My understanding is Scientific Wild Ass Guess
Best Regards, Mike From: Patrick <[email protected]> Sent: Tuesday, June 25, 2024 6:51 AM To: [email protected] 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 <[email protected]<mailto:[email protected]>> wrote: Silly wild ass guess is what I mean when I use that acronym. -- Ken Javor Ph: (256) 650-5261 From: "James Pawson (U3C)" <[email protected]<mailto:[email protected]>> Reply-To: "James Pawson (U3C)" <[email protected]<mailto:[email protected]>> Date: Tuesday, June 25, 2024 at 7:29 AM To: <[email protected]<mailto:[email protected]>> Subject: Re: [PSES] dielectric strength question Could someone define the acronym SWAG in this context please? Something With Air Gap? 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From: Adam Dixon <[email protected]<mailto:[email protected]>> Sent: Tuesday, June 25, 2024 1:24 PM To: [email protected]<mailto:[email protected]> 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&type=pdf&doi=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 [email protected]<mailto:[email protected]> On Mon, Jun 24, 2024 at 11:00 PM Patrick <[email protected]<mailto:[email protected]>> 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 <[email protected]<mailto:[email protected]>> 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 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 10.0 2.98 Mica 0.01 200 0.10 115 1.00 61 Thanks, and best regards, Rich ________________________________ This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. 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