On testing methodology of thermosetting dielectrics subjected to partial discharges: effect of temperature

Following the idea of performing tests in environmental conditions as similar as possible to the real working ones, many sets of partial discharge tests carried out on an epoxy resin within a broad environmental temperature range are reported on. Life tests were carried out on specimens with a calibrated, enclosed cavity and with embedded electrodes. In the tests performed at temperatures higher than ambient, an interesting strong decrease of data scattering resulted and emphasis on the subject is given. Actually, a strong and unexpected effect was found of the residual mechanical casting stress inside the resin on time-to-breakdown, depending on the difference between the material glass transition temperature and the temperature used in the test. Further data such as discharge amplitude distributions, discharge repetition rate and inception and extinction voltages at the investigated temperatures are also reported and commented upon