we are having an issue with a GT13E2 unit (VGIV Measurement Difference Alarm), and its recurring with no trace of what is triggering the signal.

we did following activities as recommended by OEM:

1. Remove the connection between shield and ground from VIGV transmitter side.
2. Add a capacitor between the shield and ground in the JB for VIGV transmitters.
3. Check the ground point connection in the Marshaling for VIGV transmitters.
4. Check the calibration for VIGV transmitters
5. Reduce the low pass filter in ControCad from 50 to 10

however the issue still persist, data and trends shows that it happnened on load 70 MW and 35MW but we are not sure if there is a link between low load and the issue because we still don't know what is the root cause of the alarm.

i hope that someone in this forum has ever faced this issue before.

 

Having an issue at specific MW loading should help to diagnose. Take note of the VIGV position at those loads.
When you performed the VIGV calibration, did you check the response of the VIGVs at the position for each load point (70MW and 35MW)? I wonder if there is something getting hung up, hardware or hydraulics, at those positions causing the alarm.
I know from experience that there can be mechanical issues that don't show up if you perform the typical 0, 25, 50, 75, 100% calibration checks and the actuator is allowed to sweep quickly. If you slow it down around the specific problem areas, does the actuator get hung up or slow to respond, creating a difference between demand and feedback?
Say 35, 36, 37, 38%, maybe it starts hanging up around 36% and sticks while you request 37, 38, 39%.
Check it up and down as well around your issue points.

 

@mustafa_ismail
Since you had already proven it was spurious signal.Let check your Instrument grounding resistance is in acceptable figure as well as Electrical grounding. Other options are checking your signal cable is closed or crossed the Power cable in order to avoid magnetic interference, install signal isolation 4-20/4-20 ma next to your transmitter.