We are operating GE9FA units. We are observing high tenoerarure deviation in CTD's between the two units which are operating at same load and IGV opening. Can anyone please explain on this issue
Your power plant consists of two GE-design 9FA heavy duty gas turbines. One of the seems to have "normal" axial compressor discharge temperatures and the other one has very different axial compressor discharge temperature indications.
Lots of questions because there is lots of information missing.
1) You say you "... are observing high tenoerarure deviation in CTD's between the two units which are operating at same load and IGV opening." Are they higher or lower than the machine with the more normal CTD temperatures?
2) What are the CTDn (where 'n' is a whole number, 1 or 2 or 3, etc.) readings for both machines when operating at the same load and the IGV opening? Please provide all the CTDn values for both machines, as well as load (MW) and IGV angle (CSGV).
3) What turbine control system do the units have? Mark* V, Mark* VI or Mark* VIe?
4) When did this problem start--after a machine was re-started following a maintenance outage (Combustion Inspection, Hot Gas Path inspection, or Major Inspection)? After the machine with the very different CTD temperatures was tripped from a loaded condition? Was any Mark* card replaced before the problem started or after--if so, which one(s)?
5) What have you done to try to troubleshoot the problem?
6) What Diagnostic Alarms are present on the machine with the high CTD temperature differences? This is very important information that is often overlooked and could be very helpful in troubleshooting the problem?
7) What kind of combustion system do the machines have? DLN-2, DLN 2.6, etc?
8) Was any work done recently in the turbine compartment in the area of the lower half of the combustion section? If so, what was done, and why?
9) Have any of the CTD T/Cs (thermocouples) been replaced recently on either machine? How long since CTD T/Cs were replaced on both machines?
10) What Process Alarms are present when the machine with the CTD temperature differences is running? ALL Process Alarms, please.
The normal problem cause for this type of CTD temperature mismatch is improper insertion of the CTD T/Cs into the thermowell after a maintenance outage (usually a Major Inspection but possible a Major Inspection). It's rather tricky to get the thermowell to be properly positioned in it's thermowell--because it's inside the machine and can't be visually checked or adjusted.
Another reason might be that the T/C extension wiring between the CTD T/C and the nearest junction box was damaged when some work was done in the area near the lower combustion section of the turbine compartment. MANY mechanical workers do not treat wires and cables with the respect they deserve and drop tools on them or walk on them or just mistreat them.
If there was work done on the sub-junction boxes and/or junction boxes of the CTD T/C extension wiring that connects the CTD T/Cs to the Mark* and the wiring wasn't terminated properly that can cause abnormal readings. OR, if there is a leak of hot combustion gases in the area of one of the sub-junction boxes or even of the T/C extension wires (we don't know if the T/C extension wires are encased on a stainless steel sheath OR if they are the flexible T/C extension wires that bolt on to the T/C body).
If a T/C I/O card in the Mark* was recently replaced, or a T/C terminal board in the Mark* was recently replaced and wasn't done correctly that could cause a similar problem to the one you are describing. This happens most often with Mark* V terminal boards or I/O cards that are interconnected with ribbon cables in the turbine control panel. Also the pins and receptacles of the ribbon cables can become "corroded" over time. (It is strongly recommended to use conductive grease--not too much!--when reconnecting the ribbon cables to the connector. (This has bee covered MANY times in previous threads on Control.com) Mark* VI T/C terminal boards and Mark* T/C I/O cards in the processor racks are interconnected by cables with D-sub connectors (37-pins) at each end. Those connectors are supposed to be firmly clipped to the terminal boards and to the processor rack chassis, but aren't regularly checked and can come loose. It doesn't even have to be a T/C cable/card--it could be a cable or card in the vicinity that was replaced and the T/C cable was not firmly clipped in place and was disturbed when changing a nearby cable.
Another reason which might cause this problem is that there is a leak of hot combustion gases in the area where the CTD T/Cs are located causing the metal surrounding the T/C thermowell to get excessively hot. OR, not very likely, but it could happen, is that there is a lack of cooling & sealing air in the area of one or more of the CTD T/Cs.
Finally, T/Cs do degrade over time. And when they do they can have erratic readings as the near complete failure. Sometimes they drift high; sometimes they drift low; sometimes they are not reporting any values but then mysteriously will start reporting values intermittently.
That's about it. If you want more help, PLEASE provide answers to the questions--or at least MOST of them. I know there are a lot of questions--but we aren't there alongside you. There's a lot we don't about the circumstances of the machine with the CTD differences and what, if anything, has been done to troubleshoot the problem (and how it was done). And, alarms--both Process AND Diagnostic--can help us understand what might be happening because we aren't at the power plant with you, we can't see what you see, and we don't know what's been done, what happened to possibly trigger the differences, etc. I've provided the most common causes of T/C reading problems--and most of them don't really have too much to do with the Mark* turbine control system. Yes, the T/Cs are ultimately connected to the Mark* but if they aren't properly installed or failing or actually reading abnormal temperatures the Mark* is going to report what it sees. Garbage in; garbage out.
Your power plant consists of two GE-design 9FA heavy duty gas turbines. One of the seems to have "normal" axial compressor discharge temperatures and the other one has very different axial compressor discharge temperature indications.
Lots of questions because there is lots of information missing.
1) You say you "... are observing high tenoerarure deviation in CTD's between the two units which are operating at same load and IGV opening." Are they higher or lower than the machine with the more normal CTD temperatures?
2) What are the CTDn (where 'n' is a whole number, 1 or 2 or 3, etc.) readings for both machines when operating at the same load and the IGV opening? Please provide all the CTDn values for both machines, as well as load (MW) and IGV angle (CSGV).
3) What turbine control system do the units have? Mark* V, Mark* VI or Mark* VIe?
4) When did this problem start--after a machine was re-started following a maintenance outage (Combustion Inspection, Hot Gas Path inspection, or Major Inspection)? After the machine with the very different CTD temperatures was tripped from a loaded condition? Was any Mark* card replaced before the problem started or after--if so, which one(s)?
5) What have you done to try to troubleshoot the problem?
6) What Diagnostic Alarms are present on the machine with the high CTD temperature differences? This is very important information that is often overlooked and could be very helpful in troubleshooting the problem?
7) What kind of combustion system do the machines have? DLN-2, DLN 2.6, etc?
8) Was any work done recently in the turbine compartment in the area of the lower half of the combustion section? If so, what was done, and why?
9) Have any of the CTD T/Cs (thermocouples) been replaced recently on either machine? How long since CTD T/Cs were replaced on both machines?
10) What Process Alarms are present when the machine with the CTD temperature differences is running? ALL Process Alarms, please.
The normal problem cause for this type of CTD temperature mismatch is improper insertion of the CTD T/Cs into the thermowell after a maintenance outage (usually a Major Inspection but possible a Major Inspection). It's rather tricky to get the thermowell to be properly positioned in it's thermowell--because it's inside the machine and can't be visually checked or adjusted.
Another reason might be that the T/C extension wiring between the CTD T/C and the nearest junction box was damaged when some work was done in the area near the lower combustion section of the turbine compartment. MANY mechanical workers do not treat wires and cables with the respect they deserve and drop tools on them or walk on them or just mistreat them.
If there was work done on the sub-junction boxes and/or junction boxes of the CTD T/C extension wiring that connects the CTD T/Cs to the Mark* and the wiring wasn't terminated properly that can cause abnormal readings. OR, if there is a leak of hot combustion gases in the area of one of the sub-junction boxes or even of the T/C extension wires (we don't know if the T/C extension wires are encased on a stainless steel sheath OR if they are the flexible T/C extension wires that bolt on to the T/C body).
If a T/C I/O card in the Mark* was recently replaced, or a T/C terminal board in the Mark* was recently replaced and wasn't done correctly that could cause a similar problem to the one you are describing. This happens most often with Mark* V terminal boards or I/O cards that are interconnected with ribbon cables in the turbine control panel--and the pins and receptacles of the ribbon cables can become "corroded" over time. Mark* VI T/C terminal boards and Mark* T/C I/O cards in the processor racks are interconnected by cables with D-sun connectors at each end. Those connectors are supposed to be firmly clipped to the terminal boards and to the processor rack chassis, but aren't regularly checked and can come loose. It doesn't even have to be a T/C cable/card--it could be a cable or card in the vicinity that was replaced and the T/C cable was not firmly clipped in place and was disturbed when changing a nearby cable.
Another reason which might cause this problem is that there is a leak of hot combustion gases in the area where the CTD T/Cs are located causing the metal surrounding the T/C thermowell to get excessively hot. OR, not very likely, but it could happen, is that there is a lack of cooling & sealing air in the area of one or more of the CTD T/Cs.
Finally, T/Cs do degrade over time. And when they do they can have erratic readings as the near complete failure. Sometimes they drift high; sometimes they drift low; sometimes they are not reporting any values but then mysteriously will start reporting values intermittently.
That's about it. If you want more help, PLEASE provide answers to the questions--or at least MOST of them. I know there are a lot of questions--but we aren't there alongside you. There's a lot we don't about the circumstances of the machine with the CTD differences and what, if anything, has been done to troubleshoot the problem (and how it was done). And, alarms--both Process AND Diagnostic--can help us understand what might be happening because we aren't at the power plant with you, we can't see what you see, and we don't know what's been done, what happened to possibly trigger the differences, etc. I've provided the most common causes of T/C reading problems--and most of them don't really have too much to do with the Mark* turbine control system. Yes, the T/Cs are ultimately connected to the Mark* but if they aren't properly installed or failing or actually reading abnormal temperatures the Mark* is going to report what it sees. Garbage in; garbage out.
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