At work we have dozens of tanked transformers in use. Being at 7000 feet above
sea level, with high voltages, made it a requirement for some systems. They
have been running for 40 years this way.
We have two ways of approaching it. With sealed tanks, the transformer is
dried, baked, then put into the tank. Then backfilled with oil, with a nitrogen
purge on top. Sometimes that step is omitted and we just nitrogen backfill the
last airspace at the top. We keep them under this positive (greater than 1 atm)
pressure and have a gauge that is watched.
For a few, that are in open tanks with just a loose lid, they are just filled
and that's it.
I have read that GE may have used vacuum while filling, to remove a lot of air
around and inside windings. If you have any voids that could trap air bubbles,
it would be good to somehow force oil in with a hose to those places to
displace the air. Otherwise might become corona pockets that will degrade the
thing. If you are only extending the cooling - and increasing the loading - I
think any oil is better than air. If you are extending the voltage beyond what
is normal for the clearances designed, then you don't want air pockets that can
have localized field concentrations.
We had lots of problems with potted transformers many years ago, so I was told
by my forefathers here. So they went to the oil tanked units instead. End
bells, just remove as much of that as you can to allow the oil better ability
to circulate.
73
John
K5PRO
> Message: 2
> Date: Thu, 27 Aug 2009 12:46:28 -0400
> From: "Carl" <km1h@jeremy.mv.com>
> Subject: [Amps] Running a transformer in oil?
> To: <amps@contesting.com>
> Message-ID: <012201ca2735$ee0363f0$6400a8c0@DAVES>
> Content-Type: text/plain; format=flowed; charset="iso-8859-1";
> reply-type=original
>
> Ive seen a discussion somewhere in the past but cant locate it.
>
> Anyway, I have a virgin 5 gallon jug plus a partial one of genuine PCB and
> started thinking about extending xfmr ratings. Is there any particular
> formula to use, transformer prep, etc?
>
> What about the sealed ones and also the oldies with cast iron end bells?
>
> Carl
> KM1H
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