Dears,

We have frame 5 gas turbine for power generation with Mark 5 control system. But after the shut down the following diagnostic alarms are coming continuously. Can anybody can suggest what are the possible reasons? and what check points we have to carry out resolving these issues? because first time we are facing these type of problems. Diagnostic alarms are.

1. IOMA power supply out of limits N15.

2. TCE1 power supply out of limits DCOM.

3. Voter mismatch <T> L33FP28.

4. TCQA P125-N125 over voltage.

5. TCE1 breaker1 close time out of limits.

6. Voter mismatch<S>CPD.

7. TCQA Ma short circuit voltage too high (these alarms repeating three times).

We checked all the R, S, T & C status in LCC display. S showing A7, but R, T& C LCC display toggling between "A7" & "DCC ERROR".

Your suggestions are highly appreciated regarding this matter.

 

Dear,

Usually when these kinds of problems start without some other event (lightning strike, serious battery ground, etc.) they are the result of failing power supply components. The TCPS cards in the back of each processor core (<R>, <S>, <T> and <C>) do fail over time, and some of them were built with better components than others (not GE's fault; their suppliers don't always furnish components with the same quality over many years of manufacturing).

And, site ambient conditions can also affect electronic component life expectancy. Power plants are the best environments for even industrial-grade electronics.

Based on the alarms you listed, one of two things is happening, the first being the impending failure of one or more TCPS power supply cards.

The second is that if the alarms are occuring when the generator breaker is opening and/or 20CB-1 is being de-energized, then one or more "snubbers" may not be working properly or be failing. These "snubbers" are R-C filters which were usually connected across high-current DC coils to prevent the inductive kick from opening the coils from affecting the Speedtronic (usually the power supplies). Many sites didn't install them, and if they did they were almost always installed in different locations on different sites (instead of in a consistent location)--so it's impossible to tell you exactly where to look for them.

But, again, the problem is most likely something to do with the Mark V power supplies (one or more may be failing at the same time), or it might be the DC source (battery; battery charger) has some problem or there is a large inductive kick which is causing problems during shutdown. Also, since you weren't specific when the alarms were starting we can't be sure what to tell you to try.

But, if the problem is "concentrated" in one processor I would first suggest making sure the DC supply is not grounded and has no spikes or dips during the shutdown when the alarms start, and then try replacing one TCPS at a time.

Hope this helps!