Measuring the characteristics of solid insulating materials

All electrical and electronic equipment is made up of a judicious combination of conductive materials, which transport electrical energy (or information) to where it's needed, and insulating materials, which prevent it from being lost by taking the "shortest" path from one potential to another. In addition to their primary function of preventing the flow of current between conductors, solid insulators also have the role of mechanically maintaining conductors in predetermined conditions.

In some cases, the quantity of solid insulating materials used is reduced to the extreme: for example, in the case of overhead power lines with bare conductors.

However, when it comes to reducing the size of a piece of equipment (a constant concern today), conductors need to be brought closer together, and therefore held rigidly in place to prevent them from coming into contact under their own weight, deformation, forces external to the equipment or internal electrodynamic forces. Solid insulating materials can be used alone (as, for example, in the case of extruded synthetic cable insulation), in combination with several solids (windings made of enamelled wire impregnated with thermosetting resin) or in combination with a solid and a liquid (mineral oil-impregnated paper insulation for high-voltage transformers). In the latter two cases, we speak of an insulation system.

Since the essential role of insulators is to act as a barrier, we're primarily interested in their electrical properties.

Since no insulator is perfect, the first step is to study conduction mechanisms in solid insulators, leading to the concepts of insulation resistance and resistivities 1 .

Increasing the value of the electric field applied to an insulator leads to an irreversible destructive mechanism known as dielectric breakdown 2