Hello,

I have a problem which still is persisting, that is during the synchronization of a Frame 6 turbine, Generator voltage on the sync. screen blinks, i.e. it comes on and off so we are not able to synchronise in Auto mode.

The voltage at PTBA board is steady for Gen and Line Voltage ie 104 VAC and is monitored continously by AVO meter. Where can the problem be?

Best Regards,

Mambo

 

Mambo,

If you are on Auto Synch, the screen will have no effect on your synchronization at all. You can even disconnect the <I>/ HMI and it won't have an effect. You have to make sure your Voltage PERMISSIVE is there and you can do that by running a high speed trend (view2) to see why unit is not Synchronizing. If the voltage at PTBA <P> core is stable, then it can't be the cause of your issue.

Good luck.

 

Just a guess!

I would check the scan rate settings of the animation sync file. Increase the scan rate.

 

That's a kind of odd one. In the first instance I would try the ribbon cables from PTBA to TCEB, that is JV, JU & JVA, then try all the other ribbon cables on the TCEB, last, if you have a spare, change the TCEB. Please power down before doing all of this.

 

Have you used the Prevote Data Display to look at the voltage input signals to try to get a sense for where the problem might be?

Have you looked at the Signal Flow Diagrams in Appendix D of the Mark V Application Manual, GEH-6195?

Have you recently replaced the TCEB or the TCTG or the PTBA?

Follow the Bus- and Gen PT signals through the PTBA to the TCEB on the next page, then back to the PTBA on cable JU then to the TCTG on JN then to the TCQA on JDx (JDR for <R>, JDS for <S>, JDT for <T>) then to the TCQC on JE and then to the DCC on 1PL. Complicated, but that's the path. You need to check all the ribbon cable connectors in the path(s) to be sure everything is properly seated.

It's been reported before on control.com that corrosion of the ribbon cable connectors has caused problems. GE recommends using a conductive grease (lightly applied by rubbing a thin layer on the ribbon cable connector before plugging it into the card connector; don't use too much, but make sure there's enough to coat the pins and get carried into the connector sockets). Depending on how recently you purchased spare printed circuit cards, you may find some tubes of conductive grease in the boxes with the cards. A little goes a long way.

Synchronizing occurs in <R>, <S>, and <T>, and on the TCEA cards in <P> (<X>, <Y>, and <Z>). The "wide" synchronization window occurs in <R>, <S>, and <T>. The narrow synchronization window occurs in <P> on the TCEA cards. I'm guessing that something's amiss in the cabling that takes the signals from <P> core to <R>, <S> and <T>. And that the wide synchronization window is not getting the signal it needs--but that's just a guess.

Let us know what you find.

 

Dear CSA,

Thank you and everybody for the reply.

All the card ribbon cables were checked for tightness but this time we will make sure the ribbon cables by their single strand, point to point. No cards were changed prior to start-up. All signal flow diag were referend as well as mentioned by you.

Do you have doubt about the e-proms?

At present machine is on line and I have to wait for the next shutdown of this unit. I have taken note of all the points to check and I will go through them and let you know once I am through.

Best Regards,

Mambo

 

Well, this is very interesting. You have been able to synchronize the unit. How were you able to synchronize the unit: manually or automatically? Does the Mark V perform the manual synch check function or is there a synch check relay outside of the Mark V that you used to perfom the manual synch check function/permissive?

The synch display has nothing to do with synchronization, except that is is the user interface to see what is happening inside the Mark V. With one unusual option, the operator interface performs no control or protection functions. So, it's highly unlikely that it's the <I> or the display that's causing the problem. As long as the signals are getting to the appropriate locations in the Mark V, whether or not the operator interface updates all the values in a timely fashion has no effect on the function other than making it difficult to troubleshoot. The synch display has a very fast update rate as it communicates directly RAM locations in the Mark V to display data that could be changing very quickly.

I have no doubts about the EEPROMs. It is highly unlikely, though not impossible, that this problem is related to a EEPROM failure. I highly doubt the problem could be related to the PROM chips, either, though it was recently reported that a nuisance problem was solved by replacing the IOMA PROMset. Unless you've had a voltage surge or lightning strike of high magnitude it's no normal for EEPROMs or PROMs to fail unless they've been mishandled when replacing cards.

Most of the ribbon cables used in the Mark V have "pull tabs" which are to be used when unplugging the ribbon cable from the card connector. Some of the ribbon cables require a good deal of force to remove if they pull tab isn't used to gently pull from end to end as the ribbon cable is being disconnected, loosening by pulling firmly while working the pull tab to the left and right but not tugging or jerking. If the pull tab is jerked or pulled straight with great force, the crimp connections in the ribbon cables have been known to loosen and cause all manner of intermittent and unusual problems. Whenever ribbon cables are re-inserted in card connectors one should press firmly all along the top of the connector to try to ensure that all crimped connections are as good as they can be.

You say you checked the cables; did you remove/unseat them and re-seat them? Did you use a torch (flashlight) to look at the pins in the card connectors to see if they were clean and shiny or dull or have a whitish, chalkish appearance? If the environment where the Mark V is located isn't properly maintained (particularly humidity) the ribbon cable connectors have been known to develop a high-resistance connection which also causes all manner of usually intermittent and unusual problems. Look through your spare cards to see if you have one or more tubes of conductive grease to use when you check them again. Even if you don't see signs of corrosion, it's recommended that you use a light coating of the conductive grease whenever you have the occasion the examine ribbon cable connectors.

So, please be specific about your synchronizing problem. Is it only Automatic synchronization that is not working? Can you provide any details about the synch check relays used in the auto- and manual rungs of the generator breaker close circuit? What were the synch check permissive indications doing on the synchronizing display (L3DV, L3DVERR, etc.)? Which ones were green and which ones were red and which ones were flickering red to green and then back to red?