Talk:Dielectric strength

Untitled

In the table, what are the electrode sizes?. We need this info to make real sense of he figures.--Light current 02:58, 21 March 2006 (UTC)

Is it clear that there should be a difference - whether discussing a pure material substance or a configuration of materials and electrodes - between: the maximum electric field strength that it can withstand without breakdown; and the minimum electric field that does produce breakdown? Can someone clarify whether there is a deliberate purpose in using these two different ways to expression the concept of a threshold value (of the field), when giving the two different meanings of dielectric strength. Or is this different way of expressing it purely incidental? —Preceding unsigned comment added by 138.40.94.135 (talk) 23:03, 29 November 2007 (UTC)

I think that there is a difference between the electric field that produces discharge instantaneously upon application and the electric field that will eventually produce a discharge; the latter should be smaller. Probably the latter is the maximum electric field strength that does not produce breakdown. —Preceding unsigned comment added by 193.254.231.85 (talk) 12:00, 13 December 2007 (UTC)

Major issues with values (AC vs DC, thickness dependence, etc.)

The table with values of dielectric strength does not specify if it is AC or DC voltage, niether the thickness of the sample. Typically there can be a factor of 4 difference between AC and DC for solid materials, with DC resulting in the highest value. For gases there is normally no difference between AC and DC if you take the "peak" AC voltage, but the most common case is to list the rms value, hence making the AC/DC distinction important also here. Looking at the table Air is listed as 3 kV/mm, which is a DC or peak-AC value at standard athomspheric conditions, while the rms value is about 2.1 kV/mm. However for many of the other materials it seems that AC-rms values are used based on the sources and other literature values.

Another major issue is that the kV/mm (same as MV/m) value is dependent on sample thickness for solid materials. For example thin plastic films such as used in capactitors etc. can handle up to 300 kV/mm, while if exactly the same material and grade is made into a thick plate of a few mm, such as used in high voltage cables, it can only handle some 20 kV/mm. For solid materials the dielectric strength in kV/mm is typically inversely proportional to the square root of the thickness. The cause for this is still ongoing research involving space charges etc. For gases the gap distance and pressure works into the Paschen law in how it affects the dielectric strength, hence very different compared to solid materials.

I therefore suggest that the table should only list AC-rms values (unless otherwise specified) as this is what ASTM D-149 and similar european standards specify. The table should also list values for 1 mm thick samples, or at least a recalculated eqvivilent for 1 mm thickness, with the original value as a comment. Without accounting for these aspects its impossible to compare materials. EV1TE (talk) 09:41, 30 April 2020 (UTC)

Dielectric strength of air

The link given for this value takes you to a personal site about uh "alternative physics" for lack of a better term. Looks legitimate at first, but if you poke around long enough you'll see what I mean. The length of air sparks is an important way for early scientists to measure high voltages, I think we need a better source here! Also, I agree with below, would also expect the value to be lower at higher humidities.-Grant —Preceding unsigned comment added by 108.26.105.165 (talk) 07:36, 28 March 2011 (UTC)

A 3MV/m (or 3KV/mm) doesn't quite make sense to me. It seems that the humidity of the air is a major parameter for this value. Is 3KV/mm supposed to be in dry air? What about 40%, 50% and 60% humidity levels? —Preceding unsigned comment added by 66.84.205.186 (talk) 14:46, 3 November 2008 (UTC)

Units not correct? (at least with some values for dielectric strength)

The wikipedia page for fused silica gives a DS of 4.7-6.7MV/cm, that translates into 47-57MV/m! Also for (virginal) Teflon (PTFE) the dielectric strength should be on the order of 20MV/m...(at least approximately). As I write these lines it appears to me, that with respect to PTFE a differentiation between virginal and other grades would be useful, because the DS depends strongly on the exact material composition and the production process...

composition and production process do make a difference, but it would be impractical to list all of those in detail as there are too many possibilities. instead the table is more of a general guide for the values of the materials that are commonly produced. Hrneo (talk) 19:04, 31 December 2009 (UTC)

You are right values must be revised fused silica is 400kv/cm others seem to be wrong too —Preceding unsigned comment added by 78.61.66.75 (talk) 04:38, 2 December 2009 (UTC)

What's with thin film SiO2 being quoted as having an "exceptionally strong" dielectric strength of .1MV/m, less than the bulk??? —Preceding unsigned comment added by 128.30.6.175 (talk) 06:30, 5 December 2009 (UTC)

I have corrected some of the values for this from the references provided, but it should be further improved as it depends on temperature and frequency and the values are for different temperatures and frequencies. this table needs to be re-written from a good reference book. for now i will leave a "please check" on the whole table Hrneo (talk) 18:42, 31 December 2009 (UTC)

I have corrected some values using this page, which is a copy of reference #2.

Also, i removed the entry for SiO2 in semiconductors since thin films are a special case that is discussed in the previous paragraph. Hrneo (talk) 15:48, 20 July 2011 (UTC)

Alumina can be 1,100 MV/m rather than 13.4. Ywaz (talk) 16:16, 5 October 2011 (UTC)

There really is some confusion with the table. The value for Helium is the relative difference to the dieelectric strength of Nitrogen, i.e. has no unit since it is a fraction. Tables of these ratios can be found across the internet and are quite common. The "corrected" value for air is the absolute value of the dielectric strength given in some sources for standard conditions 20°C, 50%r.h., 1013 hPa (Depending on the source values range from about 2.5kV/mm to 3kV/mm). I don't know the values for the remaining tbale, i.e. I don't know if there is a further mix-up of absolute values and ratios relative to nitrogen. Someone with enough time and expertise should go through the table and make it at least consistent. 213.164.66.20 (talk) 08:56, 11 October 2012 (UTC)

Problem with table sort

In the table, the column labeled "Dielectric Strength (MV/m)" does not sort correctly because the number specified in {{ntsh}} are not correct in some cases. –droll [chat] 20:05, 31 August 2011 (UTC)

Still a problem in 2018. ... adjusted the ntsh values and added one to fix. - Rod57 (talk) 10:49, 25 March 2018 (UTC)

What does this mean ?

"the maximum electric stress the dielectric material can withstand without breakdown".

Does 'electric stress' mean the same thing as 'electric field strength' ? If so why is this given as a separate definition ? If not, what does it mean ? And how does the meaning of 'electric field strength' differ from 'electric field' (1st 2 definitions) ? — Preceding unsigned comment added by 82.32.50.178 (talk) 06:57, 12 June 2012 (UTC)

Good point. "Electric stress" and "electrical field" are synonymous when discussing dielectric breakdown under DC and low-frequency AC excitation. In the first definition, "electrical field strength" should be changed to "electric field" to improve accuracy. The first definition is more of a physics definition ("intrinsic dielectric strength") for pure materials under ideal conditions. The second definition is a more practical definition from an engineering, material standards, and testing perspective that defines specific repeatable/standardized electrode materials, electrode shape, separation distance, applied voltage/waveform and other pertinent conditions. The combination of the first two definitions makes the third definition redundant. I've changed the article to reflect this. BTW, in the industry, electrical stress testing often combines electrical stress with other stressing factors, such as thermal, humidity, temperature cycling, etc. to insure that a dielectric will perform under expected worse-case environmental conditions.Bert (talk) 15:04, 5 September 2013 (UTC)

AC measurements and rms values

Another aspect that is not mentioned in the article is that the dielectric strength is most often measured using AC, and the noted breakdown values are in MV/m rms. This is at least true for solid materials measured according to ASTM D 149 and IEC 60243-1, I am not sure about the values for the gases since they are sometimes measured using DC and would therefore not be comparable. It would be good if someone could confirm this and add something to the article, otherwise the values might be off by up to 41 % depending on what you use them for. EV1TE (talk) 16:20, 5 September 2017 (UTC)

Dead links

I found that the reference for high vacuum dielectric strength (num [9]) corresponds to a broken link. The only other source I could find is a researchgate answered question giving a rough value of 200 kV/cm (https://www.researchgate.net/post/What_is_dielectric_strength_of_vacuum), but I dont think this can be used as a reference.

Mechanism and prediction

Is the breakdown mechanism always/usually avalanche breakdown ? and can it be predicted eg from bandgap and/or other characteristics of the material ? - Rod57 (talk) 10:54, 25 March 2018 (UTC)

Schwinger limit

The Schwinger limit is a field-strength value, but is not relevant here. Also the editor associated with that had seeded other pages with nonsense in the same timeframe. https://en.wikipedia.org/wiki/Special:Contributions/70.99.104.234 https://en.wikipedia.org/w/index.php?diff=583741154&title=Dielectric_strength 98.198.244.185 (talk) 16:30, 28 April 2018 (UTC)

What is dielectric film?

The article uses the term "dielectric film" twice and claims they have properties that seem counterintuitive. Is "dielectric film" a special form or type of material? In the world of dielectric strength do researchers make a distinction between a cube of material, a sheet of the same material, a "film" of that material, and is there a name for when that material is tens or even ones of atoms thick or is it still regarded as a "film?"

For example, the article says "Dielectric films tend to exhibit greater dielectric strength than thicker samples of the same material" without additional explanation other than "the dielectric strength of silicon dioxide films of thickness around 1 μm is about 0.5 GV/m. However very thin layers (below, say, 100 nm) become partially conductive because of electron tunneling."

That "explanation" is confusing. While it says the normal dielectric strength of silicon dioxide film is about 0.5 GV/m it does not say what the dielectric strength of much thinner sample of silicon dioxide is. It does say that a much thinner sample is "partially conductive." Is the thicker sample of silicon dioxide more or less conductive than a thin sample? The reader is not informed. It's like saying apples are a good food because of oranges.

The article also has that the dielectric strength of a material "decreases with increased sample thickness". There is no explanation of why that is the case. The article should better explain that while the dielectric strength of an insulator may be falling as more of that material is added to a sample that it falls at a lower rate than the increase in breakdown voltage resulting from having more material. A thicker insulator will insulate better than a thin one of the same material even though that thicker material may have a lower volts per meter of material dielectric strength value. --Marc Kupper|talk 15:44, 30 June 2021 (UTC)