Dielectric Materials for Electrical Engineering

Chapter 12

FLIMM and FLAMM Methods: Localization of 3-D Space Charges at the Micrometer Scale 1

12.1. Introduction

Polymer materials are widely used as basic insulator structures in many devices in electrical engineering, such as high voltage cables, transformers or capacitors. They have to resist strong voltage gradients, sometimes up to a few tens of kV/mm. Furthermore, engineers have to take into account important internal and local electric fields due to the presence of space charges which are trapped within the materials. These mainly result from the dissociation of electrically neutral species, charge injections at the surface of the insulator, or due to the orientation of the electric dipole.

In these zones affected by a strong local electric field, dissipative energy phenomena can lead to a premature ageing of the material, and potentially to a faster than expected breakdown of the dielectric. For these reasons, many efforts have been implemented over the past ten years in order to make more reliable the detection and characterization of these charges.

Several space charge measurement techniques have been developed [TAK 99], mostly non-destructive thermal ones. However, these methods present a very poor spatial resolution.

With an aim to increase this resolution, we proposed to develop a technique based on the use of focused thermal excitation as a source, allowing the characterization of space charge profiles at the scale of a few tens of micrometers.

For this purpose, ...