupling adapted to couple to the coupling flange of the other of the torque producing power source or the torque driven power load, and an additional mass added to at least one of the connecting flanges or the load coupling wherein the additional mass is selected to shift a torsional natural frequency of the power train away from an operational condition of the power train. 
         [0013]    A method has been conceived to shift a torsional natural frequency of a power train including a load coupling the torque output of a turbine to drive an electrical generator, the method comprising: determining the power train has a torsional natural frequency which is excessively excited during an anticipated operational condition of the power train; adding an annular ring or annular array to the load coupling to shift the torsional natural frequency response of the power train, and determining if the power train operating with the load coupling having the annular ring or the annular array does not excessively excite the shifted torsional natural frequency during the anticipated operational conditions of the power train. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    The invention, including its best mode, is disclosed in the following figures where: 
           [0015]      FIG. 1  is a schematic diagram a power train having a load coupling. 
           [0016]      FIG. 2  is a perspective view of a conventional load coupling. 
           [0017]      FIG. 3  is a schematic diagram of a power train having a load coupling having a mass adjustment. 
           [0018]      FIG. 4  is a perspective view of a load coupling with the mass adjustment. 
           [0019]      FIG. 5  is a perspective view of a plug to be inserted in the load coupling. 
           [0020]      FIG. 6  is a cross-sectional view of a load coupling with added ring masses. 
           [0021]      FIGS. 7 and 8  are cross-sectional views of further embodiments of additional masses added to the flanges of a load coupling and flanges of a rotor or turbine shaft. 
           [0022]      FIGS. 9 and 10  are a cross-sectional views, taken parallel to the load coupling axis and perpendicular to the axis respectively, of a further embodiment of additional masses added to the flanges of a load coupling and flanges of a shaft of a power train. 
           [0023]      FIG. 11  is a perspective view of a plate which is inserted in a chamber of a mass ring. 
           [0024]      FIG. 12  is a cross-sectional view of a further embodiment of adding mass to the flanges of a load coupling. 
           [0025]      FIG. 13  is a cross-sectional diagram of a shortened load coupling and a mass disc sandwiched between the load coupling and shaft. 
           [0026]      FIG. 14  is a cross-sectional view of a further embodiment of adding mass between the load coupling and a shaft in the power train system. 
           [0027]      FIG. 15  is a perspective view of another embodiment of a load coupling which has an added mass included with the shaft of the coupling. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0028]      FIG. 1  is a schematic illustration of a conventional power train having a steam or gas turbine  10  with a rotor shaft  12 , which is attached to a first end of a load coupling  14 . The opposite end of the load coupling is attached to the rotor  16  of an electrical generator  18 . 
         [0029]    The power train will be typically designed such that its operating conditions avoid the torsional natural frequencies. For example, the normal operating rotating speed of the rotors and load coupling may be selected to avoid the torsional natural frequencies of the power train. The design requirements of the power train may include margins each centered on a torsional natural frequency. The power train is to be operated at rotational speeds that avoid these margins so as to avoid exciting the torsional natural frequencies. 
         [0030]    Despite efforts to design a power train to avoid torsional natural frequencies it may be discovered during testing or other operation of the power train that torsional natural frequencies are excited at normal operating conditions. If one or more of the torsional natural frequencies of the power train are excited during operating conditions or if the power train has insufficient torsional frequency margins, there is a need to modify the torsional frequency of the power train. 
         [0031]    The power train has one or more natural frequencies which may be excited by torsional vibrations occurring at or near a torsional natural frequency. The natural frequencies of the power train are dependent on the inertia of the power train. The inertia of the load coupling is a component of the inertia of the power train. Because the inertia of the load coupling affects the natural frequencies of the power train, the natural frequencies of the power train may be adjusted by changing the inertia of the load coupling. 
         [0032]      FIG. 2  shows a conventional load coupling  14  having annular flanges  20 ,  22  at opposite ends of a cylindrical drive shaft  24 . The flanges include holes that receive bolts or other fasteners to attach to a mating flange at the end of the rotors of the turbine and generator. The load coupling transfers the torque applied by the rotor for the turbine to drive the rotor for the generator. The conventional load coupling  14  does not offer the ability to adjust the mass or inertia of the load coupling. 
         [0033]      FIG. 3  shows a power train  26  including a steam or gas turbine  10  having a rotor  12 , a load coupling  28 , an electrical generator  18  with a rotor shaft  16 . The load coupling  28  may include a normal sized flange  20  which couples to a similarly sized flange  30  on the rotor shaft for either the turbine or generator. The flange  32  on the opposite end of the load coupling  28  may be oversized or have mass attachments  34  on its circumference. The radially inward region of the flange  32  may attach to a similarly sized flange  36  on the rotor for the generator or turbine. In alternative embodiments, the flange which is oversized or has a ring or other mass attachment may be the flanges on the rotor for the turbine or generator. Similarly, the flange which is oversized or has a mass attachment may be coupled to one or more of the shafts  12 ,  38  and  16  for the turbine, load coupling and generator. 
         [0034]      FIG. 4  is a perspective view of the front and side of the load coupling  28  having an oversized flange  32 . As compared to the traditional sized flange  20 , the oversized flange may have a substantially larger diameter (D). The radially inward circular array of holes  40  receive the bolts that couple the load coupling to the rotor shaft of the turbine or generator. A similar array of bolt holes  42  are on the flange  20  at the opposite end of the load coupling. 
         [0035]    A radially outer region  44  of the large sized flange  32  has an adjustable mass and hence adjustable inertia. In the example shown in  FIG. 4 , the adjustable mass is provided by mass plugs  46  inserted in a circular array of holes  48 , e.g., threaded holes, in the outer region  44 . The plugs  46  may be removable from the holes  48 , and may be inserted in all of the holes  48  in the circular array. 
         [0036]    The increased diameter of the flange  32  results in a different inertia for the load coupling  28  as compared to the inertia of the conventional load coupling  14 . The change in inertia due to substituting the load coupling  28  for the conventional load coupling  14  may be used to shift the torsional natural frequencies of the power train. The shift in the inertia will change the natural frequencies of power train. The shift in the natural frequency is intended to avoid the frequencies of torsional vibrations applied to or generated by the power train. The intended shift in the natural frequencies by rearranging and replacing the plugs should result in a power train which does not experience excessive torsional vibration and has sufficient torsional frequency margin. In addition to substituting load couplings or in the alternative, plugs, rings or other additional masses may be added to the outer radial portion of one or more flanges associated with the load coupling or the rotor shafts for the turbine or generator. 
         [0037]    A substitute load coupling  28  or masses added to the perimeter of an existing flange, such as on the in-place load coupling, may be installed without moving the turbine or generator and without making substantial changes to other components adjacent the load coupling. The existing load coupling  14  may be unbolted from the rotors  12 ,  16  of the turbine and generator, and removed by a crane. The substitute load coupling  28  with large diameter flange  32  may be positioned by the crane between the rotor shafts  12 ,  16  such that the bolt openings  40 ,  42  are aligned with the bolt openings in the rotor shaft flanges for the turbine and generator. Bolts are inserted through the bolt openings to couple the load coupling  28  to the rotor shafts  12 ,  16  of the turbine and generator. 
         [0038]    Plugs  46  having various masses may be available for insertion in the holes  48 . The plugs may be used to tune the frequency response of the power train and, particularly, shift its torsional natural frequencies. For example, during initial setup of the power train, the plugs  46  inserted in all of the holes  48  may each have substantially the same density, e.g., formed of the same material, as the material forming the large sized flange  32 . If a determination is made during initial testing of the power train or at other time that a change is needed to the natural frequencies of the power train, the plugs  46  may be replaced by alternative plugs having a different mass, e.g., less dense, than the plugs initially installed in the holes  48 . Changing the density of the plugs will cause the inertia of the load coupling and the power train to shift. 
         [0039]      FIG. 5  is a perspective view of a side and front of an exemplary plug  46 . The plug  46  may be a portion of a threaded rod, such that the threaded outer surface  50  of the plug engages threads on the inner cylindrical surface of the holes  48  in the flange  32 . The plug may be circular in cross-section and have straight, center axis. A hexed recess  52  is aligned with the axis and in the front surface of the plug. The hexed recess  52  receives a hexed end tool which is used to insert and remove the plug from the holes  48  in the flange. The plugs  46  may be replaced and rearranged relatively easily and without disassembling other components of the power train. 
         [0040]    The plugs  46  are an example of a trim mass that may be used to make fine adjustments to the frequency response of the power train. The trim masses may be used in addition to adding a larger mass to the load coupling to shift the torsional frequency natural modes of the power train. Alternatively, the trim masses may be included in a load coupling provided with the initial installation of a power train. 
         [0041]      FIG. 6  is a cross-sectional view of a conventional load coupling  14  having a ring mass  53  attached to the perimeter of one of the flanges  22  of the load coupling. The ring mass  53  changes the inertia of the load coupling and hence shifts the torsional natural frequencies of the power train that includes the load coupling. The ring mass  53  may be metallic and formed of substantially the same metal as the load coupling. 
         [0042]    The ring mass  53  may be press fitted and heat shrunk on the flange  22 . The ring mass may be heated to cause it to expand. While expanded, the ring mass is moved in an axial direction to be pressed onto the outer circumference of the flange  22 . This press fitting may be performed after segments of the ring mass have been welded to form an annulus around the shaft of the load coupling or after the load coupling has been disconnected from the rotor shaft of the turbine or generator. As the ring mass cools and shrinks onto the perimeter of the flange  22 . An annular weld  54  may secure the ring mass to the flange  22 . 
         [0043]    Additional mass may be added to the load coupling  14  by one or more stacking ring masses with the first ring mass  53 . The additional ring masses  56  may be stacked axially with the first ring mass  53 . A clamp  58  may secure the ring masses  56 ,  53  together. Alternatively to stacking the ring masses axially, the ring masses may be mounted radially, e.g., superimposed, with each ring having a diameter slightly larger than the prior ring. 
         [0044]    The additional ring masses  56  may be added sequentially with the vibration frequency response of the power train tested between each application of a ring mass. When the frequency response of the power train is acceptable, such as when the power train has sufficient torsional frequency margins. 
         [0045]      FIGS. 7 and 8  are cross-sectional views of further embodiments of additional masses added to the flanges  60  of a load coupling  62  and flanges  64  of a generator or turbine shaft  66 . The load coupling and flanges are shown only partially in  FIGS. 7 and 8 . An annular ring mass  68  may be integral with one of the flanges  60 ,  64  or may be fitted onto one or both of these flanges. The perimeter of the ring mass  68  includes one or more stepped ledges  70 . Additional ring masses  72 ,  74  may be seated on the ledges  70 . The ring masses  72  may be stacked axially as shown in  FIG. 8  or stacked radially  74  as shown in  FIG. 7 . Further the ring masses may have different masses such as by having different cross-sectional shapes. The ring masses  68 ,  72 ,  74  may be formed of the same material as the flange  64  to allow for uniform thermal expansion and contraction of the rings and flanges. 
         [0046]    The addition of the ring mass  68  may by itself be sufficient to shift the torsional natural frequencies of the power train such that the torsional frequency margins are sufficient. If the ring mass  68  is not sufficient, the additional ring masses  72 ,  74  may be added sequentially to tune the frequency response of the power train and ensure adequate margins associated with the natural frequencies of the power train. 
         [0047]    The ring masses  68 ,  72  and  74  may be secured to the flange  64  by an annular ring or shank  76  that abuts the ring masses  68 ,  72  or  74 . The shank  76  may be an annular array of teeth welded  78  to the flange  60 . The ring or shank  76  may have sufficient mass to contribute to the shift in inertia and torsional natural frequencies provided by the ring masses  68 ,  72  or  74 . 
         [0048]      FIGS. 9 and 10  are cross-sectional views, taken parallel to the load coupling axis and perpendicular to the axis respectively, of a further embodiment of additional masses added to the flanges  60  of a load coupling  62  and flanges  64  of a generator or turbine shaft  66 . The ring mass  80  has an internal annular slot  82  which receives ring bands  84 ,  86  or plates  88  that add mass to the ring mass  80 . The annular slot may be continuous around the flange  64  or segmented into individual chambers as shown in  FIG. 10 . If the slot  82  is continuous, the added masses may be the ring bands  84 ,  86 . If the slot  82  is segmented, the plates  88 , see  FIG. 11 , may be added in selected segments of the slot. The ring bands  84 ,  86  and plates  88  are added to adjust the inertia of the load coupling and thereby tune the frequency response of the power train. 
         [0049]      FIG. 12  is a cross-sectional view of a further embodiment of adding mass to the flanges  60 ,  64  of a load coupling  62  and shaft  66  of a power train. An annular ring  90  with an interior chamber  92  is added to or integral with any of the flanges  60 ,  64 . If mass needs to be added to shift the torsional natural frequencies, a liquid is pumped from a liquid source  94  into the chamber  92 . The amount of fluid pumped into the chamber is determined based on the amount of mass needed to be added to shift the torsional natural frequencies of the power train and the amount of shift desired. During operation, the centrifugal force due to rotation of the ring  90  will cause the liquid to move radially outward in the chamber  92 . 
         [0050]      FIG. 13  is a cross-sectional diagram of a shortened load coupling  100  having normal diameter flanges  102 ,  104  which are bolted to the flanges  106  of the shafts  108  for the turbine and generator. The load coupling  100  does not extend the full distance between the ends of the shafts. The load coupling  100  may be substituted for an existing load coupling such as  14  in  FIG. 1 . 
         [0051]    A mass disc or ring  109  is sandwiched between the flange  102  of the load coupling and the flange  106  of the shaft  109 . Bolts  110  extend through aligned openings in both flanges and the disc or ring  109  to couple the assembly together. 
         [0052]    The mass disc  109  may be a circular or annular device having a mass sufficient to change the inertia and torsional natural frequency of the power train. The mass disc may have a radial outward region  112  that has more mass than radially inward portions of the disc. Concentrating the mass of the disc radially outward increases the shift in torsional inertia resulting from the addition of the mass disc  109 . 
         [0053]      FIG. 14  is a cross-sectional view of a further embodiment of adding mass between the flange  102  of a load coupling  100  and the flange  106  of a shaft  108  in the power train system. Whereas  Figure 13  shows a single disc  109  sandwiched between the flanges,  FIG. 14  shows a stack of two or more rings or discs sandwiched between the flanges. A first disc or ring  112  may be relatively thick and add a substantial amount of mass to the load coupling and power train. The first disc or ring  112  may be selected to approximate the desired mass needed to shift the torsional natural frequencies of the power train. One or more thinner discs or rings  114  may be stacked between the first disc  112  and a flange  106  to tune the natural frequencies and frequency response of the power train. The thinner discs may have less mass, e.g., between one half to one quarter, the mass of the first disc  112 . The thinner discs may be added sequentially and as each disc  114  is added, the power train may be tested to determine if its frequency response provides adequate margins about the torsional natural frequencies. 
         [0054]      FIG. 15  is a perspective view of the side and an end of a load coupling  120  having, as an added mass, an annular collar  122  added to the shaft  124 . The flanges  126  at opposite ends of the load coupling may be sized to connect to respective flanges on a turbine and a generator. 
         [0055]    The annular collar may be integral with the shaft of the load coupling or added, e.g., welded or clamped, to the shaft of the load coupling. The annular collar may be coaxial to the axis of the load coupling and aligned with the longitudinal center of the load coupling. The outer cylindrical surface of the annular collar may include recesses for trim masses  128 . The trim masses  128  may be threaded plugs which are inserted in threaded openings in the annular collar. The trim plugs may be removed or replaced with other trim plugs having differing masses. The removal and replacement of trim plugs may be used to make fine adjustments, e.g., tune, the frequency response of the power train which includes the load coupling  120 . 
         [0056]    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.