Breakdown, Dielectric

The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Breakdown, Dielectric

 

a sharp reduction in the electric resistance (an increase in the current density j) of a dielectric that occurs when the intensity of the applied electric field Eap reaches a certain value, usually approximately 105–106volts/cm. It is associated with the formation in a dielectric crystal of a conducting path in which the current density is substantially higher than the average for the specimen. The Joule heat generated because of the high-density current in the path leads to the destruction of the material, including melting; the appearance of an air channel as a result of volatilization; and the extensive formation of crystal defects, or cracking. Thus, dielectric breakdown is an irreversible phenomenon.

In an ideal, homogeneous, crystalline dielectric, a conducting path is formed as a result of a current pinch, which unavoidably arises when the differential electric resistance ρ = ∂E/∂j of the dielectric becomes negative. In actual solid dielectrics, the breakdown occurs at values of E lower than those in the ideal case because various inhomogeneities facilitate its onset.

Breakdown in fluid dielectrics is also due to the formation of a conducting path; Eap depends on the purity of the fluid.

REFERENCES

See references under DIELECTRICS.

A. P. LEVANIUK

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.