Mark VIe isoch speed control

Wondering if anyone can confirm my assumptions about how to achieve frequency control mode on the Mark VIe... Our unit has always run in droop speed control as it is grid connected. Our black start procedure is asks us to start the GT (90 MW frame 7) as soon as possible, prior to re-establishing the utility breaker but there aren't any specific instructions for how to do this. My assumption is that by selecting "dead bus" from the GT1 synch menu the machine will know to operate on frequency control (isoch) instead of droop, however we have not ever attempted this and I cannot say for certain. Can anyone confirm or provide some more clarity on this for me?

Difficult to say with any degree of certainty without being able to see the application code running in the Mark VIe to see if there is any special or unique code. And there's a LOT of that going around (special, unique code) these days.

Generally, though, when dead bus breaker closure is selected the application code (sequencing) checks to be sure the bus is dead AND that "the" utility tie (tie-line) breaker is open, or some breaker that connects the unit output to the grid is open, anyway. And, I've seen it done both ways, where in one set of circumstances the unit automatically switches to Isochronous Speed Control mode, and in another it does not automatically switch to Isoch mode. It depends on how the utility re-synchronization sequence for that particular location on the grid is anticipated to be (re-)synchronized to the grid. If the unit is going to power some nearby power station (say a large fossil unit which needs to be re-started and will have a relatively large amount of load to be operated for some period of time before the larger grid is connected) then the unit will likely be configured to automatically switch to Isoch control. And, the re-synchronization procedure will (should) state the steps for re-connecting to the grid at some point (possibly the power station and the GT will first synchronize to each other and the GT will switch to Droop while the power station is in Isoch (because it's probably larger and can more easily control frequency). It all really depends.

If the GT is going to be responsible for trying to power up some block of load in anticipation of resynchronizing the GT and load to the grid and they may be other units also synchronized together, then it may be a manual selection for going to Isoch. Again, it all really depends, and while many sites are similar, many are NOT alike. I don't think there's a "standard" for handling this--but probably a couple of possible configurations depending on the situation and the intended operation.

But, the answer for your site lies in the application running in the Mark VIe at your site controlling your 90 MW Frame 7. Sorry; wish I had a more definitive answer, but, I hope you understand it's really dependent on several factors. If I had to hazard a guess (a SWAG: a Scientific Wild-Arsed Guess) I would say it's more likely that Isoch selection is manual than automatic. But that's a SWAG (which can also be a Silly Wild-Arsed Guess!).

Hope this helps--somewhat!
Thank you very much for your reply, it is indeed helpful to know that the possibility exists for this setting to be configured differently depending on the particular setting in our Mark VIe.

I'm not sure this information will add anything, but our unit is a co-generation unit powering a large petrochemical facility. I know the machine is sized to carry the site load (along with the STG) in the event that utility power is unavailable (which has never, yet, been the case as our plant is in north america and the grid is very reliable).

The biggest problem for me, as a trainee, is that we upgraded from a Mark V sometime in the past before my tenure began and all the training documents are still only written for the original control system. Still can't find anyone who can provide me with the Mark VIe manual unfortunately.

If there was a manual selector switch to change the fuel control to ISOCH where would one expect to find it? I don't see one on the FSR control page or the GT1 synch page which is where I expected it to live. Are all Mark VIe HMIs configured alike or are they all site specific?

Thanks again!

GE has become really fragmented in recent years; there are different divisions of GE that are selling and configuring Mark VIe turbine control systems differently (wonderful, right?!?!). If you had a Mark V then it's likely you have one of the Mark V-to-Mark VIe "Migration" or Life Extension options--and there are multiple (per)versions of that wonderful turbine control system upgrade. (It's also possible that some really smart people in your organization recognized that it would be MUCH MORE BETTER to go for a complete "rip-and-replace", disconnecting and completely removing the Mark V, and installing a true Mark VIe (rather than just replacing some Mark V printed circuit cards with Mark VIe-compatible cards and calling it a Mark VIe). But, we, and possiblly you, don't know that--yet.)

GE actually developed a program that could take the CSP (Control Sequence Program, the Mark V "application code") and translate it Mark VIe application code--but that was deemed insufficient because it would NOT have the very "latest and greatest" tweaks and improvements and TIL (Technical Information Letter) implementations. SO, it was decided to treat EVERY turbine control system upgrade as if it were a "new unit" to get all of the best and newest software updates--MANY of which were unnecessary and MOST of which are undocumented. (Ask GE what improvements were made to the software of a running turbine when they installed the Mark VIe, and you will simply get the "deer in the headlights" look: "HUH? You want to know THAT?" and nothing more than that. Ever. Full stop. Period.

And people actually pay money for this (LOTS of money!)--and just accept what they're given. Very difficult to believe, but it's true--almost universally true.

HMIs--well, they're even more of a crap-shoot with all of the fragmentation of Mark VIe providers (and Mark VIe-compatible systems, too).

BUT, governor mode selection (Isoch and Droop) should be on the Main Display, along with START and STOP, and fuel selection (if the unit operates on multiple fuels), and the Master Selector (OFF, CRANK, FIRE, AUTO, REMOTE). The lovely Pre-Selected Load Control is usually also on the Main Display. I have seen some Generator Displays that had Isoch and Droop selection buttons, but those were usually (in my day) few and far between. Now, with different divisions making all kinds of decisions about what functions should be located where and no standardization of any kind, it really is just a crap-shoot with HMI displays on Mark* turbine controls these days. There are lots of different displays, and no two seem to be alike--even from the same division of GE.

Don't get me wrong--the Mark VIe is a fine and robust turbine control system. It's just the configurations and implementations of it that are bad--horrifically bad. GE doesn't even realize they are not competing with anyone by offering these "latest and greatest" software upgrades, because other control system suppliers will just (for the most part) duplicate what is already running (and usually running well!) in the existing turbine control system. Sure, they'll make changes the Customer asks for, and their implementations of some functions may not be exactly like GE, but in the end the units generally start and run just like they did with the old Mark* turbine control system that's being replaced. But, GE puts all this ... stuff ... in the application code, stuff they can't even tell you what has changed, and the operation (starting, usually) changes greatly from what it was before. And, they just tell you, "That's the latest and greatest!" and the unsaid part of that is, "That's what you got--and you're going to learn to love it! And you'll learn over time--because we can't tell you what's changed. And, it's all good, because, in the end, the unit starts and produces power just maybe not in the same way it did before. So, functionally, it's the same as what you had--and, again, you're going to love it!"