18-Reasons for Turbine bearings vibration

 

1. Unbalance & Bend shaft:

Unbalance is the uneven distribution of body mass in rotating machine.

Machine unbalance & shat bend or bow lead to the bearing vibrations in radial direction

2. Miss alignment:

Miss alignment is non-coincidence of shaft centers of two rotating mating machines.

Miss alignment lead to axial vibrations of bearings

3. Looseness in turbine base bolts or foundation bolts leads to radial vibrations

4. More bearing clearance:

More clearance in journal bearings leads to radial vibrations

5. Rotor rubbing:

If Turbine rotor rubbing with any other stationary parts leads to more radial & axial vibrations. If it is rubbing radially then radial vibrations increase & if it is rubbing in axial direction then there will be more axial vibrations.

Read what do you mean by turbine supervisory system???

6. Seal rubbing:

Seal rubbing with rotating parts like rotor or blades to vibrations in horizontal directions.

This rubbing may due to improperly mounted seals or eccentricity of seals.

7. Distortions in foundations & casing:

Distortion & deflection of foundation include base frame and structure on which turbine is rested. In such cases bearing vibrations are most likely in radial direction & in axial direction. Also vibrations on base frame & on foundations show more.

Similarly bearings vibrations increase in radial direction due to casing distortion. Also casing vibrations show more.

8. Defective bearings:

Bearings vibrations are high in radial direction if bearing is defective in respect to pitting, wear, cracks & more clearance.

9. Inadequate Rigidity in bearing Pedestals:

Bearings start to vibrate in horizontal, vertical & axial directions if pedestal rigidity is less in horizontal, vertical & axial directions respectively.

10. Damage of thrust bearings

This leads to the vibrations of journal bearings in axial directions

11. Defects in coupling:

Coupling defects like more run out, looseness or crack also lead to turbine bearings vibrations

Defective couplings lead to bearings vibrations in both axial & radial directions.

12. High lube oil temperature:

High lube oil temperature causes decrease in viscosity of oil, which in turn reduces the oil film between journal & bearings leading to high vibrations in radial directions.

13. Contaminants in oil:

Lube oil containing burs & other foreign materials can also lead to high bearing vibrations

14. Lube oil & Control oil pipe line forces:

Improperly aligned & non stress relieved pipe lines lead to bearing vibrations. Oil lines not having expansion bellows may transfer vibrations from pump & lines to turbine bearings

Read Top 6-Power plant O&M books

15. Steam line forces & Aerodynamic forces:

Stresses in steam line, improperly supported steam lines transfer vibrations to turbine

16. Changes in steam parameters:

If the quality of steam changes for an example, reduced steam temperature, wet steam etc

17. Overloading the Turbine:

If the turbine is loaded beyond the allowable capacity for long time without consultation with OEM can certainly lead to bearings vibrations & subsequent failure.

18. Other probable reasons for bearings vibrations are

• Turbine resonance
• Operating the turbine in critical speed
• Wrong installation

Read Power plant & calculations for all such posts

Turbine oil flushing procedure

15-Emergencies in Power plant

Why do turbines go into over speed trip???

Steam turbine, cold, warm & hot start up procedure

Turbine cold start up procedure

·         Check all turbine interlocks and protection of turbine.

·         Ensure MOT level normal.

·         Ensure DP across the Lube oil and Control oil filter is normal.

·         Start AOP and fill up the overhead tank up to normal level. Put the EOP in Auto mode.   Maintain the oil temperature within the range of 40 to 45 deg C by MOT heater on, if required. Cut off the MOT heater manually after getting 40 deg C. (Note: The minimum oil temperature for turbine start up is 25 deg C as per OEM manual). Keep stand by AOP in auto made.

·         After getting the above said temperature, start Vapour Extractor fan then start JOP. Ensure its normal discharge pressure i.e. 150 kg/cm2.

·         Put the TG on barring gear and at this speed, record vibrations & temperature at all bearing points.

·         Ensure TG runs on barring gear at least 1 hour prior to rolling. (Note: Prior to start up the steam turbine, the turning gear is operating for at least 25 minutes as per OEM manual).

• Ensure hot well level normal i.e. 850 mmwc. Start CEP and put the system in recirculation mode. If required, make up the hot well level normal by make up
• Control valve from surge tank. Put stand by CEP in auto mode. Keep Hot well control in auto mode.
• Ensure cooling tower fore bay water level normal i.e. 60% and start MCW pump to circulate the cooling water through the condenser. Ensure l/L, O/L valve of condenser and l/L valve of cooling tower opened before MCW pump starts.
• Adjust the I/L valve of cooling tower in such a way that, CW flow should not beyond the design value.
• Open all the drain 100 % of main steam line and keep warm up vent in minimum position and open MSSV bypass valve fully at main steam pressure of 60 kg/cm2 & temperature of 350 deg C.
• After ensured all condensate removed & colorless steam comes through drains, keep all the drains in crack position, then open main steam stop valve and close the by pass steam valve.
• Charge the PRDS of Ejector and gland sealing PRDS line; ensure ejector pressure is of 10 kg/cm2 and temperature of 325 deg C. Adjust the HP & LP side gland sealing pressure at 1.1 ata. Maintain the sealing steam temperature of 393 deg C at HP side and temperature of 250 deg C at LP side.
• Prior to pulling the vacuum, ensure vacuum breaker valve is closed. Then pull the vacuum through hugger ejector.
• After getting vacuum -0.7 kg/cm2 through hugger ejector, take the main ejector into service and keep both the ejector in parallel and ensure the vacuum of - 0.93 kg/cm2 through running ejector, keep the main ejector in running and slowly close hogger ejector air line and then close the steam line after ensuring vacuum stable after STG synchronized only.
• Ensure the Steam pressure at TG I/L is above 70 kg/cm2 (Alarm at 65 kg/cm2, Tripping at 52 kg/cm2), steam temperature at TG l/L is above 420 deg C (Alarm at 395 deg C, Tripping at 385 deg C), vacuum is above -0.7 kg/cm2 (Alarm at - 0.65 kg/cm2, Tripping at -0.5 kg/cm2). Acknowledge all the alarm in the annunciation panel/DCS and ensure all parameters are in healthy condition. Then reset the ESV of turbine through DCS to proceed for the rolling.
• Ensure ESV opened & control valves are at zero position after reset the ESV. Give run command in Woodward 505E and observe the speeding should be carried out according to start up curve, respecting the preceding standstill  (soaking) time (thermal condition of turbine).
• At every soaking period, record/check all the critical parameters with respect to speed as follows:

1.     Oil pressure & temperature

2.     Bearing metal temperature

3.     Main stream pressure & temperature

4.     Exhaust steam pressure & temperature

5.     Axial displacement

6.     Vibrations

What do you mean by turbo supervisory system???

• Ensure barring gear motor is switched off in auto as per interlock
•   If the oil temperature after oil cooler gets near to 48 deg C, adjust the cooling water O/L valve to maintain the oil temperature 49 deg C by keeping its I/L valve full open and ensure oil temperature should not below the 45 deg C.
• If we prefer the rolling in manual, follow the start up curves and raise the speed as per start up curves and record above mentioned parameters at every soaking period Note: Cross the Critical Speed range as fast as possible.
• Keep exhaust hood spray in auto mode. (Note: Do not allow exhaust steam temperature to exceed 105 deg C. Load Turbine or shut it off in case temperature keeps increasing.)
• Start synchronizing by excitation on and voltage build up, match the DG voltage and frequency with generator voltage and frequency. When frequency and voltage matches within tolerable limit and synchroscope LED glows and allow to close the breaker. Close the breaker and increase the load on TG as per load curve (i.e. Approximately 2% of its rated load in order to avoid the activation of reverse power relay) up to the rated load by pushing the corresponding keys on the WOODWARD GOVERNOR
• Adjust the Generator Air Cooler cooling water O/L valve to maintain the ‘Generator winding temperature by keeping its I/L valve full open.
• Close all the main steam line drains and vents.
• Start Remaining MCW pump and CT fan one by one to maintain the vacuum and exhaust temperature.
• As per interlocks, after getting the steam flow of 60 TPH or more than 60 TPH at TG I/L, QC NRV of both bleeds of 22 ata & 9 ata respectively and control extraction of 3 ata will be reset.
• Charge the Deaerator through control Extraction and ensure Deaerator pressure reaches at 1.5 kg/cm2 & temperature at 100 deg C at least.
• Charge both the HP heaters and ensure Feed Water is charged through HP heaters prior to charge steam side.

TURBINE WARM START UP PROCEDURE

When after a clearly detected tripping the causes is eliminated or when the turbine is shutdown intentionally, observe the following for standstill’s longer than 5 minutes up to max. 8 hours

Refer the Warm Startup Curve given by OEM

• Keep the live steam line up to the emergency stop valve pressurized and gland steam open unless turbine rests far longer than 60 minutes
• Pre-warming the control valve block is not required
• Open turbine drain(live steam)
• The oil unit remains in full operation: the turbine oil should not be cooled below 45 deg C
• Keep the turning gear in permanent operation
• In case of no-uniform cooling-down process of turbine and rotor or drop out of turning gear (in this case immediately all isolation valves and steam to the labyrinths), slight distortion may arise, probably within the design clearances. This occurs especially with turbine arrangements where the turbine is exposed to an air draft.
• In the case of a failure of turning gear motor or fall-out loss of electric power turn manually the turbine shaft by means of turning gear hand wheel each 5 minutes of must be turned manually at least 2 turns. If turning unexpectedly is not possible, at all circumstances do not apply undue force but let the turbine cool down.
• Observe the instructions given & check for smooth action of the turbine at speed increase when starting again. Only a completely uniform warmed up turbine rotor is in straight condition so that further acceleration may take place without any risk.

                 SOP FOR TURBINE HOT START UP

 Refer the Hot Startup Curve given by OEM

• Check the availability of import power and start DG set.
• Open the warm up vent and chest drains.
• Start AOP, MCW & CEP pumps.
• Maintain the hot well level 50% through make up
• Close the Vaccum breaker valve and restart the Vaccum pulling.
• Keep the barring gear motor in auto.
• Maintain the lube oil temperature 45 deg C.
• Check the overhead tank healthy condition.
• Check the availability of Vaccum, main steam pressure and temperature.
• Inform to higher officials about all parameters in healthy condition for rolling.
• Reset the turbine and give for rolling.
• Check the vibrations, bearing temperature and any abnormalities.
• After turbine attend 6800 RPM give clearance for synchronization.

 

 Read Boiler start up SOP

Read Steam turbine commissioning

 Turbine oil flushing procedure

 

 Vacuum pulling SOP

Why does vacuum in steam condenser reduce or drop??

 

1-High exhaust temperature:

Vacuum drops or maintains at lower side due to high exhaust steam temperature flow into steam condenser. This high exhaust temperature is mainly due to

1-Operation of Turbine at lower loads

2-More clearance in labyrinth seals

3-Not operating exhaust hood sprays

4-More load on condenser

5-Breaking of ejector U loop

2-Low circulating cooling water flow

Vacuum in condenser reduces due to inadequate cooling water flow through steam condenser. This is mainly due to;

1-Problems associated with pumps

2-Air pockets in pipe line

3-Leakages in cooling water line

4-Stuck of discharge valve of pump

3-High cooling water temperature at condenser inlet

Higher cooling water temperature at condenser inlet results into reduction of vacuum due to poor heat transfer from steam to water

4-Poor heat transfer in condenser

Very less or poor heat transfer in steam condenser reduces vacuum to very low level resulting into high exhaust temperature & disturbances in hot well level.

Poor heat transfer is due to;

1-Fouling of condenser tubes due to poor water quality

2-High cooling water temperature

5-Air ingress in condenser & other vacuum pulling system

This is the most top reason for sudden drop of vacuum in steam condenser. Air ingress into the condenser is mainly from flange joints, gaskets, valves etc

Passing of vacuum breaker valve also be the one of the reason for maintaining low vacuum in condenser

6-Low steam temperature & pressure at ejector inlet:

Parameters lesser than rec recommended leads to reduction of vacuum pulling

7-Poor heat transfer in steam jet ejectors

This is mainly due to fouling of ejector tubes

steam condenser vacuum & calculations

8-Damages to air ejector nozzles

Increase in nozzle clearances leads to reduction of vacuum creating efficiency of ejectors

9-Breaking of ejector inter condenser U seal loop.

This creates escape of hot condensate directly into condenser leading to increase in exhaust temperature & reduction in vacuum

10-Low gland steam pressure:

Gland steam pressure lesser than design creates ingress of outside air into condenser through turbine glands.

11-Loading the condenser more than design

If the condenser steam load is more than design, vacuum drops slowly

12-High a temperature & low pressure in the atmosphere reduces vacuum pulling efficiency

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Power plant & claculations

What do you mean by Turbine supervisory system???

Steam Turbine SOPs

Why does load hunting occur in steam Turbines??

 If Turbine does not maintain the load as per set load, then this condition is called load hunting.Following are the some potential reasons for load hunting

1-Problems associated with actuators:

These are related to leakages in actuators, piston stuck up, oil holes elongation etc. Because of these issues there will interruption or fluctuation of secondary oil flow through actuators, this creates the problems of actuator miss-operation & eventually load hunting.

2-Improper calibration of actuators:

This results into mismatch of actuator opening & given set point or valve demand

3-Lower control oil pressure than required:

Actuators are designed for specific pressure of control oil, if the control oil pressure at actuator inlet becomes less, then there will be more chances of mal function of actuator.

4-Fluctuation of control oil pressure/flow:

Fluctuation of control oil pressure or flow due to malfunction of pump or line PRV may lead to actuator misoperation & hence creates load hunting.

5-Control oil line leakage:

Leakages in control oil line welding & flange joints will lead to fluctuation of flow & pressure causing actuator malfunction & load hunting.

6-Contamination in control oil

Foreign particles present in oil lead to improper functioning of actuators, which causes load hunting

7-Burs or scoring marks on actuator spindle & control valves spindles:

Burs or any rough scoring marks on spindles will lead to improper operation of actuator & valves

8-Passing of control valves:

This is the major reason for load fluctuation & Turbine over speed

9-Improperly set control valve cones:

During turbine HP valve assembly after maintenance, HP control valve cones should be set as per factory set readings, if it is disturbed, then there will be issues related to load hunting, low load at more HP demand or over speed.

10-Damage or broken control valves spindle & discs (cones):

Spindle damage or disc damage makes uncontrolled operation, as there will be wrong response from control valves to governor.

11-Wrongly tuned P&IDs in Governor: The disturbed values in P&ID tuning will result into heavy load hunting

12-Malfunction of Governor: This is very rare, but certainly results into load fluctuation of Turbine trip

13-Sudden changes in inlet steam pressure & extraction steam pressure

14-Fluctuation of grid frequency

15-Failure of Turbine inlet & extraction pressure sensor

For related articles on power plant Operation & Maintenance click here

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Turbine oil flushing procedure

How do you carryout performance Guarantee (PG) test of power plant equipments??

Why do turbines go into over speed trip???

Calculated reasons for increase in Turbine specific steam consumption

1. Lower vacuum

Turbine consumes more steam, if vacuum in condenser is maintained on lower side.

Example:  Consider a 20 MW Steam Turbine having Inlet steam parameters 65 kg/cm2 & 490 Deg C & Vacuum maintained in condenser is -0.9 kg/cm2.

Calculate the steam consumption of turbine at vacuum -0.9 kg/cm2 & -0.85 kg/cm2

A-Steam consumption Q at -0.9 kg/cm2 to develop 20 MW power

P =Steam flow X( Enthalpy of inlet steam-Enthalpy of exhaust steam)/ 860

Enthalpy of inlet steam at inlet steam parameters =810 kcal/kg

Exhaust steam enthalpy at -0.9 kg/cm2 vacuum = 619 kcal/kg

Then, 20 = Q X (810-619)/860

Q1 = 90 MT

B- Steam consumption Q at -0.85 kg/cm2 to develop 20 MW power

Exhaust steam enthalpy at -0.85 kg/cm2 vacuum= 623 kcal/kg

Then, 20 = Q X (810-623)/860

Q 2= 90.9 MT

It is clear that, Turbine operating at -0.9 kg/cm2 vacuum consumes lesser steam as compared to turbine operating at vacuum-0.85 kg/cm2

2. Lower inlet main stream pressure& temperature

Turbine operating at higher main steam pressure consumes lesser steam as compared to turbines operating at lower pressure

Example: Consider a 20 MW Steam Turbine having Inlet steam temperature 490 Deg C & Vacuum maintained in condenser is -0.9 kg/cm2.

A-Inlet steam parameters: Pressure: 65 kg/cm2 & temperature 490 deg C , Enthalpy = 810 kcal/kg

Exhaust steam parameters P = 0.9 kg/cm2 & Enthalpy = 619 kcal/kg

Steam consumption of Turbine Q = P X 860 / (Enthalpy of inlet steam-Enthalpy of exhaust steam)

Q = 20 X 860 / (810-619)

Q1 = 90.05 MT

B-Inlet steam parameters: Pressure: 87 kg/cm2 & temperature 515 deg C , , Enthalpy = 818 kcal/kg

 

Steam consumption of Turbine Q = P X 860 / (Enthalpy of inlet steam-Enthalpy of exhaust steam)

Q = 20 X 860 / (818-619)

Q2 = 86.43 MT

It is clear that, Turbine operating at pressure 65 kg/cm2 & temperature 490 deg C consumes more steam as compared to turbine operating at 87 kg/cm2 & temperature 515 deg C

3. Higher extraction/bleed steam flow

Steam turbines consume more steam to develop same power on higher steam extraction as compared to lower extraction.

Example: A condensing & extraction steam turbine having Inlet steam flow 105 TPH at pressure 65 kg/cm2 & 490 Deg C & Vacuum maintained in condenser is -0.9 kg/cm2.

Here we can cross check the power generation by steam turbine by increasing the extraction flow keeping inlet steam constant.

A-Extraction pressure = 2 Kg/cm2 & Temperature = 150 Deg C, flow = 75 TPH, Exhaust steam to condenser = 30 TPH

Enthalpy of inlet steam, H1 = 810 kcal/kg

Main steam flow Q1 = 105 TPH

Enthalpy of extraction steam = H2 =660 kcal/kg

Extraction steam flow Q2 = 75 TPH

Enthalpy of exhaust team = 620 kcal/kg

Exhaust steam flow Q3 = 30 TPH

Power developed by steam Turbine P = (Q2 X (H1-H2) / 860) + (Q3 X (H1-H3) / 860 )

P = (75 X (810-660) / 860) + (30 X (810-620) / 860) = 19.7 MW

B- Extraction pressure = 2 Kg/cm2 & Temperature = 150 Deg C, flow = 65 TPH, Exhaust steam to condenser = 40 TPH

Enthalpy of inlet steam, H1 = 810 kcal/kg

Main steam flow Q1 = 105 TPH

Enthalpy of extraction steam = H2 =660 kcal/kg

Extraction steam flow Q2 = 65 TPH

Enthalpy of exhaust team = 620 kcal/kg

Exhaust steam flow Q3 = 40 TPH

Power developed by steam Turbine P = (Q2 X (H1-H2) / 860) + (Q3 X (H1-H3) / 860 )

P = (65 X (810-660) / 860) + (40 X (810-620) / 860) = 20.16 MW

It is clear that, Turbine power generation at same inlet main steam flow will increase as extraction flow gets decrease & vice versa

Related posts read.......

Power plant & Calculations

4. Higher pressure/temperature of extraction & bleed steam

Higher pressure/temperature of extraction & bleed steam leads to increased steam consumption to generate same power or power consumption reduces at same inlet flow.

Example: A condensing , extraction & bleed steam turbine having Inlet steam flow 105 TPH at pressure 65 kg/cm2 & 490 Deg C & Vacuum maintained in condenser is -0.9 kg/cm2

 A-Bleed steam 10 kg/cm2 & Temperature 200 Deg C, flow =25 TPH, Extraction pressure = 2 Kg/cm2 & Temperature = 150 Deg C, flow = 60 TPH, Exhaust steam to condenser = 25 TPH

Enthalpy of inlet steam, H1 = 810 kcal/kg

Main steam flow Q1 = 105 TPH

Enthalpy of bleed steam = H2 =674 kcal/kg

Bleed steam flow Q2 = 25 TPH

Enthalpy of extraction steam = H3 =660 kcal/kg

Extraction steam flow Q3 = 60 TPH

Enthalpy of exhaust team H4= 620 kcal/kg

Exhaust steam flow Q4 = 20 TPH

Power developed by steam Turbine P = (Q2 X (H1-H2) / 860) + (Q3 X (H1-H3) / 860 ) +(Q4 X (H1-H4)/860)

P = (25 X (810-674) / 860) + (60 X (810-660)/860) + (20 X (810-620)/860)

P = 18.82 MW

B-Bleed steam 14 kg/cm2 & Temperature 260 Deg C, flow =25 TPH, Extraction pressure = 2.5 Kg/cm2 & Temperature = 170 Deg C, flow = 60 TPH, Exhaust steam to condenser = 25 TPH

Enthalpy of inlet steam, H1 = 810 kcal/kg

Main steam flow Q1 = 105 TPH

Enthalpy of bleed steam = H2 =704 kcal/kg

Bleed steam flow Q2 = 25 TPH

Enthalpy of extraction steam = H3 =669 kcal/kg

Extraction steam flow Q3 = 60 TPH

Enthalpy of exhaust team H4= 620 kcal/kg

Exhaust steam flow Q4 = 20 TPH

Power developed by steam Turbine P = (Q2 X (H1-H2) / 860) + (Q3 X (H1-H3) / 860) + (Q4 X (H1-H4)/860)

P = (25 X (810-704) / 860) + (60 X (810-669)/860) + (25 X (810-620)/860)

P = 18.43 MW

It is clear that, Turbine power generation reduces at higher extraction or bleed steam pressure &temperature

Note: Steam consumption of turbine increases if,

1-Bleed steam & extraction steam pressure increases

2-Bleed steam & extraction steam temperature increases

3-Bleed steam flow & extraction steam flow increases

4. Increase of exhaust steam temperature due to more clearance in labyrinth seals

Turbine steam consumption increases if exhaust steam temperature to condenser increases.

Also read 16-Perfect reasons for increasing the fuel consumption of Boilers

Turbine oil and transformer oil standard testing parameters