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From: legg on 13 Mar 2010 06:31
On Fri, 12 Mar 2010 11:54:02 -0800 (PST), whit3rd <whit3rd(a)gmail.com>
wrote:

>On Mar 11, 4:27�pm, Joerg <inva...(a)invalid.invalid> wrote:
>> D from BC wrote:
>> > I'm trying to find the breakdown V for
>> > 0.0028 inches of PTFE (teflon) and 0.004 inches (~100um) of Kapton.
>
>Textbook value for PTFE aka TFE aka Teflon is 480 volts per milli-
>inch,
>and for polyimide/Kapton is 560 volts per milli-inch.
>
>That assumes pure material, clean surfaces, and no conduction
>enhancement from ambient light...
>This data, from _The_Practicing_Scientist's_Handbook_, Moses, Alfred
>J.,
>1978 edition...

It depends on what you're measuring, or require.

For FEP (Kapton), Dupont book breakdown is over 4KV/mil (170KV/mm),
but life test data to IEC343 (that includes corona resistance) at
10,000 hrs is measured in the 100s of volts/mil.

RL
From: D from BC on 13 Mar 2010 11:57
In article <m8tmp5pu376l9qre31s68f4ct5o2kb37d4(a)4ax.com>,
legg(a)nospam.magma.ca says...
>
> On Fri, 12 Mar 2010 11:54:02 -0800 (PST), whit3rd <whit3rd(a)gmail.com>
> wrote:
>
> >On Mar 11, 4:27�pm, Joerg <inva...(a)invalid.invalid> wrote:
> >> D from BC wrote:
> >> > I'm trying to find the breakdown V for
> >> > 0.0028 inches of PTFE (teflon) and 0.004 inches (~100um) of Kapton.
> >
> >Textbook value for PTFE aka TFE aka Teflon is 480 volts per milli-
> >inch,
> >and for polyimide/Kapton is 560 volts per milli-inch.
> >
> >That assumes pure material, clean surfaces, and no conduction
> >enhancement from ambient light...
> >This data, from _The_Practicing_Scientist's_Handbook_, Moses, Alfred
> >J.,
> >1978 edition...
>
> It depends on what you're measuring, or require.
>
> For FEP (Kapton), Dupont book breakdown is over 4KV/mil (170KV/mm),
> but life test data to IEC343 (that includes corona resistance) at
> 10,000 hrs is measured in the 100s of volts/mil.
>
> RL

Ahhh..
Ok for example...

Kapton CR
http://www2.dupont.com/Kapton/en_US/assets/downloads/pdf/CR_H-54506-
1.pdf
Corona resistance >100 000 hours
@ 20KV/mm <<<That's what I'm suppposed to look at.
Dielectric strength 7400V/mil
Sure one mil can withstand 7400V but the kapton will get destroyed in
less than 100 000 hours.

Corona test was done at
20KV/mm = 20kV/39.37 = 508V/mil << closer to text book figure

So text books use the long term dielectric strength (assumed practical
data) not the short term.


Thanks
From: JosephKK on 14 Mar 2010 12:02
On Fri, 12 Mar 2010 15:19:46 -0800, D from BC <myrealaddress(a)comic.com> wrote:

>In article <fa8a0108-f3dc-45a0-bdfa-04d8601470d5
>@o3g2000yqb.googlegroups.com>, whit3rd(a)gmail.com says...
>>
>> On Mar 11, 4:27 pm, Joerg <inva...(a)invalid.invalid> wrote:
>> > D from BC wrote:
>> > > I'm trying to find the breakdown V for
>> > > 0.0028 inches of PTFE (teflon) and 0.004 inches (~100um) of Kapton.
>>
>> Textbook value for PTFE aka TFE aka Teflon is 480 volts per milli-
>> inch,
>> and for polyimide/Kapton is 560 volts per milli-inch.
>>
>> That assumes pure material, clean surfaces, and no conduction
>> enhancement from ambient light...
>> This data, from _The_Practicing_Scientist's_Handbook_, Moses, Alfred
>> J.,
>> 1978 edition...
>
>Huh.. That's wayyyy different than what's on the link that Joerg
>provided.
>http://zodiaq.fr/Kapton/en_US/assets/downloads/pdf/CR_H-54506-1.pdf
>
>Table 2
>Kapton Type 150 FCR Polyimide film 1.5 mil : 4400V/mil
>
>Table 1
>Kapton Type 100 CR Polyimide Film 1mil: 7400V/mil
>
>I supppose it depends on the type of polyimide.
>Perhaps the withstand test is differant.
>
>According to (blows dust off book :O === ***)
>Reference Data for Engineers 1993
>Polyimide: 570 V/mil << Not far from your book.
>
>However..
>On ebay item 180431395463 Kapton film
>1mil Kapton + 1.4 mil silicone adhesive has breakdown at 6000V !
>
>Ebay item 330275429870
>1mil Kapton + 2mil mil silicone adhesive has breakdown at 7500V!
>
>Either silicone adhesive has an impressive breakdown or the Kapton
>breakdown is higher than the polyimide spec in text books.

DO NOT confuse nor conflate breakdown ratings with operational ratings.

Breakdown ratings are typically 8 to 10 (or more) times higher than
operating ratings. This applies to most dielectrics whether used for
insulation or to build capacitors.
From: Ecnerwal on 14 Mar 2010 13:31
In article <kr1qp5p3ojq9m40ae5gfh6t5kun8ppgc8m(a)4ax.com>,
"JosephKK"<quiettechblue(a)yahoo.com> wrote:

> On Fri, 12 Mar 2010 15:19:46 -0800, D from BC <myrealaddress(a)comic.com> wrote:
> >On ebay item 180431395463 Kapton film
> >1mil Kapton + 1.4 mil silicone adhesive has breakdown at 6000V !
> >
> >Ebay item 330275429870
> >1mil Kapton + 2mil mil silicone adhesive has breakdown at 7500V!
> >
> >Either silicone adhesive has an impressive breakdown or the Kapton
> >breakdown is higher than the polyimide spec in text books.
>
> DO NOT confuse nor conflate breakdown ratings with operational ratings.
>
> Breakdown ratings are typically 8 to 10 (or more) times higher than
> operating ratings. This applies to most dielectrics whether used for
> insulation or to build capacitors.

True dat. Also true that plain old silicone caulk (aka RTV for room
temperature vulcanizing) has impressive insulating abilities for a
common material, so it would not be surprising if a tape adhesive using
silicone rubber did as well. But confusing breakdown and operational
will lead to getting bitten. For one thing, geometry matters a lot, and
any actual test will have a specific geometry which may or may not look
like your application.

In ASCII art >| is much harder to insulate than )| or ||, for instance.

On a purely "quick test to destruction" (hipot - crank up voltage until
current flows) basis while working on some lab equipment, I got 30KV
from ordinary (well, probably 3M ordinary, but not the high-voltage
version, for sure) heat shrink tubing. Doesn't mean you should design
for that...nor did I measure what thickness it had shrunk to.

There may also be some sort of surface effect with the different unit
breakdown for different thicknesses of kapton. As such, two wraps of
thinner material may be better than one wrap of thicker material (and
that's even more true in the real world where defects and dirt may
happen.)

Generally, anything designed to the hairy edge of breakdown will
eventually blow up, short out, etc. As such, outside of a lab
environment where you need to push the hairy edge and have designed
things to fail gracefully (or at least without killing anyone) when they
do fail, it's best to avoid that.

--
Cats, coffee, chocolate...vices to live by
From: D from BC on 14 Mar 2010 13:31
In article <kr1qp5p3ojq9m40ae5gfh6t5kun8ppgc8m(a)4ax.com>,
quiettechblue(a)yahoo.com says...
>
> On Fri, 12 Mar 2010 15:19:46 -0800, D from BC <myrealaddress(a)comic.com> wrote:
>
> >In article <fa8a0108-f3dc-45a0-bdfa-04d8601470d5
> >@o3g2000yqb.googlegroups.com>, whit3rd(a)gmail.com says...
> >>
> >> On Mar 11, 4:27�pm, Joerg <inva...(a)invalid.invalid> wrote:
> >> > D from BC wrote:
> >> > > I'm trying to find the breakdown V for
> >> > > 0.0028 inches of PTFE (teflon) and 0.004 inches (~100um) of Kapton.
> >>
> >> Textbook value for PTFE aka TFE aka Teflon is 480 volts per milli-
> >> inch,
> >> and for polyimide/Kapton is 560 volts per milli-inch.
> >>
> >> That assumes pure material, clean surfaces, and no conduction
> >> enhancement from ambient light...
> >> This data, from _The_Practicing_Scientist's_Handbook_, Moses, Alfred
> >> J.,
> >> 1978 edition...
> >
> >Huh.. That's wayyyy different than what's on the link that Joerg
> >provided.
> >http://zodiaq.fr/Kapton/en_US/assets/downloads/pdf/CR_H-54506-1.pdf
> >
> >Table 2
> >Kapton Type 150 FCR Polyimide film 1.5 mil : 4400V/mil
> >
> >Table 1
> >Kapton Type 100 CR Polyimide Film 1mil: 7400V/mil
> >
> >I supppose it depends on the type of polyimide.
> >Perhaps the withstand test is differant.
> >
> >According to (blows dust off book :O === ***)
> >Reference Data for Engineers 1993
> >Polyimide: 570 V/mil << Not far from your book.
> >
> >However..
> >On ebay item 180431395463 Kapton film
> >1mil Kapton + 1.4 mil silicone adhesive has breakdown at 6000V !
> >
> >Ebay item 330275429870
> >1mil Kapton + 2mil mil silicone adhesive has breakdown at 7500V!
> >
> >Either silicone adhesive has an impressive breakdown or the Kapton
> >breakdown is higher than the polyimide spec in text books.
>
> DO NOT confuse nor conflate breakdown ratings with operational ratings.
>

That's what happened. I went for the short term spec (V breakdown). When
I should be looking at the long term spec (hours to insulator
deterioration by corona).

The text books list operational.

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