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8/13/2019 BHEL Feed Back

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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 are to be completed before starting the rolling test of the 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 also to be completed before 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


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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 screw of HP and IP casing are to installed along with dial gauges for monitoring of up and down, and

left and right movement of the casing.

d) One number hydraulic jack on each corner of the casing along with a spanner on each corner for jacking screw are also to

be made available.

e) During erection of machine the turbine rotor are generally rotated by hand with the help of periphery holes on coupling.

Two pipes of about 1250 mm long along with a pin to suit the dia of periphery may be used 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 ofthe machine.

f) Before starting the following check it should be ensured that the rotor shaft is absolutely free on manual 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 rotation of rotor over bearing in absence of jacking oil system. The type oil may be servo cylinder

1000 grade (IOC) oil.

h) During the rolling test the temporary casing packers are to be fitted with about 1.00 mm shims.

i) During the rolling test of any of the casing the same is lifted first on all four corners in a step of 0.05 mm with the help

of hydraulic jack and jacking screw. The rotor is also rotated manually side by side with the lifting of casing. The rotation 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


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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 is 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. 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 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 four 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 and fixing of a final radial keys and packers of one of the casing the rolling test of another

casing is done including the fitting of final keys and packers.


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k) Necessary offset in the radial clearance is also kept before fitting of final packers of the casing toward the lift of the shaft

during operation of the unit.

l) No inlet and outlet pipes are to be welded with the casing till completion of rolling test and installation of final keys and

packer of the casing.

m) Radial clearance of the casing are to be ensured with reference to the factory supplied protocol also.

n) After fitting of final keys and packers of the casing the final spigot 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 drop readings are also to be checked after the fitting of final packer of the casing.

p) In case of IP casing the roll test readings are to be taken with the IP front-end rear shaft scales. The spigot dial readings

are also to be taken over the spigot of shaft seals.

q) During rolling test of the HP and IP casing if the rotor is rotated over the jacking oil then the adjustment of readings are

to adjusted for the lift of the rotor also.

r) Four numbers 1.00 mm undersize packers for HP & IP casing may be used during erection for further 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 but both side joints of LP inlet bellows 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 is done after the neck welding of condenser and stiffener pipes inside the condenser. This

include the welding of stiffener pipes of LP casing and gusset plates also.


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3) After rolling test of the casing the final radial keys of the Gusset block-casing packers on all four corners are installed.

4) Necessary offset in the radial clearances of the casing is also kept before fitting of final LP inner casing packers.

5) Radial clearances of the casing are to be ensured to the design values. In case of any 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.)


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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 forbetter 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.


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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 HP-

IP 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.


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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 number temporary bolts

are preferred in place of four bolts on the coupling.


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a. After placement of HP and IP casing on four temporary packers ensure that the each corner of the casing isloaded 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 shaftthe 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 ofthe 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 workshould 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 keyof 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 HPexhaust 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 butthis pipe of upper half casing should not be fitted till completion of the horn drop test.


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h. All the four jacking screw and hydraulic jack on each corner of the casing are to be installed for the horndrop 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 furtheradjustment 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 issupported 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 ofindividual 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 helpof 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 thepacker 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 oppositeend 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.


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n. The final packers on HP & IP casing are installed only after completing the rolling test of these casing. Thehorn 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 forcomparison 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 anycorner 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 the casing.

p. During variation of horn drop reading no correction is to be made on casing packers by adjustment of shimsetc. 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 of35% + 10%.

r. The horn drop readings are not taken for LP inner outer casing due to its fabricated structure and theparting 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:


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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.


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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.


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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 form 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


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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 designers.

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 inserted 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.


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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


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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 designers. 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.



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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 their 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.


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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 thematter 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 theirpedestal. 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.


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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 ofnay 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 ofshims 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 malefemale 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 servocylinder 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 oilclearances 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 rectificationcan be carried out. If necessary, consult designers.


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m.Ensure good contact between journal and Babbitt metal of the bearing in the center. Any minor high spot may beremoved 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. Duringpouring 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 andoil 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 gapfor 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. Thebearing 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 cuttingon 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 propermaterial 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 drawingrequirement 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 operationof 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.


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v. The bearing parting plane bolt are to be tightened to required torque only no other method of tightening of these boltsmay be used.

w.Adjustment of shims between spherical / torus and bearing body is limited to 0.30 in up and down and left, rightdirection. 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 infront 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


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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) Install upper half bearing along with all pads and fix their axial keys.

m) 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.


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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.


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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 stationary.

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


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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 thehorizontal 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 1.8to 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


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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.



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FEEDBACK NO. 5

FEED BACK ON HIGH VIBRATION OF BEARINGS OF NEYVELI - 7

PROBLEMS:

The machine has a problem of high HPT Front and Rear shaft vibration from first commissioning (June93 around 90 to 100

microns) but all other bearings shell vibrations were normal. In the month May/June97, 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.


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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 loaded 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 less than 5 mm/sec.


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FEED BACK NO: 1

STEAM TURBINE GENERATOR SET CATENARY MEASUREMENT DURING OVERHAUL

During erection of TG Sets, 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 lead 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:


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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

l 1 Height of Jar on Bearing No. 1

l 2 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.


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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 R12. Journal of Radius R2


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3. Channels (to be leveled in transverse direction using sprit level).4. Distance piece L = R2-R15. Cups6. Jars7. 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)


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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


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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 July1999. 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 24thSeptember, 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) The provision made in the switchgear for the probes.

b) The number of areas in which measurement is sought by the user.


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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


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Fig 2 : The Probes attached to the Dummy shaft for Measurement at Various Locations


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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


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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 device

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.


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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.


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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.


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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.


FEEDBACK NO. 30

PROJECT : RAICHUR TPS

UNIT NO. : UNIT - 6

SUBJECT : HIGH AXIAL VIBRATIONS IN TG BEARING 4

Raichur unit 6 was having high axial vibrations of 250 microns and vertical of 80-90 microns sincecommissioning. 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 thenatural frequency of beam of bearing 4 was around 2950 rpm. High vibration of the beam around that speed was


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in torsional mode. Mass of 700 Kg. was added in bearing pedestal cover to vary the natural frequency. Checksconfirmed 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 recommendationgiven 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 inthe beam, it was preferred to add mass in the pedestal top cover. Accordingly a new brg. pedestal top cover wasmanufactured with an additional mass of around1.3 T and fixed in position. The vibration levels have come downby 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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REMARKS

After increasing the radial clearances, this problem has not appeared so far.


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.


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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.



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bhel feed back

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