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LutzH

Tue Jan 26 2010, 02:42AM

Registered Member #1721 Joined: Sat Sept 27 2008, 08:44PM
Location:
Posts: 136

Hello:

Its far to early to tell on how it holds up in the long run, but some HV experiments with Halon 1211 this weekend went very well! It all started when I needed a temporary SF-6 substitute to do some high voltage testing with no oil. I thought about trying R134, but the results were not that good. Then I noticed that the second best 2 insulating gasses are Freon 12/22. These are very hard to get now, but I had some Halon 1211, and its molecular structure is an exact match to that of Freon 12, except that one Chlorine atom in it, is replaced with one Bromine one. The density seems to play a big role in insulating gasses, and here Halon should be great, due to an even higher density than Freon. So on to testing:

I filled a cylinder with 2 electrodes (As someone in another forum had suggested.), with Air, Argon (Just for Fun), CO2, R134, and Halon. The argon as expected broke out into an arc at close to 2 x the air distance. The CO2 was the same as air, although it is supposed to be slightly inferior, maybe due to humidity in the air. The R134 was only slightly better than air, comparable to say dry N2.

Now the Halon was impressive, it held of at least 2-2.5 times the voltage at the least, probably more with the same size gap. Down to the point where it was difficult to measure, in part due to my low 10KVDC test voltage. Yes it does decompose into nasty "manure" under arcing, but not as bad as R134, or what I remember from Freon 12 from the past. Halon can still sometimes be found for free, in old fire extinguishers. I have since acquired a second 10 pound Halon extinguisher, but this one is still at 125psi, so I will save it for its intended purpose.

I scored my initial 8 pounds of Halon a couple months ago, because the extinguisher that it was in had lost most of its N2 pressurization. So I put the extinguisher in the freezer, and at first partialy discharged its contents into the empty 1 gallon propane bottle, from which I had unscrewed the valve. I then just poured the remaining Halon into the propane bottle, Once done I screwed the valve back on with Teflon tape.

It may be possible to use Halon the same way that Freon was used for HV, by putting a packet of soda-lime into the container with it to absorb any HF, HCL, and HBr in the case of Halon. The other decomposition products are not a big problem in an electrical sense, just don't breathe them! The key to the stability of the insulating charging seems to be the exclusion of water, and the insertion of a soda-lime packet. You can make this with equal parts heated chalk dust (Heat to red heat), and washing soda, sewed into a cloth packet, then glued, or attached to the container bottom. Without water far less nasty acidic products form in the first place, and they tend stay in a gas form, so that the soda-lime packet, or filter can absorb them better. With H2O these gasses will form droplets of concentrated acid solution on your contents, yuck! The lime in the packet will even absorb very small amounts of H2O, to form CaOH. This water exclusion principal is even true for SF-6 gas. For a liter container for example, I would add at least 10-20gr of soda-lime, and maybe even a packet of silica gell for any water still left. A vacuum pump would help a lot here also. For a project with more than an occasional small spark, or with heavy corona, an circulating gas filter would be better I am sure.

The only other downside of Halon is that 30PSI is that the maximum pressure that you can use with 100% Halon. Halon 1211 becomes liquid at around 30PSI, at room temp. Its boiling point is close to 0 deg.C (Minus -3C if I remember right) This is why I suspect that it was never used in very HV applications like its sister gas Freon 12 was, before finally SF-6 came along. Based on the physics involved, and the theory, Halon should be better than Freon 12. It should even have a slight edge over SF-6, but as stated before it is less stable, and 30PSI is the pressure limit. It may be possible to go slightly higher in pressure by using a Halon - N2 mix, like was done with Freon 12 historically, to get from 90 to 150PSI.

By using Halon at 30PSI, or Freon 12/22 if you can find it, should give you up to 10 times the insulation of air. Normally 10KV/inch is considered the safe maximum with dry air. Now you have 100KV per inch with 30PSI Halon while being safe. This pressure can be contained simply even by cheap off the shelf PVC pipe, with a simple tire valve. Do you still think that your project will arc over, with a conservative 100KV/inch margin? 100KV per inch should be conservative with Halon / Freon at 30PSI. If you use the 20KV/cm air breakdown figure, then here the Halon at 30PSI, should give you 200KV/cm which is about the same as good transformer oil, with far less weight and mess. An added bonus is the perfect penetration of the gas, into every nook and cranny of a transformer coil for example,

To close be careful with HF, the DC figures may not apply. Also remember SF-6 gas is better in almost all respects, but that is not the point here, the point is in recycling. Recovering the Halon would be easy also, you could liquefy it with just some dry ice. If the gas has been used DO NOT vent it indoors period, why take the chance, pipe it into a rat hole, or something, if you do not want to do the right thing which is to recover and recycle it.

Steve Conner

Tue Jan 26 2010, 11:23AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Some old books recommend carbon tetrachloride vapour as an insulating gas. If Freon works, and carbon tet works, then it follows that Halon should be good too.

It liquefies at 30PSI, but what if liquid Halon were an even better dielectric than the gas?

radiotech

Tue Jan 26 2010, 10:56PM

Registered Member #2463 Joined: Wed Nov 11 2009, 03:49AM
Location:
Posts: 1546

Carbon tet, I got raked over the coals for daring to include it in an article on cleaning tape recorders.. IN 1965 !!

The one good thing about tet, if you vaporize it from a liquid at at the site of the experiment, it makes one of the best fire extinguishers around aside from the troublesome effects of what the fire changes the gas into.

Proud Mary

Wed Jan 27 2010, 01:12AM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

radiotech wrote ...

Carbon tet, I got raked over the coals ...

A pun on phosgene, I take it!

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