Re: transformers in oil?

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Jim Lux by way of Terry Fritz <teslalist-at-qwest-dot-net>" <jimlux-at-earthlink-dot-net>

At 08:13 AM 2/26/2003 -0700, you wrote:
>Original poster: "by way of Terry Fritz <teslalist-at-qwest-dot-net>" 
><Mddeming-at-aol-dot-com>
>
>In a message dated 2/25/03 1:21:49 PM Eastern Standard Time, 
>tesla-at-pupman-dot-com writes:
>
>
>>i have a MOT, so i would take that transformer, place it in a container and
>>then fill the container with oil? i would have to drill holes in the
>>container for the wires to extend out. but as long as it's airtight it
>>should work? i was thinking that if you could have an oil pump that
>>circulates the oil, like a transmission that has an oil cooler, that this
>>might be even better. would this work? also, i would think that the colder
>>the oil, the better- right?
>
>
>        An oil cooler similar to the kind used in a 1950-1970 vintage VW 
> Beetle would be great, IF you could find a clean one. You don't want a 
> system with flecks of metal or rust in it. You might consider putting the 
> MOT in an oil bath inside one out those ~$60 mini refrigerator "cubes" . 
> It makes sense that a cooler environment will help if you are going to 
> push the envelope, but I don't know of anyone who has done a study of 
> cooling cost vs performance.

Many people have done studies of just this.. they make commercial 
equipment.  I note that commercial and industrial HV equipment that uses 
oil immersion for thermal control does not, generally, use active 
refrigeration or even active circulation of the oil.  After all, most 
transformers, etc. can run quite happily at 100C, which is more than enough 
temperature differential to get the heat out through a fairly passive 
oil/metal/air interface.  At most, the industrial things use a fan for 
moving the ambient air.

A refrigerator will be quite inefficient at getting the heat away; at the 
least, you've got the additional heat of the compressor to get rid of, and 
the COP (amount of heat moved for energy consumed) is non-ideal). 
Mechanical refrigeration should be considered if: a) you've got a space 
constraint for the thing being cooled, and need to move the heat somewhere 
else before dissipating it; or b) you need to cool it below ambient (i.e. a 
freezer); or c) you've got a very high power density and a low limit 
temperature, so you need very high thermal flux (watts/square meter; e.g. 
cooling an overclocked CPU, where you need to flow, say, 100W in 1 sq 
cm).  If all you need to do is cool to ambient temperature (or higher), 
then a fan and lots of air will generally be a better solution.




>>i think that i should do this in the garage, my wife would kill me if i
>>spilled oil in the living room. <:)
>>
>>jlbrady -richmond, va.
>
>        This is absolutely necessary for coiler longevity!  ;-)))
>
>BTW, does anyone know the electrical properties of pure ethylene glycol 
>(Antifreeze)? I know it  melts at -13C (8F) boils at 197C (387F) , ignites 
>at 398C (748F), and the flash point of the vapor is 111C (232F) -at- 8% in 
>air, but I can't seem to find a reference for its dielectric constant or 
>conductivity.


Check the Dow Website.. very first google hit: 
http://www.dow-dot-com/dog/product.htm

Kind of a pain to navigate their site to get to the data sheet, but...
http://www.dow-dot-com/webapps/lit/litorder.asp?filepath=dog/pdfs/reg/117-01095.pdf&pdf=true
Might work...



All glycols are very, very hydrophilic (they use propylene glycol as a 
dessicant) and form azeotropes with water (meaning it's very hard to dry 
them out). They are shipped and stored in tanks with a dry nitrogen gas 
blanket. I wouldn't think that a glycol would be a good insulator, off hand.

The kind of glycol you get as antifreeze typically has a lot of additives 
(various anticorrosive agents, such as sodium chromate, giving that nice 
green color), and has some water in it to help keep some of the ingredients 
in solution. And, of course water being cheaper than glycol, if you can 
somehow package water and sell it, the mfr considers it a "good thing". (ah 
yes.. premixed antifreeze/water mixture.. )

There are a number of glycols that are more useful than ethylene glycol, 
for reasons of boiling point, vapor pressure, toxicity, etc.  Consider, for 
instance, propylene glycol, which is used in Dr. Pepper, among other beverages.



>Matt D.