The unit is Frame 6 DLN, Mark VIe control. We are currently operating our gas turbine in BASELOAD. It was noticed that during BASELOAD operation, the STATUS_FLD will not stay in "BASELOAD" and goes into "PARTLOAD" occasionally. We can observed fluctuation of FSRN and FSRT with FSRN taking over occasionally (less than 5 minutes), minor load fluctuation (less than 1 MW when operating around 38 MW). During this period, it was observed that TTRX was increasing and minor drop of TTXM (and since it is already in PARTLOAD, IGV modulated in order to bring TTXM close to TTRX). Few minutes later, TTXM will again match TTRX, FSRT will be in control again.
We have tried to select PRESELECT mode (by selecting a higher value of MW, i.e. 40 MW) and the load maintained. The STATUS_FLD still changing between "PRESELECT_LD" and "PARTLOAD" but the MW is more stable. There was no more fluctuation of TTRX and IGV will remain fully open.
We would like to know why the behavior of TTRX increase during this case and why it is not happening in PRESELECT mode? How can we ensure when in BASELOAD, we can have IGV remained fully open and have stable TTRX and load?
Appreciate your clarification
Have you or your operators tried selecting BASE LOAD Load Control mode, and if so, what happens?
Using Pre-Selected Load Control to try to "stay" in Base Load (CPR-biased exhaust temperature control) IS NOT the correct way to operate any GE-design heavy duty gas turbine at Base Load (contrary to popular and false beliefs). In fact, using Pre-Selected Load Control for any other purpose than changing load (when the operators can't be bothered to click on RAISE- or LOWER SPEED/LOAD to get to the desired load) IS NOT the correct way to operate the machine continuously.
TO BE CLEAR, it IS NOT necessary nor is is recommended to use Pre-Selected Load Control for continuous operation of a GE-design heavy duty gas turbine at any load (Part Load or Base Load). The Mark* WILL NOT subconsciously drift away from a load point set using the RAISE- and/or LOWER SPEED/LOAD buttons and result in a turbine trip. That's simply a false and misleading belief that has absolutely no basis in fact.
If you want the unit to operate at Base Load continuously (on CPR-biased exhaust temperature control with the IGVs fully open), select BASE LOAD Load Control Mode (the button should be on the Main Display right next to the Pre-Selected Load Control button)--NOT Pre-Selected Load (with ANY reference). That's what the BASE LOAD Load Control button does--maintains operation with CPR-biased exhaust temperature control active at all times, until such time as a STOP is initiated, or the operator reduces TNR such that FSRN drops below FSRT and the unit transitions to Part Load. BASE LOAD, when selected and active, actually runs TNR (and FSRN) up above FSRT and maintains FSRN above FSRT so that there IS NO bouncing back and forth between Part Load and Base Load.
Operators should ONLY use Pre-Selected Load Control when changing load, and once the desired load setpoint is reached then the operators should click once on either RAISE- or LOWER SPEED/LOAD to cancel Pre-Selected Load Control. Droop Speed Control will keep the load stable (as long as the frequency of the grid the unit is synchronized to is stable) without Pre-Selected Load Control being active. Hard to believe--I know--but it's true. Try it, and you'll see. It will be EXTREMELY stressful for the first few minutes, and even for the first couple of hours, maybe even the first couple of hours of each shift--until the operators come to trust and understand that Pre-Selected Load Control DOES NOT HAVE TO BE ACTIVE AT ALL TIMES in order for the machine to hold a particular load.
Please write back to let us know how you fare by just simply selecting BASE LOAD Load Control mode, and watching the Status_Field messages. And, also, after you try letting Droop Speed Control maintain load at Part Load without Pre-Selected Load Control active.