Dielectric strength
In
physics, the term
dielectric strength has the following meanings:
*Of an insulating material, the maximum electric
field strength that it can withstand intrinsically without breaking down,
i.e., without experiencing
failure of its insulating properties.
*For a given configuration of dielectric material and electrodes, the minimum
electric field that produces breakdown.
The theoretical
dielectric strength of a material is an intrinsic property of the bulk material and is not dependent on the configuration of the material or the electrodes with which the field is applied. At breakdown, the electric field frees bound electrons. If the applied electric field is sufficiently high, free electrons may become accelerated to velocities that can liberate additional electrons during collisions with neutral atoms or molecules in a process called
avalanche breakdown. Breakdown occurs quite abruptly (typically in
nanoseconds)., resulting in the formation of an electrically conductive path and a
disruptive discharge through the material. For solid materials, a breakdown event severely degrades, or even destroys, its insulating capability.
The field strength at which breakdown occurs in a given case is dependent 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 seen for ideal, defect free, material. Dielectric films tend to exhibit greater dielectric strength than thicker samples of the same material. Multiple layers of thin dielectric films are used where maximum practical dielectric strength is required, such as high voltage
capacitors and pulse
transformers.
*
Dielectric Strength and Insulation Materials of Mineral Insulated Cable
