Generator ATT

 

 

Guidelines RELATED TO GENERATOR AIR TIGHTNESS TEST

CRITERIA FOR THE ACCEPTANCE OF TEST:

·         The test pressure drop in the system should be monitored for a period of 24 hours. No break is allowed.

·         The gas system can be considered sufficiently tight when the pressure drop during a 24 hours test with compressed air does not exceed 0.15 bar or the loss of air is below 1.5m³/24 hrs (s.t.p).

·         If air loss is higher than 0.15 bar / 24 hrs, a search for leakages must be made.

·         The test pressure should correspond to the rated gas pressure of the generator (i.e. 3.5 bar) in normal cases, otherwise 4.0 Ksc if rotor is threaded out.

RH Metal Temp Optimization

RH Metal Temp Optimization

• Causes of Rh Tube Fail:  

(a) COAL ASH CORROSION FOR TUBING
(b) UNEVEN TEMPERATURE DISTRIBUTION ACROSS THE BOILER

Dry Ash system : 500 MW

Dry Ash system : 500 MW

• Ash is oxidised form of the mineral matters present in coal
• Typical ash composition : SiO2, Al2O3, Fe2O3, CaO, MgO etc
• Coal with more SiO2 & Al2O3, Ash MP > 1400ºC

Shut-Down Procedure: 500 MW (Planned Shutdown)

Shut-Down Procedure: 500 MW

• Reduce load from 500 MW to 400 MW
• Gradualy Reduce Pr SP from 170 ksc to 130 ksc, Load is still 400 MW
• Take unit of TFM

Hydrogen Purging

Pre-Purging checklist:

1. The generator may be on barring gear or at standstill. Preferably be on barring speed of around 50-80rpm (without condenser vacuum).
 At least 60 CO2 filled cylinders should be available in the unit where purging is to be done.
 Arrangement for filling hot water on CO2 cylinder / lines (to avoid freezing) is to be ready.

Loss of Instrument Air

Loss of Instrument Air
Anticipated Problems:

1. No oil burner can be taken in service. Oil guns, oil/steam valves will remain inoperative.
The igniter will not get advance.

Boiler forced Cooling

Boiler Forced Cooling

1 In case of Tube leakage

1.1 After Tripping the boiler ,stop FD fan and keep ID fan running at
minimum load and ensure furnace pressure negative inside boiler.

Condenser : One Pass Isolation

1 Ensure the availability of both condenser de-watering pumps.
2 Decrease the load to 300 – 350 MW
3 Ensure that both CW interconnection valve are opened
4 Start Stand by Vacuum pump

Stopping one FD Fan

1 Reduce the load to 400 MW & then remove from CMC
2 Before Unloading FD Fan (to be stopped ),The following
Permissive & Protection to be kept bypassed :
“FD Fan ON & Discharge Gate close” permissive to be given
“FD Fan ON & Discharge gate auto open” to be bypassed.

Stopping one PA Fan

1 Reduce the load to 300 MW & then remove from CMC
2 Keep 4 consecutive Mills in service. If required , take oil guns in service

Stopping one ID Fan

1. Reduce Load to 300MW
2. Start Unloading corresponding FD fan & increase loading of other FD Fan through blade pitch.

Stopping one PAPH

• Reduce Load to 300MW
• Slowly close flue gas outlet damper for PAPH which has to be stopped

Stopping one SAPH

• Reduce Load to 300MW
• Slowly close flue gas outlet damper (2 in no. )for APH which has to be stopped
• Adjust other PAPH/SAPH flue gas outlet damper
• Close flue gas inlet damper
• Close SCAPH inlet , outlet & bypass damper. During Closing , Observe Air Flow.
• Close SAPH air outlet damper (2 in no.)
• Stop the SAPH motor once flue gas inlet temperature reduced below 150deg C
• Close Air motor main isolating valve & bypass isolating valve

LIGHT UP CHECK POINTS

BEFORE LIGHT UP ACTIVITIES

BOILER SIDE

• MAN ,MATERIAL REMOVED AND BOILER IS READY FOR LIGHT UP.
  

Water-chemistry: 500 MW

Recommended Parameter Values
1. Boiler Water – pH = 9.1-9.4
2. Boiler Water – Specific Conductivity < 20.0 μs/cm
3. Boiler Water – Silica < 100 ppb
4. Boiler Water - Phosphate = 1-2 ppm
5. Boiler Water - Chloride < 0.5 ppm

Turbine Governing system

Key Points

Ø  Governing- Regulation of Turbine Speed under No Load and Varying Load

Ø  Others Works: CV Actuation/ Initial Run-up & Synchronization/ Load Variation to meet Grid Freq

Ø  500 MW KWU: Throttle Governed Machine

Ø  2 Governors , EHC and HG connected in Parallel: Only One at a time through Hyd Minimum slection

Ø  CVs Open according to Secondary oil Pressure

Ø  Between 100 MW  to 525 MW , Load variation done by HPCV throttling

Important Procedures

Vacuum Pulling : Procedure:

Ø  Close RH Vents, CRH, HRH UFT drains

Ø  Close Vacuum Breaker

Ø  Open 8.5 m steam Manual valve full Both (100%), Temp> 250 Deg ( Open

Ø  Start GSC Exhauster Fan

Ø  Start Both Vacuum pumps ( Casing Empty, Receiver tank Level adeq)

Ø  At -0.2 ksc charge steam gradually ( lower Controller from 50% à 0 %)

Ø  Build Vacuum upto -0.9 ksc

Hydrogen Purging

Ø  SLC AS SOP Off, SLC DC SOP Off, SLC H2 SOP Off

Ø  Suppy of DC SOP Off

Ø  Start one AC SOP ( DP=1.5 ksc)

Ø  Dew Point Air=<-10 Deg, clearance from Chemist

Ø  H2 (Isolated Position), CO2(Isolated Position), Air Inlet(Open), Casing vent ( Closed)

Ø  Fill and Pressurise upto 0.5 ksc

Cold start-up

Points to Remember

Ø  maximum of HP casing and HP shaft is less than 150°C(more than 5 days)

Ø  It requires soaking of Turbine at 360 rpm with steam(40ksc,360 Deg)

Ø  An upper limit of 200° C/hr. saturation temp gradients can be allowed, i.e. approximately the boiler pressure can be brought to 20 Kg/ Cm² within an hour of cold start up

Ø  But actual temp gradient is limited by the thick walled Y piece provided in the main steam and HRH lines

Ø  maximum differential temp allowed between inner (98%) and mid wall temp (50%) is ±40°C

Ø  Start only two CC pumps in order to minimize flashing in down comers (and subsequent vibration) when the boiler water is in the range of 85° to 125° C

Main Equipments Tripped