Dielectric strength

Source: Wikipedia, the free encyclopedia.

In physics, the term dielectric strength has the following meanings:

The theoretical

disruptive discharge
through the material. In a solid material, a breakdown event severely degrades, or even destroys, its insulating capability.

Electrical breakdown

electrical insulator
.

However when a large enough electric field is applied to any insulating substance, at a certain field strength the concentration of charge carriers in the material suddenly increases by many orders of magnitude, so its resistance drops and it becomes a conductor. This is called electrical breakdown. The physical mechanism causing breakdown differs in different substances. In a solid, it usually occurs when the electric field becomes strong enough to pull outer valence electrons away from their atoms, so they become mobile. The field strength at which break down occurs is an intrinsic property of the material called its dielectric strength.

In practical

electric circuits electrical breakdown is often an unwanted occurrence, a failure of insulating material causing a short circuit, resulting in a catastrophic failure of the equipment. The sudden drop in resistance causes a high current to flow through the material, and the sudden extreme Joule heating
may cause the material or other parts of the circuit to melt or vaporize explosively. However, breakdown itself is reversible. If the current supplied by the external circuit is sufficiently limited, no damage is done to the material, and reducing the applied voltage causes a transition back to the material's insulating state.

Factors affecting apparent dielectric strength

  • It may vary with sample thickness.[1] (see "defects" below)
  • It may vary with operating temperature.
  • It may vary with frequency.
  • For gases (e.g. nitrogen, sulfur hexafluoride) it normally decreases with increased humidity as ions in water can provide conductive channels.
  • For gases it increases with pressure according to Paschen's law
  • For air, dielectric strength increases slightly as the absolute humidity increases but decreases with an increase in relative humidity[2]

Break down field strength

The field strength at which break down occurs depends on the respective geometries of the dielectric (insulator) and the electrodes with which the

nitrogen gas
.

Dielectric strength (in MV/m, or 106⋅volt/meter) of various common materials:

Substance Dielectric strength
(MV/m) or (Volts/micron)
Helium (relative to nitrogen)[5]
[clarification needed]
0.15
Air[6]
3
Sulfur hexafluoride[5] 8.5–9.8
Alumina[5]
13.4
Window glass[5] 9.8–13.8
Borosilicate glass[5] 20–40
Silicone oil, mineral oil[5][7] 10–15
Benzene[5] 163
Polystyrene[5] 19.7
Polyethylene[8] 19–160
Neoprene rubber[5] 15.7–26.7
Distilled water[5] 65–70
Beryllium oxide[9] 27-31
High vacuum (200 μPa)
(field emission limited)[10]
20–40
(depends on electrode shape)
Fused silica[5]
470–670
Waxed paper[11] 40–60
PTFE (Teflon, extruded )[5]
19.7
PTFE (Teflon, insulating film)[5][12]
60–173
PEEK
(Polyether ether ketone)
23
Mica[5] 118
Diamond[13] 2,000
PZT
10–25[14][15]
Perfect vacuum
1012

Units

In

centimeter
(V/cm), megavolts per meter (MV/m), and so on.

In

mil (a mil is 1/1000 inch).[16]
The conversion is:

See also

References

  1. ^ DuPont Teijin Films (2003). "Mylar polyester film" (PDF).
  2. S2CID 108697400
    .
  3. ^ Bartzsch, Hagen; Glöß, Daniel; Frach, Peter; Gittner, Matthias; Schultheiß, Eberhard; Brode, Wolfgang; Hartung, Johannes (2009-01-21). "Electrical insulation properties of sputter-deposited SiO2, Si3N4 and Al2O3 films at room temperature and 400 °C". Physica Status Solidi A. 206 (3): 514–519.
    S2CID 93228294
    .
  4. ^ Lyon, David; et al. (2013). "Gap size dependence of the dielectric strength in nano vacuum gaps". IEEE. 20 (4): 1467–1471.
    S2CID 709782
    .
  5. ^ a b c d e f g h i j k l m n CRC Handbook of Chemistry and Physics
  6. ^ Hong, Alice (2000). Elert, Glenn (ed.). "Dielectric Strength of Air". The Physics Factbook. Retrieved 2020-06-18.
  7. ^ Föll, H. "3.5.1 Electrical Breakdown and Failure". Tf.uni-kiel.de. Retrieved 2020-06-18.
  8. ^ Xu, Cherry (2009). Elert, Glenn (ed.). "Dielectric strength of polyethylene". The Physics Factbook. Retrieved 2020-06-18.
  9. ^ "Azom Materials - Beryllium Oxide Properties". azom.com. Retrieved 2023-12-05.
  10. ^ Giere, Stefan; Kurrat, Michael; Schümann, Ulf. HV dielectric strength of shielding electrodes in vacuum circuit-breakers (PDF). 20th International Symposium on Discharges and Electrical Insulation in Vacuum. Archived from the original (PDF) on 2012-03-01. Retrieved 2020-06-18.
  11. ^ Mulyakhova, Dasha (2007). Elert, Glenn (ed.). "Dielectric strength of waxed paper". The Physics Factbook. Retrieved 2020-06-18.
  12. ^ Glenn Elert. "Dielectrics - The Physics Hypertextbook". Physics.info. Retrieved 2020-06-18.
  13. ^ "Electronic properties of diamond". el.angstrom.uu.se. Retrieved 2013-08-10.
  14. ^ Moazzami, Reza; Chenming Hu; William H. Shepherd (September 1992). "Electrical Characteristics of Ferroelectric PZT Thin Films for DRAM Applications" (PDF). IEEE Transactions on Electron Devices. 39 (9): 2044. .
  15. ^ B. Andersen; E. Ringgaard; T. Bove; A. Albareda & R. Pérez (2000). "Performance of Piezoelectric Ceramic Multilayer Components Based on Hard and Soft PZT". Proceedings of Actuator 2000: 419–422.
  16. ^ For one of many examples, see Polyimides: materials, processing and applications, by A.J. Kirby, google books link

External links