15-Emergencies in power plant operation

 

Emergencies in power plant operation: Following are some of the emergencies that are normally faced during operation of power plant.

1.Tripping of boiler: Following are the main cause of tripping of boiler

• Low drum level
• High furnace pressure
• High/ low bed temperature
• Tripping of boiler due to failure of FD, PA, SA  and ID fan
• Electrical fault in Boiler MCC

2.Tripping of Boiler; Case: 2 Boilers & 2 Turbines

Actions to be taken:

• Reduce load at turbines so that inlet pressure to turbine maintains at operating value.
• Share load equally on both the turbines.
• Close main steam stop valve of the tripped boiler.
• Ensure that all coal feeders (fuel feeding system) and fans are stopped on tripping of boiler.
• Maintain drum level.
• If required stop one boiler feed pump (BFP).
• Check the cause of tripping of boiler and try to rectify the fault.
• If boiler fault is rectified, start the boiler with startup compartment and gradually increase boiler pressure and temperature (Follow hot/warm start up curve)
• Synchronize the boiler with the running boiler.
• Start one more BFP
• Take compartment one by one into line and increase the load
• Maintain the equal load on both turbines as per requirement
• Finally stabilize the power plant operation.
• If the boiler fault cannot be rectified immediately, decision of stopping of one boiler can be taken after due consultation with station manager.

3.Tripping of Turbine

Followings are some of the causes of tripping of turbine

• Any one of the protections or interlocks of turbine or generator generally initiates tripping of turbine.
• In some of the cases spurious tripping is caused due to mal functioning of instruments.
• Due to mal operation of the operating staff.

4.Non-availability of Fuel (Normal Shut Down): (Case: 2 Boilers & 2 Turbines)

Take planned shutdown of power plant in following ways.

• Reduce station load by switching off export feeders.
• Stop one turbine and put it on turning gear once turbine speed comes to zero.
• Stop one boiler by slumping the compartments one by one. Slumping of compartment is done in the reverse direction i.e. 5th compartment is slumped first and so on.
• Reduce further load by switching off the auxiliaries.
• Finally, one turbine runs on auxiliary power load. If STG running on synchronized condition, generator breaker can be opened on auxiliary load. If STG runs on islanding mode, synchronize STG with DG or grid and transfer auxiliary load to DG or grid before opening Generator breaker at minimum STG load.
• Stop the turbine and put on turning gear in due time.
• Stop ACC fans or CT fans, CEP etc. in due time.
• Keep open main steam line & other process steam line drains.
• Once fuel is made available, restart power plant as per cold start up procedure

5.Non-availability of DM Water

• Plan for normal shut down.
• Build up DM water in DM storage tank and restart Power plant as per start up procedure

6.Fuel handling / Fuel feeding system Break down

• Causes of Fuel handling & fuel feeding system failure
• Belt cut
• Mechanical equipments like gear box, coupling & pulley failure
• Electrical equipments like motor & feeders failure

Take following actions

• Inform the station Manager & reduce the steam demand
• Switch off the export feeder
• Trip the Turbine & put it on turning gear as per SOP
• Stop the other fuel feeding & fuel handling system
• Stop the fans sequentially
• Hot box up the Boiler as per SOP
• Attend the breakdown
• Re-start the plant as per SOP

7.Boiler feed pump incomer supply failure

• Causes of incomer supplier failure,
• Breaker trip
• Relay malfunction

Take following actions

• Reduce the steam demand, trip the export feeders
• If supply is not restored within minute,trip the Boiler & Turbine manually
• Hot box up the Boiler
• Put STG on turning gear as per SOP
• Stop the fuel handling system
• Identify & troubleshoot supply failure
• After restoring the BFP incomer power supply, stat the Boiler feed pump & maintain drum water level
• Start the Boiler as per SOP (Hot or Warm)

8.Main steam line leakage

• Probable Causes of main steam line leakage,
• Leakage in welding joint due to corrosion & rusting
• Uneven expansion
• Water hammering

Take following actions

• If leakage is heavy inform the station Manager & reduce the steam demand
• Switch off the export feeder
• Trip the Turbine & put it on turning gear as per SOP
• Stop the fuel feeding & fuel handling system
• Stop the fans sequentially
• Hot box up the Boiler
• Identify & arrest the leakage
• Analyze the causes of leakage
• Start the Boiler & STG as per SOP

9.Turbine HP valve gland leakage

Probable Causes of HP valve gland leakage,

• Turbine Load hunting
• Ageing
• Poor fitment of gland packings during overhauling

Take following actions

• If leakage is heavy inform the station Manager & reduce the steam demand
• Switch off the export feeder
• Trip the Turbine & put it on turning gear as per SOP
• Stop the Boiler as per SOP
• After cooling, attend the gland leakage
• Start the Boiler & Turbine as per SOP

10.Tripping of Auxiliary Transformer

• Following are the probable cause of tripping of auxiliary transformer.
• Heavy earth fault in any of the LT drives.
• Tripping on transformer protection like low oil level, high oil/winding temperature, Buchholz relay operation etc.

On tripping of auxiliary transformer, total power plant will trip. Proceed as follows to tackle the emergency.

• Resume auxiliary power immediately.
• Ensure STG have got tripped and shutdown safely
• Ensure boilers are tripped.
• Close MSSV.
• The drives, which were put on auto, take all of them on manual.
• Close all the control valves.
• Once auxiliary power is available, start one BFP and take water into boilers.
• To resume auxiliary power stand by Auxiliary transformer can be taken to service if HT voltage available in bus or by closing PCC bus coupler.
• Put STG on turning gears after starting AOPs.
• Start the power plant as per hot start up procedure.

11.Tripping of Export Transformer

• Following are the probable causes of tripping of export transformer.
• Heavy earth fault in any of the LT drives.
• Tripping on transformer protection like low oil level, high oil/winding temperature, Buchholz relay operation etc.

On tripping of export transformer,power plant will come to Island mode operation. Proceed as follows to tackle the emergency

• Ensure Turbine has not tripped on high pressure
• Maintain Boiler operating pressure by controlling start up vent control valve
• Operate Boiler & STG on home load
• If process needs steam, charge the steam from PRDSH as per SOP
• Maintain Boiler load as per steam process demand
• After troubleshooting the transformer, synchronize the Turbine with grid & start to export the power
• Slowly cut off the PRDSH steam to process & charge the process steam line through Turbine extraction steam.

Reference books for power plant O&M

 12.Tripping of Export Feeder

Probable cause of tripping of feeders are,

• Over load
• Earth fault
• Maintain main steam header pressure

Take following actions

• Ensure that dumping system has acted to cope up increase in pressure. If dumping system is not available, maintain Boiler pressure by operating start up vent CV & also take combustion system in manual mode to reduce firing as per requirement
• Reduce load on boiler, if required slump one compartment of a boiler or both the boilers.
• Ensure that dumping system ceases to operate and system is stabilized at reduced load.
• Analyze the cause of tripping of feeder and rectify.
• Once problem is sorted out and rectified, take export feeder in service after due consultation with consumer.
• Gradually increase load on power plant and stabilize.

13.Turbine Oil Leakage

• Causes of oil leakage in turbine area,
• Leakage in oil line caused by failure of joints or flanges or due to vibration in oil line.
• Spillage through centrifuge due to seal break.

Take following actions

• If it is in Lube oil (LO) oil or hydraulic oil line, plan for safe shut down.
• Try to attend leakage under emergency plan.
• Analyze the cause for oil leakage to avoid future leakages
• Do leak testing and restart the turbine
• If it is in other area like in Centrifuge, isolate centrifuge.
• Top up oil in MOT, if required.

 14.DCS failure

• Probable Causes of DCS failure,
• DCS power supply failure
• DCS controllers failure
• DCS other accessories like card, switch & SMPs etc failure

Take following actions

• During DCS failure, DCS operators cannot judge the plant operating condition so need to take following actions.
• If Turbine not tripped automatically, trip it manually through emergency push button provided in Governor panel.
• Trip the Boiler manually (Stop Fuel feeding system, Boiler fans & fuel handling system) & close MSSV manually
• Start Turbine Lube oil pump manually & put STG on barring gear.
• Start BFP manually & operate the control valves manually in field.
• Observe drum level from local level gauge glass
• Analyze the cause of DCS failure.
• After troubleshooting start the DCS as per SOP
• Then start the plant as per SOP (Hot or warm)

15.UPS  failure

• Probable Causes of UPS failure,
• UPS battery failure
• UPS cards failure

Take following actions

• After UPS failure, DCS also gets fail & DCS operators cannot judge the plant operating condition so need to take following actions.
• If Turbine not tripped automatically, trip it manually through emergency push button provided in Governor panel.
• Trip the Boiler manually (Stop Fuel feeding system, Boiler fans & fuel handling system) & close MSSV manually
• Start Turbine Lube oil pump manually & put STG on barring gear.
• Start BFP manually & operate the control valves manually in field.
• Observe drum level from local level gauge glass
• Analyze the cause of UPS failure.
• After troubleshooting of UPS start the DCS as per SOP
• Then start the plant as per SOP (Hot or warm)

 

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