Dielectric Materials for Electrical Engineering

Chapter 9

Models for Ageing of Electrical Insulation: Trends and Perspectives 1

9.1. Introduction

In the world of electrical engineering, device reliability is widely determined by the durability of the insulating materials’ properties. Electrical equipment failure is often associated with the dielectric breakdown phenomena of the insulation. These phenomena can occur for electrical fields clearly weaker than the estimated breakdown field. This is widely due to the insulating materials’ electrical ageing, a generic term which groups together all of the mechanisms by which the general characteristics of materials, and particularly their electrical properties, evolve over time under the action of working stresses.

Solid insulating materials have been introduced in a wide range of electrical equipment, from transport and distribution to the use of electrical energy. In particular, polymers are widely used for cables, capacitors, alternators, transformers and motors. We also find them in electronic devices, i.e. as coatings and in power components [LAU 99].

Although the main function of the polymer is to maintain electrical insulation, it also needs to have a good resistance to mechanical and thermal stresses. The understanding of ageing processes leading to either the loss, reversible or not, of functional properties, or to the dielectric breakdown of organic solid insulating materials must allow the behavior of this type of material to be predicted, according to the system’s life ...