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Gas turbine 7 EA Running on Primary Mode
One of our installed GE combustion gas turbine is running on primary mode and can't be switched to premix or even lean-lean.

This Abdulaziz, mechanical engineer. We are currently facing an issue in one of our GE combustion gas turbine that is driving a generator.

The turbine was commissioned on 2016. Due to low demand in power at that time, it was decided to put it out of service. initially turbine preservation was maintained. (by running auxiliary system). however, the preservation activity were stopped for quite good time due to missing parts. lately, the team managed to restore the preservation by installing all needed materials.

For now the team decided to run the turbine due to demand on power, our dilemma is as follow:

- Three weeks ago, the team has installed all other missing materials.

- All turbine start-up permissive were cleared

- Start-up attempt was done successfully.

- Generator was synched to the grid successfully.

- All operations parameters are healthy except the TTRF which reached to 1781 DegF. IBH was fully opened (info)

-Exhaust temperatures are way less than other turbine temperatures we have in the plant. the Turbine was started on may 13th and the exhaust temp were in the range of 1050 degf with an IBH 100% opening. On may 29th, the IBH went to close position although the command was 100% which accordingly affected the TTRF to be 1200 DegF as well as the exhaust temperatures to be 700 DegF.

Can we get advise of how to restore the efficiency of the machine and have it operate in premix?

Abdulaziz,

What kind of control system?

What Process Alarms are being annunciated when the unit is failing to transfer out of Primary combustion mode (which appears to be what you are saying; please confirm the unit is not transferring from Primary to Lean-Lean, and is not transferring from Lean-Lean to Premix)? Please list ALL Process Alarms--even the ones you believe are not relevant.

What Diagnostic Alarms are present? Please list ALL Diagnostic Alarms--even the ones you believe are not relevant.

Many failures to transfer from one combustion mode to another during loading are the result of problems with the purge valves not operating properly, or the block-and-bleed valves not working properly. If it's been a long time since the unit was run, have you checked the proper operation of the purge valves (timing; limit switch adjustment)?

But if the unit is not transferring combustion modes, there should be alarms (Process and/or Diagnostic) to alert the operator and technicians and mechanics to the problem(s).

While it's not widely understood, the calculation of the Combustion Reference Temperature (TTRF1) includes the compressor discharge temperature thermocouples. And, when these T/Cs are not reading correctly, then there can be lots of problems with the calculation--but there are usually either Process- or Diagnostic Alarms (or both) to indicate issues with the compressor discharge T/C values.

Is it possible to disable IBH on the unit? (Some units have the capability on the HMI screen (usually either the DLN display or the IGV display (???).) If there is a button to disable IBH, then try that. The unit won't transfer into Lean-Lean or Premix until higher loads, but that could help with understanding if the IBH control scheme is part of the problem or not. (The purpose of IBH is to get the unit into Premix combustion mode at lower loads than would otherwise be possible without IBH. Without IBH, transferring into Premix during loading would not occur until the unit was at approximately 70-80% of rated load, and would transfer out of Premix during unloading at around the same loads. With IBH, the unit will transfer into Premix at around 40% of rated load (during loading), and transferring out of Premix would occur at around the same load--so the unit gets into Premix "sooner" (at lower load during loading) and stays in Premix "longer" during unloading.

Some units do not have a Gas Transfer Valve--making them "transferless" DLN-I combustion systems. These units usually have IBH so the fuel flow-rate through the secondary fuel nozzles is lower during Primary-to-Lean-Lean and Lean-Lean-to-Premix transfers which helps with combustion stability issues. Many times these units do not have the capability to disable IBH, so depending on the configuration of your unit it may or may not have the capability to disable IBH.

However, whenever troubleshooting problems like this one should be using the Alarms (Process and/or Diagnostic) to help understand what is/isn't happening. Alarms are not nuisances--they are meant to help understand problems (contrary to extremely popular belief--which does not make it true (that alarms are nuisances)!).

Hope this helps; please write back with the answers to the questions, and let us know how you fare in resolving the problem(s)!

> What kind of control system?

MARK VI

>What Process Alarms are being annunciated when the unit is failing to transfer out of Primary combustion mode (which appears to be what you are saying; please confirm the unit is not transferring from Primary to Lean-Lean, and is not transferring from Lean-Lean to Premix)? <

Unit has transferred from primary to lean lean, later it moved to primary.

>Please list ALL Process Alarms--even the ones you believe are not relevant.

- Mega Watt transducer signal trouble
- FSR limited due to DWatt transducer failure
- Fuel gas pressure high
- VESDA fire1 indication alarm
- Gas fuel inter-valve pressure (P2) low
- IBH valve not tracking
- Comp operating limit fault
- Combustion trouble.

>What Diagnostic Alarms are present? Please list ALL Diagnostic Alarms--even the ones you believe are not relevant.<

- Analog Input (TCAT) 18 unhealthy
- Analog Input (TCAT) 19 unhealthy
- Analog Input (TCAT) 18 unhealthy
- Analog Input (TCAT) 19 unhealthy
- Analog Input (TCAT) 18 unhealthy
- Analog Input (TCAT) 19 unhealthy
- Analog input 1 unhealthy
- Analog input 1 unhealthy
- Analog input 1 unhealthy

>Many failures to transfer from one combustion mode to another during loading are the result of problems with the purge valves not operating properly, or the block-and-bleed valves not working properly. If it's been a long time since the unit was run, have you checked the proper operation of the purge valves (timing; limit switch adjustment)? <

Purge valve is okay, since it don't have alarm, or it shut down the machine during startup if late.

>While it's not widely understood, the calculation of the Combustion Reference Temperature (TTRF1) includes the compressor discharge temperature thermocouples. And, when these T/Cs are not reading correctly, then there can be lots of problems with the calculation--but there are usually either Process- or Diagnostic Alarms (or both) to indicate issues with the compressor discharge T/C values.<

Can you explain more about this point?

>Is it possible to disable IBH on the unit? (Some units have the capability on the HMI screen (usually either the DLN display or the IGV display (???).) If there is a button to disable IBH, then try that. The unit won't transfer into Lean-Lean or Premix until higher loads, but that could help with understanding if the IBH control scheme is part of the problem or not. (The purpose of IBH is to get the unit into Premix combustion mode at lower loads than would otherwise be possible without IBH. Without IBH, transferring into Premix during loading would not occur until the unit was at approximately 70-80% of rated load, and would transfer out of Premix during unloading at around the same loads. With IBH, the unit will transfer into Premix at around 40% of rated load (during loading), and transferring out of Premix would occur at around the same load--so the unit gets into Premix "sooner" (at lower load during loading) and stays in Premix "longer" during unloading.<

IBH were looked at. the system transferred from lean lean to primary because IBH closed. it was 100% and the turbine was on lean lean. it cannot be open manually though.

>Some units do not have a Gas Transfer Valve--making them "transferless" DLN-I combustion systems. These units usually have IBH so the fuel flow-rate through the secondary fuel nozzles is lower during Primary-to-Lean-Lean and Lean-Lean-to-Premix transfers which helps with combustion stability issues. Many times these units do not have the capability to disable IBH, so depending on the configuration of your unit it may or may not have the capability to disable IBH.<

We have transit fuel control valve, with IBH in auto.

1 out of 1 members thought this post was helpful...

abdulaziz,

Thanks for writing back with the answers.

Unless the Mark VI has changed significantly (and it might have, but it's doubtful) if the turbine control system has TCAT cards it is a Mark VIe.

As for Process Alarms, WOW!!! 'Fuel Gas Pressure High' AND 'P2 Pressure Low'--at the SAME TIME! And, you're telling me the unit is running? It's no wonder it's not behaving properly. It's difficult to understand how, unless there is a serious problem with inputs/transmitters, how this can be happening. And how anyone could think the turbine should be started or run with these alarms, even if they're simply the result of bad transmitters.

'IBH Not Tracking' is the least of your problems at this point; if the fuel gas pressures (supply; P2) aren't correct the unit isn't going to load and it will lose load. The 'FSR Limited to DWATT Trandsucer Failure' and 'Megawatt Transducer Signal Trouble' alarms are ALSO very bad for a DLN combustor-equipped unit. You need to sort out why the P2 pressure is low (and how that can happen with a high supply pressure!?) and get the DWATT transducer(s) working properly, and then you can try starting/running and see what issues you have left to resolve (very few if my experience is correct).

The TTRF1 calculation uses CTD(A) as part of its determination of combustion reference temperature. If the compressor discharge temperature T/Cs are providing readings that are too low or too high then the TTRF1--which is used as the "switch" for combustion modes--will be incorrect and could lead to problems with transfers.

The Mark* turbine control system is only as good as its inputs--and it would seem something is seriously amiss with the inputs to this Mark*. It's trying to run the unit but it's "conflicted"--and if the P2 pressure is really low, then it can't load the unit and will, in fact, unload the unit--and the IBH is just along for the "ride" at that point. No fuel; no load. Low P2 pressure; loss of load. No reliable DWATT signal(s); conflicted operation.

Please write back to let us know how you fare in resolving the issues.