Re: [PSES] dielectric strength question -- update

[John Woodgate]

Indeed, but the crunch question is where did that data come from. We can 
tell by the number 60664 that it originated probably in the 1970s.


On 2024-07-02 20:21, Ralph McDiarmid wrote:


I’m aware of IEC 60664-1 (insulation coordination) and I’ve referenced 
it many times over the years.  You’ll find its normative reference in 
several IEC and CSA standards and UL840 seems to rely on its 
database.  IEC 60664 has been around a long time and has several parts.


Ralph

*From:*Richard Nute 
*Sent:* Friday, June 28, 2024 3:31 PM
*To:* EMC-PSTC@LISTSERV.IEEE.ORG
*Subject:* [PSES] dielectric strength question -- update

Since my 23 June message, I may have found the answer to my quest as 
to where the air insulation (clearances) distances came from: IEC 664, 
Edition 1, 1980,  Appendix Table AI, withstand voltages, and Table 
AII, breakdown voltages.


According to IEC 664, Table AII is “experimental data” by

Prof. Dr. Ing. W. Pfeiffer, convenor of IEC TC109/MT3, 
elektrotechnische zeitschriftAusg.B, 1976.


Dr. Hermstein, elektrotechnische zeitschrift Ausg. A, 1969.

These are Germanelectrotechnical journals issue A, 1969, and issue B, 
1976.  I could not find copies of these.  Perhaps our German 
subscribers can find these.


I surmise from the tables that these two people tested air breakdown 
voltage as a function of distance.  I did find that Dr. Hermstein did 
some experimental work on electrical performance of gasses that has 
been discredited.


Table AI (IEC 664) is withstand voltages based on the breakdown 
voltages in Table AII (IEC 664). This is the source of IEC 60664-1 
clearance distance tables which have been used by a number of IEC 
standards committees.


I’ve attached a plot of both the breakdown voltage per distance and 
the withstand voltage per distance through air.  These are linear axes 
while the IEC 664 and IEC 60664-1 plots are logarithmic axes.I’ve 
included trend lines (dotted) and their equations.(The 
voltage-distance tables are not in IEC 60664-1.)


I suspect the non-linearity of the breakdown (red) line is due to 
measurement problems. I would expect the line to be straight except 
for the small dimensions that approach the Paschen voltage limit for 
air, 327 volts peak.  (Paschen studied gas breakdowns at very small 
gaps and found that various gasses do not break down at very small gap 
dimensions.)


Best regards,

Rich



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Re: [PSES] dielectric strength question -- update

[Ralph McDiarmid]

I'm aware of IEC 60664-1 (insulation coordination) and I've referenced it
many times over the years.  You'll find its normative reference in several
IEC and CSA standards and UL840 seems to rely on its database.  IEC 60664
has been around a long time and has several parts.

 

Ralph

 

From: Richard Nute  
Sent: Friday, June 28, 2024 3:31 PM
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: [PSES] dielectric strength question -- update

 

 

Since my 23 June message, I may have found the answer to my quest as to
where the air insulation (clearances) distances came from: IEC 664, Edition
1, 1980,  Appendix Table AI, withstand voltages, and Table AII, breakdown
voltages. 

According to IEC 664, Table AII is "experimental data" by 

Prof. Dr. Ing. W. Pfeiffer, convenor of IEC TC109/MT3, elektrotechnische
zeitschrift  Ausg. B, 1976. 

Dr. Hermstein, elektrotechnische zeitschrift  Ausg. A, 1969.  

These are German electrotechnical journals issue A, 1969, and issue B, 1976.
I could not find copies of these.  Perhaps our German subscribers can find
these.

I surmise from the tables that these two people tested air breakdown voltage
as a function of distance.  I did find that Dr. Hermstein did some
experimental work on electrical performance of gasses that has been
discredited. 

Table AI (IEC 664) is withstand voltages based on the breakdown voltages in
Table AII (IEC 664).  This is the source of IEC 60664-1 clearance distance
tables which have been used by a number of IEC standards committees.  

I've attached a plot of both the breakdown voltage per distance and the
withstand voltage per distance through air.  These are linear axes while the
IEC 664 and IEC 60664-1 plots are logarithmic axes.  I've included trend
lines (dotted) and their equations.  (The voltage-distance tables are not in
IEC 60664-1.)  

I suspect the non-linearity of the breakdown (red) line is due to
measurement problems. I would expect the line to be straight except for the
small dimensions that approach the Paschen voltage limit for air, 327 volts
peak.  (Paschen studied gas breakdowns at very small gaps and found that
various gasses do not break down at very small gap dimensions.) 

Best regards,

Rich

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Re: [PSES] dielectric strength question

[Richard Nute]

Hi Ralph: 

"My understanding that “clearance” is distance through air (the insulating 
medium for clearance), not through solid or liquid insulation." 
True. 

"Clearance distance is a function of peak voltage and air pressure." 
True. 

"The testing of solid insulation is generally done using an impulse withstand 
voltage test." 
Depends on the standard. Its the first option in IEC 60664-1. 

"Clearance is tested using steady-state d.c. or the rms equivalent of an a.c. 
test voltage." 

In IEC 60664-1, the first option is an impulse withstand test, followed by peak 
sinusoid and DC. 

IEC 60664-1, 6.1.2.1, Note 1 says "The electric testing of clearances will also 
stress the associated solid insulation." Solid, air (clearance), and surface 
(creepage) distance are always in parallel. They cannot be tested separately. 
See attached illustration. 

Best regards, 

Rich 

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Re: [PSES] dielectric strength question -- update

[John Woodgate]

Hi, Rich. I thought you were writing about solid dielectrics. I did a 
Google search for the German journal and it seems that its issues may be 
available up to 1995. The organization VDE should be able to help you: 
https://www.vde.com/en. Also, the search turned up a book that seems to 
have relevant information, at 
https://www.google.co.uk/books/edition/Electrical_Properties_of_Solid_Insulatin/c9qgPOK7eNwC?hl=en=1=elektrotechnische+zeitschrift=PA220=frontcover


On 2024-06-28 23:31, Richard Nute wrote:


Since my 23 June message, I may have found the answer to my quest as 
to where the air insulation (clearances) distances came from: IEC 664, 
Edition 1, 1980,  Appendix Table AI, withstand voltages, and Table 
AII, breakdown voltages.


According to IEC 664, Table AII is “experimental data” by

Prof. Dr. Ing. W. Pfeiffer, convenor of IEC TC109/MT3,
elektrotechnische zeitschriftAusg.B, 1976.

Dr. Hermstein, elektrotechnische zeitschrift  Ausg. A, 1969.

These are Germanelectrotechnical journalsissue A, 1969, and issue B, 
1976.  I could not find copies of these.  Perhaps our German 
subscribers can find these.


I surmise from the tables that these two people tested air breakdown 
voltage as a function of distance.  I did find that Dr. Hermstein did 
some experimental work on electrical performance of gasses that has 
been discredited.


Table AI (IEC 664) is withstand voltages based on the breakdown 
voltages in Table AII (IEC 664).  This is the source of IEC 60664-1 
clearance distance tables which have been used by a number of IEC 
standards committees.


I’ve attached a plot of both the breakdown voltage per distance and 
the withstand voltage per distance through air.  These are linear axes 
while the IEC 664 and IEC 60664-1 plots are logarithmic axes.I’ve 
included trend lines (dotted)and their equations.(The voltage-distance 
tables are not in IEC 60664-1.)


I suspect the non-linearity of the breakdown (red) line is due to 
measurement problems. I would expect the line to be straight except 
for the small dimensions that approach the Paschen voltage limit for 
air, 327 volts peak.  (Paschen studied gas breakdowns at very small 
gaps and found that various gasses do not break down at very small gap 
dimensions.)


Best regards,

Rich



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[PSES] dielectric strength question -- update

[Richard Nute]

 
Since my 23 June message, I may have found the answer to my quest as to
where the air insulation (clearances) distances came from: IEC 664, Edition
1, 1980,  Appendix Table AI, withstand voltages, and Table AII, breakdown
voltages. 

According to IEC 664, Table AII is "experimental data" by 
Prof. Dr. Ing. W. Pfeiffer, convenor of IEC TC109/MT3,
elektrotechnische zeitschrift  Ausg. B, 1976. 
Dr. Hermstein, elektrotechnische zeitschrift  Ausg. A, 1969.


These are German electrotechnical journals issue A, 1969, and issue B, 1976.
I could not find copies of these.  Perhaps our German subscribers can find
these.

I surmise from the tables that these two people tested air breakdown voltage
as a function of distance.  I did find that Dr. Hermstein did some
experimental work on electrical performance of gasses that has been
discredited. 

Table AI (IEC 664) is withstand voltages based on the breakdown voltages in
Table AII (IEC 664).  This is the source of IEC 60664-1 clearance distance
tables which have been used by a number of IEC standards committees.  

I've attached a plot of both the breakdown voltage per distance and the
withstand voltage per distance through air.  These are linear axes while the
IEC 664 and IEC 60664-1 plots are logarithmic axes.  I've included trend
lines (dotted) and their equations.  (The voltage-distance tables are not in
IEC 60664-1.)  

I suspect the non-linearity of the breakdown (red) line is due to
measurement problems. I would expect the line to be straight except for the
small dimensions that approach the Paschen voltage limit for air, 327 volts
peak.  (Paschen studied gas breakdowns at very small gaps and found that
various gasses do not break down at very small gap dimensions.) 

Best regards,
Rich


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Re: [PSES] dielectric strength question

[Ralph McDiarmid]

My understanding that “clearance” is distance through air (the insulating 
medium for clearance), not through solid or liquid insulation.  Clearance 
distance is a function of peak voltage and air pressure.  The testing of solid 
insulation is generally done using an impulse withstand voltage test.  
Clearance is tested using steady-state d.c. or the rms equivalent of an a.c. 
test voltage.

 

The tables for clearance and creepage along with the requirements for solid 
insulation appear to have served the industry well over the past few decades 
and there seems no compelling reason to scrutinize their origin, unless it can 
be shown that those requirements are generally inadequate or draconian.  I 
suspect there is a decent safety margin built-in to those numbers, maybe a 2:1 
factor.

 

Ralph

 

From: Richard Nute  
Sent: Tuesday, June 25, 2024 4:34 PM
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: Re: [PSES] dielectric strength question

 

 

Hi John:

 

My concern is an engineering-based prediction of clearances (air insulation) as 
a function of voltage.  What is the basis for the clearance tables in the 
standards?  I have never seen anything that allows me to independently verify 
the clearance dimensions as a function of voltage.  My assumption was that the 
volts per unit distance through the insulating medium was an insulator 
constant.  Not true.  The volts per unit distance is a variable and depends on 
the distance.  So, how do I generate a table of distance for each voltage?  As 
near as I know, the tables are empirical.  

 

Your hypothesis is that the V/d curves are due to non-uniformity of the 
insulator is sort-of verified by the papers listed by Adam Dixon.  However, the 
incident you describe seems to me to be due to partial discharge.  Any V/d 
non-uniformity area of the insulating medium is a candidate for partial 
discharge.  Air, because its V/d is very much less than a solid insulator V/d, 
is likely to have sufficient voltage across the void and can lead to a partial 
breakdown of the solid insulator.  In the 1950s, I doubt that we knew much of 
the theory of partial discharge.

 

Best regards,

Rich

 

 

From: John Woodgate mailto:j...@woodjohn.uk> > 
Sent: Tuesday, June 25, 2024 1:26 PM
To: ri...@ieee.org <mailto:ri...@ieee.org> ; EMC-PSTC@LISTSERV.IEEE.ORG 
<mailto:EMC-PSTC@LISTSERV.IEEE.ORG> 
Subject: Re: [PSES] dielectric strength question

 

I feel that those curves support the hypothesis that the variation is due to 
non-uniformity in the material. I first suggested voids (because I recall a 
spectacular failure of a line output transformer design  in the late 1950s 
whose HV winding was encapsulated in polythene. Air in the voids ionized and 
the ions gobbled up the polythene. Attempt to eliminate the voids in viscous 
molten polythene under vacuum were partly successful, but did not survive the 
moulding process. Voids are only one possibility; simple variations in density 
may be sufficient to concentrate the electric field just where it will do the 
most damage.

Can some tests be done on a solid material that has been certified to be highly 
uniform? What happens with liquids, which should be orders of magnitude more 
uniform than the average solid?

On 2024-06-25 20:35, Richard Nute wrote:

 

Thanks to Adam for all the references.  They address very thin solid 
insulations.  But they confirm that dielectric strength is not a constant for 
very small distances, and they do not have an answer as to why.  

 

My concern is verifying clearances in safety standards.  I’ve attached curves 
of three standards clearance requirements (logarithmic scale for volts per 
millimeter).  The solid curves represent the clearances in standards and are 
close to power curves (dotted lines).  The equations are for a best-fit power 
curve.

 

The solid green curve is from an old standard and depicts actual withstand 
measurements.  

 

I suspect the electric strength curves are related to the reason for Paschen’s 
finding that gases do not break down at low voltages.  

 

My objective is to predict clearance dimensions without tables.

 

Best regards,

Rich

 

 


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Re: [PSES] dielectric strength question

[Richard Nute]

 

Hi John:

 

My concern is an engineering-based prediction of clearances (air insulation) as 
a function of voltage.  What is the basis for the clearance tables in the 
standards?  I have never seen anything that allows me to independently verify 
the clearance dimensions as a function of voltage.  My assumption was that the 
volts per unit distance through the insulating medium was an insulator 
constant.  Not true.  The volts per unit distance is a variable and depends on 
the distance.  So, how do I generate a table of distance for each voltage?  As 
near as I know, the tables are empirical.  

 

Your hypothesis is that the V/d curves are due to non-uniformity of the 
insulator is sort-of verified by the papers listed by Adam Dixon.  However, the 
incident you describe seems to me to be due to partial discharge.  Any V/d 
non-uniformity area of the insulating medium is a candidate for partial 
discharge.  Air, because its V/d is very much less than a solid insulator V/d, 
is likely to have sufficient voltage across the void and can lead to a partial 
breakdown of the solid insulator.  In the 1950s, I doubt that we knew much of 
the theory of partial discharge.

 

Best regards,

Rich

 

 

From: John Woodgate  
Sent: Tuesday, June 25, 2024 1:26 PM
To: ri...@ieee.org; EMC-PSTC@LISTSERV.IEEE.ORG
Subject: Re: [PSES] dielectric strength question

 

I feel that those curves support the hypothesis that the variation is due to 
non-uniformity in the material. I first suggested voids (because I recall a 
spectacular failure of a line output transformer design  in the late 1950s 
whose HV winding was encapsulated in polythene. Air in the voids ionized and 
the ions gobbled up the polythene. Attempt to eliminate the voids in viscous 
molten polythene under vacuum were partly successful, but did not survive the 
moulding process. Voids are only one possibility; simple variations in density 
may be sufficient to concentrate the electric field just where it will do the 
most damage.

Can some tests be done on a solid material that has been certified to be highly 
uniform? What happens with liquids, which should be orders of magnitude more 
uniform than the average solid?

On 2024-06-25 20:35, Richard Nute wrote:

 

Thanks to Adam for all the references.  They address very thin solid 
insulations.  But they confirm that dielectric strength is not a constant for 
very small distances, and they do not have an answer as to why.  

 

My concern is verifying clearances in safety standards.  I’ve attached curves 
of three standards clearance requirements (logarithmic scale for volts per 
millimeter).  The solid curves represent the clearances in standards and are 
close to power curves (dotted lines).  The equations are for a best-fit power 
curve.

 

The solid green curve is from an old standard and depicts actual withstand 
measurements.  

 

I suspect the electric strength curves are related to the reason for Paschen’s 
finding that gases do not break down at low voltages.  

 

My objective is to predict clearance dimensions without tables.

 

Best regards,

Rich

 

 

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Best wishes
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Keep trying

 


 
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Re: [PSES] dielectric strength question

[John Woodgate]

I feel that those curves support the hypothesis that the variation is 
due to non-uniformity in the material. I first suggested voids (because 
I recall a spectacular failure of a line output transformer design  in 
the late 1950s whose HV winding was encapsulated in polythene. Air in 
the voids ionized and the ions gobbled up the polythene. Attempt to 
eliminate the voids in viscous molten polythene under vacuum were partly 
successful, but did not survive the moulding process. Voids are only one 
possibility; simple variations in density may be sufficient to 
concentrate the electric field just where it will do the most damage.


Can some tests be done on a solid material that has been certified to be 
highly uniform? What happens with liquids, which should be orders of 
magnitude more uniform than the average solid?


On 2024-06-25 20:35, Richard Nute wrote:


Thanks to Adam for all the references.  They address very thin solid 
insulations.  But they confirm that dielectric strength is not a 
constant for very small distances, and they do not have an answer as 
to why.


My concern is verifying clearances in safety standards.  I’ve attached 
curves of three standards clearance requirements (logarithmic scale 
for volts per millimeter).  The solid curves represent the clearances 
in standards and are close to power curves (dotted lines).  The 
equations are for a best-fit power curve.


The solid green curve is from an old standard and depicts actual 
withstand measurements.


I suspect the electric strength curves are related to the reason for 
Paschen’s finding that gases do not break down at low voltages.


My objective is to predict clearance dimensions without tables.

Best regards,

Rich



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Keep trying

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Re: [PSES] dielectric strength question

[Richard Nute]

 

Thanks to Adam for all the references.  They address very thin solid 
insulations.  But they confirm that dielectric strength is not a constant for 
very small distances, and they do not have an answer as to why.  

 

My concern is verifying clearances in safety standards.  I’ve attached curves 
of three standards clearance requirements (logarithmic scale for volts per 
millimeter).  The solid curves represent the clearances in standards and are 
close to power curves (dotted lines).  The equations are for a best-fit power 
curve.

 

The solid green curve is from an old standard and depicts actual withstand 
measurements.  

 

I suspect the electric strength curves are related to the reason for Paschen’s 
finding that gases do not break down at low voltages.  

 

My objective is to predict clearance dimensions without tables.

 

Best regards,

Rich

 

 


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Re: [PSES] dielectric strength question

[Ken Javor]

Totally of the original topic, but I have used “swag” uncapitalized in several 
papers on the topic of electromagnetic coupling to and from cables over a 
ground plane. In that context, “swag” means single-wire-above-ground.

 

 

-- 

 

Ken Javor

Ph: (256) 650-5261

 

 

From: Ken Javor 
Reply-To: Ken Javor 
Date: Tuesday, June 25, 2024 at 8:15 AM
To: 
Subject: Re: [PSES] dielectric strength question

 

Silly wild ass guess is what I mean when I use that acronym.

 

-- 

 

Ken Javor

Ph: (256) 650-5261

 

 

From: "James Pawson (U3C)" 
Reply-To: "James Pawson (U3C)" 
Date: Tuesday, June 25, 2024 at 7:29 AM
To: 
Subject: Re: [PSES] dielectric strength question

 

Could someone define the acronym SWAG in this context please?

 

Something With Air Gap?

 

All the best

James

 

James Pawson

Managing Director & EMC Problem Solver

 

Unit 3 Compliance Ltd

EMC : Environmental & Vibration : Electrical Safety : CE & UKCA : Consultancy

 

www.unit3compliance.co.uk | ja...@unit3compliance.co.uk 

+44(0)1274 911747  |  +44(0)7811 139957

2 Wellington Business Park, New Lane, Bradford, BD4 8AL

Registered in England and Wales # 10574298

 

Office hours:

Every morning my full attention is on consultancy, testing, and troubleshooting 
activities for our customers’ projects. I’m available/contactable between 1300h 
to 1730h Mon/Tue/Thurs/Fri.

For inquiries, bookings, and testing updates please send us an email on 
he...@unit3compliance.co.uk or call 01274 911747. Our lead times for testing 
and consultancy are typically 4-5 weeks.

 

 

 

 

From: Adam Dixon  
Sent: Tuesday, June 25, 2024 1:24 PM
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: Re: [PSES] dielectric strength question

 

SWAG #2:  non-uniformities in materials + multiple breakdown mechanisms make it 
difficult to model.  Mica shows up in 1940's vintage literature.  Here are some 
interesting papers that I perused after Rich posed the question:

 

https://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=9079498
Space change behavior in cross-linked polymers

https://onlinelibrary.wiley.com/doi/10.1002/app.49379
Touches on different breakdown mechanisms (see Figure 3; also the Figure 2 
reference may be worthwhile but I haven't tried accessing it)

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7764431/
electron injection and avalanche breakdown process

https://citeseerx.ist.psu.edu/document?repid=rep1=pdf=65f577afe99e3253e7e3f38054ce9ea49b16a636
Electromechanical breakdown mechanism but also states "The exact cause for the 
observed behavior remains to be investigated" 

https://apps.dtic.mil/sti/pdfs/ADA635433.pdf
Paschen Curve anomalies (for consideration of gas dielectrics)

https://www.osti.gov/servlets/purl/1656858

Describes influence of polymer chain ends (Figure 1 is a good illustration)

 

 

Cheers,

Adam in Atlanta

adam.di...@ieee.org 

 

On Mon, Jun 24, 2024 at 11:00 PM Patrick  wrote:

just a SWAG...  perhaps dielectric strength is dependent on volume, and the 
increased 'thickness' is assumed to be thickness-for-a-constant-surface-area.  
If that's the case then an increasing thickness is also an increased volume 
which also increases available charge carriers, reducing breakdown voltage.

A test of my SWAG would be to incrementally increase dielectric thickness and 
determine if breakdown voltage eventually finds a minimum and then begins to 
increase with thickness.

interesting question.

 

On Sun, Jun 23, 2024, 13:32 Richard Nute  wrote:

 

Why does air (or any insulating material) have decreasing dielectric strength, 
kV/mm, with increasing distance through the dielectric substance?  Assume 
homogenous field.  (I have assumed the dielectric strength was constant for the 
material.)   In other words, what is the physical basis for the non-constant 
dielectric strength clearance tables in various safety standards?  (I have yet 
to find the answer from the web.)  How can I predict the dielectric constant 
for a given distance through air (or any insulation)?

Charles J. Fraser, in Mechanical Engineer's Reference Book (Twelfth Edition), 
1994:

If the potential difference across opposite faces of a dielectric material is 
increased above a particular value, the material breaks down. The failure of 
the material takes the form of a small puncture, which renders the material 
useless as an insulator. The potential gradient necessary to cause break down 
is normally expressed in kilovolts/millimetre and is termed the ‘dielectric 
strength’. The dielectric strength of a given material decreases with increases 
in the thickness. Table 2.2 gives approximate values for some of the more 
common dielectric materials.

Table 2.2. Dielectric strength of some common insulators

MaterialThickness (mm)  Dielectric strength (kV/mm)
Air 0.2 5.75   
0.6 4.92   
1.0 4.36   
10.02.98   
Mica0.01200
0.10115
1.00  

Re: [PSES] dielectric strength question

[Heckrotte, Michael]

My understanding is Scientific Wild Ass Guess


Best Regards,
Mike

From: Patrick 
Sent: Tuesday, June 25, 2024 6:51 AM
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: Re: [PSES] dielectric strength question

Silly WildAss Guess.
A precursor to a hypothesis.  Plus easier to say and spell.

On Tue, Jun 25, 2024 at 6:15 AM Ken Javor 
mailto:ken.ja...@emccompliance.com>> wrote:
Silly wild ass guess is what I mean when I use that acronym.

--

Ken Javor
Ph: (256) 650-5261


From: "James Pawson (U3C)" 
mailto:ja...@unit3compliance.co.uk>>
Reply-To: "James Pawson (U3C)" 
mailto:ja...@unit3compliance.co.uk>>
Date: Tuesday, June 25, 2024 at 7:29 AM
To: mailto:EMC-PSTC@LISTSERV.IEEE.ORG>>
Subject: Re: [PSES] dielectric strength question

Could someone define the acronym SWAG in this context please?

Something With Air Gap?

All the best
James

James Pawson
Managing Director & EMC Problem Solver

Unit 3 Compliance Ltd
EMC : Environmental & Vibration : Electrical Safety : CE & UKCA : Consultancy

www.unit3compliance.co.uk<http://www.unit3compliance.co.uk/> | 
ja...@unit3compliance.co.uk<mailto:ja...@unit3compliance.co.uk>
+44(0)1274 911747  |  +44(0)7811 139957
2 Wellington Business Park, New Lane, Bradford, BD4 8AL
Registered in England and Wales # 10574298

Office hours:
Every morning my full attention is on consultancy, testing, and troubleshooting 
activities for our customers’ projects. I’m available/contactable between 1300h 
to 1730h Mon/Tue/Thurs/Fri.
For inquiries, bookings, and testing updates please send us an email on 
he...@unit3compliance.co.uk<mailto:he...@unit3compliance.co.uk> or call 01274 
911747. Our lead times for testing and consultancy are typically 4-5 weeks.




From: Adam Dixon mailto:lanterna.viri...@gmail.com>>
Sent: Tuesday, June 25, 2024 1:24 PM
To: EMC-PSTC@LISTSERV.IEEE.ORG<mailto:EMC-PSTC@LISTSERV.IEEE.ORG>
Subject: Re: [PSES] dielectric strength question

SWAG #2:  non-uniformities in materials + multiple breakdown mechanisms make it 
difficult to model.  Mica shows up in 1940's vintage literature.  Here are some 
interesting papers that I perused after Rich posed the question:

https://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=9079498
Space change behavior in cross-linked polymers

https://onlinelibrary.wiley.com/doi/10.1002/app.49379
Touches on different breakdown mechanisms (see Figure 3; also the Figure 2 
reference may be worthwhile but I haven't tried accessing it)

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7764431/
electron injection and avalanche breakdown process

https://citeseerx.ist.psu.edu/document?repid=rep1=pdf=65f577afe99e3253e7e3f38054ce9ea49b16a636
Electromechanical breakdown mechanism but also states "The exact cause for the 
observed behavior remains to be investigated"

https://apps.dtic.mil/sti/pdfs/ADA635433.pdf
Paschen Curve anomalies (for consideration of gas dielectrics)

https://www.osti.gov/servlets/purl/1656858
Describes influence of polymer chain ends (Figure 1 is a good illustration)


Cheers,
Adam in Atlanta
adam.di...@ieee.org<mailto:adam.di...@ieee.org>

On Mon, Jun 24, 2024 at 11:00 PM Patrick 
mailto:conwa...@gmail.com>> wrote:

just a SWAG...  perhaps dielectric strength is dependent on volume, and the 
increased 'thickness' is assumed to be thickness-for-a-constant-surface-area.  
If that's the case then an increasing thickness is also an increased volume 
which also increases available charge carriers, reducing breakdown voltage.

A test of my SWAG would be to incrementally increase dielectric thickness and 
determine if breakdown voltage eventually finds a minimum and then begins to 
increase with thickness.

interesting question.

On Sun, Jun 23, 2024, 13:32 Richard Nute 
mailto:ri...@ieee.org>> wrote:


Why does air (or any insulating material) have decreasing dielectric strength, 
kV/mm, with increasing distance through the dielectric substance?  Assume 
homogenous field.  (I have assumed the dielectric strength was constant for the 
material.)   In other words, what is the physical basis for the non-constant 
dielectric strength clearance tables in various safety standards?  (I have yet 
to find the answer from the web.)  How can I predict the dielectric constant 
for a given distance through air (or any insulation)?

Charles J. Fraser, in Mechanical Engineer's Reference Book (Twelfth 
Edition)<https://www.sciencedirect.com/book/9780750611954/mechanical-engineers-reference-book>,
 1994:

If the potential difference across opposite faces of a dielectric material is 
increased above a particular value, the material breaks down. The failure of 
the material takes the form of a small puncture, which renders the material 
useless as an insulator. The potential 
gradient<https://www.sciencedirect.com/topics/engineering/potential-gradient> 
necessary to cause break down is normally expressed in kilovolts/millimetre and 
is t

Re: [PSES] dielectric strength question

[Patrick]

Silly WildAss Guess.
A precursor to a hypothesis.  Plus easier to say and spell.

On Tue, Jun 25, 2024 at 6:15 AM Ken Javor 
wrote:

> Silly wild ass guess is what I mean when I use that acronym.
>
>
>
> --
>
>
>
> Ken Javor
>
> Ph: (256) 650-5261
>
>
>
>
>
> *From: *"James Pawson (U3C)" 
> *Reply-To: *"James Pawson (U3C)" 
> *Date: *Tuesday, June 25, 2024 at 7:29 AM
> *To: *
> *Subject: *Re: [PSES] dielectric strength question
>
>
>
> Could someone define the acronym SWAG in this context please?
>
>
>
> Something With Air Gap?
>
>
>
> All the best
>
> James
>
>
>
> James Pawson
>
> Managing Director & EMC Problem Solver
>
>
>
> *Unit 3 Compliance Ltd*
>
> *EMC : Environmental & Vibration : Electrical Safety : CE & UKCA :
> Consultancy*
>
>
>
> www.unit3compliance.co.uk | ja...@unit3compliance.co.uk
>
> +44(0)1274 911747  |  +44(0)7811 139957
>
> 2 Wellington Business Park, New Lane, Bradford, BD4 8AL
>
> Registered in England and Wales # 10574298
>
>
>
> *Office hours:*
>
> *Every morning my full attention is on consultancy, testing, and
> troubleshooting activities for our customers’ projects. I’m
> available/contactable between 1300h to 1730h Mon/Tue/Thurs/Fri.*
>
> *For inquiries, bookings, and testing updates please send us an email on
> he...@unit3compliance.co.uk  or call 01274
> 911747. Our lead times for testing and consultancy are typically 4-5 weeks.*
>
>
>
>
>
>
>
>
>
> *From:* Adam Dixon 
> *Sent:* Tuesday, June 25, 2024 1:24 PM
> *To:* EMC-PSTC@LISTSERV.IEEE.ORG
> *Subject:* Re: [PSES] dielectric strength question
>
>
>
> SWAG #2:  non-uniformities in materials + multiple breakdown mechanisms
> make it difficult to model.  Mica shows up in 1940's vintage literature.
> Here are some interesting papers that I perused after Rich posed the
> question:
>
>
>
> https://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=9079498
> Space change behavior in cross-linked polymers
>
> https://onlinelibrary.wiley.com/doi/10.1002/app.49379
> Touches on different breakdown mechanisms (see Figure 3; also the Figure 2
> reference may be worthwhile but I haven't tried accessing it)
>
> https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7764431/
> electron injection and avalanche breakdown process
>
>
> https://citeseerx.ist.psu.edu/document?repid=rep1=pdf=65f577afe99e3253e7e3f38054ce9ea49b16a636
> Electromechanical breakdown mechanism but also states "The exact cause for
> the observed behavior remains to be investigated"
>
> https://apps.dtic.mil/sti/pdfs/ADA635433.pdf
> Paschen Curve anomalies (for consideration of gas dielectrics)
>
> https://www.osti.gov/servlets/purl/1656858
>
> Describes influence of polymer chain ends (Figure 1 is a good illustration)
>
>
>
>
>
> Cheers,
>
> Adam in Atlanta
>
> adam.di...@ieee.org
>
>
>
> On Mon, Jun 24, 2024 at 11:00 PM Patrick  wrote:
>
> just a SWAG...  perhaps dielectric strength is dependent on volume, and
> the increased 'thickness' is assumed to be
> thickness-for-a-constant-surface-area.  If that's the case then an
> increasing thickness is also an increased volume which also increases
> available charge carriers, reducing breakdown voltage.
>
> A test of my SWAG would be to incrementally increase dielectric thickness
> and determine if breakdown voltage eventually finds a minimum and then
> begins to increase with thickness.
>
> interesting question.
>
>
>
> On Sun, Jun 23, 2024, 13:32 Richard Nute  wrote:
>
>
>
> Why does air (or any insulating material) have decreasing dielectric
> strength, kV/mm, with increasing distance through the dielectric
> substance?  Assume homogenous field.  (I have assumed the dielectric
> strength was constant for the material.)   In other words, what is the
> physical basis for the non-constant dielectric strength clearance tables
> in various safety standards?  (I have yet to find the answer from the web.)
>   How can I predict the dielectric constant for a given distance through
> air (or any insulation)?
>
> Charles J. Fraser, in Mechanical Engineer's Reference Book (Twelfth
> Edition)
> <https://www.sciencedirect.com/book/9780750611954/mechanical-engineers-reference-book>,
> 1994:
>
> If the potential difference across opposite faces of a dielectric material
> is increased above a particular value, the material breaks down. The
> failure of the material takes the form of a small puncture, which renders
> the material useless as an insulator. The potential gradient
> <https://www.sciencedire

Re: [PSES] dielectric strength question

[Ken Javor]

Silly wild ass guess is what I mean when I use that acronym.

 

-- 

 

Ken Javor

Ph: (256) 650-5261

 

 

From: "James Pawson (U3C)" 
Reply-To: "James Pawson (U3C)" 
Date: Tuesday, June 25, 2024 at 7:29 AM
To: 
Subject: Re: [PSES] dielectric strength question

 

Could someone define the acronym SWAG in this context please?

 

Something With Air Gap?

 

All the best

James

 

James Pawson

Managing Director & EMC Problem Solver

 

Unit 3 Compliance Ltd

EMC : Environmental & Vibration : Electrical Safety : CE & UKCA : Consultancy

 

www.unit3compliance.co.uk | ja...@unit3compliance.co.uk 

+44(0)1274 911747  |  +44(0)7811 139957

2 Wellington Business Park, New Lane, Bradford, BD4 8AL

Registered in England and Wales # 10574298

 

Office hours:

Every morning my full attention is on consultancy, testing, and troubleshooting 
activities for our customers’ projects. I’m available/contactable between 1300h 
to 1730h Mon/Tue/Thurs/Fri.

For inquiries, bookings, and testing updates please send us an email on 
he...@unit3compliance.co.uk or call 01274 911747. Our lead times for testing 
and consultancy are typically 4-5 weeks.

 

 

 

 

From: Adam Dixon  
Sent: Tuesday, June 25, 2024 1:24 PM
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: Re: [PSES] dielectric strength question

 

SWAG #2:  non-uniformities in materials + multiple breakdown mechanisms make it 
difficult to model.  Mica shows up in 1940's vintage literature.  Here are some 
interesting papers that I perused after Rich posed the question:

 

https://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=9079498
Space change behavior in cross-linked polymers

https://onlinelibrary.wiley.com/doi/10.1002/app.49379
Touches on different breakdown mechanisms (see Figure 3; also the Figure 2 
reference may be worthwhile but I haven't tried accessing it)

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7764431/
electron injection and avalanche breakdown process

https://citeseerx.ist.psu.edu/document?repid=rep1=pdf=65f577afe99e3253e7e3f38054ce9ea49b16a636
Electromechanical breakdown mechanism but also states "The exact cause for the 
observed behavior remains to be investigated" 

https://apps.dtic.mil/sti/pdfs/ADA635433.pdf
Paschen Curve anomalies (for consideration of gas dielectrics)

https://www.osti.gov/servlets/purl/1656858

Describes influence of polymer chain ends (Figure 1 is a good illustration)

 

 

Cheers,

Adam in Atlanta

adam.di...@ieee.org 

 

On Mon, Jun 24, 2024 at 11:00 PM Patrick  wrote:

just a SWAG...  perhaps dielectric strength is dependent on volume, and the 
increased 'thickness' is assumed to be thickness-for-a-constant-surface-area.  
If that's the case then an increasing thickness is also an increased volume 
which also increases available charge carriers, reducing breakdown voltage.

A test of my SWAG would be to incrementally increase dielectric thickness and 
determine if breakdown voltage eventually finds a minimum and then begins to 
increase with thickness.

interesting question.

 

On Sun, Jun 23, 2024, 13:32 Richard Nute  wrote:

 

Why does air (or any insulating material) have decreasing dielectric strength, 
kV/mm, with increasing distance through the dielectric substance?  Assume 
homogenous field.  (I have assumed the dielectric strength was constant for the 
material.)   In other words, what is the physical basis for the non-constant 
dielectric strength clearance tables in various safety standards?  (I have yet 
to find the answer from the web.)  How can I predict the dielectric constant 
for a given distance through air (or any insulation)?

Charles J. Fraser, in Mechanical Engineer's Reference Book (Twelfth Edition), 
1994:

If the potential difference across opposite faces of a dielectric material is 
increased above a particular value, the material breaks down. The failure of 
the material takes the form of a small puncture, which renders the material 
useless as an insulator. The potential gradient necessary to cause break down 
is normally expressed in kilovolts/millimetre and is termed the ‘dielectric 
strength’. The dielectric strength of a given material decreases with increases 
in the thickness. Table 2.2 gives approximate values for some of the more 
common dielectric materials.

Table 2.2. Dielectric strength of some common insulators

MaterialThickness (mm)  Dielectric strength (kV/mm)
Air 0.2 5.75   
0.6 4.92   
1.0 4.36   
10.02.98   
Mica0.01200
0.10115
1.0061 

Thanks, and best regards,

Rich

 

This message is from the IEEE Product Safety Engineering Society emc-pstc 
discussion list. To post a message to the list, send your e-mail to 
EMC-PSTC@LISTSERV.IEEE.ORG 

All emc-pstc postings are archived and searchable on the web at: 
https://www.mail-archive.com/emc-pstc@listserv.ieee.org/ 

Website: https://ewh.ieee.org/soc/pses/ 
Instructions: https://ewh.

Re: [PSES] dielectric strength question

[Adam Dixon]

In my case, SWAG = best guess (how I heard it used growing up in small town
USA, along the lines of Wikipedia's entry).

Cheers,
Adam in Atlanta
adam.di...@ieee.org

On Tue, Jun 25, 2024 at 8:29 AM James Pawson (U3C) <
ja...@unit3compliance.co.uk> wrote:

> Could someone define the acronym SWAG in this context please?
>
>
>
> Something With Air Gap?
>
>
>
> All the best
>
> James
>
>
>
> James Pawson
>
> Managing Director & EMC Problem Solver
>
>
>
> *Unit 3 Compliance Ltd*
>
> *EMC : Environmental & Vibration : Electrical Safety : CE & UKCA :
> Consultancy*
>
>
>
> www.unit3compliance.co.uk | ja...@unit3compliance.co.uk
>
> +44(0)1274 911747  |  +44(0)7811 139957
>
> 2 Wellington Business Park, New Lane, Bradford, BD4 8AL
>
> Registered in England and Wales # 10574298
>
>
>
> *Office hours:*
>
> *Every morning my full attention is on consultancy, testing, and
> troubleshooting activities for our customers’ projects. I’m
> available/contactable between 1300h to 1730h Mon/Tue/Thurs/Fri.*
>
> *For inquiries, bookings, and testing updates please send us an email on
> he...@unit3compliance.co.uk  or call 01274
> 911747. Our lead times for testing and consultancy are typically 4-5 weeks.*
>
>
>
>
>
>
>
>
>
> *From:* Adam Dixon 
> *Sent:* Tuesday, June 25, 2024 1:24 PM
> *To:* EMC-PSTC@LISTSERV.IEEE.ORG
> *Subject:* Re: [PSES] dielectric strength question
>
>
>
> SWAG #2:  non-uniformities in materials + multiple breakdown mechanisms
> make it difficult to model.  Mica shows up in 1940's vintage literature.
> Here are some interesting papers that I perused after Rich posed the
> question:
>
>
>
> https://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=9079498
> Space change behavior in cross-linked polymers
>
> https://onlinelibrary.wiley.com/doi/10.1002/app.49379
> Touches on different breakdown mechanisms (see Figure 3; also the Figure 2
> reference may be worthwhile but I haven't tried accessing it)
>
> https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7764431/
> electron injection and avalanche breakdown process
>
>
> https://citeseerx.ist.psu.edu/document?repid=rep1=pdf=65f577afe99e3253e7e3f38054ce9ea49b16a636
> Electromechanical breakdown mechanism but also states "The exact cause for
> the observed behavior remains to be investigated"
>
> https://apps.dtic.mil/sti/pdfs/ADA635433.pdf
> Paschen Curve anomalies (for consideration of gas dielectrics)
>
> https://www.osti.gov/servlets/purl/1656858
>
> Describes influence of polymer chain ends (Figure 1 is a good illustration)
>
>
>
>
>
> Cheers,
>
> Adam in Atlanta
>
> adam.di...@ieee.org
>
>
>
> On Mon, Jun 24, 2024 at 11:00 PM Patrick  wrote:
>
> just a SWAG...  perhaps dielectric strength is dependent on volume, and
> the increased 'thickness' is assumed to be
> thickness-for-a-constant-surface-area.  If that's the case then an
> increasing thickness is also an increased volume which also increases
> available charge carriers, reducing breakdown voltage.
>
> A test of my SWAG would be to incrementally increase dielectric thickness
> and determine if breakdown voltage eventually finds a minimum and then
> begins to increase with thickness.
>
> interesting question.
>
>
>
> On Sun, Jun 23, 2024, 13:32 Richard Nute  wrote:
>
>
>
> Why does air (or any insulating material) have decreasing dielectric
> strength, kV/mm, with increasing distance through the dielectric
> substance?  Assume homogenous field.  (I have assumed the dielectric
> strength was constant for the material.)   In other words, what is the
> physical basis for the non-constant dielectric strength clearance tables
> in various safety standards?  (I have yet to find the answer from the web.)
>   How can I predict the dielectric constant for a given distance through
> air (or any insulation)?
>
> Charles J. Fraser, in Mechanical Engineer's Reference Book (Twelfth
> Edition)
> <https://www.sciencedirect.com/book/9780750611954/mechanical-engineers-reference-book>,
> 1994:
>
> If the potential difference across opposite faces of a dielectric material
> is increased above a particular value, the material breaks down. The
> failure of the material takes the form of a small puncture, which renders
> the material useless as an insulator. The potential gradient
> <https://www.sciencedirect.com/topics/engineering/potential-gradient> 
> necessary
> to cause break down is normally expressed in kilovolts/millimetre and is
> termed the ‘dielectric strength’. The dielectric strength of a given
> material decreases with increases in the thicknes

Re: [PSES] dielectric strength question

[James Pawson (U3C)]

Could someone define the acronym SWAG in this context please?

 

Something With Air Gap?

 

All the best

James

 

James Pawson

Managing Director & EMC Problem Solver

 

Unit 3 Compliance Ltd

EMC : Environmental & Vibration : Electrical Safety : CE & UKCA : Consultancy

 

 <http://www.unit3compliance.co.uk/> www.unit3compliance.co.uk |  
<mailto:ja...@unit3compliance.co.uk> ja...@unit3compliance.co.uk 

+44(0)1274 911747  |  +44(0)7811 139957

2 Wellington Business Park, New Lane, Bradford, BD4 8AL

Registered in England and Wales # 10574298

 

Office hours:

Every morning my full attention is on consultancy, testing, and troubleshooting 
activities for our customers’ projects. I’m available/contactable between 1300h 
to 1730h Mon/Tue/Thurs/Fri.

For inquiries, bookings, and testing updates please send us an email on 
he...@unit3compliance.co.uk <mailto:he...@unit3compliance.co.uk>  or call 01274 
911747. Our lead times for testing and consultancy are typically 4-5 weeks.

 

 

 

 

From: Adam Dixon  
Sent: Tuesday, June 25, 2024 1:24 PM
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: Re: [PSES] dielectric strength question

 

SWAG #2:  non-uniformities in materials + multiple breakdown mechanisms make it 
difficult to model.  Mica shows up in 1940's vintage literature.  Here are some 
interesting papers that I perused after Rich posed the question:

 

https://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=9079498
Space change behavior in cross-linked polymers

https://onlinelibrary.wiley.com/doi/10.1002/app.49379
Touches on different breakdown mechanisms (see Figure 3; also the Figure 2 
reference may be worthwhile but I haven't tried accessing it)

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7764431/
electron injection and avalanche breakdown process

https://citeseerx.ist.psu.edu/document?repid=rep1 
<https://citeseerx.ist.psu.edu/document?repid=rep1=pdf=65f577afe99e3253e7e3f38054ce9ea49b16a636>
 =pdf=65f577afe99e3253e7e3f38054ce9ea49b16a636
Electromechanical breakdown mechanism but also states "The exact cause for the 
observed behavior remains to be investigated" 

https://apps.dtic.mil/sti/pdfs/ADA635433.pdf
Paschen Curve anomalies (for consideration of gas dielectrics)

https://www.osti.gov/servlets/purl/1656858

Describes influence of polymer chain ends (Figure 1 is a good illustration)

 

 

Cheers,

Adam in Atlanta

adam.di...@ieee.org <mailto:adam.di...@ieee.org>  

 

On Mon, Jun 24, 2024 at 11:00 PM Patrick mailto:conwa...@gmail.com> > wrote:

just a SWAG...  perhaps dielectric strength is dependent on volume, and the 
increased 'thickness' is assumed to be thickness-for-a-constant-surface-area.  
If that's the case then an increasing thickness is also an increased volume 
which also increases available charge carriers, reducing breakdown voltage.

A test of my SWAG would be to incrementally increase dielectric thickness and 
determine if breakdown voltage eventually finds a minimum and then begins to 
increase with thickness.

interesting question.

 

On Sun, Jun 23, 2024, 13:32 Richard Nute mailto:ri...@ieee.org> > wrote:

 

Why does air (or any insulating material) have decreasing dielectric strength, 
kV/mm, with increasing distance through the dielectric substance?  Assume 
homogenous field.  (I have assumed the dielectric strength was constant for the 
material.)   In other words, what is the physical basis for the non-constant 
dielectric strength clearance tables in various safety standards?  (I have yet 
to find the answer from the web.)  How can I predict the dielectric constant 
for a given distance through air (or any insulation)?

Charles J. Fraser, in  
<https://www.sciencedirect.com/book/9780750611954/mechanical-engineers-reference-book>
 Mechanical Engineer's Reference Book (Twelfth Edition), 1994:

If the potential difference across opposite faces of a dielectric material is 
increased above a particular value, the material breaks down. The failure of 
the material takes the form of a small puncture, which renders the material 
useless as an insulator. The  
<https://www.sciencedirect.com/topics/engineering/potential-gradient> potential 
gradient necessary to cause break down is normally expressed in 
kilovolts/millimetre and is termed the ‘dielectric strength’. The dielectric 
strength of a given material decreases with increases in the thickness. Table 
2.2 gives approximate values for some of the more common dielectric materials.

Table 2.2. Dielectric strength of some common insulators

MaterialThickness (mm)  Dielectric strength (kV/mm)
Air 0.2 5.75   
0.6 4.92   
1.0 4.36   
10.02.98   
Mica0.01200
0.10115
1.0061 

Thanks, and best regards,

Rich

 

  _  

This message is from the IEEE Product Safety Engineering Society emc-pstc 
discussion list. To post a message to the list, send y

Re: [PSES] dielectric strength question

[Adam Dixon]

SWAG #2:  non-uniformities in materials + multiple breakdown mechanisms
make it difficult to model.  Mica shows up in 1940's vintage literature.
Here are some interesting papers that I perused after Rich posed the
question:

https://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=9079498
Space change behavior in cross-linked polymers

https://onlinelibrary.wiley.com/doi/10.1002/app.49379
Touches on different breakdown mechanisms (see Figure 3; also the Figure 2
reference may be worthwhile but I haven't tried accessing it)

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7764431/
electron injection and avalanche breakdown process

https://citeseerx.ist.psu.edu/document?repid=rep1=pdf=65f577afe99e3253e7e3f38054ce9ea49b16a636
Electromechanical breakdown mechanism but also states "The exact cause for
the observed behavior remains to be investigated"

https://apps.dtic.mil/sti/pdfs/ADA635433.pdf
Paschen Curve anomalies (for consideration of gas dielectrics)

https://www.osti.gov/servlets/purl/1656858
Describes influence of polymer chain ends (Figure 1 is a good illustration)


Cheers,
Adam in Atlanta
adam.di...@ieee.org

On Mon, Jun 24, 2024 at 11:00 PM Patrick  wrote:

> just a SWAG...  perhaps dielectric strength is dependent on volume, and
> the increased 'thickness' is assumed to be
> thickness-for-a-constant-surface-area.  If that's the case then an
> increasing thickness is also an increased volume which also increases
> available charge carriers, reducing breakdown voltage.
>
> A test of my SWAG would be to incrementally increase dielectric thickness
> and determine if breakdown voltage eventually finds a minimum and then
> begins to increase with thickness.
>
> interesting question.
>
> On Sun, Jun 23, 2024, 13:32 Richard Nute  wrote:
>
>>
>> Why does air (or any insulating material) have decreasing dielectric
>> strength, kV/mm, with increasing distance through the dielectric
>> substance?  Assume homogenous field.  (I have assumed the dielectric
>> strength was constant for the material.)   In other words, what is the
>> physical basis for the non-constant dielectric strength clearance tables
>> in various safety standards?  (I have yet to find the answer from the
>> web.)  How can I predict the dielectric constant for a given distance
>> through air (or any insulation)?
>>
>> Charles J. Fraser, in Mechanical Engineer's Reference Book (Twelfth
>> Edition)
>> ,
>> 1994:
>>
>> If the potential difference across opposite faces of a dielectric
>> material is increased above a particular value, the material breaks down.
>> The failure of the material takes the form of a small puncture, which
>> renders the material useless as an insulator. The *potential gradient*
>>  
>> necessary
>> to cause break down is normally expressed in kilovolts/millimetre and is
>> termed the ‘dielectric strength’. The dielectric strength of a given
>> material decreases with increases in the thickness. Table 2.2 gives
>> approximate values for some of the more common dielectric materials.
>>
>> Table 2.2. Dielectric strength of some common insulators
>>
>> *Material*   * Thickness (mm)* * Dielectric strength (kV/mm)*
>> Air 0.2 5.75
>> 0.6 4.92
>> 1.0 4.36
>> 10.02.98
>> Mica0.01200
>> 0.10115
>> 1.0061
>>
>> Thanks, and best regards,
>>
>> Rich
>>
>>
>> --
>>
>> This message is from the IEEE Product Safety Engineering Society emc-pstc
>> discussion list. To post a message to the list, send your e-mail to
>> EMC-PSTC@LISTSERV.IEEE.ORG
>> All emc-pstc postings are archived and searchable on the web at:
>> https://www.mail-archive.com/emc-pstc@listserv.ieee.org/
>>
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>> unsubscribe) 
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>>
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> --
>
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> unsubscribe) 
> List 

Re: [PSES] dielectric strength question

[Patrick]

just a SWAG...  perhaps dielectric strength is dependent on volume, and the
increased 'thickness' is assumed to be
thickness-for-a-constant-surface-area.  If that's the case then an
increasing thickness is also an increased volume which also increases
available charge carriers, reducing breakdown voltage.

A test of my SWAG would be to incrementally increase dielectric thickness
and determine if breakdown voltage eventually finds a minimum and then
begins to increase with thickness.

interesting question.

On Sun, Jun 23, 2024, 13:32 Richard Nute  wrote:

>
> Why does air (or any insulating material) have decreasing dielectric
> strength, kV/mm, with increasing distance through the dielectric
> substance?  Assume homogenous field.  (I have assumed the dielectric
> strength was constant for the material.)   In other words, what is the
> physical basis for the non-constant dielectric strength clearance tables
> in various safety standards?  (I have yet to find the answer from the web.
> )  How can I predict the dielectric constant for a given distance through
> air (or any insulation)?
>
> Charles J. Fraser, in Mechanical Engineer's Reference Book (Twelfth
> Edition)
> ,
> 1994:
>
> If the potential difference across opposite faces of a dielectric material
> is increased above a particular value, the material breaks down. The
> failure of the material takes the form of a small puncture, which renders
> the material useless as an insulator. The *potential gradient*
>  
> necessary
> to cause break down is normally expressed in kilovolts/millimetre and is
> termed the ‘dielectric strength’. The dielectric strength of a given
> material decreases with increases in the thickness. Table 2.2 gives
> approximate values for some of the more common dielectric materials.
>
> Table 2.2. Dielectric strength of some common insulators
>
> *Material*   * Thickness (mm)* * Dielectric strength (kV/mm)*
> Air 0.2 5.75
> 0.6 4.92
> 1.0 4.36
> 10.02.98
> Mica0.01200
> 0.10115
> 1.0061
>
> Thanks, and best regards,
>
> Rich
>
>
> --
>
> This message is from the IEEE Product Safety Engineering Society emc-pstc
> discussion list. To post a message to the list, send your e-mail to
> EMC-PSTC@LISTSERV.IEEE.ORG
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[PSES] dielectric strength question

[Richard Nute]

Why does air (or any insulating material) have decreasing dielectric
strength, kV/mm, with increasing distance through the dielectric substance?
Assume homogenous field.  (I have assumed the dielectric strength was
constant for the material.)   In other words, what is the physical basis for
the non-constant dielectric strength clearance tables in various safety
standards?  (I have yet to find the answer from the web.)  How can I predict
the dielectric constant for a given distance through air (or any
insulation)?

Charles J. Fraser, in Mechanical Engineer's Reference Book (Twelfth Edition)
 , 1994:

If the potential difference across opposite faces of a dielectric material
is increased above a particular value, the material breaks down. The failure
of the material takes the form of a small puncture, which renders the
material useless as an insulator. The potential gradient

necessary to cause break down is normally expressed in kilovolts/millimetre
and is termed the 'dielectric strength'. The dielectric strength of a given
material decreases with increases in the thickness. Table 2.2 gives
approximate values for some of the more common dielectric materials.

Table 2.2. Dielectric strength of some common insulators

MaterialThickness (mm)  Dielectric strength (kV/mm) 
Air 0.2 5.75
0.6 4.92
1.0 4.36
10.02.98
Mica0.01200 
0.10115 
1.0061  

Thanks, and best regards,
Rich




-

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