Why are TSVO cards failing after a thunderstorm?

 

Really poor earthing practices are usually the cause of equipment failures after an electrical storm.

You have really provided very little information to be of much further help. We don't know if this is a Mark VI that was commissioned when the unit was new, or if it was commissioned as an upgrade to a previous Speedtronic turbine control system. The difference could explain grounding practices in use at the site.

Many newer units with Mark VI control systems employ two earthing systems, one called the protective earth system and the other called the functional earth system. Motors, structural steel, and transformers are usually connected to protective earth for personnel safety and protection. Control systems and their components are usually connected to function earth to provide some isolation from lightning strikes that may affect structural steel or devices connected to the protective earth.

Older control systems didn't typically have these isolated earthing grids, and so when Mark VIs are used to retrofit older systems, they can be inadvertently subjected to faults and failures such as what you are describing.

But, if there are two earths at your site, and they were not properly constructed and do not provide proper isolation between them, then this can also cause the problem you are reporting. Many sites with two earthing systems used poor construction practices which results in high differentials between the two earthing grids, and a lot of equipment was incorrectly connected to the wrong earth or wasn't designed to be connected to the proper grid.

So, there can be a lot of reason, including poor wiring practices. There's just too much we can't know about your site, how it was constructed and how it is operated and maintained for us to be able to give you specific information which might be helpful. Hopefully, the information provided will be of some use.

 

I totally agree with you on the point. Though, I would say that care has been taken about the electronic earthing [i.e. functional earthing] and their isolation from protective earthing. But moving aside from that, my question is why specifically the VSVO card of MARK VI would fail and not any others in spite of reasonably good earthing.

Its a newly commissioned MARK VI system of a new unit [not a retrofit or upgrade]

 

You first posted that the TSVO card was failing; now you're posting that the VSVO card is failing.

You say care has been taken about electronic earthing (functional earth), but then you say "reasonably good earthing." I wouldn't associate care with anything that's "reasonably good". That's like saying, "It works most of the time, so it's probably okay."

I say, "What has GE said about the problem?"

What devices are connected to the TSVO, or VSVO (I'm starting to get confused)?

Is there more than one TSVO/VSVO in your system?

Is the Mark VI TMR or SIMPLEX?

Is it the same TSVO/VSVO that fails after an electrical storm?

If the Mark VI is TMR, is it the same VSVO in the same processor rack (<R>, or <S>, or <T>) that always fails?

What is(are) the Diagnostic Alarm(s) that are annunciated during the failure?

What has been done to try to troubleshoot the problem?

Have you (after disconnecting both ends of the interconnecting wiring at the TSVO and the field devices) meggared the interconnecting wiring to be sure there are no grounds or shorts? Are you sure the shield drain wires are properly grounded, at one end only? And to the proper earthing grid?

If a functional earthing system is being used, then care needs to be taken that field devices/instruments are not inadvertently connected to protective earth in the field. In my experience, it takes a LOT of design and good construction supervision to ensure this happens, and that's costly (the design) and not very well inspected and enforced during construction.

If the same VSVO is always failing in the same processor rack in the same slot, then one has to wonder if there's something amiss with the rack (stranger things have happened, and I have seen racks damaged by improper card insertion, usually when people are in a hurry and are using a little too much force and not enough care, and not enough light (illumination) is available.

But, you're still not telling us a lot about the circumstances and the panel and the application and what's been done to try to troubleshoot the problem. And, if this is a relatively new installation, then GE or the packager that provided the control system with the equipment should be working with you to try to understand and resolve the issue. And it would be very informative if you would share with us what has transpired with the provider in regards to this issue.

 

My mistake, I actually meant VSVO card. TSVO is the terminal board for VSVO card. I apologize for the confusion caused.

I know that there are better designs regarding electronic / functional earthing. But the implementation has a cost constraint, so i used the term "reasonably good".

I am from a E&C team and have no direct contact with GE.

There are 2 VSVO cards in R rack and S rack
It has 2 flow divider magnetic pickups, 2 IGVs, Liquid Fuel Pump Servo Valve, GCV Servo

MARK VI is TMR.

The card failed just once. But the same kind of feedback is also available from another site in the region.

No annunciation alarms but only loss of functionality of the card.

The card had to be replaced. No such troubleshooting was done.

The wiring has been checked for no grounds and shorts and shield wires are properly grounded at one end only. And as I mentioned earlier a proper earthing grid is being used.

We are trying to workout what might have been the problem with the provider [GE is not our provider though].

 

There is a saying that goes like this:

You can pay my now, or you can pay me later.

There's another one that says:

You get what you pay for.

You failed one card after an electrical storm. You have a report of another failed card at another site.

If you have a TMR Mark VI, I would be very surprised to find VSVO cards only in <R> and <S>. <b>VERY</b> surprised. In fact, I would be shocked.

One of the main purposes of a TMR system is that it can withstand a fault in or loss of one entire processor and the unit can continue to run (not start, but run). So, if you lost one card in one processor, that should not have resulted in a turbine trip (not that you said it did; you didn't say much really, we've been dragging things out of you bit by bit); I'm just saying that the intent of TMR is maintain running reliability should a card in one processor fail and that processor have to be taken off-line to replace the card.

Who's to say that the card wasn't "stressed" during commissioning? (Servo cards usually get a lot of stress during commissioning; and afterwards, as well.)

I would also be very surprised to learn that no Diagnostic Alarms were annunciated as a result of the event. I would be shocked, actually, to learn that no Diagnostic Alarms were annunciated. I could believe that the Alarm Display was configured not to display Diagnostic Alarms, or that the printer wasn't configured to print Diagnostic Alarms, but I feel very certain in stating that the affected processor would have annunciated Diagnostic Alarms (viewed from Toolbox) as well as the affected card (VSVO). Most sites complain about too many Diagnostic Alarms, and so they are "disabled" one way or another; but that doesn't mean they aren't annunciated by the card or processor. It just means the operators, who can't be bothered by Diagnostic Alarms, are spared the terrible bother of Diagnostic Alarms by "disabling" them.

And, since most E&C people don't know how or never bother to learn how to troubleshoot Diagnostic Alarms, they just get reset in order to be able continue running or starting. Unless they can't be reset, in which case the usual course of action is just to replace the affected card.

Best of luck with your investigation and search.