Dielectric - Theoretical basis

Before tackling the study of insulators and insulation systems, engineers need to familiarize themselves with the basic concepts and most useful theories, so they can appreciate the exact meaning of the electrical properties that define an insulator, and make effective use of the theories they apply. Limiting itself to a presentation of the essential concepts in the field of dielectrics, this article covers the following points:

• the polarization of dielectrics, which in practice is expressed by a fundamental property, namely relative permittivity ;

• dielectric losses, which manifest themselves in a material as absorption currents under DC voltage; under AC voltage, they are expressed quantitatively by the tangent of the loss angle (tan δ) measured, if necessary, over a wide frequency range;

• relaxation phenomena in insulating liquids, for which the Pellat-Debye theory provides the simplest representation;

• interfacial polarization phenomena, of which Maxwell and Maxwell-Wagner theories provide an approximate but sufficient representation to explain the behavior of a combination of materials with different permittivities and conductivities.

Conduction current mechanisms will be dealt with in a separate article.