Effect of Space Charge Accumulation on Electric Field Distortion in Polypropylene at Different Temperatures

Under an applied electric field, charge carriers can accumulate within the bulk of the dielectric, leading to a redistribution of the internal field. This non-uniform electric field can intensify local stress, which in extreme cases initiates electrical breakdown and shortens the operational life of the insulation. Accordingly, this study measures the space charge accumulation and internal electric field distribution of polypropylene specimens within the temperature interval of 3070° C under electric field ranging from 1 to <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$90 \text{kV} / \text{mm}$</tex>, and further evaluates the corresponding electric field distortion ratio. Moreover, the influences of thermal conditions, applied field intensity, and charge behavior on the degree of field distortion are systematically examined. The findings indicate that temperature strongly influences the amount of charge injected from the electrodes as well as the mobility of these carriers, thereby altering the overall space charge distribution within the polymer. An electric field of approximately <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$25 \text{kV} / \text{mm}$</tex> appears to act as a critical threshold for electrode injection, beyond which the injection process becomes significantly enhanced. Furthermore, the electric field distortion ratio exhibits a clear upward trend as temperature rises. At 30° C and 50° C, the distortion of the field is primarily concentrated near the surface of the specimen, whereas at 70° C, pronounced distortion is observed both on the surface and throughout the bulk region. In the field range of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$40-70 \text{kV} / \text{mm}$</tex>, the distortion ratio decreases at 50° C and 70° C, which is likely attributable to the moderation of local field enhancement caused by a more uniform charge distribution.