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PROJECT: VIJAYAWADA TPS
PROBLEM: VIBRATION ANALYSIS OF UNIT 5, 210 MW
SIEMENS TURBINE - SIEMENS GENERATOR
VTPS unit 5 was rolled on 23-05-08 after rectification works carried
out for Generator Earth fault. Bently Nevada ADRE Vibration analyzer
system was used for vibration measurements and analysis. During coast
up of the unit, Generator front and rear vertical vibrations were
recorded. The coast up vibration values both amplitude in microns and
phase are given in figure 1. The bode plot shows that the run up of
generator rotor is very smooth.
Table 1 and 2 gives the bearing pedestal vibration levels for Turbine,
Generator and Exciter both in velocity and displacement units. The
table gives 1X running speed vibration component , corresponding
phase and overall vibration levels which is a sum of all vibration
frequency components. The bearing vibrations on all pedestals are
satisfactory except for exciter primarily in horizontal direction. Theexciter vibrations which were 85 microns peak - peak at 3000 RPM
showed a steady increase after synchronization and at rated load were
128 microns peak - peak. Figure 2 shows the velocity and displacement
spectrums of exciter bearing in horizontal direction. The spectrum
shows that the bearing vibrations are predominantly of running speed
component.
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Table 3 gives the control room vibration levels at rated load. The
Bearing and shaft vibrations are satisfactory except at exciter bearing.
The Exciter bearing vibrations are above alarm values . The increase in
exciter vibrations with time before stabilization could be because of the
following reason.
Design diametrical clearance between spigot and recess in Generator -
Exciter coupling should be 0.03mm to 0.05mm . But the measured
clearance at site is 0.12 mm . A 0.05 mm shim has been introduced
between recess in Generator rotor and Spigot in exciter rotor . This
was not providing a desired solution to the high exciter vibration
problem.
A permanent solution suggested would be to ream and introduce dowels
at 120 degrees apart positions on Generator Exciter couplings as
being followed in Hyderabad 120 MW units. Till such time customer
was advised to operate the unit with close monitoring of exciter
vibration levels.
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Fig 1. Generator Front Vertical and Rear vertical Bode Plot
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Figure 2. Exciter Pedestal Vibrations Horizontal, Velocity and
Displacement spectrums
Table 1. Bearing vibrations in Velocity and Displacement units at 3000 RPM
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Velocity in mm/sec Displacement in microns
pk-pk
1X Phase Overall 1X Phase Overall
Vertical 1.2 243?
6 7 333?
10Horizontal 1.0 171? 2 6 260? 8
HP
FrontAxial 1 228? 2.6 6 317? 9
Vertical 1.2 89? 3.8 8 176? 10
Horizontal 1.6 287? 2.1 10 16? 10
HP
Rear
Axial 0.4 98? 1.2 3 186? 5
Vertical 0.6 302? 1.5 4 32? 5
Horizontal 0.1 --- 1.2 1 --- 3IP
RearAxial 0.7 284? 1.1 4 14? 6
Vertical 1.8 358? 2.5 10 84? 12
Horizontal 3.6 163? 4.4 23 252? 26LP
RearAxial 5.2 294? 5.3 33 22? 34
Vertical 4.2 309?
4.2 26 41?
28Horizontal 2.4 297? 3.1 15 26? 16
Gen
FrontAxial 1.5 157? 1.8 10 246? 11
Vertical 4.4 142? 4.9 29 230? 30
Horizontal 2.3 52? 2.4 15 141? 16Gen
rearAxial 1.5 317? 1.9 9 49? 11
Vertical 0.4 180? 1.3 2 263? 5
Horizontal 13 22? 14 85 110? 86Exciter
Axial 6.2 32? 6.6 38 122? 40
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Table 2. Bearing vibrations in Velocity and Displacement units at 215 MW Load
Velocity in mm/sec Displacement in microns
pk-pk
1X Phase Overall 1X Phase OverallVertical 1.0 --- 3 7 313? 8
Horizontal 1.0 --- 3.5 6 242? 9HP
Front Axial 0.9 --- 3.0 5 295? 10
Vertical 0.5 --- 7 4 198 10
Horizontal 1.7 --- 4 10 51? 12HP
Rear Axial 0.8? 2 2 --- 5
Vertical 1.0 --- 0.3 7 120?
11Horizontal 0.5 --- 1.8 3 257 6
IP
Rear Axial 0.3 ---- 1.5 1--- 4
Vertical 4.0 330? 6.2 27 62? 29
Horizontal 5.4 177? 7.2 34 263? 35LP
RearAxial 11 161? 11 70 248? 72
Vertical 7.0 319? 7.9 46 51? 48
Horizontal 2.0 300? 3.6 12 36? 17Gen
Front Axial 2.6 156? 3.9 17 240? 19
Vertical 3.3 128? 5.4 21 213? 27
Horizontal 0.3 --- 3.2 4 146? 12
Gen
rear
Axial 1.3 ---- 2.3 9 47? 11
Vertical 1.7 ---- 3.3 10 339? 15
Horizontal 21 7 21 128 96? 128Exciter
Axial 7 33? 9 47 126? 53
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Table 3. Control room vibration values
24-05-0812.53 hoursLoad: 215.3 MW
Speed : 2954 RPM
Vacuum: -0.885 kg/cm2
Bearing Vibrations Shaft Vibrations
in microns peak
HP Front 1.3 47.3
HP Rear 2.5 39.9
IP Rear 2.4 38.7
LP Rear 2.5 56.0
Gen Front 18.4
Gen Rear 8.3
Exciter 43.4 89.7
Bearing temp
HP front Thrust HP Rear IP Rear LP Rear Gen Front Gen Rear Exciter
62.3 63.3 61.3 86.3 83.3 78.2 78.9 54.767.2 61.5 59.3 75.1 85.6 72.4 73.6 59.7
54.1 69.0 59.975.7 68.8 57.2