O&M PROBLEMS OF THERMAL POWER STATIONS

COMMONLY FACED O&M PROBLEMS OF THERMAL POWER STATIONS

 

  • BOILER & AUX (COAL, OIL, GAS FIRED):

 

  • Operational Problems ( Common )

 

  • Mech. Systems

 

1.2.1.               Pressure Parts, Furnace & Second PASS

1.2.2.               Safety valves

1.2.3.               Isolating valves ( motorised & manual)

1.2.4.               Controlled circulation pumps

1.2.5.               Control valves

1.2.6.               Soot blowers systems

1.2.7.               Superheater & Reheater Spray System

1.2.8.               Milling system (Bowl mills & tube mills)

1.2.9.               Burner tilting system

1.2.10.             Coal piping

1.2.11.             Oil/Gas firing system

1.2.12.             Rotary Air preheaters

1.2.13.             FD,PA and ID Fans

1.2.14.             Electrostatic precipitator

1.2.15.             Water Chemistry System

1.2.16.             HP Bypass system (SULZER MAKE)

 

  • Controls & Instrumentation :

 

1.3.1.               FSSS

1.3.2.               Secondary Air Damper Control

1.3.3.               Aux. PRDS

 

 

  • Electrical System :

 

1.4.1.               HT Motors

1.4.2.               ESP Controls

 

 

  • STEAM TURBINE & AUXILIARIES :
    • Common Operational Problems
    • Turbine & Auxiliary sub-systems :

 

2.2.1.               Lub Oil System

2.2.2.               Control fluid EHS System ( 500 MW Unit)

2.2.3.               Turbine Bearing Temperatures

2.2.4.               Turbine bearing vibrations

2.2.5.               Turbine Casing temperatures

2.2.6.               Turbine expansions

2.2.7.               Turbine protective devices

2.2.8.               Turbine gland sealing system

2.2.9.               LP Bypass Stop and control valves

2.2.10.             Turbine stop and control valves

2.2.11.             Condenser vacuum

2.2.12.             Condensate extraction pump

2.2.13.             Boiler feed pump

2.2.14.             Vacuum pump

 

2.3.      Controls & Instrumentation :

2.3.1.               EAST Package

 

  • TURBO GENERATOR, GENERATOR & AUX.

3.1.      Operational problems

 

4.0.      Gas Turbine (GE make)

  • Common Operational Problems of Boiler & Auxiliaries:

 

1.1.1.               Frequent trips on flame failure

 

  1. Check for proper combustion
  2. Check for correct total air flow
  3. Check for correct coal air ratio
  4. Check for correct wind box to furnace DP
  5. Check for proper functioning of SADC
  6. Check for healthiness of flame scanners
  7. Check for flame failure circuit in FSSS

 

  • Furnace draft fluctuations along with flame scanner flickering:

 

  1. Check for proper functioning of draft control on `Auto’
  2. Check for disturbed flame condition
  3. Check for proper functioning of CMC/Fuel master control on Auto
  4. Check for proper functioning of PA header pressure auto control
  5. Check for proper functioning of secondary air flow auto Control
  6. Check for proper functioning of SADC on auto control
  7. Check for furnace trough sealing
  8. Check for any boiler tube leakage

 

1.1.3.               Main Steam/HRH steam temperature low/high:

 

  1. Check for correct total air flow
  2. Check for correct burner tilt position
  3. Check for correct feed water temperature at Economiser inlet
  4. Check for slagging/scaling (external) on water wall, SH & RH tubes
  5. Operate wall blowers/LRSB at regular interval as per requirement
  6. Check for inside scaling in water walls & SH/RH tubes
  7. Check for choking of SH/RH attemperator nozzles/passing of SH/RH spray control valves
  8. Check for any undesired steam outlet due to passing of safety valves, drain valves, vent valves

 

1.1.4.               High unburnt carbon in flyash/bottom ash:

 

  1. Check for proper and stable combustion
  2. Check for plugged coal pipes and ensure equal distribution in all four coal pipes
  3. Check and adjust the fineness of coal
  4. Maintain adequate total air flow (secondary air flow + PA flow)
  5. Maintain proper oxygen in flue gas. Cross check UCB instruments with local sampling
  6. Ensure that burner tilt of all four corners is at same position.
  7. Maintain correct mill outlet temperature.
  8. Tune SADC as per requirement to optimize flame condition
  9. Carryout clean air flow test/hot traverse if required
  10. Check and optimise ball charge (Only for Tube mills)
  11. Check and replace worn out mill liners
  12. Check for proper mill clearances
  13. Maintain proper mill level (Only for Tube mills)
  14. Check classifier/reject chute for bypassing of coal air mixture

 

1.1.5.               Tripping of boiler on RH protections due to closure of HP/LP Bypass during start ups:

 

  1. Maintain stable combustion
  2. Study RH protection logic
  3. Initially keep HP/LP Bypass valves on manual mode. After stable combustion and sufficient flow only they should be put on Auto
  4. Check for proper functioning of these valves on Manual and Auto’
  5. Check protection closing circuit for any malfunctioning
  6. Maintain correct HP Bypass downstream temperature
    • Unit load not increasing to rated load :

 

  1. Check for correct parameters of main steam/HRH steam i.e. pressure, temperature, flow
  2. Check for correct quantity of coal
  3. Check for proper combustion/flame condition
  4. Check for correct total air flow/Oxygen and CO in flue gas
  5. Check for calorific value, fixed carbon, ash content, moisture etc. of coal
  6. Check for correct feed water temperature at economiser inlet
  7. Check for correct fineness of coal
  8. Inspect mill and replace worn out liners and internals
  9. Check for correct mill output and take remedial measures to get optimum output
  10. Check for any boiler tube leakage
  11. Check for undesired steam outlet due to passing of safety valves, drain valves, vent valves.
  12. Attend all valve leakages
  13. Check for very dirty furnace due to deposition of slag/scale on water wall/SH/RH tubes

 

  • High stack Emission :

 

  1. Check for functioning of all ESP fields
  2. Check for correct total air flow, Oxygen and CO in flue gas
  3. Check for correct flue gas temperature at ESP
  4. Check for proper rapping frequency
  5. Check for proper current settings
  6. Check for proper gas flow distribution in the pass during shut down
  7. Check for proper fixing of deflector plates of hoppers during shut down
  8. Check for eroded guide vanes/splitters during shut down
  9. Check for proper fixing of screen plates during shut down
  10. Check for proper closure of manhole doors, inspection doors etc. to prevent air ingress
  11. Check for proper functioning of ash handling system
  12. Check for high ash content in coal

 

  • Tripping of Unit on high/low drum level :

 

  1. Check for sudden opening/leakage of waterwall/economiser tube
  2. Check for tripping of any one of running BFPs
  3. Check for malfunctioning of drum level auto control
  4. Check for closure of any valve in feed water circuit
  5. Check for opening of HP Bypass valve on fast opening mode.
  6. Check for sudden throw off/raising of load
  7. Check for tripping of two/three coal elevations simultaneously
  8. Check for disturbance in combustion
  9. Check for malfunctioning of drum level transmitters

 

  • Frequent tube failures :

 

  1. Avoid sudden stress to boiler tubes
  2. Maintain rate of pressurisation/de-pressurisation as recommended during hydraulic test of boiler
  3. Maintain rate of rise/drop of temperature as recommended during start-up/shut down (follow start up curve)
  4. Monitor drum/SH/RH metal temperatures during start up/shut down
  5. DON’T TAKE MILLS INTO SERVICE UNLESS FLOW IS ESTABLISHED THROUGH REHEATER
  6. Maintain proper water chemistry regime as per recommendations.
  7. Check for tube thickness for any erosion. In case of erosion, tubes must be replaced
  8. Check for deposits/scales inside the tubes. If found, contact BHEL for further analysis and chemical cleaning.
  9. Check for possibility of choking
  10. Check for foreign materials/obstructions in the connected headers
    • Boiler drum pressure dropping suddenly :

 

  1. Check for interruption of coal to the furnace due to choking in the burner
  2. Check for tripping of feeder/mill
  3. Check for disturbed combustion inside furnace
  4. Check for any boiler tube leakage
  5. Check for opening of boiler drains, vent, safety valves
  6. Check for choking in mills/drop in air flow through mill
  7. Check for malfunctioning of auto control of CMC/Fuel master control

 

  • High DM Water make up :

 

  1. Check for any boiler tube leakage
  2. Check for leakages from glands and bonnets of valves
  3. Check for passing of safety valves
  4. Check for passing of drain valves
  5. Check for passing of vent valves
  6. Check for optimum opening of CBD valves

 

  • Boiler water silica level High :

 

  1. Check for proper DM water quality
  2. Check for correct chemical regime in boiler drum
  3. Check that CBD valves are operative
  4. Check the CBD lines for any possible choking
  5. Check for any condenser tube leakage
  6. Check for proper opening of CBD valves

 

1.1.13.             Sudden reduction of load:

 

  1. Check whether it is momentary due to grid disturbance or due to malfunctioning of turbine governing system
  2. Check for drum pressure. If the trend is increasing, take appropriate measures to stabilize drum pressure by reducing/cutting off fuel input to furnace.  If necessary, cut off mills, one by one.
  3. Check for drum level. See whether auto control is able to maintain drum level.  Otherwise take it on manual control.
  4. Check for furnace draft
  5. Check for secondary air flow, oxygen in flue gas.

 

1.1.14.             Ash build up in bottom ash hopper and water walls:

 

  1. Check for proper functioning of bottom ash evacuation system
  2. Check for proper functioning of clinker grinder system
  3. Check for proper functioning of scrapper conveyor wherever provided
  4. Check for any choking of ash evacuation/disposal pipes
  5. Don’t allow building up of ash level in case of non-functioning of ash evacuation and associated systems.
  6. In case problem is persisting and ash level has started building, boiler must be stopped and ash/clinker is to be removed.

 

1.1.15.             High Flue Gas temperature at APH outlet:

 

  1. Check for excess Air and total Air flow
  2. Check for fineness of coal
  3. Check for fouling of water walls, superheaters, reheaters etc.
  4. Check for proper heat transfer in Air preheaters
  5. Check for dampers position of Air preheaters
  6. Check for Burner tilting system and bring it downwards.
  7. Switch over to lower elevation mills.
  8. Check for proper Air distribution and functioning SADC
  9. Check for leakages through peep holes, manholes, seal water trough etc.
  10. Check for tube failures.

 

1.1.16. Low Boiler efficiency:

 

  1. Check for excess air flow
  2. Check for the reasons for high air preheater outlet flue gas temperature
  3. Check for higher unburnt carbon in bottom ash and fly ash
  4. Check for proper combustion and high `CO’ in flue gas
  5. Check insulation/refractory to arrest heat loss
  6. Check for entry of excess water/moisture alongwith coal. Arrest where possible.
  7. Check the fineness of coal
  8. Check for proper Air distribution and functioning of SADC.
  9. Check for steam/water leakages and tube failures.

 

1.1.17. High excess Air flow :

 

  1. Check the Air flow distribution and functioning of SADC
  2. Check the combustion
  3. Check the fouling of superheater, reheater and HTSH surfaces
  4. Check for air ingress through peep holes, manholes, seal trough etc.
  5. Check the reliability of air flow and O2 measurements
  6. Check the fineness of coal and functioning of mills.
  7. Set for proper air flow and O2 in Automatic combustion control.

 

Mechanical System :

 

  • Pressure Parts :

 

  • Water Wall tube failure :

 

  1. Check for deposits inside the tube. Analyze the deposits.
  2. Check for indications for overheating of the failed tube and the nearby tubes.
  3. Check the tube thickness of the failed tube and also nearby tubes.
  4. Check the healthiness of nearby wall blowers for steam passing
  5. Check for possibility of choking/loss of adequate flow through the tube
  6. In case of scales/chemicals deposits/Rust contact BHEL for further analysis and chemical cleaning
  7. Check for foreign materials/obstructions in water wall ring headers
  8. Check for possibility of failure of weld joint
  9. Check the orifices of the tubes in the ring header in case of controlled circulation boilers.

 

  • Superheater/Reheater/Economiser/Tube failure:

 

  1. Check for indications for overheating of the failed tubes and the nearby tubes
  2. Check for failure of weld joint
  3. Check the tube thickness of the failed tube and the nearby tubes
  4. Check the healthiness of nearby long retractable soot blower for steam passing
  5. Check for possibility of choking/loss of adequate flow through the tubes
  6. Check for foreign materials/obstructions in the connected headers
  7. Check the tube material for usage of proper grade material
  8. In case of scales/chemicals deposits/rust contact BHEL for further analysis and remedial measures
  9. Check the spacing and alignment of coils around the failed tube
  10. Check the availability/healthiness of tube shields/cassette baffles

 

  • Unloading/overloading of hangers :

 

  1. Verify the correctness of the hanger as per hanger schedule
  2. Reset all the hangers of the connected header, pipe, pressure part to the cold set values.
  3. Measure the hot value of the hanger and report to Engineering for analysis.

 

  • Fast erosion of water walls, super heaters, Repeaters & Economizers tubes:

 

  1. Check the operation of wall blowers/LRSBS w.r.t. possibility of steam erosion
  2. Provide additional tube shields/baffles for the tubes where there is faster erosion.
  3. Check the healthiness of existing tube shields/baffles
  4. Use erosion prevention methods around burner blocks, wall blowers etc.
  5. Contact BHEL for flow model studies

 

  • Distortion/dislocation of Buck stay structures:

 

  1. Check for possibility of local explosions and take preventive measures for recurrence.
  2. Check for expansion obstructions
  3. Contact BHEL for review of design

 

  • Erosion of headers in Flue Gas path :

 

  1. Check for any longstanding steam/water leakages from Hand holes etc.
  2. Apply additional refractory for the affected position after consulting BHEL.

 

 

  • Ash Deposits over water walls/superheaters/reheaters/economisers:

 

  1. Check the operation of wall blowers and LRSBS. Reset the schedule to prevent excessive deposits
  2. Check the combustion parameters
  3. Check the fineness of coal.
  4. Check the healthiness of secondary Air damper system

 

 

1.2.2.               Safety Valves (Spring Loaded and Electromatic):

 

1.2.2.1. Set pressure/blow down got disturbed:

 

  1. Check for loosening of lock nut of pressure adjusting nut
  2. Check for lower and upper lock pins looseness/non-availability / breakage
  3. Check for disturbance of overlap collar setting
  4. Reset the set pressure/blowdowns.

 

1.2.2.2. Missing of Blowdown rings lock pins:

 

  1. Check for looseness of lock pins of all safety valves which can lead to falling of lock pins
  2. Replace the lockpins after proper setting of upper and lower rings.

 

1.2.2.3. Valves passing/valves simmering:

 

  1. Check the lower ring setting and also upper ring
  2. Check for erosion of seat/disc during shut down
  3. Check the position of lift collar and its locking
  4. Check overlap collar/orifice healthiness during shut down

 

1.2.2.4. Safety valve did not, reset after floating

 

  1. Check for disturbed lift collar position. Check for missing lock pin of lift collar
  2. Check for loose locknut of pressure adjusting nut
  3. Reduce the pressure till the safety valve resets
  4. Correct the lift collar, pressure adjusting nut positions
  5. Refloat the safety valve

 

1.2.2.5. Blowdown adjustment could not be done with upper ring:

 

  1. Check for seat/disc erosion during shut down
  2. Check overlap collar and its orifice
  3. Adjust overlap collar position one notch at a time and reset blowdown.

 

 

1.2.3.           Isolating valve (Manual & motorised)

 

1.2.3.1. Gland leakages/Bonnet leakages:

 

  1. Tighten the glands/Bonnets optimally while in hot condition, while raising pressure (after servicing/overhaul)
  2. Use correct grade gland packings/bonnet ring
  3. Avoid sudden rise/drop of medium temperature warm up the system before changing
  4. Check for equal tightening of gland/bonnet tightening bolts
  5. Check the healthiness of gland box and bonnet machined surfaces

 

1.2.3.2. Passing of valves:

 

  1. Check for disc/seat erosion in shut down
  2. Check for proper closing of valves. Do not apply excessive pressures while closing
  3. Check for proper close limit switch/torque switch setting
  4. Use either limit switch or torque switch for closing protection of different types of valves as per BHEL instructions.
  5. Check for proper application of valves. A Globe stop valve/ Gate valve cannot be used for throttling

 

1.2.3.3. Valve is too hard to open/close:

 

  1. Check for over tightening of gland packing holder
  2. Check for bent spindle
  3. Check lubrication of stem nut, actuator etc.
  4. Check for actuator/stem nut damages
  5. Dismantle the Actuator and valve for servicing

 

1.2.3.4. Valve stem broken:

 

  1. Check for malfunctioning of limit/torque switches
  2. Check matching of actuator and valve ratings
  3. Check the quality of stem material

 

1.2.3.5. Erosion of disc/seat

 

  1. Check for proper use of limit switch/torque switch depending upon the application and type of valve
  2. Check for proper setting of limit switch/torque switches

 

1.2.3.6. Operational difficulty:

 

  1. Check for insufficient lubrication
  2. Check for over tightening of gland packing
  3. Check for proper usage and setting of limit/torque switches
  4. Check for damages of actuator, components, stem nut, bearings, bent shaft, disc/wedge jamming etc.
  5. Check for proper selection of rating of actuator to suit the valve

 

1.2.3.7.         Torque switch operates while trying to open the valve from close position (Gate valves):

 

  1. Set the open torque switch value more than that of close torque switch
  2. Bypass open torque switch with close limit switch contact for 5% travel of the stem in the open direction
  3. Check for jamming of the wedge

 

  • Motor trips on Torque switch protection:

 

  1. Check for jamming/obstructions
  2. Check for damage of bearings
  3. Check for damage of components of actuator
  4. Check for bent shaft
  5. Check for damage of stem/stem nut threads

 

1.2.3.9.            Components in Limit switch/Torque switch compartments damaged/ rusted.

 

  1. Check whether cover is fixed properly with proper `O’ ring/gasket and fixing bolts
  2. Service/replace the limit/torque switches and other components

 

1.2.3.10.        Hand wheel engagement is not taking place :

 

  1. Check for damages to engage lever mechanism
  2. Do not apply excess force on the hand wheel
  3. Follow manufacturer’s instructions while engaging the hand wheel for manual operation
  4. Avoid damages to hand wheel lever mechanism during maintenance and handling

 

1.2.3.11.          Leakage of oil into Limit switch compartment:

 

  1. Check for damaged oil seals and replace them
  2. Check for damaged components

 

1.2.4.             Controlled Circulation Pumps (500 MW) Boilers:

 

1.2.4.1. CC Pump differential pressure low:

 

  1. Check whether Direction of rotation is proper
  2. Check for healthiness of the DP Transmitters and the connected control system
  3. Check for choking/leakages in DP transmitter impulse lines
  4. Ensure discharge valve is open

 

1.2.4.2. Sudden rise in cavity temperature:

 

  • Check for leakages/back charging from the cavity of motor towards purge water line
  • Check for leakages in the impulse piping of cavity water pressure
  • Check for external leakages/tube leakages of the motor coolers
  • Check for accidental opening/passing of drain valve of purge line before motor
  • Check for failure of cooling water to motor coolers
  • Check for leakages from the bushings

 

1.2.4.3. Water leakages from the motor/motor cooler:

 

  • Arrest the leakages at the earliest, if possible
  • Open the purge water to motor to make up the loss and prevent boiler water entry into motor
  • Ensure the availability of cooling water to coolers
  • If the leakage is from weld/flange joint and can not attended by normal means, on line sealing methods can be resorted to.
  • If needed isolate the pump or stop the Boiler and attend to the leakages
  • Ensure that cavity temperature is maintained below 60 Deg.c. to prevent damage to the motor

 

 

1.2.4.4.            High differential temperature across the pump (with pump not in operation):

 

  1. Open the warm line and wait for reduction in differential temperature
  2. Check for plugging of warm up line

 

1.2.4.5. Leakage from cooler (High pressure side) circuit:

 

  1. Start the purging immediately
  2. Stop the motor
  3. If leakage can not be arrested, isolate the pump/stop the boiler
  4. Try for `ON LINE SEALING’ methods to arrest the leakage or attend OFF line.
  5. Prevent rise of cavity temperature beyond 60 Deg.C. to protect motor.

 

1.2.4.6. Frequent bursting of purge line strainers:

 

  1. Ensure that the DP across the strainers is less than 100 PSI (6 Kg/cm2 approx.) under all operating conditions.
  2. Arrest any leakages in the purge line system

 

 

1.2.5.             Control Valves:

 

1.2.5.1. No output from the Air Filter regulator

 

  1. Check for choking of filter element. Clean filter element, if necessary, replace it.
  2. Check the healthiness of diaphragm

 

1.2.5.2. No Output from I/P Converter:

 

  1. Check for any loose connections and the availability of curent signal
  2. Check for availability of instrument air at proper pressure
  3. Check for calibration of the I/P Converter
  4. Check for choking of Flapper/Nozzle assembly and Control relay
  5. Check for any air leakages downstream

 

1.2.5.3. Malfunctioning of positioned:

 

  1. Check for availability of instrument Air at rated pressure
  2. Check for availability of signal air
  3. Check for any air leakages in the tubing
  4. Check for the ausage of correct CAM
  5. Check for healthiness of Feedback mechanism

 

1.2.5.4. No Output from Position Feedback Transmitter:

 

  1. Check for the healthiness of linkages
  2. Check for proper cable connections (two wire/four wire type)
  3. Check for healthiness of Electronic system
  4. Check for the availability of input voltage

 

1.2.5.5. Malfunctioning of Control Valve:

 

  1. Check instrument Air supply
  2. Check the healthiness of diaphragm
  3. Check the healthiness of spring
  4. Check for proper tightening of Gland Packing
  5. Check the healthiness of trim and seat
  6. Check for any possibility of cavitation

 

1.2.6             Soot Blower System

 

1.2.6.1             Wall Blowers

 

1.2.6.1.1.         Soot blower  valve  head does not open

  1. Check   & set the pressure setting bolt.
  2. Check  the gland tightness.
  3. Check whether   valve stem is jammed/bent.
  4. Check the valve seat  for any damages.
  5. Check the limit switches.
  6. For further service , contact

 

1.2.6.1.2.         Blower Pressure/Flow is flow/high:

 

  1. Check the pressure setting bolt
  2. Check the operation of pressure control valve at soot blower station
  3. Maintain recommended pressure

 

1.2.6.1.3.         Soot blower valve head does not close after blowing:

 

  1. Inspect the stem for any pitting/bending/damages
  2. Inspect the valve body for any dirt & clean.
  3. Inspect the valve seat for any dent/scratch. Lap the seat with disc.
  4. Check whether the spring is struck up or lost its strength.

 

1.2.6.1.4.         Blower is jammed/not operating:

 

  1.          Check the swivel tube fouling with shroud tube.
  2. Check the swivel tube /guide rods for cleanliness.
  3. Check that gland packing is not too tight .
  4. Check the swivel tube against any pitting .
  5. Check the limit switch setting.
  6. Check oil level in gear box
  7. For further service ,contact

 

 

 

1.2.6.1.5.         Motor becomes overloaded:

 

  1. Check the tightness of gland packing
  2. Check the cleanliness of swivel tube,guide rods , rack & pinion.
  3. Check oil level in gear box
  4. Check healthiness of motor/cable/MCC

 

 

1.2.6.2.         Long Retractable Soot Blowers

1.2.6.2.1.         Soot blower jamming:

 

  1. Check for any physical obstruction of travelling carriage with housing .
  2. Check for limit switch failure

.                       3.         Check the gland tightness.

  1. Check for lance tube fouling with boiler tube or wall sleeve.
  2. Check whether scrapper plate bolt is broken .
  3.          Check oil level in gear box

 

1.2.6.2.2.         Motor Overload:

 

  1. Check whethert lance tube is fouling with boiler tube or wall sleeve.
  2. Check the tightness of gland bush /gland packing.
  3. Check the setting of overload relay/MCC.
  4. Check the accumulation of dirt over the rails.
  5. Check the motor for insulation & winding .
  6. Check the cables for any damage.

 

1.2.6.2.3.         Failure of Traverse Chain:

 

  1.                        Check for any  weak links.
  2. Check whether circlips in chain links are properly available.
  3. Check that chain is not too tight

  1.2.6.2.4.       Chain is coming out of housing:

 

  1. Check & tighten the chain properly

 

1.2.6.2.5.         Grinding sound in Gearbox:

 

  1. Check the oil level & oil quality

 

1.2.6.2.6.         Vibration while operating:

 

  1. Check for any obstruction of travel carriage in housing
  2. Check for proper chain tension

 

1.2.6.2.7.         Sootblower overrun:

 

  1. Check for traverse chain failure.
  2. Check the limit switches ,timer setting.
  3. Check for any failure of contactor & contactor reverse coils.
  4. Check whether thermal overload relay for traverse motor has operated/fuses are blown and find out the causes.

 

1.2.6.2.8.         Overheating of Lance Tube:

 

  1. Check the blowing pressure & verify whether valve opening bolt is available.
  2. Check the operation of valve stem.
  3. Check the flue gas temperature for any increase.
  4. Check whether flow protection is in service

 

1.2.6.2.9.         Steam leakage through travelling carriage:

 

  1. Check the quality of packing, tightness, wear & tear of glands etc.,
  2. Check the feed pipe for any surface defects such as scratches, dents etc.

1.2.6.2.10.       Steam leakage through valve stem:

 

  1. Check the quality of packing ,tightness ,wear of packing ,
  2. Check stem for any scratches, dents etc.
  3. For further service , contact

 

1.2.6.2.11.       Valve   seat   leakage:

 

  1. Check the gland packing for proper tightness
  2. Disassemble and inspect the valve disc and valve seat for any damage /corrosion.
  3. Check whether valve opening bolt is pressing while the travelling carriage is in home position .

 

1.2.6.2.12.       Limit switch failure:

 

  1. Check the limit switch contacts for quality
  2. Check the failure of internal parts such as springs, locking notches etc.,
  3. Check the assembly /direction for correctness.
  4. Check for any accumulation of foreign material /dirt in limit switch.

 

 

1.2.7.             Superheater & Reheater Spray System:

 

1.2.7.1. Heavy passing of control valves:

 

  1. Check after proper coupling of control valve with the actuator
  2. Check for proper operation of the actuator (Pneumatic/ electrical)
  3. Check the flow measuring instruments for their healthiness
  4. Check for erosion of trim/seat
  5. Check for class rating of the control valve to compare its specified passing with the actual value.

 

1.2.7.2. Heavy Passing of Isolating valves:

 

  1. Check for disc/seat erosion in shut down
  2. Check for proper closing of valves
  3. Check for proper close limit switch/torque switch setting
  4. Check for damages of valve/actuator

 

1.2.7.3. SH/RH Spray System is not controlling the SH/RH temperature:

 

  1. Check for damaged control valve/isolating valve components
  2. Check for plugging of spray nozzles
  3. Check for heavy leakages in the spray lines/valves

 

1.2.7.4. Excessive superheater/Reheater spray:

 

  1. Check the healthiness and position of burner tilting system. Bring the tilts down
  2. Check fineness and proximate analysis of coal
  3. Check the proper functioning of spray flow meter
  4. Increase wall blowers operation frequency
  5. Reduce excess Air to the rated value
  6. Check windbox/primary air pressure
  7. Operate lower elevation mills
  8. Tune Automatic Superheater/Reheater temperature control

 

 

1.2.8.             Milling System:

  • BALL (Tube) Mills :

 

  • P. Lub Oil Temperature high:

 

  1. Check the availability of adequate cooling water
  2. Check the proper functioning of heater control on Auto Mode.
    • Lub oil temperature too low:

 

  1. Check the proper functioning of heater control
  2. Regulate cooling water properly

 

  • P.Lub oil pressure/ flow too low:

 

  1. Check for leakages in the system
  2. Check the filter element clean/replace the same at proper intervals
  3. Check/set the relief valve of the pump
  4. Regulate cooling water properly
  5. Check the NRV of the standby pump for passing

 

  • Frequent choking of filter of L.P. lub oil systems :

 

  1. Check for ingress of coal dust
  2. Maintain proper seal air to Mill DP
  3. Check the healthiness of Trunion Seals

 

  • Mill bearing temperature high :

 

  1. Check for proper oil flow to bearings
  2. Check for proper cooling water
  3. Check for any rubbing of trunion with bearing liner
  4. Check for any fouling of trunion with trunion tube.

 

  • Abnormal sound in HP lub oil pump:

 

  1. Check the functioning NRVs in HP discharge lines
  2. Ensure equal pressures of all four HP discharge lines. Check leakages wherever pressure is less.

 

  • Reducer lub oil temperature high:

 

  1. Ensure adequate cooling water flow
  2. Ensure adequate lub oil discharge pressure and flow

 

  • Lub oil leakage from main reducer seals:

 

  1. Check/replace oil seals

 

1.2.8.1.9.         Girth gear grease pressure high:

 

  1. Clean the strainer to ensure proper flow and to reduce grease before strainer
  2. Ensure proper viscosity of grease. Ensure heater is switched `ON’ wherever provided
  3. Check & service grease distributor
  4. Check and clean Nozzles.

 

1.2.8.1.10.       Girth gear grease pump pressure low/pump is not developing pressure:

 

  1. Ensure free rotation of the pump
  2. Ensure proper grease level
  3. Ensure proper viscosity of grease.

 

1.2.8.1.11.       Air pressure too low/no pressure (with gear lubrication system):

 

  1. Check spray solenoid valve for opening
  2. Check air pressure before Air filter regulator
  3. Regulate Air pressure after Air filter regulator
  4. Check proper functioning of distributor limit switch

 

1.2.8.1.12.       Failure of screw conveyor ribbons

  1. Check for foreign materials ingress prevent the same
  2. Ensure proper size of raw coal
  3. Ensure proper clearance w.r.t. trunion tube
  4. Ensure use of screw conveyor ribbons of proper material
  5. Ensure that the liners in the hot air box are properly installed and secured.

 

1.2.8.1.13.       Failure of screw conveyor bearing (plumber Block):

 

  1. Check for ingress of foreign materials and prevent them
  2. Check proper size of raw coal
  3. Prevent ingress of water with raw coal
  4. Ensure proper lubrication of bearing
  5. Ensure use proper bearing and bearing block
  6. Ensure proper seal air to mill DP to prevent coal dust ingress to bearing

 

 

1.2.8.1.14.       Faster wear out of Mill Liners:

 

  1. Ensure proper size of raw coal
  2. Ensure proper quantity of ball loading as per BHEL’s recommendations
  3. Ensure liners of proper materials are used
  4. Ensure periodic removal balls of size below 20 mm
  5. Ensure proper Bypass Air Flow.

 

1.2.8.1.15.       Pulverized coal fineness too low:

  1. Ensure proper setting of classifier
  2. Check and prevent bypassing of coal air mixture in the classifier through classifier bottom struck up/damaged flaps and reject chute.
  3. Ensure proper quantity of Bypass Air flow
  4. Ensure proper ball charge
  5. Check and replace worn out mill liners.
  6. Carryout period is segregation of balls below 20mm.
  7. Check the flap of the clack box for proper functioning

1.2.8.1.16.       Pulverized coal fineness too high

 

  1. Ensure proper setting of classifier
  2. Optimise ball loading
  3. Ensure proper air flow through mill and bypass air flow
  4. Check for partial choking of classifier

 

  • Reduction in Mill output :

 

  1. Ensure optimum ball charge
  2. Segregate lower size ball (below 20mm) periodically
  3. Maintain proper Air flow
  4. Maintain proper mill outlet temperature
  5. Check the healthiness of screw conveyors
  6. Ensure proper raw coal size and quality
  7. Check classifier setting

 

1.2.8.1.18        Mill level control (DP) is not working in Auto mode:

 

  1. Ensure tapping points are cleaned by proper purging and blowdown
  2. While starting the mill raise the mill level (DP) to 40-50mm by increasing the feeder speed. Put the Mill level on Auto mode only after raising the mill level to 40-50mm.
  3. Maintain proper Air Flow, Mill outlet temperature
  4. Optimise ball charge

 

1.2.8.1.19        Prevention of Mill explosions/PUFFS:

 

  1. Be alert during start up and shut downs
  2. Avoid single end operation of Mill for longer duration
  3. Follow purging cycle during start up and shut down without fail
  4. DO NOT RUN THE MILL FOR MORE THAN TEN/FIFTEEN MINUTES WITHOUT RUNNING OF FEEDER. ALWAYS ENSURE AVAILABILITY OF COAL IN THE MILL DURING MILL OPERATION
  5. Before stopping the mill, reduce the classifier outlet temperature below 55 Deg.C.
  6. With coal inside the mill, keep the mill on barring to the extent possible except during maintenance period.
  7. Check coal characteristics like volatile matter etc. periodically
  8. It is preferable to monitor CO at classifier outlet
  9. Maintain classifier outlet temperature between 70 Deg.C.to 80 Deg.C.
  10. Check classifier, reject chute, and clack box periodically for accumulation of debris. Ensure the flaps of classifier bottom and the clack box are healthy
  11. Prevent entry/accumulation of water into the mill along with coal. Prevent entry of Rain water into Raw Coal bunker
  12. Check for coal accumulation in Mill inlet ducts
  13. Check for screw conveyor rotation periodically
  14. In case of coal lump formation inside the mill (due to water entry), utmost care to be taken in clearing it. If it is not getting cleared during operation of the mill, it is preferably to stop the mill and clear it manually, OFF line.
  15. In case of explosion/PUFF in the mill, stop the coal feeding, Stop air entry and bring the mill on barring gear. Start the steam inerting, if needed by giving manual command, utilise other fire fighting resources like water & CO2.  Inspect the mill and the connected system thoroughly and rectify the damages before restarting the mill.
  16. Maintain proper flow throughout mill operation
  17. NEVER OPERATE MILL WITH BUNKER LEVEL BELOW 20%.

 

 

1.2.8.1.20.       Fire in the Mill and the connected system:

 

  1. Fires can take place due to accumulation of coal in reject chute, classifier, Mill inlet duct, Hot air box, feeder etc.
  2. In case fire is detected, authorised person has to decided whether preventive action is to be taken while millis in operation or OFF line.
  3. Prevent accumulation of coal in the above mentioned areas
  4. Inspect and clear classifier, reject chute, clack box, mill inlet ducts, feeder, Hot air box, feeder etc. periodically
  5. Check the healthiness of screw conveyor periodically
  6. Avoid single end operation of mill
  7. Keep the mill on barring gear, especially when mill is hot
  8. Prevent entry and accumulation of water into the mill
  9. Check liners and ball charge periodically
  10. Check the healthiness of instrumentation like mill leve, noise level, pressure/temperature/flow instruments etc.
  11. Maintain proper mill level
  12. Check the operation of screw conveyor periodically
  13. Ensure non-accumulation of coal in coal piping

 

1.2.8.1.21.       Prevention of Explosions in coal pipe:

 

  1. Follow purging cycle, without fail, during starting/stopping of mill
  2. Check whether the manual damper in the common purge air duct is opened adequately. Ensure proper locking of the damper
  3. Check the operation of purge air dampers periodically (ON Line/OFF line)
  4. Check periodically that coal flow is taking place through coal pipes by feeling the pipe temperature, manually.
  5. Carryout clean air flow test, hot traverse periodically
  6. Check coal fineness periodically
  7. Maintain proper air flow, through mill and bypass air flow

 

1.2.8.1.22.       Coal flow distributions is unequal in all four coal pipes

 

  1. Check for plugging of any coal pipes
  2. Check that mill outlet gate of all four corners are full open.
  3. Carryout clean air flow test/hot traverse to check the air flow
  4. Correct/replace the orifices of the coal pipes if needed

 

1.2.8.1.23.       Noise level not showing properly and not conforming to Mill level:

 

  1. Check the location of the Microphone Relocate it, if necessary, as per BHEL’s instructions.
  2. Segregate the balls and take out balls of size below 20mm
  3. Recalibrate the Noise level (100%) with full ball charge and with mill without any coal. This can be done after segregation of undersize balls and recharging the required quantity of balls.
  4. Replace/repair the fault electronic cards of the noise level instrument.

 

1.2.8.1.24.       Too low/too high classifier outlet temperature:

 

  1. Check for ingress of water alongwith the coal
  2. Check and optimise mill temperature control
  3. Maintain proper mill level. Check for coal accumulation in mill, hot air box, screw conveyor area, mill inlet duct etc.
  4. Optimise distribution of air through mill and bypass duct
  5. Check for accumulation of coal/debris in classifier, reject chute and clack box
  6. Check for bypassing of coal air mixture through classifier & reject chute
  7. Maintain optimum hot air temperature and pressure

 

1.2.8.1.25.       Tube mill choking:

 

  1. Check for malfunctioning of mill level/noise level instruments
  2. Check for choking of classifiers
  3. Check for excessive coal feeding from feeders into the mill
  4. Check for water ingress into mill
  5. Maintain adequate air flow through mill
  6. Maintain adequate mill outlet temperature

1.2.8.2. Bowl Mills:

 

  • Abnormal Noise/vibration in Separator Body.

 

  1. Check for ingress of foreign material in the Mill
  2. Check for roller touching the bowl.
  3. Check for Bowl assembly touching the stationary parts.
  4. Check for proper compression of springs
  5. Check for Journal spring assembly bearing failure
  6. Check for increase of feeder speed to increase the coal flow to the Mill
  7. Check for loosening of separator body bolts
  8. Check the correctness of bull ring segments
  9. Check the bull-ring segments for excessive wear

 

  • Abnormal Noise in Mill side :

 

  1. Check for touching of scrapper with stationary parts
  2. Check for skirt assembly touching the mill bottom
  3. Check for breakage of scrapper assembly
  4. Check for presence of foreign material under scrapper
  5. Check for accumulation of coal in pyrite hopper and mill side

 

  • Abnormal Noise in Mill Base :

 

  1. Check for worm shaft bearing failure
  2. Check for improper surface contact of some teeth of worm wheel and worm shaft
  3. Interference of pump hub with bushing
  4. Check for worn out/dry coupling
  5. Check for failure of vertical shaft bearings
  6. Check for temperature rise of any bearing
  7. Check for lubrication of upper vertical shaft bearing

 

  • Overflow of oil from Mill Base/pressurisation of Mill base.

 

  1. Check for Air leakage through Dust guard/Mechanical face seal into gear box
  2. Check for damages of mechanical face seal/Dust Guard Seal
  3. Check for opening of upper bearing cover
  4. Check for oil cooler tube puncture
  5. Check for excess oil level in mill base

 

  • Hot Air dust leakage from cored holes of mill base :

 

  1. Check mechanical face seal/dust guard seal

 

  • No return oil from vertical shaft upper radial bearing (Internal Lubrication Mill)

 

  1. Check for plugging of vertical shaft hole
  2. Check for plugging/breakage of return oil line
  3. Check the clearance between the pump and the hub
  4. Check for plugging of holes in the lower bearing housing

 

  • Oil leakage from worm shaft packing gland

 

  1. Check for improper/damaged gland packing
  2. Air vent pipe of Mill base closed/plugged

 

  • Oil leakage from cored holes of Mill base :

 

  1. Check for puncture of oil cooler tubes.

2.              Check for breakage/leakage of return oil line

  1. Check for vertical shaft oil seal in upper bearing housing

 

 

 

  • Oil leakage from flanges :

 

  1. Check for damage of gasket or use of improper gasket
  2. Check for loose/missing bolts
  3. Use of proper sealing after proper cleaning of the making surfaces

 

  • Mill Base Oil Temp High :

 

  1. Check for choking of oil cooler pipes
  2. Check whether cooling water is charged with adequate pressure
  3. Check for proper oil level
  4. Check the quality of the oil. Check mechanical impurities and moisture in oil
  5. Check the matching of worm and worm gear
  6. Check for worn out damaged bearings

 

  • Mill Coal Spillage high :

 

  1. Check for healthiness of rolls and then clearance with respect to Bowl
  2. Check the wear out of Bull Ring segment, Bull Ring segment, worm wheel, Bowl extension ring etc.
  3. Check for the Jammed rolls
  4. Maintain proper air flow
  5. Check for water ingress along with coal
  6. Check for pyrites along with coal
  7. Check for damaged vane wheel assembly
  8. Check the clearances between vane wheel w.r.t. separator body
  9. Avoid over-loading of Mill
  10. Maintain proper Mill outlet temperature
  11. Reset Ring roll clearance, Journal head and Pr Spring seat clearance
  12. Check Journal spring compression
  13. Check the setting of the classifier

 

  • Non uniform spring deflection :

 

  1. Check unequal spring compression
  2. Check for unequal roll wear
  3. Check for improper ring-roll clearance

 

  • Mill base oil contamination:

 

  1. Check Dust Guard and Mechanical Face seal
  2. Check the oil seal of upper bearing housing

 

1.2.8.2.14.       Low pulveriser Fuel Fineness:

 

  1. Check setting of classifier
  2. Check alignment of classifier vane
  3. Check for puncture/plugging of classifier cone
  4. Check for wear out of Roller and Bull Ring segments etc.
  5. Check Ring Roll clearance
  6. Maintain proper air flow and mill outlet temperature
  7. Check for air bypassing of separator body liner
  8. Check for journal spring compression

 

1.2.8.2.15.       High Pulveriser Fuel Fineness

 

  1. Check for journal spring compression
  2. Check setting of classifier
  3. Recheck sampling technique

 

  • Mill Fires :

 

  1. Choking of Mill with coal
  2. Filling of pyrite hopper and mill bottom with coal
  3. Spill over of coal to mill inlet air duct
  4. Maintain proper air flow
  5. Check for improper classifier settings
  6. Check for excessive ingress of water along with coal leading to improper grinding
  7. Check for wear-out of parts.
  8. Check for closure of MDV and plugging of coal piping
  9. Check for quality (high volatile matter) of coal
  10. Maintain proper mill outlet temperature

 

  • Vertical shaft failure :

 

  1. Check for the equal spring compression
  2. Do not use roller with unequal wears
  3. Check for breakage of one of the spring
  4. Check for entry of heavy foreign material in the mill
  5. Check for improper locking of spring assembly
  6. Check for improper ring roll clearance
  7. Check for jamming of rolls
  8. Check for jamming of Trunion Bushing

 

  • Low Mill output :

 

  1. Check for low quality of coal
  2. Check for high moisture in coal
  3. Check and set classifier setting
  4. Check spring compression
  5. Maintain proper air flow and mill outlet temperature
  6. Check ring roll clearances
  7. Check for worn out parts
  8. Check plugging of coal pipe and closure of one or more mill discharge valves.

 

  • Mill Discharge valve not operating :

 

  1. Check the clearance between top and the body
  2. Check the seals of the power cylinder
  3. Check for proper compressed air pressure
  4. Arrest leakages in compressed air tubing
  5. Check the operation of solenoid valve and the control system

 

  • Classifier vane not operating

 

  1. Check the clearances between classifier vanes and separator
  2. Check the classifier vane shaft straightness
  3. Check uniformity in the length of the link lever
  4. Check for damage to bearings and oil seals

 

  • Oil leakage from journal assembly

 

  1. Check for damage of oil seal (O ring)
  2. Check for damage for upper journal assembly lip seal
  3. Check for damaged journal shaft (seating area of oil seal)

 

  • Journal Oil Contamination :

 

  1. Check for quality of oil
  2. Check for damaged seals
  3. Check for damage of bearings
  4. Check oil level
  5. Check for oil filling cap missing/loosening

 

  • Spring Adjusting Stud failure

 

  1. Check for entry of heavy foreign material in Mill
  2. Check spring compression
  3. Check ball bearing failure

 

  • Mill bottom cracking :

 

  1. Check for inadequate clearance between skirt and mill bottom
  2. Check for warpage of skirt causing rubbing
  3. Check for Mill fires and inadequate insulation

 

  • Bull Ring segment Crack :

 

  1. Check for improper surface contact between bull ring and bowl
  2. Check for heavy foreign material ingress in mill
  3. Check for excessive wear of bull ring
  4. Check for any mill fires
  5. Check for material quality

 

  • Worm shaft bearing failure :

 

  1. Check the quality of oil and replace the oil id needed
  2. Check the quality of the bearings
  3. Check the bearing housing damage
  4. Check for improper installation methods
  5. Check for excessive backlash in worm gear
  6. Check for improper matching of worm and worm gears
  7. Check for damage of thrust bearing spring

 

  • Vertical Shaft Gear Lub lock nut failure

 

  1. Check for failed worm shaft bearings
  2. Check for proper matching of worm shaft and worm gear
  3. Check for damaged bearings
    • Insulation cover plate warpage :

 

  1. Check for damage to cover plate due to fire
  2. Check for improper expansion clearances between segments of cover plate
  3. Check the quality of the cover plate material

 

  • Roller Assembly Slipping into Mill :

 

  1. Check for keeper plate screw failure
  2. Check for journal shaft Pin/Lock nut failure
  3. Check for improper lubrication

 

  • Frequent Oil Filter choking :

 

  1. Check mechanical face seal
  2. Check that proper filter is used
  3. Check the quality of the oil (mechanical impurities)

 

 

1.2.9.             Burner tilting system :

 

  • Burner tilts fail to operate

 

  1. Check for adequate compressed air pressure and also clean air filter.
  2. Check that compressed air is free of moisture & mechanical impurities
  3. Arrest leaks in compressed air tubing and also signal air tubing
  4. Check for synchronised installation of the sections of each corner burner tilting mechanism
  5. Check for failed shear pins
  6. Check for distorted coal and air buckets (tips) in shut down
  7. Check for fouling of coal, air nozzles in shut down
  8. Check for damaged oil gun/flame scanner assemblies in shut down
  9. Check for centering and proper clearances of coal nozzles and buckets in shut down
  10. Check for damages of linkage mechanism during shut down
  11. Check for proper alignment of power cylinder with burner tilting mechanism
  12. Do not exceed design firing rate per elevation
  13. Lubricate in pins of linkages and coal/air buckets during overhaul
  14. Check the connected control system

 

  • Breaking of shear pins of one or more sections :

 

  1. Check for jamming/distortion of linkage mechanism
  2. Check for fouling of buckets with each other and also with stationary parts.
  3. Check for fouling of coal buckets (tips) with nozzles
  4. Check for centering of coal nozzles w.r.t. coal buckets.
  5. Check for distortion/overheating of coal buckets/nozzles
  6. Check for erosion of coal nozzles/buckets
  7. Check for free movement of coal/air buckets
  8. Check for proper clearances of linkages, coal/air buckets (tips)

 

1.2.9.3. Erosion of coal nozzles/buckets/burner panels

 

  1. Check for proper velocities of coal/air mixture. Carryout clean air flow test/hot traverse
  2. Check the erosion properties of coal
  3. Carry out hard facing of coal nozzles/buckets/burner panels etc. in consultation with BHEL

 

1.2.10.           Coal Piping:

 

1.2.10.1.          Unequal flow through four pipes of any elevations:

 

  1. Check for full opening of mill outlet gates
  2. Check for full opening of isolating gates at burner inlet
  3. Check for coal deposits in coal pipes
  4. Ensure purging of all four pipes during every start up and shut down of mills
  5. Check for proper closing of purge air dampers (for tube mills) during mill operation
  6. Check for erosion of orifices in coal pipes. Replace them
  7. Carry out clean air flow test and ensure that variation in flow through four coal pipes is within limits

 

  • Explosions in coal pipes (for tube mills) :

 

  1. Ensure proper PA flow through coal pipes to avoid setting of coal dust in coal pipes
  2. Ensure purging of all four pipes with adequate PA flow during every start up and shut down of mills
  3. Maintain adequate mill outlet temperature

 

 

  • Oil/Gas Firing system :

 

  • Oil firing system :

 

  • LDO/HFO (LSHS) pump is not developing adequate pressure :

 

  1. Check for proper line up of the system i.e. the required valves are open.
  2. Check whether strainers are clean
  3. Check for adequate level in LDO/HFO tank
  4. Check for proper setting of pumps relief valve
  5. Check for optimum opening of pressure control valve and proper functioning on auto
  6. Check for proper functioning of team tracing / electrical heat tracing for HFO system
  7. Check for adequate temperature for HFO system
  8. Check for any air pockets in the system. Vent out air from filter vents
  9. Check for DP across filter
  10. Check for water contamination in HFO system
  11. Check for mechanical impurities in HFO system
  12. Check for solidification/choking of oil in the lines

 

1.2.11.1.2.       HFO(LSHS) circulation from FOPH to boiler and back not getting established:

 

  1. Check for correct line up of the system through short/long recirculation
  2. Check for correct pump discharge pressure (refer 1.2.11.1.1.)
  3. Check for proper functioning of steam tracing/electrical heat tracing along with the lines
  4. Check for DP across all filters in the circuit. Clean filters if required
  5. Check for air locking in system. Vent out entrapped air
  6. Check for correct temperature of oil at pump suction and heaters outlet
  7. Check for any solidification in the lines (for LSHS).

 

1.2.11.1.3.       Oil gun not proving:

  1. Check for gun choking
  2. Check for HEA ignitor spark
  3. Check for correct position of HEA spark
  4. Check for healthiness of flame scanners
  5. Check for correct pressure of atomizing medium
  6. Check for correct pressure of LDO/HFO/LSHS
  7. Check for correct temperature of HFO/LSHS
  8. Check for correct secondary air flow
  9. Check Wind box pressure and furnace draft
  10. Check for proper line up for oil guns w.r.t. manual isolating valves and local gun maintenance switch
  11. Check the permissives for oil gun are available.
  12. Check for proper functioning of FSSS system

1.2.11.2.       Gas Firing system :

 

  • Gas burner not proving :

 

  1. Check for correct gas pressure
  2. Check for proper functioning of igniter
  3. Check for proper functioning of scanner
  4. Check for proper functioning of FSSS circuits
  5. Check for correct secondary air flow
  6. Check for proper functioning of secondary air dampers

 

 

1.2.12.           ROTARY AIR PREHEATERS:

 

1.2.12.1.          Excessive Air leakage from Air side (Primary/Secondary) to Flue Gas side

 

  1. Inspect all seals (Radial/leaf/Axial/static)
  2. Adjust the seal gaps as specified
  3. Replace the damaged/distorted seals
  4. Check O2 % in Fluegas at Air preheater outlet

 

1.2.12.2.          Excessive Noise/Vibrations from Air Preheater

  1. Check seal gaps which may be too less
  2. Check whether secondary/primary Air side dampers are open
  3. Check whether Air preheater is in bottled up condition
  4. Check for foreign objects over rotor
  5. Check for bad bearings
  6. Check whether there is water/Mechanical Impurities in lub oil of bearings.
  7. Check for any loosening of seals
  8. Check the main drive and the pin rack alignment.
  9. Check for low lub oil level in bearings

1.2.12.3.          Rotor does not turn:

 

  1. Check the Drive unit
  2. Check the oil level in Hydraulic coupling. Also check for blown fuse of hydraulic coupling.
  3. Check for foreign objects on rotor
  4. Check for bearing damages
  5. Check whether the drive pinion fell down from its position
  6. Check Electrical system/Air motor problems
  7. Check for excessive ash accumulation over the rotor

 

1.2.12.4.          Drive Unit overheats:

 

  1. Check lubrication in drive unit
  2. Check for bad seals/rubbing seals
  3. Check for drive pinion/pin rack rubbing
  4. Check for foreign objects/Ash accumulation over rotor
  5. Check the condition of bearings
  6. Check for expansion problems
  7. Check for low lub oil level in bearings

 

 

1.2.12.5.          Support bearings/Guide bearing lub oil temperature too high:

 

  1. Check the quality of lub oil. Check for water/mechanical impurities in lub oil.
  2. Ensure cooling water availability to lub oil coolers
  3. Check whether lub oil pumps not operating/pumps not developing pressure leading to no lub oil circulation
  4. Check for excess hot air leakage around the bearings. Arrest the hot air leakage
  5. Check for damaged bearings

 

 

1.2.12.6.          Lub oil Foamy:

 

  1. Check for Air entry into lub oil system on the suction side of the pumps
  2. Check for the quality of oil. Replace lub oil if necessary

 

1.2.12.7.          Excessive pressure drop across Air Preheater:

 

  1. Excessive Ash accumulation (which is normally wet) over the heating elements.
  2. Oil/Ash deposits in heating elements, particularly cold end/middle basket.
  3. Operate the soot blower (if necessary continuously)
  4. Water wash OFF line, if soot blower is not effective
  5. If water washing is not effective, take out the heating elements and clean them
  6. Check for damaged/eroded heating elements

 

1.2.12.8.          Fluctuations in Main drive Ammeter current:

 

  1. Check & adjust seal gaps
  2. Replace damaged/distorted seals
  3. Check the bearings for damages
  4. Check whether there is water mechanical impurities in lub oil

 

1.2.12.9.          Abnormal increase in Air/Flue gas temperatures or in temperatures detected by Fire Sensing Scanners

 

  1. Check for possibility of fires inside the air preheater
  2. In case of fire, stop the boiler and isolate the air preheater. Stop all fans.
  3. Quench the fire using large quantities of water. Do not use CO2 Foam/steam.
  4. Refer `Air preheaters fires’ Section of O&M manual

 

1.2.12.10.        Increase in gas outlet temperature and steady fall in Air preheater outlet temperature.

 

  1. Check for dampers position. One or more dampers might have closed.
  2. Check for rotor rotation. Check for rotor stoppage alarms.
  3. Isolate the Air preheater in case rotation stopped

 

1.2.12.11.        Excessive pressure build up/No pressure build up of lub oil pumps:

 

  1. Check for filter choking. Clean/replace the filter
  2. Check for closed valves. Line up the system properly
  3. Check for damaged lub oil pump
  4. Check for availability of lub oil in the bearing
  5. Check for quality of lub oil

 

1.2.12.12.        Erosion of PIN RACK:

 

  1. Check Air leaks/flue gas leaks over the pin rack. Arrest the leakages
  2. Replace the damaged pin rack

 

 

  • Erosion of connecting plate components in the flue gas path :

 

  1. Contact BHEL for advice/service for hard facing/providing shields to prevent erosion.

 

  • Jamming of Air Motor :

 

  1. Check for lub oil level/quality of lub oil
  2. Dismantle and service the air motor
  3. Replace the damaged components
  4. Ensure the working of the lubricator/filter in the compressed air line

 

  • Melting of thermal plug and draining of oil from Fluid coupling :
  1. Check for free rotation of Main drive and the rotor.
  2. Replace the thermal plug and maintain proper oil level.

1.2.12.16.        Heavy ash accumulation over rotor, on flue gas side

 

  1. Check for tube leakages in second pass, which leads to wetting/ accumulation of ash
  2. Check for plugging of hopper below economiser
  3. Check for fouled air preheater elements

 

1.2.12.17.        Oil deposits in heating elements, especially in cold end baskets:

 

  1. Check the combustion of oil guns
  2. Check the operation of soot blower
  3. Check the water washing system and its nozzles. Water wash the elements when flue gs temperature is below 100 Deg.C. after stopping the boiler.
  4. In case of heavy choking, take out the elements and clean

 

1.2.12.18.        Soot blower not functioning:

 

  1. Check and trouble shoot electrical/mechanical problems
  2. Check whether swivel tube got free from the gear box
  3. Check the alignment of swivel tube
  4. Replace the damages parts
  5. Operate the soot blower atleast once in eight hours

 

 

1.2.13.           FD, PA & ID Fans:

1.2.13.1.          FD Fan (Axial Reaction Type with Blade Pitch Control):

 

1.2.13.1.1.       High Vibrations:

 

  1. Check the looseness of bearing pedestal bolts, impeller hub bolts, blades fixing bolts, coupling bolts etc.
  2. Check proper seating of lub on shaft flange
  3. Check whether any balance weights of the blades fell down
  4. Check whether the blades are installed serially as per the punch marks and of the same series.
  5. Check whether there are deposits over the impeller, over the blades, etc.
  6. Check the alignement with motor
  7. Check for any abnormal sound from the bearings of Fan and Motor
  8. Check for any temperature rise of the bearings.
  9. Carryout vibration analysis to pinpoint possible reason.
  10. In case it is unbalance, carry out balancing to correct the vibrations

 

1.2.13.1.2.       Unquite running:

 

  1. Check for any deposits on impeller, rotor etc.
  2. Check bearing clearances/bearings healthiness
  3. Check for touching rotating parts with the stationary parts. Check the clearances.
  4. Check the impeller clearances w.r.t. casing and correct

 

1.2.13.1.3.       High bearing temperatures of bearings of Fan/Motor:

 

  1. Check that lubrication is proper. Check oil level, flow, pressure etc.
  2. Check the functioning of lub oil system and cooler.
  3. Check the quality of oil and impurities in oil (Moisture/mechanical impurities)
  4. Check for bearing damages
  5. Check alingment

 

1.2.13.1.4.       Fan attains fall-load immediately after starting/no control on Fan output:

 

  1. Check whether impeller blades are in full open position
  2. Check whether servomotor got free from the actuator. If so, reconnect and set the operation of blades with the actuator.
  3. Check the setting of servomotor w.r.t. actuator. If found disturbed, reset it.

 

1.2.13.1.5.       Blade pitch control inoperative:

 

  1. Check the actuator and the connected control system
  2. Check whether control oil pressure is adequate
  3. Check whether servomotor is operative
  4. Check whether blades are jammed

 

1.2.13.1.6.     Control Oil leakage from Servomotor:

 

  1. Check the servomotor and replace the damaged seals

 

1.2.13.1.7.       Two Fans operating in parallel do not absorb same power:

 

  1. Check the setting of servomotors of the fans and correct
  2. Check the control systems and ensure the blade pitch controls operation is in Unison

 

1.2.13.1.8.     Large pressure fluctuations in control oil pressure:

 

  1. Check that the speed of the actuator is matching with that of servomotor
  2. Check the position of manual recirculation valve
  3. Check the setting of pressure relief valve
  4. Check for leakages in the servomotor and control oil system
  5. Check the N2 pressure in accumulator

 

1.2.13.1.9.       Frequent drop in oil level in the tank:

 

  1. Check the leaks in lub oil system
  2. Check the leakages in control oil system
  3. Check for damaged seals of bearing housing
  4. Check the damage of seals of servomotor
  5. Check the cooler for any leakages

1.2.13.1.10.     Water Contamination in lub oil:

 

  1. Check the cooler for any lube leakages, by HT Rectify the leaking tubes

 

1.2.13.1.11.     Drop in oil pressure:

 

  1. Check the filter elements
  2. Check for leakages in lub oil/control oil system
  3. Check the operation/setting of recirculation valve/pressure relief valves
  4. Check the lub oil pressure control valve
  5. For further service/advice contact………

 

 

1.2.13.2.       PA Fans:

 

1.2.13.2.1.     PA Fans (Axial Reaction Type with Blade Pitch Control)

 

1.2.13.2.1.       High Vibrations:

 

  1. Check the looseness of bearing pedestal bolts, impeller hub bolts, blades fixing bolts, coupling bolts etc.
  2. Check proper seating of hub on shaft flange
  3. Check whether any balance weights of the blades fell down
  4. Check whether the blades are installed serially as per the punch marks and of the same series.
  5. Check whether there are deposits over the impeller, over the blades, etc.

15.           Check the alignement with motor

  1. Check for any abnormal sound from the bearings of Fan and Motor
  2. Check for any temperature rise of the bearings.
  3. Carryout vibration analysis to pinpoint possible reason.
  4. In case it is unbalance, carry out balancing to correct the vibrations

1.2.13.2.2.       Unquiet running:

 

  1. Check for any deposits on impeller, rotor etc.
  2. Check bearing clearances/bearings healthiness
  3. Check for touching rotating parts with the stationary parts.
  4. Check the clearances.
  5. Check the impeller clearances w.r.t. casing and correct

 

1.2.13.2.3.       High bearing temperatures of bearings of Fan/Motor:

 

  1. Check that lubrication is proper. Check oil level, flow, pressure etc.
  2. Check the functioning of lub oil system and cooler.
  3. Check the quality of oil and impurities in oil (Moisture/mechanical impurities)
  4. Check for bearing damages

5.       Check alingment

 

1.2.13.2.4.       Fan attains fall-load immediately after starting/no control on Fan output:

 

  1. Check whether impeller blades are in full open position
  2. Check whether servomotor got free from the actuator. If so, reconnect and set the operation of blades with the actuator.
  3. Check the setting of servomotor w.r.t. actuator. If found disturbed reset it.

 

1.2.13.2.5.       Blade pitch control inoperative:

 

  1. Check the actuator and the connected control system
  2. Check whether control oil pressure is adequate
  3. Check whether servomotor is operative
  4. Check whether blades are jammed

 

1.2.13.2.6.     Control Oil leakage from Servomotor:

  1. Check the servomotor and replace the damaged seals

1.2.13.2.7.     Two Fans operating in parallel do not absorb same power:

 

  1. Check the setting of servomotors of the fans and correct
  2. Check the control systems and ensure the blade pitch controls operation is in Unison

 

1.2.13.2.8.     Large pressure fluctuations in control oil pressure:

 

  1. Check that the speed of the actuator is matching with that of servomotor
  2. Check the position of manual recirculation valve
  3. Check the setting of Relief valve
  4. Check for leakages in the servomotor and control oil system
  5. Check the N2 pressure in accumulator

 

1.2.13.2.9.       Frequent drop in oil level in the tank:

 

  1. Check the leaks in lub oil system
  2. Check the leakages in control oil system
  3. Check for damaged seals of bearing housing
  4. Check the damage of seals of servomotor
  5. Check the cooler for any leakages

 

1.2.13.2.10.     Water Contamination in lub oil:

 

  1. Check the cooler for any lube leakages, by HT Rectify the leaking tubes

 

1.2.13.2.11.     Drop in oil pressure:

 

  1. Check the filter elements
  2. Check for leakages in lub oil/control oil system
  3. Check the operation/setting of recirculation valve/pressure relief valves
  4. Check the lub oil pressure control valve

 

1.2.13.3.          ID Fans ( Radial Fans – NDZV Type) :

 

  • High Vibrations :

 

  1. Check for any looseness of bearing pedestal bolts, impeller hub bolts, coupling bolts etc.
  1. Check for deposits over the impeller
  2. Check for uneven erosion of the impeller
  3. Check the alignment with the motor
  4. Check for the clearances between rotating and stationary parts and correct
  5. Check the bearings for any damages. Check the bearing clearances
  6. Check for any temperature rise of bearings
  7. Carry out vibration analysis to pin-point possible cause
  8. In case of unbalance, carryout balancing to correct the vibrations

 

1.2.13.3.2.     High bearings temperatures of the bearings of Fan & Motor:

 

  1. Check the correctness of lubrication. Check oil level, flow, pressure etc.
  2. Check the functioning of lub oil system and cooling water system
  3. Check the quality and impurities in oil (moisutre/mech impurities)
  4. Check for bearing damages and clearances
  5. Check alignement
  6. Check for any mechanical rubbing

 

1.2.13.3.3.       Fans could not be loaded:

 

  1. IGV inoperative
  2. VFD/Scoop tube inoperative
  3. Check inlet/outlet gate
  4. Check other gates/dampers of the gas path

 

  • Frequent drop in oil level in the tank :

 

  1. Check the leakages of the lub oil system
  1. Check the damaged seals of the bearing housing
  2. Check the cooler for any leakages
  3. For further service/advice contact………

 

1.2.13.3.5.     Water Contamination in lub oil:

 

  1. Check the cooler of the lub oil system for any leakages
  2. Check for water leakages in the Fan bearings, lub oil tank

 

1.2.13.3.6.       Drop in oil pressure:

 

  1. Check filter elements clean/replace
  2. Check the operation/setting of the recirculation valve/ pressure relief valves

 

 

1.2.14.           Electrostatic Precipitator:

 

  • Field Trips on Undervoltage:

 

  1. Check electronic controller/High voltage rectifier transformer for Rated Voltage build up on no load
  2. Check the functioning of the Ash disposal system
  3. Check the functioning of collecting & Emitting rapping mechanism
  4. Check for cracks in support, bushing insulator
  5. Check for cracked shaft insulator in shut down
  6. Check for shorting in the field like snapped loose wire in shut down
  7. Check for overfilled hoppers and distorted emitting system in shut down
  8. Check for any bent collecting electrodes in shut down

 

  • Rapping Motor Trips on Overload :

 

  1. Check for IR value and winding resistance of motor
  2. Check for functioning of Motor & Gearbox after decoupling
  3. Check for alignment of Gearbox with rapping system
  4. Check the rapping shaft alignment during shut down
  5. Check for dislocation of internals
  6. Check for over-filled hoppers
  7. Check for blown fuses, overload relay healthiness in MCC

 

  • Heaters are not operating :

 

  1. Check for any blown fuse
  2. Check for terminals in MCC/Field JBS for any burnout
  3. Check for any short circuit in heating elements/cables
  4. For further service/advice contact…..

 

  • Excessive sparking/flash over in fields :

 

  1. Check for S&T settings in the Electronic Controller and adjust, if needed
  2. Check for excessive current settings
  3. Check for any loose connections at transformer HT side, including disconnecting switch.
  4. Check for snapped emitting electrodes and collecting to emitting electrodes gaps in shut down
  5. Check the functioning of rapping system
  6. Check the functioning of ash disposal system and overfilled hoppers.

 

  • High Stack Emission :

 

  1. Check for proper rapping frequency
  2. Check for proper current settings
  3. Check for high flue gas temperature
  4. Check for proper gas flow distribution in the pass during shut down
  5. Check for eroded guide vanes/splitters during shut down
  6. Check for proper fixing of defector plates of hoppers during shutdown
  7. Check for proper functioning of ash handling sysgtem
  8. Check for proper fixing of screen plates during shut down
  9. Check for proper closure of manhole doors, inspection doors etc. to prevent air ingress.

 

 

1.2.15.           Water Chemistry:

 

1.2.15.1.          Phosphate dozing is ineffective in PH control of boiler water:

 

  1. Check the Boiler pressure
  2. Check for phosphate hideout beyond boiler pressure of 180 Kg/Cm2.
  3. Resort to all volatile treatment, taking all precautions

 

1.2.15.2.          Phosphate dozing is not reaching drum water:

 

  1. Check the healthiness of pumps
  2. Check for plugging of piping
  3. Check for proper setting of relief valves.
  4. Check for plugging of nozzles inside the drum
  5. Check for passing of NRV of standby pump.
  6. Check the quality of phosphate

 

1.2.15.3.          Scales/rust formation over water walls/superheater tubes.

 

  1. Check for improper water chemistry regime/Improper dozing over a length of time.
  2. Check the operation of DM plant and quality of DM water
  3. Contact BHEL for remedial actions like chemical cleaning etc

 

1.2.15.4.          Feed Water/Condensate PH/Conductivity could not be maintained:

 

  1. Check the quality of Ammonia/Hydrazine
  2. Check for healthiness of pumps and ensure pump is developing adequate pressure
  3. Check for possibility of leakage condenser tubes.

 

 

  • HP Bypass (Sulzer make)

 

  • Oil Supply Unit :

 

1.2.16.1.1.       Pump fails to start:

 

  • Ensure that `start’ command is issued from the panel. Reset alarms on Control desk.
  • Check MCC and LPB status
  • Check healthiness of motor and switch gear

 

1.2.16.1.2.       Pump fails to develop pressure:

 

  • Check for any leakage
  • Check oil level in the tank
  • Conform that the vents are all tightly close
  • Prime the pump (vent air)

 

1.2.16.1.3.       Alarm `Switch Failure’ appears

 

  • Check and if needed readjust the pressure settings.

 

 

1.2.16.1.4.       Alarm `pump over run’ appears

 

  1. This happens if `low pressure’ alarm does not reset even after 10 minutes of pump running or if the pump continues to run beyond 10 minutes.
  2. Check that the pump actually runs and develops pressure.
  3.                      Check the N2 pressure of accumulator
  4. Check the healthiness of bladder of accumulator.
  5. Check the pressure switch settings and wiring.
  6. Check for heavy leaks.

 

1.2.16.1.5.       Alarm `pr very low’ or `pr very high’ appears

 

  • Check the actual pressure achieved
  • Check the pressure switches settings and wiring

 

1.2.16.1.6.       Pump discharge is OK but operating pressure is low:

 

  • Check for loose connections or leakage in the line
  • Check and if needed service the PRV
  • Adjust the pressure reducing valve

 

 

1.2.16.1.7.       Oil Pressure drops very fast/pump takes frequent starts

 

  • Check the nitrogen pressure in accumulator
  • Check for damaged bladder of the accumulator
  • Check for leakage in the system
  • Confirm that the air vents are closed.

 

 

 

1.2.16.2.       Servo Units:

 

1.2.16.2.1.       Valve fails to operate:

 

  • Check drive card outputs i.e. 48V to blocking unit and +/- 10 to 15V to servo.
  • Check tightness of connections to the servos
  • Check the healthiness of the coils after switching off the drive card
  • If these are OK the problem is in the hydraulic elements. Ensure proper oil supply to the valve and the position of the throttle valve in drain.
  • Check the valve operation from manual hydraulic lever
  • Check the filters and replace if needed

 

1.2.16.2.2.       Valve operates in one direction only:

 

  • Check the operation from local
  • Check the filters inside the servos
  • Confirm proper drift adjustment of the coil
  • Check proper functioning of the electronic system (open/close) commands, correct voltages, interlocks etc)

 

1.2.16.2.3.       Valve operation very slow/very fast

 

  • Check the filters
  • Adjust the speed adjusting valve in the return line

 

 

1.3.                 Controls & Insatrumentation (Boiler & Aux.)

 

1.3.1                FSSS

 

1.3.1.1 COMMON SYSTEM

1.3.1.1.1 Purging not possible / gets interrupted

 

  1. Check if any scanners are detecting or are on the verge of detecting flame.
  2. Check that all fuel valves/gates are closed and correct feedback is available at the respective panel as well as at the unit panel.
  3. If SADC was in auto earlier, it might have reverted to too low opening. Confirm its position.
  4. Adjust the air flow suitably and ensure its permissives are available steadily.
  5. Confirm that the burner tilt is normal (horizontal)

 

 

1.3.1.2.             OIL FIRING

 

1.3.1.2.1          Trip valves not operating

 

  1. Check that all permissives are available at the respective panel. Check the isolating valves feedback.
  2. Check for proper voltages.
  3. Check the healthiness of the coil.
  4. Confirm that no other trip commands (software as well as hardwired) are present.
  5. Check proper air supply at the field. Ensure that there are no leakages.
  6. Check the filter and air lock relays.
  7. Check the position of the speed adjusting valve.
  8. Check the solenoid valve for proper port change over.
  9. Check the valve & actuator for leaks, punctured diaphragm, mechanical obstructions etc.

 

1.3.1.2.2          Oil firing not possible (not taking start).

 

  1. Check that all permissives are available at the respective panel.
  2. Confirm availability of all panel power supplies.
  3. In case of first guns, check interlocks like nozzle tilt, air flow etc.
  4. Check corner-wise permissives like position of the LGM switch, status of the limit switches of gun, scavenge valve, oil valve, manual valves etc.
  5. Check proper air supply at the corner(s). Check for leakages, choked filters/ air lock relays, needle valve etc.
  6. Ensure that the scanner of the respective corner is not sensing flame already.
  7. Confirm at which step the sequence gets interrupted.
  8. Check the suspected valve as in 1.2.1.1 (ii) 5 to 9.

 

1.3.1.2.3          Oil firing not stable.

 

  1. Confirm the pressure of fuel and atomizing media and the fuel temperature in case of heavy oils.
  2.         Check for restricted opening of the valves.
  3.         Check for possible choking of the gun.
  4.         Check that scanner supply is ON and settings are in order.
  5.         Check the ignitor for proper travel and spark.
  6.         Visually check the nozzle and flame from opposite corrner.
  7. Maintain the windbox pressure, differential pressure and proper opening of corresponding auxiliary damper.
  8. Check the healthiness of the electronic modules and field inputs.

 

 

1.3.1.3.       COAL FIRING

 

1.3.1.3.1          Coal firing not possible(Not taking start).

  1.                     Confirm that the inter panel communication is healthy.
  2. Check all permissives at the corresponding panel (PA permit, ignition start permit, no protection trip, closed status of all PA dampers, brake position, luboil protection etc)
  3. Confirm that start command is issued from the panel.

1.3.1.3.2          Coal firing sequence gets interrupted

 

  1. Confirm how far the start sequence proceeds and where it gets blocked.
  2. Check the interlocks of individual steps.

 

1.3.1.3.3          Coal firing not stable / trips frequently.

 

  1. Identify the cause of trip and the individual cause as per

appropriate check list.

  1. If the indicated cause appears spurious / unreasonable,

check for healthiness of control panel cards , communication and data integrity.

 

1.3.1.3.4          Trips on ignition energy / flame failure

 

  1. Check that PA pressure is maintained.
  2. Confirm that sufficient ignition support is available.
  3. Confirm that scanners are all in service and detect a reasonable level of flame.
  4. Confirm the frequency setting of the fire ball scanners are as per recommendation.
  5. Check the SADC for proper damper position.

 

 

  • SEQUENCE INTERRUPTION / TRIPS DUE TO AUX.EQUIPMENT (TUBE MILL)

 

1.3.1.4.1          Purge dampers not opening

 

  1. Check open interlocks are present (e.g. all PA/ coal dampers closed, ignition permit OK, no mill trip etc..)
  2. Confirm that no contrary commands are present.
  3.         Check card and voltage healthiness.
  4. Check all 4 coils and feed backs are properly looped.
  5. Verify actual operation of all the dampers from local. Ensure full opening.
  6. If any damper is not operating attend the same. (Refer section on pneumatic devices.)
  7. Check the limit switch and its wiring.

 

1.3.1.4.2.         Purge damper not closing

 

  1. Confirm healthiness of card, relay and voltages.
  2. Check healthiness of coils, cabling and air supply.
  3. Confirm operation of all dampers.
  4. Check for proper change over of limit switch contacts and their wiring.
  5. Check for healthiness of steam inerting system (panel, valves, air supply etc.)

 

1.3.1.4.3          Sequence interruption due to problems in Seal air fans and its dampers

 

  1. Confirm that the seal air fan starts on Auto. Otherwise start it

manually.

  1. Monitor the current on starting and ensure that discharge

damper opens after current normalises.

  1. Check if the respective discharge damper opens fully within

one minute of starting and proper feed back is received at         the panel. Attend if necessary.

  1. Check that adequate seal air pressure is developed and

pressure switch changes over.

  1. Check the operation of the control damper to ensure

adequate diff. pressure.

 

  • LP lubrication not OK

 

  1. Check the start permissive (level OK) is available.
  1. Check that MCC and LPB are properly lined up.
  2. Check the lub oil level in the tank.
  3. Check the lub oil temperatures in the tank as well as after

the cooler.

  1. Confirm the auto operation of the heater.
  2. Check the oil flow to the bearing. Check the flow switches for proper operation.
  3. Check the filters for any choking.

 

1.3.1.4.5.         HP and B&S lubrication not OK.

 

  1. Check the start permissives (temp OK, LP pump ON, suction pr OK )
  2. Confirm .that MCC and LPB are lined up properly and pump starts on command.
  3. Check the suction line pressure; adjust if needed.
  4. Check the discharge pressures in all the lines. Ensure sufficient pressure. Check the pressure switches and their feed back loop.
  5. Check and maintain correct oil temperature.
  6. Ensure smooth change over of filters so that it doesn’t cause dips in pressure or flow.

 

1.3.1.4.6          Reducer lubrication not OK

 

  1. Check the proper line up of the equipments like MCC, EPB, filters, coolers etc..
  2. Confirm that the pump starts on command.
  3. Check the oil flow is sufficient. Check the flow switches and their feed back loop.
  4. Confirm the availability of the standby pump in auto.

 

1.3.1.4.7.        Girth gear greasing not OK.

 

  1. Check for adequate grease level in the barrel.
  2. Ensure correct air pressure for spray nozzles.
  3. Check that the pump develops sufficient pressure.
  4. Check the spray solenoid valve operation. Check the voltage and coil healthiness.
  5. Check the timing of the distributor limit switch change over.
  6. Check for choked distributor and nozzles. Check the spray physically.
  7. Ensure sufficient fluidity of the grease. Provide and check heating arrangement in cold weather.

 

1.3.1.4.8          Mill main motor not starting.

 

  1. Check all permissives and trips (lubrication OK, bearing temp OK, ignition permit Ok, status of aux motor and brake, seal air DP etc..)
  2. Check for any hard wired or electrical trip commands.

 

1.3.1.4.9        PA inlet shut off gate not opening.

 

  1. Confirm that mill main motor has started.
  2. Confirm that cold air gate is open.
  3. Check that proper voltage is extended to the correct coil.
  4. Check for loose cables, earth faults, damaged coils etc..
  5. Check the position of the manual lever on the solenoid.
  6. Ensure that the manual locking pin of the damper is removed.
  7. Check that the damper is pneumatically lined up properly.
  8. Check the solenoid for proper port change over.
  9. Check the air piping for leakages.

 

 

 1.3.1.5 FEEDER (GRAVIMETRIC)

 

1.3.1.5.1        Not getting start command

 

  1. Ensure the remote start permits like ignition permit, no mill trip, outlet gate open, outlet temperature OK, coal on belt , feeder inlet gates open
  2. Check for presence of any hard wired trips.

 

 

 

1.3.1.5.2          Feeder not starting.

 

  1. Ensure the panel power is ON and phase failure relay is reset.
  2. If not, check the power supply in all phases, internal fuses, PS fail module connection etc.
  3. Check the control switch positions at the remote as well as local panels.
  4. Check for presence of coal on belt. Check its limit switch paddle and switch contact.
  5. Check for choking of discharge. Check its limit switch paddle and switch contact .
  6. Ensure that the panel electronic rack is energized and all cards are properly fixed.

 

1.3.1.5.3          Feeder gets on but belt not moving.

 

  1. Check motor power supply, cabling and motor healthiness.
  2. Check whether motor is operating.
  3. Check the clutch coil healthiness and confirm proper voltage is fed to it.
  4. Check the clutch mechanically for choking or obstructions.
  5. Check the belt for damage or obstructions.
  6. Check for proper tightness of the belt.

 

1.3.1.5.4          Feeder not going to gravimetric mode

 

  1. Check that remote and coal on belt feed backs are received.
  2. Check that the feeder local panel power is ON and cards are in place.
  3. Check that the status l.e.d on FRC card is lit and no LED are lit on LCA card.
  4. If any lamps are ON in LCA, find out the defective component / card and attend.
  5. Check for feedrate error alarm.

 

1.3.1.5.5          Feeder speed not being controlled.

 

  1. Check the clutch and its control for proper operation.
  2. Check for failure of the tacho-generator and its feed back.
  3. Check the demand signal for proper range and change.
  4. Recheck the settings of the panel electronics.

 

1.3.1.5.6          Problems due to defects of control panel

 

  1. If field devices are OK and still problem is faced in operation, or if tripping / interruption appear to be spurious, check the Procontrol system healthiness.
  2. Ensure that all the panel supplies are ON and all relevant cards are in place.
  3. Check for Alarm LEDs on the cards.
  4. Confirm that data communication is healthy (inter panel and intra panel.)

 

 

1.3.1.6        FLAME SCANNERS NOT DETECTING FLAME

 

  1. Check the power supply to the panel as well as to the racks.
  2. Check the power supply module output voltages.
  3. Confirm all cards are properly inserted.
  4. Check the field wiring for loose connections, earth faults, improper screen connections etc. Check the plugs of the scanner.
  5. Check the settings of pick up and drop off levels and the frequency.
  6. Ensure that the scanner is mounted properly and the cooling air OK.
  7. Check the scanner assembly and the electronic cards separately.

 

 

  • SECONDARY AIR DAMPER CONTROL (SADC)

 

1.3.2.1. No output from the panel.

 

  1. Check the control panel for proper functioning.
  2. Check the power supply and the healthiness of cards in the panel.
  3. Confirm data transfer between console, I/O cards and processor.

1.3.2.2.             Output not varying.

 

  1. Check the signal to the output cards separately and establish it.
  2. Check the output cards separately.
  3. Check the field cabling for earth faults, short circuits and proper

polarity.

  1. Check for any overriding protective interlocks ( e.g, ID-FD fans off, MFT, furnace to WB DP high.)

 

1.3.2.4.             Damper opening not matching with the demand

 

  1. Ensure correct air supply to the I/P (current to pressure)
  2. Check the cabling for polarity, healthiness of connections
  3. Check the current input and signal output at the I/P outlet port.
  4. Check the signal tubing for leakages. Conduct pressure decay test if doubt persists.
  5. Check the damper separately for mechanical freeness.
  6. Check the power cylinder air supply for proper quality and pressure.
  7. After ensuring proper signal and power air supplies to the actuator,

check its response (output air pressure).

  1. Check the setting of the air lock relay on the actuator.
  2. Service the actuator.

 

1.3.2.5.              Failure of Auto control of Auxiliary damper

 

  1. Check the furnace to WB diff pressure transmitters for proper functioning. Check for high mismatch between measured values.
  2. Confirm that ALL the dampers are responding properly and the damper position in all corners of the same elevation are matching.
  3. Check the response of the DP when dampers are manually adjusted.
  4. Adjust the bias to get suitable DP demand.
  5. Check the healthiness of reference signal used to generate DP demand ( boiler load index)
  6. Check for any over riding interlocks.
  7. Check the secondary air system for proper status.

 

  • 3.2.6 Failure of Fuel air dampers.

 

  1.                      Check that no override commands are present.
  2. Check that the reference input ( e.g PA flow) is OK.
  3. Check the damper operation in manual.
  4. Tune the parameters to suit the firing regime.

 

1.3.2.7       Failure of over fire dampers

 

  1.                      Check that no override commands are present.
  2.                      Check that the reference input ( boiler load) is OK.
  3.                      Check the damper operation in manual.
  4.                      Tune the parameters to suit the firing regime.

 

1.3.3.          APRDS

 

  1.                 Not taking any command.

 

  1. Ensure panel healthiness (voltage, card insertion, bus communication etc…)

2          Check the communication between console and panel.

 

  1.                Steam isolation valves not operating.

 

  1. Check the inter locks of the valve (typically steam parameters OK, control valve closed, bypass valve open )

2          Check the MCC and actuator healthiness.

  1. Check the control relay loop. (Output card, wiring, interposing relays etc)

 

  1.                 Steam pressure control valves not operating

 

  1. Check the interlocks are OK. Typically these are isolating valve open, down stream temperature not very high, upstream parameters are OK.
  2. Check the drive card healthiness.
  3. Check the output and feedback loops are healthy.
  4. Confirm that the fail safe air lock solenoid is energised. Check the relay and field wiring and voltage.
  5. Confirm that the valve is lined up properly. (Check air supply, filter, air lock relay, leakages, wiring etc)
  6. Check the valve operation locally.

 

  1.                 Spray isolating valves not operating.

 

  1. Check the interlocks from other valves.
  2. Check the control wiring loop (output card, relay, wiring etc.)
  3. Check the valve and switch gear are properly lined up.
  4. Check the valve operation locally.
  5. Check for valve jamming, torque / limit switches functioning.

 

  1.                 Spray control valves not operating.
  2. Check the interlocks are OK. Typically these are isolating valve open, steam valve open.
  3.          Check the drive card healthiness.
  4. Check the output and feedback loops are healthy.
  5. Confirm that the fail safe air lock solenoid is energised. Check the relay and field wiring and voltage.
  6. Confirm that the valve is lined up properly. (Check air supply, filter, air lock relay, leakages, wiring, position of auto/manual selection etc)
  7. Check the valve operation locally
  8.                 Spray block valve not operating.

 

  1.          Check the inter locks.
  2. Check the command loop (output card, wiring, relays and voltage)
  3. Check for proper pneumatic lining up of the valve.

 

  1. Auto controls not working.

 

  1. Check the pressure and temperature measurement loop.
  2. Check the individual valves operation separately.
  3. Check the valve calibration.
  4. Check for any auto blocking inter locks.

 

 

1.4.                 Electrical System:

 

1.4.1.               HT Motors:

 

1.4.1.1. Motor Winding temperature high:

 

  1. Check for overload on the motor
  2. Check for opening of cooling water valves.
  3. Check for the cooling water temperature/pressure/ adequate flow
  4. Check Air ducts for cleanliness
  5. Check for healthiness of cooling fan
  6. Check that the operating voltage is within the permissible limits
  7. Check for inter turns short after stopping of motor

 

1.4.1.2. Abnormal noise from the motor:

  1. Check for rubbing of rotating parts with the stationary parts
  2. Check the healthiness of bearings
  3. Check for foreign materials or loosening of parts of the motor

1.4.1.3. High vibrations of the motor:

 

  1. Check the tightness of fasteners
  2. Check the alignment and runout
  3. Check for any loose parts of rotors
  4. Check for touching of rotating parts with the stationary parts
  5. Check the healthiness of bearings
  6. Check the healthiness and possibility of resonance from the foundation.
  7. Check the healthiness of springs of spring loaded deck
  8. Check for unbalance of rotating parts.

 

1.4.1.4. High Bearing Temperature:

 

  1. Check the healthiness of the RTD and the cable connections.
  2. Check the healthiness of bearings
  3. Check for misalignment and overloading
  4. Check the quality and quantity of lubricant
  5. Check for adequate cooling flow where applicable
  6. Check the bearing clearances.
  7. Check the insulation resistance of bearings and prevent flow of circulating currents through the bearings.

 

1.4.1.5. Motor fails to start:

 

  1. Check the driven equipment/rotor for jamming/overloaded.
  2. Check the healthiness of power supply source and the connected cables.
  3. Check the continuity and insulation resistance of the winding
  4. Check that the winding is connected properly for star or delta formation.
  5. Check for existence of any electrical protection and reset it.
  6. Check for single phasing

 

 

1.4.1.6. Motor starts, but trips immediately:

 

  1. Check the insulation resistance of the motor
  2. Check for any jamming/overload of rotor
  3. Check the healthiness of the power supply source
  4. Check setting of protection relays and modify, if needed
  5. Check for single phasing

 

1.4.1.7. Motor starts, but trips on stalling protection:

 

  1. Check for any jamming/overloading of rotor
  2. Check the setting of stalling protection and modify, if needed.
  3. Check the healthiness/settings of speed switch where applicable.

 

1.4.1.8. Motor starts abruptly:

 

  1. Check for any inter turn short or phase short circuit in rotor winding
  2. Check the cable connections at the terminals
  3. Check the healthiness of starter

 

1.4.1.9. Humming noise during starting/operation

 

  1. Check for single phasing
  2. Check for overloading of motor
  3. Check for open circuit in rotor winding
  4. Check the connections at the motor terminals
  5. Check for inter turn shorts in stator/rotor winding

 

1.4.1.10.          Low insulation resistance of winding

 

  1. Check for water ingress points into the motor and arrest them
  2. Check for accumulation of water at the bottom of the motor
  3. Check for any leakages in the cooler
  4. Ensure closure of cooling water to motor, when motor is not running to prevent moisture condensation inside the motor
  5. Check for the healthiness of the winding

 

1.4.2.             ESP Controls:

 

  • Electronic Controller does not switch ON

 

  1. Check the interlock key
  2. Check the control fuses and control supply
  3. Check the coil of main contactor for healthiness
  4. Check the healthiness of overload relay
  5. Check for safety lines
  6. Check the healthiness of microprocessor controller
  7. Check the selector switch on microprocessor controller for local/remote operation, as required

 

1.4.2.2. HT does not switch OFF

 

  1. Check `OFF’ relay of the controller for healthiness
  2. Check the local/Remote selector switch for desired position

 

1.4.2.3. Output Voltage does not build up:

 

  1. Check the firing pulses from the controller
  2. Check the firing circuit and the cabling connections
  3. Check the healthiness of firing card

 

1.4.2.4.            Output Voltages builds up, but DC ammeter does not read (no current)

 

  1. Check for meter connections at MCRP card
  2. Check the healthiness of Ammeter
  3. Check for disconnecting Switch position

 

1.4.2.5. Low precipitator Voltage:

 

  1. Check for ash bridging in ESP
  2. Check for any snapped electrodes

 

1.4.2.6. Current shoots up during sparking

 

  1. Check the spark sensitivity adjustment on the controller

 

  • Low Primary Voltage :

 

  1. Check for power cable connection between EC & HVR
  1. Check the healthiness of voltmeter

 

 

  • kV meter does not read :

 

  1. Check the Feedback signal from HVR
  2. Check the healthiness of kV meter

 

1.4.2.9.         Current shoots up as soon the HT is switched `ON’

 

  1. Check for missing firing pulse to Thyristers
  2. Check the healthiness of firing card
  3. Check the current Feedback from HVR for any discontinuity
  4. Check the healthiness of HVRC card inside the transformer
  5. Check the healthiness of Thyristers

 

1.4.2.10           Frequent operation of top Float of Buchholz relay of HVR

 

  1. Check for proper oil level in HVR
  2. Check for any accumulation of Air/Gas
  3. Check for any fault in core laminations
  4. Check for any overheating in the winding
  5. Check for any loose connections

 

1.4.2.11.          Buchholz relay Bottom Float operates:

 

  1. Analyse the accumulated Gas
  2. Check the healthiness of A/C reactor
  3. Check the healthiness of H.F. Choke
  4. Check for any inter turn short
  5. Check for any failure of rectifier diodes
  6. Check for Breakdown value of oil

 

 

2.0.                 Steam Turbine & Auxiliaries:

 

2.1.                  Operational problems (common):

 

2.1.1.               Load on turbine is not increasing beyond a certain limit.

 

  1. Check the load limiter setting
  2. Check the restriction of opening of control valve
  3. Check the operation of limit switch of ATT of Control valve
  4. Check whether both the stop valve are open physically.
  5. Check for shearing off valve stem of stop valve/control valve in shut down
  6. Check for rubbing of valve cone with guide
  7. Check for the rated steam parameters of pressure and temperature
  8. Check for abnormal rise in curtis-wheel/first stage steam pressure.
  9. Check for any rise in primary oil pr.with respect to actual speed.This can restrict the load by closing of control valves from hydraulic mode.

 

2.1.2.               Sudden total load rejection by opening of GCB but turbine & generator remains in operation:

 

  1. Check that control valves are proportionately closed by turbine governor to reduce steam flow through the turbine
  2. Check that HP & LP Bypass valves are opened on Fast opening Mode and Auto Control is in Service.
  3. Cut off Mills (Fuel input) by 50% to 60% immediately to reduce steam generator output
  4. Maintain Drum level, if needed manually.
  5. Maintain/Regulate Main steam/Reheater temperature.
  6. To sustain the machine on house load, ensure that UAT’s are in service.
  7. Ensure that over speeding of the turbine does not take place.
  8. Set reference speed setter to rated speed. In case of abnormal rise in speed, trip the turbine.
  9. Check that turbine exhaust steam temperature within limits
  10. Investigate the cause of load rejections/GCB opening
  11. Re-synchronise the unit after fault finding

 

2.1.3.               Turbine tripped on same protections, but reverse/Low Forward protection fails to open Generator Circuit breaker:

 

  1. Check the position of stop valves/Control valves of turbine
  2. If they are closed, open the GCB manually.
  3. Prevent the motoring of generator for a longer time.
  4. Check the functioning of reverse/low forward protection relays and the protection logic.
  5. Check the functioning of Limit switches of stop valves
  6. Check Pressure switch contact of trip oil system.

2.1.4.             Turbine/Generator trips due to Grid supply failure:

 

  1. Check that DC lub oil pump and DC seal oil pump are started automatically and the lub oil pressure/seal oil pressure are normal.
  2. Start the DG set if not started automatically. Extend emergency AC supply to all essential auxiliaries
  3. Close main steam stop valves
  4. Ensure that Reheaters are not pressurized
  5. Prevent pressurization of condenser by closing all the steam drains to condenser, if needed manually.
  6. Monitor the coasting down of turbine
  7. Perform manual barring, incase AC supply is not restored and AOP is not started
  8. Prevent hammering in piping by opening the respective atmospheric vents/drains, manually.

 

2.1.5.               Sudden partial load reduction on turbine:

 

  1. Check that control valves/extraction valves are throttled to reduce steam flow to turbine
  2. Ensure that turbine is not overspeeded beyond the limits. If necessary trip the turbine
  3. Check that HP & LP Bypass valves are opened to control the steam pressure
  4. Cut off Mills (Fuel input) immediately to reduce steam generator output
  5. Maintain drum level, if necessary, manually
  6. Maintain main steam/reheat temperature
  7. Ensure all other parameters are within limits
  8. Check that turbine exhaust steam temperature is within limits
  9. Investigate the cause of load reduction.

 

2.1.6.               Control valve/Stop valve fails to open after testing with ATT:

 

  1. Keeping the turbine running
  2. Reduce the load, on the turbine and the steam generator output, to the required extent
  3. Ensure that all parameters are within limits
  4. Open the drains on the upstream and downstream of defective stop/control valve
  5. Monitor the steam temperature of parallel steam supply lines
  6. Investigate the reason for failure of opening of stop valve/control valve. If necessary, stop the unit for rectification of the problem

 

2.1.7.               Failure of AOP and EOP and the turbine coasts down without lub oil

 

  1. If D.G. set failed to start on ‘Auto’ start D.G.set manually.
  2. Start DC Jacking oil pump, if DC JOP is provided or start standby JOP (Emergency bus)
  3. Take measures to restart EOP or AOP at the earliest
  4. Monitor bearing metal temperatures and record coasting down time.
  5. Keep running seal oil pump to prevent escape of Hydrogen from generator
  6. Requisition fire brigade to tackle emergencies.
  7. Kill condenser vacuum to shorten coasting down
  8. Try manual barring after the shaft comes to standstill if possible. Do not apply excessive pressure.
  9. Allow the turbine to cool down
  10. Check the bearing and rotor for damages

 

2.1.8.               Shaft comes to standstill when fire protection operated:

 

  1. Ensure starting of DC JOP/ACJOP
  2. Ensure the running of DC-EOP, while coasting down, to prevent damages to bearings and turbine
  3. Rotate the shaft manual barring after the turbine comes to standstill
  4. Investigate the reason for fire protection operation and rectify the problem
  5. Acknowledge, initiation of fire protection measures and reset
  6. Restart lubricating and control fluid/control oil system
  7. Put the turbine on barring gear
  8. Restart the turbine

 

2.1.9.               Leakage of oil from control oil/control fluid system

 

  1. Operate fire protection push button-1. Ensure closure of emergency gate valve of control oil system
  2. Ensure switching `OFF’ of control Fluid pumps immediately. If result in tripping of unit, close control oil rack isolating valves in case of 210/250 MW KWU units.
  3. Investigate the reason for leakage and rectify
  4. Clean off the leaked oil
  5. Restart the control fluid system or recharge the control oil system after ensuring safety
  6. Restart the unit

 

2.1.10. Leakage of oil from lubricating oil system with turbine in operation.

  1. Operate fire protection-2.
  2. Ensure tripping of turbine
  3. Ensure starting of Jacking oil pumps immediately
  4. Ensure the running of DC-EOP during coasting down, to the extent possible, to prevent damages to the turbine and the bearings. Any emergency decision to stop DC-ROP is to be taken, taking into consideration the consequent damages to the turbine.
  5. Requisition fire brigade for handling emergencies and fires.
  6. Try manual barring with JOP in operation, if possible. Do not apply excessive pressure.
  7. Investigate the reason for leakage and rectify
  8. Check the extent damages of bearings/turbine, if any and rectify
  9. Clean off the leaked oil
  10. Replace the soaked insulation
  11. Restart the lub oil pump and check for leakages
  12. Restart the unit.

2.1.11. Excessive steam leakage from piping turbine components

 

  1. Depressive/isolate the leaking system, if possible.
  2. Cordon off the area to protect the personnel
  3. If the leakage is excessive or there is rupture hazard, stop the turbine immediately.
  4. Coast down the turbine and bring it to barring gear
  5. Investigate the extent of damage and rectify

 

2.1.12. Severe Earthquake

 

  1. Shutdown the turbine immediately
  2. Monitor the coasting down and put the turbine on barring gear
  3. Isolate the steam from the boiler
  4. Requisition fire brigade to handle emergencies/fires
  5. Check the extent of damages
  6. Check the alignment, bearing, foundations, structures, piping, hangers etc.

 

2.1.13. Turbine shaft comes to standstill after a trip out/planned stopping

 

  1. Try for manual barring. Do not apply excessive force
  2. Check the jacking oil leader pressure
  3. Check the DP across filter and change over to standby, if needed
  4. Check the setting of Jacking oil header relief valve. Readjust it, if needed
  5. Check the jacking oil pressures, and the shaft lift of individual bearings. Readjust if needed
  6. Investigate for any possible leakage from the jacking oil flexible hoses to the bearings.
  7. Check the healthiness of barring gear valve and ensure its full opening (210 MW/500 MW)
  8. Check the temperature of seal steam and the possibility of quenching due to moisture entry
  9. Check differential expansions and casing temperatures
  10. Check the healthiness of barring gear assembly
  11. Cool down the turbine and try intermittently for manual barring
  12. If rotor is free on manual barring, try for putting the turbine on hydraulic barring gear.

 

 

2.2.                 Turbine & Auxiliaries:

 

2.2.1.               Lub Oil System:

 

2.2.1.1. Moisture content in lub oil high:

 

  1. Remove water from oil system by separation through Centrifuge or by draining if oil pumps are not in service and turbine at standstill
  2. Check vacuum in bearing housings
  3. Check excessive leak-off steam from shaft seals
  4. Change over lub oil cooler and check for any tube leakages in lub oil cooler which was in service.

 

2.2.1.2. Mechanical impurities in lub oil high:

 

  1. Check oil centrifuge is in service
  2. Check bucket filter of MOT
  3. Check proper vacuum in the bearing pedestals
  4. Check vapour exhauster fan is in service

 

2.2.1.3. Oil Level in Oil Tank low:

 

  1. Open oil tank cover
  2. Check strainer and if heavily fouled change strainer

and clean; examine residues in strainer.

  1. Check systems for leaks, if a large leak occurs,

unload turbine generator immediately and/or initiate fire-protection measures,

  1. Change lub oil cooler
  2. Top up with oil of the same make and type
  3. Check duplex filter drain valve
  4. Check MOT drain valves

 

( Attention! 2 out of 3 fire protection ineffective during turning gear operation)

 

2.2.1.4.         Oil Pressure Low:

 

2.2.1.4.1.         In pressure oil system during shut down of turbine generator unit:

 

  1. Check auxiliary oil pump is in service.
  2. If sub loop control fails: start auxiliary oil pump manually from control desk.
  3. Check lub oil duplex filter
  4. Check lub oil cooler throttle

 

2.2.1.4.2.         In pressure oil system at rated speed

 

  1. Check whether MOP has taken over, if not start AOP
  2. Check pressure downstream of auxiliary oil pumps
  3. Check standby pumps for reverse rotation.
  4. Start/Stop auxiliary oil pump with defective NRV once more.
  5. Check Oil system for any leakage in case of excessive leakage shut down the turbines.
  6. Check the functioning of injectors
  7. Check oil level in oil tank and top up if necessary
  8. Check for air lock in the system
  9. Check proper venting of oil cooler
  10. Check DP across the duplex filter
  11. Change over the filter if DP is high

2.2.1.5.         Oil Temperature High:

 

  1. Check temperature controller is `ON’.
  2. Check the set point
  3. Check positions of cooling water isolating valves for oil cooler in service.
  4. Open the cooling water isolating valves, if closed or throttled.
  5. Check for proper cooling water through oil cooler
  6. Check vents, both cooling water side and oil side.
  7. Check cooling water inlet temperature

 

  • Oil Temperature Low :

 

  1. Check the set point of the controller
  2. Check that temperature controller is `ON’
  3. Manually control the oil temperature through temperature control valve

 

2.2.1.7.         Turning Gear does not start-up automatically:

  1. Check that turning gear oil valve open & JOP ` ON’
  2. Check for proper jacking oil header pressure
  3. Check actual shaft lift oil pressures with set pressures. Correct pressure, if necessary
  4. Check clogging of JOP filter
  5. Check leakage from hose connections of jacking oil lines
  6. Check malfunctioning of pressure regulating valve.
  7. Check oil temperature and maintain at 45 Deg.C.
  8. Check using manual turning gear whether shaft turns easily
  9. Check for any mechanical obstruction

(Warning : Do not rotate the shaft system forcibly)

If Turbine Casing temperature > limit temperature Let turbine cool down, run JOP continuously till temperature comes down.  Rotate the shaft by 180 Deg. through hand barring.

2.2.1.8. Emergency shut off valve does not open:

 

  1. Check manual isolating valve in oil supply line of shut off valve is open.
  2. Check the healthiness of filter in oil supply line of shut off valve
  3. Check for any leakage in oil supply line of shut off valve
  4. Check solenoid valves of emergency shut off valve for its smooth operation.
  5. Release solenoid valves mechanically.

 

2.2.1.9. Oil vapour coming from bearing pedestal:

 

  1. Check vapour exhauster fan is in service
  2. Readjust the flap valve of vapour exhauster system.
  3. Clean or replace the wire mesh of oil catcher
  4. Start-up standby vapour fan.
  5. Check the proper vacuum in the bearing pedestals

 

2.2.1.10           Test oil pressure built up during normal operation and turning  gear operation.

 

  1. Check the rotor earthing brushes.
  2. Check the insulation under generator rear pedestal.
  3. Replace damaged MOP components.
  4. Check MOP coupling insulation

 

2.2.2              Control Fluid System (500 MW Unit) :

 

2.2.2.1.            Rise in neutralisation number -NN (Observed on the basis of constant values measured continuously under the same conditions)

 

  1. Check control fluid samples
  2. Check regeneration unit is in operation
  3. Check control fluid for water content (take sample from surface). Change over to other control fluid cooler
  4. Replace Fuller’s earth even if replacement not yet scheduled/ Activate alumina cartridge
  5. Clean fine mesh filter

 

2.2.2.2. High Water Content in control fluid

 

  1. Check for tube leakage in cooler.
  2. Change over to other control fluid cooler and attend to tube leakage.

 

2.2.2.3. Level in control fluid tank low

 

  • Check control fluid cooler drain valve;
  • Top up with control fluid of same make, if level further drops;
  • Stop turbine immediately
  • Stop control fluid pumps
  • Initiate fire protection measures

 

2.2.2.4. Control fluid pressure low:

 

  1. Check control fluid pumps;
  2. Change over to standby pump
  3. Check for any leakages
  4. Check air lock
  5. Check for DP across interchangeable filter
  6. If DP is high, changeover to other filter

 

2.2.2.5. Control fluid temperature low:

 

  1. Check temperature controller;
  2. Check control valve if open, switch off temperature regulator
  3. Close control valve;
  4. Switch on heater when control valve is closed.

 

2.2.2.6. Control fluid temperature high:

 

  1. Check temperature controller
  2. Check cooling water temperature
  3. Check cooling water is adequately vented,
  4. change over to other control fluid cooler
  5. Switch off heater

 

2.2.2.7. Control Fluid/oil leakage monitor responds:

 

  1. Check carefully which medium is escaping: oil, control fluid or both
  2. Identify the leakage area
  3. Operation of the turbine generator may be continued provided that the escape of fluid is continuously monitored.
  4. Repair Leak in earliest available opportunity

 

2.2.2.8. Control Fluid/water leakage monitor responds:

  1. Check carefully which medium is escaping: control fluid, water
  2. Identify the leakage area
  3. Operation of the turbine generator may be continued provided that the escape of fluid is continuously monitored.
  4. Repair Leak in earliest available opportunity

 

2.2.3.             Turbine Bearing Temperature High:

 

  1.          Check temperature measurement system
  2. Check oil pressure upstream of bearing
  3. Check oil throttle setting
  4. Check drain oil flow through view cap provided in bearing drain oil lines
  5. Check duplex filter
  6. Check temperature control valve setting
  7. Check cooling water flow through cooler
  8. Check oil cooler I/O temperature of cooling water
  9. Changeover oil cooler and check the above
  10. Check the oil sample.
  11. Check return oil temperature of the bearing

Caution:           In case of rapid rise of one or all bearing metal temperature beyond alarm level, stop the turbine.

 

 

2.2.4.             Turbine bearing vibrations:

Caution:           In case rapid or instantaneous increase in vibration over the permissible limits stop the turbine immediately even when accuracy of reading is doubtful.

 

2.2.4.1. Loud Noise and or the following operating parameters exceed their limits:

Wall temperature, Casing differential temperature, bearing metal temperature:

 

  1.          Check casing differential temperature
  2. Check whether increased vibration is maintained after load is reduced and when running down measure coasting down time.
  3. Check and listen any noise during this period.

 

2.2.4.2. Vibration values more than permissible limits.

 

  1. Check main frequency of vibration,
  2. Check vibration at all bearings in the three planes
  3. Check shaft vibration in two directions at right angles if possible.
  4. Check the phase relationship of the bearing and shaft vibration
  5. Check the foundation vibration
  6. Check the vibration in relation to all principal operating parameters and their variation

2.2.4.3.           Increased Vibration at rated speed above previous values:

 

  1. Check magnitude and direction of vibrations.
  2. Check the couplings for Firm and proper fit of coupling bolts during shut down.
  3. Check Fit of centering spigot during shut down
  4. Check radial runout of couplings during shut down
  5. Check Axial runout of coupling faces during shut down
  6. Check alignment during shut down
  7. Initial corrective action – dynamically rebalance the turbine,

 

2.2.4.4.            Temporary increase in vibration during non-steady-state operating conditions (start-up, loading and unloading, main-steam temperature changes, etc.)

 

  1. Check temperature changes during this period.
  2. Reduce speed, load and/or temperature rates of change.
  3. Wait until vibration improves when steady-state conditions are reached.
  4. Remove restriction to expansion by improving sliding of bearing housings and casing guides.

 

2.2.4.5.            Increased vibration during warm-up:

 

  1. Check the warm-up speed is within permissible range.

 

2.2.4.6.            Increased vibration during turbine acceleration. No improvement in vibration at rated speed

 

  1. Reduce turbine speed to less than 400 rpm and eliminate shaft distortion before increasing speed.

 

 

 

 

2.2.4.7. Sudden sharp increase in vibration with accentuated low-frequency components

 

  1. After finding out the stability limits, determine operating parameters affecting vibration to aid to determining cause.

–           Oil temperature

–           Load

–           Control valve lift

–           Expansion

–           Shaft displacement

–           Bearing metal temperatures

 

2.2.4.8. Vibration is related to load and valve lift

 

  1. Increase bearing loading by changing the alignment during shut down.

 

2.2.4.9. Vibration related to lubricating oil temperature changes

  1. Change oil temperature

 

2.2.4.10.          Shaft Vibration High:

  1. Check and maintain rated sealing steam temperature
  2. Check vapour exhaust fan is in operation
  3. Check proper opening of butterfly valves in return line from seals.
  4. Reduce main steam temperature. Avoid high HP exhaust temperature during low load operation.
  5. Check function of CRH NRV for its proper opening
  6. Check free movement of turbine bearing pedestals, if applicable.
  7. Check L.P. exhaust temp. if high during low load operation, start water injection or increase load on turbine
  8. Avoid rapid changes in M.S. Temp. and load
  9.          Check for touching of any seals with the shaft
  10. Check that the gland steam temperature is within permissible limits. Check for condensate/moisture ingress in gland steam.

2.2.5.             Turbine Casing Temperature:

Casing temperature differential top/bottom high

+ (positive) = higher temperature in top half casing

– (negative) = lower temp in top half casing :

 

2.2.5.1. During start-up δθ + or –

 

  1. Increase steam flow through turbine to obtain uniform warm-up

 

2.2.5.2. After load reductions, during low power operation δθ + or –

 

  1. Increase steam flow through turbine to obtain uniform warm-up

 

 

2.2.5.3. After load reductions δθ +

 

  1. Open drain valves in extraction lines. Test functioning and leak-tightness of extraction valves.

 

2.2.5.4. During power operation δθ + or –

 

  1. Check condition and measure clearances at sealing elements during overhaul and refit or replace leaky elements as necessary

 

2.2.5.5. During start-up δθ –

 

  1. Check position of drain valves, open any closed drain valves.

 

2.2.5.6. During start-up δθ +

1.       Close drain valves further or completely

 

2.2.5.7. During standstill or turning gear operation

 

  1. Start turbine very carefully to soaking speed. Soak until the steam admitted begins to reduce temperature differentials before running up to rated speed.

 

2.2.5.8. During standstill or power operation δθ is high

1.       Repair casing insulation

 

 

2.2.6.             Turbine Expansions:

 

2.2.6.1.            Differential expansion of HP Turbine at front end high during non steady state operation

 

2.2.6.1.1.         (+) Positive Diff.Exp.

 

  1. Reduce main steam temperature
  2. Wait for temp.equalisation between rotor and casing, soak the turbine
  3. Stop load changes (during loading)
  4. Check overall expansion if any restriction of the pedestal is there
  5. Check temp. margin in T.SE.
  6. Check if bearing pedestal is tilted.

 

2.2.6.1.2.         (-) Negative diff. expansion

 

  1. Raise main steam temp. if it is low
  2. Wait for temp.equialisation between rotor and casing
  3. Soak the turbine
  4. Stop load changes
  5. Check temp margin in T.SE.
  6. Check if bearing pedestal is tilted.

 

2.2.6.2.            Differential Expansion of IP turbine at rear end high during non steady state operation

 

2.2.6.2.1.         (+) Positive differential expansion:

 

  1. Reduce reheat temp. if it is already high
  2. Check temp.margin in T.SE.
  3. Soak the turbine with little increase in load
  4. Wait for temperature equalisation before changing further load
  5. Check if bearing pedestal tilted.

 

2.2.6.2.2.         (-) Negative Differential Expansion:

 

  1. Stop reheater temperature drop immediately
  2. Improve sliding of bearing pedestal
  3. Check for any restriction of expansion in bearing pedestal at front end of HP turbine and/or between HP & IP turbine section.

 

2.2.6.2.3.         Casing temperature differentials excessive:

 

  1. In any operating mode (additional turbine protection not operative)

Observe proper functioning of additional turbine protection and rundown; record rundown time

 

2.2.7.             Turbine protective devices:

 

2.2.7.1.             Manual Trip out:

 

  • Check condition that was the reason for turbine trip locally or from control room
  • Check the unit can be restarted.

 

 

 

2.2.7.2.             Automatic Trip out:

 

  • Check the reason for turbine trip
  • Check whether the trip is actuated due to protection criteria within turbine
  • Check for damages or irregularities that would preclude further operation of the turbine
  • If the trip actuated due to faults outside turbine, check whether turbine trip operation was called for in accordance with the protection concept.

 

2.2.7.3.             Automatic Turbine Trip:

 

Main trip valves operated:

 

  1. Check whether both the main trip valves opereated simultaneously
  2. If not, check signalling circuit (limit switches, wiring etc.)
  3. Check any mechanical fault in the trip valve
  4. If any internal damages repair it.

 

2.2.7.4.             Overspeed Trips operated:

 

  1. Check whether the present speed limit is reached
  2. Check the system frequency at the time of G.B. open
  3. Check when the breaker is opened whether the system frequency is high and machine on full load.

 

2.2.7.5.          Overspeed operated at lower speed:

 

  1. Perform oil pressure test
  2. Check the oil pressure where over speed trip occurs and compare with the pressure previously set.
  3. Perform over speed test with turbine at operating temperature

 

2.2.7.6.             Turbine control mal-functioning:

 

  1. Check movement of hydraulic control element

–           CV

–           Convertor

  1. Check E.H. Controller action
  2. Remove blockage or other malfunction

 

 

2.2.7.7.          Load Shedding relay failed to operate:

 

  1. Check the LSR solenoid valves
  2. Actuate contacts and check the secondary oil pressure of solenoid valve opening
  3. If secondary oil pressure does not collapse check the coils of solenoid valves
  4. Check measuring circuit, if LSR operation is not annunciated.

 

2.2.7.8.                        Thrust bearing trip responded:

 

  1. Check the play in thrust bearing – find out cause of high thrust bearing wear (axial thrust, damage, lack of oil)
  2. Check bearing metal temperatures

 

2.2.7.9.          Electrical low vacuum trip responded:

 

  1. Check the cause of condenser vacuum fall.
  2. Check circulating water pumps are running and flow of circulating water through condenser is proper.
  3. Check position of control valves of gland steam controller, if there is fault in the controller, switch off controller. Maintain gland steam pressure manually with the bypass motorised valve.
  4. Check operation of vacuum pump/ejectors
  5. Check any leakage in the system.

2.2.7.10.          Hydraulic low vacuum trip responded:

 

  1. Check the cause of condenser vacuum fall.
  2. Check circulating water pumps running and flow of circulating water through condenser
  3. Check position of control valves of gland steam controller, if there is fault in the controller, switch off controller. Maintain gland steam pressure manually with the bypass motorised valve.
  4. Check operation of vacuum pump/ejectors
  5. Check any leakage in the system.

 

2.2.7.11.          Main trip valves fails to operate

 

  1. Turbine generator unit must not be operated if main trip valves are not functioning perfectly
  2. Locate and repair fault immediately

 

2.2.7.12.          Trip solenoid is malfunctioning

 

  1. Do not operate turbine generator unit if trip solenoids are not functioning perfectly
  2. Locate and repair fault

 

 

2.2.7.13.          Both overspeed trips fail to operate during overspeed testing

 

  1. Repeat testing by test oil pressure several times until turbine trips at normal test oil pressure values
  2. If the defective overspeed trip still does not operate satisfactorily operation of the turbine generator unit must not be continued
  3. Locate and repair fault immediately
  4. Check speed indicator
  5. (compare frequency of excited generator with system frequency by means of synchronizing device)
  6. Adjust speed indicator

 

2.2.7.14.          One overspeed trip fails to operate during overspeed testing.

 

  1. Perform testing by test oil pressure, if testing by test oil pressure reveals that the two overspeed trips respond at slightly staggered settings, no further action is necessary

 

2.2.7.15.        Overspeed trip operates at too high a test oil pressure when tested by test oil:

 

  1. Check speed indicator; (compare frequency of excited generator with system frequency by means of synchronising device)
  2. Check movement of overspeed trip mechanism.
  3. Check test-oil line inside the bearing for any leakages at next opportunity

 

2.2.7.16.          Overspeed trip fails to operate when tested by test oil pressure

 

  1. Adjust test oil pressure.
  2. Increase speed with generator unsynchronised and perform test, if the defective overspeed trip still does not operate satisfactorily, operation of the turbine generator unit must not be continued until fault has been corrected.

 

2.2.7.17.          Overspeed trip operates at too low a test oil pressure when tested by test oil pressure

 

  1. Check speed indicator, whether speed is too high and generator is not synchronised.
  2. Check at normal speed
  3. Check the drift of trip speed

 

 

2.2.7.18.          One overspeed trip fails to operate when tested by test oil pressure; test oil pressure maximum, second trip responds normally

 

  1. Test intact overspeed trip daily by test oil pressure until fault can be corrected at next opportunity.

 

2.2.7.19.          Hydraulic low vacuum trip operates too early at too high a condenser vacuum:

 

  1. Check the setting
  2. Check diaphragm for any damages

 

2.2.7.20           Protection systems operating at too high or too low limit levels:

 

  1. Check signal transmitter

2.       Check signal path.

3.       Check protective devices for any mal-operation

 

 

2.2.8.             Turbine Gland Sealing system:

 

2.2.8.1. Seal steam escaping from gland:

 

  1.          Check whether one of the steam exhauster fan is running
  2. Check position of valves upstream of exhauster fan, and

it should be opened.

  1. Check valves of standby exhauster fan is closed
  2. Check any mechanical or electrical fault in the seal steam exhauster fan.
  3. Check the seal steam pressure set point and correct it

 

  • Seal Steam Pressure Low :

 

  1. Check proper functioning of gland steam controller.
  2. Check control valves operating sequence:

 

  • Check for any mechanical or electrical fault
  • Operate motorised bypass valve and maintain pressure.

 

2.2.8.3. Mechanical fault in seal steam/leak off control valve:

 

  1. Check header pressure
  2.          Reset seal steam supply valve
  3.          Check DP across filter of hydraulic actuator
  4.          If choked clean it
  5.          If damaged replace it
  6. Change oil of the actuator if required
  7. Check manual operation of valve locally through pump

 

2.2.8.4. Electrical fault in seal steam control valves:

 

  1. Check for any problem on the basis of valve description and correct.
  2. Check the module output to control valves
  3.          Check remote manual operation of the valve
  4.          Check if temperature protection acted.
  5.          Check manual operation of valve locally through pumps

 

 

2.2.9.             L.P. Bypass Stop and Control Valves:

 

2.2.9.1. L.P. Bypass Stop and Control Valves are not operating

 

2.2.9.1.1.         Reheat pressure > constant or variable pressures set point

 

  1. Check condensate pressure,
  2. Check condenser vacuum
  3. Check bypass steam temperature
  4. Check operating conditions of condensate pump or condensate system
  5. Check condensate pressure downstream of condensate pump(s).
  6. Establish normal conditions
  7. Check actuators of injection water control valves
  8. Check slide value of water injection
  9. Check signal oil pressure and control oil pressure of water injection and stop/control valves
  10. Check bypass steam temperature .
  11. Check reset solenoid valve of temperature protect, if operated reset
  12. Reduce Boiler/HRSG out put.

 

2.2.9.1.2.         Reheat pressure < constant pressure set point but > variable  Pressure set point

 

  1.          Lower constant pressure set-point.

 

2.2.9.1.3.         Reheat pressure > constant or variable pressure set-point; Interlocks ineffective:

 

  1. Check fault annunciation in control cabinet.
  2. Control reheat pressure manually
  3. Rectify the problem

 

2.2.9.2. Bypass stop and control valves close or fail to open:

 

  1. Condensate pressure down-stream of injection water control valves < interlock pressure :
  2. Locate fault in regulator or hydraulic control gear and remedy.
  3. Remedy fault in changeover valve for injection water control valves
  4. Open bypass valves until fault is remedied.
  5. Remove blockage in injection water control valve

 

2.2.10.           Turbine Stop and Control Valves:

 

2.2.10.1.          Stop valves fail to open:

 

  1. Check starting and load limitting device is in 0% position.
  2. Check trip oil pressure above piston to stop valve has built up
  3. Raise the starting device
  4. Check start up oil pressure is reducing
  5. Check pressure below the piston has built up more than press. Above piston.
  6. Check pressure above the piston reduces to zero.
  7. Check opening of stop valve locally by test valve

 

2.2.10.2.          Control valves fails to open:

 

  • Check isolating valve in secondary line is open.
  • Check isolating valve in control oil line is open
  • Check damping device orifice
  • Check gear of ATT valve into operating position
  • Check position feed back transmitter.

 

2.2.10.3.          Control valves open and closes astatically

 

  1. Slight changes in secondary oil pressure
  2. Check feed back system for blockages
  3. Check the relationship between secondary oil pressure and control valves
  4. Check Hydraulic Governor, converter and actuators
  5. Record the following:
  6. Travel of start-up device and load limit device
  7. Travel of converter
  8. Aux.secondary oil pressure
  9. Check secondary oil pressure
  10. Travel of control valves
  11. Check for Restriction in movement of valve stem:
  12. Check the required clearance between valve cone and bush
  13. Slightly reduce the tightening at the glands of the valves

 

2.2.11.        Low Condenser Vacuum:
  • Maintain proper C.W. flow through condenser
  • Maintain proper seal steam supply press.
  • Check proper operation of vacuum pump
  • Air leakage should be attended on top priority
  • Clean the tubes on water side
  • Reduce exht. Temp. by spray
  • Maintain adequate hot well level
  • Maintain rated CW inlet temp.

 

 

2.2.12.           Condensate Extraction Pump:

 

2.2.12.1.          Does not take suction/hunting of discharge pressure/motor current:

 

  • Check for any air ingress from drains, stainer cover, pump seal, check for sufficient sealing water, well vent to condenser should be opened.
  • Maintain adequate hot well level

 

2.2.12.2.          Motor taking high current/vibration high/bearing temp.high

 

1)         Check the grease in the bearings for quality and quantity

2)         Check Oil level in thrust bearing

  • Check for sufficient cooling water flow
  • Check the healthiness of bearings
  • Check for proper line of the system
  • Ensure adequate flow through the pump

 

 

2.2.13.           Boiler Feed Pump:

 

2.2.13.1.          Does not develop sufficient flow:

 

  • Clean suction filter
  • Maintain adequate level in deaerator
  • Correct scoop feed back position indication w.r.t. scoop position

 

2.2.13.2.          Working oil/lub oil temp. High:

 

  1. Increase cooling water supply
  2.          Clean oil cooler
  3. Clean oil filters/check pressure regulating valve end set

 

2.2.13.3.          Low discharge pressure:

 

  1. Check for recirculation valve remaining open even at higher flow

 

2.2.13.4.          Low recirculation flow:

 

  1. Dismantle valve and clean absorber
  2. Check full opening of recirculation valve

 

2.2.13.5.          Thrust Brg. Temp. High:

 

  1. Increase oil flow
  2. Increase feed flow
  3. Check Balance piston clearance

2.2.14.           Vacuum Pump:

 

2.2.14.1.          Pump having abnormal sound

 

  • Check whether suction valve is opened
  • Maintain adequate water level

3)         Check adequate water flow through cooler

4)         Check for clogged cooler tubes

5)         Check whether differential temperature is high

 

2.2.14.2.          Low vacuum being developed by pump:

  1.          Check opening of hogging ejector if differential temp high

2)         Check exhaust flap is free and opens with exht pressure as soon as the pump starts.

 

2.3.                  CONTROLS & INSTRUMENTATION (TG):

 

2.3.1.               EAST package:

 

2.3.1.1. Dynamic monitoring appearing frequently:

 

  1. Check the tightness of TSE Thermocouples pertaining to that channel.
  2.          Check the J.B. Temp. Monitoring for this thermocouple
  3.          Check the monitoring card
  4.          Check the set value

 

2.3.1.2. Junction Box temperature monitoring:

 

  1.          Check the tightness of RTD wires for cold JB temperature
  2.          Check the temperature limits for monitoring
  3.          Check the healthiness of 24 V heater power supply

2.3.1.3.         Thermocouple failure:

 

  1.          Check the mVs at T/C head by isolating the cable
  2.          Check the cable for wire breakage
  3. Check the input module for temperature signal.

 

2.3.2.             Electro-hydraulic Controller Fault:

 

2.3.2.1. EHC Fault:

 

  1. Check the Collins feed back
  2. Check the turbine trip feed back to EHC.
  3. Check that trimming device is ON
  4. Check the power supply for starting device, speeder gear Collins

Transmitters

  1. Check for missing module
  2. Check for failure of speed measurement or power measurement
  3. Clean the filters at governing rack.

 

2.3.2.2. EHC Failure:

 

  1. Check calibration of Collins feedback
  2. Check that plunger coil is ON
  3. Check the panel power supplies
  4. Check the healthiness of EHC coil
  5. Check the trip oil and control oil going to EHC.

 

2.3.2.3. Speed measurement fault:

 

  1. Check the power supply going to pulse converter card
  2. Check the pulses coming from speed probe
  3. Check the healthiness of all cables connecting pulse converter,

panel pedestal J.B.

 

2.3.2.4.         Load measurement fault:

 

  1. Check the power supply for load transducers
  2. Check the healthiness of CT & PT signals
  3. Check the output of load transducer
  4. Check the cables from load transducer to EHC panel

 

2.3.2.5.         Hydraulic governor interfering:

 

  1. Check that tracking in ON
  2. Check the regulation of hydraulic governor

 

2.3.3.             Cabinet Power Supply Failure:

 

  1.          Check the healthiness of charger
  2. Check the healthiness of battery
  3. Check the healthiness of supply supervision module
  4. Check the panel racks for healthiness

 

2.3.4.             IPB Communication Failure:

 

  1. Check the healthiness of 70 FV01, 70BK02, 70FK01 modules
  2. Check the healthiness of RC networks
  3. Check the healthiness of XV7715, 17,18 modules
  4. Check the healthiness of IPB cable for proper connections and breakage

 

 

2.3.5.             Local Bus Failure:

 

  1. Check the healthiness of power supplies in all racks
  2. Check the healthiness of all the modules in the local bus
  3. Check the healthiness of all the racks and 70BL01, 02, 03 cables

 

2.3.6.             Hunting in Vibration Measurements:

 

  1. Check the screen earthing of all signal cables
  2. Check the tightness of pickups
  3. Check the power supplies in the cabinet
  4. Check the DC/DC converters for healthiness

 

2.3.7.             Emergency lub oil pump fail to start:

 

  1. Check the availability of 220 V DC supply.
  2. Check that EOP is on Remote at EOP panel
  3. Check the healthiness of pressure switch cable for direct starting
  4. Check the healthiness of memory relay and its contacts
  5. Check the remote start stop cable for healthiness
  6. Check the brushes in the DC motor commutator
  7. Check the motor speed and discharge pressure of the pump

 

2.3.8.             LP Bypass Control Failure:

  1. Check the control oil supply
  2. Check the healthiness of coil
  3. Check the cable connection between panel & rack
  4. Check the healthiness of control panel
  5. Check the healthiness of Cond. Temperature protection & reset if reqd
  6. Check the availability of condenser vacuum, condensate pressure
  7. Check the oil filters at control rack.

2.3.9.             Seal Steam Control Valve not opening:

 

  1. Check the oil pump discharge pressure for seal steam control valve & Leak steam control valve.
  2. Check the cable connection between control panel and control valves.
  3. Check the healthiness of seal steam control panel
  4. Check the seal steam inlet temperature permissive
  5. Check the cleanliness of filters in control valves & oil units
  6. Check the healthiness of pressure transmitter signals.

 

2.3.10.           Seal Steam Hunting:

 

  1. Check the healthiness of seal steam pressure transmitters for leakage

 

2.3.11.           Lub Oil temperature control valve failure:

 

  1. Check the power supply 415 V for valve
  2. Check the healthiness of control signal.
  3. Check the operation of valve mechanically & see the feed backs for limit/ torque switches and position feed back
  4. Check the lub oil RTD’s for feed back signal.

 

2.3.12.           H2 Gas Temperature Control Valve failure:

 

  1. Check the 415 V supply to the valve
  2. Check the healthiness of control module
  3. Check the valve on manual control mode
  4. Check the feedback signal
  5. Check the healthiness of control signal from panel

 

 

2.3.13.           Primary Water Temperature Control Valve Failure:

 

  1. Check the 415 V supply for the control valve
  2. Check the healthiness of control module
  3. Check the healthiness of control valve for position & torque limit switches
  4. Check the position feed back
  5. Check the feedback signal for primary water temperature

 

2.3.14.           Malfunctioning of Load Shedding Relay:

 

  1. Check the availability of 220 V DC supply
  2. Check the solenoids for healthiness
  3. Check the settings on LSR as per test instructions
  4. Check the healthiness of CT & PT signals
  5. Check the 24 V DC supply to LSR

 

2.3.15.           ATT Malfunctioning:

 

2.3.15.1.          Stop/Control Valve program mal-operating:

 

  1. Check the limit switches for all the stop & control valves
  2. Check the control panel healthiness
  3. Check the release available for starting
  4. Check all the pressure switches for healthiness
  5. Check all the solenoids for healthiness and operation
  6. Check all the root valves are open

 

2.3.15.2.          Protective devices Maloperating:

 

  1. Check all the pressure switches in protective devices for healthiness.
  2.          Check all the limit switches for the ATT protective devices
  3.          Check all the solenoids
  4.          Check the operation of all solenoids
  5.          Check the operation of changeover valve
  6.          Check the healthiness of control panel.

 

2.3.16.           MOT level Fire Protection not operating:

 

  1. Check the healthiness of level signaling probes.
  2. Check the power supplies & feed back contacts for all the probes

 

2.3.17.           Control Panel MCB’s Tripping:

 

  1. Check the voltage coming from battery or battery charger for permitted tolerances.
  2. Check for short circuit in panel racks.

 

2.3.18.           Module Failures:

 

  1. Check the healthiness of modules by isolating the process

 

2.3.19.           Turbine Protections not operating:

 

  1. Check the healthiness of input changeover contacts
  2. Check the healthiness of trip solenoids
  3. Check the healthiness of DC supply to control panel
  4. Check for some module failure.
3.0.             TURBO GENERATOR & AUX

3.1.              Sparking of the carbon brushes at the rotor slip rings accompanied by over heating of individual brushes and uneven wearing of slip ring surface

  1. Check proper fixing of brush gear.
  2. Check that all the brushes are of same grade and make on the slip rings.
  3. Check no oil and carbon dust are deposited on slip ring
  4. Check proper working surface of the slip ring
  5. Check proper pressure and contact of brushes on the slip ring
  6. Check for excessive vibrations on slip ring.
  7. Change the polarity of the slip rings once in every three months as a preventive measure.

 

3.2.             Ingress of seal oil into stator body indicated by liquid level detector.

 

  • Check the proper operation of the shaft seals.
  • Check for increase in seal oil flow on TE/EE.
  • Check the differential pressure between seal oil and

Hydrogen and ensure that it is within limits.

  • Check the functioning of the differential pressure regulator.
  • Ensure that ring relief pressure is as per operating guidelines.

 

3.3.             Presence of water in Stator casing indicated by LLD.

 

  • High moisture content in turbine/seal ore.
  • Coolers may have to be isolated one by one to establish leaking

cooler, if any.

  • Check for water leakages from gas coolers.
  • Check for excessive moisture in hydrogen gas.

4)         Check the functioning of H2 Dryers.

5)         Run the Dryers continuously till moisture level come down

6)         Leakage of water from stator winding (applicable for THW generators).  Always maintain stator water inlet pressure about 0.5 Kg/cm2 less than H2 pressure.

 

 

3.4.                 Excessive consumption of H2:

 

  • Check and identify all external joints, flanges for any leakage                         and rectify it.
  • Check for proper functioning of seal oil system

 

3.5.                 High cold Gas temperature inside the generator:

 

1)         Check for proper venting of Gas coolers.

2)         Check the gas cooler for any contamination, dirt inside the  tubes.

  • Check the Gas cooling inlet temp of cooling water and

maintain at proper value.

  • Check for proper cooling water pressure at Gas cooler inlet.
  • Check the flow of cooling water. If required increase the flow
  • If the temperature crosses beyond limit value, reduce generator load

 

3.6.                  Difference in slot temperature:

Between top and bottom bar of stator winding

 

  1. Check the healthiness of RTDs.
  2. Re-Calibrate the temp.monitor
  3. Check stator current in three phases for any difference
  4. Stop the unit if the difference is more than 20 Deg.C.

 

3.7.                 Gen. Bearing temp. Very high:

  1. Check inlet oil temperature to the bearing
  2. Check the inlet pr. of oil to the bearing
  3. Increase the oil flow to the bearing, if needed.
  4. Check for Insulation break down of bearing and possibility of excessive circulating leakage currents.
  5. Check for bearing damages.

 3.8.                High Stator winding core Temperature:

 

  1. Check the cooling water temperature at gas cooler inlet
  2. Check for choking/contamination of gas cooler
  3. Check the cooling water pressure at gas cooler inlet
  4. Check healthiness of RTD’s/Thermocouples and temperature monitoring system.
  5. Reduce the load on the generator.

 

3.9.                 Bearing vapour exhauster 1 failed:

 

  1. Check the fuses and overload relay
  2. Check proper mechanical and electrical condition
  3. Check operating points of vac. Transmitters.

 

3.10.                Low seal oil pressure TE/EE:

 

  1. Check the setting and functioning DPR.
  2. Check the oil filter for any contamination
  3. Check if pressure collapses during pump change over

 

3.11.                High seal oil temperature after cooler:

 

  1. Check the cooling water flow and temperature
  2. Ensure proper venting of cooler on its oil and water side
  3. Check the position of changeover valves.

 

3.12.                Seal oil pump-1 failed:

 

  1. Check the fuses and thermal O/L relay
  2. Check whether seal oil pump-2 has taken over
  3. Check Voltage is available
  4. Ensure starting of 2nd pump automatically
  5. Check the seal oil pump for its mech.& Elect.condition

 

3.13.              H2 purity dropping gradually:

 

  1. Check the instrument for correct value
  2. Check for presence of moisture in hydrogen
  3. Ensure that the vacuum in seal oil tank is maintained at normal operating value
  4. Purge few fresh cylinders of H2 to restore the purity value.

 

3.14.              Stator core temperature high:

 

  1. Ensure that the measurement is correct
  2. Check C.W. temperature and flow in gas coolers to ensure proper cooling of core
  3. Reduce load on the machine, if required
  4. Trip the machine if high temperature persists.

 

 

4.0.                 Gas Turbine & Aux. (GE make) :

4.1.                  GT Not coming on Ratcheting on Cool down :

 

  1. Check ratchet pump is developing adequate pressure
  2. Check 20 CS-1 solenoid for proper function
  3. Check 33 SE limit switch for proper function
  4. Check VR-5 relief valve for proper setting
  5. Check Jaw clutch is engaged properly
  6. Check ratcheting function using manual J06 switch

 

4.2.                 GT Failure to break away:

 

  1. Check for normal ratcheting function
  2. Check torque converter charge pump primer valve VPR38 for proper function
  3. Check torque converter charge pump relief valve VR23 for any passing.

 

4.3.             GT Failure to Ignite:

 

  1. Check for blown fuse in ignition circuit
  2. Check for healthiness of ignition transfomer
  3. Check for healthiness of HT cable to spark plug
  4. Check for healthiness of spark plug
  5. Check for any atomising air leakage (for liquid fuel firing)
  6. Check for proper operation of SRV and GCV
  7. Check for healthiness of flame scanners

 

4.4.                 GT Tripping on Excessive fuel flow

 

– For Gas Fuel:

 

  1. Check fuel gas pressure at GT inlet
  2. Check pressure switch for natural gas to GT Low pressure Trip for correct setting
  3. Check proper operation
  4. Check LV DT for SRV position for proper feedback

 

– For Liquid Fuel:

 

  1. Check all fuel lines after stop valve upto nozzle are filled
  2. Check all purge drain valves for any passing or any valve is open
  3. Check liquid fuel HP filter for proper venting
  4. Check for proper operation of liquid fuel bypass valve
  5. Check for proper liquid fuel flow feedback from flow divider

 

 

4.5.             GT Tripping on Flame Failure:

 

  1. Check for any leakage of trip oil to stop valve (SRV/liquid fuel stop valve)
  2. Check pressure switch for low fuel pressure at GT inlet for proper functioning
  3. Check healthiness of flame scanners

 

4.6.                 GT Tripping on OFF base lube oil system trouble:

 

  1. Check OFF base skip lub oil tank level
  2. Check OFF base skid lub oil temperature
  3. Check OFF base return line pressure
  4. Check for any seal leakage in warren pump

 

4.7.                 GT Failure to Reach FSNL:

 

  1. Check any OFF base lub oil system trouble if firing liquid fuel
  2. Check proper acceleration of GT
  3. Check any change in control constraints in FSR control from the one specified in control specification
  4. Check proper functioning of inlet guide vane and position feedback LVDT
  5. Check any hunting in supply fuel pressure while GT is accelerating
  6. Check divertor damper and guillotine gate position for any exhaust pressure high trip.

 

4.8.                 GT Tripping on Excessive Combustion Trouble:

 

  1. Check malfunctioning of any exhaust thermocouple.
  2. Check for almost equal pressure on selector valve for all nozzles after flow divider in case firing liquid fuel.
  3. Check for any passing of purge drain valve for liquid fuel.
  4. Check for any combustion chamber leakage.
  5. Check for any liquid fuel leakage near nozzles.
  6. Check for any atomising air leakage near nozzle
  7. Check for proper feedback of liquid fuel flow from flow divider.

 

4.9.                 GT Exhaust Spread High:

 

  1. Check for healthiness of all exhaust thermocouples, compressor air inlet thermocouple and compressor discharge thermocouple.
  2. Check for almost equal pressure in all fuel lines to combustion chamber at selector valve
  3. Check for any choking of liquid fuel nozzle
  4. Check for any passing of purge drain valve
  5. Check for any combustion changer leakages
  6. Check for any atomising air leakages

 

4.10.              Diesel Engine failure to stop on Auto:

 

  1. Check for healthiness of 20 DV solenoid valve
  2. Check for any passing of 20 DV solenoid valve

 

 

 

 

 

28 thoughts on “O&M PROBLEMS OF THERMAL POWER STATIONS”

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