In modern power plants, extensive protections and interlocks are provided to isolate faulty equipment without causing further damage and allow reserve equipment to start up automatically. Protections detect abnormal parameters and trip equipment to prevent major damage. Interlocks make equipment states dependent to prevent incorrect operation. Protections include tripping the turbine for issues like high/low steam pressure, temperature, exhaust hood temperature, axial shift, differential expansion, eccentricity, pump failures, and low lubricating oil pressure.

2. PROTECTION AND INTERLOCKS
Introduction :-
In modern power plant continuous and reliable
operation of various auxiliaries if a unit becomes necessary.
Extensive protection are provided to trip the boiler or turbine or
any individual auxiliary in case of faults so that the faulty
equipment is isolated without causing further damage.
Interlocking is provided to switch on the reserve equipment in
case of tripping of the running equipment to enable continuity of
functions.

3. Turbine Safety Protection
Turbine protection are provide to detect the abnormal
condition by constantly measuring the various parameter under normal
and faulty condition. If any abnormality happened trip the Turbine to
prevent from major damage.
What is an Interlock
 An interlock is a feature that makes the state of two mechanisms or
functions mutually dependent.
 It prevents incorrect operation to avoid possible damage of equipment.
 Interlocks can be considered as start permissive of any equipment
What is Protection
 The state of action to prevent possible damages of any equipment or
system.
 It is necessary to safeguard the equipment against abnormal deviation
of process parameters to unacceptable values .

4. Turbine and Generator can trip on following Interlocks
 Turbine I/L Steam Pressure High and Low
 Turbine I/L Steam Temperature High and Low
 Turbine Exhaust Hood temperature High
 Shift Axial High
 Differential Expansion - Positive
 Differential Expansion – Negative
 Eccentricity High
 CEP pumping System Failure
 HP heater Level High
 LP Heater Level High
 Lube Oil and Control Oil Pressure Low
 Lube Oil Temperature Low
 Lube oil Temperature High
 MCW pumping System Failure
 ACW pumping System Failure
 Fire in Lube Oil System
 Lose of Vacuum
 Bearing Temperature High
 Bearing Vibration High
 1St Stage Pressure High
 Loss of Barring Gear
 Condenser Tube Failure
 Instrument air Failure

5. Turbine I/L Steam Pressure High
Cause:-
 Sudden drop the load
 Sudden drop the steam flow.
 Turbine trips.
Effect :-
 Turbine may trip on high pressure.
 Turbine RPM go to high
 Turbine Exhaust temperature.
Action :-
 Open start up vent valve.
 Control the boiler Pressure
 Adjust the load on unit, if it has dropped.
 If turbine has tripped first allow boiler to trip but safety valve may lift.

6. Turbine I/L Steam Pressure Low
Cause:-
 Sudden increase the plant load
 Sudden increase the process steam flow.
 Some Problem at Boiler
Effect :-
 Turbine may trip on Low pressure.
 Turbine RPM go to down
 Turbine internals damage
Action :-
 Turbine load reduced
 Control the boiler Pressure
 Adjust the load on unit, if it has dropped.
 If turbine has tripped first allow boiler to trip but safety valve may lift.

7. Turbine I/L Steam Temperature High
Cause:-
 Some Problem at Boiler
Effect :-
 Turbine may trip on High Temperature
 High steam temperature may damage the turbine, as the metallurgy
of the turbine is designed for a particular temperature
Action :-
 In this case turbine should be stopped immediately
 Control the boiler Temperature
 Check the boiler Desupeheater Valve Open or not
 If turbine has tripped first allow boiler to trip but safety valve may lift.

8. Turbine I/L Steam Temperature Low
Cause:-
 Some Problem at Boiler
Effect :-
 Turbine may trip on Low Temperature
 Turbine internals damage
 produces thermal shock on the hot turbine
 Saturated steam enters turbine and damages it severely
Action :-
 In this case turbine should be stopped immediately
 Turbine load reduced
 Control the boiler Temperature
 Check the boiler Desupeheater Valve
 If turbine has tripped first allow boiler to trip but safety valve may lift.

9. Exhaust Hood Temperature High
Cause :-
 Vacuum falls.
 Cooling water Pump trip.
 High steam temperature during cold start up.
 Turbine running at rated rpm without synchronizing/or running at low load for a longer
period.
Effect :-
 Expansion will go towards negative side.
 Prolonged high exhaust hood temperature may lead to vibration.
Action :-
 Check the reason for the fall in vacuum.
 Start stand by C.W. pump if available. (Restore the C. W. supply). Start second C.W.
pump if unit is running at higher load.
 H. P. drains to condenser hot well should be reduced.
 Control system temperature and pressure during the cold start.
 If possible, synchronize and load the machine
 Control gland steam pressure and temperature.
 Start make up water spray in condenser. (Start make up from TOP).
 If machine is required to run at 3000 RPM (or at lower load) for a longer time, take
following necessary action to control the exhaust hood temperature (make-up) surplus
can be establish to check temp rise.
 Keep the vacuum as high as possible (by keeping 2 ejection in service).
 Keep steam temperature and pressure in unit, do not allow to rise.

10. Axial Shift High
Cause :-
 Abrupt changes in load. (fast pick up of load)
 Sudden drop in steam temperature.
 Sudden drop in vacuum.
 Lubricating oil failure to thrust bearing.
 Salt or Silica deposition in turbine.
 Worn out thrust pads.
Effect :-
 Overloading of thrust pads.
 May contribute turbine vibration.
 Abnormal turbine differential expansion.
Action :-
 Check the boiler parameters and control the sudden changes.
 Control the turbine vacuum.
 Reduce the unit load.
 Check the flow pressure and temperature through bearing.
 For deposition of the salt unit shut down is required for washing the turbine.
 If axial shift has increased rapidly and is beyond control even after reduction in load
trip the m/c and bring to standstill condition as soon as possible. (by breaking the
vacuum)

11. Differential Expansion High (Positive)
Cause :-
 High steam temperature.
 Poor insulation.
 Salts deposition on the interior surface of the casing preventing good heat transfer.
 Gland steam temperature high.
 Fast rolling or fast pick up of the load.
 Inadequate soaking period.
 High condenser vacuum, (LP side Effect on differential expansion).
Effect :-
 Seal rub can be expected.
 Metallic rub sound from the turbine when interference exist.
 Turbine vibration may increase.
Action :-
 Use flange heating in turbine (When differential expansion are higher towards + ve
direction).
 Soak the turbine properly.
 It should not increase more than limit Maintain the steam temperature accordingly.
(as per starting diagram).
 Load the turbine gradually.
 Check the insulation and found poor get it attended (shut down requires).
 Remove the salt deposition by washing if required.
 If it is beyond control try to control the boiler parameters and if turbine is tripped, drop
the vacuum immediately.
 If LP side differential expansion is increasing drop the vacuum to a certain extent (to
an acceptable limit).

12. Differential Expansion High (Negative)
Cause :-
 Time taken during rolling, and loading is more than required or rolling at
rated RPM for longer time.
 Increment in exhaust hood temperature.
 Low condenser vacuum.
Effect :-
 Seal rub can be expected.
 Metallic rubbing sound from the turbine when interference exists.
 Increment in vibration.
Action :-
 During hot start up rolling and loading of the machine should be as per the
starting curve.
 Start 2nd ejector to improve the vacuum.
 Try to bring down the exhaust hood temperature.
 If turbine tripped due to-ve maximum differential expansion open the vaccum
bkr, to avoid the possible damage.
 Increase the boiler steam temperature and load the machine little faster.
 If differential expansion is extremely-ve and machine rolling has started don’t
trip the turbine control the boiler parameters.

13. Eccentricity High
Cause :
 Deflection of turbine rotor.
 Machine could not be put on bearing gear after tripping.
 Improper heating during start up.
 Improper draining of steam lines and casing.
 Abrupt drop in M.S. temperature due to carry over of moisture in glade, deformation of cylinder.
Effect :-
 Turbine vibration will increase.
 Unusual noise from the turbine.
 Bearing oil and metal temperature will rise.
 If machine is on barring gear, it will draw more power.
Action :-
 Strictly follow the start up procedure while starting. Maintain the steam parameters while starting.
Give proper heating and soaking time at required speed while rolling, drain the steam lines and
casings as per recommendations.
 It eccentricity is not accompanied with bearing. Vibration and increment in the bearing Metal
temperature, there is nothing wrong with the rotor (turbine).
 If eccentricity is high when machine is on barring gear it is due to rotor bent. Continue the machine
on barring gear for a longer time. Soak the m/c at 500 rpm, for a longer tome. So that bent rotor
may get even out.
 When eccentricity increases with vibration, reduce the unit load and allow it to come back to the
original value and stop the machine for checking for any abnormally.
 Control the turbine vacuum.
 Check the flow pressure and temperature through bearing
 For deposition of the salts unit shut down is required for washing the turbine.
 If axial shift has increased rapidly and is beyond control even after reduction in load trip the m/c
and bring to standstill condition as soon as possible. (by breaking the vacuum)

14. Condensate Extraction Pump Failure/ Trips
Cause :-
 Motor protection.
 Hotwell level very low.
 CEP discharge pressure very low (not on discharge header pressure).
Effect :-
 Deaerator level will start falling.
 Hotwell level will start increasing.
 Condenser vacuum will start falling.
 If no CEP is running unit will have to be tripped
Action :-
 Start standby CEP if it not starts on auto.
 If only one pump is running then reduce the load accordingly.

15. HP Heater Level High
Cause :-
 HP heater drain to Deaerator level controller is faulty (not operating properly) or
control valve stuck-up.
 HP heater - 2 drain to HPH - 1 valve do not open/operate particularly at low load.
 Deaerator pressure is higher than normal.
 Inadequate extraction pressure to HP heater.
 Tube failure In HP heater
Effect :-
 HP heater – 2 drain to HPH – 1 will open on HP heater – 1 level high (provided inter
locks are through).
 HP heater gat by passed from water and steam side on auto (if interlocks are
through). If level in HP heater build up rapidly there is a possibility of water entering
into the turbine.
Action :-
 Take HP heater’s level controller on manual and maintain the level.
 Check the operation of heater’s drain to HPH - 1 valve. Open it manually if required.
 Adjust Deaerator pressure if it is more.
 Adjust the steam extraction pressure if valves are throttle open them.
 By pass HP heaters manually if level is very high and are not getting by passed
automatically, and ensure has opened.

16. LP Heater Level High
Cause :-
 LP heater level may go high due to difficulty in level controller valves.
 Tube failure in LP heaters.
 Low extraction pressure in LP heaters.
Effect :-
 Possibilities of water entering into turbines if level high and un-controllable.
Action :-
 Check the level controller of the heaters, if require take it on manual and try
to maintain the level.
 Adjust the extraction pressure of valve are throttle.
 By pass the heaters if level in high (Bypass the better if level in it is very
high and uncontrollable)

17. Turbine Lubricating Oil Pressure Low
Cause :-
 Air lock in oil cooler.
 MOP suction failure.
 Oil filter chocked up/line filters chocked up.
 Leakage in oil lines flanges, bearings etc..
 Excessive oil consumption in generator seal oil system.
 MOP failure.
Effect :-
 Rise in bearing Metal temperature.
 Turbine trips on lubrication oil pressure Low
Action :-
 Check oil pressure and adjust the pressure by adjusting LOW valves if possible.
 Check for any oil leakages in the oil System
 Start Second oil Pump in auto
 Trip the turbine if oil pressure does not improve.
 Check the oil cooler change over the defective one to the stand by. Remove the air
lock from the cooler if so.
 Check the oil filters regularly change over to stand by. If difference in pressure
increase gets it clean. Check the line filters spares and isolate them, whenever unit is
in shut down and if requires cleaning.

18. Lube Oil Temperature Low
Cause :-
 Water side valves in oil coolers are open more than required. (Especially low
load) Hence, it is necessary for control room operator to inform regarding
load variation to temp controller (operator).
 In cold season during start up. (temperature not increasing even the CW
valves of the cooler are closed).
Effect :-
 Unstable oil film in Bearings
 It may damage the Bearings.
 Bearing Vibration may rise.
Action :-
 Throttle the cooling water valves of the oil coolers. (if required).
 If the machine is off load-do-not roll it till oil temperature attains an
acceptable working value.
 If the machine is on-load-temperature should be rapidly raised to the
acceptable.
 Oil centrifuge heater can be taken in service.

19. Lube Oil Temperature High
Cause :-
 Failure of C.W. system.
 Cooling tower fan stop/trip.
 High Cooling water inlet temperature.
 Oil coolers are dirty. (Heat transfer is very low).
 Air locking in oil coolers.
Effect :-
 Rise in bearing Metal temperature.
 Bearing Vibration may rise.
 Rise in seal oil temperature.
Action :-
 Restore the CW system / Restart the CTID fan/fans.
 Bring down the CW inlet temperature. Open the CW valves of the coolers if they
are throttled.
 Remove the air lock from the cooler if so.
 Put stand by oil cooler in service if available.
 Spare and isolate the dirty oil cooler for cleaning if possible.
 Trip the unit if lubricating oil temperature rises continuously and is uncontrollable.
 External cooling of oil cooler can help to bring down the oil temperature

20. Main Cooling water pump(MCW) Trip
Cause :-
 Motor protection relay operated.
 Auxiliary supply failure.
Effect:
 Turbine vacuum is fall
 Unit will trip exhaust Temperature and Pressure High if all CW
pumps trip.
Action:
 Restore Cooling water pumps after checking.
 Restore Auxiliary supply starts the pump (Which is on station bus)
 Start the stand by CW pump immediately if available.
 Reduce the load on machine till the 2nd pump is taken in service.
 Trip the unit, if vacuum drops considerably.
 Watch the exhaust pressure, temperature and load.
 If not a single C.W. pump is put into service for long time prime the
C.W. tunnel and start C. W. pump.

21. ACW Pumping System Failure
Cause :-
 Motor protection relay operated.
 Auxiliary supply failure.
Effect:
 Generator winding temperature rise
 Boiler feed pump bearing temperature rise
 Service air compressor element temperature rise
 AC Package compressor element temperature rise
 Lube oil temperature
 Turbine, Gearbox and Generator bearing temperature rise
Action:
 Start the stand by ACW pump immediately if available.
 Restore Auxiliary supply starts the pump (Which is on station bus)
 Restore Cooling water pumps after checking.
 Reduced the Plant load.

22. Fire in Lube Oil System
Cause :-
 Oil leakage from oil lines.
 Bearing Oil collected on laggings and reaches to the ignition
point.
Effect :-
 Extensive damage to the turbine and surroundings.
Action :-
 Take care of oil leakage and try to arrest it.
 Use dry CO2 powder as soon as smoke is detected. Inform
the fire section. If the fire is extensive use CO2 powder
cylinders.
 Trip the turbine, if fire is beyond control.
 Expell the H2, if fire is near the H2 zone (with CO2).
 Do not allow the oil to lodge on the leggings. Take corrective
and do not neglect even very small leakage or collection of all
to prevent the fire.


23. Loss of Vacuum (Partial or Completely)
Cause :-
 Cooling water Pump/Fan trip.
 Loss of gland steam pressure.
 Defect in gland steam pressure regulator.
 Loss of ejector steam pressure.
 leakage in vacuum system or puncture.
 Malfunction of vacuum breaker valve.
 Turbine rupture disk damaged or leaking.
 C.E.P. trip.
Effect :-
 Vacuum may drop slowly.
 If it drops rapidly-unit will trip on exhaust pressure high.
 Over heating of casing and exhaust hood.
Action :-
 Start stand by CW pump if available (if CW pump in service has tripped). Rectify
the problem in tripped CW pump and make it available. Maintain the load
accordingly.
 Find out the reason of tripping of CT Fan/pump.
 In case of gland steam lost, please check the Aux Steam Header pressure, if it
is not proper maintain it by opening it’s control valves bypass valve if required.
 In case of defect in gland steam pressure regulator, put it on manual or control
by bypass valve.

24.  When the vacuum falls suddenly and cannot be established again on
while starting the unit (and while establishing vacuum) if it is not
obtained there may be leakage/puncture in the system under
vacuum. So please check the system under vacuum thoroughly. Find
the leakage or puncture and arrest the leakage/attend the puncture.
 Check the position of vacuum breaker valve. It should be close, while
establishing the vacuum or during normal running operation unless
anything is abnormal.
 Check for leakage/damaged rupture disk , if it is so then shut down
the unit to attend the same.
 If CEP has tripped start the stand by CEP (if does not start on auto) if
available. Rectify the problem in fault, and maintain the load
accordingly.
 Change over the ejector if the first one is not maintain vacuum.
 If vacuum falls at a slower rate, one may put the second ejector in to
service to maintain the vacuum (in the maintain the leakage may be
found). Also starting ejector can be taken in service.
 If vacuum falls at a faster rate, trip the unit immediately. (if not trip an
exhaust pressure high protection)

25. Bearing Temperature High
Cause :-
 High lubricating oil inlet temperature to the turbine bearing.
 Excessive vibration of the Bearings.
 Bearing failure.
 Contaminated lubricating oil high moisture dirt etc.
 Inadequate oil flow or low lubricating oil pressure.
Effect :-
 Result to bearing failure.
 Increment in bearing vibration.
Action :-
 Check and maintain the oil temperature, oil pressure, oil low flow through the
turbine bearing. Check duplex oil filter, if requires change over it also check
the line filters.
 Check the oil for moisture and contamination periodically. Keep oil
continuously in service as per recommendation. Drain the collected water
from the MOT regularly.
 Keep watch on oil cooler out let temperature.

26. Bearing Vibration High
Cause :-
 While turbine is passing through it’s critical speed.
 Rapid changes in the turbine inlet steam temperature (carry over in
extreme case).
 Low lubricating oil temperature.
 Unbalance steam flow through each of the machine.
 In correct shaft alignment.
 Gland steam pressure and temperature are not proper.
 Rotor mechanically unbalance.
 Eccentricity high.
 Uneven expansion (high differential expansion and temperature
difference between top and bottom cylinder exceeds).
 Over speed of the machine.
Effect :-
 Eccentricity may go high.
 If machine is allowed to run at higher vibration. Vibration may exceed
the safe limit and may damage the machine.

27. Action :-
 Roll the machine smoothly and do not allow the machine to settle on
to critical speed band.
 Maintain the steam parameters. Don’t allow any vapid change in the
steam temperature.
 Maintain the lubricating oil pressure temperature properly
 Try to maintain the turbine vacuum, if, it falls (Prevent the heating of
the LP side rotor).
 Check the gland steam temperature and pressure
 Ensure that HP side Pedestal expansion regularly. It should be equal
on both the sides. Check the freeness of the all expansion washers.
 Try to control the differential expansion
 Control the eccentricity if found high.
 Reduce the unit load, if bearing vibrations are still high.
 Get the rotor balanced unless it is so.

28. Stage Pressure High
Cause :-
 Deposition an blades.
 High load when HP beaters are not in service.
 Over loading of the machine.
 Turbine Exhaust Temperature
 Process steam flow High
Effect :-
 Full load may not be obtained.
 Axial shift may rise.
 Thrust load an turbine increase and may result in damage of the
thrust pad.
Action :-
 Clean the rotor by water washing.
 Maintain the unit load as permitted by the curtish stage pressure.
 Put HP heater in service if not available reduce the unit.
 Reduce the process steam flow

29. Loss of barring Gear
Cause :-
Barring gear motor trips, fuses blown off.
Barring gear start permissive are not satisfied
(defective pressure switch).
Barring gear motor shaft failure.
Effect :-
Shaft may start to hog.
Action :-
Try to restore the barring gear motor supply as
quickly as possible.
Rotate the shaft manually as mentioned below.

30. Condenser Tube Leakage
Cause :-
 Corrosion erosion of the tubes.
 Condenser inlet CW pressure high-leads to take the tube from
expanded part.
 Low CW flow through condenser tube causing the high terminal
difference and weakens the expansion joint.
Effect :-
 Conductivity of condensate will go high.
 Boiler PH will fall and boiler water conductivity will rise.
Action :-
 Isolation one side of the condenser and ensure, if conductivity falls
after the isolation or if not.
 Reduce the turbine load by 50%.
 Repair the leakage and after bringing back the condenser in to
service, check the conductivity.

31. Instrument Air Failure
Cause :-
 Sudden increase in air consumption.
 Sudden line leakage develops.
 Compressors trip.
 Auxiliary supply is not available.
Effect :-
 All the auto controls using air will become in operative (all valves will
get lock in their position).
 Ash handling operation is not possible.
 Boiler drum level Deaerator level hot well, HP & LP heaters level
expander level etc. will have to maintained by operating the local
valves (may by pass valves).
 Unit may trip due to disturbances.
Action :-
 Try to put the control compressors into service and if, not possible or
not maintaining the required pressure station to control air
interconnecting, if station compressors air available.
 Isolate the leaky airline, if possible and restore the system back.
 Restart the unit, if it has tripped after taking corrective action for
instruments.