Dielectric strength

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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.

Breakdown field strength

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 of various common materials
Material Dielectric Strength (MV/m)
Air 3
Bakelite 24
Neoprene rubber 12
Nylon 14
Paper 16
Polystyrene 24
Pyrex glass 14
Quartz 8
Silicone oil 15
Strontium titanate 8
Teflon 60

**Dielectric strength of various common materials**
Material	Dielectric Strength (MV/m)
Air	3
Bakelite	24
Neoprene rubber	12
Nylon	14
Paper	16
Polystyrene	24
Pyrex glass	14
Quartz	8
Silicone oil	15
Strontium titanate	8
Teflon	60

External links

[Dielectric Strength and Insulation Materials of Mineral Insulated Cable]

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