Operational Problems [Compatibility Mode]

MOST LIKELY EMERGENCIES IN OPEATION OF TURBINE

By: A.K.KHAN, AGM(TURBINE)

TURBINE SUPERVISORY INSTRUMENTS

SPEED & LOAD BEARING & SHAFT VIBRATION ECCENTRICITY DIFFERENTIAL EXPANSION CASING/ROTOR EXPANSION TURBINE STOP V/V & GOV V/V POSITION

INDICATOR METAL TEMPARATURE OF HP/IP TURBINE

CASING, HP/IP SHAFT, V/Vs CHEST. HPT EXHAUST TEMPERATURE AXIAL SHIFT LUBE OIL PRESSURE/TEMPERATURE BEARING BABBIT METAL TEMP./DRAIN OIL TEMP VACUUM MOT LEVEL LPT EXHAUST HOOD TEMP.

MOST LIKELY EMERGENCIES IN TURBINE OPERATION HIGH DIFFERENTIAL EXPANSION (+IVE SIDE) AXIAL SHIFT HIGH MOP DISCHARGE PRESSURE LOW LUB OIL PRESSURE LOW BEARING METAL TEMPERATURE HIGH CONDENSER VACUUM LOW LP TURBINE EXHAUST HOOD TEMPERATURE MORE BEARING / SHAFT VIBRATION HIGH TURBINE OVERSPEED FIRST STAGE PRESSURE HIGH. HPT EXHAUST TEMP HIGH B/G JAMMING PROBLEM AC POWER FAILURE

1. HIGH DIFFERENTIAL EXPANSION (+IVE SIDE)

POSSIBLE CAUSES:Too high steam temperature for rolling.Too fast rolling or too fast pick up of load.Overall expansion is less due to inadequate soaking during

rolling and during turbine loading.Flange heating is not in service or not effective during cold

start.Restriction in expansion of turbine casing.Poor lubrication of sliding surface.Prolonged no load operation increases LPT D.E Improper Turbine casing insulation

1. HIGH DIFFERENTIAL EXPANSION (+IVE SIDE)

IMMEDIATE ACTION:Control steam temperature.Check HP flange metal temperature. If metal temperature is

not increasing ensure the opening of flange heating valve bychecking the valve physically.

Soak the turbine at soaking speed sufficiently as per O&Mmanual instruction.

Check for any restriction in turbine casing due to fouling withtemporary supports / pipes.

If LPT D.E. increases try to increase load

2. HIGH DIFFERENTIAL EXPANSION (-VE SIDE)

POSSIBLE CAUSES: -VE DIFFERENTIAL EXPANSION OCCURS ONLY

UNDER EXTREME UNFAVOURABLE CONDITION ASBELOW:-

SEVERE RESTRICTION IN TURBINE EXPANSIONDURING COOLING DOWN OF TURBINE.

STEAM TEMPERATURE TOO LOW DURING HOTSTART UP

3. AXIAL SHIFT HIGH

POSSIBLE CAUSESSalt deposit on turbine blades. Interceptor Valve / IP governor valve not full open.Oil flow to thrust bearing less.Thrust pad damaged.Overloading of turbineAbrupt change in load/vacuum

Improper assembly of thrust bearing.Restriction in steam flow of Turbine due to malfunctioning of

NRVs at HPT exhaust.High bearing / Shaft vibration of combined journal cum thrust

bearing.

3. AXIAL SHIFT HIGH

IMMEDIATE ACTIONCheck nozzle/first stage pressure pressure if more restrict

load.Check relay oil pressure and correct it(applicable for old 120

mw only).Ensure IV & IP governor valve full open.Check Lub. Oil pressure to thrust bearingCheck lub oil filter which is in service after change over for any

babbit material. If problem still persists trip the turbine

4. MOP DISCHARGE PRESSURE LOW

POSSIBLE CAUSESMOP suction i.e. booster pump discharge pressure low or oil

injector performance is not satisfactory.AOP discharge NRV is passing.Oil consumption is more due to leakage in oil system (lub oil /

seal oil / relay), disturbance in setting of throttles in lub oil systemPassing of NRV of AC flushing/emergency oil pump.Disturbance in adjustment of oil injectors throttlesMOT level is very low.Air content of oil too highMOP faulty

IMMEDIATE ACTIONCheck booster pump discharge pressure gauge provided near

MOT and MOP suction pressure at front pedestal. If not O.K.check that isolating valve of booster turbine is full open.

Ensure that NRV of AOP / ACFOP is not passing by closingisolating valve one by one.

Check safety valves.Check MOT level by dipstick locally and compare with MOT

level indicator to ensure actual levelOil properties need checking for air content

4. MOP DISCHARGE PRESSURE LOW

5. LUB OIL PRESSURE LOW

POSSIBLE CAUSESLub oil filter chocked.Oil pump pressure lowSetting of lub oil pressure relief valve disturbed.Bearings oil flow more.Lub oil cooler oil side inlet and outlet valve not open full/mal

functioning of lub oil cooler control valve or oil cooler chockedon oil side.

IMMEDIATE ACTIONChange over filter.Check oil pump pressure as in Sl.No.5 & 6.Check oil flow in sight glass of bearings..Ensure cooler oil side inlet/outlet valve full open . If valves are

full open change over oil cooler.

6. BEARING METAL TEMPERATURE MORE

POSSIBLE CAUSESLub oil temperature after oil cooler more.Oil flow to bearing less.Lub. Oil pressure low.Excessive vibration of bearing.Lub oil cooler bypass relief valve passing or lub oil control

valve malfunctioningSteam leakage from turbine gland more.Contaminated lub.oilMaloperation during change over of lub oil filter/cooler

IMMEDIATE ACTIONChange over ACW strainer if chocked. If steam leakage from gland is more, reduce load and maintain

HRH temperature at 490o C.Check oil flow and lub. Oil press at each bearing.Ask chemist to analyze lub oil for moisture, dirt etc.Maintain sealing steam pressure and HRH temperature.Check passing of cooler bypass relief valve. Lub oil cooler/filter to be changed over after ensuring proper

venting/filling

6. BEARING METAL TEMPERATURE MORE

7. CONDENSER VACUUM LOWPOSSIBLE CAUSESHogging ejector /main ejector is not working due to abnormal

steam parameter, abnormal condensate level, passing ofstandby ejector NRV etc

Performance of vacuum pump is not satisfactory duemalfunctioning of its valve, high seal water temp, separatortank level abnormal, passing of standby pump etc

Cooling water to condenser is lessSealing steam pressure is low.Drain valves of vacuum system like LP heaters shell/gauge

glass etc. are passing / open.Sealing water-isolating valve for vacuum system valve is

closed.Condenser hot well level high.Condenser CW flows is less.Air ingress into vacuum system is highPassing of steam drain valves/LP bypass valve

7. CONDENSER VACUUM LOW

IMMEDIATE ACTIONMaintain normal PRDS parameter , sealing steam pressure

,seal water temp of vacuum pump, condensate level of ejector,water level of separator tank of vacuum pump.

Check for passing of all atmospheric drain valve of vacuumsystem.

Check valves sealing water pressure.Check CW header pressure ,cw temp rise/cw diff. pressure of

condenser if more reduce load and clean condenser one byone

Ensure all steam line drain valves and LP bypass v/v areclosed

For checking air ingress point, fill the water in vacuum systemup to level as per OEM instruction after cooling down theturbine.

POSSIBLE CAUSESLow vacuum.Prolonged idle running of turbine at no/low loadLPT exhaust hood spray valve is not operating on interlock.Passing of high pressure drain/lp bypass valve to condenserHigh steam parameter during cold start upOperation of turbine at higher load without HP heaters I/S

IMMEDIATE ACTIONCheck as in Sl.No.12.Try to load the machine.Ensure exhaust hood spray valve open on interlock.Control steam parameterTake hp heaters I/S

8. LP TURBINE EXHAUST HOOD TEMP HIGH

POSSIBLE CAUSES Abnormal fluctuation in steam parameter Sudden drop in sealing steam temp HP sealing steam cooling water spray system is passing. Lub. Oil temperature and lub. Oil pressure too high or too low

destroying oil film under bearing. Differential expansion and axial shift more or machine is not

expanding. Water induction into turbine Turbine rotor at critical speed Malfunctioning of HP/LP bypass valve causing abnormal increase in

hot reheat / CRH pressure. Low vacuum / high exhaust hood temperature. Rotor eccentricity high due to bow in rotor. Shaft vibration high due to unbalance ,mis alignment,high run out at

journal, blade failure etc

9. VIBRATION MORE

IMMEDIATE ACTIONCheck maintain steam/casing metal/pipe metal temp, sealing

steam and lub oil temperature, lub. oil pressure and vacuum.Trip the turbine if hot reheat pressure is increasing due to

malfunctioning of HP/LP bypass valves.Open HP flange heating valve if differential expansion is more.Control LPT exhaust temp/vacuumCross-checked the vibration reading by portable instrument.Check bearing drains/lub oil filter for any damage indicationDo not roll turbine when eccentricity exceed 50 micron on

barring gear.Trip the turbine if bearing/shaft vibration/eccentricity high

9. VIBRATION MORE

POSSIBLE CAUSES Sticking of stop valve and control valve or heavy passing in case of

turbine trip. Malfunctioning of turbine control In case of turbine trip, the non-return valves of extraction not closed,

resulting in steam admission through extraction line. High grid frequency and malfunctioning of load shedding relay/ over

speed limiting gear during load throw off Generally over speed by 7 to 9% is possible in the case of operation of

Class-A trip protection due to serious situation like electrical fault in rotor,stator and other abnormal running conditions where the generator issubjected to electrical and mechanical stresses

Emergency Governor failure at the time of over speed.

10. TURBINE OVERSPEED

IMMEDIATE ACTIONPeriodically check over speed mechanism by oil injection at

least once in two months.Routine checking of all control / stop valves for full closing

daily at lower load.Check closing of non-return valves on extraction line every

month at lower loadCheck the operation of load shedding relay Over speed load

limiting gear

10. TURBINE OVERSPEED

POSSIBLE CAUSESProlonged no load or low load operationObstruction in steam flow due to high down stream pressure of

HP bypass valveCRH NRV not openingMalfunctioning of Trimming Device

11. HPT EXHAUST TEMP.HIGH

POSSIBLE CAUSESSalt Deposits on Turbine Blades.OverloadingOperation with low Steam Parameter at High LoadCondenser Vacuum low at High Load

IMMEDIATE ACTION

Reduce the Load. Maintain Steam Parameter as per Operation Instruction.Monitor Axial Shift & Thrust Bearing Temp Constantly.

12. FIRST STAGE PRESSURE HIGH

POSSIBLE CAUSESGrid disturbance due to fault in transmission line leading to

tripping of unit one by one including station transformer

13. AC POWER FAILURE

Total AC Power failure is very serious condition in a powerplant operation. In such condition, system is designed insuch a way that with the help of 220V DC power (BatteryBank)/ DG Set power (Emergency Power), unit can beshutdown safely.

OPERATOR ACTION:Ensure DC lub oil /seal oil /Jacking Oil pump has taken

start on auto.Ensure DG set started on auto & emergency power

restored.Close MS valve / Gland Steam isolating v/v and open

vacuum breaker at 200 mm of Hg.

13. AC POWER FAILURE

OPERATOR ACTION:Ensure Extraction Valves to LP/HP Heaters and Deareator.Put the M/c on Barring Gear.

13. AC POWER FAILURE

B/G IS PROVIDED IN ANY STEAM TURBINE FOR UNIFORMCOOLING AS WELL AS TO AVOID TEMPORARY SAG BYSLOW ROTATION OF ROTOR SYSTEM.IN THE PASTTURBINE ROTOR SYSTEM WAS ROTATED BY ELECTRICMOTOR THROUGH GEAR SYSTEM.AFTERINTRODUCTION OF KWU TURBINE HYDRAULLICTURNING GEAR WAS EMPLOYED.

POSSIBLE CAUSES:LOW JACKING OIL PRESSURE DUE TO

MALFUNCTIONING OF ITS CONTROL VALVE. INSUFFIENT JOURNAL LIFT .HIGH TOP/BOTTOM DIFFERANTIAL TEMP OF TURBINE.

14. BARRING GEAR JAMMING

POSSIBLE CAUSES:SUDDEN DROP/INCREASE IN SEAL STEAM

TEMPERATURE.LOW MOTIVE OIL PRESSURE. IMPROPER DISTRIBUTION OF RADIAL CLEARANCES IN

TURBINE.FAILURE OF JACKING OIL FLEXIBLE CONNECTION.UNDUE PIPE FORCES.EXTRA FRICTION AT SEALING STRIPS OF TURBINE

BLADES.

14. BARRING GEAR JAMMING

OPERATOR ACTION:CHECK THE JACKING OIL HEADER PRESSURE AND JO

PRESSURE AT EACH BEARING.CHECK THE MOTIVE OIL PRESSURE. ENSURE SEAL STEAM TEMPERATURE IS WITH IN THE

LIMITS.CHECK TURBINE TOP/BOTTOM DIFFERENTIAL TEMP.ENSURE THE LIFT OF JOURNAL ON EACH BEARING IS

NORMAL.CHECK THE LEAKAGE IN JACKING OIL LINES.

14. BARRING GEAR JAMMING

THANK YOU