Charge Characteristics in Low-Density Polyethylene with and without Antioxidant Using Current Integration Method

Measurement data on charge characteristics in the insulation layers of power devices, DC power cables, and enamel windings of electric vehicle drive motors under strong electric fields, high temperatures, and long-term voltage applications are critically important. The current integration method used in this study can measure both fast-moving carrier charges (shallow-trapped charges) and accumulated charges (deep-trapped charges). While the existing pulsed electro-acoustic method is excellent for observing the distribution of accumulated charges, it has difficulty measuring carrier charges moving at high speeds. In this study, we measure the charge characteristics of low-density polyethylene (LDPE) with and without phenolic antioxidants using the current integration method. Antioxidants are typically added to suppress material oxidation. However, the results show that they also suppress charge characteristics. Although a chemical analysis using differential scanning calorimetry reveals that the melting and crystallization temperatures of LDPE do not change significantly, its melting enthalpy and degree of crystallinity are higher in the presence of antioxidants than in their absence. The increase in crystallinity due to antioxidants suppresses the temperature dependence of LDPE charge carriers.