What is dielectric strength?

The dielectric strength of a material is a measure of the electrical strength of an insulator. It is defined as the maximum voltage required to produce a dielectric breakdown through the material and is expressed in terms of Volts per unit thickness. The higher the dielectric strength of a material the better an electrical insulator it makes.

IEC 60243 is a standard referred to for a method of testing dielectric strength of a material. The test is conducted in either air or oil and involves placing the test material between two electrodes and increasing the voltage between the electrodes until an electrical burn-through punctures the sample or decomposition occurs. Usually the specimen is between 0.8 and 3.2mm thick. Samples which are over 2mm in thickness are usually tested in oil to prevent flash over before breakdown.

 

 

The dielectric strength is then calculated by dividing the breakdown voltage by the thickness of the sample.

Most plastics have good dielectric strengths in the order of 10 to 30kV/mm.

Examples:

Low Density Polyethylene LDPE = 27kV/mm

Polypropylene PP = 22kV/mm

Polyvinylchloride PVC = 14kV/mm

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