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Old 02-09-2019, 12:01 PM   #1
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Default oil vs dry low voltage transformer

I have a customer who is speccing out 480 volt x 120/240 volt 100 kva single phase oil filled transformers. They are a real oddball, seem to be purpose built,not UL listed unless done in the field for a ridiculous fee. I can' figure why they want this route instead of available, listed dry types. Are there advantages that I do not see? The application is a large dairy site with long runs 1000' or more to the house, apartments, and scale house. The smallest is to the scale house with a 10 kva seasonal load. I would use a 15 kva or whatever is available there.
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Old 02-09-2019, 12:24 PM   #2
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The only thing I know about the comparison is cooling. About 15 years or so ago I asked a similar question when I was a Maintenance Supervisor and was told it was a matter of cooling ability; the conditions that the xmfr were installed allowed better cooling with oil-filled.

There was some issues about PCBs too, but from what I understand those issues has been pretty much eliminated with modern xmfrs.

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Old 02-09-2019, 02:55 PM   #3
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Oil filled are more maintenance, and require specialized test equipment. And there's always a slight chance of leakage.
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Old 02-11-2019, 07:45 AM   #4
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Does anybody have experience with where to find them in low voltage and are they listed?
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Old 02-11-2019, 08:01 AM   #5
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I had to look at my cliff notes. The liquid type are quieter and tolerate transient overvoltage better, I don't know if that could be a factor. Although the liquid type demand more maintenance, I also imagine they may tolerate the dirty and corrosive environment around livestock better, but I am just guessing.
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Old 02-11-2019, 10:04 PM   #6
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One possibility is that in my experience, dry-pacs don't do well when continuously underloaded. Especially when grossly underloaded.........

Oil-Filled models don't seem to mind sitting there doing basically nothing all day long.
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Old 02-12-2019, 09:45 AM   #7
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Never bought one, but I would perhaps call a xmfr maintenance company; like a garage / mechanic they would know what ones they see and what ones they do not see.

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Old 02-12-2019, 09:53 AM   #8
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Dry type don't like dust, dairy or dry area equals dust. Maybe look at a cast coil epoxy dry type they don't care about dust. If I remember correctly oil filled needs to be in a vault if inside and fenced if outside, due to if it blows up.
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Old 02-12-2019, 04:01 PM   #9
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Quote:
Originally Posted by just the cowboy View Post
Dry type don't like dust (OR WATER), dairy or dry area equals dust. Maybe look at a cast coil epoxy dry type they don't care about dust. If I remember correctly oil filled needs to be in a vault if inside and fenced if outside, due to if it blows up.
Due to wash down water could be a factor as well
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Old 02-12-2019, 04:05 PM   #10
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Oil filled are more maintenance, and require specialized test equipment. And there's always a slight chance of leakage.
All transformers require specialized test equipment that few contractors have and if they do they even fewer are not sure how to properly perform the required test (dry or oil filled).

A while back had to test a transformer because the contractor said the windings were shorted, seems all the primary leads were shorted as were the secondary or so they thought..
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Old 02-12-2019, 04:12 PM   #11
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Due to wash down water could be a factor as well
These will all be pad-mounted outside so wash down is not a problem. Thanks for all of the replies. It seems that the only I will get a listing is from an engineering firm that will look at them on the job-site and issue an approval letter.
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Old 02-12-2019, 05:20 PM   #12
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These will all be pad-mounted outside so wash down is not a problem. Thanks for all of the replies. It seems that the only I will get a listing is from an engineering firm that will look at them on the job-site and issue an approval letter.
What is the cost difference?

I would be 2-3 times more?
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Old 02-12-2019, 05:27 PM   #13
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I have not priced the dry types because I was not given the option. The project manager said the dry types that are located outdoors were flagged by the insurance company as a possible fire hazard due to the build up of debris on the coils. a 100 kva 480 pri 120/240 sec single phase is quoted at 4000 dollars. It will a made to order unit.
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Old 02-12-2019, 09:19 PM   #14
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Originally Posted by brian john View Post
All transformers require specialized test equipment that few contractors have and if they do they even fewer are not sure how to properly perform the required test (dry or oil filled).

A while back had to test a transformer because the contractor said the windings were shorted, seems all the primary leads were shorted as were the secondary or so they thought..
Maybe it was low on oil? jk Did you keep a straight face when you handed them the bill? You didn't sell them a whole new one..........did you?
But, yeah, not many contractors have an oil Hi-Pot, a filter press, or a lab for gas testing. Or, know that if the oil smells like mothballs, it's PCB's that have been heated to the turning point.
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