The other day we experienced a unit trip with fault code 379 & 728 on the EX2000. During operation we were islanded from the grid and one unit was in ISOCH and the other was in L/S. The unit in L/S then tripped after a few hours of operation like this. Fault codes that we found on the unit were 379 and 728. The description mentions 379 as UCP_WDOG DCP/UCC Watchdog Time Out and 728 as Offline Trip. According to the descriptions it seems like it was either a loose 2PL/3PL, a problem with the DCFB or TCCB or a low voltage on 5V.
To me it seems very unlikely that this problem would present itself during an islanding scenario and not any other time during unit operation. I don't want to rule out a bad board or loose cable. After inspection of the unit and cables we reset the fault (hard reset) and spinning the unit up to full speed the exciter came on fine with no errors. We did not close the unit breaker and won't until we feel comfortable with the EX2000.
For more information from GEH-6121:
379 UCP_WDOG DCP/UCC watchdog time out - microapplication card not detected or not
Microapplication card enabled by EE.1.8 but not installed
For EX2000, 5 V supply from DCFB sensed lowTrip fault
2PL cable loose or worn (tighten or replace)
DCFB supply bad (replace)
3PL bad (replace)
TCCB failed (replace)
728 OFFLTRIP Trip fault generated via ee.OFL@TR
The pins and receptacles of the ribbon cables of EX hardware are prone to corrosion. Each spare card usually came with a tube of conductive grease to apply to the female side of the connector--a little goes a LONG way--before inserting the connector into the receptacle with the male pins. If the environment is the least bit humid the corrosion came occur. The grease should be re-applied approximately every two years. Again, too much is worse than none.
It could just be that the pins/receptacles are dirty/corroded and need to be cleaned. If you don't have any conductive grease just removing and re-seating the connectors several times (WITHOUT power!) may be sufficient to clean the pins and improve conductivity.
And, if the watchdog was lost then maybe that explains why the trip occurred?
I'm no EX expert, but I've worked an a LOT of TC2000 hardware.
Could be power supply issues, too....
Just an update for a bit of closure:
We ended up replacing the DCFB board, verifying test points and reseating all connectors on the DCFB and other boards. A very small amount of grease was used on the 2PL connector. So far so good...