Ge 9fa mark 6e
In logic
Ac seal oil pump start when there low differential pressure between oil and hydrogen
Dc seal oil pump start when the differential still for 10 second
and also run if there low seal oil inlet pressure
Questions is why ac seal not run first when there is low seal oil inlet pressure

 

Low seal oil pressure assumes the AC pump is already running. If the system is enabled, the AC pump starts first.

 

But what hapeen is
Alarm active / low hydrogen purity or seal oil differential pressure shut down
And then DC seal oil pump run
And ac seal pump not running

 

Typically DC pumps are on a fail-safe and drop-out-to-run. They will always run if the pressure in the system is LOW. This is to protect the system in the event of an AC power failure. In order to prevent the DC pump from running, you usually need to open the breaker for the DC pump.

So what I am hearing from you is this in order:
System running normally
Alarm for low hydrogen purity or seal oil differential pressure shut down
AC seal oil pump stop
DC seal oil pump start

IF this is correct, I suspect the logic is telling the AC pump to stop, the oil pressure is going low and the DC pump is starting on low oil pressure.

 

In our system
In normal operation Seal oil supplied from lube oil
So when this alarm active the DC run first and ac not running
And there is no event that control try to run ac
And in logic ac related to low differential and if still low dc run
And DC related to low seal pressure switch
My question is why control didn't try to run ac first before DC
Because DC still running due to problem in lube oil pressure and ac not running