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HiPot/Meggers and Vacuum

HiPot/Meggers and Vacuum

HiPot/Meggers and Vacuum

(OP)
This is purely personal curiosity.  I could do some testing on this, but I wouldn't be able to renew my professional liability insurance after the first few claims came in.

There are a couple of threads about this, but I don't understand the science of it.  I know air can ionize, but what about electrons moving through a vacuum?  There are enough anecdotes that I have no doubts that the issue is valid.  OK, I know that if you raise the pressure to above atmospheric, arcs are suppressed, and harder to initiate.  In fact, I remember using a spark plug tester (40 years ago, when you serviced spark plugs, rather than just replacing them) that operated on this principle.  So, going on that, if the pressure drops from, say 100 PSIG and the spark is easier to initiate, then it seems reasonable to think that atmospheric pressure is not the floor, and under relative vacuum, arcs may be even easier to initiate.  Going further in that direction, I also know that vacuum breakers are highly effective.  So, is there some bathtub curve, where the low end ("hard vacuum") is fine for hipot/megger testing, and then as the pressure rises, hipot is verboten, and then as you get towards atmospheric pressure, it's OK again?  For simplicity, I'd say lets leave moisture out of the discussion.  I remember talking with a friend that services Xray machines, and I told him I try to get below 300 microns Hg of vacuum to "dry out" air conditioner refrigerant circuits, and he told me that an Xray machine wouldn't even function at that high of an absolute pressure.  So, does anyone have any hard data on what pressures are acceptable on the high and low ends?

Regards,
Rotorbar

RE: HiPot/Meggers and Vacuum

Quote:

So, going on that, if the pressure drops from, say 100 PSIG and the spark is easier to initiate, then it seems reasonable to think that atmospheric pressure is not the floor, and under relative vacuum, arcs may be even easier to initiate.  Going further in that direction, I also know that vacuum breakers are highly effective.  So, is there some bathtub curve, where the low end ("hard vacuum") is fine for hipot/megger testing, and then as the pressure rises, hipot is verboten, and then as you get towards atmospheric pressure, it's OK again?  For simplicity, I'd say lets leave moisture out of the discussion
I think each piece of equipment and each situation deserves to be examined separately. But following on your comment of bathtub curve, there is Paschen's curve that shows air is a good insulator at high pressure and high vacuum, and not as good between.
http://en.wikipedia.org/wiki/Paschen%27s_law
Sorry if I'm telling you what you already know or missed the point of your question.

=====================================
(2B)+(2B)'  ?

RE: HiPot/Meggers and Vacuum

(OP)
Well, that gave me enough to think about for a while, and a new direction to look at on an old curiosity.  Thanks.

Rotorbar
 

RE: HiPot/Meggers and Vacuum

I think your question is the basis for the hard limits on voltage when doing vacuum integrity tests.  

RE: HiPot/Meggers and Vacuum

Zog,

Please explain what you are referring to when you say "hard limits" for vacuum bottle integrity test.

Thank.

 

RE: HiPot/Meggers and Vacuum

The "Warning do not exceed" test voltages for vacuum integrity tests found in the OEM manuals.  

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