I have a problem of expelling oil out from the bearing drain enlargement resulting in the escape of oil level in the reservoir. so I would like to know the reasons leading to the floating of the oil in the bearing drain enlargement?

 

This is almost always due to a bad seal, either on a shaft or in a bearing.
Or maybe:
Over filled oil reservoir.
Careless filling of the reservoir.
Over pressurization of the lube system.

 

<b>When did this problem start?</b> is always the first question that should be asked whenever something like occurs on a machine that has been running fine.

After a maintenance outage? Were the generator bearings/seal oil rings removed and/or replaced during the outage? Was the generator oil drain piping disturbed (disassembled/reassembled) during the outage?

Did the machine experience high vibrations on the end with the bearing drain enlargement problem (TE, Turbine End; or CE, Collector End)?

Did the machine experience a trip from high load while the rotor was hot, and maybe a loss of AC lube oil pump flow because of a slow-to-react/start Emergency L.O. Pump?

A review of the generator oil system P&ID should show you the path the oil takes from the enlargement tank back to the L.O. reservoir. If we're talking a GE-design heavy duty gas turbine generator, the path is to the loop-seal then back to the L.O. reservoir. There's not much piping between the bearing drain enlargement tank and the loop-seal. So, an obstruction in that piping or an improperly installed flange gasket in that piping could be the cause.

Oil is supposed to reside for a short period in the bearing drain enlargement tank--that's it's purpose, to allow any entrained hydrogen to be liberated from the surface of the oil in the enlargement tank (the tank is horizontal to make the surface larger--hence the name "enlargement"). So there should be some oil level in the enlargement tank at all times.

If the flow from the bearing drain is too high then it could be possible that somehow the flow to the bearing has gotten too high--not very likely on a running machine without some other indication, such as increased vibrations and maybe a change in L.O. header pressure (decreased). Without looking at the P&ID for the generator oil system, it's not possible to know if there is or should be an orifice in the oil feed line to the affected bearing that isn't there or is the wrong size (too large). But, you have the drawings and can review them so see the oil paths, and investigate why the flow out of the enlargement tank is restricted <b>OR</b> why the flow into the enlargement tank has increased, either because of improper reassembly after an outage, or increased wear of the bearing, or some other similar problem.

Lastly, I don't think I've ever seen a "vent" line on an enlargement tank that is "visible." Because the vent is usually connected to some piping that is also connected to seal drain enlargement tanks (Hmmm....) and to a location where any hydrogen can be vented to atmosphere without fear of fire or explosion--which is usually a location pretty high above the generator deck.

Again, the first question to always be asked is: What changed prior to the start of this problem? Because, it usually happens that something triggered this problem (high or increased vibration; improper reassembly; trip from high load; etc.). These things don't usually just
start by themselves.

More information about the site, type of machine (gas turbine-generator; steam turbine-generator; make and model; etc.) may allow others to provide more information. But this should get you going. Always refer to the appropriate P&ID for the system, and then start checking the possible causes--in this case, a restricted outflow or an excessive inflow. And, <b>ALWAYS</b> ask: When did this problem start? And what happened or changed at about the same time as this problem started?

Please write back to let us know what you find and how you resolve the issue.