Hello, i'm new in the forum, in a gas turbine mechanical maintenance comany too.
Recently a customer ask if can provide IGVs LVDTs replacement services on a GE frame5, in this case the machine works with speedtronic Mark V.

Mechanically the replacement is easy to me (because we do mechanical services), but i need to know if i must re define max and min values. In case it has to be done, how can i acces to I/O configuration, what software and wire connection is necessary for speedtronic to PC comunication, any acces code or password is required?. once the max and min values are fixed, how autocalibrate is excecuted.

Sorry if i seem to be so amateur, but i'm very interest on gas turbines and i'm excited to learn about it as much as possible. More important i won't loose a new customer and the opportunity to learn new skills, so i'll be grateful for your help, maybe CSA know the answer as always.

Thanks, best regards.

 

CSA I'm not. And my best advice is to work with someone who's done this a time or four and can explain it you clearly and concisely.

What I can offer is the 35,000 ft. view of the process. What I can't do is write a procedure a novice could use without an experienced mentor. It's not clear to me why the LVDTs need to be replaced. Was the IGV ring/actuator worked on or removed and replaced?

Let's start with what LVDTs do. They provide a linear output voltage (when properly set up during installation) that is proportional to position. The Mark* V provides an excitation voltage to LVDTs of approximately 7.0 VAC RMS at about 3 kHz. To read that voltage you need a True RMS voltmeter that can read frequencies around 3 kHz. (Be very careful, there are Fluke multimeters that say True AC RMS but can't read voltages at frequencies above 1 kHz. (By the way, they're not inexpensive.)) Yes, it is possible to read the LVDT output, which is between approximately 0.7 VAC RMS and 3.5 VAC RMS, with the Mark* V, but it's not easy to explain how.

LVDTs need to be adjusted after installation to get the fully closed IGV angle/position to cause the LVDT output to be approximately 0.70 VAC RMS, +/-0.02 VAC RMS. That's really critical because LVDTs have a non-linear region below approximately 0.58 VAC RMS, so by setting the fully closed IGV LVDT voltage to approximately 0.7 VAC RMS that ensures the LVDT will be on the linear portion of its output throughout the total range of movement (stroke) of the IGVs. So, that's the first thing (after installing the LVDTs and paying attention to the color codes when changing removing the old LVDTs and installing the new LVDTs): Setting what's called the LVDT zero-stroke voltage to ensure the LVDT output will be linear across the range of travel (stroke) of the device (in this case the IGVs) is very important and necessary.

(I'm presuming the IGV electro-hydraulic servo-valve wasn't changed, but if it was it's necessary to perform a servo-valve polarity verification before doing anything else. Yes; the servo-valve leads/wires are also color-coded--but it very often turns out that the color-coded leads aren't the same from one servo-valve to the next, even if the servo-valve is brand new out of the box. So, a servo-valve polarity verification is very necessary and needs to be done properly--which IS NOT per the procedure in the Mark* V Control Specification.)

To set the zero stroke voltage the LVDTs need to be at the fully closed position, so the GT hydraulic system needs to be used, along with the AutoCalibrate display, specifically the Manual positioning feature of the AutoCalibrate display.

AutoCalibrate, in the calibration mode, is really dumb. It only knows when the LVDT feedback voltage(s) aren't changing at the fully closed position and the fully open position. AutoCalibrate needs to be told what those positions are for the IGVs. So, one needs to measure the IGV position at the fully closed position and the fully open position, and then put that information in an ASCII text file called ACALIB.DAT (or one of its possible variants). AutoCalibrate uses this information to know what position (angle) the IGVs are in when they are fully closed and fully open. It needs that information to calibrate the LVDT feedback.

Once the zero-stroke voltage is set and the fully closed and -open positions measured and put into ACALIB.DAT, then you need to use the hydraulic system to perform an AutoCalibrate of the LVDT feedback(s).

Once the AutoCalibration of the LVDT feedback is complete one then needs to verify the accuracy of the calibration. One uses the Manual positioning feature of AutoCalibrate display to do this. The important calibration is the one at the maximum operating angle of the IGVs (usually 84 DGA), so if the calibration isn't accurate at the lower angles of the IGVs but is accurate at the higher angles that's acceptable. (The Base Load of a GE-design heavy duty gas turbine is designed to be occur when the IGVs are at the design maximum operating angle (which is NOT the fully open position!), so the IGV LVDT feedback needs to be most accurate at that position.) If the calibration isn't accurate, that needs to be resolved and AutoCalibrate used to re-calibrate the LVDT feedback and that needs to be verified.

All of these steps involve lots of intermediate steps (the hydraulic system requires the L.O. system to be running; moving the IGVs requires forcing of logic signals, one of which allows the IGV actuator to operate. Measuring the IGV angles properly requires knowledge how the IGVs work (they have "backlash"or hystersis which must be accounted for), and the use of a machinist's protractor--one that has been specially modified for Frame 5s. There is usually a scale on the side of the axial compressor but there's no way to prove that it's accurate and mechanics tend to use it as a ladder rung so it's quite often pretty inaccurate. (A modified machinist's protractor can be used to verify the scale and adjust it to make it more accurate.) So measuring IGV angles is something that takes knowledge and some practice. Several measurements have to be taken and averaged to arrive at the angle for a particular position.

So, hopefully you are getting a sense of how involved this process is. AND, not all GE-design Frame 5 heavy duty gas turbines have the same auxiliaries and equipment and devices, so one procedure isn't applicable to every machine. (Some Frame 5's don't have an Aux. L.O. pump or even an Aux. Hyd. pump so the unit's have to CRANKed to establish L.O. and/or Hydraulic pressure.) It's NOT a simple process, and you would be very well-served to be able to work with someone knowledgeable and capable of explaining it so you can understand what's required and how to do it. Once you've seen it done and participated with someone who's knowledgeable and capable, it will seem easy. And, then when you go to another machine and try to do something similar you'll probably find different auxiliaries and logic and you'll require time to study and figure everything out even knowing what the basics are.

That's all I can do. There's too much we don't know about the machine and the circumstances to write a procedure; it would be a lot of guessing on our part or require a lot of answers on your part. And you don't probably have the luxury of time to try to do this over a World Wide Web forum. And, believe me, it's going to take longer than you think if you're doing this for the first time by yourself, or even with some help from site personnel. Someone else on this forum may jump in and give you more than this.