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Registered Member #1321
Joined: Sat Feb 16 2008, 03:22AM
Location:
Posts: 843
I know there are silicone type oils, ester and synthetic ester oils and mineral oil. Does anyone know if there are there any significant differences in dielectric strength between them?
Registered Member #2099
Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716
As John said on the other forum: any place where there's electric power, you are not far from stockpiles of "real" transformer oil. The choice of chemical family is up to the user, and depends mostly on considerations other than dielectric strength. For an amateur, it might be "which kind can I conveniently obtain without buying a whole barrel?" I was fortunate, when Carl Pugh offered to decant some Diala AX from his 5-gallon pail.
All transformer fluids have to pass standard HV breakdown tests, with acceptability criteria that I think don't vary widely. New-in-barrel performance could determine the amount of margin for a fluid to degrade in service. Then again, different fluids can be more or less susceptible to picking up gas, moisture, acidity, etc. Here's one white paper with a nice overview and tabulated data.
Training materials emphasize transformer oil-handling hygiene. I just learned that ordinary rags are a no-no. Hydrophilic lint fibers that wind up in the oil are attracted to places with high E-field gradients and motivated to form bridges, not unlike iron filings on magnets.
Here's one video of oil sampling and testing in the real world: The voltage ramping is done manually, with first breakdown at 3:05, Might seem primitive, but probably represents the norm for most of the world's population.
Registered Member #1321
Joined: Sat Feb 16 2008, 03:22AM
Location:
Posts: 843
I'm contemplating using transformer oil to insulate a Tesla coil secondary in an arrangement where k = 0.6.
I looked around for examples, and I found this (see page 5): which is similar to what I had in mind, but the type of insulating oil used in the design isn't mentioned in the paper.
Anyway, I just found this paper: which is interesting because the tests are done under pulsed comditions. And under under the conditions of this study, Shell "Diala D" was superior to the other oils in terms of breakdown voltage and breakdown voltage as a function of gap length.
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Edit: I remember seeing a paper where the breakdown voltage of transformer oil was increased (under certain conditions at least) by adding powdered graphite or something to the oil; apparently because of some kind of a field grading effect. I'm trying to find that paper again.
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What type of transformer oil has the highest inherent dielectric strength?
