[AMPS] transformer oil revisited
Tue, 2 Oct 2001 15:37:29 -0500
I'm sure you are relieved to find transformer oil for your dummy load.
Some hams use mineral oil but frankly its not comparable.
There use to be several manufacturers of transformer oil but I'm not
for sure that all still do it. The ones I use to purchase when I
managed a large transformer manufacturing facility was Sun Oil in
Pennsylvania where W3HNK, the worlds best QSL Manager worked for many
years and from Shell Oil in Martinez, CA. The oil was shipped in a
tanker rail car and would typically take 10-14 days to reach us.
During the transit time, the transformer oil would absorb moisture and
the net effect would be that the dielectric strength would be greatly
reduced, necessitating processing prior to including in a transformer.
This process involves pumping the oil into a large pressure vessel
that is under high vacuum conditions and heating up the oil while in
this state. Gasses would be liberated and the moisture removed, thus
increasing the dielectric strength. Ideally this oil should be
capable of 45,000 volts but it was not uncommon to see it arrive at a
dielectric strength of 20,000 volts. My point is that depending on
where you live, particularly if you live in a real humid environment,
your oil will absorb moisture so you will need to replace it and in my
case on my own dummy load here in Mississippi, once per year.
Within a transformer, the oil served two main purposes. One as a heat
transfer agent and one as an insulator. Within your dummy load it
does exactly the same thing. You CAN NOT seal the dummy load because
as you heat the load immersed in the oil, gases are expelled and must
be vented through a relief valve on your dummy load.
Transformer oil is very difficult to set on fire but once you do it is
very difficult to extinguish so keep this in mind and be very careful
to not overheat.
Don't know what you paid for the transformer oil but it would not
surprise me that it was in the range of $18-24/gallon as it was
costing over $2.00/gallon in the 70's when I purchased it for our
transformer manufacturing plant. That price would be in line compared
to other price escalation in aluminum, steel copper etc.
I'm a retired electrical engineer and no longer involved in
manufacturing but thought you may be interested in these comments.
J. Leon Pringle, Jr W 5 N A
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