Wikipedia
In physics, the term dielectric strength has the following meanings:
- Of an insulating material, the maximum electric field that a pure material can withstand under ideal conditions without breaking down (i.e., without experiencing failure of its insulating properties).
- For a specific configuration of dielectric material and electrodes, the minimum applied electric field (i.e., the applied voltage divided by electrode separation distance) that results in breakdown.
The theoretical dielectric strength of a material is an intrinsic property of the bulk material and is independent of the configuration of the material or the electrodes with which the field is applied. This "intrinsic dielectric strength" corresponds to what would be measured using pure materials under ideal laboratory conditions. 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 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
Usage examples of "dielectric strength".
To achieve a high capacitance, you want the dielectric to be as thin a sheet as its dielectric strength permits, and you want to maximize the effective cross section (the surface area of one flat dielectric sheet, times the number of those sheets).
Think of getting condenser plates so close togetherperhaps only one or two molecules apartand still have a dielectric strength capable of resisting thousands of volts!
Think of getting condenser plates so close together-perhaps only one or two molecules apart-and still have a dielectric strength capable of resisting thousands of volts!