Re: [PSES] Scientific principles behind Surface Creepage & Air Clearance

[Lubo Cekov]

Vincent, please reference IEC 60664-1 for detailed answer of your question.

"NOTE The breakdown voltage of a clearance in air for a homogeneous field
(withstand voltage case B in table A. 1) is, according to Paschen’s Law,
proportional to the product of the distance between electrodes and the
atmospheric pressure. Therefore experimental data recorded at approximately
sea level is corrected according to the difference in atmospheric pressure
between 2 000 m and sea level. The same correction is made for
inhomogeneous fields." (IEC 60664-1)

"However the test voltages and the minimum values of CREEPAGE DISTANCES and
AIR CLEARANCES specified in IEC 60950-1 are derived from IEC 60664-1 and
are based on assumptions about possible overvoltages in mains and other
circuits, particularly the frequency of occurrence of various levels of
overvoltage. According to the understanding of the working group experts
who revised the corresponding requirements of this standard, compliance
with the requirements of IEC 60664-1 or IEC 60950-1 leaves a RISK that
transient insulation breakdown could occur with a frequency up to about
once per year." (IEC 60601-1)

Lubo

On Tue, May 9, 2017 at 11:00 PM, Vincent Lee <
08e6c8d35910-dmarc-requ...@ieee.org> wrote:

>
>
>
> Hi all,
>
> Good day,
>
> 1) May I know what is the scientific relationship between Paschen's Law (
> https://en.wikipedia.org/wiki/Paschen%27s_law) and surface creepage and
> air clearance distance ?
>
> 2) If there is a relationship, how can one calculate the surface creepage
> and air clearance distance (such as those in IEC 60601-1 3rd) based on
> Paschen's Law ?
>
> 3) If Paschen's Law is not applicable for such calculation, then how are
> the surface creepage and air clearance distance (such as those in IEC
> 60601-1 3rd) obtained ? On what scientific basis or principles ?
>
> Hope to hear from you soon.
>
> Thank you & have a nice day.
>
>
> Regards, Vincent
>
>
> -
> 
>
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-- 
Lubo Cekov

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Re: [PSES] Scientific principles behind Surface Creepage & Air Clearance

[Peter Tarver]

Hi, Vincent.

As Bernd pointed out, IEC 60664 gives the best information on the scientific 
basis for Clearance and Creepage distances.

Paschen’s Law will (theoretically) have no effect on Creepages. Theoretically, 
Creepages exists in two dimensions. Realistically, even the thinnest copper on 
a board has some height, so it’s possible that, under the right circumstances, 
Paschen’s could have an effect on Creepages as well as Clearances.


Peter Tarver


From: Vincent Lee
Sent: Tuesday, May 09, 2017 21:00


Hi all,

Good day,

1) May I know what is the scientific relationship between Paschen's Law 
(https://en.wikipedia.org/wiki/Paschen%27s_law) and surface creepage and air 
clearance distance ?

2) If there is a relationship, how can one calculate the surface creepage and 
air clearance distance (such as those in IEC 60601-1 3rd) based on Paschen's 
Law ?

3) If Paschen's Law is not applicable for such calculation, then how are the 
surface creepage and air clearance distance (such as those in IEC 60601-1 3rd) 
obtained ? On what scientific basis or principles ?

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[PSES] AW: [PSES] Scientific principles behind Surface Creepage & Air Clearance

[Dürrer Bernd]

Dear Vincent,

I do not know IEC 60601-1, but as it references IEC 60664-1, I assume the same 
principles of insulation coordination are applied. In fact there is a book on 
that topic by Klaus Stimper "The Physical Fundamentals of Low-Voltage 
Insulation Co-Ordination", but the English version seems to be out of print, 
and only the German original can be ordered from VDE Verlag 
(https://www.vde-verlag.de/books/403447/isolationskoordination-in-niederspannungsanlagen.html).
 There is also an application guide IEC TR 60664-2-1:2011 
(https://webstore.iec.ch/publication/2797) that might be helpful.

You are right that the definition of air clearances refers to Paschen's Law, 
while the definition of creepage distances is based on a statistical evaluation 
of long-term measurement results (e.g. impulse withstand voltage, insulation 
resistance) for different insulation materials after endurance and field 
testing under varying environmental conditions (e.g. temperature, humidity, 
pollution).

Kind regards,

Bernd


Von: Vincent Lee [mailto:08e6c8d35910-dmarc-requ...@ieee.org]
Gesendet: Mittwoch, 10. Mai 2017 06:00
An: EMC-PSTC@LISTSERV.IEEE.ORG
Betreff: [PSES] Scientific principles behind Surface Creepage & Air Clearance



Hi all,

Good day,

1) May I know what is the scientific relationship between Paschen's Law 
(https://en.wikipedia.org/wiki/Paschen%27s_law) and surface creepage and air 
clearance distance ?

2) If there is a relationship, how can one calculate the surface creepage and 
air clearance distance (such as those in IEC 60601-1 3rd) based on Paschen's 
Law ?

3) If Paschen's Law is not applicable for such calculation, then how are the 
surface creepage and air clearance distance (such as those in IEC 60601-1 3rd) 
obtained ? On what scientific basis or principles ?

Hope to hear from you soon.

Thank you & have a nice day.


Regards, Vincent

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