Hi there, it has been observed since couple of starts with our Gas Turbine GE 9E that after synchronization of generator, GT took initial load more than normal and then its load came back to zero and operator manually ramping up the load to meet the preselect. Although, grid frequency and related parameters were remain in range. What might cause this issue, this is not usual, load jerk is observed before actual loading, at several instances, load followed accordingly with preselect setpoint and sometimes this unusual behavior happened.
Kindly share your experience related with this.

 

Hi

Any job/work done around this unit these last days

Could it be possible for you to share parameters related to the unit during the mentionned operations

When you say GT take load more than normal ...how much it is ?

 

Hi

Any job/work done around this unit these last days

Could it be possible for you to share parameters related to the unit during the mentionned operations

When you say GT take load more than normal ...how much it is ?

Recently generator rotor has been replaced in Feb24, after that startup carried out in GE presence and machine to put on standby. GT startup carried out as per grid requirements and almost daily startup and shutdown to meet power demands.
During last few startups, this abnormal load ramp up observed and reported by OPS. Yesterday, 3 times GT desync due to grid frequency was 50.34, when frequency achieved at 49.8 GT got sync. Also, during desync, reverse power alarm also appeared. Abnormal load ramp up was recorded 44MW, 22MW & 12MW respectively. In last normal startup yesterday, GT load ramp up was normal 7MW and setpoint was 10MW but GT didn't pick spinning load when the automatic synchronization was initiated and desync with reverse power.

Date - Time - load jerk - Frequency
03-04-2024 - 16:30 hrs. - 44.2MW - 49.95 Hz
04-04-2024 - 16:02:28hrs - 22.2MW - 50,2Hz
05-04-2024 - 16:46:58hrs - 12.95MW - 49.83Hz

 

The situation:

1. A GE 9E gas turbine recently had its rotor replaced in February 2024.
2. Since then, the turbine has experienced abnormal load ramp-up during startups, with sudden increases followed by a drop to zero before manual load adjustment.
3. Three desynchronizations from the grid occurred due to grid frequency fluctuations.
4. This behavior is not typical and requires investigation.

Potential Causes:
Based on the information provided several factors could contribute to this issue:

• Governor Control System:

The governor might be overreacting to initial load changes after synchronization, causing a temporary overshoot and subsequent correction.
Reviewing governor settings and tuning parameters might be necessary.​

1. Sensors Malfunction:

Faulty sensors (DWATT Transducers) feeding data to the control system could provide inaccurate load readings, leading to erratic behavior.​

Fuel Control valve Aswell really important to dig deep on them.​

Verifying the health and calibration of load sensors is crucial.​

1. Incomplete Commissioning after Rotor Replacement:

The post-rotor replacement commissioning process might not have been thorough enough to account for potential control system adjustments needed with the new rotor.​

Reviewing commissioning procedures and verifying proper tuning for the new rotor is important.​

1. Grid Frequency Fluctuations:

While the grid frequency remained within range, rapid fluctuations could be causing control system instability.​

Analyzing grid data and control system response during desynchronization events might reveal insights.​

Troubleshooting Steps:

1. Data Analysis: Analyze historical data from the control system, focusing on load profiles, governor settings, sensor readings, and grid frequency during startups with abnormal behavior.
2. Governor System Review: Evaluate governor settings and consider consulting a GE TA for potential adjustments.
3. Sensors Calibration: Verify the calibration of load and other relevant sensors to ensure accurate data feeding into the control system.
4. Review Commissioning Data: Review data from the post-rotor replacement commissioning process to identify any discrepancies or areas requiring further adjustment.

Please don't jump to any conclusion without clear evidence.

 

I agree with most everything @Kalia Gaser Reda wrote.

I find it difficult to believe that changing the turbine rotor would cause this to happen; it's most likely a governor (turbine control system issue--and by that I mean a turbine control system sensor issue or LVDT calibration issue) or something like that, something outside the control of the turbine control system (read on below).

BUT, if the grid frequency is erratic (and being able to see a graph of grid frequency prior to, during and after synchronization would be a GREAT help!) that's not going to make the job of synchronizing and remaining synchronized any easier. Combine that with one or sensors being incorrect or calibrated improperly or something like that is most likely the issue(s).

What kind of grid/system does this machine synchronize to? A "captive" load (such as a refinery or cement plant or something similar)? Are there other large machines (similar capacity to the GE-design Frame 9E) running on the grid/system prior to synchronizing this machine? If the grid/system frequency is unstable prior to and during synchronization, does any have any information about the cause(s)? And is the grid/system frequency usually unstable, or just at certain times?

What is the hydraulic system pressure doing when this sync/de-sync is happening? Has anyone verified the hydraulic accumulator is properly charged AND the block and bleed valves are in the proper position? (The block valve should be open and the bleed valve should be closed--but if the charge isn't correct valve position doesn't mean a thing.)

What are the IGVs doing just prior to and after synchronization?

WHAT OTHER ALARMS (EVEN IF THEY SEEM TO SOMEONE/OTHERS TO BE UNRELATED!) ARE BEING ANNUNCIATED BEFORE, DURING AND AFTER THE FAILURE TO SYNC AND REMAIN SYNCHRONIZED? (The presumption is the machine has a GE Mark* turbine control system that performs automatic synchronization.)

Usually during a "major" outage (such as replacing a rotor) other work is done, possibly to the electrical switchgear (were the protection relay(s) "calibrated;" was any wiring in the PT and/or CT circuits disturbed?

Are the axial compressor bleed valves open or closed at the time of synchronization--and when do they normally close, at synchronization or when load gets to some "minimum" level?

WHAT IS THE SPINNING RESERVE VALVE PROGRAMMED INTO THE MARK*???

Specifically, which relay initiates the de-sync? Is it the 32 device (reverse power)--or the Mark*?

If the turbine control system is a Mark* do you have any Trip History displays you can share with us? (We would need to get that information in a "text" format, CSV format (Comma-Separated Values) which can be imported into a spreadsheet application.) Files, and CLEAR photographs, can be attached to responses to this thread.

What fuel is the machine burning when this sync/de-sync occurs? If it's liquid fuel (distillate) are you sure the liquid fuel supply pressure is stable (the pressure upstream of the Liquid Fuel Stop Valve (VS1-1)? What is the LFBV doing (presuming the Liquid Fuel Bypass Valve has LVDTs for monitoring position--if not, has anyone visually observed the operation of the LFBV??? Prior to starting the unit after the outage was all air vented from the Liquid Fuel piping and filter vessels? (Were the Liquid Fuel filters replaced?)

If the machine is burning natural gas (or LNG), are you sure the supply pressure is stable? What are the SRV (Stop-Ratio Valve) and Gas Control Valve(s) doing? Are they any filters upstream of the SRV--and if so, were they replaced during the outage? Was air properly vented from the filter vessel? Is there any liquid discharge from the bottom of the filter vessel(s)?

It could be any number of things--but I caution anyone to not blame the turbine control system too quickly. A programmable control system is only as good as its inputs, and the Mark* doesn't usually control things like fuel supply pressure (it's presumed the supply pressure is stable!). Also, if the fuel filters were NOT changed, what is the differential pressure reading for the filters that are in service? (Dirty, choked, plugged filters can restrict fuel flow and cause problems as fuel flow-rate increases after synchronization).

But, again, erratic frequency readings are not usually normal and can cause difficulties in remaining synchronized--especially if the frequency is oscillating quickly. Digital control systems are pretty good, but sometimes they can be playing a game of cat-and-mouse when trying to sync to a grid/system with unstable frequency--especially if it's oscillating quickly and/or by large amounts.

Anyway, LOTS of questions--I know. BUT, if you could have solved the problem(s) without our help you wouldn't have written here for assistance, and there is precious little usable information about the plant and system and what's been done to try to troubleshoot and resolve the problem--and what the results of the troubleshooting and resolution efforts were. You need help--we, the experts you asked for help, need information. Actionable date, not anecdotal data. Answer as many of the questions as you can; provide as much data/graphs as you can, and you will be happy with the results.