Dielectric Materials for Electrical Engineering

Chapter 14

The Thermal Step Method for Space Charge Measurements 1

14.1. Introduction

The principle of non-destructive methods allowing the measurement of space charges is to detect the charges and access their distribution without modifying the electrical state of the material. The principle is therefore to make the influence charges vary at the electrodes with the aid of a non-homogeneous excitation in time and in space. The excitation can have several origins (thermal, mechanical, electrical, etc.). According to the experimentation conditions, we obtain in the external circuit linking the electrodes a signal whose analytical expression is a function of the volume charge density distribution. From this signal, the internal electric field and charge distributions can be determined after adequate processing.

Historically, a thermal stimulus was used at the Laboratoire d’electrotechnique de Montpellier(LEM). Indeed, the Thermal Step Method (TSM) has been developed at the LEM since 1986 and is based on the application of a temperature step to an insulating sample. In this chapter, after describing the principle of this technique, we shall present in detail its conditions of use, the numerical resolution methods allowing a space charge density distribution to be taken from the experimental signal, as well as the method’s recent evolutions and perspectives related to its application.

14.2. Principle of the thermal step method (TSM)

This method originally developed in 1987 [TOU 87], ...