Solid dielectrics and space charge

Device reliability in electrical engineering is largely determined by the durability of insulation properties. Failures in electrical equipment are often due to dielectric breakdown of the insulators. These phenomena occur at electric fields much lower than the breakdown fields measured in the laboratory on the insulators themselves or on system models. This is largely due to the electrical ageing of insulating materials, a generic term that covers all the mechanisms by which the electrical characteristics of materials evolve over time under the action of system operating stresses. In fact, it can be assumed that the insulation's breaking range decreases with the duration of the stresses applied.

After a brief review of insulator failure modes, we'll focus more specifically on materials used under high electric field conditions. Under these severe conditions of use, recent designs suggest that internal electrical charges (also known as space charges) are involved in aging and breakdown phenomena. It is therefore essential to characterize the insulator with regard to these charges.

After describing the mechanisms by which charges are generated, we'll consider their influence on electric field distribution.

We will then discuss techniques for the quantitative assessment of internal loads and the study of their spatial distribution.

Breakdown involves the propagation of electrical trees, the main characteristics of which are described below.