# 14.4/25kv stepdown transformer



## Bbsound (Dec 16, 2011)

How long would it take to get a new transformer if that one blew up? And how much other damage would it have caused?
I am sure they ran the numbers either way and talked to plenty of smart people and they decided on the cheapest route. 
That outage probably allowed them to do many other repairs at the same time.


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## Big John (May 23, 2010)

Our maintenance is similar. We do DGA, TTR, doble or megger, protection testing, and infrared on our transformers annually. If we have reason to believe one is acting up we might start doing a DGA every couple months. 

We don't do transformer replacements as a matter of course, but if we find an issue, absolutely. Large machine planned maintenance is always, always, always cheaper than uncontrolled failure.

Just a suggestion but we do monthly visuals on all the transformers for oil leaks, pressurization, cooling fans, etc. If you think your transformer was overheating then having someone regularly reset the drag-arms and record the max temperatures would've shown it. We've caught a couple major problems this way, like a 10MVA unit that was slowly losing it's blanket pressure. It probably wouldn't have made it between yearly checks.

-John


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## Zog (Apr 15, 2009)

jontar said:


> Hi
> 
> I work in industrial and we have 25kv on our site, we were doing our perventive maintenance work orders for our oil filled transformers, we do this afew times a year. We send the oil into be tested and IR scan the bushings and found that the oil in one of our 2500kva transformers had been contaminated. There's no fans on this unit just natural conv and heat rad on the back side, so it may have gotten hot at one time or several times. So rather then risk unseen failure, our maint super and electrical eng, made the decision to change it so we scheduled an outage for that side of the main plant, we have 3 services feeding the main plant lot of horsepower in motors, theres 2 - 2500kva and a single 1500kva all 25kv to 460v 3ph etc.
> 
> ...


You replaced a transformer because the oil tested bad???? You know you can process that oil without even having to perform a shutdown??

There HAS to be more to the story, can you post your DGA results?


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## jontar (Oct 11, 2009)

How long would it take to get a new transformer if that one blew up? 

Not long we stock one in edmonton, thats at a storage yard, but we share it with other sites as an exterme backup (like if one caught fire and burnt up), most of our sites have switched to 600v as a secondary but i think 3 of us still use 480 delta or resistor grounded wye. The spare in edmonton is actually loaded on a low boy ready to go, at anytime day or nite, christmas or easter.

And how much other damage would it have caused?

Can't say, the last time we got spiked and burnt up alot of motors ($70,000 worth I think). After that, we put it great big equipment that does phase lost, under/overvoltage and acts like a recloser, 3 cycles in 60 is how fast it works, any more than 3 and your open, more then 3 reclosers and its open til you manually reset it. So not sure if it would really hurt anything the PLCs and DCSs are on UPS (battery backup for an hour), the motors are programmed though the PLCs to shutdown on phase loss, under/over voltage, we also have back up generation. So we would lose the one service but have 3 services to the main plant, they can not be interconnected (backfed) however. So we would lose about 1/3 of the plant and one of the main lines but the second line wouldn't be affected.

I am sure they ran the numbers either way and talked to plenty of smart people and they decided on the cheapest route. 

Oh for sure, they most likely ran some numbers, just wondering if it was a bad transformer only 5-7yrs old or if this is a normal thing to see the contamination issues. There was talk that the new one would have cooling fans so we could actually draw more current from the unit. But it never came with the fans. The main on the secondary side is a 4000amp sqd pump with smart panel and we never to rarely get up that high.

That outage probably allowed them to do many other repairs at the same time. 

Yes, that why we went 6 months, the millwrights and heavy duty mechanics were scheduled to do certain things, (like stand around and joke about whats taking so long) while we had the outage, but we actually took longer (we are issued max allowable time on any task and this one was 2hrs max) but becuase of the bushings being higher, older trans bushings were at waist height, new one bushings were at shoulder height it took longer, thankfully the vault had some slack and we just used the crane to pull up the big copper secondaries. There was also a problem with the vault that I never mentioned, because of the new footprint. Nothing a grinder and a hammer didn't fix.

25kv side was good, bushings lined up good, just gelled up and pushed back in by hand, good thing too, because we had burn off on the one 25kv lead there before, (so its alittle short) we upgraded to a 2500kva unit 5-7yrs ago, the oringal upgrade put that one there that we changed.

I'm not complaining it was a nice day, ot was good, had some fun, would do it again tomorowo, just seems strange we upgraded to 2500kva and 5-7yrs later the transformer is damaged. So the company has to buy another 2500kva unit.


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## jontar (Oct 11, 2009)

Yes 

we changed the transformer because the oil was bad, I believe one of the other staff guys or contractors preformed an oil change and within a few months sent the oil out to be tested and it came back contaminated again. 

Like I said the staff maintenance superintendient and staff electrical eng made the call, I'm not sure if ABB warrentied the whole unit and give them some credit, I just do as the work orders say, weather preventive maintenance or corrective maintenance, I'm sure they were on the side of caution. Sometimes they use words like arc flash and stuff like that to be able to do things they want to do. Maybe the electrical eng was mad at the electrical dept for something and thought why not blow something out of proportion and make them do some heavy lifting, cause it will be funny, its happened before usually if they are mad at the contractors they will make them do certain things, the only reason we did this one was starting a few years ago our contractors are not allowed to work on certain equipment (usually main services, becuase we rarely turn them off or work on energized circutis except to test for voltage on a lock out, who knows that discussion was between other higher powers.

I get paid either way weather we have chair races in the electrical shop or i'm change out a transformer or motor or light bulb, programming in safety shutdown etc, the ot was nice, it was sunny day, I haven't done one since I left working for contractors years ago. Like I said above not complaining just wondering why it only last 5-7yrs. Maybe bad windings, may have been overloaded, we had a 1500kva turn cherry red one nite


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