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 maximum electric stress the dielectric material can withstand without breakdown

The theoretical dielectric strength of a material is an intrinsic property of the bulk material and is 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 from background radiation 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.

Factors affecting apparent dielectric strength

• it decreases slightly with increased sample thickness. (see "defects" below)
• it decreases with increased operating temperature.
• it decreases with increased frequency.
• for gases (e.g. nitrogen, sulfur hexafluoride) it normally decreases with increased humidity.
• for air, dielectric strength increases slightly as humidity increases