Breakdown Field Strength
The field strength at which breakdown occurs depends on the respective geometries of the dielectric (insulator) and the electrodes with which the electric field is applied, as well as the rate of increase at which the electric field is applied. Because dielectric materials usually contain minute defects, the practical dielectric strength will be a fraction of the intrinsic dielectric strength of an ideal, defect-free, material. Dielectric films tend to exhibit greater dielectric strength than thicker samples of the same material. For instance, the dielectric strength of silicon dioxide films of a few hundred nm to a few μm thick is approximately 0.5GV/m. However very thin layers (below, say, 100 nm) become partially conductive because of electron tunneling. Multiple layers of thin dielectric films are used where maximum practical dielectric strength is required, such as high voltage capacitors and pulse transformers. Since the dielectric strength of gases varies depending on the shape and configuration of the electrodes, it is usually measured as a fraction of the dielectric strength of Nitrogen gas.
Dielectric strength (in MV/m, or 106 Volt/meter) of various common materials:
Substance | Dielectric Strength (MV/m) |
---|---|
Helium (relative to nitrogen) | 6999150000000000000 0.15 |
Air (relative to nitrogen) | 7000300000000000000 3.0 |
Alumina | 7001134000000000000 13.4 |
Window glass | 7001118000000000000 9.8 - 13.8 |
Silicone oil, Mineral oil | 7001125000000000000 10 - 15 |
Benzene | 7001160000000000000 163 |
Polystyrene | 7001197000000000000 19.7 |
Polyethylene | 7001203000000000000 18.9 - 21.7 |
Neoprene rubber | 7001216500000000000 15.7 - 26.7 |
Distilled Water | 7001300000000000000 65 - 70 |
High Vacuum (field emission limited) | 7001300000000000000 20 - 40 (depends on electrode shape) |
Fused silica | 7001325000000000000 25–40 at 20 °C |
Waxed paper | 7001500000000000000 40 - 60 |
PTFE (Teflon, Extruded ) | 7001600000000000000 19.7 |
PTFE (Teflon, Insulating Film) | 7001600000000000000 60 - 173 |
Mica | 7001450000000000000 118 |
Read more about this topic: Dielectric Strength
Famous quotes containing the words breakdown, field and/or strength:
“The chief lesson of the Depression should never be forgotten. Even our liberty-loving American people will sacrifice their freedom and their democratic principles if their security and their very lives are threatened by another breakdown of our free enterprise system. We can no more afford another general depression than we can afford another total war, if democracy is to survive.”
—Agnes E. Meyer (18871970)
“The little toy dog is covered with dust,
But sturdy and stanch he stands;
And the little toy soldier is red with rust,
And the musket moulds in his hands.
Time was when the little toy dog was new,
And the soldier was passing fair;
And that was the time when our Little Boy Blue
Kissed them and put them there.”
—Eugene Field (18501895)
“Out of the mouth of babes and sucklings hast thou ordained strength because of thine enemies, that thou mightest still the enemy and the avenger.”
—Bible: Hebrew Psalms, 8:2.