The characterisation and comparison of different materials using the thermal step method

This work focuses on the performances of different materials submitted to high electric fields in particular conditions. The Thermal Step Method (TS) allows one to determine and to localise the charge density in solid dielectrics. This kind of characterisation allows one to compare the insulating structures to choose the best one for a particular use and so to improve the reliability and the lifetime of electrical systems. The Thermal Step Method has already been used on polymers, such as polyethylene and PVC. In this study the method permits the characterisation of new materials which have different interesting properties for industrial use, such as polyetherimides (PEI). The measurements we made revealed interesting mechanical, thermal and electrical properties of the PEI. This study gives space charge distributions in the different high temperature PEIs, submitted to identical electrical and thermal stresses. The results obtained allow one to optimise the insulating structure for a particular application