GE-9fa gas turbine DC emergency seal oil pump is not developing discharge pressure >80 psi instead of 90 psi as a result H2 seal oil dp low pressure

Dear sir,

Please be informed that GE-9FA gas turbine DC emergency seal oil pump failed to maintain H2 seal oil DP also same pump is not developing discharge pressure more then 80 psi instead of 90 psi. Could you please advise how to resolve the issue.



88QS-1AC Seal oil pump and 88QS-2 DC emergency seal oil pump TEST run observation given below.


1. 88QS-2 DC emergency seal oil pump started manually for 5 minute to confirm pump discharge pressure, pump disch press recorded 80 Psi.


2. unit cool down made off , hydraulic Pump and main lube oil got off , 88QS-1AC seal oil pump started on auto pump discharge pressure reached to 90 Psi ,

Seal oil DP maintained 0.52kg/cm2.(Normal)


3. 88QS-1AC seal oil pump made off manually 88QS-2 DC emergency seal oil pump started on auto pump discharge pressure reached to 80 Psi,

Seal oil DP came down to 0.21kg/cm2 with seal oil DP low alarm.


4. 88QS-2 DC emergency seal oil pump made off manually 88QS-1AC seal oil pump started on auto DP maintained 0.52kg/cm2. alarm got reset.
 
Amanat Hossain,

Is this the first time you have tested the DC pump running solo and noted this problem?

Are the AC and DC Seal Oil Pump motors rated for the same kW/horsepower?

Are the Aux. and Emergency Seal Oil Pumps the same pump?

What is the speed of the DC Emergency Seal Oil Pump motor when it's running without the Aux. Seal Oil Pump motor running?

What is the current draw of the DC Emergency Seal Oil Pump motor when it's running without the Aux. Seal Oil Pump motor running?

Finally, it's NOT the purpose of the DC Emergency Seal Oil Pump to maintain seal oil pressure indefinitely when the Aux. Seal Oil Pump motor is unavailable. The purpose of the DC Emergency Seal Oil Pump is to prevent hydrogen from leaking out along the generator rotor shaft as the unit is coasting down to zero speed when the Aux. Seal Oil Pump Motor is unavailable. Once the unit reaches zero speed, then the generator will go into purge mode, and the DC Emergency Seal Oil Pump's purpose is to prevent hydrogen from leaking out of the generator along the generator rotor shaft.

The purpose of the DC Emergency Seal Oil Pump is to prevent hydrogen from leaking out of the generator during coastdown and during purging. That's it. It's NOT intended to indefinitely maintain Seal Oil Pressure, without alarm, while the Aux. Seal Oil Pump is being restored to normal operation. That is a huge fallacy--that the DC Emergency Seal Oil Pump should maintain Seal Oil pressure indefinitely, without alarm, until the Aux. Seal Oil Pump can be restored to operation. Full stop. Period.

It's likely that the speed adjustment of the DC Emergency Seal Oil Pump is not correct; the speed should match the motor nameplate rating. It's also likely that the Emergency Seal Oil Pump is not rated for exactly the same pressure/flow as the Aux. Seal Oil Pump, which means that unless the DC Emergency Seal Oil Pump Motor is running at nameplate rated speed the pressure/flow is probably not sufficient to prevent a low Seal Oil Differential Pressure Alarm--BUT is still capable of supplying sufficient pressure/flow to prevent hydrogen from leaking out during coastdown and purging, thereby preventing a possible hydrogen fire.

Lots of things to check and verify--and it's also important to understand the intent and purpose of the Emergency Seal Oil Pump and it's motor. The philosophy is to prevent hydrogen leakage during coastdown and purging--nothing more and nothing less. as long as the Seal Oil differential pressure is positive and greater than 0 (bard or psid) then it is working to prevent hydrogen leakage and a possible hydrogen fire. Anything else is icing on the cake (meaning that if there is no Low Seal Oil Differential Pressure alarm and the Seal Oil Differential pressure is greater that 0 (bard or psid) and no hydrogen is leaking out along the generator rotor shaft during coastdown and purging--then the operational philosophy has been met and all is good.

Hope this helps! If you want to continue the discussion, you need to provide more data. No further data; no further discussion. And the answers to all the questions posed fall under the category of 'further data.' (We will be the judge of relevancy; you asked for help, we need data. That's relevant.)
 
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