Claims:We claim:
1. A method for balancing a rotor (101) of a turbo generator, the method comprising:
determining unbalance location on the rotor ();
computing unbalance response of the rotor (101) by rotor dynamic analysis;
calculating balancing weight to be added in the rotor (101) for balancing;
replacing aluminium fan blade (104) of fan collar with fibre glass blade;
if difference of the balancing weight to be added in the rotor (1010) is more than weight difference between the aluminium blade and the fibre glass blade:
adding balancing weight equal to the weight difference between the aluminium blade and the fibre glass blade in grooves of the rotor (101) in direction of unbalance of.
2. The method as claimed in claim 1, wherein the weight difference between the aluminium blade and fibre blade is equal to the weight which is to be removed from the rotor (101) for balancing.

3. The method as claimed in claim 1, wherein material of the fibre glass blade is selected from Kelver 49, carbon graphite, S-glass.

4. The method as claimed in claim 1, wherein the fibre glass blade is made as per profile contour.

5. The method as claimed in claim 1, wherein the determined unbalanced locations on the rotor (101) are fan collar (103) and centering ring.

6. The method as claimed in claim 1, wherein the method of balancing of the rotor (101) at centering ring comprises:
adding balancing weight at fan collar (103) in place of the centering ring as grove in the centering ring is occupied with weight and no place for weight addition;
replacing the aluminium blade of the fan collar with the fibre glass blade as the balancing weight to be put on the fan collar (103) is higher than the balancing weight to be put in the centering ring;
adding difference of weight to be added on the fan collar grooves on the rotor (101) in direction of unbalance.

7. The method as claimed in claim 1, wherein the balancing weight to be put in the fan collar (103) is higher than the weight to be put in the centering ring.

8. The method as claimed in claim 1, wherein the addition of balancing weight depends on unbalance location and magnitude of unbalance.

9. A turbo generator comprising:
a stator with armature winding; and
a rotor (101) having field winding and with integrated fan collar (103), wherein the fan collar (103) is assembled with fibre glass blade.
10. The turbo generator as claimed in claim 9, wherein a plurality of grooves is made on face of the fan collar.
, Description:A METHOD OF ROTOR BALANCING FOR TURBO GENERATOR ROTOR
FIELD OF INVENTION:
[001] The present subject matter described herein, relates to rotor balancing in turbo generators. More particularly the present invention pertains to the smaller and medium rating turbo generators operated in power plants or industrial establishments and especially on the approach to be followed for balancing the rotor to improvise the design and performance. The present subject matter relates to rotor balancing carried out in situ.
BACKGROUND AND PRIOR ART:
[002] A turbo generator consists of a rotor to carry the field winding and stator to carry armature winding. The rotor of a typical two pole generator operating at 50 Hz frequency rotates at 3000 rpm during the operation. The rotor needs to be balanced during its manufacture to keep the rotating parts in safe condition and minimize the vibrations during its operation. Balancing is required to compensate for the possible unequal distribution of mass in the rotor with respect to its axis. To carry out balancing, special planes are provided in the rotor in the form of plug holes on the rotor body, dove tail grooves at appropriate locations which are accessible after rotor is assembled into the stator. The locations in a typical rotor lie in centering ring, fan collar, rotor body and coupling.
[003] The response of dynamic behavior of the rotor for any addition of balancing weight depends on its location and magnitude of unbalance. The fan collar which is integral with the rotor will have a limitation on its outer diameter to enable shrink on parts to be taken over the collar during rotor assembly. Hence the groove which is made on the face of the fan collar will also be limited by the collar outer periphery. The effect of any trail weight in the groove is smaller due to smaller diameter of the groove. However, the fan collar groove is the correction plane where trail weights can be added easily during in situ balancing. In the event the unbalance correction requires dumping of larger mass in the groove and if it is not possible to compensate the same due to constraint of insufficient groove space.
[004] This is especially due to the requirement of keeping the balance weight at exact angular location. Hence an alternative location which is the centering groove is to be accessed. Due to locational offset though the trail weight compensates the unbalance force it introduces a couple for which another plane has to be chosen for compensation.
[005] Many methods of rotor balancing and apparatus used for carrying out balancing are described in the patents US20090133494A1, US4535411A, US4489606A, WO2014178759A1 andEP2677119A2.
[006] Hence an alternative method of providing the balancing weight shall be provided in such situations.
OBJECTS OF THE INVENTION:
[007] The principal objective of the present invention is to provide a method for balancing the rotor.
[008] Another object of the present subject matter is to provide replace aluminium blade of fan collar of the rotor with fibre glass blade for weight reduction.
[009] Another object of the present subject matter is to provide an alternative method of locating correction weights especially in two cases. The first case is the unbalance correction that requires addition of weight at a location in the fan collar groove where already weights are existing. The second case occurs during in situ balancing where the magnitude of the correction weight is not adequate and needs further addition.
SUMMARY OF THE INVENTION:
[0010] The subject matter disclosed herein relates to method of locating correction weights especially in two cases. The first case is the unbalance correction that requires addition of weight at a location in the fan collar groove where already weights are existing. The second case occurs during in situ balancing where the magnitude of the correction weight is not adequate and needs further addition.
[0011] During rotor balancing, correction weights are added in specific locations along the length of the rotor. Trail weights are added in different planes as per the balancing requirement. The plug holes drilled on the rotor barrel or the dove tail grooves turned on the other mountings or coupling are used for putting the weights. In the event it requires either much higher addition of trail weight at a location where weight already exists and the requirement is on higher side, the invention gives an approach to meet the requirement. One of the planes is the fan collar on which fan blades made out of aluminium die forgings are assembled. The groove is made on the face of the fan collar. The approach in the present invention uses the fan blade replacement with a blade made out of alternative material.
[0012] In order to further understand the characteristics and technical contents of the present subject matter, a description relating thereto will be made with reference to the accompanying drawings. However, the drawings are illustrative only but not used to limit scope of the present subject matter.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] It is to be noted, however, that the appended drawings illustrate only typical embodiments of the present subject matter and are therefore not to be considered for limiting of its scope, for the invention may admit to other equally effective embodiments. The detailed description is described with reference to the accompanying figures. In the figures, the left-most digit(s) of a reference number identifies the figure in which the reference number first appears. The same numbers are used throughout the figures to reference like features and components. Some embodiments of system or methods in accordance with embodiments of the present subject matter are now described, by way of example, and with reference to the accompanying figures, in which:
[0014] Fig. 1 illustrates cross section of a typical generator showing the relative locations of balancing planes; and
[0015] FIG. 2 illustrates the cross section of the fan collar.
[0016] The figures depict embodiments of the present subject matter for the purposes of illustration only. A person skilled in the art will easily recognize from the following description that alternative embodiments of the structures and methods illustrated herein may be employed without departing from the principles of the disclosure described herein.
DESCRIPTION OF THE PREFERRED EMBODIMENTS:
[0017] The subject matter disclosed herein relates to a method for balancing of generator rotor is one of the prime activities during the design and manufacture of a turbo generator. In the present subject method, identifying the location of balancing planes during the design stage is based on the dynamic behaviour of the rotor during operation. As the provision of balancing planes contribute to the geometry of the rotor, the location and size of the plane is carefully decided by prudent designer. Further, the present subject matter is to provide an alternative method of locating correction weights especially in two cases. The first case is the unbalance correction that requires addition of weight at a location in the fan collar groove where already weights are existing. The second case occurs during in situ balancing where the magnitude of the correction weight is not adequate and needs further addition.
[0018] It should be noted that the description and figures merely illustrate the principles of the present subject matter. It should be appreciated by those skilled in the art that conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present subject matter. It should also be appreciated by those skilled in the art that by devising various arrangements that, although not explicitly described or shown herein, embody the principles of the present subject matter and are included within its spirit and scope. Furthermore, all examples recited herein are principally intended expressly to be for pedagogical purposes to aid the reader in understanding the principles of the present subject matter and the concepts contributed by the inventor(s) to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions. The novel features which are believed to be characteristic of the present subject matter, both as to its organization and method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures.
[0019] These and other advantages of the present subject matter would be described in greater detail with reference to the following figures. It should be noted that the description merely illustrates the principles of the present subject matter. It will thus be appreciated that those skilled in the art will be able to devise various arrangements that, although not explicitly described herein, embody the principles of the present subject matter and are included within its scope.
[0020] Balancing of generator rotor is one of the prime activities during the design and manufacture of a turbo generator. Identifying the location of balancing planes during the design stage is based on the dynamic behaviour of the rotor during operation. As the provision of balancing planes contribute to the geometry of the rotor, the location and size of the plane is carefully decided by prudent designer. The approach in recent times is to minimize the balancing planes in view of the goal to arrive at a compact generator. One approach where the turbo generator is made compact and retaining the plane at the same time is described in the present invention.
[0021] During rotor balancing, correction weights are added in specific locations along the length of the rotor. Trail weights are added in different planes as per the balancing requirement. The plug holes drilled on the rotor barrel or the dove tail grooves turned on the other mountings or coupling are used for putting the weights. In the event it requires either much higher addition of trail weight at a location where weight already exists and the requirement is on higher side, the invention gives an approach to meet the requirement. One of the planes is the fan collar on which fan blades made out of aluminium die forgings are assembled. The groove is made on the face of the fan collar. The approach in the present invention uses the fan blade replacement with a blade made out of alternative material.
[0022] A turbo generator consists of a rotor to carry the field winding and stator to carry armature winding. The rotor of a typical two pole generator operating at 50 Hz frequency rotates at 3000 rpm during the operation. The rotor needs to be balanced during its manufacture to keep the rotating parts in safe condition and minimize the vibrations during its operation. Balancing is required to compensate for the possible unequal distribution of mass in the rotor with respect to its axis. To carry out balancing, special planes are provided in the rotor in the form of plug holes on the rotor body, dove tail grooves at appropriate locations which are accessible after rotor is assembled into the stator. The locations in a typical rotor lie in centering ring, fan collar, rotor body and coupling.
[0023] As illustrated in figure 1 and figure 2, the present subject matter discloses an alternative approach to compensate the unbalance identified in rotor 101 especially when it requires weight addition on the balancing groove 102, 201 located on the face 202 of fan collar 103. Attaching the weight to the fan blade 104, 203 through lump welding at its profile base or trimming the fan blade at its tip has the drawback of interfering with the ventilation system. Increasing the existing weight is not possible due to limitation in the groove size. Use of balancing weights made of higher density materials is one alternative which will give effect to a limited extent. If the requirement is still higher the approach is to compensate the weight through attempting on other planes which is a time consuming process.
[0024] The present method describes replacing the aluminium fan blade at the angular location of the unbalance with fibre glass blade made out of high strength fabrics. As the density difference between aluminium and Kevlar’ or S-glass is marginal, the above procedure meets the correction requirement. The difference in weight between the existing aluminium and fibre glass blade shall be equal to the weight to be removed and replacement shall be done along the direction of unbalance. If the difference is more, then the same shall be compensated by putting the groove weights at the direction of unbalance. Some of the fabrics include Kevlar 49, carbon graphite, S-glass etc. These composite materials have the advantage of lower density with respect to aluminium, increased wear resistance, substantially lower weight. The fibre glass blade can be conveniently made to the required profile contour by artisan skilled in the trade.
[0025] In another embodiment, during balancing sometimes the weight is added in the fan collar when it actually requires the weight addition in the centering ring (105). This situation occurs when the groove in the centering ring is already occupied by a weight. However the weight to be put in the fan collar is much higher than required weight in the centering ring. In such an event the blade replacement is the easier option. Thus the present invention provides a novel approach for balancing that prevents requirement to drill addition holes or adding weight through welding which are very difficult in situ and also weaken the existing part.
[0026] Present day rotor dynamic analysis computes the unbalance response very accurately and hence the rotor can be designed with the precision. This also avoids provision of many planes. A grooved balancing plane leads to unwarranted noise during operation due to whistling effect caused by balancing groove correction weight assembly. Hence the above plane on fan collar can be totally removed as the weight compensation can be done in the remaining planes. In the event the correction is required at site, the method of present invention can be followed. This not only improves the operational performance through reduced noise levels but also reduces the fan collar length.
[0027] The present method for balancing a rotor 101 of a turbo generator. An unbalance location is determined on the rotor and unbalance response of the rotor 101 is computed by rotor dynamic analysis. Further, balancing weight to be added in the rotor 101 for balancing is calculated by the rotor dynamic analysis. Aluminium fan blade of fan collar is replaced with fibre glass blade. If difference of the balancing weight to be added in the rotor is less than weight difference between the aluminium blade and the fibre glass blade, a balancing weight is added in grooves of the rotor 101 in direction of unbalance. Further, the material of the fibre glass blade is selected from Kelver 49, carbon graphite, S-glass.
[0028] In order to balance the rotor at centering ring location, a balancing weight is added at fan collar in place of the centering ring as grove in the centering ring is already occupied with weight and no place for weight addition is left. Further, the aluminium blade of the fan collar is replaced with the fibre glass blade as the balancing weight to be put on the fan collar (103) is higher than the balancing weight to be put in the centering ring. Furthermore, the balancing weight is to be added on the fan collar grooves in the direction of unbalance if the weight difference between aluminum blade and fibre blade does not meet the requirement of balancing. The addition of balancing weight depends on unbalance location and magnitude of unbalance.
[0029] A turbo generator consists of a stator with armature winding and a rotor 101 with field winding. The rotor 101 has integrated fan collar 103 with assembled fibre glass blade. The rotor has a plurality of groves is on face of the fan collar.
[0030] Although embodiments for the present subject matter have been described in language specific to structural features, it is to be understood that the present subject matter is not necessarily limited to the specific features described. Rather, the specific features and methods are disclosed as embodiments for the present subject matter. Numerous modifications and adaptations of the system/component of the present invention will be apparent to those skilled in the art, and thus it is intended by the appended claims to cover all such modifications and adaptations which fall within the scope of the present subject matter.