Patent Publication Number: US-2004055138-A1

Title: Generator rotor jacking assembly and methods of use

Description:
BACKGROUND OF THE INVENTION  
       [0001] The present invention relates generally to the assembly and disassembly of generator rotors using a jacking assembly and particularly relates to a rotor jacking assembly for and methods of fluidically jacking an end of the rotor to relieve the weight of a rotor end on an associated rotor end bearing.  
       [0002] In electrical generators, the generator field or rotor must be positioned vis-a-vis the stator frame to enable removal or assembly of the lower bearing, seals, outer and inner oil deflectors, and other ancillary equipment. It will be appreciated that during disassembly of a generator, the rotor must be supported, at least at one end, by other than the rotor support bearing to enable removal of the lower halves of the bearing, hydrogen seal and inner oil deflector. Similarly, upon assembly of the rotor, ancillary support for the rotor must be provided in order to install the inner oil deflector, hydrogen seal and bearing. Currently, jack bolts installed on a yoke are used to raise and lower a rotor end relative to its end bearing. Particularly, a saddle is secured to the stator end shield. Jack bolts are screwthreaded through the yoke and engage at their lower ends on anvils or flanges of the saddle. The yoke, of course, underlies and bears the weight of the rotor end and places a significant point load on each of the jack bolts. This results in large friction forces which are difficult to overcome.  
       [0003] More particularly, large impact wrenches, together with torque multipliers, are oftentimes required to rotate the jack bolts to displace the rotor end relative to the saddle. This is labor-intensive and of such difficulty that in certain situations, a crane must be utilized to elevate the rotor, removing the weight from the yoke in order to free the bolts to displace the yoke upwardly relative to the saddle. While the use of a crane enables the jack bolts to be more readily turned and hence elevate the yoke to a location to support the rotor end off the end bearing, use of a crane is an additional, laborious, expensive and time-consuming task.  
       BRIEF DESCRIPTION OF THE INVENTION  
       [0004] In accordance with a preferred embodiment of the present invention, there is, provided apparatus and methods for fluidically elevating at least one end of the rotor from its end support bearing, i.e., to relieve the bearing from the weight of the rotor. To accomplish that, a saddle is secured to the end shield and has anvils located on opposite sides of the rotor. A yoke is disposed above the saddle and underlies the rotor end. The yoke includes laterally projecting flanges in vertical registration with the anvils on the opposite sides of the rotor. Fluid-actuated cylinders are coupled to the flanges and anvils such that the yoke, together with the rotor end, can be elevated relative to the saddle upon actuation of the cylinders to relieve the weight of at least one end of the rotor from the corresponding end rotor support bearing. The cylinders are preferably hydraulic and located between the flanges and anvils of the yoke and saddle, respectively. As a result, the rotor end may be displaced vertically up or down within the stator frame without the use of jack bolts or a crane. Additionally, the typically large holes that are required to be drilled in the yoke for the jacking bolts and the wear and tear on tools associated with efforts to rotate the oftentimes stuck jacking bolts, i.e., large impact wrenches and torque multipliers, are eliminated. The present process is thus less labor-intensive and safer in comparison with the previously discussed prior process.  
       [0005] In a preferred embodiment according to the present invention, there is provided a method of displacing a rotor in a generator for unloading the weight of the rotor from a rotor bearing, comprising the steps of (a) supporting a pair of anvils along opposite sides of the rotor adjacent the rotor bearing, (b) disposing a yoke about an underside of the rotor with a pair of flanges along opposite sides of the yoke in substantial vertical alignment with the respective anvils, (c) providing fluid-actuated cylinders to the anvils and flanges on opposite sides of the rotor and (d) actuating the cylinders to displace the yoke and rotor in an upward direction away from the anvils thereby relieving the rotor bearing of at least a portion of the weight of the rotor.  
       [0006] In a further preferred embodiment according to the present invention, there is provided a method of displacing a rotor in a generator for unloading the weight of the rotor from a rotor bearing, comprising the steps of (a) securing a saddle to an end shield of the generator locating a pair of anvils carried by the saddle along opposite sides of the rotor, (b) disposing a yoke about an underside of the rotor with a pair of flanges along opposite sides of the yoke in substantial vertical alignment with the respective anvils on the saddle, (c) providing fluid cylinders to the anvils and flanges on opposite sides of the rotor and (d) actuating the cylinders to displace the yoke and rotor in an upward direction away from the saddle thereby relieving the rotor bearing of at least a portion of the weight of the rotor.  
       [0007] In a further preferred embodiment according to the present invention, there is provided a generator comprising a housing having end shields and bearings adjacent opposite ends, a rotor within the housing and carried by the bearings, an anvil secured to one of the end shields adjacent one end of the housing, a yoke disposed above the anvil and underlying an end portion of the rotor adjacent the one housing end and a pair of fluid-actuated cylinders coupled to the anvil and the yoke for elevating the rotor end portion from the bearing adjacent the one housing end in response to actuation of the cylinders. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0008]FIG. 1 is a schematic cross-sectional view through a centerline of a generator;  
     [0009]FIG. 2 is an enlarged cross-sectional view of a portion of an end shield at one end of the generator housing with a jacking assembly of the prior art attached to the end shield;  
     [0010]FIG. 3 is a view similar to FIG. 2 illustrating a jacking assembly according to a preferred embodiment of the present invention secured to the end shield;  
     [0011]FIG. 4 is an enlarged end elevational view of a saddle and yoke forming a portion of the jacking assembly of the present invention;  
     [0012]FIG. 5 is a perspective view illustrating a support device for the rotor end; and  
     [0013]FIG. 6 is an end view of the generator with the rotor supported by the support device of FIG. 5 and the end shield in a lowered position. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
     [0014] Referring now to the drawings, particularly to FIG. 1, there is illustrated a generator, generally designated  10 , having a rotor or field  12  disposed in a generator housing  14  including end shields  16  and  18  at the turbine and collector ends of the generator, respectively. The stator punchings  20  and end bars  22  are also illustrated about the field  12 .  
     [0015] As best illustrated in FIG. 2, the lower end shield  24  at the collector end shield  18  includes an inner oil deflector  26 , a hydrogen seal casing  28 , a bearing  30 , a bearing ring  32  and, in this instance, a prior art shaft jacking device  34  which has been secured in place of an outer oil deflector, not shown. It will be appreciated that the rotor  12  rests on the bearing  30  during normal usage and that the rotor, at least at one end, must be elevated to relieve the weight of the rotor end from the bearing to remove the lower half of the bearing and gain access to the hydrogen seal casing and inner oil deflector for repair or replacement.  
     [0016] As indicated previously, the prior jacking assembly  34  includes a saddle  36  secured to the lower end shield  24  and a yoke  38  underlying the rotor. With the jacking device assembled to the end shield, jack bolts, not shown, interconnecting the yoke  38  and saddle  36  are rotated to elevate the yoke relative to the saddle to lift the rotor end from the bearing thereby relieving the bearing of the weight of the rotor at one end of the generator.  
     [0017] In accordance with the present invention and referring particularly to FIG. 4, a jacking assembly according to the present invention is generally indicated  40 . Jacking assembly  40  includes a lower saddle  42  having an enlarged concave recess  44  along its upper side for receiving a corresponding generally semi-cylindrical portion of a yoke  46 . The saddle  42  is secured to the lower end shield  24  by bolts  48  subsequent to removal of the outer oil deflector, not shown. Opposite sides of the saddle  42  have upwardly facing surfaces or anvils  50  which straddle the yoke  46  as well as the end of the rotor  12 .  
     [0018] The yoke  46  includes a generally semi-cylindrical section  52  having a padded concave recess  54  for engaging about the lower half of an end of the rotor  12 . Opposite sides of the yoke  46  are provided with flanges  56 . The arcuate recess  54  extends beyond the horizontal diameter of the rotor, i.e., the upper surfaces of flanges  56  lie above a horizontal plane through the diameter of the rotor when the rotor is to be elevated. A pair of fluid-actuated, preferably hydraulic cylinders are connected between the flanges  56  of yoke  46  and the anvils  50  of saddle  42 . While the cylinders and pistons of the fluid-actuated cylinders can be located on opposite sides of the flanges  56 , the cylinders and pistons are preferably disposed between the flanges  56  and anvils  50 . The preferred hydraulic cylinders  58  may be of the type manufactured by Enerpac, Milwaukee, Wis. In FIG. 4, the solid line represents the position of the saddle and yoke, with the fluid cylinders in a retracted position and the rotor  12  resting on the bearing  30 . The dashed line configuration in FIG. 4 illustrates the position of the yoke and the rotor upon actuation of fluid cylinders  58  to displace one end of the rotor from an end bearing  30  thereby relieving the weight of the rotor end on the bearing.  
     [0019] In FIGS. 5 and 6, there is illustrated a support sling, generally indicated  60 , for supporting the end of the rotor when the various ancillary parts of the end shield are removed for maintenance and repair as well as when the bearing has been removed. The sling  60  includes a flexible strap  62  which engages the underside of the rotor  12  to support the latter during maintenance and repair. The sling  60  may be mounted on support bracing  64  mounted to and along the upper portion  66  of end shield  18 .  
     [0020] In order to service the bearing, oil deflectors and ancillary parts, the outer oil deflector, not shown, is first removed from the end shield  18 , for example, at the collector end of the generator. In its place, the saddle  42  is secured by bolts  48  to the lower end shield  24 . The yoke  52  is located below the rotor  12  with the flanges  46  resting on the fluid cylinders  58 . With the yoke and saddle in place and the weight of the rotor on the bearing, the fluid cylinders  58  are actuated. Upon actuation, the cylinders elevate the yoke and consequently the end of the rotor to raise the rotor end off the bearing by a small distance, for example, 0.005 inch. With the weight of the rotor transferred to the lower end shield  24  and off the bearing  30 , the lower bearing is removed. The sling  60  is then disposed about the rotor  12  to support the rotor in its elevated position. With the weight of the rotor off the bearing, the lower end shield, including the yoke and saddle, is lowered, as illustrated in FIG. 6, to a position enabling ready access to the oil deflector, hydrogen casing seal and other ancillary parts for service and repair.  
     [0021] It will be appreciated that the reverse procedure can be used to reinstall the various parts carried by the end shield for supporting the generator rotor. Thus, after service and maintenance has been performed, and the various serviced or replaced parts are in place, i.e., the bearing, inner oil deflector and hydrogen seal casing, the lower end shield  24  is raised. The yoke is thus reengaged in its hydraulically extended position with the rotor end. The sling  60  is then removed to transfer the weight of the rotor end onto the yoke and saddle. With the bearing in place, the hydraulic cylinders are retracted, lowering the rotor end onto the bearing. With the weight transferred to the bearing, the yoke and saddle are removed and the outer oil deflector is secured to the end shield.  
     [0022] 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.