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Preparing High Voltage Oil.

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klugesmith

Fri Jul 13 2018, 01:11AM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1714

I've got spiral-reinforced vacuum hose available for the cost of shipping.

And know that when industrial pad-mounted transformers are vacuum potted,
they evacuate the chamber without oil. Then admit dry, degassed oil into the vacuum. This is better than putting in the oil first, then expecting all tiny bubbles to escape just because they expand under partial vacuum. (High vacuum is impossible under oil, unless you turn off the gravity. Even then, the internal pressure & expansion ratio of gas bubbles would be limited by surface tension of the oil).

For simply applying vacuum to oil, it's silly to aim for vacuum pressure lower than the hydrostatic pressure at the bottom of whatever depth of oil is in your container. A few torr?

Ash Small

Fri Jul 13 2018, 04:52PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

I'd reccomend an old Welch roughing pump your side of the pond, the older belt driven ones are pretty simple to maintain.

If you use a chamber with a window (I designed one once that was cylindrical steel, with a plate welded on one end, with a 1/2" thick perspex or similar window in the top), you can see when it stops bubbling.

You can buy 'L' shaped rubber seals for bell jars, they stretch, so you need a steel tube slightly larger than the nominal seal size.

There's a recent thread here somewhere where John F advises using a glass storage jar as a bell jar. Always best to use a perspex or similar safety screen, although I've even used a cracked bell jar without incident. As the crack enlarged, it started leaking more.

Patrick

Sat Jul 14 2018, 04:31AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

ok take a look at the series of elements.

some trains from Dad too.

there is that mysterous thing. i'd like to change it to FIP or something, not compression and not flare. but that thing looks important.

2Spoons

Sat Jul 14 2018, 06:10AM

Registered Member #2939 Joined: Fri Jun 25 2010, 04:25AM
Location:
Posts: 615

klugesmith wrote ...

For simply applying vacuum to oil, it's silly to aim for vacuum pressure lower than the hydrostatic pressure at the bottom of whatever depth of oil is in your container. A few torr?

I disagree. Oil by itself in a container will allow both diffusion and convection to occur - so any water deep in the oil will eventually make its way to the surface and evaporate. Though obviously this will happen faster in a wide shallow container.

What you don't want to do is go below the vapor pressure of the oil - or it will boil off and contaminate your vacuum pump oil. Which will then limit your ultimate vacuum when you try to use the pump for other things.

That 'funny thing' looks like it might be a valve meant to stop pump oil getting back into the evacuated system.

the_anomaly

Sat Jul 14 2018, 12:43PM

Registered Member #19 Joined: Thu Feb 02 2006, 03:19PM
Location: Jacksonville, FL
Posts: 168

For epoxy you might have a hard time degassing if the viscosity is much higher than water/oil. I used a thermal epoxy with a CPS around 30,000 which gave dismal performance after vacuum. We cut a side view of the bond and looking under a microscope, I saw lots of voids still. I've used 15 mins under vacuum and had good results with oil.

One thing I have wanted to try is using an old cell phone vibrator motor. It's not the same as ultrasound but I wonder if its vibration would be enough to aid degassing/mixing.

Patrick

Sat Jul 14 2018, 09:53PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

the_anomaly wrote ...

For epoxy you might have a hard time degassing if the viscosity is much higher than water/oil.

Its water thin.

ConKbot of Doom

Tue Jul 17 2018, 04:39PM

Registered Member #509 Joined: Sat Feb 10 2007, 07:02AM
Location:
Posts: 329

Ash Small wrote ...

I'd reccomend an old Welch roughing pump your side of the pond, the older belt driven ones are pretty simple to maintain.

Seconded on the belt drive Welch pumps. I've had a 20+ year old one at work used for degassing epoxy spit out a wad of dried epoxy when using something with high solvent content. Apparently years back before I even worked there it had ingested some epoxy that had overflowed and just kept on going.

Definitely mind your hose ID as the flow rate on the vacuum side is pretty much constant, and with a small hose, the pressure drop can limit your ultimate vacuum more than you'd imagine, so a gauge mounted on the pump skid may show a nice low pressure, when the transformer tank is still at the vapor pressure of the water, misleading you to think your oil has dried out.
So at 1-2 CFM that a nice belt drive rotary vane can move, trying to keep your pressure drop at a few millibar/torr/unit-of-choice you end up with 1/2"-1"ID wire reinforced hose.

For drying operations, keep the gas ballast open to reduce pump oil water contamination, and mind your exhaust, which will have a lovely oil mist.

Patrick

Thu Jul 19 2018, 04:47AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

pics

Here we see the string of tubes valve and ball valve.

Pretty strong it seems, i like small robust modular "pull it out of storage and use it" solutions. I dont like chasing components all over the place.

I think this shows it pretty well,

The vacuum trap at an angle. Im going to make a label that says "Vacuum trap, Not a bomb." and put it on that pipe side. or i can sew together a canvas tube-like bag that has two holes.

Im wondering if i can make an oil exhaust trap with cloth and a open pipe end, like one of those tiny 2-cycle pocket bike exhausts. Its an open ended pipe with no restriction, just has cloth around the length and ID of the pipe. The guage is just to reveal the presence of near or zero pressure or atmopsheric pressure or what not. many experiments may only need like 1/3 of an atmosphere or whatever, this will be use for many things not just super low pressure. obviously the guage of this quality (12$) doest show the real low pressure stuff.

ConKbot of Doom wrote ...

....keep the gas ballast open to reduce pump oil water contamination...

i dont know what this means, please elaborate. Ive read some simple articles.

Patrick

Sun Aug 19 2018, 07:54PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

ok i solved the compression MIP FIP fiasco.

1534708441 2431 FT182547 Vac Pump With Mod 1

I milled the original end off, opened up the threaded end to a tight fit, milled the barbed end down to a tight fit and then pressed the two together with "no clean" flux. removing the plastic end i then soldered the two together then fully air-tight i then cleaned it thoroughly with acetone. i then used aircraft epoxy with added glass microfiber to mechanically prevent the barbed end from breaking off if its hit by something.

1534708441 2431 FT182547 Pump With Mod 2

i reassembled it and it seems to work well, better than a long string of magic conversion pieces.

vircator

Sat Aug 25 2018, 08:23AM

Registered Member #3217 Joined: Mon Sept 20 2010, 06:14AM
Location: Switzerland
Posts: 15

What kind of oil do you guys use for HV application and from where did you get it? I have several big capacitors in need for a refill.

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