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PROJECT : RAICHUR UNIT 3

PROBLEM : BALANCING OF LP ROTOR AT SITE

Generator rotor replacement was carried out on Unit 3 , 210 MW unit(Seimens Turbine Russian Generator ) of Raichur thermal power

station during May 2006 due to rotor earth fault. The IP turbine rear

shaft vibrations increased to alarm levels of 120 microns peak from

earlier levels of 75 microns peak at rated load parameters. The control

room vibration levels are given below as recorded on 06-06-2006.

Load: 172 MW Freq : 49.28 Hz

Shaft Vibrations

in microns

peak(pk)

Bearing Vibrations in

microns peak(pk)

HP Front 49.5 2.9

HP Rear 34.0 3.0

IP Rear 119.8 14.9

LP Rear 26.2 10.7

Vibration analysis of bearing and shaft vibrations indicated predominant

presence of running speed vibration components. The LP front pedestal

vibrations are given below.

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The LP front vibrations for Seimens turbine are normally in the range

of 25 to 30 microns pk-pk. Here the pedestal vibrations were high and

also the phase difference between vertical and horizontal directions

were 111 degrees very near to 90 degrees which results in good

vibration reductions to balance correction.

Balance correction was carried out on LP rotor using LP front Plane. A

total number of 11 balance weights of 90 grams were added at LP

front plane to arrive at satisfactory shaft and pedestal vibration levels

on turbine. The LP front pedestal vibrations after balancing are given

below.

1X- micronspk-pk

Phase Overall

Vertical 26 58 26

Horizontal 27 283 27

Axial 24 136 25

The control room vibration levels at 180 MW load are given below as

recorded on 07-06-2006.

1X- microns

pk-pk

Phase Overall

Vertical 49 46 49

Horizontal 56 295 56

Axial 57 192 57

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Load : 180 MW Freq : 49.42 Hz

Shaft Vibrations in

microns pk

Bearing Vibrations in

microns pk

HP Front 22 2.8HP Rear 21 4.5

IP Rear 72 9.2

LP Rear 46 5.2

The IP rear shaft vibrations coast up plots before and after balancingare given in figures 1 & 2. It is observed that there is no critical

speed sharply reflected at IP rear . The coast up plot shows

considerable reduction in shaft vibration levels after 2700 rpm

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0

20

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60

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RPM

micronspk-p

Bode plot IP rear shaft Coast up , Raichur Unit 3 - initial run

0

60

120

180

240

300

360

600 900 1200 1500 1800 2100 2400 2700 3000 3300

Phasedegrees

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0

20

40

60

80

100

120

140

600 900 1200 1500 1800 2100 2400 2700 3000 3300

RPM

micronspk-p

Bode plot IP rear shaft Coast up , Raichur Unit 3-after balance correction

0

60

120

180

240

300

360

600 900 1200 1500 1800 2100 2400 2700 3000 3300

Phasedegrees