Following Diagnostic alarm has happened at the time of rolling of our steam turbine, which was stopped and started (rolled, synchronised). On rolling after two hours (with out any job on machine or control system) following diagnostic alarms related to <S> processor have come. These are related to overspeed, but the loopback alarm of ETD is not clear and may be a threat (?)...

There is a button for 'Master reset' which in Steam turbine we have never used, but in gas turbine we are using this reset feature many times with out any problem. In the rungs this master reset button in Steam turbine MarkV is resetting many cards including TCEA. We are not sure if this Master reset button can be used to clear these alarms, and also not sure if by doing so will it initiate a Trip? can anybody guide us...
Diagnostic alarms:<pre>
S1 1 C 2374 Voter mismatch, <S> L4ETR1_FB
S1 1 C 2375 Voter mismatch, <S> L4ETR2_FB
S1 1 C 2378 Voter mismatch, <S> L12H_ACC
S1 1 R 1696 TCE1 TMR check trouble, ETR1
S1 1 R 1697 TCE1 TMR check trouble, ETR2
S1 1 S 1696 TCE1 TMR check trouble, ETR1
S1 1 S 1697 TCE1 TMR check trouble, ETR2
S1 1 S 1713 TCE1 Loopback, solenoid, ETD1/SOL1/MTSV
S1 1 S 1714 TCE1 Loopback, solenoid, ETD2/SOL2/ETSV
S1 1 T 1696 TCE1 TMR check trouble, ETR1
S1 1 T 1697 TCE1 TMR check trouble, ETR2</pre>
If not what could be the problem..?

 

RP,

First of all, a Master Reset can not cause a trip. Or, to be correct, I have never seen a software implementation where this could happen and I can not imagine any reason to implement it otherwise.

In any software there is a number of alarms, some signals and all the trips that are latched. This means that once the signal goes to 1, it stays 1 until it is reset. Let's forget for the moment about the signals that are neither alarms, nor trips.

So, in case of some alarms and all the trips, it is important that they remain active until the real problem that created them is cleared. In order for this to happen, the signals in the software related to them are self-sustaining. Even if the measurements that led to the alarm/trip go back to normal, the alarm/trip is kept to 1.

Once the problem is solved, the alarm/trip can be eliminated by pressing "Master Reset". This will break the latch and, if the triggering conditions were cleared, the alarm/trip will disappear.

So, "Master Reset" will either do nothing when pressed (because the conditions that triggered the alarm/trip are still active), or will clear the alarm/trip.

Now, back to your actual problem. It looks like the <S> controller in your MarkV panel has a problem. Actually, you have 3 alarm there. Two of them are related to the Trip Solenoids (MTSV and ETSV). The diagnostic alarms tell you that either the ETR relay drivers or relay drivers feedback monitor on the TREG terminal board has failed, or there is a cabling problem.

The third diagnostic is "Voter mismatch, <S> L12H_ACC" meaning that <S> sees a loss of protective speed signals or a very high speed increase.

Since I never saw all these 3 alarms coming in the same time and I don't really see how this could happen, I suspect you have either a cabling or a card failure. The easiest is to check the cabling, then, if you can find no problem there, change the card (sorry for not giving you details, my MarkV knowledge is a bit rusty, documentation is not at hand and I don't want to give you wrong information).

As for operation, if you have a normal implementation, you should be able to keep running the unit as before. The only thing is that you are now 33% closer to a trip in case one of the other controllers fails. The common recommendation is to try to fix the problem as soon as possible, even if it clears after a while.

 

Dear MK6TA,

Thanks for the info. We tested the reset button, and the all the mentioned diagnostic faults got reset. We had an observation from long back that the speed sensor reading get an induction, due to running pump, and this is predominant only when the steam turbine is on turning or at low speeds. The diagnostic has come during the rolling, and normally engineers monitor them and clear it with master reset before grid connection, which was missed by all this time. But on machine loaded condition this reset button was not tried as it gives command sto the ETD devices, due to risk of a trip.

 

RP,

Thanks for the feedback!

 

Dear RP,

Thanks for the feedback. I am glad to hear your problem is restricted to the cabling of the speed sensors. I was expecting a card failure there.

 

Dear Mark6TA and CSA,

Thank you