High HP Front Shaft and Bearing Vibratio

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PROBLEM : HIGH HP FRONT SHAFT AND BEARING

VIBRATIONS

PROJECT : RAMAGUNDAM STPS , UNIT-5 , 500 MW

Unit 5, 500 MW at RSTPS Ramagundam was operating with high HP

front shaft and bearing vibrations since year 2003. Shaft vibrations

were of the order of 140 150 microns peak and bearing vibrations35 microns peak as per UCB readings .During the capital overhaul

carried out in Sept-Oct 2005 detailed analysis and works were carried

out to find a permanent solution and resolve this problem.

Observations:

1. In IP and LP Rear Bearings the blue contact between the torus

and cylindrical support was not as per design requirement and only

point contact was observed. Also, in Bearings 1 & 2, bolts of thetorus were found to be sheared off at the head and also the blue

contact between torus and spherical support was only 50 %.

2. Heavy rubbing marks were observed in HP casing and most of the

sealing fins in HP casing and sealing segments were found

damaged.

3. Heavy pull was observed towards right in CRH ( R ) pipe.

4. Swing check value of HP front journal was found to be 0.25 mm.

5. Mis-alignment was observed in HP/IP & IP/LP couplings.

6. Blade damages of LP rotor.Stage 1 R : 31 blades were found with Root crack

Stage 2L : 2 blades were found with Root crack


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Stage 2R : 1 blade was found with a small piece broken away at

tip

Corrective actions:

1. Bearings 1, 3 & 4 were sent to BHEL/RC Puram and bluecontact between cylindrical/spherical support and torus wasmaintained as per design recommendations by machining.

2. HP casings and all the sealing segments of inner glands weresent to BHEL/RC Puram for re-finning and machining to

maintain design clearances.

3. Coupling face run out of HP rear was found to be 0.01 mm andIP front coupling was found to be 0.03 mm. As the swing

check value was also high corresponding in the same area , IP

coupling face run out was rectified by scrapping almost one halfportion of the coupling and face run out was reduced to 0.01

mm. This brought the swing check value at HP Front to a

very good level of 0.05 mm.

4. Entire 68 blades on 1-R stage on LP rotor were replaced withbest possible moment- weight matching. Sequence of fixing

the blades was taken from BHEL/Hardwar.

5. Slow speed balancing of HP and IP rotor was carried out atBHEL/RC Puram at 350 RPM.


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Balance correction weights added :

HP Rotor IP Rotor

Forward Plane : 515 grams Forward Plane : 594 grams

Aft plane : 549 grams Aft plane : 274 grams

The Unit after overhaul was rolled and synchronized on

31-10-05. The performance of the unit is smooth with a marked

reduction in HP Front Shaft and Bearing vibration levels.

Load : 315 MW, Freq: 50.03 Hz

Shaft Vibrations Bearing Vibrations

HP Front : 46 HP Front: 6HP Rear : 50 HP Rear : 5

IP Rear : 58 IP Rear : 11

LP Rear : 22 LP Rear : 10Alarm : 120 Alarm :35

Trip : 200 Trip :45

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High HP Front Shaft and Bearing Vibratio