FEEDBACK NO. 18
ROLL CHECK General Description: In KWU machine the minimum radial clearances HP, IP and LP casing are measured by actually by moving the casing radially at site while rotor is rotated by hand. This is a very accurate and fast method of measuring the minimum radial clearance of any of the casing. The major variation in these reading may cause vibration in the machine and obstruction in barring gear operation etc. Such facilities are not available in many of the designs of machine and causes longer duration in erection and overhauling of the units. After completing the alignment of rotors the casing alignments are carried out by roll check method but equal importance should also be given to the centering of HP and IP casing. The centering of casing may not be fully sacrificed in comparison of rolling test readings and a compromise between these two readings should be made. The rolling test should be carried out in cold machine only. Procedure: Roll check of HP and IP casing: a)
Alignment and coupling of HP-IP and LP rotors rotors are to be completed before starting starting the rolling rolling test of the casing casing in normal case but this can be done without coupling of LP rotor also.
b)
Centering of the casing on HP front, HP rear IP front and IP rear spigot are are also to be completed before starting starting of the rolling test. These readings can be compared as per the factory protocol also. Fix temporary radial and axial keys of the casing before rolling test of casing. During dialing on spigot a proper care should be taken that the dials are properly
mounted over the fixture and the fixture fabricated at site is strong enough to give the correct readings. The point dial indicator may be used here for the better results of the dial readings. c)
All the four jacking jacking screw of HP and IP casing are are to installed along along with dial gauges gauges for monitoring of up and down, down, and left and right movement of the casing.
d)
One number hydraulic jack on each corner of the casing along with a spanner spanner on each each corner for jacking screw are are also to be made available.
e)
During erection erection of machine the turbine rotor rotor are generally generally rotated rotated by hand with the help of periphery periphery holes on coupling. Two pipes of about 1250 mm long along with a pin to suit the dia of periphery may be u sed for rotating the rotor shaft. The initial jerk to the rotor is given by the help of crane and it is further rotated by these pipes through periphery holes of the coupling.
During overhauling generally the jacking oil system is available and the rotation of rotors are achieved with the hand barring of the machine. f)
Before starting the following check it should be ensured that the rotor rotor shaft is absolutely absolutely free on manual manual rotation rotation / hand barring as the case may be. During manual rotation two persons are to be employed for this work and during hand barring only one person is enough. Rotate the rotor in direction of normal rotation of the unit.
g)
Always use thick oil for for rotation rotation of rotor over bearing in absence of jacking oil oil system. The type oil may be servo cylinder 1000 grade (IOC) oil.
h) i)
During the rolling test the temporary casing packers packers are to be fitted with about about 1.00 1.00 mm shims. During the rolling test of any of the casing the the same same is lifted first on all four corners in a step of of 0.05 mm with with the help of hydraulic jack and jacking screw. The rotor is also rotated manually side by side with the lifting of casing. The rotati on of rotor and lifting of casing continued till it becomes little bit tight on the seals of the casing. After this the casing is lowered by about 0.05 mm and rotor is rotated again if it is completely free. In case the rotor is still tight on its manual rotation the casing is further lowered by 0.05 mm on all four corners. After ensuring the freeness of rotor it is again rotated and casing
mounted over the fixture and the fixture fabricated at site is strong enough to give the correct readings. The point dial indicator may be used here for the better results of the dial readings. c)
All the four jacking jacking screw of HP and IP casing are are to installed along along with dial gauges gauges for monitoring of up and down, down, and left and right movement of the casing.
d)
One number hydraulic jack on each corner of the casing along with a spanner spanner on each each corner for jacking screw are are also to be made available.
e)
During erection erection of machine the turbine rotor rotor are generally generally rotated rotated by hand with the help of periphery periphery holes on coupling. Two pipes of about 1250 mm long along with a pin to suit the dia of periphery may be u sed for rotating the rotor shaft. The initial jerk to the rotor is given by the help of crane and it is further rotated by these pipes through periphery holes of the coupling.
During overhauling generally the jacking oil system is available and the rotation of rotors are achieved with the hand barring of the machine. f)
Before starting the following check it should be ensured that the rotor rotor shaft is absolutely absolutely free on manual manual rotation rotation / hand barring as the case may be. During manual rotation two persons are to be employed for this work and during hand barring only one person is enough. Rotate the rotor in direction of normal rotation of the unit.
g)
Always use thick oil for for rotation rotation of rotor over bearing in absence of jacking oil oil system. The type oil may be servo cylinder 1000 grade (IOC) oil.
h) i)
During the rolling test the temporary casing packers packers are to be fitted with about about 1.00 1.00 mm shims. During the rolling test of any of the casing the the same same is lifted first on all four corners in a step of of 0.05 mm with with the help of hydraulic jack and jacking screw. The rotor is also rotated manually side by side with the lifting of casing. The rotati on of rotor and lifting of casing continued till it becomes little bit tight on the seals of the casing. After this the casing is lowered by about 0.05 mm and rotor is rotated again if it is completely free. In case the rotor is still tight on its manual rotation the casing is further lowered by 0.05 mm on all four corners. After ensuring the freeness of rotor it is again rotated and casing
is lifted simultaneously on front end till the rotor rotation becomes tight on seals portion of the casing. As soon as the shaft becomes tight the lifting of casing and rotation of shaft is stopped and dial readings on front end are recorded. The average lift on front end of the casing is the bottom clearance front end of the casing. After this the casing on front end i s lowered by 0.05 mm and freeness of rotor is ensured. In case it is still tight the casing is further lowered by 0.05 mm. on front end and the freeness of rotor is achieved. Now the rear end of the casing are lifted similar to front-end bottom clearance of rear end are recorded. After recording the bottom clearance of front and rear end of individual casing the casing is lowered with the help of hydraulic jacks and jacking screws to its original zero-zero position. Repeat similar operation of rotating the rotor and lowering the casing on front and rear end for deciding the top clearance in front and rear end of the casing. Before starting the rolling test in downward direction of the casing remove about 1.00 mm shims from each packer of the casing, but kept the casing on hydraulic jacks and jacking screws on its original position. position. The casing is again brought back to its original position by installation of the shims back to the packers of the casing after recording the top clearances of the casing. After recording the up and down rolling test values the radial keys of the casing are removed and again rolling test for left and right direction are done similar to up and down. During this process the radial dial on the casing are also installed. Af ter this check the casing is brought back to its zero position in radial direction direction also. After completing the rolling test readings of one of the HP/IP casing in up/down and left/right direction the clearances are readjusted as required at site in radial direction by moving the casing packers. The casing is then locked on f our corners and final dial readings of spigot are recorded on front and rear end. Immediately after this the final radial key of the casing are fixed and the locked of the casing are released for fitting of the final casing packers. The final spigot dial reading are repeated and confirmed with the earlier readings. j)
After doing the full rolling test test and fixing of a final radial radial keys and packers packers of one of the casing the rolling rolling test of another casing is done including the fitting of final keys and packers.
k)
Necessary offset in the radial radial clearance clearance is also kept kept before fitting of of final packers of the casing toward toward the the lift of the shaft during operation of the unit.
l)
No inlet and outlet outlet pipes pipes are to be welded with the casing till completion completion of rolling rolling test test and and installation installation of final final keys and packer of the casing.
m) n)
Radial clearance clearance of the casing are to be ensured with reference to the factory factory supplied protocol protocol also. also. After fitting of final keys and packers of the casing the final spigot spigot dial dial of HP front, HP rear, IP front and IP rear casing are to be recorded for future reference in the protocol.
o)
The horn horn drop drop readings readings are are also also to be checked checked after after the the fitting of final final packer packer of the casing.
p)
In case of IP casing the roll test readings are are to be taken with the IP front-end rear shaft shaft scales. scales. The spigot spigot dial dial readings are also to be taken over the spigot of shaft seals.
q)
During rolling rolling test of of the HP and IP casing if the rotor is rotated rotated over the jacking oil then the adjustment adjustment of readings readings are to adjusted for the lift of the rotor also.
r)
Four numbers numbers 1.00 1.00 mm undersize undersize packers packers for HP HP & IP casing casing may may be used during during erection erection for for further further roll roll test during overhauling of the unit. If any taper is left on final packers of the casing then these four packers may be made to similar taper also.
Rolling test of L.P. Turbine: 1)
The rolling test of LP turbine is done similar to the HP or IP casing casing but both side joints of LP inlet bellows are are kept free or bellow itself are not positioned at all, till completion of rolling test. But during overhauling the rolling test is done with already welded bellows.
2)
Rolling test of LP inner casing casing is done after after the neck welding of condenser condenser and stiffener pipes pipes inside inside the condenser. This include the welding of stiffener pipes of LP casing and gusset plates also.
3)
After rolling test of the casing the final radial keys of the Gusset block-casing packers packers on all four corners are are installed.
4)
Necessary offset in the radial radial clearances clearances of of the casing is also kept kept before fitting of final LP inner casing casing packers. packers.
5)
Radial clearances clearances of the casing are to be ensured to the design design values. In case of any variation variation the matter may be referred to the designers.
(If the rotor is rotated on jacking oil then the rolling test readings are to be adjusted for the lift of the rotor also.)
FEEDBACK NO. 19 SWING CHECK General Description The swing check is the measurement of radial throw at the free end of the coupled rotor caused due to non parallelity of the coupling faces and / or their out of square ness wrt rotor axis etc. The high swing check value may cause high shaft vibration, high bearing shell temperature etc. The value of swing check depends on axial run out of coupling faces, the diameter of the coupling and the length of the rotor. During the machining of rotors in the works some tolerances are permitted by designers on the coupling faces of the rotor resulting to some radial throw at the free end. The maximum permissible swing values caused due to the above tolerance for different diameter and length of the rotor can be worked out from the enclosed graph. However it is recommended to keep the swing values to minimum for better results during operation of the machine. In a multi rotor turbine – generator system it is essential to measure the swing value in both extreme end where the weight of the rotors are light. For example 200/210 MW machine with Russian Generator and static excitation system the swing check values are measured on HP rotor front end only. In 500 MW machine the swing values measured in HP front and on exciter rear end. It is advisable to measure value on IP rotor front end also for better results during operation of the units. This can be done initially during erection with temporary coupling bolts on LP-IP coupling before reaming / honing of coupling.
Any variation in swing values may be corrected during erection of machine. Any compromise at erection stage may cause serious problem during operation of the unit and any correction becomes much more tedious at a later stage. The correction may be carried out either by interchanging the coupling position or by correcting the coupling faces by scraping / cutting in consultation of designers. Procedure 1)
Before placement of Module / Rotor in position the coupling faces of all the rotors are to be checked for concavity / convexity of their coupling faces. This can be checked with the help of a thin rectangular lightweight straight edge. No concavity of about 0.02 / 0.03 mm is permitted to manufacturing units.
2)
After placement of individual Module / Rotor the coupling faces are to be checked / measured for axial run out before taking up alignment of various rotors. The HP rotor rear coupling face can be measured after placing it on both of its bearing. The IP rotor faces are to be measured after placing IP rear end on bearing and front end on lifting tackle. Similarly LP rotor may be placed on bearing on its rear end and front end supported on lifting tackle. Axial run out on coupling faces more than 0.02 mm. may be referred to designers before taking up further works.
3)
After completing final alignment of various rotors they are to be coupled with temporary bolts, taking into account the axial run out of the coupling faces. During coupling with temporary bolts the highest point of one of the rotor face is to be coupled with lowest point of coupling face of the adjoining rotor.
4)
During coupling on temporary bolts the equal tightening on all the four temporary bolts is to be ensured otherwise it can disturb the swing value of the rotor.
5)
First IP-LP coupling is to be made with temporary bolts and swing in IP rotor front end is recorded. After this only HPIP rotor is to be coupled with temporary bolts and the swing value on HP front rotor is recorded.
6)
During swing check of IP rotor its front end is to be supported on auxiliary bearings and suspended by a sling of 24 mm diameter with a distance of 3.0 to 3.5 meter from crane hook, without making any connection between HP-IP rotor.
7)
While recording swing check of HP rotor the front end of the rotor is to be supported on auxiliary bearings and suspended by a sling of 18 mm diameter with a distance of 3.0 to 3.5 meter from crane hook.
8)
During checking of swing measure radial movement of rotor on parting plane and rotate the rotor in normal direction of rotation either on jacking oil with hand barring or with the help of E.O.T. crane with thick oil on bearings. Avoid jerk during rotation of rotor while recording the swing check values. If jacking oil system is used during rotation of the rotor while recording swing check values, the readings are to be taken stopping the JOP.
9)
After ensuring the swing check values as per the graph with temporary coupling bolts, the HP-IP coupling may be cleared for reaming / honing of the coupling holes. Any variation need correction of the coupling before reaming / honing of the holes.
10) The final swing check value of HP front rotor is to be recorded after fitting / elongation of all the coupling bolts of HP-IP & LP-IP rotors. For improvement of the swing values, the uneven and non-sequential tightening of the coupling bolts may be avoided. 11) During checking of swing readings, 8-10 initial rotations are to be given and then only the readings are to be recorded. 12) Similar method is to be adopted while measuring the swing check value of the exciter and t he rotor is to be hanged on the suitable size of sling. 13) While recording the swing initially with temporary bolts for HP & IP rotor, the fitting of eight nu mber temporary bolts are preferred in place of four bolts on the coupling.
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FEEDBACK NO. 21 HORN DROP TEST General Description By horn drop test the loading of the casing on each corner is determined. The horn drop test is repeated at various stages in individual casing i.e. first without connection of any pipe lines the horn drop readings are recorded then it is compared after welding of inlet, outlet and extraction pipe lines etc. The horn drop readings are very important in HP & IP casing. First the proper horn drop readings are made without connection of any pipe lines and then the reading are taken after welding of all pipe lines on HP & IP casing. As such the influence of t hese major pipe lines are notices on each corner of HP/IP casing by comparing the horn drop test readings. The horn drop test will indicate the quality of work during assembly / welding of pipelines with the HP & IP casing. This is a very important check and may cause serious problem in operation of the machine like vibration in the machine failure of barring gear in hot / cold machine, obstruction during expansion of machine etc. In horn drop test a drop is measured on an individual corner of the casing with the help of a dial indicator by removing the support of individual corner and then it is compared with the opposite corner. As such this gives an indication of indifferent loading of the casing. In Russian design machine the value of direct dynamometer loadings are recorded in place of this horn drop test. Procedure
a. After placement of HP and IP casing on four temporary packers ensure that the each corner of the casing is loaded on temporary packers and if necessary the shims may be given on packer for loading of the casing. The load of shaft is also taken on transport device during this stage.
b. After transferring the load of the rotor on bearing and ensuring the casing centering with respect to shaft the horn drop check may be carried out.
c. Before taking the horn drop reading ensure that the enough clearance is available on front & rear portion of the shaft with their seals in the casing inside. After completing the centering of the casing the some may be lifted by 0.20 mm on all four corners by providing shims. This will help in avoiding the touching of seals with the rotor during the horn drop test readings.
d. No piping may be connected to HP & IP casing till initial horn drop readings are over. The piping work should not be postponed for want of horn drop the only thing the last joint with HP/IP casing may be left free till completion of horn drop check.
e. While recording the horn drop readings the casing must be absolutely free and even the radial and axial key of front and rear portion of the casing are either to be removed fully or these are to be made completely free by removing their shims etc. Actually during this stage of erection only temporary axial and radial keys are fitted in the casing and even they carry some shims also. Before making the casings free on axial and radial key portion the dial gauges are to be installed to monitor the movement of the casing on radial and axial direction. Immediately after the completion of the horn drop test these keys / shims may be installed back and centering of casing may be rechecked before further works.
f. In HP casing the initial horn drop test may be done even after fitting of breach nut assembly and HP exhaust elbow of both sides.
g. In IP casing the initial horn drop test may also be done after fitting of IP inlet pipe lower half assembly but this pipe of upper half casing should not be fitted till completion of the horn drop test.
h. All the four jacking screw and hydraulic jack on each corner of the casing are to be installed for the horn drop test readings. A dial indicator is also to be installed on each corner of the casing for measuring the drop of the casing.
i.
After initial centering of the casing the each corner packer may be fitted with a shim about 1 mm for further adjustment during the horn drop test.
j. During the horn drop test the individual packer of the casing is removed and the load of that corner is supported over the jacking screw of t he casing. Now gradually the jacking screw is also relieved with the help of hydraulic jack on that corner and drop reading is recorded. This is repeated for each corner of the casing. In case of variation in left and right side reading the drop is adjusted by ± adjustment of shims from left to right side or vice-versa. No subtraction / addition in shim sizes from outside is done here and only the shims are adjusted from left to right or vice versa till equal loading are achieved in left / right side of individual casing. The sizes of these casing packers are recorded after completion of horn drop to avoid any confusion at a later date while fitting the final packers.
k. While recording the horn drop readings the drop on each individual corner may be controlled with the help of jacking screw so that during this test the casing is not touching with the shaft in gland portion of the seals at all and enough clearance is left there to avoid damage to the seals inside the casing.
l.
During the initial horn drop the best reading within 0.05/0.06 may be achieved by fine adjustment of the packer shims. The comparison in horn drop value should always be made in left and right side only of an individual casing.
m. In case of HP casing the drop on rear end is so high that unless the casing is locked on diagonally opposite end the horn drop check is not possible. Therefore while recording drop on HP rear end the front end of the casing diagonally opposite to it should be locked with casing clamp. The pedestal is also required to be locked on all four sides with its sole plate with the help of the clamps. In case of IP casing no locking of any corner of the casing is necessary during the horn drop test.
n. The final packers on HP & IP casing are installed only after completing the rolling test of these casing. The horn drop reading for an individual casing may be recorded after the fixing of final packers also. If necessary a fine adjustment may be carried out at this stage to achieve correct value of the horn drop reading.
o. After completing the welding of all pipelines with the casing, the horn drop readings are repeated again for comparison with the earlier readings. These readings are taken along with its radial and axial keys of the casing. During this stage exactly this cannot be defined that how much variation is permitted on these values of horn drop readings. But this variation will indicate the influence of the piping load on the HP/IP casing caused due to welding / connection of various pipe lines with the casing. The variation in horn drop readings are permitted as long as sufficient positive loading is there on each corner of the casing. But if any corner of the casing is fully unloaded / heavily loaded then there is no choice left and pipe lines are to be corrected by dismantling it and making again a free joint with t he casing.
p. During variation of horn drop reading no correction is to be made on casing p ackers by adjustment of shims etc. The variation at this stage is caused due to the piping pull / push only so if any correction is required then the same may be carried out in piping joints and support etc. And any adjustment in piping supports can be carried out only after disconnecting the pipeline with the casing. Even some time it is necessary to cut the individual or more piping joint for correction of horn drop readings.
q. The variation in horn drop reading of left and right side of a casing may be permitted upto a difference of 35% + 10%.
r. The horn drop readings are not taken for LP inner outer casing due to its fabricated structure and the parting plane of the casing are leveled on four corner with the help of water level jar arrangements.
s. The IP casing horn drop is done in three steps:
i)
Firstly, without connecting any pipe lines with the casing
ii)
Then after welding of IP inlet upper half pipe (without even any temporary supports), and,
iii)
And, finally horn drop readings are taken after welding of all pipelines in the casing.
The horn drop readings obtained at (iii) are compared with readings obtained at (i) in light of readings obtained at (ii). This is necessary wherever the IP casing are supplied with one side inlet in upper half casing. In case of a T-joint in upper half casing where the inlet steam is supplied from both left & right sides, the additional horn drop check after welding of upper pipe, as indicated at (i) above, is not necessary.
FEEDBACK NO. 20 AXIAL CLEARANCE TEST (BUMP CHECK) The axial clearance check is determined after radial clearance measurement has been completed. In this case the shaft is shifted in the ‘+’ and ‘-‘ directions from its operating position and the dimensions with the shaft in limit position are measured using a depth gauge. Note: Enter the measured values (actual dimensions) on the record sheet and compare them with the specified dimensions. If the deviation from the specified dimensions is greater than the permitted tolerances, the manufacturer must be consulted. Note : Based on the readings of bump check, position of the shaft wrt casing is not to be altered.
FEEDBACK NO 17 COUPLINGS & ALIGNMENTS OF ROTORS General Description The coupling on turbine shaft are generally rigid coupling but in case of generator sometime the coupling head are shrunk fit and remachined. The basic function of nay coupling is to connect two or more shaft together to f orm a shaft assembly. A very high accuracy is required during manufacturing of these rotors shaft at works. The axial run out on the coupling face may not exceed 0.02 mm. and an additional check is also made at works / site to ensure that the geometry of the entire coupling surface does not deviate by more than 0.02 mm. except the concavity on the coupling face which may be permitted up to 0.02 / 0.03 mm. The radial and axial alignment of the various shafts are to be completed before their coupling and alignments are to be done in such a way that the entire shaft assembly follow the continuous deflection curve given in the drgs. / Log sheets for a particular machine. The coupling checks determines both the radial and axial position of the two adjacent coupling flanges relative to one another. The radial measurements are performed on the circumstance of the couplings and the axial measurements are performed on outer most diameter of the coupling. During the alignment of two couplings both are to be turned in same direction and by the same amount when the measurement are taken to avoid the influence of the axial & radial run out present in the shaft caused due to the machining. After completion of the alignment and coupling of the shaft the casings are aligned radially and axially. Here equal importance is given to the radial & axial alignment of stationary parts to avoid any rubbing during operation of the machine due to expansion of stationary and rotary parts. Procedure
1)
Before placement of module / rotor in position measure and record the coupling hole and journal dia of the shaft.
2)
Check coupling faces for the concavity / convexity with the help of a thin rectangular straight edge before placement of module / rotor in position.
3)
Measure spigot and recess of the coupling and ensure their fitting before placement in position.
4)
Place the module / rotor in position and check the radial run out of journal and axial run out of the coupling faces independently of each shaft. During checking of radial and axial run out of the shaft place H. P. rotor on both of its bearing and IP/LP rotor one end on its bearing and another end on the lifting tackle. The radial and axial face run out on the shaft should be within 0.02 mm accuracy. Compare coupling face mapping at site with the shop values. Any variation may not be permitted here and matter may be referred to the designer‟s.
5)
The HP, IP & LP rotors are aligned together and then their coupling is made. After full completion of HP/IP & IP/LP coupling with tightening of their final bolts the complete shaft is cleared for generator rotor alignment.
6)
During initial alignment of HP/IP & IP/LP rotor the radial checks are generally done with the help of depth micrometer and axial gap are measured with the slip gauges. After completion of the radial alignment the rotor are in serted in their spigot even with some minor variation in their axial gap values.
7)
During final alignment only the axial gap values are checked at left, right and top on four places by rotating both the rotor together and average of these three reading are taken. The radial alignment reading along with axial gaps are necessary wherever two shafts adjacent to each other rare resting on two separate bearings. In case of LP – Generator coupling the radial and axial alignment readings are necessary after taking out the rotor from their spigot.
8)
Avoid rotation of two shafts in their spigot. If necessary these may be rotated after taking out from their spigot.
9)
During alignment of shafts the adjustment of shims in bearing torus may be fully avoided. The margin of ± 0.30 mm. in height & left / right direction may be kept for emergency works only. Any adjustment during erection may be done by adjusting shims between spherical / cylindrical seat and pedestal only. For left and right adjustment the complete H.P. front and HP rear pedestal may be moved with the help of their radial keys.
10) The final packers of the pedestal and base plates are fitted before the grouting of the pedestal itself and here no adjustment is necessary during erection of the machine. But during overhauling of the machine the adjustment may be carried out in these packers for correction of catenary of the machine. 11)
During alignment of rotor make HP/IP and IP/LP coupling gap parallel. After completion of final alignment no adjustment of packers and keys etc are recommended on pedestals and packers and keys etc are recommended on pedestals and bearing. The final alignment of HP/IP & IP/LP rotors should be checked after fitting of all the final keys and packers of the pedestals.
12) Before alignment / coupling position the two shaft adjacent to each other depending upon the higher and lower point of the shaft with respect to their axial face measurement values. 13) After alignment couple the HP-IP & IP-LP rotors on temporary bolts. Record coupled run out of the rotor and ensure that the coupled run out is not more than 0.03 mm any where in the journal as well as in coupling area. Variation between coupled & uncoupled run out should not be more than 0.01 mm at the same location. Before coupling of rotor on temporary bolts record their spigot clearances by actually moving the rotor radially. 14) During erection IP-LP swing check on IP front and HP-IP swing check on HP front are to be recorded on temporary bolts. These reading are to be ensured within the design limit. 15) The HP-IP & IP-IP coupling may be cleared for reaming / honing after ensuring the run out and swing check values of the rotors. In case of variation the cause of the error may be identified and corrected before further work of reaming and honing of the coupling. 16) During coupling of rotor s two taper pins may be used for proper alignment of coupling holes so that there is minimum enlargement of holes are done at site during reaming / honing. Unnecessary enlargement of holes may be avoided during reaming / honing at site as this may cause serious problems at a later date during overhauling of the unit. 17) As for as possible ream/hone all the coupling bolts holes to same size. In exceptional cases only, the variation in hole size are permitted. Each hole during honing should be checked for bananas shape with the help of a parallel ground
straight pin of 0.02 / 0.03 undersize. No banana shape is permitted in any of the hole. The hole should be made to 0.005 mm accuracy. 18) Perpendicularity of axis of the holes to coupling face should be checked and ensured. 19) All the coupling bolts are to be machined and ground by 0.02/0.03 mm undersize than the hole dia. These bolts are to be fitted with thumb pressure only and no additional force is recommended while fitting these bolts. 20) A very thin layer of molykote may be applied on all the coupling bolts during their fitting. The molykote should not be applied on seating face of the coupling bolts. This may cause in breaking of their locking pin during elongation of coupling bolts. 21) All the coupling bolts are to be weighed before final fitting / tightening in position. These are to be weighed within an accuracy of 5 gms each along with their nuts. 22) During tightening of coupling at any stage first tighten four bolts on 90° location. Always tighten bolts in proper sequence with 180° opposite bolts. These bolts are to be elongated to the value given over drgs. 23) During tightening of coupling the radial run out on journal and coupling may be checked at various stages during tightening of bolts. The variation in coupled and uncoupled free run out should be more than 0.01 mm. 24) After final tightening of LP-IP and HP-IP coupling the swing check value on HP front rotor is to be rechecked. In case of variation in value a proper correction is to be made with consultation of designer‟s. The uneven or unsequential tightening for achieving the swing check value or coupled run out value may be avoided. 25) After completing the coupling work the casing radial and axial alignment may be done. Back to Technical Services
FEEDBACK NO 16 ASSEMBLY OF BEARINGS AT SITE General Description The KWU design machine are supplied with four bearings out of which three the journals bearing and one is combined thrust and journal on H. P. rear of the shaft. All the turbine bearing is self-aligning type and they adjust themselves as per the catenary of the machine. The function of a journal bearing is to support the turbine shaft but the thrust bearing support the shaft as well as work as a fix point for the turbine shaft. The contact arrangements between bearing and bearing supports are of two types i.e. sphere to sphere in HP front and HP rear bearing and torus to cylindrical in other bearings. The bearings are supplied to site after their contact at works. During erection all the bearing are supplied to site aligned and assembled conditions in the ir individual pedestal from the works. After alignment of the bearing in their pedestal the seat of the bearing are doweled before dispatch to site. In case of thrust and journal bearing the seat of the bearing neither doweled from the works nor it is recommended to be doweled at site. The bearings need preparation before placement of module in position at site. This can be done even before the placement of pedestal in position for grouting. Assembly Procedure
a. After opening the pedestal remove and clean the bearing including its spherical / cylindrical seat.
b. Remove oil guard ring and its duct and keep them in proper place for their storage at site. c. Handle bearing carefully to avoid any damage to the Babbitt and its torus / spherical piece. During storage at site avoid direct loading of bearing on its torus. A thick rubber seat may be used during handling of bearing at site its torus.
d. Ensure 0.03 feeler tightness on bearing shell parting plane after tightening both halves. In case of any variation the matter may be referred to designers.
e. Measure bore dia of the bearing and journal dia at site and complete the oil clearances. If any discrepancy is observed, designer may be referred.
f. Check torus / spherical contact with their seats at site. While checking the contact the seat may be bolted with their pedestal. In case any variation in the contact from their specified diagrams are noticed then following may be carried out at site: 1)
In case of cylindrical seats the line contact are recommended by designers. If these lines are not straight and are in angle then the baring may be rejected straight way and sent to works for rectification. These line contact may be in a width of about 20 mm throughout on its seat leaving with small area on both sides. The contact may be wide in center and then gradually reducing on sides. In case no contact is achieved in the center and only sides are having contact then a feeler gap may be recorded in bottom. In case the bottom is tight to a feeler of 0.03 mm the bearing may be accepted at site without doing any rectification. In a reverse case the contact is achieved in center only through the 0.03 feeler is not going in the side. The bearing may be still accepted at site. In case if the feeler is going in the bottom or in sides by 0.03 mm. the bearing are not accepted at site and can be sent back for the rectification to the works. Similarly if the contact is intermittent on its seat but in a straight line and no feeler is going the bearing may be accepted. In case of very wide contact also the bearing may be sent back for the rectification. While checking these contact very light colour may be put on torus of the bearing.
Before sending back the bearing to the works the matter may be referred to designers and their concurrence is to be obtained. No scrapping / lapping is recommended in these bearing for improvement of the contact. 2)
In case of spherical to spherical bearing the contacts are called in the center like a moon shape. In these bearings even full contact may be accepted. But in case if there are contact on sides and a feeler gap is noticed on center then the bearing may not be accepted. In such cases if the gap is upto 0.03 mm then the lapping / scrapping may be carried out at site. But in case of higher gap the matter may be referred to designers.
g. Before checking the contact between torus and its seat ensure that the seat is feeler to 0.03 mm without tightening of nay bolts with the pedestal. If necessary this may be corrected.
h. The sizes of all the shims may be recorded in bearing body and spherical / torus piece of the bearing. The number of shims are to be limited to 3-4 numbers only even after complete alignment of machine. A protocol for number of shims added and their size is to be prepared by the site.
i. Check jacking oil lines of the bearing and clean them thoroughly. Ensure jacking oil lines fittings also for their male female threads etc. otherwise this may create the oil leakage through these lines during operation of the machine.
j. Whenever jacking oil is not available, use thick oil during rotation of shaft over bearing. The type of oil may be as servo cylinder 1000 grade of IOC.
k. After installation of bearing in position the oil clearances may e checked after few rotation of the shaft. But the final oil clearances are to be checked after final coupling of the shaft. In case of variation in side oil clearances no cutting of Babbitt metal is permitted at site. In case of nay variation, investigation may be done and necessary rectification can be carried out. If necessary, consult designers.
l. Similarly, in case of any variation in the askew side oil clearances, investigation may be done and necessary rectification can be carried out. If necessary, consult designers.
m. Ensure good contact between journal and Babbitt metal of the bearing in the center. Any minor high spot may be removed from the Babbitt metal while checking with blue colour. Ensure full contact of shaft over the jacking oil pocket also.
n. Always cover rotor journal with the upper half bearing to avoid entry of any sand particles etc. in the bearing. During pouring of oil the upper bearing may be removed and replaced back after the pouring of oil.
o. After completing the reaming / honing and final tightening of coupling bolts the work of bearing side pad, yoke keys and oil guard fitting may be taken up.
p. Before starting the side pad and top keys ensure that the bearing is perfectly level on parting plane. Ensure that the gap for the side pads are parallel otherwise these are to be made by cutting / scrapping.
q. After fitting of the bearing cap if the gap for the radial top keys are in taper a proper correction is to be made here. T he bearing cap may also be repositioned to achieve the parallelity of the key way. The taper are to be re-doweled after repositioning it but no taper is to be left on this area. If repositioning of cap is not helping then the cutting may be carried out in bearing cap.
r. The gap for the top packer of bearing may also be checked. In case of any taper the same is to be corrected by cutting on bearing cap. Sometime the size of this packer comes to very low i.e. even below 5.00 mm. this may be corrected by matching the cap and size for this packer may be kept around 6.00 mm.
s. On all these bearing cap key a proper fitting and clearances are to be maintained during assembly. These keys of proper material are to be only used and no welding deposits are permitted here.
t. Use of local made shims in bearing may be avoided & shims of correct specifications should be used. Ensure drawing requirement of maximum adjustment at site by ± 0.3 mm in shim size from as manufactured condition.
u. A proper care should be given during fitting of bearing oil guard ring otherwise it causes the oil leakage during operation of the machine through pedestals. Parting plane joint of oil guard ring and duct should be feeler tight and no elongation of holes on this area may be permitted.
v. The bearing parting plane bolt are to be tightened to required torque only no other method of tightening of these bolts may be used.
w. Adjustment of shims between spherical / torus and bearing body is limited to ± 0.30 in up and down and left, right direction. This margin may be left for emergency work during overhauling of the machine any adjustment during erection and normal overhauling may be done by adjusting shims between spherical / cylindrical seat and pedestal base only. For left and right adjustment the complete pedestal of HP front and HP rear may be moved with the help of their radial keys. The above-discussed points were common for journal bearing and combined thrust and journal bearing. Now some specific points are detailed here for the assembly of combined thrust and journal bearing. a)
Remove all the thrust pads before placement of bearing in position and store them in a proper place.
b)
Check proper fitting of Babbitt metal liner in the bearing body including necessary pinch in the fitting of its liner.
c)
During alignment of rotor, align the bearing with respect to the shaft by moving spherical seat of the bearing radially and axially.
d)
No elongation of holes is to be carried out in spherical seat of the bearing for the purpose of its alignment.
e)
Before deciding axial position of the bearing the axial position of the rotor is to be determined. If necessary the H. P. rear pedestal as a whole may be shifted axially to ensure correct position of the thrust bearing.
f)
Align the thrust bearing in such a way that the thrust pad gap achieved are parallel and no difference are noticed in front and rear pad thicknesses.
g)
Movement in the thrust pads should be ensured and a difference in thickness of packers including shims should be within ± 0.10 mm may be permitted on front and rear pad sizes.
h)
After ensuring the perfect alignment of the bearing the axial keys are fitted after assembly of upper half bearing. These axial keys are to be fitted in perfect parallel slots without any clearances. The keys are to be fitted in such a way
that there is no movement to the bearing during fitting of the axial keys. Necessary dial gauges are to be installed on bearing during fitting of these keys. i)
After completion of axial key works of the bearing the thrust pads fitted in the bearing with a clearance of about 0.10 / 0.15 mm.
j)
Before fitting of pads in the bearing ensure that there dimension are made parallel to suit the front and rear slot size of the bearing (size between thrust collar and bearing body).
k)
Install lower half bearing in position along with their pads and put very small quantity of oil on journal then rotate the rotor and put blue colour on the thrust collar of the rotor on both front and rear side.
l) m)
Install upper half bearing along with all pads and fix their axial keys. Rotate the rotor and move ± direction axially with the help of wooden planks. Remove both halves of the bearing and see the blue contact on thrust pads. If necessary some cutting may be carried out on the pads to achieve the colour contact. This exercise may be repeated few times to achieve the blue contact.
n)
Ensure a float of 0.30 ± 0.10 mm during colour matching of the thrust pads. If necessary the minor adjustment of shims may be carried out in the bearing pads.
o)
Before installation of thrust bearing along with thrust pads in position the both halves may be bolted out side and their pads may be checked for colour contact over a surface plate also in front and rear both sides. This will contact of the bearing with the rotor.
p)
During overhauling of the unit the bearing contact are to be rechecked and need correction. In case of torus to cylindrical type of bearing if the contact are not satisfactory then the bearing and its seat may be remachined at works. In spherical to spherical bearing the variation in contact if noticed can be corrected by matching / lapping at site. Sometimes the heavy pitting marks are also noticed on same of the bearing and these need correction by machining it.
BEARING CONTACTS 1.0 SPHERICAL TO SPHERICAL SEATS
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FEEDBACK NO. 15 CATENARIES AND ALIGNMENTS General Description The catenary of the machine is very important for a turbine and Generator assembly to achieve proper alignment of various rotors and loading on their bearing. Any deviation may lead to various operational problem in the machine like high shaft vibration, high bearing vibration, high Babbitt metal temperature of the bearing vibration, high Babbitt metal temperature of the bearing etc. to avoid these problems it is necessary to maintain the catenary of the machine during erection and subsequent realignment / overhaul of the unit. Many times it is observed that through the alignment of rotors are within limit but the catenary as a whole get deviated from the prescribed design value of the machine. In order to avoid such derivation a need is felt to devise a procedure, which shall ensure rotors alignment along with proper catenary of the machine. During first few years of the operation of the unit the possibility to the disturbance of the catenary are much more due to settlement of the foundation frame. In each overhaul of the unit the catenary of the machine is to be corrected. The L. P. front and L. P. rear pedestal are directly grouted here without any sequence base plate. As such any correction on lifting or lowering on these pedestals are not very convenient so if necessary the rotor may be lifted or lowered with respect to pedestal seal bore and required catenary may be achieved. In extreme cases these pedestals may be even regrouted during major overhauls of the unit to correct the catenary of the machine. Procedure a.
Install a benchmark plate near L. P. rear pedestal as height of the machine centerline with the consultation of civil Engrs. at site. A S. S. plate of 200 mm x 300 mm size with 20 mm thickness machined / ground on top side may be welded over a I-Beam or a channel in level condition.
b.
Check half bore error of all the four pedestals and compare the readings with the factory records also. The half bore error may be checked in both upper half and lower half of the pedestal. To avoid concealment of the punch mark by subsequent painting, a yellow coloured box may be painted during erection indicating location of the punch mark.
c.
During alignment of pedestal at the time of grouting with non-shrinking cement set the height of the pedestals as per required catenary of the machine considering
± value for the half bore error of the pedestals. While setting the
height of the pedestals it should be kept in mind that the height for the center of the pedestal bore are to be kept as per the catenary of the machine and not the parting plane of the pedestal. d.
For better results four water level jars connected to each other with a polythene pipe of approx. 20 mm diameter may be installed on each pedestal. Portable water may be used here and leakage through polythene tubes should be avoided fully while making the connections. These jars may be fabricated at site out of about 125 mm. dia pipes with a plate welded in bottom and then machined for better seating on pedestal base. The height of the jar may be kept, as about 175 mm. a depth micrometer installed and clamped over a magnetic base is also required for measurement of the water level in the jar. The micrometer point is to be made sharp by grinding it.
e.
During measurement of water level in the jar the micrometer is to be kept approximately in center of the jar. The micrometer along with the magnetic base is to be transferred from one pedestal to another pedestal very carefully so there is no disturbance to the height of the micrometer. All the necessary care is to be taken during this measurement. There should not be any air bubble in the polythene pipe and the polythene pipe should be kept as st ationary.
f.
While finalizing the pedestal parting plane level of the machine, these measurements are to be repeated 3-4 times in a day at different intervals to avoid any possibility of the error.
g.
The height of the L.P. rear pedestal is the reference point for setting the height of all other pedestal and L.P. base plate. The L.P. rear pedestal height is to be first made with the benchmark plate as per the centerline of the machine with the help of water level jar.
h.
The parting plane height is to be counter-checked after grouting all the pedestals. The final value of the catenary may be worked out as center of the shaft on each pedestal bore after taking the final seal bore readings. The final
catenary should match with the design value of the catenary otherwise a necessary correction may be carried out during alignment of the rotors. i.
After ensuring the required catenary of the machine the coupling alignments are to be made as parallel coupling.
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FEEDBACK NO.9
SUB: RADIAL CLEARANCE IN LPT BLADE PLAN OF KWU DESIGN TURBINE – KWU – 120/210/500 MW & KN SERIES. 1.
Due to static sag in the inner outer L.P. casing, because of its long span and weight, the radial clearances at the horizontal joint between rotor and stationary blades / casing are found to be less than the designed value when they are checked during assembly with only bottom half of casing and L.P. rotor in position (top half casing not assembled). The sag influences stages 6 to 8 in 210 MW turbine and stages 4 to 6 in 500 MW turbine i.e. the stages whose guide blade carries are mounted in the stages whose guide blade carriers are mounted in the inner outer casing. This sag gets almost eliminated when the top half of the inner outer casing is assembled and its bolts are tightened.
2.
The sag in the inner-inner casing is negligible due to its smaller span and weight therefore it does not influence the radial clearance of the stages within inner-inner casing.
3.
The normal radial clearance of 1.5 mm as given in the drawing no. 9-103-04-01000 for 210 MW and 2.0 mm in the drawing no. 9-103-04-0500 MW, have the in built tolerance in the range of 1.3 to 1.85 mm in 210 MW turbines and 1.8 to 2.35 mm in 500 MW turbines are acceptable.
4.
Prior to checking the radial clearance at the horizontal joint of casing during erection, it is recommended that the inner-outer casing lined to be jacked up from the bottom, at the location of centralizing key, till the support palm just starts lifting. The radial clearances are to be checked in such jacked up condition, so as to compensate for the static sag. The jacks should be removed only after putting the top half of the casing and tightening the parting plane bolts.
5.
Thus by considering the permissible tolerance in the radial clearance as mentioned in Para 3 and compensating the effect of sag as mentioned in Para 4 above, unnecessary grinding of the fins due to false indication of less clearance can
be avoided. Sealing fins should be ground to increase the radial clearance only when the required minimum clearances are not achieved even after considering the above aspects. Back to Technical Services
FEEDBACK NO. 5 FEED BACK ON HIGH VIBRATION OF BEARINGS OF NEYVELI - 7 PROBLEMS: The machine has a problem of high HPT F ront and Rear shaft vibration from first commissioning (June‟93 – around 90 to 100 microns) but all other bearings shell vibrations were normal. In the month May/June‟97, there was a sudden rise of shell vibration bearing # 2 – vertical 22 mm/sec. OBSERVATION / ACTION During the overhauling of LP – Generator works that started on 12.10.1997 and completed on 20.11.1997, following abnormalities were observed and corrective action taken.
A gap of 0.35 mm between sole plate and the TG Deck. - The gap was filled up by pressure grouting with special quick setting compound (Monopol Liquid)
Non-uniformity in the loading of packers of pedestal No. 2 - All packers were l oaded uniformly.
Swing check value at bearing No. 1 was as high as 0.44 mm - The same was corrected.
Failure of thrust pads in NDT Test. - A total number of 14 thrust pads were replaced with new ones.
RESULT Significant reduction in HP shaft vibration level observed after overhaul. Shaft of HPT Front and Rear reduced to 70 & 50 microns respectively. Velocity of bearings No. 2 pedestal vibration reduced to l ess than 5 mm/sec.
FEED BACK NO: 1 STEAM TURBINE – GENERATOR SET CATENARY MEASUREMENT DURING OVERHAUL During erection of TG S ets, bearing pedestal elevations are kept with required differences to match with the Rotor Catenaries. After grouting of pedestals minor corrections are done on the bearings to get the required alignment of rotors. But over a period of time, the pedestal elevations get disturbed due to the settlement of foundation resulting misalignment of rotors. This misalignment is corrected by altering the bearing positions whereby the co -axiality of bearing and pedestal get disturbed in both vertical and horizontal direction. The disturbance in vertical plane l ead to the situation, that the catenaries measurement with reference to the pedestal-parting plane will no longer be correct. In this case measurement of elevation differences of bearing parting plane can give more or less correct value of catenaries. Bearing parting plane will be above the journals axis by half of the top oil clearance. Before this measurement is taken up the bottom half of the bearings are to be leveled in transverse direction using a Sprit Level. Example is given below:
1j & 2j
Journals
1b & 2b
Bottom halves of bearings
3.
Sprit Level
4.
Water Jars
c1
Half Top oil clearance of Bearing 1
c2
Half top oil clearance of Bearing 2
a1
Height of jar above water level on Bearing 1
a2
Height of jar above water level on Bearing 2
l1
Height of Jar on Bearing No. 1
l2
Height of Jar on Bearing No. 2
h
Elevation difference (Elevation Difference between Journal No. 1 & 2)
h = (l2 + c2a2) (l1 + c1a1) if l1 = l2 h = (c2 – a2) – (c1-a1) OR (a1-c1)-(a2-c2) This method can be used even if there are more than 2 journals, whose elevation differences are to be measured. Comparatively more accurate values can be obtained if „U‟ blocks are used over each journal over which water jars can be placed. As each journal is of different in diameter each requires separate „U‟ block. Manufacturing of these „U‟ Blocks will be difficult and highly expensive. Besides, this method does not have the versatility and flexibility.
This problem can be overcome by using “Channel” Blocks, which can be used on any journal by changing the distance piece, this method is explained hitherto. This channel can be used for journals of f 200 mm and above. L = Effective length of distance piece. (All items can be manufactured of mild steel or cast iron)
1. Journal of Radius R1 2. Journal of Radius R2
3. Channels (to be leveled in transverse direction using sprit level). 4. Distance piece L = R2-R1 5. Cups 6. Jars 7. Sprit Level. g1 Gap to channel on Journal No.1 g2 Gap l
Effective length R2-R1.
l1
Height of Jar on channel at No.1.
l2
Height of Jar on Channel at No.2.
a1
Height of Jar 1 above water level.
a2
Height of Jar 2 above water level.
h = (g2 + L2 – a2) – (g1 + L1 – a1) if L1 = L2 h = (g2 – a2) – (g1 – a1)
This method can also be used where elevation difference of more than 2 journals are to be measured by changing the distance pieces. Distance pieces are to be made with respect to the journal whose radius is largest. Distance L must be = largest journal Radius – Radius of the journal whose elevation to be compared. For example on 210 MW (KWU design) TG set journal No. Is of 225 mm radius. L for journal 1 in mm -----
225-140 = 85
L for journal 2 in mm -----
225-145 = 80
L for journal 4, 5 & 6 in mm -----
225-200 = 25 each
Measurement can be done between any two i.e. 1 & 2 or 1 & 4 or 4 & 6 etc. Catenary measurement in overhauls is for recording purpose only. If deviations are noticed in journal elevations, but the machine does not have any vibration problem, correction is called for only in the alignment with least disturbance and no major change to be incorporated for the sake of Cantenary correction. Centenary correction along with alignment correction has to be resorted to those machines, where the vibrations has gone up over a period of tome during operation and vibration analysis points out to problem in Bearing loading.
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SUB: A Report on Alignment of HP-IP Casing with Dummy Shaft --BHEL,SLPP Mangrol After modification at Hyderabad, all the consignments of the K- Turbine of Unit # 2 were received at site by end July‟1999. All the modifications in design and manufacture at Hyderabad were carried out with the advice of Siemens‟, Germany. It was also decided to seek the help of Siemens‟ expert during re-erection. On 24th September, 1999, Mr.Kaluza Micheal, Siemens‟ erection expert arrived from Germany. On arr ival, Mr. Micheal asked for a dummy shaft for alignment of HP Inner casing with Outer casing. This came as a surprise as the use of dummy shaft is not in vogue in BHEL. Alignment with dummy shaft requires measuring feelers (alignment probes) which resemble dial gauges and work on the principle of LVDT. Arrangement of Dummy Shaft The dummy shaft or false shaft as it may be called, is a round piece of steel pipe with flanges on either ends. The length of the dummy shaft is governed by the length of the casings and is required to be projecting beyond the extreme ends of the casings which are being aligned. One end of the shaft rests on the rotor lifting device located on the front bearing pedestal and the other rests on a specially made bracket located on the rear bearing pedestal. Alignment probes are fixed to the dummy shaft by clamps mounted on it. The number of alignment probes that can be fixed on the dummy shaft depends on 2 factors : a) b)
The provision made in the switchgear for the probes. The number of areas in which measurement is sought by the user.
The probes are lead out of the dummy shaft through a hole in the shaft, to a switchgear unit. It may be noted that only as many probes can be used as the provision in the switchgear unit. The switchgear unit that was used at GIPCL had a provision for 8 probes. The switchgear unit is in turn connected to the measuring device. More than one switchgear unit can be used if there is a provision for connecting them to the measuring device. In case only one switchgear unit is available, the user may judiciously decide on the critical areas that require measurement. The measuring device used, resembles a multimeter and has an accuracy of 0.0001mm. Fig 1 : Dummy shaft placed in Inner Casing Bottom
Fig 2 : The Probes attached to the Dummy shaft for Measurement at Various Locations
Fig 3 : Centering of Dummy shaft being Verified Why Dummy Shaft? The idea of using a dummy shaft is to center the Inner casing with respect to the Outer casing. Concentricity is the key word. It is required to maintain concentricity of the Inner casing and Outer casing so that the two casings expand in the same direction. Also, box up conditions can be simulated with a dummy shaft and the behavior of the casing studied when the Top halves of the Inner and Outer casings are installed. Installation of the top halves of the Inner and outer casings leads to an addition in weight of approx. 40MT. The addition of weight is expected to lead to changes in the top/bottom clearances during box up. This
variation can be recorded on the measuring device and corrective action if any can be taken during actual box up of the machine. Alignment with Dummy Shaft and Box up The following is procedure for alignment of the Inner casing with respect to the Outer casing using a dummy shaft. 1.
Place outer casing bottom half.
2.
Place Inner casing bottom half.
3.
Lower the dummy shaft.
4. Support the dummy shaft on the bracket provided for the purpose on HP rear bearing pedestal and on the shaft lifting devic e of the HP front bearing pedestal. Note: It is not required to center the dummy shaft with respect to the pedestal seal bore. The idea is to maintain concentricity of inner & outer casings and assemble the module as if there were no bearing pedestals. 5.
Fix alignment probes in desired locations.
6.
Set the alignment probes to „Zero‟.
7.
Center the outer casing bottom half with respect to the dummy shaft.
8.
In the above condition, check centering of the Inner casing bottom half. In case of misalignment, center the inner casing on left/right by radial movement of the inner casing and top/bottom by adjusting the jack screws.
9.
Install bottom eccentric pins.
10. Place inner casing top half and heat tighten the parting plane bolts. 11.
Set the desired centerline offset of the inner casing with respect to the outer casing, in the top/bottom direction, by adjusting the jack screws. Check centering readings again.
12. Insert temporary inner casing resting packers (u-Packers), thickness of which shall be equal to the gaps at the respective locations. 13. Transfer the load of the inner casing on the temporary U-packers and remove the jack screws. Check centering again to see if there has been any disturbance during transfer of load from jack screws to U-packers. In case of any disturbance, the same may be adjusted in the temporary U-packers. 14. Place outer casing to half and completely heat tighten the parting plane bolts. It is expected that the placement of outer casing top half will result in some deflection to the entire assembly thereby causing disturbance to the centering in step 12. 15. Install top eccentric pins. 16. Check centering again. Any variation in the centering readings shall be corrected as below: a)
center the outer casing to the values achieved in step 12.
b)
In the above condition, check centering of the inner casing. Any variation in the inner casing centering in the top/bottom direction may be noted down and correspondingly reduce or increase the thickness of U-packers during final assembly.
Any variation in the left/right centering may be corrected by rotating the eccentric pins at the top and bottom. 17. After the left/right centering has been completed by rotating the eccentric pins, lock the eccentric pins in that position. Installation of the eccentric pins in this position during final boxup will restore left/right centering of the casings. 18. Dismantle the outer casing top half. 19. Dismantle the inner casing top half after transferring the weight of the inner casing on to jack screws. 20.Disconnect the alignment probes and remove dummy shaft. 21. Place rotor and check flow path clearances. 22.Fix axial position of the rotor. 23.Finalise inner casing axial locating keys. 24.Carry out roll check at this stage for determining the minimum radial clearances at the left, right and bottom. 25.Install top half of inner casing and heat tighten parting plane bolts. 26.Inner casing resting packers made to thickness recorded in step 16b shall be installed. 27.Transfer the load of the inner casing on to U-packers and remove the jack screws. 28.Carry out roll check at this stage to determine the minimum inner casing radial clearances at left, right, top and bottom. 29.Install outer casing top half and heat tighten parting plane bolts. 30.Carry out roll check once again.
This completes box up of the turbine using a dummy shaft. The method can be universally adopted for box up of IP module and LP module of HMN series machines too.
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FEEDBACK NO. 30 PROJECT
UNIT NO. SUBJECT
: : :
RAICHUR TPS UNIT - 6 HIGH AXIAL VIBRATIONS IN TG BEARING 4
Raichur unit 6 was having high axial vibrations of 250 microns and vertical of 80-90 microns since commissioning. Various exercises like alignment checking, trim balancing, did not help. With the assistance of BHEL R & D and collaborators, dynamic analysis was carried out. It was found that the natural frequency of beam of bearing 4 was around 2950 rpm. High vibration of the beam around that speed was
in torsional mode. Mass of 700 Kg. was added in bearing pedestal cover to vary the natural frequency. Checks confirmed the same has shifted from 2950 to 2850 rpm. Further exhaustive study done by SERC confirmed the cause of the vibration as above and the recommendation given by them is given below : 1.
Damping of Brg. 4 foundation beam
2.
Stiffening of concrete structure
3.
Additional mass in foundation beam
Out of the above, adding of extra mass was selected, as that is only feasible. As it is cumbersome to add mass in the beam, it was preferred to add mass in the pedestal top cover. Accordingly a new brg. pedestal top cover was manufactured with an additional mass of around1.3 T and fixed in position. The vibration levels have come down by half and the values are steady at all loads and speeds. The natural frequency of the beam has also got shifted to 2650 rpm. The machine is running at full load steadily
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FEEDBACK NO. 25 TRANSIENT VIBRATION RISE (UNIT 4, 5 AND 6, KSTPP) PROBLEM During sudden load changes of the machine, rise in bearing vibration and shaft vibration noticed at around 200 MW loads. Otherwise, during start-ups and normal operations of the machine vibration patterns were observed to be satisfactory. OBSERVATIONS Transient vibration problem appeared at around 200 MW. Following observations were made: i)
The variation in gland steam parameters noticed when sealing system changed over from self-sealing to external sealing.
ii) iii)
Heavy sparking noticed at LP gland boxes front and rear indicating rubbing of seals with LP rotor. All other operating parameters were found to be normal.
ACTION TAKEN Centering of LP gland boxes was checked and found to be disturbed. Top clearance was found to be very less. It was also experienced that even after carrying out perfect centering (as prescribed), the set clearances were observed to be disturbed during subsequent checkings. The distortion of gland box seal assembly was also anticipated during variation in gland steam parameters at the point of changing over of supply system. The radial clearances were increased (to the highest value prescribed in the drawing) to eliminate possibility of sealing strips rubbing due to suspected distortion of gland box assembly during variation in gland parameters.
REMARKS After increasing the radial clearances, this problem has not appeared so far. Back to Technical Services
FEEDBACK NO.9
SUB: RADIAL CLEARANCE IN LPT BLADE PLAN OF KWU DESIGN TURBINE – KWU – 120/210/500 MW & KN SERIES. 1.
Due to static sag in the inner outer L.P. casing, because of its long span and weight, the radial clearances at the horizontal joint between rotor and stationary blades / casing are found to be less than the designed value when they are checked during assembly with only bottom half of casing and L.P. rotor in position (top half casing not assembled). The sag influences stages 6 to 8 in 210 MW turbine and stages 4 to 6 in 500 MW turbine i.e. the stages whose guide blade carries are mounted in the stages whose guide blade carriers are mounted in the inner outer casing. This sag gets almost eliminated when the top half of the inner outer casing is assembled and its bolts are tightened.
2.
The sag in the inner-inner casing is negligible due to its smaller span and weight therefore it does not influence the radial clearance of the stages within inner-inner casing.
3.
The normal radial clearance of 1.5 mm as given in the drawing no. 9-103-04-01000 for 210 MW and 2.0 mm in the drawing no. 9-103-04-0500 MW, have the in built tolerance in the range of 1.3 to 1.85 mm in 210 MW turbines and 1.8 to 2.35 mm in 500 MW turbines are acceptable.
4.
Prior to checking the radial clearance at the horizontal joint of casing during erection, it is recommended that the inner-outer casing lined to be jacked up from the bottom, at the location of centralizing key, till the support palm just starts lifting. The radial clearances are to be checked in such jacked up condition, so as to compensate for the static sag. The jacks should be removed only after putting the top half of the casing and tightening the parting plane bolts.
5.
Thus by considering the permissible tolerance in the radial clearance as mentioned in Para 3 and compensating the effect of sag as mentioned in Para 4 above, unnecessary grinding of the fins due to false indication of less clearance can be avoided. Sealing fins should be ground to i ncrease the radial clearance only when the required minimum clearances are not achieved even after considering the above aspects.
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