TURBINE GENERATOR PKG ERECTION PART-X, DIFF.CHECKS BUMP ,SWING ,HORN DROP ,CATENARIES ETC.- ABC OF THERMAL POWER PLANT.

Part – X

After colour matching axial zero position is achieved and this will be reference point of

future axial measurement of HP,IP and LP casing. During Turbine supervisory  instrument calibration

rotor is given to instrument group at axial zero position .

 After completion of colour matching of the thrust bearing pads the casing alignment work

can be taken up. In case of spring loaded foundation after completing all other works the HP /

IP , IP/LP , LP/GEN , GEN/EXCITER couplings are to be reopened and realigned after completing

the reaming /honing . The rotors alignment are to be checked with TG deck in floating condition

as per the laid down procedure. After checking of alignment /catenary the final couplings are to

be tightened including their coupled run out and swing check of rotors on HP front and Exciter

end of the shaft.

The boxing up of LP inner inner and LP inner outer casing can be taken up before starting

the alignment of HP-IP & LP rotor for coupling work.

After completing the welding of HP inlet, HP exhaust, IP inlet, IP exhaust and other piping of

HP/IP casing the final horn drop readings are recorded as per the laid down procedure

mentioned in the manual for horn drop check. However the IP casing horn drop is also to be

recorded with IP inlet upper half pipe welded with casing alone.

ASSEMBLY OF BEARING AT SITE

The KWU/BHEL design machine are supplied with four bearings out of which three are the

journal bearing and one is combined thrust and journal bearing on H.P. rear end of the

shaft. All the turbine bearing are 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 ensuring their contact at works. During erection all

the bearing are supplied to site in aligned and assemble condition in their individual

pedestal from the works. After alignment of the bearing in their pedestal the seat of the b

earing 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 is available in the erection manual of 500MW turbine.

CRITICAL CHECKS OF TURBINE ERECTION.

BUMP TEST

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.

ROLL CHECK

In KWU machine the minimum radial clearances HP, IP and LP casing are measured by

actual by moving the casing radial direction 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 other 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 roll

 

CATENARY AND ALIGNMENTS

The catenaries of the machine are 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 problems in the machine like high shaft vibration, high bearing

vibration, high Babbitt metal temperature of the bearing etc. To avoid these problems it is

necessary to maintain the catenaries of the machine during erection and subsequent

realignment/overhaul of the unit. Many times it is observed that though the alignment of

rotors are within limit but the catenaries 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 catenaries of the machine.

During first few years of the operation of the unit the possibility to the disturbance of the

catenaries are much more due to settlement of the foundation frame.

In each overhaul of the unit the catenaries of the machine is to be corrected. The L.P. front

and L.P. rear pedestal are directly grouted here without any separate base plate. As such

any correction on lifting or lowering. These pedestals are not very convenient so if necessary

the rotor may be lifted or lowered with respect to pedestal seal bore and required

catenaries may be achieved. In extreme cases these pedestals may be even re grouted

during major overhauls of the unit to correct the catenaries of the machine.

HORN DROP TEST

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 these 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 pipe lines with the HP & IP casing.

This is a very important check and may cause serious problem in operation of the machine

like high 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 dynoxmetre

loadings are recorded in place of this horn drop test.

SWING CHECK

The swing check is the measurement of radial throw caused due to coupling face geometric

form of the two rotor coupled together. This is measured on opposite end of the coupling

and at the free end of the rotor. The higher swing check value may cause higher shaft

vibration, higher 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 Designer's on the

coupling faces of the rotor resulting to some swing check values. The maximum swing check

values permitted 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

minimum swing check values for better results during operation of the machine.

In a multi rotor Turbine-Generator system it is essential to measure the swing check value in

both extreme end and where the weight of the rotors are light. For example 200/210 M.W.

KWU machine with Russian Generator and static excitation system the swing check values

are measured on HP rotor front end only. In 500 M.W. machine the swing check values are

measured in H.P. front end and on exciter rear end. After having general experience of

number of 200 MW & 500 MW units, a necessity is felt to measure swing check 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 check values may be corrected without any hesitation

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 a later stage.

The correction may be carried out either by interchanging the coupling position or by

correcting the coupling faces by scrapping/cutting in consultation of Designers.

 CONTINUED TO PART -XI

PS; I HAVE ASSEMBLY REPORT (PICTORIAL) PREPARED BY BHEL ENGINEER FOR FIRST
660 MW LP TURBINE IN PDF FORMAT. THOSE WHO WISH TO SEE MAY SEND REQUEST
ON MY EMAIL . THE SAME WILL BE SENT TO THEM FOR KNOWLEDGE PURPOSE.

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