Creepage and clearance requirements in vacuum

[Fitzgerald]

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

[George Herold]

If you are talking about electrical breakdown you need to be a bit careful.
There's a sweet spot in the pressure range.
http://en.wikipedia.org/wiki/Paschen'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.

[RobertMacy]

On Fri, 17 Oct 2014 02:05:08 -0700, Fitzgerald <john....@mailinator.com>
wrote:

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.

[Neon John]

On Fri, 17 Oct 2014 11:05:08 +0200, Fitzgerald
<john....@mailinator.com> wrote:

>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.

The conductivity (ionization) of air increases rapidly with dropping
pressure, peaks at about 2 Torr and rises very rapidly as the vacuum
increases. Above about E-4 Torr the limit is point electron emission.
Beyond my capabilities to calculate but I know that some 5kV rated
vacuum relays I have separate the contacts by less than a mm.

I don't know of any standards but NEMA would most likely have some
specifications for such things as MHV and UHV (500-750kV) utility
breakers.

>
> 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?

You didn't mention what you're doing but you might want to consider
SF6 fill instead of a vacuum. Much easier to fill and maintain in the
enclosure plus SF6 will provide at least a little cooling. Though its
thermal conductivity is quite low, it's better than a vacuum.

John
John DeArmond
http://www.neon-john.com
http://www.fluxeon.com
Tellico Plains, Occupied TN
See website for email address

[mako...@yahoo.com]

>
> >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.
>

search terma for you are

CRITICAL PRESSURE

and

MULTIPACTION

Mark

[whit3rd]

On Friday, October 17, 2014 2:05:08 AM UTC-7, Fitzgerald wrote:
> Where could I find requirements for creepage and clearance distances for
> electronics in a vacuum (1e-5 mbar) environment?

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.

[John Larkin]

Yeah, Philo Farnsworth! His cottage, where he invented modern
television, is near here, on Green Street. There is a small plaque.

Some of the satellite RF guys, inadvertently, rediscovered the
multipactor.


--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

[Martin Riddle]

On Fri, 17 Oct 2014 11:05:08 +0200, Fitzgerald
<john....@mailinator.com> wrote:

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

[Phil Allison]

Fitzgerald wrote:

> 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.

** That standard is for lab test equipment.

> 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 :).

** 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

[Maynard A. Philbrook Jr.]

In article <06941265-9f4f-4950...@googlegroups.com>,
palli...@gmail.com says...

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

[Phil Allison]

Maynard A. Philbrook Jr.

>
> 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.

** Well, not any narcissistic, bullshitting, radio ham, code scribblers

- that's for sure !!!




... Phil

[Maynard A. Philbrook Jr.]

In article <bd394ed0-86d4-4066...@googlegroups.com>,
palli...@gmail.com says...

You're just jealous, because you can't fill my shoes.

Jamie

[Michael A. Terrell]

"Maynard A. Philbrook Jr." wrote:
>
> You're just jealous, because you can't fill my shoes.

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.

[Fitzgerald]

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.

[Chris Jones]

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