All good info.
I also use the vacuum method to force in the transformer varnish while the
transformer is still hot from an extended baking in an oven.
All my vintage amps and modulators are using similar vintage iron and Ive
had no failures yet when baking and varnishing.
The one Ive been thinking of oil dunking is too big for the oven or the
pressure tank I built. Its around 1946 vintage and 6000/7000V CT @ 1A CCS.
It sat in the detached garage for 20 years getting regular doses of full
condensation moisture. Bought it inside, placed meters in the primary and
secondary and put a short on the secondary. Cranked up the Variac in steps
over 4 days until both meters confirmed about 1/2 the ratings and then let
it run another day. The iron was not excessively warm and that method was
heating from the inside and driving moisture out. Ive run it another day the
normal way with a 1000W load of resistors across the full secondary.
My basement can get very damp at times and I dont want to have problems and
figure the oil will do the job of insulating. I dont plan on pushing it at
this time but if I ever come across a couple of 750TL's I could be tempted.
Carl
----- Original Message -----
From: "Roger" <sub1@rogerhalstead.com>
To: <jtml@vla.com>
Cc: <amps@contesting.com>
Sent: Thursday, August 27, 2009 6:17 PM
Subject: Re: [Amps] Running iron in oil
>
>
> 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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>> http://lists.contesting.com/mailman/listinfo/amps
>>
>>
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