We have GT Frame 9E with Mark Vie control. While fuel change over from Liquid to Gas, we are facing issue as explained below:

After giving command of fuel change over from Liquid to Gas, Gas vent valve before SRV closes and Shut Off valve opens but in the meantime inter valve pressure FPG2 becomes too high and machine takes shut down command.
During several attempts it has been noted that SRV opens fully i.e. 95 % when shut Off valve opens/Fuel change over command is initiated and P2 pressure becomes too high.

What could be the reason of this SRV full opening? the regulator gain is set at 2.5 while Null bias is 2.9.

Would appreciate support for resolution of this issue.

 

Adding some trends with the mentionned parameters could help to understand what is happening at your plant

 

It's very likely the problem IS NOT the Mark* VIe, or any of its configuration parameters--UNLESS something was changed BEFORE the problem started.

The 20VG-1 (usually the device number) intervalve vent should close, and 20FG-1 should be energized to allow hydraulic pressure/flow to reach the SRV actuator.

What we DON'T know is: Does the Mark* VIe test the SRV prior to allowing gas fuel operation to be sure it can stop the flow of gas fuel in the event of a trip or shutdown? This test is common in newer machines; you didn't say how long this machine has been in service.

You also didn't say if the machine has conventional or DLN combustors.

You also didn't say if the Mark* VIe is an upgrade from a previous version of Mark* was the turbine control system the machine was originally commissioned with.

How often does the machine run on liquid fuel and transferred from liquid fuel to gas fuel?

If this liquid-to-gas transfer operation is "regular" (meaning more than 5 or 7 times per year) has it worked without problems in the past?

AND, as ControlsGuy25 mentioned, actionable data (meaning recorded values from different devices/parameters--using Trender (sometimes called Trend Recorder, accessible in ToolboxST) would be MOST helpful in understanding the sequence of events when a transfer is initiated AND what is actually happening during the transfer.

If the oil quality is not properly maintained it could be that the servo-valve is sticking and unable to properly control the SRV. OR, it could be if the machine is older, the SRV actuator may have issues.

You need to provide some actionable data obtained using Trender/Trend Recorder. Since many of us don't have easy access to ToolboxST when you've captured the data you need to export the data to a comma-separated value (csv) file so we can analyze it with a spreadsheet--VERY IMPORTANT, and very simple to do. Then attach the csv file to a reply to this thread. We would need to see the states of 20VG-1, 20FG-1, 20FG-2 (if so equipped), the servo current to the SRV actuator (usually signal name fagr or fprg_out, something like that), the LVDT feedback from the SRV (both LVDTs, please), and P2 pressure (before and during the transfer attempt).

We know it will probably mean the test to obtain the data will result in a trip, but sometimes that's necessary to obtain meaningful, actionable data instead of word-of-mouth (hearsay) data and observations. You could run the test at FSNL.

It's possible one of the HMIs (presuming there is more than one) captures data after a trip and that data can be opened using Trender/Trend Recorder, and converted to csv format and attached to a reply to this thread. It's likely that the Trip History or Trip Log data will not have all the points which would be useful and are listed above, but it would be a start. In the meantime you can configure a Trend and get it running before the next attempted transfer.

But, if liquid-to-gas fuel transfers have been successful in the past, and NOTHING in the Mark* VIe has changed recently (INCLUDING valve calibrations after a recent maintenance outage or in attempts to "fix" the problem) AND no one has recently changed the SRV servo valve (and didn't properly perform a servo valve polarity check) then it's not very likely it's a Mark* VIe issue--unless there are Diagnostic Alarms which are being ignored (Diagnostic Alarms try to warn of something amiss with Mark* VIe hardware, and can sometimes alert conscious operators and technicians to impending field device issues).

PLEASE provide at least the answers to the questions above. If you can, please open the Trip History or Trip Log file from the most recent failed fuel transfer attempt and convert the data to csv file format and attach it to your reply with the answers to the above questions. But without more information, there's not too much more we can say.