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Re: [Amps] Running iron in oil

To: jtml@vla.com
Subject: Re: [Amps] Running iron in oil
From: Roger <sub1@rogerhalstead.com>
Date: Thu, 27 Aug 2009 18:17:37 -0400
List-post: <amps@contesting.com">mailto:amps@contesting.com>
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 
>>     
>
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