Has anyone encountered a situation where the 3 pressure transmitters for the Mark VI SRV/GCV system sends the wrong pressure to the HMI, but on the field, the gas skid pressure, the srv/gcv pressure and the intervalve pressures correspond in operation.

Note: The pressure transmitter has been changed and certified ok

The voltage level that was measured at the vme card termination in the LIOS panel indicates that the transmitters are send signal to the mark vi ,but not corresponding with the right pressure.

 

cheedee,

If the value being shown on the CIMPLICITY display on the HMI is incorrect, but the unit is starting and running properly (meaning the P2 pressure--the pressure between the SRV and GCV--is correct), then the problem is not with the Mark VI. It is with the configuration of the HMI or the Toolbox .hmb file.

The formula for P2 pressure is:<pre>FPG2=(FPKGNG * TNH) + FPKGNO

Where FPKGNG is the P2 Pressure Reference Gain Control Constant
and FPKGNO is the P2 Pressure Reference Offset Control Constant
and FPRG is the P2 Pressure Reference</pre>

(A certain French division of GE has changed the formula to make the offset constant positive and the operator between it and the parenthetical value negative--but it's the same formula, because the offset is usually a negative number (unless you have the French version and then the offset is usually positive).)

The GE Mark VI HMI does <b>NO</b> control or protection functions--it's just a way to operate (monitor and send commands to and view and respond to alarms of) the Mark VI. The Mark VI does all the control and protection--so if the turbine is starting and running properly--with three P2 pressure transducers--then it's pretty safe to say the problem is with the HMI configuration (specifically the CIMPLICITY display) or with the Toolbox .hmb file configuration. The HMI scales the values it gets back from the Mark VI for data shown on the CIMPLICITY displays, and if it gets back bad data for a requested signal name then it will display bad data.

If someone has recently made changes to the Mark VI using Toolbox and didn't properly update the .hmb file afterward, and properly update the CIMPLICITY project, then that would be the cause of the problem of the P2 pressure reference not displaying properly. (Sometimes the solution is as simple as re-starting the HMI--but not always. And, re-starting the HMI when the unit is running will NOT affect unit operation.)

Sometimes the signal names of the P2 pressure transducer feedback are (and they change, depending on the whims of the GE division or the programmer):

96fg2a
96fg2b
96fg2c

or:

fpg2a
fpg2b
fpg2c

Usually the median-selected signal is used in the application code by the Mark VI, and it's signal name is usually FPG2. You can find it by following the input signal to the MED SELect block to see the block output's signal name.

It's possible that someone used one of the P2 pressure transducers on the CIMPLICITY display instead of the MED SELected value and one of the transducers is not working correctly. (Many CIMPLICITY displays have configuration problems from the "factory"--too many.)

Please write back to let us know what you find.

(Also, what is an LIOS, please? Thanks!)

 

peace
i didnt understand when you said that the intervalve pressure corresponds in operation with srv/gcv?

and from the other hand are the transmitters giving the same wrong indication?

what i can tell you to do is to confirm the calibration of the 3 transmitters(zero and span)and make sure that the same configuration is made at the each input point in the software configuration at the TBAI (low and high value in the engineering unit)

After doing all that try to open the srv valve a little bit and read both the indication given by each transmitter and the PI on the skid.

hope this has helped, good luck

 

It's really not safe to open the SRV with gas pressure upstream of the SRV. If there is any leak of the GCV, then fuel can get into the combustors and exhaust.

There is no way to set a P2 pressure reference for the SRV when manually positioning the SRV, so the fuel flowing into the interstate area would be uncontrolled.

Finally, there is a solenoid-operated valve (20VG-1) between the SRV and GCV which may be open when manually positioning the SRV. While gas will vent to atmosphere through this valve the tubing line is very small and all of the gas may not vent, further leading to a possible leak into the combustors/turbine/exhaust.

 

Thank you very much for your reply. I will continue the troubleshooting with the options you provided.

LIOS--Low Input Output Signal
HIOS-- High Input Output Signal

 

Hi,
The problem with the pressure transmitters have been resolved. I will try and write a concise summary to help anyone who might encounter the problem.

<b>Initial Problem</b>
The GE Mark VI has a three pressure transmitter voting system where the median pressure. In my case when the gas pressure from the skid is increase the transmitter responds accordingly ,but at a certain pressure the transmitter fails to respond to the increased inlet gas pressure increase. While troubleshooting from the GE toolbox this disparity was noticed.

<b>Troubleshooting</b>
We changed the P.Ts and tested for leakages , but that didn't solve the problem. We measured the voltage and discovered that as we increased the pressure the voltage responded slightly but would get "stuck" at certain level.

We noticed two(2) things when measuring the voltage from the LIOS panel
(i) When the PT was disconnected from the terminal board card and the voltage measured from the terminals, it was OK
(ii) When the PTs were connected back to terminal board card and the voltage measured , the voltage drop was observed.

The terminal boards were changed but it didn't solve the problem.

<b>Solution</b>
After consulting the GE manual we discovered that a jumper setting(open/return) on the terminal board could cause the malfunction. We change the jumper setting to RETURN and it fixed the problem.

<b>Observation</b>
We had earlier recovered the GT hard disk from a total crash and the .hmb config file could have been changed thereby causing the conflicting setting with the terminal board.

****In theory i suspect that to be the cause, but if anyone else think it problem cold have been caused by something else, please let me know*****

Thanks

 

cheedee,

Thanks very much for the feedback!

The .hmb file is used to configure the HMI--primarily for CIMPLICITY. It has nothing to do with the hardware jumpers on the TBAI card. And, again--the HMI has nothing to do with control or protection. Yes, the HMI can be used to configure a Speedtronic turbine control panel (using software applications ("tools")) but the HMI is primarily an operator interface. One can use Toolbox (or ToolboxST) an a computer that's not running CIMPLICITY to monitor or configure a Mark VI )or Mark VIe). Just because one can view a signal using Toolbox doesn't mean Toolbox is running on an HMI. An HMI, in the case of GE-design heavy duty gas turbines, is a PC running MS-Windows and, usually, CIMPLICITY--for use in controlling and monitoring the operation of and alarms associated with a GE-design turbine control system. Toolbox (or ToolboxST) is not normally (or at least it should NOT normally be) left running on an HMI unless it's being used for troubleshooting or maintenance or configuration. Toolbox (or ToolboxST) is simply an application that GE provides on their HMIs--Toolbox (or ToolboxST) is not necessary for monitoring turbine operation and sending commands to the turbine control system; CIMPLICITY is the primary method for monitoring operation, sending commands and responding to alarms. It's really helpful when describing issues or relating observations to the application on the HMI. To simply say a signal is not being seen correctly on an HMI (strongly) implies the signal is being watched on a CIMPLICITY display--not Toolbox (or ToolboxST). They are two separate applications (programs) which coincidentally can be installed and used on a single computer, so it's important to properly identify which application is being used to observe a signal or phenomenon.

I presume this installation was working fine for some time (years) and then this problem started. I also presume the RET jumpers were not installed for all that time. And, then recently something changed which increased the common mode noise in the control system and that resulted in the inability of the Mark VI to distinguish the transmitter output from electrical noise.

Those RET jumpers are almost always supposed to be set to the "IN" position during commissioning. About the only time they are NOT set to the IN position is when the mA signal is powered by the source device--not by the Mark VI. So, for example, if a 4-20 mA signal is used for some signal from a DCS (Distributed Control System) or PLC (Programmable Logic Controller) as an input to the Mark VI and the power signal for the mA signal is grounded at the source (not the interconnecting cable shield drain wire--the actual power source (usually 24 VDC)--then grounding the signal at the Mark VI can cause serious signal stability issues.

But, these particular P2 pressure transducers are most likely powered by the Mark VI, and so they should normally have the RET jumper set to IN to reject common mode voltage/noise and ensure proper operation of the input and Mark VI.

So, the real question is: What has changed to cause the common mode noise to increase to an unacceptable level--and, more importantly, left unchecked how is it going to affect other similar input signals?

The Mark VI (and Mark VIe) were built to have two separate earthing (grounding) systems, one for safety purposes (to prevent electrical shocks, and the other to ground the control system and help prevent problems with high-voltage transients like lightning strikes. HOWEVER, to make this scheme work properly there must be two properly constructed and isolated earthing "pits," and construction workers and their supervisors, and plant maintenance personnel and electrical technicians need to understand how this system works and how to prevent interconnection of the two earthing systems. When there is a protective earth system (safety) and a functional earth system (instrument) the two must remain separated, and only devices intended to be connected to protective earth (motor neutrals; transformer neutrals; structural steel; cabinets; etc.), and only devices intended to be connected to functional earth (control signals; control cable shield drain wires; control system power supplies; etc.) be connected to the respective earths.

A lot of people believe that, "Earth is earth." And so they just connect whatever device they are installing to the closest earthing point. And, that leads to problems--maybe not right away, and maybe not big problems, and maybe not constant problems--but eventual problems.

If the Mark VI at your site was installed as an upgrade or retrofit of an older turbine control system, then it's pretty likely there is only one earthing system at the plant for both safety and instrument purposes. And, there are literally tens of thousands of plants around the world that have only a single earthing system--and they work just fine. Except, maybe, if they are occasionally struck by lightning. Or, if there's a very serious motor or transformer ground or short, and the earthing pit isn't properly designed or has become "weak" over time.

But, rebuilding the HMI shouldn't (necessarily) result in any changes to the .hmb file, and certainly shouldn't have resulted in anyone moving the RET jumpers on the TBAI cards, and then having to move them back. No; something else has caused the need to ground the mA input signals in questions--and that something hasn't been identified yet. And, again--most of the time those RET jumpers should be installed during commissioning (and left installed permanently) unless the signal source power supply is also grounded and installing the RET jumper causes problems, in which case the RET jumper needs to be permanently removed.

Hope this helps!

 

Peace

i totally agree with all what you said CSA. thanks you very much
and for that i want to ask cheedee about the difference between the old and new transmitters (two three or four wire transmitters)?

My regards