I have a Frame 7 GE with a MK IV Speedtronic. During startup at approx. 3600 RPM, I am losing a bunch of indication. IGV, vibration, gas valve postion, MW readings. All of these either go high or low at the same time, then recover at the same time, about 15 seconds later. Has anyone seen anything like this?

 

What, if any, Diagnostic Alarms are being annunciated during this "loss of indication"?

Did this problem just start, or was there some maintenance work recently performed on the unit (combustion- or hot gas path- or major inspection)? Was there any maintenance recently performed on the 125 VDC battery, including setting the charger to Equalize mode? Have you monitored the battery charger output voltage/current during the loss of indication?

3600 RPM is usually 100% speed for a Frame 7 GE-design heavy duty gas turbine, so you're saying that at about 100% of rated speed you are experiencing the "loss of indication"?

Are you referring to loss of indication on the CRT on the door of the Mark IV panel, or a remote CRT (sometimes called a <D>), or some device connected to the Mark IV via the DataDump output or a MODBUS output or a CSF connection (like a GE CIMPLICITY-base HMI or someone else's HMI)?

If it's not the "local" CRT on the Mark IV panel door, then what is happening on the CRT on the Mark IV panel door when the other device is experiencing the loss of indication?

During this loss of indication, does the unit continue to run or does it trip? Is automatic synchronization enabled and active during the loss of indication? Do you have to initiate a Master Reset or another START signal after the loss of indication to get the unit to synchronize and load, or does it just operate normally?

Usually when a Frame 7 reaches approximately 95% speed (called "14HS") lots of things start happening, including closing the compressor bleed valves (on some units, depending on the vintage of the control system), starting of the exhaust frame blowers, and stopping of the Aux. L.O. and -Hydraulic Pumps. Also, some machines also flash the field of the generator at or just slightly above 95% speed. Field flashing requires a fairly significant current draw from the 125 VDC battery for a short period of time. Also, at just around this time, the exciter regulator of some units switches from DC (or Manual) Regulator to AC (or Automatic) Regulator, and even others switch their exciter regulator power supply from station AC to generator terminal AC power. So, it can be quite a busy time and even more difficult to try to associate one of these events with what you're seeing.

The <C> processor is the most heavily loaded (highest power requirement) in the Mark IV. Any problems with the 125 VDC power supply, such as voltage dips or even spikes, can cause <C> to have problems, like flickering displays, etc. This is the first place to be looking.

 

To start with the battery. The voltage was suspect. We put in a new battery. The 125Vdc bus was very stable, as was the voltage off the battery charger. This did not fix the issue.
When I stated a loss of indication, what I intended to say was that some of the indication from the Mark IV was incorrect. The HMI we have is communicating with the C processor. The communication was never lost. The indications would either take a step jump or drop. This only happened after the turbine had reached approx. 99% speed. From our indications we have determined the change in indication happens while the unit is attempting to auto sync. The indication would be affected for only 15 seconds. At the end of the 15 seconds the unit would either trip or sync in. After this the indications would be fine. We have changed out the auto sync card and the problem appears to have been taken care of. Unsure as to how the sync card could cause the inputs on all of the three processors (R, S, T) to be affected without giving a voting mismatch alarm.

As for the Diagnostic Alarms that came in during the trip, it was almost always IGV trouble and trip. That has caused us to do extra work on the IGVs for no reason. With the aid of an HMI we were able to see that there were a lot more being affected than just the IGV. Gas valve indication, exhaust thermocouples, vibration probes, and a few others.

To answer your question on when it started. It has been happening off and on for more than 15 years, but has just gotten to the point where it was doing it all the time. There was no work to speak of before any of the past trips.

As for the question on the D computer. We are using a third party HMI in place of the D computer or a Cimplicity unit.

The local CRT is still in place and working.
As for the question on the trip. It does take a Master Reset to get the unit back. I would like to hear from anyone who has seen or heard of any problems with the auto sync circuit. We hope to have the problem fixed, but it has gone away before for a period of time, just to come back at a later date. There appears to be no trend to it.