Abstract:
A system for securing a nut ( 24 ) used to compress a compliant seal ( 23 ) surrounding a radial conductor lead ( 21 ) of an electric generator ( 10 ). The generator has a rotor ( 11 ) with the radial conductor lead arranged in a radial lead bore ( 20 ) of the rotor and the seal coaxially arranged surrounding the radial lead. A receiving pocket ( 15 ) is arranged in a body of the rotor adjacent to the radial lead bore. The nut is arranged coaxially with the radial conductor lead, the nut including a seal contacting surface ( 35 ) and a ligament ( 26 ) arranged opposite the seal contacting surface, wherein a portion of the ligament is deformed into the receiving pocket to lock the nut against rotation, thereby maintaining a desired degree of compression on the seal.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates generally to the field of electrical generators, and more specifically to a system for securing a radial lead nut of an electrical generator. 
       BACKGROUND OF THE INVENTION 
       [0002]    Turbomachines include a rotational shaft known as a rotor and a stationary portion known as a stator. Turbomachines include, but are not limited to steam turbines, gas turbines, electrical generators, compressors, and pumps. For example, an electrical generator typically includes main components like a rotor and stationary electrical conductors. The rotor typically includes rotor electrical conductors that produce a magnetic field when energized with an electric current. 
         [0003]    The rotor of a generator receives the energizing current from an energizing device coupled to an end of the rotor. The rotor typically contains conductors that mate to the energizing device and route the energizing current along the rotor axial centerline via an axial conductor. A radial lead conductor then routs the energizing current radially from the rotor centerline to the rotor surface where the energizing current is then directed to the magnetic field generating conductors. 
         [0004]    If the energizing current is direct current, then the magnetic field produced is constant in magnitude. However, as the rotor rotates, the field strength at a stationary point will vary as the magnetic field poles pass by. The stationary electrical windings surround the rotor and are arranged to intersect the rotating magnetic field such that an alternating current is induced in the stationary electrical windings. The stationary windings are connected to an electrical network such that the induced alternating current is distributed to many users. 
         [0005]    Operation of the generator produces heat within the internal components of the generator. Typically, generators are cooled by a cooling medium, such as air, water or hydrogen gas. In the case of hydrogen gas, care must be taken to prevent mixing of the hydrogen gas with the surrounding air to avoid an explosive mixture of hydrogen and oxygen. Typically, hydrogen cooled generators are operated under positive pressure and high hydrogen purity to ensure that a combustible mixture of hydrogen and oxygen does not result within the generator. A hydrogen cooled generator is typically enclosed within a strong shell-like frame that supports the weight and operational and transient loads of the generator, and also contains the hydrogen gas and prevents it from escaping into the atmosphere where it can form a combustible mixture. 
         [0006]    In order to prevent a hydrogen gas leak path along the radial lead conductor, the conductor is sealed against surrounding structures. One means of sealing against hydrogen gas leakage is to employ deformable seals stacked around the radial lead conductor, thereby forming a gas tight barrier between the radial lead conductor and the rotor body. The deformable seals are compressed by a radial lead nut that surrounds the radial lead conductor and threads into the rotor body. The axial compression of the seals causes the seals to expand radially, forming a gas tight seal against the surrounding rotor structure. The compression of the deformable seals is critical to maintain proper sealing during operation. The amount of compression of the seals is determined at assembly of the rotor by the extent that the radial lead nut is threaded into the rotor body. In order to preserve the correct compression of the deformable seals, the radial lead nut should advantageously be restrained from further rotation, either clockwise or counter clockwise, with respect to the rotor body. 
         [0007]    Typically, to prevent undesirable rotation of the radial lead nut, a portion of the rotor body is deformed into the radial lead nut using a blunt tool such as a punch and a hammer. The hammer is used to impact the tool to plastically deform a portion of the rotor body into the threads or receiving slots of the radial lead nut, thereby binding the radial lead nut and preventing unwanted rotation. Deforming the rotor body material into the radial lead nut to prevent rotation is a well known process known as staking. However, the deformed rotor body material resulting from staking can lead to undesirable stress risers and crack initiation sites. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    The invention is explained in the following description in view of the drawings that show: 
           [0009]      FIG. 1  is a longitudinal view of an electric generator; 
           [0010]      FIG. 2  is a detailed cut-away view of the generator rotor exciter end; 
           [0011]      FIG. 3  is a detailed view of the rotor radial lead; 
           [0012]      FIG. 4  is a top view of  FIG. 3 ; 
           [0013]      FIG. 5  is an embodiment of the nut of  FIG. 3 ; 
           [0014]      FIG. 6  is a further embodiment of a radial lead nut; 
           [0015]      FIG. 7  is an embodiment of tool; 
           [0016]      FIG. 8  shows the tool of  FIG. 7  at the beginning of use; 
           [0017]      FIG. 9  shows the tool of  FIG. 7  at the end of use. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0018]    The present invention is disclosed in the context of securing a nut relative to a rotor within an electric generator of an electric power production facility. The principles of the present invention, however, are not limited to use with an electric generator or within an electricity power production facility. For example, the methods and/or systems could be used within the aerospace, transportation or manufacturing industries or any other area where fixation of a rotatable component is needed relative to a stationary component. One skilled in the art may find additional applications for the systems, kits, and arrangements disclosed herein. Thus the illustration and description of the present invention in context of the exemplary electric generator is merely one possible application of the present invention. However the present invention has particular applicability for use as a means of fixing a component against rotation within an electric generator. 
         [0019]    Referring to  FIG. 1 , a hydrogen cooled electric generator  10  typically comprises a rotor  11  centered along a centerline  1  and surrounded by a stator of the generator  10 . The rotor  11  is connected to an electrical excitation device  13  that electrically energizes the rotor  11 . Opposite the excitation device  13  is a prime mover (not shown for clarity) that operatively rotates the rotor. The rotor  11  contains electrical rotor conductors that are connected to the excitation device  13  that provides an excitation current in the rotor conductors. The excitation current in the rotor conductors creates a magnetic field of variable strength proportional to the magnitude of the provided current. The rotor  11  operatively rotates while producing the aforementioned magnetic field. The rotating magnetic field induces an alternating current in the stator  12  that surrounds the rotor  11 . The stator then is electrically connected to a power distribution network that carries the induced alternating current to users. 
         [0020]    The excitation current is conducted between the excitation device  13  and the rotor conductors via an axial conductor  22  and a radial lead conductor  21  as seen in  FIG. 2 . The axial conductor  22  is arranged along the rotor centerline  1 . The radial lead conductor  21  intersects the axial lead  22  and conducts the excitation current radially from the rotor centerline  1  to the rotor outer diameter for electrical connection to the rotor field conductors. The radial lead  21  is set within a radial lead bore  20  as seen in  FIGS. 2 and 3 . There is a radial clearance between the radial lead  21  and the radial lead bore  20  which could permit leakage of hydrogen cooling gas absent a positive sealing mechanism. 
         [0021]    To seal the hydrogen cooling gas, a seal, or a plurality of seals,  23  can be employed which seals the radial gap between the radial lead bore  20  and the radial lead  21  when compressed between nut  24  and shoulder  25  as seen in  FIG. 3 . The compression of the seals  23  is a function of the radial position of the seal contacting surface  35  of nut  24  relative to the shoulder  25 . During operation, vibration, centrifugal loading, thermal cycling and other factors can effect the radial position of the seal contacting surface  35  due to rotation of the nut  24  in the radial lead bore  20 . Therefore, rotation of the nut  24  affects compression of the seals  23  and ultimately the effectiveness of the seals  23  against leakage of the hydrogen gas. To maintain the proper compression of the seals  23 , it is preferable to fix the rotational position of the nut  24 . 
         [0022]    As seen in  FIG. 3 , a receiving pocket  15  is provided at the outer diameter of the rotor body  11  adjacent to the radial lead bore  20 . The receiving pocket  15  can be configured such that the receiving pocket  15  opens into the radial lead bore as seen in  FIGS. 3 and 4 . However, the receiving pocket can be configured such that the receiving pocket  15  does not open into the radial lead bore  20 . In either case, the pocket  15  is adjacent the bore for receiving a deformed portion of a radial lead nut, as described more fully below. 
         [0023]    The cyclic stress state during rotor operation is at a relatively minimum value along the rotor centerline axis  1  and at a relatively maximum along an axis  2  that is perpendicular to the rotor centerline as seen in  FIG. 4 . The operative stress state of the rotor therefore is a gradient between the rotor centerline axis  1  and the perpendicular axis  2 . The receiving pocket  15  may therefore be arranged advantageously away from the areas of highest stress. The receiving pocket  15  can be arranged based on the quadrants A and B where the quadrants A contain a location of minimum cyclic stress and quadrants B contain a location of maximum cyclic stress. Specifically, quadrant A is the area of the rotor  11  between the lines  3  and  4  that contains the rotor centerline  1  and quadrant B is the area of the rotor  11  between the lines  3  and  4  that contains axis  2  as seen in  FIG. 4 . Therefore, the receiving pocket  15  may be arranged in quadrant A rather than in quadrant B. Furthermore, it is desirable to avoid arranging the receiving pocket  15  along axis  2  where the operative cyclic stresses are a maximum. Furthermore, the receiving pocket  15  is preferably formed in accordance with common engineering practices having smooth surfaces and radiuses to avoid sharp corners that can result in stress concentrations, reducing the likelihood of crack initiation and potential rotor failure. 
         [0024]    The receiving pocket  15  is further configured to receive a deformable portion of the nut  24 . The deformable portion of the nut  24  can be embodied as a radially outermost ligament  26  as seen in  FIGS. 5 and 6 . 
         [0025]      FIG. 5  shows a particular embodiment of the nut  24  where the radially outermost ligament  26  is the sole ring like protrusion extending up from an axial surface of the nut  24  opposite the seal contacting surface  35 . The radially inner most side of the radially outermost ligament  26  defines a tool contacting surface  28  as seen in  FIG. 5 , where the tool contacting surface  28  is configured to interface with a tool for deforming the radially outermost ligament  26  into the receiving pocket  15 . 
         [0026]      FIG. 6  shows an alternate embodiment of the nut  24  where the radially outermost ligament  26  is separated from a radially innermost ligament  27  by a groove  29 . The groove  29  defines a tool contacting surface  28  configured to receive a tool  30 . Nut  24  may be a spanner nut as embodied in  FIGS. 5 and 6  but also may be of another configuration where the specific configuration for rotating the nut  24  is not a limiting factor of the invention. 
         [0027]      FIG. 7  shows the tool  30  having a nut contacting portion  31  sized and configured for insertion into the groove  29  as seen in  FIG. 8 . The tool  30  also has a lever portion  32  arranged opposite the nut contacting portion  31 . The lever portion  32  is configured for applying a deforming force to the tool contacting surface  28  via the contacting portion  31  that deforms a portion of the radially outermost ligament  26  local to the nut contacting portion  31  into the receiving pocket  15  as seen in  FIG. 9 . Arranged between the nut contacting portion  31  and the lever portion  32  is a rotor contacting portion  33 . 
         [0028]    Tool  30  is advantageously designed to sufficiently deform the radially outermost ligament  26  into the receiving pocket  15  while not excessively straining the radially outermost ligament  26  such as to cause cracking of the radially outermost ligament  26  or the base material of nut  24 . The deformation of the radially outermost ligament  26  can therefore be controlled by the advantageous determination of the angle θ between the nut contacting portion  31  and the rotor contacting portion  33  as seen in  FIG. 7  where the nut contacting portion  31  deforms the radially outermost ligament  26  until the rotor contacting portion  33  contacts the outer surface of the rotor  11  preventing further deformation of the radially outermost ligament  26  as seen in  FIG. 9 . Therefore, the proper determination of the angle θ provides for sufficient deformation of the radially outermost ligament  26  to adequately engage the receiving pocket  15  to prevent rotation of the nut  24  while simultaneously preventing over straining of the radially outermost ligament  26 . 
         [0029]    The radially outermost ligament  26  is therefore configured to be deformed into the receiving pocking  15  to effectively prevent rotation of the nut  24  relative to the rotor bore  20 . Therefore, once the radially outermost ligament  26  is deformed into the receiving pocket  15  by the tool  30 , the radial position of the seal contacting surface  35  is fixed relative to the shoulder  25  and the compression of the seals  23  is preserved during operation of the generator  10  to properly seal against the escape of the hydrogen gas. 
         [0030]    An advantage of the present invention is that any angular portion of the radially outermost ligament  26  can be deformed into the receiving pocket  15 . The angular position of the nut  24  therefore is not dependant upon the relative angular position of the receiving pocket  15  as would be the case with a nut or system having predefined locking locations such as a hexagonal shaped spanner nut or a similar device that would require indexing a nut to a next nearest predefined locking location which could negatively effect an optimum compression of the seals  23 . Therefore the angular position of the nut  24  is not required to be indexed to a predefined position for securing the nut  24  against rotation relative to the rotor body  11 . 
         [0031]    While various embodiments of the present invention have been shown and described herein, it will be obvious that such embodiments are provided by way of example only. Numerous variations, changes and substitutions may be made without departing from the invention herein. Accordingly, it is intended that the invention be limited only by the spirit and scope of the appended claims.