dear Sir,

One of our GT tripped on IGV control trouble as IGV opening came down to just below 50 degree from 56.3 degree at 15 MW load.

But during that time Hyd oil pressure was normal only. At that time our Mark VI panel room temperature was more as one of our A/C unit got tripped in night time. Some told due to this high temp instrument malfunctioned. Is it true sir?

Thank you

 

Its very unlikely that the defective a/c could cause the malfunction of the IGV. Check your servo and LVDT. I'm sure something is wrong there

 

Dear Sir,

Now onward while raising query. Please mention the GT frame,control system ,base load capacity etc.....i.e. As you explain the problem in detail, you will get much better answer.

Mostly your LVDT core or core block might be loose.There is less chance of failure due to <b>One</b> AC.

But let me know :

Whether it IGV position reduced slowly for both LVDT or single LVDT?
Before tripping whether there was hunting in IGV position or hyd oil?
Have you taken trial after Tripping for opening IGV from control panel? What is result?Matching with physical angle? Take Few more stroke? it is diff reading at each command voltage for angle?

 

How high was the temperature in the control room where the Mark VI panel is located?

You didn't say what was happening to the unit at the time the trip occurred. Was the unit being loaded? Unloaded?

Does the unit have IGV Exhaust Temperature Control (for combined cycle applications; not to be confused with CPD-biased Exhaust Temperature Control)? If so, was it enabled?

Does the unit have conventional combustors or DLN combustors?

Have you re-started the unit and is the IGV control/actuator working properly?

If you're simply asking if the Mark VI can be adversely affected by hih temperature, the answer is yes. There is usually a 'Control Panel Temperature High' alarm that is announciated by the Mark VI to warn the temperature inside the Mark VI enclosure is getting higher than it should be, but it doesn't cause a turbine trip. Was that alarm announciated before the IGV Control Trouble Trip occurred?

It's not likely that a high compartment temperature caused a trip, but that's just a guess. We have no way of knowing how hot it was in the room where the Mark VI was located, and, again, there's usually that 'Control Panel Temp. High' alarm which is programmed into most Mark VI panels.

The likely cause for an IGV Control Trouble trip is a problem with dirty oil, or a sticky actuator, or a worn or intermittently functioning LVDT. If the actuator is sticking, then what usually happens is the Speedtronic keeps increasing the servo current to try to get the IGVs to move, and when the force from the hydraulic actuator gets high enough they move too quickly and too far.

Some of the Speedtronic turbine control panels also have logic that alarms when servo-operated devices are not following their references. So, an alarm is announciated before the condition gets so bad the unit trips. Was this alarm or something like it announciated before the IGV Control Trouble trip?

What Diagnostic Alarms were announciated prior to the trip?

What other Process Alarms were announciated prior to the trip?

You really haven't given us much to go on, so I'm guessing you were just asking if high ambient temperature could cause the Mark VI to not properly control the IGVs and a trip would be the result. Again, not likely, but not entirely impossible, either.

 

Dear sir,
first of all, you must give us more information about what its frame? is it using fuel oil or gas?

how big differential hydraulic pressure?

according to your description above... I'm quite sure the causes is about the malfunction of IGV to reach demand opening. when the unit on full speed no load condition, the angle is 57 degree..if the operation mode is base load, the opening increase until 84 degree. if IGV can't open according to its demand for xx second (**i'm not sure exactly, you can check on control constant) the unit will be tripped.so, it's definitely the malfunction of IGV system.

These are some steps you need to do:

1. check the LVDT excitation voltage
2. check the servovalve
3. replace the hydraulic filter with new one
4. recalibrate the IGV opening
5. check hydraulic cylinder, it could be worn-out.
5. check AIO card
6. if all step above ok, it's mechanical problem.

hope these help...

 

nanang,

Why are you so quick to propose recalibrating the LVDT feedback? Why didn't you suggest that they verify the accuracy of the calibration, and recalibrate if needed?

How do they check the servo-valve? What are they looking for?

How would they know if the hydraulic cylinder is worn?

Wouldn't a worn hydraulic cylinder be a mechanical problem?

Which AIO card in the Mark VI should the originator be checking?

I still think the originator was just trying to pooh-pooh the notion that a high compartment temperature could cause the unit to trip on IGV trouble. Because he didn't provide any other information, and really only asked if that could be the cause.

If the unit was running at 15 MW and the IGVs actually closed from 56.3 DGA to 50 DGA, and nothing else was happening, then the load would have decreased as the IGVs closed. And the exhaust temperature would have increased, presuming the fuel flow-rate was unchanged. The Trip Log of the Mark VI would likely show the above if the real cause of the trip was the IGVs closing.

A lot of time, what happens is that there are many alarms annunciated at approximately the same time when a unit is tripped. Some of them even read "Trip" when the unit has already been tripped by some other condition.

Reading an Alarm Printout, or the Alarm Display, of a GE Speedtronic turbine control panel takes some familiarization. Usually the list is sorted by time, with the newest alarm at the top of the list. So, one has to read down through the list and find the trip message/indication which is the "lowest" one on the list, since the real trip will be the earliest trip condition annunciated, not the latest one.

It's kind of a shame that GE doesn't write their code to block all "trip" alarms which might be generated after a unit is tripped for some reason, but they don't.

So, many people look at an Alarm Display, or an Alarm Printout, and the first trip message they come to when reading down the list is the one they interpret as being the condition that initiated the trip. That's rarely the case.

If the unit has variable IGVs, then it likely has a 20TV-1 solenoid. If the solenoid failed or power was lost to the solenoid for whatever reason, then the IGVs would close and the unit would lose power and the exhaust temperature would increase. The Trip Log should show all of these.

If the unit was on Pre-Selected Load Control when the event occured, if the IGVs went closed and were the cause of the trip, then the Speedtronic panel would have responded initially to the load decrease by increasing fuel, which would have increased the exhaust temperature even faster. Again, the Trip Log would show all of these occurring, if the IGVs closing were the cause of the trip.

The originator didn't say, but I'll bet the unit is running with no problems as we speak. Likely the operators initiated a 'Master Reset' after the trip or before the re-start, and a START was initiated and the unit's back on line.

So, it doesn't really seem like the originator is interested in what might have caused the IGVs to suddenly close. More like he's interested in whether or not a failed air conditioner and a high compartment temperature would have caused problems for the Speedtronic. Without telling us how high the temperature was, or for how long, or much of anything else. Just asking if a high compartment temp could cause problems for the Mark VI.

Last thing, the Mark VI System Guide, GEH-6421, lists the maximum recommended temperature as 60 deg C (140 deg F), in Vol. I, Chapter 4, 'Environment'. It doesn't say what could happen if the ambient temperature is higher than that, but it probably wouldn't be predictable, anyway, or very "agreeable".

 

please check diagnostic alarm regarding voting miss match (TCQA /TBCA CARD ERROR), and IGV temperature control function and LVDT feed back.

 

Dear Sirs,

Thank you for your valuable suggestions,

That Mark VI GT is having speedtronics control system TMR, Base Load capacity 23MW. Before tripping Mark VI panel room temp raised to 30 Deg C due to A/C problem & there was no hunting in other parameters except CPD, Exhaust Temp & IGV feedback. GT was not in temperature control mode. GT was running at 15MW load as per trend just 45Sec before trip. Only IGV was getting closed & Exhaust temp was getting raised, but load was almost constant. All Oil pressure (Hydraulic Pr 85kG/cm2, Lube Oil Pr 1. 8 kG/cm2, Trip Oil Pr 4.3kg/Cm2) were not varying till trip. At the end of 45 Sec IGV opening just crossed 50 Deg & unit tripped. Unfortunately this GT is a newly commissioned in the trip log servo current tag was not assigned so we were unable to check the servo current.

Before trip no diagnostic & process alarms appeared, only at the time of trip first alarm was IGV CONTROL TRIP then MASTER PROTECTIVE TRIP.

This incident occurred in the evening around 7 PM. After founding other parameters normal, again it was started back within 2 & 1/2 Hour. & it was running normal from that day.

<b>Thank You</b>

 

Same problem occurs with our machine also. but it happens during startup and GT IGV get opened from 34 DGA to 84DGA and creates tripping on IGV fault. in our case this happens due to IGV cable fault which is a very rare and new thing. so you can check that also..

thank you

 

dear CSA,

we can see the condition of servo valve and cylinder hydraulic actuator using servo current (CAGV) if the value more or less higher than 3 mA, the servo valve could be stumped by poor oil quality or it could be the cylinder hydraulic actuator has worn out therefore the output of servo current get higher and higher to reach the demand value...

ooh... i forgot one thing...we also have to check the mechanical bias adjustment on servo valve. mechanical bias adjust how much oil flow to actuator and how much it drained. but be careful, if we want to adjust the mechanical bias, we have to know how long the response time of actuator from closed to open condition. long response time
will cause the actuator difficult to reach the demand position and the indication is the servo current get bigger..

and also you should see the setting trip condition on control constant for time response of IGV to get demand position and how big bias value between actual position and demand position.

hope these help...

 

The originator has a problem of IGV control trouble trip with CSGV moving down and under a prefixed value, now understanding this is pretty simple considering that a preset value is never crossed on a lower side after machine crossing 14HS.

What I gather is that the machine would be at a pre-select of 15 MW and the entire episode would be owing to a clogged cigarette filter, mechanical jamming or the power loss to instrumentation device. The parameters otherwise mentioned are fine. What could be found from the post trip log was the 20TV status just at the time of occurrence or the CAGV values (just a few seconds prior to the event) which would be incrementing in case of a higher demand and a stuck actuator. Even the trip oil value mentioned is of 45 secs prior to event which would not help much to analyse.

The values just preceding the event would be of some aid. Try looking for the above in second and 10 second data, maybe it would not be a difficult task to ascertain the reason that led to it.

Nanang, what is this mechanical bias adjustment of servo. Sounds something relatively unkown. Also what do you mean by -trip condition on control constant for time response of IGV - as what I understand there is no such trip directly related to opening of guide vanes. Lastly it is not at normal to construe that an air conditioning system failure (that too one of the units) and the 30 degree centigrade temperature could have resulted in the trip. For older speedtronics, panel temperature high indication was at 49 degree centigrade. Check for TCQA_CJ_Q (I don't know if this mnemonic would be on your system) and the respective settings on your panel