transformer damage?

[zog]

I agree that testing the oil can determine many things, but to fully analyze the transformer, isn't it necessary to check all the failure modes, which, includes mechanical, electrical, and dielectric; both internal and external.

Looking at the oil only, may give some indication of the trouble ahead, and this may be enough by itself to make a determination on whether to replace immediately. However, say the decision was that based on the oil test it could last a while longer. Then, unexpectedly the transformer fails and it is because the whole transfomer wasn't tested, of which the other tests would have given a better understanding of the actual situation.

Based on this, oil tests alone may lead you to a conclusion that gives a false sense of security, which ultimately could lead to a unscheduled and undesired outage.

there is a big difference between a regular oil analysis and a DGA oil analysis, a DGA analysis tells you the type of problem and to what degree it occured by looking at the presense and levels of 9 different gasses, all of which are indictitive of different problems.

Yes ideally you would do a full barrage of tests as I stated in my first post but in thos case I think it would be a waste of money, if the DGA sample is within all the ANSI limits, then I would recommend a full set of tets before saying this unit is good, but I suspect the DGA levels will just confirm what seems to be obvious, this unit is toast.

 

[zog]

Good luck getting the power company to replace your transformer . Unless you have some kind of fault event data to back up your claim , they are going to tell you that it's YOUR responsibility to protect YOUR transformer .
What ARE you using to protect the transformer and isolate the primary side during a fault ?
A DGA test will tell you a lot about the internal condition of the transformer , but it should have had other testing done prior to energizing .
You rolled the dice when you re energized . That thing could have been full of all sorts of combustible gases .

No matter where you live it is never the POCO's fault, just ask them.

 

[mxslick]

Some wild guesses:

Some wild guesses:

<snips>
The fault was on the next pole upstream from our meter. I don't really know how it happened, only that A and B phases ended up touching. Transformer is pad-mounted 34.5 kV ground wye to 480/277 wye.


At that time, the transformer outside was buzzing extremely loudly. After a few minutes we noticed smoke coming out from under it, so I got out the thermal camera and started taking pictures. Like I said, it increased to as much as 560 degrees F on the OUTSIDE of the transformer.

A possible scenario:

The "C" phase remained energized, so if it is on a common core with "A" and "B" phases, you basically had a dead short on the two phases "A" and"B" and the "C" phase was trying to excite the shorted phases' coils.

Another possibility if I'm visualizing the current paths right is that the short from "A" to "B" was somehow impressing higher-than-normal voltages through those two coils and the "C" phase by shifting the common point away from the center of the wye.

In any event, the fact that you had smoke visible and oil expulsion means that the transformer WILL fail again, and violently, possibly this time creating a serious phase imbalance or worse (and most likely) a severe overvoltage event on your facility's service. Not to mention the risk of personal injuries and fire damage when (not if) it fails.

Ask the "wise ones" of management how much the unplanned outage, equipment damage and lost production (as well as your customer's goodwill) will cost and compare that to the cost of a new transformer. Methinks the transformer will be VERY cheap in comparison.

The POCO may not replace the transformer for you, BUT they can and should, upon your request, provide a lever-operated, pole mounted switch to your transformer that you can request the key and proper operationg proceedures for it.

We recently had an underground transformer fail here in my neighborhood. It suffered a dead-short failure on the secondary windings, and spiked several homes with very high voltages as it failed, while also killing our primary feed three times till the protective fuses blew.

 

[djohns6]

No matter where you live it is never the POCO's fault, just ask them.

Again I ask , what type of protection did the customer have to protect his
investment ? You don't want to get me started telling war stories about industrial customers damaging our ( POCO ) eqpt. by not being able to clear faults on THEIR side . That stuff works both ways . :smile:

 

[drbond24]

There are pole mounted fuses outside our facility (which never tripped during this event, by the way) that are the protection for this transformer. We have no way to operate them manually.

Requesting a primary side switch sounds like a good idea to me. I'll look into that.

 

[Jraef]

There are pole mounted fuses outside our facility (which never tripped during this event, by the way) that are the protection for this transformer. We have no way to operate them manually.

Requesting a primary side switch sounds like a good idea to me. I'll look into that.

In the severe imbalance situation described above, it is entirely possible that your pole fuses would not blow. The current levels may not have been high enough to clear the fuses, but in a sever imbalance like that the heating effect on the core is magnified multifold. So even though the currents were "normal", the oil may still have cooked. I agree with the assessment of contamination as well, that transformer, no matter what the cause, is compromised and WILL fail in short order now.

Do the analysis, but order the transformer now. The lead times are horrible and you may end up with an extended shutdown of your facility or may end up paying through the nose for a rebuilt / rental a transformer when yours fails. It is most likely going to be an insurance claim situation though, the POCO will not usually accept "collateral damage" responsibility if your equipment had no protection.

 

[quogueelectric]

From the description of the events it seems to me a higher voltage line may have come in contact with the primary feeding your xformer. This scenario would logically explain all events. I cannot imagine with temps like that on the xformer that the primary wire and loadbreaks and secondary wire insulation have not been damaged. One of my partners was just recently killed by a scenario very similar to this one. They sent him in to get an oil sample for a pseg xformer which had been having trouble. When he wrenched the oil plug off the xformer exploded sending a large chunk of metal through his head. Young mechanic 2 kids and a wife left behind. Maybe it was in a strong vacuum which would evaporate all moisture present and when the vacuum was broken moisture was introduced. I strongly suggest oil testing be done with a shut down on a compromised xformer.

 

[drbond24]

I appreciate all the advice on this topic.

An oil sample was taken Saturday morning and sent out for testing. I don't know how long it is supposed to be before we get it back, but it appears that management is going to wait for those results before making a decision.

Believe me, I have made my opinion clear. I cannot ethically sit by and let this one go since the potential exists for people to get hurt, but at the same time I can't FORCE anyone to do anything. At least if something happens I have documented proof that I have voiced my opinion.

 

[RHJohnson]

Your transformer was still humming with power off? Sounds like your transformer was single phasing. I have seen pole mounted fuses blow that did not completely open. Weather, moisture, dust, whatever, over a period of years caused the fuse to swell so much that when it did blow there was not enough tension on the trip arm to open - which would also give you a visual indication. Your transformer is what KVA, must be rather small if it is pole mounted. In a previous life I was responsible for probably 100 of these oil filled, single phase transformers. They are tough! Much better than dry type in my opinion - especially in dirty, humid, wet, and hot environments.
I started a campaign to exchange them with ones we ran through our shop. We would drain the transformer oil and clean up the transformer and check it out - not really much to those transformers. We found lots of them were low on oil, and found several which had been in service for many many years -
the oil had congealed, and even laying the transformer on its side it took a long time to empty - was a consistency like tar. Mind you - these transformers were still operating when we removed them for service. You should be able to purchase a rebuilt replacement - then clean up the one you have and keep for a spare.

 

[drbond24]

The transformer is a 2500 kVA pad-mounted three phase. 34500Y primary, 480Y secondary.

 

[quogueelectric]

2 1/2 megawatts Holy Cow thats a lotta watts. Biggest I ever installed was 1 megawatt padmount.

 

[wirenut1980]

So is the utility going to provide a report of what happened? I think we'd all be interested in hearing the "official" report. They at least owe you that!

 

[RHJohnson]

O.K. DRBOND24 - Now you're talking a transformer! Get that oil sample sent in. Better make sure all your safeties are still operational. I used to have an outfit out of Ohio come with their truck about every 5th year to clean/recycle the oil in our larger transformers. I did not have them do all the large transformers each time, as I liked the idea of them showing up every other year. That way if I had doubts about something I knew that at a later date they would be available. That outfit was "Transformer Consultants" - and as I said they were from Ohio. They have service trucks running all over the lower 48. I'll bet you would not have to wait to long for a service truck to show up. Then can filter the oil while the transformer is energized. I never had to shut anything down - ever! Don't waste time before checking your oil and the blanket.

 

[drbond24]

2 1/2 megawatts Holy Cow thats a lotta watts. Biggest I ever installed was 1 megawatt padmount.

2500 kVA is sort of small to me. At my last job there were a couple each of 10 MVA, 7.5 MVA, and 5 MVA. Now I just have this one 2.5 MVA to worry about.

So is the utility going to provide a report of what happened? I think we'd all be interested in hearing the "official" report. They at least owe you that!

They have said that a phase-to-phase fault on their line outside our plant was the problem. They also said 'stuff happens' and they aren't paying for it. :grin: Not surprised here. It will be a few days before we get the results of the oil test. I'll post them here when I get them.

 

[kingpb]

2 1/2 megawatts Holy Cow thats a lotta watts. Biggest I ever installed was 1 megawatt padmount.

2.5MVA is pretty small in the scheme of things. Try qty 6 @ 1000 MVA each.

 

[coulter]

...They have said that a phase-to-phase fault on their line outside our plant was the problem. They also said 'stuff happens' and they aren't paying for it. :grin: Not surprised here. ...

I'm not surprised either - it's your (the company's) transformer, your responsibility for protective relaying. Just curious, where is the service point? Where is the metering?

You may want a ground level operator for the primary for other reasons, but it would not have helped at all in this case. Who are you going to send out to open it under a fault? If I were to ask anyone to open it, it would have to be a junior engineer

Y primary: I am not at all familiar with protective schemes for that. Blackburn should be. Unfortunutely, my copy is loaned out for another few weeks.

I did get a look at IEEE C37.91. Section 12.5 talks about what may be the issue that overheated your xfm:
C37.91, 12.4 Unbalanced voltage protection for Y-connected, three-legged, core-type transformers.

Possibily you can get the primary fuse curves and match them against the transformer damage curve. Since the management won't give you any money to add protective relaying, maybe the only avenue open is to size the fuses closer.

edit to fix fonts

carl

 

[drbond24]

More good news in the swirling spectacle of nonsense that is my job. The POCO guy that came Saturday morning didn't pull enough oil out of the transformer to do the test. They showed up again today wanting us to shut down so they could get some more oil. They were informed that we don't just shut down production in the middle of the week and told to come back Saturday morning. If this transformer is failure-imminent, we are giving it plenty of time to blow. :-? :-?

 

[augie47]

They were informed that we don't just shut down production in the middle of the week and told to come back Saturday morning. . :-? :-?

How inconsiderate on your part :grin:

 

[RHJohnson]

I am puzzled. Why would the POCO be pulling oil samples from your transformer? Why would the transformer need to be shut down to open a drain valve and get a small oil sample.

 

[drbond24]

I am puzzled. Why would the POCO be pulling oil samples from your transformer? Why would the transformer need to be shut down to open a drain valve and get a small oil sample.

We could pull a sample ourselves and send it out, but the POCO here offers that service so we're having them do it. They were chosen as the vendor for this particular test (not by me, I might add).

The drain valve is located such that you practially have to crawl inside the secondary compartment to get to it, and the fact that we have 7 parallel runs of 600 MCM cable connected to the secondary makes it less than roomy. It would be dangerous to attempt to manuveur through it with the power on.