Influence of Space Charge on Dielectric Property and Breakdown Strength of Polypropylene Dielectrics under Strong Electric Field

Space charge accumulation in polypropylene (PP) affect the dielectric properties and breakdown strength of the material. The pre-injected charge in PP under the action of different polarity voltage is quantitatively characterized, and the effects of the pre-injected charge inside the dielectric on the dielectric properties and breakdown strength are measured and analyzed. Based on the molecular simulations, the influence mechanism of the temperature on dielectric properties and breakdown are discussed. The experimental results show that the injected charges in PP under the negative polarity voltage is significantly larger than that of the positive polarity. These charges have a great influence on the dielectric constant and breakdown performance of PP, and the effect is different for different charge polarity. The effect of negative polarity pre-voltage conditions on the dielectric constant is much greater than that of positive polarity, and the dielectric constant of PP decreases from 2.2 to 1.3, decreasing about 41% under the negative polarity pre-voltage. By contrast, the dielectric constant slightly increases under the effect of the homopolar preload. Furthermore, the breakdown strength of the dielectric after the heteropolar preload is 249 kV/mm, which is 36% lower than that of PP without pre-voltage, and it slightly increases after the positive polarity prevoltage. As the temperature increases, the increase in free volume favors the development of electron collision ionization and electron collapse processes, leading to a decrease in breakdown voltage at high temperatures. This work has a good guiding significance for the comprehensive evaluation of energy storage parameters.