wet oil ??? (fwd)

[Steven Roys <sroys@xxxxxxxx>]

---------- Forwarded message ----------
Date: Sat, 11 Oct 2003 16:04:29 -0500
From: Godfrey Loudner <ggreen@xxxxxxxx>
To: hvlist@xxxxxxxxxx
Subject: wet oil ???

I have three 1-phase x-ray transformers, with two converted to AC output and
one left as a DC supply.
The one with a round tank is my favorite and, after sitting idle for about
two months, I decided to fire
it up. As I dialed up the variac, I heard the sound of arcing under oil and
noticed that the arcing would
begin at various variac settings. Upon opening the port for changing value
tubes, I could see that the
arcing was occurring on the underside of the transformer. I drained about 20
gallons of oil from the tank
and pulled the transformer. The core had brownish deposits on it's upward
facing surfaces, otherwise the
rest of the core was clean. The deposits looked like rust, but could be
easily cleaned off with a rag. The
bottom of the tank had the same deposits, but now the metal looked rusted.
The deposits could be
wiped off with a rag, but the rusted appearing areas could not be cleaned up
with a rag. In fact some sort
of plastic film was peeling from the bottom of the tank. The inside wall of
the tank was not affected.
When I had made the conversion to AC output, the transformer and tank were
absolutely clean, except
for a brownish deposit on the bottom of the tank that I cleaned up with
rags. With the transformer out of
it's tank, I decided to bring up the voltage to see just where the arcing
was occurring. I stopped dialing the
variac after hearing only the sound of hissing corona. I was surprised that
there was no arcing, considering
that a rather low setting on the variac had produced an arc while the
transformer was under oil. The bottom
of the high voltage coils are only several inches about the bottom of the
tank, and I think that the oil was
contaminated with water. The water was allowing arcing over between the
bottom of one of the high voltage
coils to the bottom of the tank. Perhaps water slowly settled on the bottom
of the tank.

I got the transformer from the back of a medical clinic, with permission of
course. It had been raining that
day and the top of the tank was wet. I decided to change out the oil when I
made the conversion to AC. With
a large stock of transformer oil from an ebay seller, I did an oil change. I
filtered the oil with wire mesh and
paper filters. I experimented with the transformer for about seven month
with no problems. Maybe the seller
sold me some water contaminated oil. But the seller is an x-ray service
person, so I assumed that the oil
was okay. The seller did ship some of the oil in plastic containers used for
concentrates in developing
x-ray film. Maybe there were salt residues in the containers that attacked
the protective film on the bottom
of the tank. The coils are covered with a dark varnish that looks like
shellac. Some of this varnish apparently
flowed to the bottoms of the high voltage coils forming nodes. Most of these
nodes have smooth surfaces, but
a few are pitted and look burned.

The seller of the oil once send me a box of plastic film and insulation
board used to shield filament and x-ray
transformers. With this stuff, I fashioned a barrier between the
transformer's bottom and the tank. Also I am
refinishing the bottom of the tank. I also have a 1000 pound 3-phase x-ray
transformer, from which I will get
new oil. I plan to reshape the core of this big transformer in a square
core, with an easily removable top leg.
With about 30 high voltage coils (about half actually unused) from x-ray
transformers, I plan to fool around.

Is there a simple test by which I can see if the transformer oil is
contaminated with water? Do you think the
oil is contaminated by water or salts.

Godfrey Loudner