Generator Air Tightness Test

Generator Air Tightness Test

• Period Of Test= 24 Hrs without a Break
• Air Pressure Drop (Allowed in 24 Hrs) : <=0.15 ksc
• Air Test Pressure = 3.5 ksc
• All LLDs Drain Closed.
• Ensure Seal Oil system in Operation
• Seal Oil DP >1.5 ksc
• AS Seal Oil Pr>4.5 ksc, start H2S Seal Oil system
• H2 Cooler Isolated
• PW in Winding is in filled condition, Winding Isolated. PW also kept Isolated.
• PW Tank at Atmospheric Pressure
• Ensure availability of  Instrument air and Bleed Out moisture from it by keeping it open till 
• Connect flexible air hose with the gas plant through the coupling and ensure no air leakage is there 
• The filling is to be done by opening the valves in the normal H2 filling line where as the valve from H2 rack side will remain closed.
• Once the air filling is commenced the test record data sheet 
• The air valve is to be opened full.
• While pressurising the LLD / Seal oil DP / Seal oil parameters are to be recorded as per the enclosed sheet.
• The generator casing is to be pressurised with instrument air up to pressure of 3.5 ksc.
• The approximate time to attain rated pressure will be around 7- 8 hrs 
• Record the time when the pressure has reached at 3.5 ksc at the special gauge fixed in the gas rack 
• Stop the air filling and shut off the valve when the test pressure has been reached (3.5bar) and then disconnect the air hose from the system to avoid further pressurisation of the system. 
• Once the rated pressure has been attained, the test can be commenced. 
• Once the test is commenced the test record data sheet is to be filled at hourly basisfor continuous 24 hrs. No break is allowed. 
• During test ensure the LLD‘s are not getting oil 
• If a pressure increase was observed in the primary water tank, a leak of the primary water system with in the generator would be expected and must be located and attended 
• If an air loss higher than 0.15 bar/ 24 hrs, a search for leakages must be made.
• Suspected areas should be brushed with Diprol or other foaming solution. The formation of bubbles (foam) indicates a leak. 
• Attend the leakages and then repeat the test until satisfactory results are obtained.
• If a satisfactory tightness is established the generator may be filled with CO2 and subsequently with H2 as per normal operation practice. 
• After the test is declared complete, the air is to be depressurised and the system is to be normalised 
• After completion of the test, the electrical purity meter system should be calibrated with pure CO2 and H2 
• Normalise the primary water coolers and take the primary water system into service.
• Normalise the all-4 hydrogen coolers 
• Then the generator may be filled with CO2 and subsequently with H2 as per normal procedure.   
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Seal Oil system Charging

Pre – start checks 

(For air side seal oil PPS)

1. Turbine lube oil system is in service.
2. Seal oil storage tanks level is normal ( low level alarm not persisting )
3. Ensure that following valves are open :----

• Shut off valve from seal oil storage tank at oil canal.
• Shut off valves before seal oil Pumps ( air side )
• Shut off valves after seal oil Pumps ( air side )
• Shut of valves before and after DPR valves
• Shut of valve before float valve in oil inlet to seal oil tank.
• Shut off valve after float valve in oil drain line from SOT
• Shut off valves after flow indicators of air side, H2 side and ring relief seal oil at 8.5 m rack.
• Air side and H2 side seal oil signal to pr. Equalizing valve at 8.5 m rack.

4. Ensure venting of air side seal oil cooler and filters.
5. Ensure cooling water is available for seal oil coolers.
6. Ensure root valves of all instruments are open at “O” m & 8.5 m
7. Ensure interconnecting valve to H2 side seal oil system is close.
8. Gen. Brg. Exhaust fan is in service.
9. By pass valve of float valve in oil drain line from SOT is close.

Pre – start checks 

(For H₂ side seal oil Pumps)

1. Air side seal oil circuit is in operation.
2. Air side seal oil pr. > 4.5 Ksc at 8.5 m.
3. Seal oil Tanks level is adequate.
4. Ensure that following valves are open

• H₂ side seal oil Pump suction valve.
• H₂ side seal oil Pump discharge value.
• Manual isolating value after DPR valve
• Isolating valve before H₂ side seal oil cooler.

5. Ensure proper venting of H₂ side seal oil coolers and filters.
6. Ensure cooling water is available for seal oil coolers.
7. Ensure that manual isolating valve in H₂ side seal oil Pump discharge header for seal oil storage tank is close. 

ROUTINE CHECKS FOR SEAL OIL SYSTEM

1. Air side and H₂ side seal oil pumps discharge pr. is ( 10  1) Ksc
2. Air side and H₂ side seal oil temp in the range of 35 to 40C
3. Air side and H₂ side seal oil filters are not chocked.
4. SOT level is normal
5. Inter connecting valve between H₂ side and Air side seal oil circuits is close.Inter connecting valve in between DPR valves is close
6. Stand-by pump is lined up and not rotating in reverse direction.
7. Seal oil flow and pressure is adequate in air side, H₂ side and ring relief supply line at 8.5 m rack.
8. Air side seal oil / H₂ gas differential pr. is 1.3 to 2 Ksc
9. H₂ side and air side seal oil DP at seals is 10-20 mbar.
10. Gen. Brg. Vapour exhaust fan is running and ensure vapour is coming out to atmosphere.
11. Ensure no oil in LLD ( Liquid Level Detector)
12. By-pass valve of float in oil drain line from SOT is close. 

24V DC Fail

24V DC Fail

EMERGENCY INSTRUCTIONS

Identification of the Emergency

• 1. Boiler trips on loss of 24V DC Supply protection. Turbine trips on boiler trip protection followed by generator.
• 2. All controls operating on DDC becomes inoperative

Response in Handling the Emergency
Action Responsibility Remarks

• 1 Confirm tripping of turbine. In local governing rack the trip oil pressure should be ‘0’ otherwise trip turbine from emergency trip lever in governing rack. Trip TD BFPs from local governing rack UCE & TG Engineer
• 2 Confirm tripping of generator i.e. opening of GCB. If GCB has not opened, open 952 and 852 breakers from switchyard UCE 
• 3 Confirm starting of AOP (local) on turbine trip, otherwise start EOP from local for both main and TDBFP turbines. UCE & TG Operator 
• 4 Confirm running of ACSOP(local) if no seal oil pump is running immediately start DCSOP from local UCE & TG Operator 
• 5 Confirm AC scanner fan is in service(local),else start DC scanner fan from starter panel in LT switch gear room in TG floor Boiler Engr & Operator 
• 6 As controls are in operative do the following operations 
• A Stop FD fan, ID fan and BCW pumps (from local push buttons or switch gear). Close boiler stop valves Boiler Engr & Operator 
• B Stop MD BFP (from local push buttons or switch gear), if it was in service as D/A and drum levels cannot be monitored. TG Engr. & Operator 
• C Depressurise MS, CRH and HRH lines, Kill vacuum. Open atmospheric drains of MS,CRH and HRH lines TG Engr & Operator 
• D Stop CEPs and isolate make up to hot well since hot well level indication is not there TG Engr & Operator 
• E At 540 rpm turbine speed start DC JOP from local, and at 210 rpm open turning gear valve manually UCE,TG Engr. & Operator 
• F Continue to run DMCW pumps. Monitor and maintain DMCW tank level from local Boiler Engr & Operator

HP bypass valve starts opening : Emergency

Emergency Handling by Opn Gr-II:Unit in CMC

Unit Status before 

Unit Load : 350 MW 
Coal Flow : 260 TPH
Mills I/S : BDEFG 
Oil Guns I/S : Nil

INCIDENT:

• 12:59:00 HP bypass valve BP-2 started opening & got opened up to 98% & at 12:59:31 BP-1 also started opening & opened up to 98%.

ACTION TAKEN:

• Machine came in CMC- pressure control mode (earlier in CMC-load control mode) due to pressure deviation and load came down to 174MW. Machine taken in TF mode pressure control after reducing throttle pressure
• HP bypass OSU pump buttons in vertical panel acknowledged, OSU pump-2 took start, but still the valves stayed in open condition.
• AB elevation oil gun taken in service and feeder F unloaded to min followed by oil support at CD elevation for flame stability.
• MDBFP kept in service and TDBFP- A hand tripped to maintain drum level.
• Further as Drum Level was still increasing TDBFP-B also hand tripped due to which runback acted and tripped mill G.
• MDBFP suction flow maintaining high and drum level also increasing rapidly so drum level control taken in manual.
• Air flow master taken in manual and total air flow increased from 950 to 1050 tph
• HP bypass BP-1 and BP-2 closed from local and unit stabilized. Drum level kept in auto at 280MW with MDBFP and one TDBFP in auto.

ANALYSIS:

• At 12:59 HP bypass valve BP-2 opened up to 98% while demand was 0 followed by opening of BP-1 valve also up to 98% . 
• Load came down to 174 MW from 350 MW and drum level was fluctuating. For controlling the drum level MDBFP taken in service and later both TDBFPs hand tripped one by one.
• It was observed that HP bypass OSU pump-2 took start and run time exceeded alarm came followed by opening of HP bypass valves. HP bypass OSU pump-1 also took start but from MMI close command for BP valves not executing. OSU pump faults acknowledged from vertical panel and OSU pump-2 took start but still valve were full open.. Local checked no oil leakage observed .Both bypass valves closed from local

OBSERVATIONS :

• HP bypass valves did not trip on downstream temperature high.
• OSU pumps operation was normal till 12:56.
• Drum level variation: +ve 138mm & -ve 320mm.
• TDBFP A ESV not getting opened after resetting.
• It is learnt that while doing cleaning by C&I mtc in the HP Bypass area (No PTW/LWC issued) inadvertently BP2 fast opening accumulator valve was opened which was earlier kept closed due to suspected drifting in BP2 valve

SUGGESTION :

• Any PM or Mtc work in HP Bypass valves area should be properly intimated to Operation by taking PTW/LWC.
• HP Bypass valve area being the most vulnerable, any maintenance/operation work should be carried out under proper supervision by respective executives.

NOTE:

• No PTW/LWC was issued from operation related to HP bypass on dtd: 06.09.2016 i.e.; the day 

CHECK LIST FOR AIR INGRESS IN CONDENSER

CHECK LIST FOR AIR INGRESS IN CONDENSER

Sl No	Description	Location	Checked status
1.	Valve gland sealing water pressure (UCB).	UCB
2.	Gland steam pressure & temp	UCB
3.	Vacuum breaker Valve	17 mtr
4.	HPT / IPT / LPT glands	17 mtr
5.	TDBFP-A  gland	17 mtr
6.	TDBFP-B  gland	17 mtr
7.	LPT Diaphragm	17 mtr
8.	TDBFP-A  Diaphragm	17 mtr
9.	TDBFP-B  Diaphragm	17 mtr
10.	LPT Manholes  ( both side )	17 mtr
11.	TDBFP-A  exhaust valve	8.5 mtr
12.	TDBFP-B  exhaust valve	8.5 mtr
13.	LPH-2/3 vents to condenser	8.5 mtr
14.	HPHs vents to condenser	8.5 mtr
15.	LPH-2 shell side vent line valves & flanges	8.5 mtr
16.	LPH-3 shell side vent line valves & flanges	8.5 mtr
17.	Vaccum p/p-1/ 2 suction line manual valve glands at condenser	8.5 mtr
18.	Condenser Man holes (8.5 mtr both sides)	8.5 mtr
19.	LPH-1 Emergency drip to condenser( LCV-0700)	0 mtr
20.	LP Header-2 drip line ( LCR-0757B-HD4-022)	0 mtr
21.	LP Header-3 drip line to condenser	0 mtr
22.	HPH-5A/5B emergency drip to condenser	0 mtr
23.	Drainn valves connected to TFT-1/2	0 mtr
24.	TFT-1/2 header connections	0 mtr
25.	Condenser level transmitters.	0 mtr
26.	Condenser level Switches.	0 mtr
27.	Vaccum pump-1, 2 suction line manual and motorised valve glands and flanges.	0 mtr
28.	Deaerator  to condenser valve glands (Co-I5I)	0 mtr
29.	CEP recirculation lines-A, B, C valve glands.&vents and drains	0 mtr
30.	LPH-1 normal drip top condenser valves.	0 mtr
31.	CEP – A/B/C glands	(- m  mtr)
32.	CEP – A/B/C   suction strainers & vents	(- m  mtr)
33.	CEP – A/B/C suction line drains	(- m  mtr)
34.	Hotwell drain line passing	(- m  mtr)
35.	CEP suction and discharge line flanges	(- m  mtr)
36.
37.