MARK Vie TMR controlled


Thread Starter



We have GT which is frame 5 and MARK Vie TMR controlled. Recently during the unit started up after the unit reached speed of 80 %, we observed that the 63FGL pick up to 1 than reduce TNR.

Would you please tell me are there some factor must be checked.

l63fgl usually goes to a logic "1" when the gas fuel supply pressure is low. If the speed is below 95% what usually happens is that flame is lost because gas fuel supply pressure is decreasing or has decreased and gas fuel flow has decreased.

TNR is driven by L70L (Lower) and L70R (Raise). You would need to look at the logic driving those signals to see what might have caused TNR to decrease.

If the unit is dual fuel (gas and distillate), then when the unit is above 95% speed and l63fgl picks up the Speedtronic should try to transfer to liquid fuel--but most Speedtronic control systems DO NOT allow automatic fuel transfers to occur below 95% speed during acceleration (or during shutdown). (Even operator-initiated fuel transfers are only allowed below firing speed (TNK14HM1) or above synchronous speed (TNK14HS1).)

A Mark VIe should be controlling FSR strictly to control THNA (Acceleration) during start-up, below approximately 95% speed. FSRN, Speed Control FSR--which is driven by TNR--should NOT be active below approximately 95% speed during start-up.

All the different FSRs (FSRN--which is driven by TNR; FSRT; FSRSU; FSRACC; FSRSD; even FSRMAN) go through a Minimum Select function, and the lowest value is written to FSR. During Starting, FSRN should be much higher than FSRACCC until the unit gets close to 95% speed, at which time the unit should smoothly transition to FSRN and TNR should be 100.3%, or thereabouts.

So, without being able to see the application code running in the Mark VIe at your site, it's very difficult to say what might have driven TNR down. But, it the application code is typical of what GE has been doing for decades, l63fgl would not--by itself--cause TNR to decrease during start-up. Nothing should cause TNR to decrease--again, because the unit is not on Speed Control, or it shouldn't be on Speed Control--during start-up. It should be on acceleration control, which does not drive TNR.

So, it would seem you need to examine all the inputs to L70L to see what might be causing it to decrease FSRN. But, it doesn't seem--unless there is new philosophy in place from GE--that l63fgl should be driving L70L. I would expect l63fgl picking up below 95% speed would initiate an automatic shutdown (L94X), and the unit would start decelerating on FSRSD before it might lose flame if gas fuel supply pressure dropped excessively.

Hope this helps.
Quite often when I encounter something like this, I sometimes come to learn that some manager or supervisor demanded that, in this example, TNR be driven down on low gas fuel pressure to try to prevent the unit from tripping on loss of flame.

This kind of thing usually happens when during commissioning the unit is tripped on low gas fuel pressure (which is NOT a turbine control system problem, by the way!) once or more and some owner or operations supervisor or plant manager insists the Speedtronic be made to prevent a loss of flame on low gas fuel pressure (which it can't unless it directly controls gas fuel supply and gas fuel supply pressure--which it almost never does).

And, the TA that implemented it under duress didn't contemplate the knock-on effects it might when something like low gas fuel pressure happened during starting.

And, it later gets wrongly attributed to GE or the turbine packager when it was never originally included with the Speedtronic application code, should never have been implemented as an attempt to solve a problem outside of the turbine control system's ability to control, and gives the Speedtronic a bad name.

Also, the person who originally demanded the change either (conveniently) forgets the demand--and is quite often the person who is now complaining about the aberration it has created, or that person has since moved on to "greener" pastures. And, usually it only gets mentioned to me later because the person who mentioned it, and perhaps several others in the plant, were not sad to see that person go.

I'm <b>NOT</b> saying that's what happened in this case, only that it has been the reason for some "unusual" sequencing.

In any case, please write back to let us know what you determine.