GE Unit Turbine,(30MW Base load), Model (Frame VI, Mark VI) and used Diesel fuel. the problem is drop on hydraulic pressure and load drop during interval of certain load.

we Observed that, there is oscillating the value of fql_pr#1,2 among of its actual value and zero value (as along the unit is running).

My question, please is, What is the impact of this rapid feedback's oscillation? On:

1. Bypass servo position current (FAL%) that compares a fuel command with feedback.

2. Amount of fuel (Reference FSR% and actual FQROUT%),

3. Turbine speed (Reference (TNR%) and actual (TNH%)), specially with TNR because of as known TNH relatively constant with grid's constant frequency.

(fqrout is fuel servo bypass command and fql_pr#1&2 is flow divider magnetic pick up pulse rate input % which it is as a feedback for servo to positioning the bypass valve, No LVDT's with bypass)

And thanks so much for any helping...

 

You wrote:

> the problem is drop on hydraulic pressure and load drop during interval
> of certain load.

You say this occurs during certain loads, but you don't say at what load or if it only occurs at this certain load (implied, but asking for clarification).

The mission, should you decide to accept it, is to determine what is "driving" the feedback oscillations. Is the actual fuel flow-rate changing and is the Mark VI trying to respond to the changing flow-rate feedback, or is the the Mark VI causing the actual flow-rate to change?

Flow-rate feedback is compared to flow-rate reference and the servo-valve output current is adjusted to try to make the feedback equal to the reference. FSR is converted to fqr (the liquid fuel flow-rate reference which ultimately drives fqrout). The reference is compared to the feedback, and the amount of servo-current is varied to try to make the feedback equal to the reference.

You haven't told us if the unit is operating at Part Load (less than Base Load) or at Base Load?

If it's operating at Part Load, is Pre-Selected Load Control enabled and active? Or some kind of external load control, by either discrete RAISE/LOWER inputs, or by some kind of analog input signal.

Does the load fluctuate when these rapid oscillations occur?

Have you used the Trender in Toolbox to record the various data at high speed rates? If so, does the feedback oscillation precede the servo current change or does the servo current change precede the feedback oscillations?

Have you observed servo current oscillations?

What happens to the flame detector intensity when the flow-rate feedback oscillates?

What happens to the exhaust temperature when the flow-rate feedback oscillates?

To my mind, if the actual fuel flow-rate were changing (oscillating from zero to normal or higher values and back to zero, repeatedly) then there would be flickering flame indications, and exhaust temperature swings and possibly even loss of flame trips.

If the load is remaining stable when these flow-rate feedback oscillations occur, and exhaust temperature is stable and flame intensity is stable, then the actual flow-rate isn't changing by much.

 

Firstly, thank you for replying Mr. CSA ,

>You haven't told us if the unit is operating at Part Load (less than Base Load) or at Base
>Load?

@ Part Load.

>If it's operating at Part Load, is Pre-Selected Load Control enabled and active? Or some
>kind of external load control, by either discrete RAISE/LOWER inputs, or by some kind
>of analog input signal.

Pre-Selected Load Control NOT active (as shown on screen)

>Does the load fluctuate when these rapid oscillations occur?

When unit reach to lets say to "A CRITICAL INTERVAL" that Fqrout=from 43% to 48% and Load= from18 to 21MW) hydraulic pressure will fluctuate and load will fluctuate (from 18 drop to 16 and up to 22)

note:
1. the feedback oscillations do not impacting until (fqruot close to 43% till 48%) which it goes up to (higher) than its normal value and back to normal repeatedly until 48%.

2. About the case of hydraulic fluctuating:
there are alarms during the critical interval (1. hydraulic supply main pump default, 2. hydraulic supply aux. pump discrepancy).
At that moment,the drop of load will happens.

>Have you used the Trender in Toolbox to record the various data at high speed rates? If
>so, does the feedback oscillation precede the servo current change or does the servo
>current change precede the feedback oscillations?

The feedback oscillation precede the servo current change.

>Have you observed servo current oscillations?

Yes, it is little oscillate until (fqruot close to 43% till 48%) which be high oscillate (reach 95% and sometimes -85%)

>What happens to the flame detector intensity when the flow-rate feedback oscillates?

it is random at all time, sometimes 95% or 101%..

>What happens to the exhaust temperature when the flow-rate feedback oscillates?

Before critical interval (TTXM =715 deg. F) and during the interval (decrease by 5 deg. and up by 5 deg.)

>To my mind, if the actual fuel flow-rate were changing (oscillating from zero to normal or
>higher values and back to zero, repeatedly)
>then there would be flickering flame indications, and exhaust
temperature swings and
>possibly even loss of flame trips.

yes,in the past,the unit was tripping by loss of flame.

thank

 

This sounds like a combination of a couple of things.

First, the actuator for the LFBV (Liquid Fuel Bypass Valve) probably has some excessive wear in the cylinder that is causing leakage when the unit is operating at fuel flow-rates corresponding to the "critical level".

Second, the valves of the hydraulic accumulator (presuming there is one) may not be in the proper positions (the block valve should be open and the bleed valve should be closed), or the charge in the accumulator isn't what it should be.

The hydraulic pressure is probably fluctuating because the actuator is passing (leaking) and the servo is having to increase the flow of hydraulic oil to the actuator to try to maintain the desired fuel flow-rate when the actuator piston is at the worn area in the actuator cylinder. If a properly charged accumulator with its valves in the proper positions were working, it would probably make the problem not so noticeable.

<b>OR</b>, the accumulator may have been masking a problem with the LFBV actuator for some time and it's gotten so bad now that it (the accumulator) can't compensate sufficiently any longer.

But, this isn't likely a "controls" problem. It's more likely a mechanical problem with a control element (the LFBV actuator).

If this is a TMR Mark VI, then it could also be that one of the servo coils is receiving servo current of the wrong polarity, which could make any other problem seem worse. It's very difficult to test the servo current polarity of the LFBV of a Frame 6, because there are no LVDTs. One has to remove the piping from the valve to be able to see the plug move in response to current changes. This can be done while you are checking/replacing the LFBV actuator (hint).

Let us know how you fare.

 

And to preclude any questions about using AutoCalibrate to stroke the LFBV, it can't be done on a device without LVDT feedback.

[Actually, the LVFB actuator could be stroked, but it will still require removing the piping from the LFBV to see the valve plug, and it would also require a frequency generator and forcing of the servo valve output--all of which would take too much to describe here, and would take too long to perform if not familiar with the Mark VI inputs, outputs, and regulators.]

 

Greetings.
Mr.CSA

During analyzing the unit problem and make a comparing with other same unit (that has no problem), it has reaching to some of results like:

I) Fuel system notes:

1. the bypass servo has a (fuel) leakage (after asking they saying this is a venting for servo ! How there is a fuel venting ?! maybe VR21 relieving of servo, but how! it is close fuel bypass cycle.

2. three magnetic pick up sensor of flow divider (fql1, fql_p1 and fql_p2), at all time ,two of them (fql_p1 and fql_p2) are swinging between normal and zero, even when FAL has stable!!

II) Hydraulic oil system notes:

1. the position of a hydraulic accumulator is (only) on the hydraulic Oil line that going to IGV system!! (which means that there is no real benefit of accumulator for hydraulic Oil system!!).

2. about the full opening of IGV is 86.5 which must be 86 deg.

3. As known the TRIP oil system is using to trip two valves: a) IGV solenoid valve (20TV-1) , b) fuel stop solenoid valve (20FL) ,BUT here the VS1 is feeding by the hydraulic Oil system!!( meaning that if any Fluctuating on hydraulic Oil system, it will effects on stop valve opening!).

III) Mark VI Files:

1. more than once there are alarm appear on HMI like,

(1) <T > slot 10 VTUR diagnostic alarm, and (<R&S&T > slot 10 VIAC diagnostic alarm,

(2) flow divider fuel high flow difference.

Need to your opinion, please.

BEST REGARDS,

 

I.1) No one said anything about the servo leaking; the suggestion was that the hydraulic actuator that the servo is attached to might have a worn area that is allowing <b>hydraulic oil</b> to leak past in a certain area of the stroke.

Certainly, the actuator is small, but they have been known to leak hydraulic oil, which is at a higher pressure than fuel.

I.2) This is the first mention of three speed pick-ups; GE has subtly been moving away from using three liquid fuel flow divider speed pick-ups for TMR panels (and, we don't know if the Mark VI at your site is TMR or SIMPLEX).

This is one of the problems of posting to forums like this for help: we can't know all of the details of the unit at your site or of the control system at your site. All GE-design heavy duty gas turbines suck and squeeze and burn and blow, but they all do so with slightly different auxiliaries and systems. Without the ability to know exactly how the unit and control system at your site is configured we can't really be specific. UNLESS, THAT IS you provide as much information in your original post as possible.

What have you done to check to see if the mag pick-ups are working properly? Have you checked the gaps of all three pick-ups? Have you checked to see that they are are tight and do not vibrate?

How old is the flow divider? Are you certain the flow divider toothed wheel(s) is(are) in good condition?

Have you removed the speed pick-ups to check their faces to see if they are undamaged? They're not expensive; have you tried replacing one of the ones experiencing the problem to see if that helps to resolve the problem with that particular speed pick-up? Have you tried shifting speed pick-ups to see if the problem follows the speed pick-ups?

II.1) Again, we can't know all of the details of the auxiliaries at your site without being able to see the P&IDs or without information from you. I would be very surprised to see an accumulator that ONLY serves the IGVs, but then I haven't seen every configuration there is in the world. Certainly, the liquid fuel system doesn't require the flow-rates that the IGV actuator does, but I'm accustomed to seeing an accumulator that serves the entire hydraulic system, not just one portion of it. If the accumulator at your site doesn't serve the LFBV, then an accumulator problem can be ruled out for now.

[By the way, have you physically reviewed the P&IDs for the Hydraulic System and the IGVs to be sure what you are being told is correct? Many times people misinterpret P&Ids, or just go on what they are told by others without physically reviewing them personally, and are very surprised later to learn what they've been told is not correct.]

II.2) The IGV angle has nothing to do with the LFBV.

II.3) Trip Oil has nothing to do with the problem you described. Hydraulic oil is used to open the Liq. Fuel Stop Valve (it's an open or closed valve; it's not controlled with a servo--unless this is a very old unit that has been retrofitted with a Mark VI and even then, the older trip servos still just operate to open or close the valve not control it's position between open and closed). Certainly if the hydraulic pressure fluctuations are severe enough they might cause problems with the Liq. Fuel Stop Valve. But the pressure fluctuations you describe are not that severe.

III.1(1) This is just the CIMPLICITY HMI Alarm Viewer alarm message; you need to use Toolbox to check the exact Diagnostic Alarm that's being annunciated by the VTUR cards. If the liq fuel flow divider speed pick-ups are connected to the VTUR card, then that's likely the cause of the Diag. Alarm, but to be certain one needs to look at the VTUR using Toolbox.

III.1(2) This would certainly seem to be indicated by the problems you describe.

At this point, without knowing what's been done
to troubleshoot the liq fuel flow divider speed pick-ups it's difficult to provide any further assistance. I would still maintain the problem is NOT the Mark VI, but something that's connected to the Mark VI, like the speed pick-ups or the servo, or the actuator the servo is connected to, or the liquid fuel flow divider toothed wheel.

And, please, what's with all of the exclamation points? We just want the facts, with normal punctuation, please.

And, from the alarm indication you provided it would seem that the Mark VI is a TMR panel. (Though I don't always trust CIMPLICITY alarms.) But, it would still help if you would confirm that.

And all you can get from a forum like this, without infinitely more detail than you've provided or the ability to review the documentation and drawings for your site, is someone's opinion. Unless we're there alongside you, or have access to lots more information than we have been given we can't offer any more than an opinion or suggestion.

 

Hi Mr.CSA

We replaced the bypass and make the true calibration, but same problem!

Regards,

 

<b>I would absolutely love to know how to calibrate the LVDT feedback from a device with no LVDTs.</b>

There were several questions about the speed pick-ups and their gaps and their tightness and the condition of the toothed wheel(s) of the liquid fuel flow divider.

So you've now eliminated the LFBV (but not the exclamation points).

I will stick with my statement that this is not a Speedtronic problem but a problem with the input devices or the output devices.

But it would be very informative if you could describe the calibration procedure. Seriously.

Really and truly seriously. It would be a real learning experience for all of us.

Seriously.

 

> I will stick with my statement that this is not a Speedtronic problem but a
> problem with the input devices or the output devices.

I would also not rule out a wiring problem, but that's unlikely, though not unheard of.