We had carried out combustion inspection of our gas turbine GE Frame 9 running on Mark-V control. When the unit was started after end of combustion inspection, the load was less than before by about 2-3MW and turbine compartment temperature after running for a few days started increasing and alarm appeared for Hi-Hi temperature. We had both turbine compartment vent fans 88BT-1 and 2 in service already due to this problem which started 2-3 years ago, but was not so bad.

Leak search was carried out and found leakage at combustion wrapper joint and near cans #4 and 11 at each end of horizontal joint of the wrapper. The unit was shut down and bolts re-tightened. The unit was re-started, but still temperature of the compartment is running high and load is also low. All other parameters have been checked and found to be ok. Just 2 purge air valves VA33-1 and VA33-2 for water injection were found closed due to wiring problem, which were opened, but there is no effect on load or turbine compartment temperature. Water injection system is for NOX control when running on HSD oil, but we have never used it. The unit runs at 100% fuel gas. I am wondering could there be any effect inside the hot gas path parts of the turbine due to closure of these two purge air valves?

Thanks.

 

A 2-3 MW loss of output on a Frame 9E (rated at approximately 120 MW) is a pretty significant load loss. If there is an axial compressor leak sufficient to raise the exhaust temperature in the turbine compartment, that could be the cause but it would have to be a relatively large leak. What is the difference in compressor discharge pressure before and after the combustion inspection when operating at Base Load?

Was an off-line water wash performed before or after the combustion inspection?

Were the IGV LVDT feedbacks "calibrated" during or after the combustion inspection?

Was (Were) the CPD transducer(s) calibrated during or after the combustion inspection?

Are you certain the compressor bleed valves are both closed? If one of them is partially open there will be a flow of heated compressed air through the piping which would increase the air temperature in the turbine compartment, and result in a loss of power output. When the valves are closed, the temperature of the piping shouldn't be much higher than compartment temperature; if the valve(s) is(are) not fully closed the piping temperature will be higher than compartment temperature. Non-contact infrared temperature sensors can be used to check the temperature of the compressor bleed downstream of the valve(s) to try to help determine if the valves are closed when they should be.

If the Water Inj. Purge valves are not open when the unit is running on gas fuel, hot combustion gases can flow into the Water Inj. piping and a circulating flow can occur which will heat the piping. But, that's not very likely, but not impossible either. There should be some kind of check valves, and one or more of them would have to fail also. But stranger things have happened.

 

We have a similar problem in our 9E. We calibrated the LVDT's because of a problem in our IGV's which were closing from 84deg to 78 deg at base load. We also performed the offline wash during the shutdown.

Now again, our IGV's are closing and turbine compartment temp are above 175 deg C. The ambient is 50 deg C.

Both the vent fans and the exhaust frame blowers are running but the temperature is not coming down.

We even tried to open the compartment doors but all efforts are in vain.

What else could we do to bring the temp down.

We also checked the bleed valves with the thermography camera...

Regards,
MZI

 

I am completely at a loss for the relation of a problem with IGV control to turbine compartment temperature. I have seen some turbine compartment ventilation fans that take their suction (inlet) from the filtered, and sometimes cooled, turbine (axial compressor) inlet air--upstream of the bellmouth and IGVs. But even for those applications a problem with the IGVs wouldn't cause a problem with the turbine compartment temperature.

<b>WHEN DID THIS IGV PROBLEM START?

WHEN DID THE HIGH TURBINE COMPARTMENT TEMPERATURE PROBLEM START?

WHAT PROCESS ALARMS AND DIAGNOSTIC ALARMS ARE PRESENT WHEN THE IGVs MOVE WHEN YOU BELIEVE THEY SHOULDN'T BE MOVING?</b>

Because you are describing two probably distinct and unrelated problems.

Did the problems start after a maintenance outage when the turbine compartment vent fans were removed and reinstalled? Did the problems start after some kind of forced outage (emergency trip) when CO2 or whatever fire extinguishing agent was discharged into the turbine compartment?

Let's take the two problems separately (because they are separate problems most likely, unless there's something very peculiar with the unit and its design and enclosure that we are no privy to because the original posted didn't tell us).

The IGV position reference signal name is CSRGV (Control Stroke Reference, Guide Vane). If the IGVs are closing at Base Load (which is incredibly difficult to understand because, by definition, Base Load is defined to occur only when the IGVs are full open) then something is causing the IGV position reference to make them go closed. A problem with the LVDT feedback calibration isn't likely to cause the IGVs to move from one position to another--especially if the unit is being operated at Base Load with BASE LOAD enabled and active.

You need to look at all of the references feeding the CSRGV block and determine which one of them is causing CSRGV to close. All of the IGV position references feed into a MIN SEL (Minimum Select) function that takes the minimum input value and passes it to the output, CSRGV. So, find which input is below CSKGVMAX (the maximum IGV position Control Constant) and you will find your IGV problem.

We would be very interested to know how the plant arrived at the decision to "re-calibrate" the IGV LVDT feedback as the solution to this problem. Also, we would be very interested to know if you verified the IGV LVDT feedback before you performed a "re-calibration" of the IGV LVDT feedback by actually measuring the IGV angle and comparing it to the reference to determine if the IGV LVDT feedback was out of calibration? Or, during your IGV LVDT feedback verification did you determine some non-linearity in one of the IGV LVDTs that prompted you to replace the suspect LVDT?

Now, for the high turbine compartment temperature problem. The turbine compartment centrifugal vent fans provided with many GE-design heavy duty gas turbines have what are called reverse tangential blades. This means that when one looks at the direction of the fan blades one would assume the fans would rotate in a particular direction, but, because the fan blades are actually reverse-tangential fan blades the rotor should spin in the opposite direction.

It's a very common mistake when vent fans are removed during a maintenance outage and then re-installed that the direction of rotation gets reversed, or isn't even verified after the fans are re-installed and re-connected. And, it's also very common for the direction of rotation arrows painted on the vent fan housing to get painted over by over-zealous painters.

When reverse-tangential centrifugal fans are rotated in the wrong direction two things happen. First, the air flow through the fans is very low. There is discharge pressure where there should be discharge pressure, but it's very low. As a result, the amount of air being circulated by the vent fan is very low, leading to high turbine compartment temperatures.

Second, the current drawn by the vent fan's motor is very high, sometimes high enough to trip the motor starter's thermal overload.

Most of the turbine compartment vent fans provided with GE-design heavy duty gas turbines have some kind of damper on either the inlet to the fan or the discharge of the fan, sometimes both inlet and discharge. Sometimes these dampers are just opened by air flow and closed by gravity when air is not flowing. Sometimes the dampers are latched open by a mechanism that is unlatched when fire extinguishing agent is discharged into the turbine compartment (which could happen during a test of the fire protection system, also!). These latched dampers (which are closed by large weights pulled down again by the force of gravity) must be manually opened and latched after such an event. Sometimes, these latches vibrate loose, or if someone is working on the turbine compartment roof they bump the latch and it accidentally releases.

Most times there is no limit switch on the compartment vent fan dampers to indicate they are not in the open position or that they have closed. So, you need to check the operation of the dampers, and make sure they operate as intended, and are not sticking.

Lastly, sometimes on the walls of the turbine compartment enclosure there are also dampers which open when the turbine compartment vent fans are in operation. These dampers are also closed by gravity, and have been known to be improperly re-installed after a maintenance outage, or to somehow get damaged (miraculously, according to the mechanics who were working in the area of the dampers but <b>never</b> damaged them) and don't operate properly.

There should be a P&ID (Piping Schematic) drawing titled "Heating & Ventilation" which should should show the general locations of the dampers and the directions of air flows.

But, if you want to continue this thread, you are going to need to provide a LOT more information. First, and foremost, you are going to need to tell us what kind of Speedtronic panel the unit has. Second, you are going to need to tell us <b>every</b> alarm, Process- and Diagnostic, that is present on the Alarm Displays of the operator interface when the IGV position problem is occurring. Third, you are going to need to tell us what mode the unit is being operated in. That means, you need to tell us if it's being operated in AUTO or REMOTE mode from the Master Selector on the operator interface, and then which Load Selection is active (BASE LOAD, PRESEL LOAD, EXTERNAL LOAD Control, etc.).

And, fourth, it would be very informative for us if you could describe how it was determined that re-calibration of LVDT feedback would resolve the IGV position problem you are facing.

Thanks, and good luck with your problem. Again, if you want more help you need to provide the information requested<b>--including when the problems started--</b>.

 

Dear CSA,

Thanks for the reply. Please note that the compartments temp. is an issue at our site as we suspect hot gas leakage from the horizontal joint (wrapper). This was evident after a thermal scan with a thermography camera. We also checked the bleed valves whether they were closed or not but we found them to be closed during operation at base load.

Also note that the isotherm control settings of all our machines have been modified. The old settings were 1025 degF and now they are at 1075degF. This was done last year by a Control TA from the OEM. Prior to that, studies were conducted by both the turbine manufacturer and the HRSG manufacturer regarding the increase in exhaust temp.

We have Mark V at our site.


18-04-2011 Unit load decreased itself from 120MW to 110MW, it was checked thoroughly & found IGV opening reduced from 84deg to @65deg at local mechanical IGV position indicator while on MKV it was showing full open 84deg. Informed to all concerns. HRSG A inlet gas temperature high high alarm appeared on DCS, unit load reduced from 110MW to 105MW to reset the alarm.JR#2011-2316 raised in CMMS. To attend the IGV problem unit shutdown request for maintenance outage faxed to the Grid authority.

19-04-2011 At the start of shift, IMD & MMD were working on IGV inspection, calibration and LVDTs replacement of IGV. Job
completed and PFW 2011/00310 & 2011/00311 cancelled. However when cranking was stopped after a force cooling cycle, IGV servo trouble alarm appeared again which was conveyed to IMD. Later after force cooling and water wash, the turning gear, lube oil pumps stopped and IMD started replacing a trip oil solenoid valve L20TV1X to fix this trouble. Replacement Job is in progress at end of shift.

19-04-2011 GT-A lined up for water wash, water wash completed and normalized. Some plugs and valves found stuck closed which were got opened with assistance of MMD. During water wash heavy leakage of water observed from combustion wrapper and from bearing no 2 lube oil drain piping flanges with casings. Informed to MMD who noted the leaking points. Fuel oil fittings of fuel oil nozzles # 2 and # 3 found very hard, black with leakage marks and over heated conditions. Replacement of these fittings is in progress by MMD at end of shift

21-04-2011 Unit load dropped down from 120MW to 114MW due to closing of IGV from 84DGA to 74DGA readings noted from local mechanical indicator while IGV reading at MKV was 84DGA. C & I performed checks online & found one IGV LVDT faulty, suspected LVDT #1 disconnected temporally with the consent of Plant Mgr. Unit load increased from 114MW to 119MW as IGV opening increased from 74DGA to 81DGA.

21-04-2011 IGV angle checked at local on the mechanical dial indicator and found showing around 79 ~ 80 deg open while it was read 84 deg by MK V control LVDTs. Load of GT-A was found 119.5 MW which was approximately 2.5 MW /1.5 MW less than that of GT-B and GT-C respectively. Informed to concerns

23-04-2011 GT- tripped at high exhaust temperature during investigation of IGV-LVDT problem by IMD. Investigation to resolve the IGV problem is in progress at end of shift by IMD
01-05-2011 IGV manual control selected by IMD and IGV gradually closed to 80 DGA as read by MK -V. Load dropped noted. . Control normalized

01-05-2011 MMD carried out inspection, repair or replace the main hydraulic oil pump and pressure relief valve of hydraulic oil header under PFW#2011-00372.Main hydraulic oil pump Teflon coupling found damaged and was not available in the store so unit was prepared to start with Auxiliary hydraulic oil pump, damaged coupling may be replaced on the availability of the new one.

01-05-2011 IMD carried out the stroke of IGV’s to make sure the smooth movement and to measure the angle locally on dial indicator of IGV

02-05-2011 At start of the shift loading was in progress, unit base load 116 MW achieved. Initially it was same as the load of GT1C but after some time a difference of about 0.5 ~ 0.6 MW has been established. IGV position on dial found
moving b/w 76 to 79 degree with some interval, IGV also varying on Mark V b/w 81 ~ 86 degree.

02-05-2011 IGV position on dial found moving b/w 76 to 79 degree Intermittently, IGV position was also varying on Mark V b/w 81 ~ 86 degree, Informed to concerned.

02-05-2011 Sharp variation in unit load was started from 115MW to 108MW, Load decreased from 112MW base load to 108 pre-selected but variation found unchanged informed to concerned. During investigations IGV locally found at 64 degree opened whilst at MK V showing 84 degree, load further reduced up to 100MW to stabilized the unit.

02-05-2011 C&I started the investigation of IGV to resolve the IGV problem.

02-05-2011 IGV control was selected on manual by C&I but variation in load & IGV angle were continued, Local IGV angle indicator was also varying. IGV was moved from 84 to 80 degree in manual mode (on MK-V) and then back to 84 degree successfully. C&I investigated & found that LVDT # 1 was reading higher than LVDT # 2 and is very
unstable, causing the load & IGV hunting. The IGV control was switched to LVDT # 2 from LVDT # 1 to reduce this variation, Unit tripped during this transition. C&I investigated further and replaced the suspected TCQA card in <R> processor. Recalibration of the IGV after TCQA card replacement is in progress at the end of shift

02-05-2011 LWC#2011/377 issued to MMD to carry out calibration of IGVs.Investigation to resolve the IGV problem is in progress at end of shift.

03-05-2011 At start of the shift C&I was doing calibration of IGV, after completion of calibration LWC# 2011/00377 cleared and cancelled, provided isolation removed, unit was started and got fired in first attempt, synchronized and
loaded up to 65 MW, fuel conversion carried out and further loaded up to base load. IGV position remained stable since start up till shift end both on Mark V and local at 84 / 80 degree respectively

18-05-2011 Unit load observed less 2~3 MW than other two units, IGV angle position checked at local on mechanical indicator & found on 76~77DGA while on MKV IGV position is 84DGA.

18-05-2011 Diagnostic alarm TCQA LVDT position differential REG#5 appeared and 1.5 to 2 MW load decreased as compared to GT-C and four MW load drop than GTB. On checking, local indicator of IGV was showing only 74 DGA which was found 78 DGA in the morning. The IGV found varying from 74 to 78 DGA, Informed to all concerned. IMD carried out some checks and LVDT suspected reading higher than normal. Turbine compartment temp HI Hi was got cleared during IMD job. Further investigation will continue.

21-05-2011 Diagnostic alarm TCQA LVDT position differential REG# 5 appeared on R,S,T and 1~2 MW load drop observed. Locally checked and IGV position found 75º which increased to 80 deg after half an hour but again it was found 77º at 05:45 hrs. Turbine compartment temperature was noted 115~135 deg C on these occasions.

22-05-2011 Diagnostic alarm TCQA LVDT position differential REG# 5 cycled and about two MW load drop observed as compared to running load. Locally checked, IGV position found drifted from 80º to 75º. The load and IGV found back to previous state for short time but again load dropped and IGV verified to be at 75

23-05-2011 GT-A IGV was 80 deg Open at the start of shift. Diagnostic alarm TCQA LVDT position differential REG# 5 cycled and about two MW load drop observed as compared to running load. Locally checked, IGV position found drifted
from 80º to 75º. The load and IGV found back to previous state after short time but this repeated few times and even IGV observed down to 72 deg once. Later IGV reset to 80 deg. At the end of shift, IGV was recorded as 75 deg open.

 

MZI,

It's really wonderful that you can copy-and-paste from your operations logs, but <b>you haven't provided the requested information.</b> No Process- or Diagnostic Alarms, and no results of any of the "tests" (that word is used very loosely in this context as the "work" performed seems very haphazard and unplanned) are provided.

You've some very serious problem(s) with IGV position and LVDT feedback. It's not clear that the issue(s) have been properly identified. Simply referring to the pointer on the compressor casing is not enough to confirm actual IGV position; many times that pointer is inaccurate and it's only meant to be a rough indication of position. Unless it's "calibrated" after every time the compressor inlet case is disassembled/reassembled or some work is performed on the IGVs/IGV bushings/IGV actuator or IGV actuator linkage then it's <b>NOT</b> an accurate indication of actual position.

If there is that much discrepancy between actual position and required position, then there should be some other Diagnostic Alarms or Process Alarms indicating an inability of the IGVs to follow reference or a problem with IGV servo current. You <b>have NOT</b> provided any Process- or Diagnostic Alarm information and as such we cannot continue to help with this problem.

Also, you should be able to use the Prevote Data Display or the AutoCalib Display to check the actual servo currents from each processor, as well as what each processor sees the actual position to be. You can open AutoCalib and view operating data while the turbine is running; you will get some nuisance Diagnostic Alarms because AutoCalib accesses the RAM on the TCQA cards, but it's the best way to see both LVDT feedbacks and the actual servo currents for all three processors.

As for the high compartment temperature, you could have told us that you've identified the source of the high temperature and were just looking for additional ways to cool the compartment.

Best of luck with your problems.

 

Let me guess. Probably your controller is fed with the "wrong" input. I suggest the controller is responding to ambient/compressor inlet temperature. This temperature reading somehow is not stable.

 

Dear CSA,

I am gathering info which you have requested. Will get it by today.

 

MZI,

I have re-read all of the copied-and-pasted operations log entries and have seen that you have listed some Diagnostic Alarms. But there's a lot of information that's not clear and not provided. Such as individual servo currents during the IGV position problems; individual LVDT feedbacks (both of these are best viewed and recorded using AutoCalibrate when the unit is running--just to view the parameters!).

It seems that one of the departments "calibrated" the LVDT feedback with the indicator on the compressor casing showing 80 DGA and the Mark V showing 84 DGA. We don't know how the LVDT feedback is being calibrated (manually or AutoCalibrate) but it's pretty clear that the actual position of the IGVs isn't being measured and compared to the reference or the feedback to see if the calibration is accurate (at least not from the information provided).

AutoCalibrate has two features, both documented in the Mark V Maintenance Manual, GEH-5980, Sect. 5-7.2.1, called 'Verify Position' and 'Verify Current.' These can be used to help pinpoint problems with LVDTs and servo-valves. But, if I recall correctly, they will only work after an AutoCalibrate procedure has been completed on the servo-operated device (and before the processors have been re-booted). One can perform an AutoCalibration just to get data into TCQA RAM for the purposes of running either of the 'Verify' tools, then just re-boot the processors afterward (to get the previously known good calibration information from EEPROM into TCQA RAM) to revert to a previously known good calibration configuration.

Again, it's not clear from the information provided if a root cause has been determined. It just looks like a TCQA card was changed, some "calibrations" were done (and it's not clear if they were necessary or if they were even verified properly), and the unit re-started. It's not clear why the TCQA was changed. Both LVDTs are wired to the TCQA cards of all three processors (<R>, <S>, and <T>). It could be that the LVDT excitation for one of the IGV LVDTs comes from <R>, but a problem with that would likely have a Diagnostic Alarm to indicate such a problem.

And, you haven't told us <b>WHEN THIS PROBLEM STARTED.</b> After a maintenance outage? Suddenly? Over time? After a servo-valve was replaced?

It also seems that LVDT #1 has been replaced twice, with no change in operation. The TCQA Position Differential alarm for SVO5 (the typical IGV servo-valve output) is likely related to a disparity in the LVDT feedbacks from the IGV LVDTs. So, there's still something wrong there. I would recommend a complete review of the wiring of those two LVDTs: excitation, feedback, etc. Also, have a look at GEH-6195, Sect. 7.6, to see hoe a Type 43 regulator works and how the related signals "flow" through the Mark V. The drawing for the Type 43 regulator is for a GCV for SVO3, so one should mark up a copy to reflect the wiring for SVO5 to be clear for this troubleshooting effort of verifying wiring and connections.

I wish to warn you that without being able to see screen captures, it's going to be very difficult to provide enough information in a forum like this to be of much help.

And, there's one more thing you should know about some Mark Vs and LVDT feedback. I don't have access to the information right now, but there are some Mark Vs that, due to galvanic action (I think that's what it is attributed to) will react opposite to intended reaction to an open circuit in the LVDT feedback.

Once you have verified all of the wiring to be correct and provided more information (servo currents; LVDT feedbacks; the results of AutoCalibrate 'Verify' tools, etc.), we can investigate this possibility. But, let's not go there just yet as it's a remote possibility and we don't have enough information to say if it's applicable to this Mark V or not.

 

Dear CSA and Namatimangan08,

Now I gathered some information which might be fruitful.

At the Time of CALIBRATION We measure feedback from inside of Inlet plenum with the help of PROTECTOR as well we confirmed that angle on Dial Indicator TOO. Both were matching and a slight difference is of +-1 on some positions has observed.
LVDT Feedback is being calibrated with the help of Auto calibrate.

Now I will summarize what was happen from the beginning.

The unit Load was dropped sudden from 120MW to 110MW and the IGV Angle shift from 84 to 79DGA. Exhaust Temperature High Alarm appeared. So the load Reduced from MK-V to 100MW.

Then Gradually raise the load up to 120MW. IGV Opened to 84DGA. After some time IGV Starts variation in b/w 84 to 78DGA (This was observed on the Dial Indicator). Then unit load was dropped about 114MW. At that time we checked the Readings of LVDT on DIAGC screen. LVDT1 was reading higher while LVDT 2 reading was actual. I mean LVDT 1 Stuck at 3.15 Vrms while LVDT 2 shows 2.98Vrms.

LVDT2 actually responding according to the motion of IGV Angle. While LVDT1 Moves Mechanically with Hydraulic Jack but its reading freeze at maximum Position. So it was decided to change the LVDT with spare one. After replacement of LVDT . We make Auto calibration according to the procedure given in the GE Manual. Note: After calibration take angle from Inlet Guide Vane with the Help of Protector. It was the same as on AUTO CALIBRATE Screen.

After Calibration unit starts at base load. We make continue observation on IGV Position at Dial Indicator and on MK-V Screen. Initially Both LVDT match their values in terms of Vrms. After Achieving Base Load unit was at 120MW but after 2 Hrs. It lose 2 MW. Next Day was observed that unit was totally loose 4 MW. Observed the Behavior of LVDT,S on DIAGC screen. LVDT1 Again Stuck at high value and LVDT2 Responds according to the Physical Position. At this time LVDT 1 Disconnected from the TBQC Card the machine take more load and run smoothly at Base Load. So again unit shut down make some calibrations again. But all the efforts were Vain.

We also took the IGV on manual and gradually dropped its angle from 84 to 80. (On dial indicator Angle was ok I mean slightly different as compare to LVDT’s Feedback on MK-V.)

One most important thing is this that after replacement of LVDT-1 when we again observed the same behavior then we swapped LVDT’s such that position is same in field but Make Connections vice versa. So the fault shift from LVDT 1 to LVDT2 Observed on DIAGC Display.

After that we checked all the wire of LVDT 1 and 2, performed maggering, continuity test, connection verification from field. But no Improvement.

So it was decided that to change the TCQA Card of <R> Core and also Servo of the IGV.

One more important thing is this that the unit is running on Auxiliary Hydraulic Pump as the main Pumps Coupling damaged. And this Coupling Damaged after this problem arouse. Hydraulic Pressure is at 1420Psi which is slightly lower than the main pump which is around 1500 Psi.

 

MZI,

This is pretty strange, because the Mark V servo-valve regulator is supposed to be a high-select of the two inputs. If one input is lower than the other then the lower value should be "ignored". This means that if one of the LVDTs is reading 3.15 VRMS and the other is reading 2.98 VRMS, then the Mark V would believe the valve is at the position indicated by the 3.15 VRMS value (presuming the calibration values were similar for the two LVDTs).

And this does appear to be happening on the unit. But, for some reason, the IGVs are closing and the LVDT position from one LVDT isn't changing. That's just very, very odd.

You haven't provided any servo current information for the three processors (CAGV I believe is the typical signal name) when this problem is occurring and when it's not.

And you haven't told us what the IGV references feeding the MIN Select block that produces CSRGV are when this is happening.

The hydraulic pressure is low, but not excessively low. You haven't told us about the Hydraulic Accumulator condition (valve positions; charge pressure; etc.).

I keep going back to the issue that the feedback from LVDT1 is not changing when the IGVs are actually moving. You have changed LVDT #1, and the problem still persists. You have changed one of the three TCQA cards, and the problem still persists. You have changed the IGV servo (more money for Moog!) and the problem still persists.

Finally, you have exchanged the wiring for the two LVDTs at the Mark V and the problem follows LVDT #1. It certainly seems to be indicating that there is some problem with the wiring of LVDT #1. And, it seems that the problem only exists after some time, <b><i>such as when the LVDT gets heated up</b></i>.

And, you are complaining of high turbine compartment temperatures.... And, you indicated that there was water leaking from the #2 Bearing Flange on the combustion wrapper, which would likely mean that axial compressor discharge air is leaking from that area when the unit is running.

Could it be that hot air is blowing predominantly on LVDT #1? Can you build a small, temporary "shield" out of thin metal to place around the LVDTs, without completely isolating them from any air flow, but primarily to try to prevent any hot air from impinging directly on the LVDTs, particularly LVDT #1?

I believe the IGV servo is kind of "exposed" there, too, and could be susceptible to issues caused by excessive temperatures or lack of cooling air.

How many wires are in each of the two LVDTs on the IGVs? Four or five? If there are five wires on either or both of the LVDTs, describe how they are connected in the JB at the IGV actuator.

 

How stable is your grid frequency? You can express in term of amplitude of deviation from base to peak for half "wave" and average frequency of occurrence such as 0.3Hz (base -to-peak)once every 30 seconds.

Do you normally operate the GT with frequency influence on or operate it under temperature limiter?

My first impression based on your feedback is that mechanical system that cannot hold the IGV at the desired position. I'm just try to confirm it by asking these two questions.

This is not my final proposal. Just first impression. You have nothing to lose to look from this direction.

Thank you.

 

Dear CSA. Coincidentally, I'm also trying relate this problem with heat.

 

Servo, LVDT actual values could be a problem; We had cases where the LVDT internals got rubbed off due to inadvertible alignment issues of core, and oil ingress and was giving erratic readings , due to which higher value got selected and subsequent trips.

LVDT can be identified from command, feedback from Historian data..

If suspected LVDT is replaced and still problem is there servos and cylinder blocks to be attended...

Due to poor oil quality cylinders can also get malfunction..though it can affect other controls also... Are the Pre-servo filters replaced every year..

 

That was a very wonderful compilation of lectures...Nice one there.

Thanks

 

This is very-very good advice---

>A 2-3 MW loss of output on a Frame 9E (rated at
>approximately 120 MW) is a pretty significant load loss. If
>there is an axial compressor leak sufficient to raise the
>exhaust temperature in the turbine compartment, that could
>be the cause but it would have to be a relatively large
>leak. What is the difference in compressor discharge
>pressure before and after the combustion inspection when
>operating at Base Load?

--- sniped by Moderator ----

 

A compressor leak may indeed cause a load loss, but that would be because the flow is down. an increase in turbine compartment temps has no bearing on the load, unless of course it is so high it causes a trip.