John Lyles wrote:
> 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.
>
Using a vacuum instead of pressure is a much better way to make sure
those voids are filled. Pressure compresses the air, which then expands
back when the pressure is released.
73
Roger (K8RI)
> 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
>>
>
> _______________________________________________
> Amps mailing list
> Amps@contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
>
>
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|