Carl wrote:
> 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.
Put a big honkin diode in series with the secondary if you really want
to warm up the core<:-))
73
Roger (K8RI)
>
> 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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