Dielectric Strength


From Xmultiple Engineering Dept.

Dielectric Strength Overview

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 dependent on the configuration of the material or the electrodes with which the field is applied. The "intrinsic dielectric strength" is 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.

Dielectric Strength Of Connectors

Dielectric strength is a measurement that is related with the insulating material in a connector. An insulating material behaves like an insulator only up to a certain higher voltage ranges, after that dielectric breakdown occurs and the material suddenly starts conducting electricity like a conductor. Dielectric strength is the maximum voltage up to which the insulating material can keep its insulating property without causing dielectric breakdown. It is otherwise called Dielectric withstanding voltage, Breakdown voltage, Withstanding voltage, Voltage proof etc. Operating the connector above this range may cause dielectric breakdown. Hence this parameter is very important in high voltage applications. The Dielectric Strength Voltage of an unshielded RJ male plug is typically 1000V AC (RMS 60Hz).

Factors Affecting Dielectric Strength With Connectors and Components

1. Increases slightly with increased thickness.
2. Decreases with increased operating temperature.
3. Decreases with increased frequency.

Breakdown Field Strength

The field strength at which breakdown occurs depends 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 of an ideal, defect-free, material. Dielectric films tend to exhibit greater dielectric strength than thicker samples of the same material. For instance, the dielectric strength of silicon dioxide films of a few hundred nm to a few £gm thick is approximately 0.5GV/m. However very thin layers (below, say, 100 nm) become partially conductive because of electron tunneling. Multiple layers of thin dielectric films are used where maximum practical dielectric strength is required, such as high voltage capacitors, and pulse transformers.

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