Turbo Supervision
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Transcript of Turbo Supervision
The history
From Sub-critical to super critical
Turbo SupervisionTurbo Supervision
THENEED
FORFOR
• Safety• Cost of spares• Cost of repair• Procurement
difficulties• The criticality• The process • The thermal effects• The speed
TURBINEHYDROHYDRO
SLOW SPEED
MODERATE TEMPERATURE
QUICK TO START / STOP
MOSTLY SELF LUBRICATION
SUITABLE FOR GENERATOR/SYCHRONOUSCONDENSER OPERATIONS
ONCE ERRECTED REQUIRES LITTLE MAINTENANCE
NO THERMAL ENCOUNTERS
THERMALTHERMAL
HIGH SPEED
COMBINATION OF HIGH AND MODERATE TEMP. AND PRES.
LONG START UP TIME
FORCED LUBRICATION
SOFT ROTORS ( soft & rigid )
REQUIRES LOT OF CARE EVEN DURING SHUT DOWN
PERFORMANCE DEPENDS ON PURITY OF STEAM AND COOLANT, AND ALSO OF THE LUB
LOT OF MAINTENANCE WORRIES EVEN AFTER ERRECTION
$ SLOW SPEEDSLOW SPEED
$ $ MODERATE TEMPERATURE MODERATE TEMPERATURE
$ $ QUICK TO START / STOPQUICK TO START / STOP
$ $ MOSTLY SELF LUBRICATEDMOSTLY SELF LUBRICATED
$ $ SUITABLE FOR GENERATOR / SUITABLE FOR GENERATOR / SYCHRONOUS CONDENSER SYCHRONOUS CONDENSER OPERATIONSOPERATIONS $ $ ONCE ERRECTED REQUIRES ONCE ERRECTED REQUIRES LITTLE MAINTENANCELITTLE MAINTENANCE
DYNAMIC BALANCING
OF
TURBO MACHINES
HRD -TTI -TNEB
HIGH SPEEDHIGH SPEED
COMBINATION OF HIGH AND MODERATE TEMP. / PRES.COMBINATION OF HIGH AND MODERATE TEMP. / PRES.
LONG START UP TIME :: FORCED LUBRICATIONLONG START UP TIME :: FORCED LUBRICATION
SOFT ROTORS ( soft & rigid )SOFT ROTORS ( soft & rigid )
REQUIRES LOT OF CARE EVEN DURING SHUT DOWNREQUIRES LOT OF CARE EVEN DURING SHUT DOWN
PERFORMANCE DEPENDS ON PURITY OF STEAM ANDPERFORMANCE DEPENDS ON PURITY OF STEAM AND COOLANT, AND LUBCOOLANT, AND LUB
LOT OF MAINTENANCE WORRIES EVEN AFTER ERRECTIONLOT OF MAINTENANCE WORRIES EVEN AFTER ERRECTION
TURBINE TURBINE - GENERATOR- GENERATOR
TURBINE
T – G BLOCK DIAGRAMT – G BLOCK DIAGRAM
5405400 0 C, 135 C, 135 ATAATA
54054000C, 40 ATAC, 40 ATA
Vacuum, 100Vacuum, 10000CC
statorstator
RotorRotorHeavy shell,
Fixed impellers/blades,
Slow expansion
Hollow shaft,
moving blades / impellers,
quick expansion,
affected by flow and temperatureHPHP--MPMP--LPLP
EXPANSION EXPANSION ??
TURBINETURBINEBearings out-of-operational areaBearings out-of-operational area
hpf hpr
Mpr || lpf
lpr
HP IPLP
JB
JB AND AXIAL THRUST
JB
JB
300 bar /600°C for the HP turbine
The LP turbine consists of adouble flow with a horizontal split casing.The typical steam conditions are up to 7 bar and 350°C. The steam will expand to thecondenser at condenser pressures in therange of 30 - 100 mbar. Because of the high volumetric flow rates special care has to be attributed to the appropriate choice of LP turbine exhaust area and design.The development of optimal last stage blade families and long last stage blades is the key for reasonable exhaust areas, i.e. reduced exhaust losses.
GeneratorGeneratorBearing in operational areaBearing in operational area
• Moderate temp. and just hydrogen pressure, added with electromagnetic and bearing - shaft interaction forces
gdegnde
generator
Assembly of turbine rotorsAssembly of turbine rotors
• No !
• They are not done as below, because….
HP IP LP
~gEN
Assembly of turbine rotorsAssembly of turbine rotors
• Catenary : a bow : bearing level , slope
||
DatumDatum
HP IP LP G
Assembly of turbine rotorsAssembly of turbine rotors
Assembly of turbine rotorsAssembly of turbine rotors
Assembly of turbine rotorsAssembly of turbine rotors
• THEY ACHIEVE LEVEL PLAYING WHEN ON NORMAL RUN AS THE THERMAL GROWTH ARE ACCOMPLISHED
• When the machine achieves its normal speed and parameters
HP IP LP g
Turbo supervisionTurbo supervision
HP – to measureHP – to measure
• Thermal growth of
• stator ( casing or shell ) - overall
• rotor ( shaft ) - differntial
• Oscillation of rotor in the bearing w.r.t housing ( relative motion of the shaft in relation to the stator )
• Overall vibration of bearing measured on the housing
IP- to measureIP- to measure
• Thermal growth of
• stator
• rotor
• Oscillation of rotor in the bearing w.r.t housing ( relative motion of the shaft in relation to the stator )
• Overall vibration of bearing measured on the housing
LP- to measureLP- to measure
• Thermal growth of Rotor
• Oscillations of the rotor w.r.t stator
• Vibration of the bearing
• The LP cylinder sits literally on the spring foot condenser. Hence it will be forced to float. The casing bolts are not set to full tight
Generator – to measureGenerator – to measure
• Only vibration of the bearings
• The heavies part of the T-G , which is solidly placed on the basic structure.
• Hardly subjected to any thermal growth of its own
• In many cases bearings are located on its shell or body
Common Common datadata
• The axial shift – the axial movement of the shaft due to forces of electrical, mechanical, hydraulic and structural interaction when the machine attains full dynamic status and also in-service
• ( salt formation in HP area is diagnosed by slightly higher curtis pressure than normal, and increase in axial shift )
• Rotational speed ( RPM )
The salient parametersThe salient parameters
• Overall expansion ( casing )• Differential expansion ( rotor )• Axial shift ( rotor movement on the axis of the entire
machine )• Eccentricity ( oscillation of the rotor with respect to
stationary body, ie., shaft axis with respect to machine or neutral axis )
• Speed ( especially to cross over critical speeds of the Gen., LP, IP, AND HP VERY CAUTIOUSLY – the cross over should be gradual and quick , as stalling at or near about critical will create resonance forcing the operator to stop and restart the machine )
TURBO - GEN
• STARTUP : process, expansion, eccentricity, axial shift, vibration ( at critical N )
• OPERATION : process, vibration ( monitoring : continuous and periodical ) VIBRATION ANALYSIS : on alarm and on demand
Stator ExpansionStator Expansion
In Turbine Supervisory Instrumentation (TSI), case expansion is an important measurement.
Case expansion (or shell expansion) is the growth of the machine shell with increase of temperature during machine startup and on-line operations.
Stator ExpansionStator Expansion
Stator ExpansionStator Expansion
The LVDT is mounted to the foundation at the opposite end from where the turbine casing is attached.
The LVDT provides information on the change of position of the point measured relative to the foundation.
Stator ExpansionStator Expansion
• This is primarily a startup parameter allowing the machine casing and rotor growth to increase at a proportional rate. Thermal growth
• As different growth rates can cause internal rubbing between rotating and stationary parts of the machine.
Stator ExpansionStator Expansion
• Case expansion should be measured by a pair of LVDT as this provides information on the position of both of the sliding feet on the machine case.
• This allows for a comparison of readings preventing damage should one foot become obstructed or jammed.
• Case expansion measurements also allow determination of whether expected thermal growth differentials are being exceeded on the machine.
Stator ExpansionStator Expansion(overall expansion)(overall expansion)
• Normally referred to as overall expansion
HP STATOR
lvdt
Linear Variable Differential Transformer
LVDT
Features:• 2" Range• Stainless Steel Housing• NEMA 4X• 1-6 VDC Output• 2.5 mV/mil
LVDT
The growth watchThe growth watch
• The turbine will be rolled initially to 500 RPM to warm the cylinders when starting from cold condition
• Then the speed is maintained at about 1000 RPM so that more steam can enter the shell allow it to develop thermal expansion. At the same time rotor also achieves some growth
Moving onMoving on
• Until the turbine stator attains the required growth the speed will not be increased further
• This type baking the machine in steam is referred to as SOAKING
Rotor DifferentialRotor Differential
• Using LVDT
Shaft disc
lvdtlvdt
Bearing
housing
Eddy probe
• Proximity or Non-contact pickup
Eddy ProbeEddy Probe
Eddy Probe MountingEddy Probe Mountingtoto
measure rotor differentialmeasure rotor differentialEddy probe
Air gap
Eddy Probe to measureEddy Probe to measureEccentricityEccentricity
• To measure rotor oscillations or vibrations of the shaft with respect to bearing housing ie., w.r.t stationary part
• Referred generally as ECCENTRICITY
Eddy Probe mountingEddy Probe mounting to measure eccentricityeccentricity
Probe
Shaft center line
Machine axis
Bearing housing
Eddy Probe for SpeedEddy Probe for Speed
Teeth wheel
probe
Tacho genShaft end
Teeth pulses
Typical probe in serviceTypical probe in service
Dual probe setupDual probe setup for orbit analysis to examine alignmentfor orbit analysis to examine alignment
Typical probe set up Typical probe set up recommended by western recommended by western
manufcturersmanufcturers
Bearing Overall VibrationVelocity Pickup
Mounting of Vibration pickups• On all turbine bearings as per
recommendations
H
v
a
Recommended by TNEBRecommended by TNEB
• Pickup locations : _|_ _|_ , and , and || || to axis to axis
H
V
SHAFT
Bearing
BEARING HOUSE
A
The circuit block
Continuous monitoring
DCS ON DATA MODEDCS ON DATA MODE
DCS on TIME MODE
TREND CHARTHourly, Weekly, MonthlyHourly, Weekly, Monthly
Variation of one parameterone parameter w.r.t anotheranother
RESONANCERESONANCE
NATURAL FREQUENCYNATURAL FREQUENCY
CRITICAL SPEEDCRITICAL SPEED
RESONANCERESONANCE
RESONANCERESONANCE
While designing the machine every care is taken to keep the natural frequency of the rotating (dynamic) and stationary (static) parts including that of civil structures very well above or well below the operating speed
RESONANCERESONANCE
Critical speed any rotating part of T – G will be crossed on its way from zero to rated RPM
While crossing critical speed of any part of the machine that particular component will experience high vibration
RESONANCERESONANCE
• If resonance sets in due to any reason, then the only recourse is to trip the machine and restart it
• If the machine continuous to stay at critical speed for long, the rotor will be subjected to severe fatigue due to abnormally high continuously raising vibration, which may result in damage to the rotors and its component parts
It is a must that the critical speed should It is a must that the critical speed should
be crossed smoothly and quicklybe crossed smoothly and quickly
RESONANCERESONANCE
• The natural frequency of bearing housing and structures are not identified openly as is done for critical speed
• If due to any external excitation like grid disturbance or sudden abnormality in the process, the area whose natural frequency coinciding with the excitation frequency will start resonating
RESONANCERESONANCE
• Then the only way out is to reduce or increase load to change stress
• When that fails the one and only option available is to stop the machine and restart it from rest
• If the high vibration vanishes on restarting the cause is resonance
RESONANCERESONANCE
• Analysis will reveal only 1XRPM component which may be due to unbalance or eccentric alignment of rotor
• Only the gradual increase of the vibration to abnormal levels in spite of our effort is the clear indication of the presence of resonance
Identifying critical speedsIdentifying critical speeds
• From the front pedestal legends :
Typical ::
Gen 1200 rpm
LP – IP 1700 – 1900 rpm
HP 2350 rpm
Identifying Critical speedby the rise in vibration at specific speed
Critical speedsCritical speedswhen more than one occurswhen more than one occurs
Identifying critical speedIdentifying critical speed
by rise in vibration of individual rotors
SPEED
AM
PLIT
UD
E
1 2 3
( x 1000 rpm )
Gen. LP IP HP
What happens when the machine What happens when the machine crosses over critical ?crosses over critical ?
• The SHAFTSHAFT under goes some bending movements
• This is christened as MODE SHAPESMODE SHAPES
• At each critical the SHAFT AXIS or MACHINE AXIS undergoes several modes
• Care is taken at the time of design to accommodate this modes by adopting necessary bearing clearances, and spacing between the stator – rotor, not forgetting alignment
Mode ShapesMode Shapes
Instruments to monitor vibration
H
A
v
Portable Portable vibrationvibration monitormonitor
AnalyserAnalyser
Periodic MonitoringPeriodic Monitoring / Alarm investigationAlarm investigation
• Machine : UNIT IV T-GT-G Load : 214 MW214 MW
• d / v d / v H H V V AA
• Beag. 5 ( LPR) 25/4 18/3 59/1059/10
Continuous monitoring Continuous monitoring Y Y N
No alarm from DCS - yet scheduled vibration measurement revealed high Axial vibrationhigh Axial vibration indicating development of a fault requiring detailed investigation and diagnosis
Alarm from DCSAlarm from DCS
• On instrumentation front :• Verification of the data by portable meter• Checking the cable, connections, and
pickup fastening
• On condition monitoring side :• If confirmed that high vibration is
present do investigate to diagnose
the fault/defect
InvestigationInvestigation
• Signature analysis Signature analysis
• Phase analysisPhase analysis• Coast / run-down time signature (to study
critical speed behavior, compatibility to the last recorded plot )
• Stethescoping ( scanning the vibration on the bearing house and supports inclusive of the civil structure )
Vibration signaturesVibration signaturesFrequency Frequency vs vs amplitudeamplitude
In service Time waveIn service Time waveBode / coast down plotBode / coast down plot
Some cluesSome clues
PhasePhase ?- the direction of forces of individual parts
• Talks about bearing – journal misalignment, and coupling misalignment between any two consecutive stages
OIL WHIRLOIL WHIRL---- due to insufficient bearing clearancedue to insufficient bearing clearance
1XRPM 2XRPM
1 / 2 X RPM
shaft
bearing
Oil clearance
MISALIGNMENT – PHASE MEASUREMENTMISALIGNMENT – PHASE MEASUREMENT • HIGH AXIAL VIBRATION• UNEVEN PHASE DIFFERENCE BETWEEN TWO BEARINGS
ACROSS ANY COUPLING• 360 /12 = 30 8X30 = 240 2X30 = 60• 240 – 60 = 180 OFF-SET MISALIGNMENT• ie., the centre lines of A and B are not in line
• 900 for angular and in-between for other positions
8
8
8
82
2 22
a b
Misalignment - orbitMisalignment - orbit
Dual input FFT
Dual trace oscilloscope
rubbingrubbing
Casing DistortionCasing Distortion
• When casing was prevented from free expansion
• Uneven heating in casing
• Rotor – stator clearances are uneven
• Unit III at ETPS : DUE TO TIGHTENING OF CASING BOLT IN EXCESS –
• The HP rotor got bent near curtis – confirmed by shaft run out test at works
Casing DistortionCasing Distortion
• Confirmed by the vibration data obtained on casing of HP on all corners and sides
• Overall expansion could not detect it
• Added evidence that the speed could not be taken beyond 2790 RPM
• Observation of the casing noise pattern
Loose Discs on rotorLoose Discs on rotor
• Vibration changing abnormally even when machine is operating on constant load
• Abnormal noise occasionally
• No change in phase – no misalignment detected
in a day
Loose discs on rotorLoose discs on rotor
• During overhaul the LP rotor root gap between discs were found to be “ nil ” for one and in “ excess ” for other
• Rotor was taken to works and checked and found the run out with discs and without discs were found to be much beyond permitted levels
Loose discs on rotorLoose discs on rotor
• Analysis confirmation of rotor trueness difficiency and moving of discs while in service were based on the large variation of vibration levels over a day ( trend ) and the noise pattern indicating the changes in blade excitation due to shifting of discs
Interference in BearingInterference in BearingUnit I at ETPSUnit I at ETPS
• Machine could not be run up to rated speed of 3000 RPM on commissioning just after overhaul
• The critical speed of generator was down to about 950 RPM instead of the design speed of 1200 RPM
• Shows mass or stress changed the machine generator rotor resonance
• Since mass could not be changed drastically to create such a situation only stress need to be suspected
Interference in BearingInterference in BearingUnit I at ETPSUnit I at ETPS
• Discussion with the maintenance revealed the presence of interference in GDE bearing due to catenary restrictions
• Suggested the reduction interference to zero or better bringing some clearance in the bearing setup
• Interference reduced to possible extent and machine was on bars
• The critical speed was found to be as per design after bearing correction
Journal – Bearing misalignmentJournal – Bearing misalignmentUnit II at ETPSUnit II at ETPS
• Uneven bearing clearance
• Poor journal – bearing blue matching ( the contact area should be upwards of 90 % )
• Machine was stopped and checked
gnde
generator
24 / 4 ( 17 / 3 ) 67 / 7 . 5 ( 19 /
4. .3 )
Rotor thermal instabilityRotor thermal instabilityUnit V at TTPSUnit V at TTPS
• The machine vibration in turbine were normal, but the generator vibration varied with time just after synchroning from mere 12 / 3 to 77 / 12 ( as observed during one of the several trials at GNDE in H )
• m/s BHEL suggested balancing and after umpteen attempts started blaming the machine structure
• TNEB did its own study and concluded that the rotor is thermally unstable and is beyond any possible repair based on previous experience on rotors
Rotor thermal instabilityRotor thermal instabilityUnit V at TTPSUnit V at TTPS
• No structural abnormality could be detected after conducting extensive study of the pillars, bearing pedestal fastening and other possible areas including causes for suspected resonance
• The rotor was replaced thereafter and unfortunately that was placed in UNIT II at NCTPS and experience was the same as encountered at TTPS.
Machine could not be loaded Machine could not be loaded beyond certain levelbeyond certain level
• Unit III at ETPS could not be loaded beyond 65 MW after R & M
• Detailed vibration analysis, especially the phase analysis revealed that the catenary was deficient
Machine could not be loaded Machine could not be loaded beyond certain levelbeyond certain level
• The IP rotor bearing was below its correct level, causing severe LP – IP coupling misalignment causing excessive loading of IP bearing revealed by high vibration in IP
• Due to this the machine could not be loaded beyond certain level, in this case it is 65 MW
• It was encountered every time the machine was subjected to load beyond 65 MW
Machine could not be loaded Machine could not be loaded beyond certain levelbeyond certain level
• The same could occur if the journal bearing alignment and clearances are not adequate
• The effort of M/S BHEL to correct this by balancing was in vain, only resulted in further straining and causing damage to the machine
• Never attempt to repair a running Never attempt to repair a running machine if it is performing absolutelymachine if it is performing absolutely
• When attempted, please note down the existing alignment and clearance values at the time of opening the machine
• If no change in components and modifications are in schedule, set the old levels before closing
No overhaul, pleaseVote for condition based maintenanceVote for condition based maintenance
Please care for them, as Please care for them, as they are like childrenthey are like children
Thank you,Thank you,Wishing you all the Wishing you all the
very bestvery best