GE Frame V GT experiences load drop during C/O from gas to liuquid fuel

hello expert,

we have a GE Frame V GT, Speedtronic MK V, experiences ~5 MW drop in load during change over from Gas fuel to Liquid fuel. Flow divider was replaced with a new one, speed pickups gas was adjusted as per the control specs, Atomizing air bypass valve checked and verified found ok. check valves, fuels nozzles we replaced with new ones. the liquid fuel supply pressure after the LP Filter is 3 bar, despite all that, the drop in load of 5 MW still persists.

Has anybody experienced a similar issue?



You are working on a GE-design Frame 5 heavy duty gas turbine-generator with a Mark V Speedtronic turbine control system.

When did this problem start? Has this been an ongoing problem for some time, or has it just recently started?

What alarms (Process and Diagnostic) are active when the fuel change-over starts? What alarms are annunciated during the fuel changeover?

What initiates the fuel changeover--a drop in gas fuel supply pressure, or an operator?

What happens when the unit is switched back to gas fuel--does the load increase or does it remain the same requiring the operator to raise the load to the desired setpoint?

Is the unit being operated in Pre-Selected Load Control mode during the changeover from gas to liquid fuel? Or, is the unit being operated at Base Load (exhaust temperature control)? Please describe the load(s) the unit is at before and after the changeover, and what is done to restore the desired load.

Does the unit have DLN or conventional (diffusion flame) combustors?

What usually happens when a fuel changeover is initiated is that the FSR of the fuel being transferred to is ramped up from zero to match the FSR of the fuel which was being burned at the start of the changeover, and conversely, the FSR of the fuel which was being burned at the start of the changeover is reduced to zero. That's why it's important that the energy flow-rates of the fuels be "matched" so that they smoothly transition from one to the other without any bobble or change in load. But, if the energy flow-rates are not "matched'' then the transition will not be smooth and/or it will not start and end at the same load. AND, if Pre-Selected Load Control is active during the changeover then it can cause problems with the changeover as well. (Pre-Selected Load Control IS NOT a good mode to operate a turbine with--no matter what anyone thinks or has been told. Full stop. Period.)

To achieve a "bumpless" transfer it's usually necessary to perform a procedure called 'fuel matching' which attempts to make the energy flow-rates of the two fuels similar at some load(s) so that when a changeover is initiated there won't be a large load change such as you are describing. Gas fuel flow is NOT measured/monitored and used for anything other than basing Wet Low NOx emissions. Liquid fuel, on the other hand, is monitored using the speed pick-ups on the liquid fuel flow divider. And, those speed inputs are scaled to provide the desired feedback to assist with fuel matching efforts. So, one usually matches liquid fuel to gas fuel by adjusting the scaling factors of the liquid fuel flow divider speed pick-ups. Not always, but that's the normal way things are done.

BEFORE you go changing anything realize that when you do change something it's going to affect other aspects of operation--such as firing on liquid fuel and acceleration on liquid fuel, etc. So, it's NOT just a simple thing.

But, if the unit is being operated on Pre-Selected Load Control during the fuel changeovers from gas to liquid, that could also be part of the problem. Disable Pre-Selected Load Control and try the changeover again. I promise the unit is not going to drift willy nilly without a Pre-Selected Load Control Reference; I promise. Grow a pair, pull up your big boy panties and just do it. If, after the changeover is complete you can re-enable Pre-Selected Load Control.

Also, when performing a changeover before you initiate it record the value of TNR and FSR and FSR1 and FSR2 and DWATT (or DW). And, when the changeover is complete, record the same values again.

I strongly suggest you get some experienced help if you feel that fuel matching is inadequate or was not properly done during commissioning. I have also seen over many years and decades that fuels can change and cause this kind of problem if operations are not paying attention to the fuel characteristics over time.

As always! Ready to help and share experience. thank you for the quick feedback.

Yes, GE Frame V, MK V, Gen drive. this problem persisted for a quite sometime. but after the major overhaul, we decided to sort this issue of load drop down to 4-5 MW out during the change over from liquid to gas fuel.

No process nor diagnostic alarms were present during the changeover and after. there was a 125 Vdc ground and it was already fixed. the MW Control was on 'Manual', so no 'Preselect', it is usually set manually at 10-12 MW. there was no drop in the liquid fuel pressure (3.2 bar) after the LP Filter, ~4.5 bar upstream.
When we change back to Gas fuel, load increases by ~1.8 MW during the change over, but settles in right before c/o is complete. this is a standard non DLN unit.

I really am not sure/aware about/of 'Fuel matching', but it does sound like it is the issue this unit is facing. since load drops (speed drops, exhaust temp drops, which means there is a really lack of liquid fuel during the c/o). can you please shed more light on that. how is it done? does anyone here happen to have such procedure?

I have attached the trends from the previous trials indicating the load drop issue. I have also attached the fuel spliter (3.3).

Any thoughts would be very much appreciated.




I have tried this a couple of times--writing a procedure for fuel matching. (Actually, there's usually one in Sect. 05 of the Control Specification. It's usually pretty obtuse, but there is one (a procedure) that can be used to begin to understand the intent of fuel matching.) But, writing a procedure for someone half way around the world just doesn't work.

Think about liquid fuel like this. There is a liquid fuel flow-rate reference, FQR. And there is a liquid fuel flow-rate feedback, FQL (that name seems to have changed a little over time). The Mark* changes the current applied to the LFBV (Liquid Fuel Bypass Valve) to make the feedback equal to the reference.

Now, here's the rub. If the flow feedback scaling is not correct, then the energy flow-rate of the liquid fuel won't be what's required to make the liquid fuel energy flow-rate equal to the gas fuel flow-rate. So, if the flow feedback is scaled such that when the feedback is equal to the reference BUT the energy flow-rate is LESS than it actually is then the Mark* won't do anything to increase the energy flow-rate, because it thinks it's okay.

It's pretty common for liquid fuel flow divider feedback scaling to be incorrect from the factory (all too common, actually). So, it's necessary to change the feedback scaling to make the energy flow-rate equal to what it needs to be. Also, flow dividers have different numbers of teeth, which can also cause unintended differences (SURPRISE--all flow dividers are not the same as all other flow dividers).

Here's what you should do. You should start the unit on gas fuel and record FSR (FSR2 for gas fuel) at FSNL (Full Speed-No Load, usually TNR=100.3%). Then, synch and load the unit to approximately 10 MW (in Droop Speed Control Part Load ("manual MW control?)) and change fuels to liquid. unload the unit to 1 or 2 MW and then open the generator breaker and adjust TNR until it's 100.3% and record FSR (FSR1 for liquid fuel). The task here is to adjust the liquid fuel feedback scaling to try to make FSR1 at 100.3% TNR equal to FSR2 and 100.3% TNR. The problem with this and the Mark V is that every time you make a change to I/O Configuration, you have to download and re-boot all three processors. You could download to all three processors, and then reboot them one at a time, waiting about 5 minutes between re-boots, and you should be able to avoid tripping the unit, or shutting down the unit to reboot when the turbine is not running. The other issue is I don't know of any way to calculate what the change should be to achieve the desired FSR.... so, it's all kind of guessing. I have had some success making a change and noting how much the FSR changed and then ratioing further changes to get as close as possible--but it's always guessing, and it takes several attempts.

I cannot fathom what happened to TTXM in the Trend on the left. Why did it go up and down, and why did it increase after the changeover? Again, without being able to have the full Trend file to analyze it's simply NOT clear what happened. And,the load isn't shown on the Trend, either...????!!!

Anyway, that's all I'm going to add to this thread. There's too much that can go wrong, and I'm very worried about misunderstanding. And, just about every time I've ever done fuel matching the Customer Site Manager just got tired as hell of all of the rebooting and changes and testing. So, they called a halt to the process, to which I wrote a letter saying the process hadn't been allowed to be completed and GE wasn't going to return at a later date to complete it. (I had to cover my arse with my Manager and for GE, because unscrupulous Customer Site Managers have tried many time to say tests and adjustments weren't completed and demanded GE return to finish them, after stopping commissioning works.)

Best of luck!