MOST LIKEL LI KELY Y EMERGENCIES EMERGE NCIES IN OPEA OPE ATION OF TURBINE
By: A.K.KHAN, AGM(TURBINE)
TURBINE SUPERVISOR SUPERVISORY Y INSTRUMENTS
SPEED & LOAD BEARING & SHAFT VIBRA VI BRATION TION ECCENTRICITY DIFFERENTIAL DIFFERENT IAL EXPANSION EXPANSION CASING/ROTOR EXP EXPANSION ANSION TURBINE STOP V/V & GOV V/V POSITION INDICATOR METAL TEMPARATURE OF HP/IP TURBINE CASING, HP/IP SHAFT, V/V’s CHEST. HPT EXHAUST TEMP TEMPERA ERATURE TURE AXIAL SHIFT LUBE OIL PRESSURE/TEMPERATURE BEARING BABBI BABBIT T METAL METAL TEMP./DRAIN TEMP./DRAIN OIL OI L TEMP
VACUUM MOT LEVEL TE MP.. 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 Poor
in expansion of turbine casing.
lubrication of sliding surface.
Prolonged Improper
no load operation increases LPT D.E
Turbine casing insulation
1. HIGH DIFFERENTIAL EXPANSION (+IVE SIDE) IMMEDIATE ACTION: Control Check
steam temperature. HP flange metal temperature. If metal temperature is
not increasing ensure the opening of flange heating valve by checking the valve physically. Soak
the turbine at soaking speed sufficiently as per O&M
manual instruction. Check
for any restriction in turbine casing due to fouling with
temporary 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 AS BELOW:
SEVERE RESTRICTION
IN
TURBINE EXPANSION
DURING COOLING DOWN OF TURBINE.
STEAM TEMPERATURE TOO LOW DURING HOT START UP
3. AXIAL SHIFT HIGH POSSIBLE CAUSES Salt
deposit on turbine blades.
Interceptor Oil
Valve / IP governor valve not full open.
flow to thrust bearing less.
Thrust
pad damaged.
Overloading Abrupt
of turbine
change in load/vacuum
Improper
assembly of thrust bearing.
Restriction
in steam flow of Turbine due to malfunctioning of
NRV’s at HPT exhaust. High
bearing / Shaft vibration of combined journal cum thrust
bearing.
3. AXIAL SHIFT HIGH IMMEDIATE ACTION Check
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 bearing
Check
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 CAUSES MOP
suction i.e. booster pump discharge pressure low or oil
injector performance is not satisfactory. AOP Oil
discharge NRV is passing.
consumption is more due to leakage in oil system (lub oil /
seal oil / relay), disturbance in setting of throttles in lub oil system Passing
of NRV of AC flushing/emergency oil pump.
Disturbance MOT Air
in adjustment of oil injectors throttles
level is very low.
content of oil too high
MOP
faulty
4. MOP DISCHARGE PRESSURE LOW IMMEDIATE ACTION Check
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 closing
isolating valve one by one. Check
safety valves.
Check
MOT level by dipstick locally and compare with MOT
level indicator to ensure actual level Oil
properties need checking for air content
5. LUB OIL PRESSURE LOW POSSIBLE CAUSES Lub Oil
oil filter chocked.
pump pressure low
Setting
of lub oil pressure relief valve disturbed.
Bearings Lub
oil flow more.
oil cooler oil side inlet and outlet valve not open full/mal
functioning of lub oil cooler control valve or oil cooler chocked on oil side. IMMEDIATE ACTION Change
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 CAUSES Lub Oil
oil temperature after oil cooler more.
flow to bearing less.
Lub.
Oil pressure low.
Excessive Lub
vibration of bearing.
oil cooler bypass relief valve passing or lub oil control
valve malfunctioning Steam
leakage from turbine gland more.
Contaminated Maloperation
lub.oil
during change over of lub oil filter/cooler
6. BEARING METAL TEMPERATURE MORE IMMEDIATE ACTION Change If
over ACW strainer if chocked.
steam leakage from gland is more, reduce load and maintain
HRH temperature at 490o C. Check Ask
oil flow and lub. Oil press at each bearing.
chemist to analyze lub oil for moisture, dirt etc.
Maintain Check Lub
sealing steam pressure and HRH temperature.
passing of cooler bypass relief valve.
oil cooler/filter to be changed over after ensuring proper
venting/filling
7. CONDENSER VACUUM LOW POSSIBLE CAUSES Hogging
ejector /main ejector is not working due to abnormal
steam parameter, abnormal condensate level, passing of standby ejector NRV etc Performance of vacuum pump is not satisfactory due malfunctioning of its valve, high seal water temp, separator tank level abnormal, passing of standby pump etc Cooling water to condenser is less Sealing 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 high Passing of steam drain valves/LP bypass valve
7. CONDENSER VACUUM LOW IMMEDIATE ACTION Maintain
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 vacuum
system. Check
valve’s sealing water pressure.
Check
CW header pressure ,cw temp rise/cw diff. pressure of
condenser if more reduce load and clean condenser one by one Ensure
all steam line drain valves and LP bypass v/v are
closed For
checking air ingress point, fill the water in vacuum system
up to level as per OEM instruction after cooling down the
8. LP TURBINE EXHAUST HOOD TEMP HIGH POSSIBLE CAUSES Low
vacuum.
Prolonged LPT
idle running of turbine at no/low load
exhaust hood spray valve is not operating on interlock.
Passing High
of high pressure drain/lp bypass valve to condenser
steam parameter during cold start up
Operation
of turbine at higher load without HP heaters I/S
IMMEDIATE ACTION Check Try to
as in Sl.No.12.
load the machine.
Ensure
exhaust hood spray valve open on interlock.
Control
steam parameter
Take
hp heaters I/S
9. VIBRATION MORE POSSIBLE CAUSES Abnormal Sudden HP
fluctuation in steam parameter
drop in sealing steam temp
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 ACTION Check
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/vacuum
Cross-checked Check Do
the vibration reading by portable instrument.
bearing drains/lub oil filter for any damage indication
not roll turbine when eccentricity exceed 50 micron on
barring gear. Trip
the turbine if bearing/shaft vibration/eccentricity high
10. TURBINE OVERSPEED POSSIBLE CAUSES Sticking
of stop valve and control valve or heavy passing in case of
turbine trip. Malfunctioning In
of turbine control
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 is subjected to electrical and mechanical stresses
Emergency
Governor failure at the time of over speed.
10. TURBINE OVERSPEED IMMEDIATE ACTION Periodically
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 load Check
the operation of load shedding relay Over speed load
limiting gear
11. HPT EXHAUST TEMP.HIGH POSSIBLE CAUSES Prolonged
no load or low load operation
Obstruction
in steam flow due to high down stream pressure of
HP bypass valve CRH
NRV not opening
Malfunctioning
of Trimming Device
12. FIRST STAGE PRESSURE HIGH POSSIBLE CAUSES Salt
Deposits on Turbine Blades.
Overloading Operation
with low Steam Parameter at High Load
Condenser
Vacuum low at High Load
IMMEDIATE ACTION Reduce
the Load.
Maintain Monitor
Steam Parameter as per Operation Instruction.
Axial Shift & Thrust Bearing Temp Constantly.
13. AC POWER FAILURE POSSIBLE CAUSES Grid
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 power plant operation. In such condition, system is designed in such a way that with the help of 220V DC power (Battery Bank)/ DG Set power (Emergency Power), unit can be shutdown 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 Put
Extraction Valves to LP/HP Heaters and Deareator.
the M/c on Barring Gear.
14. BARRING GEAR JAMMING B/G IS PROVIDED IN ANY STEAM TURBINE FOR UNIFORM COOLING AS WELL AS TO AVOID TEMPORARY SAG BY SLOW ROTATION OF ROTOR SYSTEM.IN THE PAST TURBINE ROTOR SYSTEM WAS ROTATED BY ELECTRIC MOTOR
THROUGH
INTRODUCTION
OF
GEAR KWU
SYSTEM.AFTER
TURBINE
HYDRAULLIC
TURNING GEAR WAS EMPLOYED. POSSIBLE CAUSES: LOW
JACKING
OIL
PRESSURE
DUE
TO
MALFUNCTIONING OF ITS CONTROL VALVE. INSUFFIENT HIGH
JOURNAL LIFT .
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 UNDUE EXTRA
OF JACKING OIL FLEXIBLE CONNECTION.
PIPE FORCES. 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.
THANK YOU
