Ours is a 9FA machine. 2 days back, we measured generator seal oil flow measurement by conducting bucket test as per GE manual procedure & in presence of GE TA. Found that 14.5 lits in 1 min, where as 2 yrs back it was found 22 lits in 1 min. During this period H2 consumption also increasing day by day. What could be the reason for less flow & what is the optimal flow?

 

Vinu,

You failed to mention when the increased hydrogen consumption started. After a maintenance outage? After a trip from load? After a period of increased generator or load coupling vibration?

Seal Oil is intended to keep hydrogen from leaking out along the shaft of the machine.

If hydrogen consumption is increasing, and Seal Oil flow-rate is decreasing, then, presuming there are no other leaks out of the generator casing or hydrogen coolers, etc., that there is insufficient Seal Oil flow-rate to prevent hydrogen from escaping along the shaft of the generator.

Now, the question is: Why has Seal Oil flow-rate decreased? Well, that would seem to occur when something prevents flow. Some blockage or obstruction. Either to the Seal Oil Differential Pressure Regulator, or from the Seal Oil Differential pressure regulator, or through the the Seal Oil flowmeter (sometimes called a "flowrator" I think).

You failed to mention what the Seal Oil Differential Pressure was before, during, and after the test.

You failed to mention if you were measuring Seal Oil flow at the Turbine End or the Exciter End of the generator, or if you were measuring total Seal Oil flow to both Turbine- and Exciter End seals. Because, this makes a HUGE difference. If the total flow-rate decreases, does that mean the flow-rate to one, or both ends, has decreased, since on most hydrogen-cooled generators provided with GE machines there is a single Seal Oil Differential Pressure Regulator supplying Seal Oil flow to both Turbine- and Exciter End seals.

So, presuming you have determined that hydrogen is NOT leaking from anywhere else in the hydrogen supply system or from any other possible location, AND you have properly determined that, in fact, the Seal Oil flow-rate to one, or both, of the shaft seals is low, then it's safe to presume one, or both of the shaft seals has insufficient flow to prevent hydrogen leakage.

Your dilemma is to determine which shaft seal is experiencing the decreased flow rate (presuming only one seal is!), and then opening the end-shield to determine why the flow-rate has decreased to that shaft seal. Could be seal ring problems, or some blockage in the supply piping, or some problem with the seal drain enlargement tank drain (not likely).

If the flow-rate to BOTH shaft seals has decreased by the same amount, then it's safe to presume either there's something wrong with Seal Oil Differential Pressure Regulator or the Seal Oil Flowmeter (because there's usually only ONE flowmeter for both seals!), or something wrong with the Seal Oil supply (some blockage).

But, you also failed to mention what the Seal Oil Differential pressure has been doing during this period of increase hydrogen consumption. If there was some kind of blockage causing decreased flow to one or both seals then it would seem logical that the Differential Pressure would have increased, and that it would have had to have been adjusted to decrease the Differential Pressure.

Or, if there was a problem with the supply of oil to the Seal Oil system, it's logical to presume that the Seal Oil Differential Pressure would have decreased, which would mean that someone would have had to increase the Differential Pressure.

All of these things work together. It would seem that if you have had to do this "bucket test" before, that you would have considered installing individual Seal Oil flowmeters at each end of the generator to help with monitoring flow-rates without having to perform the "bucket test."

Please write back to answer the above questions, and to let us know how you progress with the troubleshooting, and what the final resolution to the problem is.

Thanks!