We've got a dual fuel 7EA DLN gas turbine, and we just finished a hot gas path inspection. We also replaced all of our electro-mechanical generator protection relays with solid state relays. When we started up yesterday, immediately after the breaker closed, we got a slew of diagnostic alarms and the GT tripped. The indicated alarm trip was L86TXT. All of our cards have status lights that say that they are good. Here is a list of the diagnostic alarms we received:<pre>
R 0324 No arcnet communication with R
R 0325 No arcnet communication with R
T 0326 No arcnet communication with R
R,S,T 1708 TCE1 Loopback, relay, PTR1
R,S,T 1713 TCE1 Loopback, solenoid, ETD1/SOL1/MTSV
R,S,T 0312 LCC <unused> #8
R,S,T 1251 TCQA 4-20ma output disagrees w/ref CH.8
R,S,T 1696 TCE1 TMR check trouble, ETR1
R,S,T 1697 TCE1 TMR check trouble, ETR2
C 2701 Voter mismatch, <T> L14h_ZE</pre>
Any suggestions on where to start with this?

Thanks,
Jeff

 

jhurt,

Large DC solenoids can cause the Mark V to have problems; many generator breaker closing solenoids draw a pretty hefty amount of current and then exhibit a pretty large inductive kick when the circuit opens. GE worked around this issue by putting "snubbers" on many of those large solenoids (including 20CB-1, 20FD-1, and 52G/CLOSE). For the generator breaker close circuit, the snubber was usually located in the Generator Protection Panel--and quite frequently didn't appear on any drawings because it was added during commissioning and wasn't included on any drawing mark-ups.

So, if any snubber was removed from the Generator Protection Panel during the change-over to solid-state relays, well, that could be the "smoking gun" you're looking for.

Some DLN-I units energize 20CB-1 at breaker closure, rather than 14HS, and other energize 20CB-1 at some small load (approximately 5 MW or thereabouts). These circuits can draw a lot of current (hence the slow-blow fuse in the circuit) during inrush, but then only use a small amount of current for hold-in. If that circuit was not rewired correctly or the current reduction method has failed, that could contribute to DC voltage problems during generator breaker closure, especially if 20CB-1 is energized at the same time as the generator breaker is closed.

Those are the most likely suspects. DENET and/or IONET Communication problems can lead to problems with fuel control and/or erroneous high exhaust temperature sensing. If any servo-valves were replaced during the outage, were the individual servo current polarities verified after replacement?

 

No servos were replaced but the snubbers you mentioned is something I'll look at. Thank you very much for your help.