Influence of space charge on the breakdown of multilayered epoxy: a study by the thermal step method

In this paper, the authors study the part played by the space charge upon the electrical breakdown of a multilayered epoxy used in power electronics. By depositing known charges on the different layers of the sample (the Thermal Step Method applied to a "charged plan" within the insulating structure), we first found the material parameters needed for the mathematical processing of the measure signals (calibration). The samples were then subjected to high electric fields (12.17 to 23.33 kV/mm) at 125/spl deg/C until breakdown occurred. Periodically, space charge measurements were made using the Thermal Step Method. The measurements were correlated with a Thermally Stimulated Discharge Current experiment, which has given the energy levels of the traps. The results prove that the quantity of space charge increases with the poling time and becomes very important before the breakdown occurrence. Space charge accumulation can therefore be considered as an important factor accelerating polymer degradation and decreasing polymers lifetime.