52G Re-Closure Logic

S

Thread Starter

saurabhstalone

Please explain the functionality of generator breaker automatic re-closure logic in MKV GE Frames gas turbines logics. What is the significance of signal L2G? My understanding is GE allows automatic re-closure of generator breaker within 30 seconds after breaker opens up first time following a Start. Is this true? In my opinion the breaker should not be allowed to re-close automatically and operator has to intervene for safer operation. However, if the breaker opens up from some part load then operator has to interven and press the START button in order to re-close the breaker but during first time breaker closure following unit start, this is not the case and the logic tries to re-close the breaker automatically until timer 30 seconds get lapsed thereby unlatching 1X. Please put some light on this logic and process.

Thanks,
SSV
 
saurabhstalone,

This sounds like some field modification to the basic automatic synchronization logic--and a bad field mod, at that.

If the breaker is being closed/synchronized automatically, what's supposed to happen if the AutoSynch logic is in the Speedtronic turbine control is that the auto-synch permissive is supposed to be unlatched--preventing another AutoSynchronization unless the operator has taken action. And, the L2G logic was to put some time delay (I've seen as short as 2.0 seconds) before the AutoSynch logic could be re-enabled by the operator.

Methinks there is something very non-standard about the AutoSynch logic at your site. Are you certain the breaker status contact (52G) is working correctly? It's supposed to be from a contact ON the breaker, not an auxiliary contact operated by the breaker mechanism or an auxiliary relay.

Is your site one of those that has a Synch Enable contact from another control system (DCS) that needs to be set to enable an AutoSynch?

We would really need to see the logic/application code running in the Speedtronic turbine control panel to even try to determine what it might be doing.

But you are correct--under NORMAL circumstances, once the breaker closes that should be the end of synchronization attempts, until an operator chooses to try another synchronization if the breaker opened for some reason. So, either the feedback is not working correctly, or the logic has been modified.

But, the real question is: Is the breaker closing? And if it is, and it's opening very quickly again--<b>WHY</b> is it opening again? Is it because of a protective relay that is operating (including reverse power), or because of a problem with the breaker (something mechanically wrong that is not allowing the breaker to stay closed), or because of some other signal from the Speedtronic that is telling the breaker to open as soon as it's closed?

<b>AND,</b> when did this problem start happening? After some kind of maintenance outage, when possibly the breaker was racked-out and then racked-in, or the breaker was worked on?

It's very possible the logic is confused because either the breaker status contact is not working correctly, or there is something which is tripping the breaker as soon as it's closed and the breaker status contact isn't getting fully closed. OR, someone has or had at some time, modified the logic because of problems with the breaker not closing or not staying closed.

But without being able to see the logic/application code in question, and without a lot more information about why the breaker isn't closing or if it's "tripping free" (opening as soon as it's closed) and WHY it isn't closing or WHY it's tripping free, or what signal is telling the breaker to open very soon after it's closed--we are just guessing.

The more information you can provide about the event--the synchronizing and breaker closing and/or opening, and the synchronization permissives--the more we might be able to help.
 
S

saurabhstalone

Hi CSA,

Please note that it is old MKII logic. The breaker is opening because we had bad MW Transducer (we found out that). so as soon as breaker get closed, MW shows -10 MW and breaker gets opened due to reverse power. However, below I am showing the MKV logic of L2G / 1X / 52SX. I don't know how to copy the logic from word to this forum, the fonts / texts are not appearing properly. Let me know how can I paste the logic in a better readable format. Or if there is way to attach the file, I am sure you wont be able to read the below logic:<pre>
L52GX L94X L2GX
───┤ ├───────────┬───┤/├──────────────────────────────────────────( )
│
│
L4 L2GX │
───┤ ├──────┤ ├──┘


L2GX -- Generatore Breaker Closed Latch

╔══════════════════════╗
â•‘ TMV - Time Delay â•‘ L2G
L2GX Input L0║ ┌─────┐ ║
───┤ ├──────────────────────────────────────────────────╫─────────┤ ├──────╫──────────( )
║ │ TD │ ║
K2G 0║final │ │ curr║1 T2G
──────────────────╫─────────┤ ├──────╫──────────────────
║ │ │ ║
║ dt │ │ ║
║ ──────┤ │ ║
║ └─────┘ ║
╚══════════════════════╝

K2G -- Generator Breaker Reclose sec <30 sec>


L94X L2G L62TT2 L3ACS L1XX1 L3SMT L1XX
───┤/├──────┤/├──────┤/├──────┤ ├──────┤ ├──────┤/├───────────────( )



L1S L1XX L5EX L1X
───┤ ├──┬───┤ ├──────┤/├──────────────────────────────────────────( )
│
│
L1X │
───┤ ├──┘



L1S L52GX L52SX
───┤ ├──┬───┤/├───────────────────────────────────────────────────( )
│
│
L1X │
───┤ ├──┤
│
│
L52SX │</pre>
<b>Moderator's Note:</b> did not even try to do anything with the text above.

Now we removed this timer of 30 seconds and there is no re-closure. But main reason of posting the article was to know WHY GE allows re-closure within first 30 seconds of 52G opening following a Start? However, if the unit is sitting on some part load and if breaker opens up then it is fine because the timer 30 seconds get already lapsed during first closure. Note that this L2G is logic is pretty standard in all GE Frame CTs (3, 5, 6, 7, 9), I've worked on. However I dont see this type of synch logic in LM6000 and other GE aeroderivatives.

52SX is the final auto synch permissive and was true before the generator breaker closed the first time and was false when the breaker closed the first time (which is all OK). It should have remained false when the breaker opened the first time but it didn't happened because 1X was not False, because 2G was not True because 30 sec delay timer was not lapsed so as soon as breaker opened first time 1Y (based on 1X) became True making 52SX True thereby allowing auto breaker re-closure.

Thanks,
SSV
 
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