Dear Experts...

First of all, i am really sorry for my english capability...
We have a GE Frame 9 Hydrogen Cooled Generator, right now we are facing a big problem for our generator. Until right now, the alarm of Seal Oil Drain Enlargement Level high still active, and we have to drain the flooding oil at the Seal Oil Drain Liquid Detector every time. Could u imagine it, that total of oil loss due the problem approximately 200 litre per a day.

The alarm will activate when the Generator's load above 75 MW, and also when the Generator's load at 75 MW but the Hydrogen pressure at 30 psi.

We already tried to reduce the differential pressure between H2 and Seal Oil system, from 5,5 psi to 4,8 psi at the Seal Oil Regulator, but the action was not the answer of the problem. We also throttled the bypass float trap valve but the problem still exist.

Based on GE-manual book, the source of the problem above could be from the failure of the float trap or drain valves. But we already checked the drain valves (The result is good). And we already checked the float trap performance by seeing the float trap's sight glass, for your information, the sight glass of the float trap is not flooded by seal oil, but the movement of the float trap (as captured from the sight glass) is very active.

Please, help us, what is the source of the problem?

For your information, we have a problem in Generator's vibration too. Could the vibration give the contribution to the problem?

Thank you very much for your help...

 

The Seal Oil Float trap should not be bypassed and if the bypass valve is open could be part of the problem.

Have you looked at the Seal Oil Flow-rate "Rotameter" (I think that's what it's called; an odd name since it doesn't rotate!). How much oil are you consuming?

Have you compared the reading from the flow meter to past readings to see if the seal oil flow-rate has increased?

How long has it been since the seal rings were replaced? They do wear, and vibration can make seal oil consumption worse.

The seals are usually made of a soft metal (bronze or bronze-like) and high vibrations can cause them to flatten and pass more oil. If the consumption is bad enough it will flood the generator cavity, and that's not good.

The seal drain enlargement tanks are not very large and if they are flooding then it's likely that the seal oil flow-rate is excessive, and worn or damaged seal oil rings and/or worn or broken seal oil ring retaining springs would be the most likely cause.

You didn't say how bad the vibration was, or if the vibration increased before or after the seal oil problem began.

 

Thank you very much for your reply, CSA. Based on Logsheet, we found that :

1. Before the problem, the seal oil's GPM approximately : 9GPM ; Differential Pressure of Seal Oil System : 6,5 psi ; Hdyrogen Pressure : 26 psi.This data was taken when the GTG's load at 76,7 MW.

2. Right now, the seal oil's GPM is increasing from 9 GPM to 11 GPM, Differential Pressure of Seal Oil System is decreasing from 6,5 psi to 5 psi (we already mentioned it that we have resetting the differential press. regulator) and Hydrogen Pressure : 27 psi. The data is taken when the GTG's load at 84,9 MW

3. The Generator's vibration approximately 7 mm/s

We replaced our seal rings 2 years ago. When our generator have some trouble in vibration at the first time, the seal oil system still worked in a good condition although sometimes the Seal Oil Drain Level High Alarm was active but we could say it that the problem was happened rarely.

What about the Regulator itself, CSA? We curious that the regulator have some defects, because there is a diaphragm in the regulator that controls the seal oil system. Could the failure of diaphragm give the contribution of the problem?

How do we know, that the Seal Oil's regulator still work in a good condition or not?

Thank you very much...

 

The Seal Oildifferential pressure regulator is principally (is that even a word?) no different from any other pressure regulator--except that it has hydrogen gas pressure on one side of the diaphragm. Wouldn't you agree, then, that if the diaphragm was leaking that it wouldn't be able to hold a constant differential pressure very well? Again, it's just a differential pressure regulator in principle, so it would fail just like any other differential pressure regulator.

Seal rings fail, just like every other mechanical (and electrical) component. Dirty oil is one cause. I don't recall exactly where the Seal OIl system gets its "supply" from but I think when the unit is running it's off the Main L.O. Pump discharge but I'm not certain if that's before or after the Main L.O. Filters; check your L.O. P&ID (Piping Schematic Diagram).

High vibration can cause increased clearances which can cause increased "consumption". I'm not really clear but you seem to have said that you have to manually drain oil from the Seal Drain Enlargement "tanks" which would indicate that there is high Seal Oil flow-rate, higher than the drain lines, piping, and Seal Oil Float Trap can accommodate.

Again, seal rings are made of very soft material, and the springs which hold them in place have been known to break, though I believe that would result in a very high seal oil flow-rate. If they're not installed properly (I think they even need to be "fitted" to the shaft when new using some kind of abrasive if necessary to achieve the desired clearance during installation) they can fail prematurely.

One of the shortcomings of GE hydrogen-cooled generators is that there is usually only one Seal Oil Flow-rate indicator, for both ends of the generator. This makes it extremely difficult to isolate how much each end of the generator is consuming. It wouldn't be too difficult to install a second indicator, and that would make trouble-shooting much easier in the future. This is presuming you don't know which end is having the higher flow at this point.

Can you estimate the temperature of the Seal Oil? If it's coming off the L.O. System after the coolers and filters, then it's probably equal to L.O. Header temperature. If it's coming off the system ahead of the coolers and filters then it's equal to L.O. Tank Temperature. Higher temperature oil would likely result in slightly increased flows to maintain the same differential pressure, but probably not enough to cause the kind of problem you're reporting.

Certainly, the differential pressure regulator could be the problem. Rebuild kits should be available from the manufacturer for the diaphragm assembly, though that would likely require a shutdown to perform safely.

Please write back and let us know what you ultimately find.

 

Dear Mr. CSA

During the Generator's inspection, we have found that the source of the problem is located on the lower spring of Hydrogen Seal Ring at Turbine Side. The spring's hook is broken at one side, perhaps it could make the hydrogen seal ring not in the right place.

The question is:
1. In what condition that the spring's hook can
be broken ?

2. How long is the spring's life time ?

We very thanks for your helps in our problems.

 

Good to hear you've located a source for the problem. If the seals are not maintained close to the shaft all around the shaft, then the amount of oil required to maintain the seal will increase, which will increase the amount of air liberated from the oil in the seal drain enlargement tank.

Incorrect installation and vibration are the major causes of sealing ring and seal ring spring problems.

As for how long sealing ring components will last (including springs), well, that is a function of how they are installed and how they are "maintained", including how much vibration they are exposed to, and alignment of the unit as well as of the seals in the generator end-shields is also important.

I have seen seal ring components which looked like new after more than 12 years of service. They were well-maintained and the units had not experienced any high vibrations or alignment problems. I've also seen some brand new seals fail after only a couple of hours of operation. The seals were installed at the factory (in Japan) opposite of what they should have been, and the one of the spring hooks broke.

Again, it's all about installation and maintenance, including vibration. Some sites will operate a machine for long periods of time with high vibrations just because they aren't at the trip levels and the Speedtronic hasn't tripped the unit. But, prolonged operation with high vibrations will eventually lead to failure(s), and if allowed to continue in a hydrogen-cooled generator the seal rings and/or the retaining springs will likely fail eventually.

 

thanx