Case Studies on Vibrations.ppt

A.K.SINHA, DGM (TURBINE)
BHEL, POWER SECTOR – TECHNICAL SERVICES (HQ), NOIDA
360 0
Ø
WHAT IS PHASE ANGLE

USES OF PHASE ANGLE MEASUREMENT
1. BALANCING
2. STRUCTURE MOTION STUDY
3. DETECTION OF RESONANCE FREQUENCY
 RUN UP & RUN DOWN BEHAVIOUR
 BODE PLOT
4. HEALHINESS OF MATING SURFACES OF TWO VIBRATING MASSESS
5. UNDERSTANDING THE DEFLECTION MODE OF THE SHAFT

`
0
1
2
3
4/5
6
7
8
9
10
11
12
13
220
212
127
107
87
56
24
7
-14
-25
220
230
170
120
94
63
33
11
-9
-23
245
209
138
101
71
51
245
228
165
112
96
53
LEFT SIDE RIGHT SIDE
14
15
16
17
18
19
20
21
22
23
14
15
16
17
18
9
10
11
12
13
19
20
21
22
23
FRONT REAR
FRONT
REAR
STRUCTURE MOTION STUDY

STRUCTURE MOTION STUDY

10
11 12
4
5
6
7
8
9
13
14
15
GENERATOR SIDE
TURBINE SIDE
3
2
1
C A
B
D
LEFT
RIGHT
16
17
18
19
20
21
BASE PLATE
SECONDARY GROUT
HEALHINESS OF MATING SURFACES OF TWO VIBRATING MASSESS

UNDERSTANDING THE DEFLECTION MODE OF THE SHAFT
B1 B2 B3 B4

Case Studies
on
Vibration Problems in Steam
Turbine Generators

HIGH VIBRATION IN
500 MW TG SETS

HIGH VIBRATION IN 500 MW TG SETS
PROBLEM
HIGH HP FRONT SHAFT AND BEARING PEDESTAL VIBRATION
OBSERVATIONS
(A) FREQUENCY ANALYSIS CARRIED OUT WHICH INDICATED
PREDOMINANT 1-X VIBRATION COMPONENTS FOR BOTH SHAFT AND
BEARING PEDESTAL VIBRATION
STEADY PHASE ANGLE
(B) BEARING PEDESTAL VIBRATIONS AND SHAFT VIBRATIONS WERE
HAVING RISING TENDENCY AT RATED SPEED HOWEVER, THEIR RATIO
WAS FOUND TO BE ALMOST CONSTANT

ANALYSIS
PREDOMINANT 1-X VIBRATION WITH SLIGHT CHANGE IN PHASE
ANGLE INDICATED THERE WAS UNBALANCE IN THE ROTOR SYSTEM
LEADING TO INITIATION OF MINOR RUB
MAIN SOURCE OF VIBRATION WAS HIGHER DYNAMIC LOADING FROM
THE SHAFT WHICH WAS GETTING TRANSMITTED TO BEARING
ACTION TAKEN
• TO REDUCE THE HP FRONT SHAFT VIBRATION LEVEL, INSITU
BALANCING WAS CARRIED OUT USING LP ROTOR BALANCING PLANES

RESULT OF INSITU BALANCING
HP SHAFT VIBRATION BROUGHT DOWN TO STEADY VALUE OF 120
MICRONS, 0-PK FROM EARLIER VALUE OF 150 - 200 MICRONS, 0-PK
HP FRONT BEARING VIBRATION CAME DOWN INITIALLY TO 15
MICRONS, 0-PK AT 3000 RPM FROM EARLIER VALUE OF 25 – 40
MICRONS, 0-PK
LATER, WITHIN 2-3 HOURS OF OPERATION, HP FRONT BEARING
VIBRATION INCREASED BEYOND ALARM VALUE (35 MICRONS, 0-PK).
DURING THIS PERIOD, NO INCREASE IN SHAFT VIBRATION WAS
OBSERVED

INTREPRETATION OF RESULTS AFTER INSITU BALANCING
AS HP FRONT BEARING PEDESTAL VIBRATION INCREASED, EVEN
WHEN HP FRONT SHAFT VIBRATION WAS CONSTANT, INDICATED THAT
THE CAUSE OF HIGH BEARING PEDESTAL VIBRATION WAS SOME
FACTORS APART FROM UNBALANCE OF THE SHAFT
ANALYSIS DONE
• BASED UPON THE VIBRATION BEHAVIOUR OF BEARING PEDESTAL AND
SHAFT VIBRATION, IT WAS DECIDED TO SCAN FRONT BEARING
PEDESTAL BY PORTABLE VIBRATION ANALYSER

RESULTS OF SCANNING OF FRONT PEDESTAL
VIBRATION ON LEFT AND RIGHT HAND SIDE OF FRONT BEARING
PEDESTAL (NEAR HP CASING FRONT PALMS) IN THE VERTICAL
DIRECTION WERE HAVING LARGE VARIATION
(LHS VIBRATION IS ABOUT 5 TIMES MORE THAN RHS VIBRATION)
HP CASING PALM VIBRATION AMPLITUDE IN VERTICAL DIRECTION ON
LEFT AND RIGHT PALM WAS FOUND TO BE OF LOWER MAGNITUDE
AND SAME
SCANNING INDICATED THAT THERE WAS NO PROBLEM WITH BASE
PLATE, SECONDARY GROUT & FOUNDATION MATING SURFACES

HP CASING PAM
(RIGHT HAND
SIDE)
HP FRONT BEARING PEDESTAL

ANALYSIS
SCANNING DATA INDICATED THAT LOAD DISTRIBUTION BETWEEN
PALMS OF HP CASING WAS NOT PROPER
THERE WAS GAP BETWEEN CASING PALM AND PEDESTAL ON LEFT
HAND SIDE
ACTION TAKEN
• 0.15 MM SHIM WAS ADDED BELOW LEFT HAND SIDE PALM WHEREAS
0.1 MM SHIM WAS REMOVED FROM RIGHT HAND SIDE PALM FOR
IMPROVING THE LOADING PATTERN OF HP CASING ON PEDESTAL

RESULT OF CORRECTION IN SHIMS
VIBRATIONS ON BEARING PEDESTAL REDUCED FROM 35 MICRONS, 0-
PK TO 15 MICRONS, 0-PK AND NO INCREASING TENDENCY WAS
OBSERVED
HP FRONT SHAFT VIBRATION WAS FOUND TO BE REDUCED FROM 120
MICRONS, 0-PK TO 90 MICRONS, 0-PK AND BEARING VIBRATION
SETTLED DOWN TO 10 MICRONS, 0-PK AT FULL LOAD
RATIO OF LEFT AND RIGHT HAND SIDE VIBRATION ON FRONT
PEDESTAL IN VERTICAL DIRECTION CAME DOWN TO 2:1 FROM
EARLIER VALUE OF 5:1
HENCE, UNBALANCE OF ROTOR SYSTEM & UNLOADING OF
LEFT SIDE PALM WAS FOUND TO BE THE ROOT CAUSE OF THE
HIGH HP FRONT SHAFT AND BEARING PEDESTAL VIBRATION

VIBRATION SCANNING IS A VERY
IMPORTANT TOOL FOR DIAGNOSTICS
PURPOSES
VIBRATION SCANNING SHOULD BE USED AS
FREQUENTLY AS POSSIBLE
IT HELPS IN RULING OUT OR PIN POINTING
CERTAIN DEFECTS
CONCLUSION

HIGH VIBRATION IN
210 MW TG SETS

BACKGROUND
 MACHINE IS OF KWU DESIGN STEAM TURBINE COUPLED WITH LMW
GENERATOR (LP REAR BEARING AND GENERATOR FRONT BEARING IS
LOCATED IN COMMON PEDESTAL)
 VIBRATION BEHAVIOUR WAS FOUND TO BE NORMAL DURING FIRST
COMMISSIONING ON ALL BEARINGS AND LATER ON VIBRATION ON
BEARING NO. 4 / 5 PEDESTAL DETERIORATED GRADUALLY BEYOND
ALARM LEVELS (35 MICRONS, 0-PK)

PROBLEM
 HIGH LP REAR BEARING VIBRATION
 HIGH GENERATOR FRONT BEARING VIBRATION
OBSERVATIONS
FREQUENCY ANALYSIS CARRIED OUT WHICH INDICATED
 PREDOMINANT 1-X VIBRATION COMPONENT FOR BOTH LP REAR AND
GENERATOR FRONT VERTICAL AND AXIAL VIBRATION
 VERTICAL VIBRATION AT LP REAR AND GENERATOR FRONT BEARING
WAS OF THE ORDER OF 100 MICRONS, PK-PK
 AXIAL VIBRATION WAS ABOUT 200 MICRONS, PK-PK FOR BOTH LP
REAR BEARING AND GENERATOR FRONT BEARING

ANALYSIS
BASED ON VIBRATION SYMPTOMS, FOLLOWING CHECKS WERE
SUGGESTED IN PLANNED OVERHAUL
LP / GENERATOR ALIGNMENT
BEARING ASSEMBLY CHECKS
RESULT OF ABOVE WORKS
AFTER CARRYING OUT THE ABOVE MENTIONED CHECKS &
CORRECTIONS DURING PLANNED OVERHAUL, VIBRATION LEVEL DID
NOT IMPROVE

ACTION TAKEN
FOLLOWING WORKS WERE CARRIED OUT
 VIBRATION ANALYSIS
 SCANNING OF LP REAR BEARING PEDESTAL AND ITS SECONDARY
GROUT AND BASE PLATE AREA
OBSERVATIONS / ANALYSIS
• FREQUENCY BEHAVIOUR OF BEARING VIBRATION FOUND SIMILAR TO
EARLIER OBSERVATION
• WIDE DIFFERENCE IN PHASE ANGLE IN VERTICAL DIRECTION
ACROSS BASE PLATE OF LP REAR PEDESTAL AND SECONDARY
GROUTING WHICH INDICATED THAT VERTICAL LOAD TRANSFER
FROM BEARING TO FOUNDATION IS NOT AS EXPECTED

10
11 12
4
5
6
7
8
9
13
14
15
GENERATOR SIDE
TURBINE SIDE
3
2
1
C A
B
D
LEFT
RIGHT
16
17
18
19
20
21
BASE PLATE
SECONDARY GROUT
SCANNING OF PEDESTAL

ACTION PLAN SUGGESTED
 REGROUTING OF LP REAR PEDESTAL
 REPLACEMENT OF FOUNDATION BOLTS OF LP REAR PEDESTAL AND
PROPER MATCHING OF ANCHOR PLATES
 IN-SITU BALANCING OF GENERATOR ROTOR TO REDUCE EXCITATION
FORCES TO MINIMUM
DUE TO TIME CONSTRAINT AND POWER REQUIREMENT,
FOLLOWING WORKS CARRIED OUT
• EPOXY GROUTING (PRESSURE GROUTING) OF LP REAR PEDESTAL
• RESTRETCHING OF FOUNDATION BOLTS OF LP REAR PEDESTAL
• LP / GENERATOR REALIGNMENT
• BEARING INSPECTION

AFTER CARRING OUT THE ABOVE MENTIONED CHECKS DURING NEXT
OVERHAUL
VIBRATION LEVEL FOUND REDUCED TO 25 MICRONS, 0-PK ON
BEARING NO. 4 / 5 PEDESTAL
 PHASE DIFFERENCE WAS FOUND TO BE MINIMUM BETWEEN BEARING
PEDESTAL BASE PLATE AND SECONDARY GROUTING
BUT AFTER FEW DAYS OF OPERATION,
• VIBRATION LEVEL STARTED INCREASING GRADUALLY AND TOUCHED
ALARM VALUE OF 35 MICRONS, 0-PK
• PHASE ANGLE DIFFERENCE WAS ALSO FOUND TO BE INCREASING
BETWEEN BASE PLATE AND SECONDARY GROUTING

ANALYSIS
EPOXY GROUTING WAS INSUFFICIENT TO CURE THE VIBRATION
PROBLEM ON PERMANENT BASIS
AT THIS POINT OF TIME, CIVIL EXPERT ALSO CONDUCTED STUDIES ON
FOUNDATION WHICH CONFIRMED THE BAD CONDITION OF
SECONDARY GROUT

ACTION PLAN SUGGESTED:
ONCE AGAIN THE PREVIOUS ACTION PLAN WAS SUGGESTED, THAT IS,
REMOVAL OF LP REAR BEARING PEDESTAL AFTER BREAKING
SECONDARY GROUTING COMPLETELY
REPLACEMENT OF FOUNDATION BOLTS
IN-SITU BALACNING OF GENERATOR ROTOR
DISMANTLING OBSERVATION
• DURING REMOVAL OF LP REAR PEDESTAL, SECONDARY GROUT
MATERIAL WAS FOUND IN PIECES
• OIL SEEPAGE WAS OBSERVED UNDER PEDESTAL

 AFTER THE ABOVE MENTIONED WORKS CARRIED OUT (INCLUDING
IN-SITU BALANCING OF GENERATOR ROTOR) IN THE NEXT PLANNED
OVERHAUL, VIBRATION LEVEL OF LP REAR AND GENERATOR FRONT
IMPROVED IN BOTH VERTICALAND AXIAL DIRECTION
 MACHINE IS RUNNING SATISFACTORILY SINCE THEN
HENCE, LOOSENESS / VOID BETWEEN LP REAR PEDESTALAND
SECONDARY GROUTING WAS FOUND TO BE THE ROOT CAUSE
OF HIGH LP REAR PEDESTALAND GENERATOR FRONT
VIBRATION

HISTORY OF THE PROBLEM SHOULD BE GIVEN DUE
WEIGHTAGE FOR ANALYSING THE PROBLEM
ATTENTION SHOULD BE PAID TO INTERFACE AREAS BETWEEN
MACHINE AND SUPPORTING SYSTEM / STRUCTURE IN
ADDITION TO MAIN MACHINE
CONCLUSION

HISTORY OF MACHINE WITH RESPECT TO ITS DYNAMIC
BEHAVIOUR SHOULD BE STUDIED
REGULAR VIBRATION READING ON BEARING PEDESTAL AT
PRESCRIBED LOCATIONS SHOULD BE TAKEN FOR ASSESSING
THE TREND OF VIBRATION BEHAVIOUR ACCURATELY
SHAFT VIBRATION IN TWO ORTHOGONAL DIRECTIONS
SHOULD BE MEASURED FOR ORBIT ANALYSIS
TIPS FOR BETTER DIAGNOSTICS

RECOMMENDED LOCATIONS OF VIBRATION MEASUREMENTS ON
BEARINGS AS PER ISO

OR
Measuring
Amplifier
45O 45O
PROXIMITY
PICK-UP
L R
SHAFT
Measuring
Amplifier
VERTICAL
HORIZONTAL
L R
SHAFT
RECOMMENDED LOCATIONS OF SHAFT VIBRATION
MEASUREMENTS AS PER ISO

EVERY UNIT SHOULD HAVE KEY PHASOR ARRANGEMENT FOR
VIBRATION ANALYSIS.
SCANNING OF VIBRATION PRONE AREAS INCLUDING SYSTEM /
FOUNDATION AROUND THE PROBLEMATIC AREA SHOULD BE
CONDUCTED
DEVIATION IN OPERATING PARAMETERS SHOULD BE
RECORDED AND ANALYSED FOR THEIR EFFECT ON VIBRATION
BEHAVIOUR

RUN UP & RUN DOWN VIBRATION BEHAVIOUR SHOULD BE
RECORDED FOR ALL BEARINGS AND SHAFT POSITIONS FOR
REFERENCE WHICH CAN BE USED DURING TROUBLESHOOTING
PRE-OUTAGE SURVEY SHOULD BE CONDUCTED PRIOR TO
OVERHAUL FOR BETTER PLANNING OF ADDITIONAL
ACTIVITIES / SPARES, IF REQUIRED
RECORD OF PREVIOUS BALANCING AT SITE SHOULD BE
MAINTAINED FOR REFERENCE PURPOSES

LAST BUT NOT THE LEAST, DURING TROUBLESHOOTING,
EVERY FEEDBACK / OBSERVATION NEEDS TO BE CONFIRMED.
IF EVERYTHING IS ALRIGHT, VIBRATION PROBLEM WOULD
NOT HAVE BEEN THERE. SO VERIFY EACH & EVERY
POSSIBILITY AND CONFIRM FROM WRITTEN DOCUMENTS

Thank you

Case Studies on Vibrations.ppt

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Case Studies on Vibrations.ppt