Dear all,
Currently our 6FA have "SRV servo 2 output suicided active" alarm on Mark VI for 2 months and sometimes "SRV nonvoted current disagreed" activated, Panel Operator Master reset and SRV valve suddenly close from 35% to 18% make GTG load fluctuation.
My question is have any relation between Master reset command and SRV opening in this case? How can we resolve it?
Thank you so much!

 

Good day ,

Is that VSVO card involved on that issue ...

Did you perform any job/work on this unit before that issue came up ..like LVDT (re) calibration

 

There seems to be a big misunderstanding of how a TMR (Triple Modular Redundant) Mark* turbine control panel works--in this case especially with regard to servo-valve outputs. The Diagnostic Alarms are indicating there is a problem with the SRV (Stop-Ratio Valve) servo-valve outputs (there are three of them--one from <R>, one from <S> and one from <T>). The Mark* VI can operate a GE-design heavy duty gas turbine when one of the servo-valve outputs is not working correctly, or even when one of the two LVDTs providing position feedback is not working correctly, or in the case of a SRV when one of the pressure transmitter feedbacks is not working correctly. The Mark* can "compensate" for these problems--but only to a degree. The responses to other stimuli may not be as quick as when everything is working correctly, but the unit can generally continue to run (presuming the wiring of the field devices was done properly and the configuration of the Mark* was done correctly, and in the case of a SRV the feedback devices (in particular the pressure transmitters) are all calibrated and working correctly).

The purpose of the Diagnostic Alarm is to warn a conscious operator, his Operations Manager, the I&C (Instrumentation & Controls) technician and his supervisor of a serious problem--that left unattended will likely result in a failure or forced outage.

In newer Mark* turbine control systems, a Diagnostic Alarm reset was incorporated into the MASTER RESET function (because the original purpose of the MASTER RESET function has been perverted over the last couple of decades to become something it was never intended to be--and can't be). In this case, involving a SRV, initiating a Diagnostic Alarm reset has apparently caused a problem which was being "dealt with" by the TMR Mark* turbine control system over some period of time (too long!) and caused the Mark* to not be able to no longer respond appropriately because it is essentially being told, "There are no problems; continue as if there are no problems." And, it can't.

MASTER RESET is not the answer to every problem. Certainly not this one, that seems obvious (based on the information provided).

I suggest there is a problem with either an LVDT (perhaps both--could be a wiring issue, could be a loose jam nut, could be an intermittent LVDT output signals), or the servo-valve (could be a wiring issue (loose terminations; poor crimps; failed or failing TSVO (servo-valve output terminal board card), or one of the VSVOs (the servo-valve output I/O (Input/Output) card), or the P2 pressure transmitters (if there is more than one P2 pressure transmitter there have been know issues with some of the transmitters provided with new units drifting--a lot--and causing a similar issue; or the valve positions of the manual valves in the sensing/venting lines of the P2 pressure transmitters). BUT, there is a problem which needs more than a MASTER RESET.

When a Diagnostic Alarm is left unresolved (and uninvestigated) for too long, the situation it is warning of can become worse than when it was first annunciated. That may have (probably did) happen in this case. Diagnostic Alarms are NOT nuisance alarms, contrary to popular belief. They need to be investigated and resolved sooner rather than later. Leaving Diagnostic Alarms unresolved for two months (as indicated in the original post) is just begging for knock-on problems--and maybe even forced outages.

I know--the alarm text messages can be very cryptic and misleading. But, that's NO reason to ignore them--even if they don't result in a turbine trip. And that's another wildly popular misbelief about Diagnostic Alarms: A single Diagnostic Alarm can't result in a turbine trip. That is true--unless there are multiple unresolved Diagnostic Alarms and then sometimes just one more (related) Diagnostic Alarm is detected and annunciated, and WHAM! Trip! (No; there are far TOO MANY Diagnostic Alarms to try to document what combinations can result in a turbine trip--but combinations of Diagnostic Alarms can and do result (not always, but sometimes) in turbine trips (forced outages). And why? Because most often Diagnostic Alarms are left unattended, unresolved for too long. (How long is too long? In my personal opinion, 24 hours is too long. Actually, 8-12 hours is too long for lots of sites that start and stop on a frequent basis.)

This problem--of a drop in load while operating--was self-inflicted. A serious misunderstanding of the purpose of Diagnostic Alarms AND a lack of attention to long-standing Diagnostic Alarms suddenly being attended to with a MASTER RESET (which is NOT the be-all, end-all solution to any problem--ever!) caused this problem of load drop.

Many people mistakenly believe that if the turbine continues to run with a Diagnostic Alarm (or multiple Diagnostic Alarms) that the programmers of the turbine control system must have allowed the turbine to continue to run because it isn't really a serious problem. FALSE. Diagnostic Alarms are warning of problems with the "health" of the printed circuit cards and/or the turbine control outputs (in this case) which could lead to more serious problems if left unattended (and usually do--as indicated by the information provided). The root cause of this problem IS NOT the Diagnostic Alarm--so resetting the Diagnostic Alarm (in this case, based on the information provided) IS NOT going to solve the root cause of the problem, and in fact, attempting to reset the Diagnostic Alarm without troubleshooting it led to a worse problem.

Diagnostic Alarms have numbers associated with them (called "drop numbers"). You can use the Diagnostic Alarm to search in the Mark* VI System Guide, Vol. II (or sometimes Vol. III, if a Vol. III is provided) to understand some of the causes of most Diagnostic Alarms. In this case, you need to find the section in the System Guide for the VSVO card (since that's the printed circuit card which is driving servo-valve outputs) and look for the Diagnostic Alarm information for the VSVO and then find the drop number of the alarm to find troubleshooting information.

If nothing was done to troubleshoot the Diag. Alarm for two months, well, ....

 

Dear all,
Currently our 6FA have "SRV servo 2 output suicided active" alarm on Mark VI for 2 months and sometimes "SRV nonvoted current disagreed" activated, Panel Operator Master reset and SRV valve suddenly close from 35% to 18% make GTG load fluctuation.
My question is have any relation between Master reset command and SRV opening in this case? How can we resolve it?
Thank you so much!

When it was your Last Overhauling of the SRV, what brand model and PN (bottom fisher 4"?)

 

Hi mate,

It's possible that there might be an underlying issue in the control system logic or a communication problem between the Mark VI and the SRV control system. To resolve this, I would recommend reviewing the system logs as well as checking the control logic.

 

This thread is over a year old, and the original poster never responded to any of the suggestions or questions.

Save your keystrokes, boys.