This site has Mark V turbine controls for eight of its 7FAs. While performing the verify current to determine the validity of the LVDTs, the Mark V applies a small amount of negative current required to ramp the gas valve open, then reverses the current to ramp the gas valve closed. This occurs on all gas valves and IGVs on 7 of our 8 units. But for one unit, the SRV does not open. It appears to perform the test but when you view verify the valve feedback is either a flat line or a very low peak with a kink at 30% and 70%. The auto calibration works as expected and the null bias looks great at the factory setting of 2.67. The current gain match settings of the other units. I've replaced the RVDT and the servo and various null bias settings with the same results. I suspect that a Mark V card is bad that provides the reference for the op amp to drive the servo current. If this is correct, which board would perform this function? This is an HMI configuration, and the regulator changes from 77 to 43 as it should during the test to ignore the P2 pressure feedback.

Thank you in advance for your time,
Jack

 

gilariver Jack,

I can't tell from the post if the valve actually moves during the 'Verify Current ' test or not. If the valve doesn't move, then the test isn't really being performed.

And the Mark Vs at Gil's River are TMR panels--so there SHOULD BE current (negative current to open; positive current to close) from all three (3) control processors. Unless there's a servo wiring problem causing the polarity being applied to one or more servo coils to be incorrect it's hard to imagine three TCQA cards all being bad.

The "common" thing for all three TCQA cards is ACALIB.DAT. This is the AutoCalibrate configuration file which contains the "commands" and parameters to tell each of the servo-valve output regulators what to do and how to read the TCQA RAM and display the values on the AutoCalibrate screens. (Every unit-specific directory (F:\UNIT1, -2, -3, etc.) has its own ACALIB.DAT.)

It could be that the SVO1 portion of the ACALIB.DAT file in the HMI for that unit (I presume you're using the local HMI in the PEECC of each unit.?.?.?) may have some difference(s) that are causing the SRV for that unit to behave oddly.

If the valve is actually moving, then the bumps/spikes are likely the result of some physical problem. What happens when you use 'Verify Position' on that SRV?

Is there another HMI that can communicate with that unit's Mark V, and how does 'Verify Current' and 'Verify Position' behave from that HMI?

Please write back to let us know what you find!

 

The SRV valve does not move. it is a TMR and this is from the HMI in the PEECC.

The acalib.dat file is the same for all other 8 7FAs. I edited the acalib.dat file to include additional servo references but the Mark V appears to not attempt to ramp the feedback command to allow the servo current a reference. Verify position also shows a much flatter current trend. And this does only occur on the SRV valve. The servo and RVDT were replaced prior to this and the response was the same prior to replacement. That is what prompted the replacement of both. But strangely the auto calibration does drive the valve and calibrate the LVDTs. Given the separate TCQA cards for each core, independent drivers, and separate servo coils, this has become baffling. This is why I had also checked the acalib.dat file. I didn't try it from the remote server. That gives me something that might shed more light. This unit is back on line with no issues so it might be a while before I can test again.