Abstract:
A method of determining an alignment of a floating seal for a turbo machine, including establishing a reference surface on a rotor of the turbomachine that is essentially perpendicular to an instantaneous centerline of the rotor, establishing a control surface that radially aligns a floating seal member that surrounds the rotor, providing an inflatable member arranged between a stationary portion of the turbomachine and a surface of the floating seal, inflating the inflatable member such that the inflatable member urges the floating seal firmly against the control surface, measuring an axial distance between the floating seal and the reference surface at a plurality of locations, determining a parallelism between the facing surfaces of the floating seal and the rotor based upon the plurality of measured axial distances, comparing the determined parallelism with a predetermined threshold, and adjusting an orientation of the control surface based upon the comparison.

Description:
FIELD OF THE INVENTION 
     The present invention provides a method and system for determining an alignment and adjusting a turbomachine gland seal, and more particularly a method and system for determining an alignment and adjusting a gland seal ring and a rotor of a hydrogen cooled electric generator. 
     BACKGROUND OF THE INVENTION 
     Turbomachines include a rotational shaft known as a rotor and a stationary portion known as a stator where a gas tight seal is required between the rotor and the stator. Turbomachines include, but are not limited to steam turbines, gas turbines, electric generators, compressors, and pumps. For example, an electric 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. If the energizing current is direct, 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. 
     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 can not only support the weight, operational and transient loads of the generator, but also contain the hydrogen gas and prevent it from escaping into the atmosphere where it can form into a combustible mixture. 
     There are many locations on the generator where internal components of the generator must penetrate or pass through the frame, such as the rotor and the stationary electrical conductors. Because the rotor must be free to rotate, a sufficient clearance must be provided between the generator frame and an outer surface of the rotor. Typically, a gland seal is provided between the rotor and the frame to prevent the rapid escape of hydrogen gas. 
     A gland seal, also known as a hydrogen seal, is well known and functions by forcing a fluid, typically sealing oil, under a pressure greater than that exerted by the opposing hydrogen pressure through a radial gap provided between the rotor and a sealing surface of the gland seal. The sealing oil effectively seals the gap between the rotor and the gland seal thus preventing the leakage of the hydrogen gas and the resultant dangerous mixture of hydrogen and air. 
     To effectively seal the generator, the radial gap between the gland seal and the rotor must be as small as practical while leaving sufficient clearance for rotation of the rotor. The diametrical clearance between the gland seal ring and the rotor is proportional to the rotor diameter at the axial location of the gland seal ring and typically is on the order of several thousands of an inch as measured on diameter. Due to the tight radial clearance between the rotor and the gland seal, radial and angular alignment of the gland seal to the rotor is critical. Improper alignment of the gland seal can lead to contact of the rotor with the gland seal causing impermissible wear of the gland seal and/or excessive rotor vibration. Both situations are unacceptable and will likely result in a forced shut down of the generator to remedy the situation. 
     The rotor is typically supported at its opposite ends by bearings arranged outside of the gland seals, see  FIG. 1 . Due to the large span between the bearings and the weight of the rotor, the rotor will, sag in its middle causing a difference between a theoretical centerline of the machine and an instantaneous centerline of the rotor, see  FIG. 5 . The rotor sag forms an angle between the instantaneous rotor centerline and the theoretical centerline of the machine. If the gland seal is aligned to the theoretical machine centerline, the slope of the rotor at the axial location of the gland seal will result in an inconsistent radial gap from an outboard edge of the gland seal to an inboard edge of the gland seal and from a top to a bottom of the gland seal resulting in uneven pressure and flow of the sealing oil circumferentially around the gland seal. Therefore, the gland seal should advantageously be aligned to the instantaneous angle of the rotor and not to the theoretical rotational centerline. 
     The orientation of the gland seal is determined by the gland seal housing that supports the gland seal. Furthermore, the orientation of the gland seal housing depends upon an orientation of a mating surface between the gland seal housing and a structural bearing support bracket that the gland seal bracket attaches to. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is explained in the following description in view of the drawings that show: 
         FIG. 1  is a simplified view of a known electric generator that employs the present invention; 
         FIG. 2  is an isometric view of a known gland seal and rotor that employs the present invention; 
         FIG. 3  is a cross-sectional view of the gland seal and rotor of  FIG. 2 ; 
         FIG. 4  is a view of a pressure bellows; 
         FIG. 5  shows the relationship between machine centerline and rotor instantaneous centerline; 
         FIG. 6  is a side view of  FIG. 2  with a deflated pressure bellows installed; 
         FIG. 7  is a top view of  FIG. 6 ; 
         FIG. 8  is a close up view of  FIG. 7 ; 
         FIG. 9  shows the system of  FIG. 8  with the pressure bellows inflated; 
         FIG. 10  shows the axial measurement of the gland seal. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention is disclosed in context of determining an alignment 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 alignment of a slidable seal is needed between a stationary and rotating component. One skilled in the art may find additional applications for the methods, systems, apparatus, and configurations 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 method for determining an alignment within an electric generator. 
     An overview of the invention is provided below followed by a more detailed explanation. Referring to  FIG. 1 , a hydrogen cooled electric generator  10  typically comprises a rotor  20  arranged along a centerline  12  of the generator  10 . At the ends of the generator  10  are bearing brackets  11  that include bearings that rotatably support the rotor  20 . 
     Components 
     Referring to  FIG. 2 , attached to the bearing bracket  11  is the gland seal bracket  31 . The gland seal bracket is removably affixed to the bearing bracket  11  where the gland seal bracket  31  is shown bolted to the bearing bracket  11 , however, one skilled in the art will readily appreciate that the gland seal bracket  31  can be fixed to the bearing bracket  11  in any manner suitable to removably affix the gland seal bracket  31  to the bearing bracket  11 . The gland seal bracket  31  has a recess  32  arranged circumferentially around the rotor  20 . Arranged along an axial face of the recess that is operatively exposed to the hydrogen gas of the generator interior  39  is a further circumferential recess or groove  33 . The axial face of the recess opposite the further recess  33  is the air side axial face  38  (see  FIGS. 8 through 10 ). 
     Referring again to  FIG. 2 , the recess  32  is configured to receive and support a gland seal  30 . The gland seal  30  is a well known structure forming a ring surrounding the rotor  20 . The gland seal  30  may be formed of several segments joined together or may be a unitary ring. However, the particular formation of the gland seal  30  is not determinative to the scope of the present invention and one skilled in the art will readily appreciate that there are many configurations of a gland seal  30  that are operative within the scope of the present invention. 
     Referring to  FIG. 3 , the gland seal inner diameter  35  is slightly greater than the rotor outer diameter  22  to form a radial gap R. The gland seal has internal passages (not shown) running from outer diameter openings onto the inner diameter of the gland seal  35  that operatively provide pressurized oil that fills the radial gap R such that the gland seal  30  rides upon an oil film  34  between the rotor and the gland seal inner diameter and effectively seals-off the radial gap R against the escape of the generator internal hydrogen gas. The gland seal  30  is rotationally restrained from rotating along with the rotor by anti-rotation pins (not shown) that engage the gland seal  30  and the gland seal bracket  31 . 
     Referring again to  FIG. 2 , the rotor has a radial shoulder  21  arranged at an axial distance from the gland seal  30 . The radial shoulder  21  is formed such that the shoulder is essentially perpendicular to the instantiations centerline of the rotor  13  (see  FIG. 5 ). 
     Referring to  FIG. 4 , a pressure bellows  40  is a flexible tube like structure having a middle hose portion  41 , a pressure tight closed end  42  and a selectively sealable and preferably pressure tight connecter  44  arranged at an open end  43  opposite the closed end  42 . The pressure bellows  40  is sized and configured such that it can be easily inserted into the further recess  33  and having an inflated diameter sufficient to expand within the further recess  33  and engage the gland seal  30  and secure the gland seal  30  against the recess air side axial face  38  (see  FIGS. 8 and 9 ). The pressure bellows  40  is inventively employed to assist with the proper alignment of the gland seal  30  such that the gland seal  30  effectively seals the rotor  20  against the leakage of hydrogen gas. 
     Operation 
     To effectively seal the radial gap R between the gland seal  30  and the rotor  20 , the oil film  34  must exert a force greater than that exerted by the internal hydrogen gas, otherwise the hydrogen gas would blow out the oil film  34  and escape through the radial gap R (see  FIG. 3 ). In order to ensure a consistent radial gap R and therefore a properly sealing oil film  34 , the gland seal inner diameter surface  35  must be parallel to the rotor outer diameter surface  22 . Direct measurement or verification of the parallelism of the gland seal inner diameter surface  35  and the rotor outer diameter surface  22  is not practical. However, by ensuring that an easily measurable axial face of the gland seal such as the gland seal hydrogen side axial face  36  is manufactured essentially perpendicular to the gland seal inner diameter surface  35 , and a radial shoulder  21  of the rotor is manufactured essentially perpendicular to the instantaneous rotor centerline  13  an axial distance can be easily measured to determine that the gland seal hydrogen side axial face  36  and the radial shoulder  21  are parallel and therefore inferring that the gland seal inner diameter surface  35  is parallel to the rotor outer diameter surface  22  (see  FIGS. 2 ,  5  and  8 - 10 ). 
     In order to achieve accurate results when measuring the axial distance between the gland seal hydrogen side axial face  36  and the radial shoulder  21 , the gland seal  30  should be restrained such that the gland seal air side axial face  37  is firmly secured against the recess air side axial face  38  (see  FIGS. 8 and 9 ). 
     The present invention makes use of an inventive tube like pressure bellows  40  to reliably secure the gland seal  30  against the recess air side axial face  38  ( FIG. 9 ). The deflated pressure bellows  40  is guided into the oil well  33  provided in the gland seal bracket  31 , at least partially along a length of the circumferential further recess  33 , as seen in  FIGS. 6 through 8 . Preferably, a length of pressure bellows  40  is inserted to span at least a 45° arc, more preferably a 90° arc and most preferably a 180° arc or an entirety of the further recess  33 , however at a minimum, a length of pressure bellows  40  is required such that once inflated, sufficient force is exerted onto the gland seal  30  by the pressure bellows  40  to seat and secure the gland seal  30  against the recess air side axial face  38 . Once the pressure bellows  40  is in place, the pressure bellows connector  44  is attached to a pressurizing device (not shown), for example but not limited to a pump or compressor, to form a selectively sealable and preferably leak tight connection. Once the pressure bellows  40  is pressurized, the pressure bellows  40  expands within the further recess  33  and engages the gland seal  30 . The internal pressure of the pressure bellows  40  exerts a contact force in the axial direction against the gland seal  30  which urges the gland seal  30  against the recess air side axial face  38 , see  FIG. 9 . 
     Feeler gauges can be inserted in the resultant gap between the recess hydrogen side face  39  and the gland seal hydrogen side axial face  36  to verify that the gland seal  30  is properly seated against the recess air side axial face  38 . 
     With the pressure bellows  40  inflated and the gland seal  30  secured and seated against the recess air side axial face  38 , the axial distance X between the gland seal hydrogen side axial face  36  and the radial shoulder  21  as shown in  FIG. 10 . By repeating the measurement of the axial distance X, at least three times, a plane defining the surface of the gland seal hydrogen side axial face  36  can be determined relative to the rotor radial shoulder  21 . Because the radial shoulder  21  is manufactured essentially perpendicular to the rotor instantaneous centerline  13 , and the gland seal hydrogen side axial face  36  is manufactured essentially perpendicular to the gland seal inner diameter surface  35  then the parallelism of the gland seal inner diameter surface  35  and the rotor instantaneous centerline  13  can be inferred. Furthermore, the parallelism of the gland seal inner diameter surface  35  and the rotor instantaneous centerline  13  can be compared with a predetermined acceptable parallelism value. If the parallelism of the gland seal inner diameter surface  35  and the rotor instantaneous centerline  13  is determined to be unacceptable, an alignment of the gland seal  30  can be adjusted by adjusting the orientation of the gland seal bracket  31 . For example, the mating surface of the gland seal bracket  31  can be machined appropriately to achieve the desired orientation of the gland seal  30 . Specifically, when the gland seal  30  is firmly secured against the recess air side axial face  38  by the inflated pressure bellows  40  the recess air side axial face  38  serves as a control surface that effectively determines the parallelism of the gland seal inner diameter surface  35  and the rotor instantaneous centerline  13 . Therefore, by adjusting the orientation of the gland seal bracket  31  relative to the rotor  20  the orientation of the gland seal  30  and ultimately the parallelism of the gland seal inner diameter surface  35  to the rotor instantaneous centerline  13  can be adjusted. 
     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.