We have recently (in the last couple of weeks) started getting 3 "TCE1 Slow synch check 25X relay" diagnostic alarms on 4 of our 8 Frame 7EA DLN1 units that have Mark V. It has never happened on our other 4 units.
The event is somewhat random, in that it happens sometimes but not others when attempting to close generator circuit breaker using autosynch.
It is getting progressively more frequent and is now sometimes followed with "AUTO SYNCHRONIZING LOCKOUT" (L86S). Up until today the breaker closed anyway. The operator turns synch mode to "OFF" and does multiple "master resets". The diagnostic 25X alarms clear within about a minute. Once they are no longer active the L86S can be cleared with Master Reset.
Today, autosynch would not close the breakers due to the L86S alarm. Autosynch was turned off until the 25X diagnostics cleared, the L86S was cleared, then autosynch selected again.
After doing this sequence several times, the breakers all got closed.
What are your thoughts?
I am wracking my brain trying to remember the two times I have had to deal with this alarm and what the fixes were. Unfortunately, I can only remember one of them....
Has the site (or sites??) experienced any severe electrical storms in the recent past?
Have you been experiencing any other Diagnostic Alarms on the TCEA cards, or the TCTG card?
Do you have any spare TCEB cards, possibly putting a known good spare in place of the TCEB card in one of the Mark V's that's giving the Diagnostic Alarms?
When was the last time anyone put dielectric grease on the ribbon cables of the Mark V's???
Now, the one instance I can remember having to deal extensively with this problem was the result of a problem with the secondary disconnects of the roll-out PT drawers. The grease was nearly gone and the copper contacts of the secondary disconnects were beginning to tarnish. And, one of them was pretty badly bent and probably was not making contact very well, either, for mechanical misalignment reasons.
I know it doesn't seem like corrosion can suddenly become an issue on more than one unit, but stranger things have happened. And, it can be intermittent. Also, there was a period when the secondary disconnects of the PT drawers were pretty flimsily-built and were not very good. If, as part of some lock-out/tag-out procedures, the PT drawers are regularly withdrawn and re-inserted the secondary disconnects could be not holding up very well to the movement.
Have there been any changes or disturbances of the PT wiring recently--such as new digital protection relays being installed, or possibly calibrated?
When was the last time anyone went through the GAC and the GCP with a screwdriver and checked all the screws for tightness? Not gorilla tight, but just firm and tight. Again, it doesn't seem like this could happen suddenly on multiple units, but it's always a good thing to check periodically, and if it hasn't been checked for a while it's not a waste of time.
The very odd thing about synchronization schemes in Mark* turbine control systems is that they generally look at turbine speed instead of generator frequency when matching turbine speed. But, for the synch check (and auto synch) functions the Mark V must look at both PT signals (running and incoming) to determine phase angle. When you look at the Synchronizing Display, what are the red/green status indicators doing when this is happening? What are the phase angle measurements doing when this is happening? What is the synch scope needle doing when this is happening?
If I recall correctly, the Mark V does the auto synch function in <Q> and the synch check function in <P>. Which is why I'm kind of concentrating some of the troubleshooting suggestions on the <P> core and its cards.
Are there any Diagnostic Alarms in any of the <Q> cores? Any related to chips on the DCC/SDCC cards or the LCC/SLCC cards?
I'll keep trying to think of the other exasperating time this same alarm occurred, and what it took to fix it. I don't think it was a Mark V issue, though; something in the field wiring.... Actually, I think I'm confusing this with a different alarm on Mark VIe panels (slow breaker close feedback); but I'll keep noodling this.
Hope this helps!
Our problem seems to be resolved.
I swapped K2(L25X) & K3(L25) relays with unused k16 & K17. Then applied Nyogel 760G to every ribbon cable at both ends.
Some of these are closing breaker faster than they did before.
Thanks CSA and CuriousOne