What causes dielectric breakdown?

Question

Can any insulator start to conduct current after high voltage breaks it down?

Answer 1

Dielectric breakdown occurs when a high electric field accelerates electrons which happen to tunnel into the conduction band to energies where they can ionize other atoms in an insulator. Since there are more carriers released this way, the conductivity increases dramatically after break down.

While not completely understood, it is implied that there must be some damage at the atomic level for the breakdown to be irreversible.

Answer 2

If the voltage gets high enough, nearly every insulator will flash over.

Heat is one condition that ages insulation and causes it to deteriorate.

In the case of underground cable, electrical stress points can cause insulation failure. Tiny nicks in the conductor or insulation cause concentrated electric fields that cascade the problem until you have a cable fault. Cables and terminations are carefully made with semi-conducting layers that help "smooth out" these stresses.

In the case of insulating fluids such as mineral oil, water will reduce the dielectric strength. Carbon due to under-oil arc quenching can also eventually reduce the fluids insulating properties.

Nearly all practical insulators have some type of leakage current. Fortunately it is measured in micro-amps or smaller units.

Answer 3

Dielectric Break

Answer 4

Insulator have comparitively more forbidden gap ie. 6-7eV.
When there is high voltage applied to it electron from
valence band jumps into conduction band because of which
little conductivity is observed.
Concept of conduction band & valence band introduced by
Molecular Orbital Theory plays important role.
For referance read Engineering Chemistry by Malvino & Paulo.

Answer 5

Heat and over voltage will cause the dielectric to break down. And time, as it gets older, it will break down. And yes allow current to pass.

Answer 6

you need to remember that C = (8.854E-12 F/M)* 3E6 (V/M) / (2.4^2*pi M^2) / (0.0007 M) = 1.602E-10 / 0.0007 M = 2.29E-7 F = 2.29E-7 C/V *(2.4^2*pi M^2) = (8.854E-12 F/M)* 3E6 (V/M) + V = dielectric breakdown constant thing, which I think is 3E6 V/M * Q = CV = 2.29E-7.