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Gas turbine Frame VI lub oil vacuum drop

Gas turbine Frame VI lub oil vacuum drop

(OP)
On Dt. 01.05.2017 we had replaced mist eliminator filter element with new one, post filter replacement MOT vacuum remained in range of 130 to 150MMWC with atmospheric air inlet valve 40% open. On date 15.06.2017 MOT vacuum start falling suddenly and element DP rose up to 100mbar, with both blowers in line. Gradually MOT vacuum killed and got pressurized, which leads to lube oil leakage from AGB i.e. from jaw clutch shaft seal and main output shaft seal. Unit safe shutdown was taken to identify cause of MOT pressurization, following checks done before re-starting unit.

1. All lube oil JB checked for any air ingress.
2. Mist eliminator skid all butterfly valve& NRV checked.
3. Bearing-1&2 Dresser coupling checked for any air ingress.
4. All MOT inspection windows checked for any air ingress.
5. MOT extra opening beneath diesel engine and torque converted checked and sealed.
6. LGB and Generator associated piping checked for any air ingress.
7. Both Blower suction vacuum relief also found OK.
8. Both blower casing drain OPEN to drain out collected oil iff any.
9. Mist eliminator bypass check valve blinded to rule out localized air short circuit.


After above checks, we have again replaced the filter element and unit started. At FSNL with one blower in line MOT vacuum was 200MMWC with atmospheric air inlet 40% OPEN, on loading vacuum start falling and element DP rose up to 95mbar within 4 hours after synchronization.

Following are live lube oil parameters of GT-3 at 23 MW with exhaust blower in operation & other in stand by.

MOT Level=350mm from TOP.
MOP Discharge Pressure=5.9 kg/cm2
Lube oil HDR pressure=1.82bar
Lube oil Temperature=54.7 deg C
MOT vacuum=70mmwc.
Metal temperature:
Active Thrust bearing=67/67 deg C
N-active thrust=68/72 deg C.
bearing 1=88/66 deg C
bearing 2= not available.
LGB= 67/--- ,72/---
Generator front/rear= 64/65 76/74 deg C

Bearing 1 drain=66(T) and 64 (j)deg C
Bearing 2 drain=82 Deg C.
Lub oil analysis report is also attached herewith.Where no major deviations observed.

Can anybody suggest possible casuse?

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