Creepage and clearance requirements in vacuum

Where could I find requirements for creepage and clearance distances for electronics in a vacuum (1e-5 mbar) environment? The EN-IEC 61010-1 specifies these distances for use in air and also lists derating factors for use at altitudes up to 5000 m (reduced pressure) but vacuum conditions are not mentioned at all.

From experience I can tell that a few kV/mm is easily doable, but I guess that my experience alone is not sufficient for certification :). Can anyone point me to a relevant standard?

Thanks

Reply to
Fitzgerald
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If you are talking about electrical breakdown you need to be a bit careful. There's a sweet spot in the pressure range.

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's_law Way back I ran some fairly low voltage stuff in vacuum and you had to turn off the power as you were pumping down.. low pressure is fine and high pressure is fine.. but in between look out.

George H.

Reply to
George Herold

Remember, you have to GET to vacuum before you can count on that V/m capability.

A little like the 'brown out' sensitivity many AC switching power supplies had, worked at zero V, worked at 120Vac, but at 70-80Vac disaster!

Same with vacuum.

PS: check the NASA website. They list everything, including the outgassing properties of materials.

Reply to
RobertMacy

Creepage relates to surfaces; if your surfaces are perfectly clean (and to achieve vacuum, you have to clean them), there's very little difference from the bulk insulator material. So, no creepage issues apply.

And clearance relates to spark and corona discharge, which depends on the fill gas (which is why Ne + He is a good fill gas for discharge lamps, it has the lowest field breakdown for a visible light emitter). Vacuum usually means you have a non-atmospheric fill gas, so there aren't any simple guidelines.

Reply to
whit3rd

Try IEC 60613:2010 I don't remenber if it goes into detail of spacing inside a tube. Maybe IEC 62271-111, Its for HV switch gear, again not sure it will help. It maybe a grey area, where a dielectric stress test is all that is needed.

Cheers

Reply to
Martin Riddle

** That standard is for lab test equipment.
** It this for reasons of user safety or not ?

If so, the user must still be safe whenever the vacuum is lost and or the surface becomes contaminated.

If this is for functionality alone, is it really compulsory to meet a particular standard ?

Electron tubes like CRTs have small clearances and creepage distances yet operate at tens of thousands of volts. Failure modes include internal arcing, partial or full loss of vacuum and contamination from loose particles of cathode coating.

... Phil

Reply to
Phil Allison

Nothing that a turbo pump can't take care of! Of course, one needs to start with the roughing pump.

It also may come down to installing a getter ring, who knows.

Jamie

Reply to
Maynard A. Philbrook Jr.

They already have 295 pounds of crap in them. What's left to fill?

--
Anyone wanting to run for any political office in the US should have to 
have a DD214, and a honorable discharge.
Reply to
Michael A. Terrell

Thanks. Yes, it is for a lab measurement device and that is why I first started looking in the EN-IEC 61010-1.

There is an interlock present that will only switch on the high voltage supply when the system is at a pressure below 1e-4 mbar. The interlock is designed to work under single-fault conditions. So it is more of a compliance question than it is a user safety issue. At 5kV I want to make sure to comply to the relevant standards - the question remains which standard as the EN-IEC 61010-1 doesn't seem to apply.

I will have a look into the IEC 60613:2010 and the IEC 62271-111 as suggested by Martin and report back my findings.

Reply to
Fitzgerald

I am not familiar with 61010, but you may find (as Phil alluded to) that basic or reinforced insulation is only required where its failure is in some way dangerous. In some standards, if there is a spacing less than the allowable figure then the test house will say they don't trust it as basic insulation and then put a short circuit across it during the testing. If nothing dangerous happens (no shock hazards, no fires etc.) then they might call it "functional" insulation and pass it regardless of the spacing. Better read the standard carefully. You might have to add some over-current protection to deal safely with the case of the short-circuiting, but that is often a good idea with vacuum anyway in case an arc occurs, which if it occurs (due to a sudden leak, cosmic rays or whatever) can be self-sustaining if it vapourises enough metal to sustain the arc.

Chris

Reply to
Chris Jones

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