Re: NST secondary (OBIT secondary?)

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

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



> Canola (rapeseed) oil:  I don't know much about the dielectric properties
> of it, but I know the particular   fatty acids in this make it much less
> suitable for human consumption than for industrial use... so now I have
> like 2 gallons of the stuff sitting around which I've decided not to use
> for cooking, ever...  wait, I'm just thinking aloud here- is transformer
> oil just a pure hydrocarbon oil, or is it a "fatty" oil?  Probably devoid
> of -O-OH groups which I'd imagine would make the stuff break down at HV
> (just a guess, never tried it).  But then, I just found Fuji Electric and
> Kansai Electric Power are using a rapeseed-based transformer oil...
> http://www.japancorp-dot-net/Article.Asp?Art_ID=1758
> 

It might work just fine.. Castor oil is a commonly used insulating oil in
capacitors (nice because the dielectric constant is higher than that for
petroleum oils).  It's pressed from castor beans, so its origin is similar
to that of rapeseed oil.

Just about any pure liquid will make a good insulator.  Highly polar
liquids (water) tend to be lossy and/or conductors (depending on how easily
they ionize).  The key is purity.  If there are particle contaminants
(water droplets, microscopic plant fibers, etc. all of which would be just
fine in cooking oil) then the breakdown strength is substantially lowered.

Spoilage might be your biggest concern for cooking oil.  Even commercial
transformer oil and USP mineral oil (both of which are basically straight
chain saturated hydrocarbon oils) have a small amount of anti-oxidant added
to retard spoilage.  BHA, BHT, and alpha-tocopherol (Vitamin E) are popular
anti-oxidants. Not that I'd recommend solid vegetable shortening (aka
Crisco) as a dielectric, but at least it doesn't seem to spoil sitting on
the shelf, and it melts at a fairly low temperature and resolidifies nice
and solid.  Heating it would probably drive off the dissolved water.