Two techniques for an optimal characterisation of PTFE: the thermal step method and the thermally stimulated discharge currents

In our day and age, space charge measurements are considered as essential for the characterisation of insulators. For this purpose, we used the thermal step method (TSM) to obtain remnant electric field and space charge distributions in PTFE samples. To complete characterisations, we coupled the TSM with thermally stimulated discharge current (TSDC) measurements, which give the charge detrapping phenomena. Two PTFE samples are studied : a normal one and a one filled with CaF₂. The results showed the importance of the fabrication process of insulators on the space charge appearance: an important presence of space charges was detected before poling. The influence of the mineral filler on the appearance and the development of space charges is also studied. It was found that the filled sample exhibits more space charge after DC poling than the normal one. We believe the reasons are multiple interfaces existing between the PTFE and the CaF₂. TSDC measurements showed that space charges existing before poling are deeply trapped, whilst the charges induced by the poling process are easily removed. Moreover, we showed, using the TSM, the variation of the heat capacity of the PTFE around +20°C