We have Alstom Steam turbine with H2 cooled generator with capacity of 400MW with 02 9HA.01 Gas Turbines in CCPP operation.

Problem Statement:
During ST seal oil AC pump change over, DP for ST seal oil system becomes 0 and then returns back after few sec while seal oil pump is running.
For change over both pumps are kept in running and then when one pump is stopped, DP drops to 0 and after few seconds it gets back to normal.
If DP is not maintained at 0.5bars within 15sec then ST trips on Safety of H2 gas leakage.

System Description:
Steam Turbine Generator is H2 cooled and its sealing is ensured by Seal Oil system.
As per design, Seal oil pressure should be 0.5bar above the pressure of H2 inside the generator and to ensure this 02EA self-operated pressure regulators are installed that routes the extra flow back to seal oil tank and ensure 0.5bar DP. There are 02 AC pumps and 01 DC pump (Emergency Pump) installed for the seal oil system.
Some more system details are as follows

1. Seal oil pressure DP to be maintained at 0.5bars
2. Seal oil temperature to be maintained between 25- 39 Deg C
3. If DP reduces to 0.2bars then standby AC pump cuts in and if it is not increased within 5 sec then DC seal oil pump cuts in and if still not increased then ST trips after 15 sec
4. If DP increased above 0.8bars, the extra flow is transferred back to either seal oil tank or suction of seal oil pipe via self-operated pressure regulators
5. System can handle flow from both pumps because of flow adjusting valves
6. IF seal oil system fails, then H2 will be purged from generator and through air extraction ports to air extraction tank to atmosphere

Concerns:

1. Is change over method we used is OK since it is not mentioned in OEM manual?
For pump change over activity we perform following steps

• Both AC pumps in running mode on "Manual"
• One pump is turned "Off" and kept on manual and DP drops to 0.
• DP remains zero while one AC pump is in service.

2. We have doubts on 02EA pressure regulators slow response. Is there any check recommended. (Please note: During normal running condition, DP is maintained as recommended by OEM at 0.51bars)

I have attached the trend of DP vs Pumps changeover activity.

 

We have Alstom Steam turbine with H2 cooled generator with capacity of 400MW with 02 9HA.01 Gas Turbines in CCPP operation.

Problem Statement:
During ST seal oil AC pump change over, DP for ST seal oil system becomes 0 and then returns back after few sec while seal oil pump is running.
For change over both pumps are kept in running and then when one pump is stopped, DP drops to 0 and after few seconds it gets back to normal.
If DP is not maintained at 0.5bars within 15sec then ST trips on Safety of H2 gas leakage.

System Description:
Steam Turbine Generator is H2 cooled and its sealing is ensured by Seal Oil system.
As per design, Seal oil pressure should be 0.5bar above the pressure of H2 inside the generator and to ensure this 02EA self-operated pressure regulators are installed that routes the extra flow back to seal oil tank and ensure 0.5bar DP. There are 02 AC pumps and 01 DC pump (Emergency Pump) installed for the seal oil system.
Some more system details are as follows

1. Seal oil pressure DP to be maintained at 0.5bars
2. Seal oil temperature to be maintained between 25- 39 Deg C
3. If DP reduces to 0.2bars then standby AC pump cuts in and if it is not increased within 5 sec then DC seal oil pump cuts in and if still not increased then ST trips after 15 sec
4. If DP increased above 0.8bars, the extra flow is transferred back to either seal oil tank or suction of seal oil pipe via self-operated pressure regulators
5. System can handle flow from both pumps because of flow adjusting valves
6. IF seal oil system fails, then H2 will be purged from generator and through air extraction ports to air extraction tank to atmosphere

Concerns:

1. Is change over method we used is OK since it is not mentioned in OEM manual?
For pump change over activity we perform following steps

• Both AC pumps in running mode on "Manual"
• One pump is turned "Off" and kept on manual and DP drops to 0.
• DP remains zero while one AC pump is in service.

2. We have doubts on 02EA pressure regulators slow response. Is there any check recommended. (Please note: During normal running condition, DP is maintained as recommended by OEM at 0.51bars)

I have attached the trend of DP vs Pumps changeover activity.

Thanks for sharing such datas /informations on this issue.

I am little bit surprised that nothing, is mentioned in OEM manual regarding this Pumps CHANGEOVER.
After I have check the trend file ( Is that created with OVATION DCS,,? or new version from Mark6e Control toolbox system?), Change over is not doing what you actually decribed .

You said that both pump are runing ( in the trend only one is running then a start signal command is sent to second pump ).

Phase 1
Pump 1 is stopped
Pump2 is runing
DP is around 0.57bar

Phase 2
Before DP DROP BELOW 0.5bar
Pump1 is started ( CMD SIGNAL SENT)
Pump 2 still runing
DP IS DROPPING till 0 bar

After a time delay Pump2 is stopped .
Pump 1 is runing
After another timed delay DP raise till 0.57bar

That's what it is displayed on the trend.


You surely need to review app code and confirm with OEM, about correct operation mode of SEAL OIL PUMPS change over.
This is what is
Is the Application code is in accordance, with what it is displayed on this trends?
I mean did you check that changeover sequencing/logic?

Any tracking documents, procedure from commsissioning staff ??
What the as built documents/drawings tell about this procedure

I am not 100% sure about that change over displayed on the trend......You need to clarify that with OEM.

Also the change over time delay (12 sec duration from DP about 0bar till DP raise and maintained around 0.57bar ) is pretty close to the Trip setpoint ( 15 sec) that you pointed in your post.

Something is missed here, and without be able to check App code and OEM Manuals draqwings, That's pretty difficult to perform a correct troubleshooting.

I do not use to see such change over arrangement in powerplant operations ( all sub systems that need change over are not same but philosophy remains pretty same) .

Hope that can help !

Controls Guy25.

 

Doubt. Not a nice word.

But, since it's being used in this thread, I have doubts about the information provided and the information that is missing. Where is the P&ID for the Seal Oil System?

What has the OEM said about this issue of a prolonged drop in seal oil pressure during a pump changeover? What would happen if one just selected the standby pump to be the lead pump? Or, if the control system tried to start the standby pump in the event of loss of pressure while the lead pump was running? What has tried, other than starting the standby pump manually and then shutting down the lead pump?

If you are not getting the support you need from the OEM, contact the pressure regulator manufacturer or the seal oil system manufacturer for information and assistance. Be prepared to provide P&IDs and more detailed information than provided here in this thread. You may find the pressure regulators provided with the seal oil system are not optimal for the application, or there should be a check valve installed in the system somewhere, or two pressure regulators aren't necessary and can cause issues such as you are experiencing.

This really isn't a controls-related issue. I suggest you join the 9F User's Group and post your issues in their forum(s) where you are much more likely to get the kind of feedback you want with these non controls-related issues.

And be prepared to work with vendors and manufacturers to sort out and resolve issues the OEM was allowed to ignore and not resolve under warranty. Some OEMs and some OEM employees are good to work with; others not so. But if the warranty was allowed to expire before the OEM resolved the problem(s), they become the responsibility of the owner/operator. And posting for help in the wrong free World Wide Web forum isn't always going to yield the desired outcome (which is to get very lucky and have some other poor soul tell you, more or less, how they resolved their problem(s)). And with this problem and the seal oil leakage problem your chances of getting lucky are much better in the 9F User's Group forums. (Just be prepared for a lot of whinging.) Personally, I have found many times--even when I worked for the OEM--that working with manufacturers and vendors was very successful in resolving issues. They want their equipment to work--and work well. And, they often like the feedback and the experience of working to resolve problems and improve their equipment.

We are very happy and anxious to help you with your controls-related problems (exclusive of MBC/ARES issues, which only the OEM can help with).

Best of luck!

 

Thanks for the detailed response and feedback.
We will expect answers from OEM in this scenario.

Moreover, i have made some progress in stated issue 2 days back.

During last pump changeover, there are 03EA DP sensors and all were showing values above 0 and these 03 DP valves are then being averaged out and displayed separately as Sensor "R" and that sensor was bad during change over and was showing "Zero" even though none of the 03 DP sensors were at "Zero".
So we are now checking the logic behind Sensor"R" as if its a average function then it should not be displayed as "Zero" and hopefully we will reach to Root cause.

Thanks for the help CSA and control Guys.

 

A few years back, after the European Gas Turbine outfit was acquired by GE (the Belfort, France, facility) the decision-making responsibility for Frame 9 (E- and F- and now HA-class machines) was given over to the GE Belfort engineering department. Of course--tried and true and time-tested control schemes and philosophies immediately started being replaced. Why? Because GE Belfort had a "better" idea about how to control and operate and protect GE-design heavy duty gas turbines that GE (Schenectady, NY, and Greenville, SC, and Salem, VA) had. So, MANY things started changing--and mostly they just became overly complicated and very, very messy and difficult to understand. This sounds amazingly like one of those things--which was overly complicated and made very messy and difficult to understand. And, along with all of these "improvements" GE Belfort has butchered many signal name conventions which makes it even more difficult to understand what's happening without a secret decoder ring.

Now, in most of GE (heavy duty gas turbines, anyway) they are beginning to really use a LOT of model-based control schemes (also known as MBC in some industries). GE has a new name for this: ARES (Adaptive Realtime Engine Simulation). Mostly the same, but, "new and improved." This may be a part of that MBC/ARES thing--it seems to be encroaching on many aspects of turbine control and protection (Why? Because it can--and because GE Belfort always has a better idea). Without being able to see the application code running in your machine, it's difficult to say.

Good on you, though, for digging into the application code and finding this! Again, whenever GE Belfort is involved one never really knows what to expect.... It will be interesting to know if this "R" value is used for anything other than display purposes.

Please write back to let us know what you find! And what you hear from the OEM...!