At 09:22 AM 4/4/2006, jcowens@NETSCAPE.COM wrote:
>Is anyone familiar enough with the HN-31 Heathkit Dummy Load (History
>Lesson)to know how much power you can run to this thing in other than "key
>down". I don't know if it has transformer oil or Mineral Oil in it. Will
>it handle 1500W on a 50% duty cycle for a short time?? Does anyone know
>where I can buy transformer oil, or has OSHA outlawed it by now??
>
>John Owens - N7SEJ
Transformer oil *is* mineral oil. It's fairly low viscosity, and often has
a small amount of an oxidation inhibitor added so it doesn't spoil. The
other important thing for this kind of use is that it is (very)dry and
clean. A very small percentage of dissolved water (well below where you'll
see droplets) greatly reduces the HV breakdown strength. Particulate
contaminants (cloth fibers, in particular) also cause problems with HV
breakdown. This probably isn't an issue for cooling a dummy load.
It's available in 5 gallon pails at most oil jobbers, and should run you
about $4-5/gallon. Shell Diala, Exxonmobil Univolt, etc.
If you know anywhere local that does transformer rebuilding or servicing
(e.g. a small electric utility), they might be able to sell/give you a
gallon (they buy it in 55 gallon drums).
If you can't get real insulating oil in small quantities, you can go to a
feed store and get regular old USP white mineral oil (used as a laxative
for horses/cows/etc.) by the gallon. It's not guaranteed dry or clean, so
I wouldn't use it for HV insulating. You also want to get the lowest
viscosity grade (so that thermal forces can make the oil circulate in the can).
Certain kinds of hydraulic fluid will also work (NOT brake fluid. You want
the stuff used for cylinders on tractors, etc.). You want something that's
low viscosity, and with minimal additives.
Tesla coil hobbyists also use straight weight non-detergent motor oil. You
want the cheapest of cheap, with minimal additives.. all those additives
help with lubrication, but cause problems with insulation.
Now, to the OSHA thing...A LONG digression
Some decades back, a class of miraculous HV insulating liquids (askarels)
were developed that was a) nonflammable, b)a good insulator, c)immiscible
with water, d)didn't chemically decompose or oxidize. They were a
wonderful material for the HV industry: oil fires are a BIG problem
(particularly in an urban environment) and were a big motivator to going to
Gas Insulated Switchgear using SF6, but that raises its own set of
problems. Imagine the effect of a large fault in a piece of oil filled
switchgear. The extreme heating of the arc causes the oil to decompose, and
the evolved gas causes the oil to be sprayed out in a large cloud of
droplets which is ignited by the spark. Kind of a king-size molotov
cocktail. So, Askarels were a god-send. But....
These were all in the generic class of PolyChlorinatedBiphenyls (PCBs), and
for the most part are non-toxic and pretty inert, EXCEPT, that there are
inevitable small amounts (ppm,ppb) contaminants of certain other compounds
(dioxins) which ARE toxic. And, sadly, because they're so darn inert, they
never decompose, so they accumulate and never go away. By the way, toxic
effects occur just because the molecule is there, and it doesn't get
consumed in the process of doing its evil work, so that contaminant can do
its stuff for a long, long time.
So.. big process of getting rid of PCBs (which are contaminated with
dioxins), leading to superfund sites, etc. Note that if the PCB is sealed
into a metal can (as in a fluorescent light ballast), there's little
likelihood of it ever being released, and even if it did, it's a small
quantity. The problem comes in with truckload lots of used insulating
fluid being used, for instance, as road oil on dirt roads to keep the dust
down, or with manufacturing facilities draining their (supposedly) inert
stuff into a big pit. That's when those ppbs and ppms start to add up
(especially because the stuff never degrades and tends to sit down in the
mud in the bottom of the pond/river).
The PCB problem as applied to hams and electrical hobbyists is that that
there's an enormous amount of really old electrical gear around, some
filled with oil, some filled with PCBs, some re-filled with oil after
having had the PCBs drained. Think of all those pole transformers
scattered around the country, many having been sitting up there since the
1940s and the REA. Think of all the non-existent records of just what's in
that piece of electrical gear in the salvage yard. You have no idea
whether that "oilfilled" widget might have PCBs in it.
Then there is superfund, which creates cradle to grave liability for those
materials. Cradle to grave liability comes from the practice back in the
bad, old days, of hazmat disposal by hiring a guy with a tanker to drive
down the road with the valve "accidentally on purpose" cracked. The waste
generator says: "We transferred it to our (now-out-of-business with no
assets) hazmat hauler" {No surprise that this kind of thing was a big money
maker for organized crime, eh?}
NOBODY who deals with this stuff on any large scale wants the prospect of
being the "bad guy" in the next Erin Brockovich style movie. So, they tend
to take a VERY conservative view of handling. You want to store a piece of
electrical equipment with "oil" in it? Either you have ironclad
documentation showing it was made recently OR you have concrete pads with
berms, absorbtion blankets, hazmat spill procedures, etc., etc., etc. This
tends to foster a sort of "PCBs are the devil incarnate" sort of
paranoia. The actual hazard is quite low, the potential legal and
publicity exposure is HUGE (particularly if you have assets, and the fickle
finger of fate points at you).
The upshot is:
Get your oil from somewhere "known good", preferably in brand new
containers. Keep the records.(put them in a plastic bag and tape it to the
dummy load) Somewhere down the road, someone might want to dispose of your
dummy load, and life is much easier if you can prove it's nice safe oil.
By the way, there are a couple quick and dirty tests: oil floats on water,
askarel sinks. A piece of paper soaked in oil burns (real well), a piece of
paper soaked in askarel doesn't burn very well, if at all.
These tests won't tell you, though, whether you've got one of those
horrible PCB contaminated equipment refilled with oil situations.
Jim, W6RMK.. (who's bought and spilled a lot of Diala AX over the years)
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